OCTET Workshop Report

The Solubility Pump Working Group evaluated human-induced andclimatic influences on spatial and temporal scales ofsolubility-driven storage of carbon in the oceans in relation totheir impact on the atmospheric CO₂. The solubility pumpis often defined as the carbon exchange mediated by physicalprocesses such as heat flux, advection, and diffusion. In contrast tothe biological pump the fundamental processes controlling theexchange are well understood. The questions thus focus on quantifyingand constraining the processes, and assessing possible changes due toclimate change. The solubility pump is also intricately linked to thebiological pump since the same advective and diffusive processes thattransport carbon also control nutrient supply into the euphotic zoneand to some extent export of biological products from the mixedlayer. The group addressed the perturbations of the solubility pumpthat arise through changes in seawater temperature and circulation onseasonal, interannual, decadal and centennial time scales. Emphasiswas placed on large-scale controls and processes which can provide aframework for the specialized studies in the biological pump section.The group separated the problem into two main directions: (1)processes affecting the air-sea exchange of carbon dioxide; and (2)processes affecting the changes in carbon inventories and transportin the ocean interior.

Primary Question: What is the global oceanic CO₂uptake on the seasonal, interannual, decadal and centennial timescales, and what are the physical controls that will determine futureatmospheric CO₂ levels?

Primary Hypotheses

Changes in ocean circulation and short-term meteorological forcingare the primary controls on the oceanic variability of CO₂fluxes with the atmosphere on seasonal to interannualtime-scales.

Changes in ocean circulation and thermocline ventilation rates dueto climate change controls the decadal to centennial scale uptake ofCO₂.

Changes in ocean circulation primarily controls the strength andefficiency of the biological pump by controlling the supply ofnutrients to the euphotic zone on seasonal to interannual timescales.

AIR-SEA EXCHANGE

The ocean plays a critical role in the global CO₂ cycleas it is a vast reservoir of CO₂, naturally exchangesCO₂ with the atmosphere, and takes up a substantialportion of anthropogenically-released CO₂ from theatmosphere. In addition, estimates of the ocean sink can be used inconjunction with atmospheric measurements to provide an independentconstraint on the terrestrial carbon sink reservoir. Several of themajor program elements and activities for the Global Carbon CyclePlan, therefore, require ocean-based observations. Answering thecentral questions posed by OCTET requires, in part, systematicobservations of surface water CO₂ and hydrographicproperties, hydrographic sections of CO₂, tracer, andassociated parameters; and interpolation schemes using remotelysensed parameters such as SST, color, wind and SSS.

The flux of CO₂ between surface waters and theatmosphere can be constrained using data of the partial pressuredifference between the air and the water, combined with estimates ofthe gas exchange coefficient (Takahashi et al., 1999). The value ofthe technique lies primarily in determining the spatial distributionand temporal variability of air-sea CO₂ fluxes on shorttime-scales. It is particularly useful where the signals are large,as in the North Atlantic and Equatorial Pacific, or to study temporalvariability such as the contrast between El Niño andnon&endash;El Niño years.

One important issue is to gain a better understanding of thespatial patterns of surface ocean pCO₂ and its seasonaland interannual variability. Seasonal and interannual variability ofpCO₂ in the surface ocean is one to two orders ofmagnitude greater than their annual increase due to uptake ofanthropogenic carbon (e.g., Bates et al., 1996, Winn et al., 1994;Feely et al., 1999). Because the signal to be detected is muchsmaller than this variability, it takes a decade or longer to observeanthropogenic trends in the surface water if we don’t have theability to “subtract” natural variability. In addition, the seasonaland interannual variability in pCO₂ gives information onhow the carbon cycle functions, and can be used in conjunction withother methods to help understand regional and global patterns ofcarbon uptake. A very promising development of the last decade is newinstrumentation that will make it possible to measure pCO₂(DeGrandpre et al., 1995, Friederich et al., 1995, Goyet et al.,1992, Merlivat and Brault, 1995) and other properties autonomouslyfrom moorings, drifters and volunteer observing ships (VOS). OCTETenvisions that platforms with these capabilities will allowestablishment of many more time-series stations and repeat surfacewater transects at feasible cost in otherwise remote locations.

Key Questions

• What is the seasonal and interannual variability of pCO₂ and CO₂ flux?
• What physical and biological controls account for observed relationships in atmospheric signals in CO₂, O₂, ¹³C and ¹⁴C?
• What are the physical, chemical and biological controls on air-sea flux?
• How will changes in circulation and ocean chemistry affect the buffer capacity of the ocean and its ability to take up CO₂ in the future ?
• How will climate related temperature changes and surface forcing affect the air-sea fluxes of CO₂?

Long-term goals for CO₂ research in the ocean are,first, to quantify the uptake of anthropogenic CO₂ by theocean, including its interannual variability and spatialdistribution; and, second, to understand and model the processes thatcontrol the ocean’s uptake of CO₂. Uptake of anthropogenicCO₂ can be determined by measuring either the air-sea fluxitself, or the resulting change in carbon inventory for longer termquantitative information on uptake patterns. Both should be carriedout, with a strong emphasis on disaggregating the global uptake intocontributions from major ocean regions and monitoring temporalvariability to facilitate a regional sensitivity analysis to changesin uptake and release rates due to climate change.

In addition to estimating the overall magnitude of the oceananthropogenic carbon sink (e.g., Takahashi et al., 1999), the spatialpattern of air-sea fluxes can be used to constrain global patterns ofcarbon sources and sinks on land (Fan et al., 1998). The change inpCO₂, and thus the air-sea flux of CO₂ isvariable in space and time due to changes in circulation,temperature, and salinity, as well as biology. The key to determiningthis flux and understanding its variations is through in situmonitoring; including both time-series stations and regularmeasurements along transects using ships of opportunity.

Temporal variations in some areas, such as the Equatorial Pacific,have been identified as major causes of variability in air-seaCO₂ fluxes. The limited existing time-series studies arelocated mostly in the subtropical ocean gyres, while there are majorgaps in data on regions of active ocean mixing and high biologicalvariability, especially in subpolar and polar latitudes. Temporalvariability is greatest in surface and subsurface layers, locationswhere biological and physical feedbacks are most likely to alter theocean’s ability to absorb CO₂. Characterization andunderstanding of this “natural” temporal variance is a prerequisitefor understanding the processes that limit rates of oceanCO₂ uptake.

Remote measurements are an essential tool for extrapolating insitu measurements to the global scale. Several parameters essentialfor estimating air-sea fluxes can now be observed from space,including wind, sea surface temperature, eddy circulation patterns,and biological productivity. Methods to extrapolate discrete in situmeasurements to a larger region will be needed and can be testedagainst parameters sensed on a coarser resolution. In situmeasurements will be critical for validating the accuracy ofremote-sensing algorithms.

Strategy

• Instrumented VOS with pCO₂, temperature, salinity, nutrients, and chlorophyll sensors (in collaboration with CLIVAR).
• Moorings and drifters in key oceanographic provinces with atmospheric and ocean pCO₂, temperature, salinity, nutrients, chlorophyll, mixed layer depths.
• Surface pCO₂ at time-series stations (tied to moorings at each station) and/or transects.
• Surface atmospheric and boundary layer free troposphere measurements of CO₂, O₂ and ¹³ C.
• VOS and time-series work should be interfaced with large-scale survey work.
• Emphasis on autonomous and semi-autonomous sensors on VOS, drifters, profiling floats and moorings.
• Need to focus on improved interpolation techniques including data assimilation into models.
• Need to focus on physical mechanisms controlling gas exchange in high-wind speed regimes.
• Need to better characterize the relationships between surface ocean pCO₂ and remote sensing products.

CIRCULATION, CO₂ TRANSPORT AND INVENTORIES

The strategy is to put in place a global ocean-observing networkfor CO₂ and tracers to document the continuing large-scaleevolution of the CO₂ fields. Such a strategy calls for aprogram of repeat oceanic sampling of carbon system parameters,tracers and hydrography as part of OCTET. The program is critical toour understanding of climate change, both natural and anthropogenic.The objectives are: (1) to quantify changes in the rates and spatialpatterns of oceanic carbon uptake, fluxes and storage ofanthropogenic CO₂; (2) to detect and quantify changes inwater mass renewal and mixing rates; and (3) to provide a validationof the time integration of models of natural and anthropogenicclimate variability.

Key Questions

• What is the present rate of changes of natural and anthropogenic carbon inventories and transports in the major ocean basins?
• What are the implications to carbon transport and inventory estimates of assuming that the large-scale circulation has been in steady state?
• How will the spatial patterns of carbon transport and inventories respond to changes in circulation and climate forcing in the future?
• What feedback mechanisms related to global change affect carbon transport?
• What are the physical controls on the transport of Fe, DOM, and DIC in intermediate waters (100-1000m)?
• What are the physical controls on fluxes from the main thermocline to the mixed layer?
• What is the effect of climate change on nutrient distributions and transport?
• Can we improve techniques for estimating anthropogenic CO₂ in near-surface waters and in Southern Ocean?

Global CO₂, tracer and hydrographic surveys arerequired to monitor the oceanic CO₂ inventory and itsevolution in space and time. Since the oceans and atmosphere are theprimary reservoirs where CO₂ is redistributed on earth, itis important, for a better understanding of climate variability, todetermine the mechanisms and rates of its redistribution. It isproposed that a set of the hydrographic sections, many of themrepeats of WOCE Hydrographic Program sections, be occupied at timeintervals of between 5 and 10 years to provide broad-scale globalcoverage of ocean variability (Fig. 1). The sampling time intervalshould provide resolution of the local ventilation time-scales withinthe main thermocline to determine interannual and decadal scalechanges in oceanic fluxes. The repeat sections should be integratedwith the high-frequency sampling networks (e.g.,VOS ships, drifters,profilers, moored instruments) and process studies in OCTET toquantify seasonal and other high-frequency variability, validatemodel simulations, and to ground truth the accuracy of thein-situ measurements. If possible, the occupations of thesesections should be coordinated with CLIVAR to reduce ambiguities ininterpretation of spatial/temporal variations. The measurement suiteshould include dissolved inorganic carbon and total alkalinity, andshould frequently include a third/fourth CO₂-systemproperty such as pH and/or pCO₂ to assure internalconsistency. Other measurements should include¹³C/¹²C ratios and TOM (total organic matter).The hydrographic measurement program should also include transienttracers, which provide temporal information about ocean mixing andwater mass history that is essential to interpreting anthropogenicCO₂ distributions. In addition to the hydrographic andcarbon system parameters including: temperature, salinity, oxygen,nutrients, and CO₂ parameters, transient tracers (i.e.,³H/³He, ¹⁴C,¹³C/¹²C, CFCs, and HFCs) should be measured onthese sections to estimate transport fluxes, provide water mass ages,and document changes in anthropogenic carbon inventories. Some ofthese tracers reveal mixing over the critical longer (decadal andcentury) time scales; and some help identify current short-terminvasion rates for comparison with older data. Station spacing on theproposed sections should be eddy-resolving to avoid aliasing ofeddies and other variability into the climate signal. Meridionalsections are important for understanding variations in basin-scalecirculation patterns and inventory changes. Repeat occupation ofzonal sections allows for the detection of variability in the rates,pathways, and properties of deep and intermediate waters carriedtowards the equator from the high latitudes. Ideally, they should belocated downstream of the deep and intermediate water formationregions.

Because one of the main gaps hindering progress in defining thespatial and temporal variability of carbon uptake in the ocean islack of data, strategies are needed to increase spatial coverage andfrequency at reduced per datum cost. A particular emphasis is placedon the development of new technology, in particular instruments formeasurement of CO₂ and related quantities on moorings,drifters, VOS and towed vertical samplers, rapid water samplingtechniques, and high throughput multi-element analyzers for carbonsystem measurements, etc. A complementary focus is the identificationand utilization of platforms such as ships of opportunity, andenhancing the suite of measurements on other suitable observationalplatforms to maximize the benefit for both climate and the carbonsystem.

The lateral transport of carbon by ocean currents plays a key rolein the exchange of carbon between the ocean and atmosphere. Accuratemeasures of the physical transport of carbon are a necessity in orderto fully interpret independent estimates of air-sea flux and localaccumulation. For example, the southern ocean has been identified asa region of large carbon uptake by the ocean, however, the locationof the accumulation of anthropogenic carbon is primarily in thesubtropical gyres. Thus, significant meridional advection of carbonis required to link the regions of air-sea flux with those ofincreasing inventory. High-resolution hydrographic surveys currentlyoffer the only direct method for estimating ocean transport ofcarbon. Geostrophic currents are determined from the observed densityfield, often utilizing an inverse box model to estimate unknownreference level velocities. The net carbon transport is theintegrated product of the distribution of the currents and carbonconcentrations. Previous estimates of carbon transport (Brewer et.al., 1989, Martel and Wunsch 1993, Holfort et al., 1998) reveal thataccurate estimates require sufficient spatial sampling of physicalparameters to resolve the mesoscale eddy field. While the CTDsampling must be sufficient to resolve the eddy variations (60-100km), regression and interpolation analysis has demonstrated that thecarbon field, especially below the seasonal thermocline, can beaccurately reconstructed from a sub-sampled distribution ofsignificantly lower resolution (Goyet et al., 1995).

The WOCE/JGOFS/NOAA CO₂ survey provides the firstglobal data set with which to estimate the oceanic transport ofdissolved inorganic carbon. Analysis in the South Atlantic (Holfortet al., 1998) reveals a significant southward transport of -0.81± 0.08 Pg C/yr. Analysis of the Pacific and Indian basins isunderway. The existent data set will be insufficient to answer keyquestions regarding ocean transport. For example, the WOCE/JGOFSsurvey can only provide for estimates of the inorganic component ofthe total carbon flux. Lateral advection of DOC also contributes tothe net of carbon (Hansell and Carlson, 1998) and additionalmeasurements are required before accurate calculations of thiscomponent are possible.

Temporal variability and evolution of the ocean carbon transportcannot currently be determined from observations. The carbondistribution in the ocean is evolving in response to anthropogenicperturbations. How the ocean transport of carbon will respond to thissecular trend is, as yet, undetermined. In addition to the long-termtrends in carbon accumulation, temporal variability of transport atshorter time scales (mesoscale, seasonal, inter-annual) are likely tobe significant. A single survey of the global dissolved inorganiccarbon distribution cannot provide a basis for estimating thisvariability. Repeat upper ocean temperature measurements have beenconducted, however, and offer a illustration of the magnitude oftemporal variability. For example, in the North Pacific, over 27 XBTlines have been completed between California and Taiwan. The meanmeridional heat transport calculated from this data is 0.77 ±0.12 PW, with an interannual range of 0.3 PW (Roemmich et al., 2000).In the North Atlantic, analysis of historical hydrography at36°N indicates the annual mean transport is 1.4 PW but with aninterannual range of 0.6 PW (Sato and Rossby, 2000). The temporalvariability of the carbon transport is likely to have similaramplitudes.

Biological archives such as banded corals and mollusks represent apotential resource for providing tracer data to help reconstructspatial and temporal variations in CO₂ exchange andintra-annual to centennial-scale ocean circulation changes. For asubset of the parameters which monitor the state of the solubilitypump, calcareous recorders of water properties such as known-ageannually banded corals and mollusks can provide data at sub-annualresolution to extend the instrumental record in space and time.Records of del¹⁸O, trace metals, and the carbon isotopes(del¹³C and Delta¹⁴C) are conventionallyobtained from warm-water archives such as corals (Dunbar and Cole,1993), and existing efforts in this direction should be continued andexpanded. In addition, banded mollusks, other calcareous organismssuch as bryozoans, rhodoliths, and deep-sea corals, and fishotoliths, are all worthy of investigation as potentialcarbonate-based recorders of conditions in colder waters, includingthose of the sub-polar oceans and the main thermocline. Thesematerials represent a unique and underutilized resource for helpingto determine the state of the solubility pump in remote andundersampled areas such as the NW Atlantic and Pacific, and theSouthern Ocean.

Strategy

• Transport: seasonal repeat coast to coast sections with full water column carbon, CFC, nutrients, DOM and hydrographic measurements with 30-60 km station resolution (in collaboration with CLIVAR)
• Inventory: 5-10 year repeat sections to measure changes in large-scale biogeochemistry with full water column carbon, CFC, nutrients, DOM, POM, trace metals, HPLC pigments and hydrographic measurements (in collaboration with CLIVAR).
• Moorings and drifters in key oceanographic provinces with atmospheric and ocean pCO₂, temperature, salinity, nutrients, chlorophyll (in collaboration with CLIVAR).
• Profiling floats with TCO₂, pH (or pCO₂), temperature, salinity, nutrients, and chlorophyll (in collaboration with CLIVAR).
• Full water column carbon, tracer and hydrographic profiles at time-series stations.
• Large-scale surveys should be interfaced with process studies, time-series stations, and VOS work.
• Biological integrators (e.g., high resolution coral records and archived fish scales) to assess past variability on all time scales.

Figure 1. Locations of proposed repeat sections for studies ofcirculation, transport anthropogenic CO₂ inventories. Thegrey lines are proposed CLIVAR cruise tracks and the black lines arecommitted cruise tracks by similar international programs.

References

Bates, N.R., A.F. Michaels and A.H. Knap (1996) Seasonal andinterannual variability of the oceanic carbon dioxide species at theU.S. JGOFS Bermuda Atlantic Times-series Study (BATS) site. Deep-SeaRes. 43, 2-3, 347-383.

Brewer, P.G. and C. Goyet and D. Dyrssen (1989) Carbon dioxidetransport by ocean currents at 25N latitude in the Atlantic Ocean.Science, 246, 477-479.

Caldeira, K., and P.B. Duffy (2000) The role of the souther oceanin uptake and storage of anthropogenic carbon dioxide. Science 287,620-622.

DeGrandpre, M. D., T. R. Hammer, S. P. Smith, and F. I. Sayles(1995) In situ measurements of seawater pCO₂, Limnol.Oceanogr., 40, 969-975.

Dunbar, R.D. and J.E.Cole (1993) eds, Coral records ofocean-atmosphere variability, Report from the Workshop on CoralPaleoclimate Reconstruction, La Parguera, Puerto Rico, Nov 5-8, 1992,UCAR, 37pp

Fan, S.-M. M. Gloor, J. Mahlman, S. Pacala, J. L. Sarmiento, T.Takahashi, and P. Tans (1999) A large terrestrial carbon sink inNorth America implied by atmospheric and oceanic CO₂ dataand models. Science, 282, 442-446.

Feely, R.A., R. Wanninkhof, T. Takahashi, and P. Tans (1999) Theinfluence of El Niño on the equatorial Pacific contribution toatmospheric CO₂ accumulation, Nature, 398, 597-601.

Friederich, G. E., P. G. Brewer, R. Herline, and F. P. Chavez(1995) Measurements of sea surface partial pressure of CO₂from a moored buoy, Deep-Sea Research, 42, 1175-1186.

Goyet C., D. M. Walt and P. G. Brewer (1992) Development of afiber optic sensor for measurement of pCO₂ in sea water:design criteria ans sea trials, Deep-Sea Research, 39, 1015-1026.

Goyet, C., D. Davis, E.T. Pelzter and P.G. Brewer (1995)Development of improved space sampling strategies for ocean chemicalproperties: total carbon dioxide and dissolved nitrate. Geophys. Res.Letters, 22, 945-948.

Gruber, N. and J.L. Sarmiento and T.F. Stocker (1996) An ImprovedMethod for Detecting Anthropogenic CO₂ in the Oceans.Global Biogeochemical Cycles, 10, 809-837.

Hansell, D.A., and C.A. Carlson (1998) Deep-ocean gradients in theconcentrations of dissolved organic carbon. Nature 395, 263-266.

Holfort J, Johnson KM, Schneider B, Siedler G, Wallace DWR (1998)Meridional transport of dissolved inorganic carbon in the SouthAtlantic Ocean. Global Biogeochemical Cycles 12, 479-499.

Martel F., and C. Wunsch (1993) The North Atlantic Circulation inthe Early 1980’s – an Estimate From Inversion of a Finite DifferenceModel, J. of Physical Oceanography, 23, 898-924.

Merlivat, L., and P. Brault (1995) CARIOCA buoy: Carbon DioxideMonitor, Sea Technology, 10, 23-30.

Roemmich, D., J. Gilson, B. Cornuelle, and R. Weller (2000) Themean and time-varying meridional transport of heat thetropical/subtropical boundary of the North Pacific Ocean,submitted.

Sato, O.T, and T. Rossby (2000) Seasonal and low-frequencyvariability of the meridional heat flux at 36N in the North Atlantic,J. of Physical Oceanography, 30, 606-621.

Takahashi, T., R.H. Wanninkhof, R.A. Feely, R.F. Weiss, D.W.Chipman, N. Bates, J. Olafsson, C. Sabine, and S.C. Sutherland (1999)Net sea-air CO₂ flux over the global oceans: An improvedestimate based on the sea-air p CO₂ difference. 2ndInternational Symposium on CO₂ in the Oceans, the 12thGlobal Environment Tsukuba, 18&endash;22 January 1999, Tsukuba,Japan, 9&endash;15.

Winn, C. D., F. T. Mackenzie, C. J. Carillo, C. L. Sabine and D.M. Karl (1994) Air-sea carbon dioxide exchange in the North PacificSubarctic Gyre: Implications for the global carbon budget, GlobalBiogeochemical Cycles, 8, 157-164.

Wunsch, C. (1996) The Ocean Circulation Inverse Problem, CambridgeUniversity press, 442pp.

The North Atlantic: A Natural Ocean Laboratory for ClimateChange and Carbon Cycle Science

Improved quantification of the zonal distribution of terrestrial,fossil-fuel carbon sinks depends critically on continued and improvedobservation and modeling of the North Atlantic ocean carbon sink(Sarmiento and Wofsy, 1999). This need has been identified as a highpriority in the the US Carbon Cycle Science Plan (CCSP). We believethat OCTET can, and should, address this issue with process studiesto identify, and quantify more accurately the mechanisms responsiblefor carbon fluxes and their variability in the North Atlanticbasin.

The North Atlantic is a relatively small ocean basin with aconfined geometry and high biogeochemical and physical variability.The physical regime is dominated by vigorous meridional mass and heattransports in the Gulf Stream and Deep Western Boundary Current.Water mass transformations, associated with air-sea interactions,lead to ventilation of the main thermocline by subduction atmid-latitudes and deep water formation in the subpolar regions. Alarge fraction of the ocean’s deep waters and their propertiesoriginate in the North Atlantic. The vigorous surface heat exchangesdrive the strong regional net uptake of carbon dioxide from theatmosphere. Indeed, the North Atlantic is the most intense carbonsink among the major basins on an areal basis. The basin is rich inmesoscale activity, particularly in the western margin, associatedwith baroclinic instability of the Gulf Stream system. The basin isbiologically very active: The high latitude spring phytoplanktonbloom is one of the most conspicuous seasonal planetary features seenfrom space and is an icon of the unique biogeochemical features ofthis basin. The basin has a rich iron source from Saharan and Saheldust, and geochemical evidence indicates that the North Atlanticsubtropics are a region of active nitrogen fixation (Michaels et al.,1996; Gruber and Sarmiento, 1997).

There is significant physical and biogeochemical variability oninterannual and decadal timescales (e.g., Deser and Blackmon, 1993;Bates, 2000). A significant fraction of the physical variability isassociated with the North Atlantic Oscillation (NAO). The NAO is acharacterization of regional climate variability, regimes of whichare indicated by the difference in sea level pressure between Icelandand Portugal (e.g., Hurrell, 1995). Clear relationships betweenbiogeochemical and physical variability associated with the NAO havebeen documented, but the underlying mechanistic connections are notyet understood (e.g., Bates, 2000; Taylor and Stephens, 1980). Thenatural variability of the basin, as characterized by the NAO,provides a context in which to conduct natural experiments on changesin ocean biogeochemistry that will occur with change in oceanclimate. Variability in aeolian dust transport, the balance oflimiting nutrients, or community structure may also influence thebiological carbon pump either in connection with, or independent of,changes in the physical environment. By observing and understandingthe interannual and decadal connections, and revealing the underlyingmechanisms of the physical and biogeochemical environment of theNorth Atlantic, we will proceed towards a better understanding ofbroader issues of longer term, global change.

Further details and overviews on scientific advances and researchprograms in the North Atlantic can be found in the recent JGOFSliterature (Ducklow and Harris, 1993; Ducklow et al., 1997; Hansell,1999; Doney et al., 1999; Karl and Michaels, 1996; Siegel et al.,2000).

We recommend a North Atlantic strategy for OCTET, encompassing adecadal-scale research program, emphasizing a focus on observing andunderstanding variability in bloom dynamics, margin fluxes and therelationship to regional climate change (including changescharacterized by the NAO). The ongoing time-series station atBermuda, along with required studies of the biogeochemical responsesto mesoscale eddies, will provide a basis for comparative studieswith the subpolar gyre. The small size of the North Atlantic makesbasin scale study relatively tractable, both observationally and fornumerical simulations. Patterns of physical variability associatedwith the NAO suggest “action centers” where local observations mayreveal wider scale variability. Strong contrasts with the NorthPacific system in bloom amplitude, iron limitation and physicalregime, all within regions at the same latitudes and with similarmeteorological forcing, will provide the basis for unique interbasincomparisons. As one of the smallest of ocean basins, the NorthAtlantic also has large areas of continental margin relative to theopen ocean, affording the potential for regional studies of theimportance of shelf processes and exchanges.

Here we outline the unique features, uncertainties and prioritiesidentified by the OCTET North Atlantic Working Group and providerecommendations to OCTET for specific studies in the North Atlanticbasin. We identify four areas of more specific focus which areexpanded upon in the following sections. Most of these themes havewider oceanic relevance, but we identify them here as particularlysignificant for the North Atlantic:

1. What is the magnitude of the carbon sink (natural and perturbed) in the North Atlantic? How significant is this on the global scale?
2. What is the natural variability of this carbon uptake? What physical and biological processes control the interannual and decadal variability?
3. What is the regional (and temporal) variability in remineralization length scales for sinking particulate material? What factors in the upper ocean and mesopelagic control these scales in time and space?
4. What are the relative contributions to fossil fuel carbon sequestration, over decadal time scales and beyond, of the ocean margins and open ocean? How does the proportion respond to climate change?

Research Questions

1. North Atlantic Carbon Sink:

What is the magnitude of the carbon sink (natural and perturbed) in the North Atlantic? How significant is this on the global scale?How accurately must we quantify the North Atlantic sink to sufficiently define the distribution of fossil fuel carbon sinks (oceanic and terrestrial)?

How is the sink related to fluxes of freshwater and materials from the Arctic Ocean?

A primary motivation for OCTET will be to determine thedistribution, magnitude and interannual variability (see nextsubsection) of oceanic carbon sources and sinks on a regional basis.North Atlantic CO₂ uptake is the most intense, per unitarea, of the major basins. Current estimates infer a North Atlanticcarbon sink (natural and perturbation) of between 0.23 and 0.48 Gt Cper year (Lefevre et al., 1999). Approximately one third of this fluxmay be anthropogenic carbon. While the North Atlantic is the bestresolved basin in terms of our knowledge of the spatial distributionand temporal variability of air-sea CO₂ flux, betterconstrained estimates are crucial to improve the identification andquantification of the regional distribution of fossil fuel carbonsinks (Fan et al., 1999).

The magnitude of the biological export of carbon to depth in thebasin is uncertain, with estimates ranging from <10% to ~40% ofthe global total. The supply of nutrients by alternative processes,such as nitrogen fixation and atmospheric deposition, may take onadded significance in the North Atlantic. The North Atlantic isrelatively iron rich, so the extreme phosphorus deficits in thesurface Sargasso Sea will play a central role in limiting nitrogenfixation there.

2. Variability of the North Atlantic Carbon Sink:

What is the interannual and decadal variability in the uptake of carbon in the North Atlantic basin?What are the mechanisms (physical and biological) which give rise to this variability? Is this variability significant in global terms?

What uncertainty does this impose on our time mean estimates?

Can we relate the variability in the carbon pumps to shifts in climate regimes such as the NAO?

What are the links between large-scale, low-frequency variations like NAO and higher frequency phenomena which seem to exert strong control on regional to local fluctuations in biogeochemical cycling?

Coupled atmosphere-ocean model simulations have predicted asignificant warming of the surface waters of the ocean (e.g.,+2.5°C in 100-150 y) (e.g., Sarmiento et al., 1998). Such atemperature change would probably result in increased surface oceanstratification in the low to mid-latitudes and increasedprecipitation at high latitudes. An overarching goal of carbon cyclescience is to understand how such changes in ocean stratification andmixing would affect the carbon pumps, through modulation ofsolubility effects, total and export production, plankton communitystructure, and their biogeochemical consequences. These questions areparticularly significant for the North Atlantic, where much of theoceanic deep water is formed and its properties set.

We may use the natural variability of the system to address suchquestions in a natural laboratory. Increased stratification reducesthe input of nutrients to the euphotic zone by vertical mixing, aneffect already seen at the BATS site as reduced primary and newproduction during positive phases of the North Atlaintic Oscillation(see below). Long term changes in such conditions may drive lastingchanges in the taxonomic composition of both the primary producersand consumers, thereby changing the efficiency of export of biogenicparticles.

Biological Variability.

To some extent, biological variability of the North Atlantic oceanis controlled by the variations of the physical environment. Indeed,it is the response to climate changes that is the major question ofinterest. In the next sub-section, we outline the nature of physicalvariability in the basin, and how the observed natural patterns ofvariability may provide a focus for OCTET studies. Here, first, weidentify some open questions regarding biological variability:

Would changes in vertical mixing result in changes in primary andexport production via changes in N and P delivery or in light supply(Dutkiewicz et al., 2000)? What fraction of the total export isdelivered from the spring bloom and will it change?

How will changes in total and export production be reflected inpartitioning among DOC, DON, DOP and their particulatecounterparts?

How is export production related to the balance of variousbiological processes (nitrogen fixation, denitrification, andcalcification), and how will the relationship change?

How do changes in mixing and stratification result in changes inplankton community structure during and following the spring bloom(e.g., dominance shift from diatoms to picoplankton and from largecrustacean grazers to microzooplankton)?

Variations in primary and new production at higher latitudes dueto changes in stratification, whether forced by thermal or freshwaterinputs, remains subject to conjecture. The absence of a long runningdata set of the appropriate biogeochemical variables precludes a moredeterministic view of the effects. The partitioning of the biologicalpump between dissolved and particulate material appears to bestrongly impacted by stratification/nutrient availability, though themechanisms are unknown. Net DOM production in nutrient impoverishedprovinces is a much larger fraction of net production than in systemsrich in nutrients (Hansell and Carlson, 1998). The export of netcommunity production, whether as DOM or as sinking biogenicparticles, too will be controlled by the ecosystem structure and therate of overturning circulation, all of which are modulated byphysical variability. Increased concentrations of CO₂ inthe surface North Atlantic will lower the pH and, therefore, thecarbonate concentrations. These changes may affect the potentialrates of calcification both by free living calcifiers and hardcorals.

Physical Variability and the North Atlantic Oscillation.

A significant fraction of meteorological variability in the NorthAtlantic region, on interannual to decadal timescales, can becharacterized in terms of the NAO (e.g., Hurrell, 1995). Patterns ofNorth Atlantic ocean variability reflect those in the atmosphericforcing (e.g., Dickson et al., 1996) and may feed back on theatmosphere (e.g., Cjaza and Marshall, 2000). The NAO is a unique modeof climate variability, distinct from ENSO in its non-equatorial inorigin, and characterized by a dipole meridional oscillation inatmospheric pressure between the Iceland Low and the Azores High.Weather systems track the westerly jet from North America to Europe.During negative phases of the NAO, storm tracks shift southwardenhancing heat loss from the surface of the subtropical ocean,thereby enhancing mode water formation and deepening winter-timemixed layers (Dickson et al., 1996). In the positive NAO phase theopposite effect occurs, increasing temperature and stability in thesubtropical gyre and deep convection in the subpolar regions shiftsfrom the Greenland to the Labrador Sea. These interannual and decadalchanges in the physical system have been observed to cause stronganomalies in the biological and solubility pumps in the Sargasso Sea(Bates et al., 2000). At higher latitudes, relative changes incopepod abundances have been shown to correlate with the NAO andother indicators of regional climate change such as the position ofthe north wall of the Gulf Stream (Taylor and Stephens, 1980).

These observed correlations between regional climate indices andbiogeochemical variables are suggestive, but the underlyingmechanistic connections, and larger scale quantification of theimpact on carbon fluxes remain open questions, the answers to whichwill provide insight into more general climate-biogeochemicalconnections. Understanding the system within the NAO framework willprovide a structure for ongoing and future studies of climate andcarbon cycle interactions. The classical tripole pattern of the NAO,in sea level pressure or SST variations, suggests centers of action,where a judicious, yet limited, observational framework (perhaps asmall number of time-series stations supplemented with regionaltransects) may provide key data which can be leveraged to understandand quantify the large scale variability. Coordination with theclimate and modeling communities from the outset of suchobservational programs will enhance the likelihood of a successfulobservational program in this regard.

Although these questions are focused on large-scale, low-frequencyphenomena, it is recognized that some of the underlying controls mayreside in processes which operate on much smaller spatial scales andshorter temporal scales. For example, it has been suggested thatmesoscale flows are responsible for supplying the nutrients requiredto sustain high levels of new production observed in oligotrophicregions of the main subtropical gyres (e.g., McGillicuddy andRobinson, 1997). Understanding interannual to decadal scalefluctuations of the biological pump requires knowledge of the linksbetween the mesoscale and basin-scale phenomena such as NAO. In orderfor future programs to develop sufficient mechanistic understandingto allow skillful quantification and prediction, they must addressthe issues of physical-biogeochemical interactions across the varietyof scales on which they operate.

3. Remineralization of Sinking Particles:

What is the variability in remineralization length scales for the spring bloom and what factors in the upper ocean and in the mesopelagic control these scales in time and space?Why is the strong north-south gradient in ocean color and annual production observed in the euphotic zone not observed in export and seafloor metabolism?

How does the recycling efficiency of the mesopelagic layer differ between low vs. high latitudes?

How will changes in vertical mixing affect the annual cycle of mesopelagic community structure and function?

It is enigmatic that a very strong meridional gradient exists inocean color and rates of primary production, with higher plantbiomass and rates of growth in the subpolar waters than in thesubtropics, yet only a weak gradient is found in the rates ofcatabolism at the ocean floor. This finding suggests that theremineralization length scale, that is the depth to which a fractionof the sinking particles reaches prior to mineralization, may beshallower in the higher latitudes. With shallow remineralizationlength scales, the effect would be to put relatively more of themineralization into the shallow water column than into deep water orthe sediments. A new research initiative aimed at the mesopelagic”twilight zone” of net remineralization below the euphotic layer isneeded to uncover the biogeochemical mechanisms and ecologicalprocesses underlying length scale variability.

4. Coastal and Open Ocean Carbon Uptake:

What is the proportion of carbon sequestration over multi-decadal time scales contributed by ocean margin vs. deep ocean processes and how does the proportion respond to climate change?

The spring phytoplankton bloom in the North Atlantic is intensebecause of deep vertical mixing and the iron-replete nature of thebasin, releasing phytoplankton from nutrient limitation each spring.The subpolar bloom contributes about half the annual organic particleflux to the deep sea in a brief interval in the late spring. Thebloom was studied in the US JGOFS North Atlantic Bloom ExperimentPilot Study in 1989 at a single site for a brief period and somewhatmore comprehensively by European JGOFS and related programs. However,even this conspicuous phenomenon may not dominate carbon fluxes inthe North Atlantic. Due to the North Atlantic basin’s small size, andthe generally broad extent and shallow depth of continental shelvessurrounding the basin, continental margin-derived fluxes may beespecially important. The flux from the subpolar bloom area is lessthan 1/4 of that needed to balance deep AOU requirements for thetotal North Atlantic (from the equator northward). Margins and lowerlatitude areas must contribute significantly, as must export of DOMwith deep and intermediate water formation. How the contributions ofthe open ocean and the ocean margins to carbon fluxes vary overinterannual or decadal time scales is unknown. The volume transportand patterns of thermohaline circulation will certainly controlexport as DOM and, therefore, its contribution to AOU.

The North Atlantic receives large inputs from rivers drainingabout half the North American continent, and additional inputs fromthe Arctic Ocean, itself a river-dominated basin. The Arctic Ocean’sstock of dissolved organic matter receives strong inputs from therivers draining the north slopes of the continents; how thiscontribution to total carbon flux may change with a warming Arctic isuncertain.

Suggested Research Strategies

One of the most valuable insights taken from the many US JGOFSprograms is that a long-term, continuous presence in and above theocean is necessary in order to identify the major gaps in ourunderstanding of processes of interest. Interannual changes that werenot predicted led to some of the most important advances andquestions in our science. This continuous presence took the form ofwell-supported time series stations in the North Atlantic and NorthPacific during the JGOFS program. Such high cost observatories cannotbe reproduced at numerous sites in the ocean, but some form ofcontinuous observing capability will be necessary and valuable. TheNorth Atlantic subtropical gyre is the best resolved in terms oftemporal variability, particularly if the existing time seriesprograms (BATS, CARIACO, CaTS, and ESTOC) are better linked. Ourbiggest need in the context of OCTET is a continuous spring andsummer presence in the subpolar waters of the North Atlantic, whichwill provide the requisite biogeochemical data. The classical tripolepattern of the NAO in sea level pressure or SST variations suggestslikely centres of action, where a judicious, yet limited,observational framework may provide a key to understanding thebroader regional variability. Strong ties to the physical oceanobserving programs of CLIVAR and GOOS could help provide the datarequired for observing winter time air-sea exchange processes andexport with thermohaline circulation. We must continue to exploitspace observing programs to the fullest extent possible (e.g., oceancolor and derivable products relevant to ocean biogeochemistry).Preliminary modeling studies will help to determine the optimalobservation sites. Models will also provide a framework forinterpretation of the data in the wider context.

We must make continuous observations of the major physical systemsthat impact directly on the major biogeochemical processes. Suchdistinct systems include the equatorial upwelling zone, the zone ofhigh nitrogen fixation in the tropical Atlantic, the strongmeridional flow in the Florida Strait, the primary sites ofshelf/basin exchange, the regions of mode and deep water formation,the oligotrophic zones in which biogeochemical cycles are stronglyimpacted by intermittent events such as eddies, the areas of deepwinter mixing experiencing strong spring blooms, and the equatorwardflow at mesopelagic depths.

Focus on the mesopelagic zone, employing gradients in thebiogeochemical signals in this zone to gather integrative informationon the surface ocean processes, will prove a particularly powerfultool. Data on bioactive and time tracers in the mesopelagic haveprovided valuable information on fluxes from the surface ocean. Inthe North Atlantic, gradients in subsurface layers such as thesubtropical mode water provide mass balance constraints onbiogeochemical processes that are highly variable in time and space,and therefore difficult to constrain with surface-only measurements.The integrated contributions of the ocean margins too may beresolvable via study of geochemical gradients on subsurface isopycnallayers replenished by margin exchange.

North Atlantic Ocean: Unique Features

Prominent Physical Features:

1. Confined geometry
2. Strong meridional overturn over all depths into one small basin
3. Strong transport from tropical/subtropical to ventilation regions
4. Arctic ocean exchanges
5. Large ratio margin area: basin area
6. Broad shelves
7. High riverine inputs
8. High dust inputs
9. Strong surface and thermocline eddy structures

Biogeochemical and Biological Features:

1. Intense high latitude spring phytoplankton bloom & biogeochemical impacts
2. Conspicuous coccolithophorid blooms
3. Excess of N₂-fixation over denitrification (positive N* signal)
4. Possible net heterotrophy (in a small basin)
5. Iron replete basin
6. Strong CO₂ sink (per unit area)
7. Non-Redfield DIC draw down in some regimes
8. Anthropogenic inputs (atmospheric and river derived)

Resources and Advantages for Study:

1. Relatively small basin surrounded by major seagoing nations and population centers: ease of logistics
2. Valuable archived data resources (e.g., WOCE, JGOFS, TTO etc)
3. Ongoing focus of major biological & physical programs [e.g., several ocean biogeochemistry time-series programs (BATS, ESTOC, CaTS, CARIACO), CPR, Argo, CLIVAR, GOOS]
4. High level effort with sophisticated models (including hurricane forecasting, etc.)

Arctic Oscillation Impacts:

1. AA climate oscillation not Equatorial in origin &endash; distinct phenomenon
2. Understanding primitive and still emerging
3. Effects on: convection, biogeochemistry, ecology
4. Interannual &endash; multi-decadal time scales

References

Bates, N.R. 2000. Interannual changes of oceanic CO₂and biogeochemical properties in the western North Atlanticsubtropical gyre. Deep-Sea Research II (in press).

Czaja, A. and J. Marshall. 2000. Observations of atmospheric jetstream – ocean gyre coupling in the North Alantic. Journal of Climate(submitted).

Deser, C. and M.L. Blackmon. 1993. Surface climate variations overthe North Atlantic Ocean during winter: 1900-1989. Journal of Climate6, 1743-1753.

Dickson, R., J. Lazier, J. Meinke, P. Rhines and J. Swift. 1996.Long term coordinated changes in the convective activity of the NorthAtlantic. Prog. Oceanography 38, 241-295.

Doney, S. C., D. W. R. Wallace and H. W. Ducklow, 1999. The NorthAtlantic Carbon Cycle: New Perspectives from JGOFS and WOCE. Pp375-391 In: R. Hanson, Ducklow, H. W., and J. G. Field, Eds. TheChanging Carbon Cycle in the Oceans. Cambridge, UK: Cambridge Univ.Press. 500 pp.

Ducklow, H. W., Goyet, C. and J. Marra. 1997. North AtlanticPlanning Report. US JGOFS Planning Report 20. WHOI. 92 pp.

Ducklow, H. W. and R. Harris. 1993. Introduction to the JGOFSNorth Atlantic Bloom Study. Deep-Sea Research 40, 1-8.

Dutkiewicz, S., Follows, M.J., J.C. Marshall and W.W. Gregg. 2000.Interannual variability of phytoplankton abundance in the NorthAtlantic. Deep-Sea Research (in press).

Fan, S., M. Gloor, J. Mahlman, S. Pacala, J. Sarmiento, T.Takahashi, P. Tans. 1998. A large terrestrial carbon sink in NorthAmerica implied by atmospheric and oceanic carbon dioxide data andmodels. Science 282 (5388), 442-446.

Gruber, N. and J. L. Sarmiento. 1997. Global patterns of marinenitrogen fixation and denitrification. Global Biogeochemical Cycles11, 235-266.

Hansell, D.A. 1999. Sargasso Sea Ocean Observatory(http://w3.bbsr.edu/cintoo/s2o2/s2o2.html)

Hansell, D.A. and C.A. Carlson. 1998. Net community production ofdissolved organic carbon. Global Biogeochemical Cycles 12,443-453.

Hurrell, J.W. 1995. Decadal trends in the North AtlanticOscillation: regional temperatures and precipitation. Science 269,676-679.

Karl, D.M. and A.F. Michaels. 1996. Ocean Time-Series: Resultsfrom the Hawaii and Bermuda Research Programs. Deep-Sea Research II43 (2-3), 127-683.

Lefevre, N., A.J. Watson, D.J. Cooper, R.F. Weiss, T. Takahashiand S.C. Sutherland. 1999. Assessing the seasonality of the oceanicsink for CO₂ in the northern hemisphere. GlobalBiogeochemical Cycles 13, 273-286.

McGillicuddy, D.J. and A.R. Robinson. 1997. Eddy-induced nutrientsupply and new production in the Sargasso Sea. Deep-Sea Research 44,1427-1449.

Michaels, A.F., D. Olson, J.L Sarmiento, J.W. Ammerman, K.Fanning, R. Jahnke, A.H. Knap, F. Lipschultz and J.M. Prospero. 1996.Inputs, losses and transformations of nitrogen and phosphorus in thepelagic North Atlantic Ocean. Biogeochemistry 35, 181-226.

Sarmiento, J. and S. Wofsy. 1999. A US Carbon Cycle Science Plan.A Report of the Carbon and Climate Working Group. 69 pp.

Sarmiento, J. L., T. M. C. Hughes, R. J. Stouffer, and S. Manabe.1998. Simulated response of the ocean carbon cycle to anthropogenicclimate warming. Nature 393, 245-249.

Siegel, D.M., D.M. Karl and A.F. Michaels. Interpretations of OpenOcean Biogeochemical Processes at the U.S. JGOFS Bermuda and HawaiiTime-series Sites. Deep-Sea Research II (in press).

Taylor, A.H. and J.A. Stephens. 1980. Latitudinal displacements ofthe Gulf Stream (1966-1977) and their relation to changes intemperature and zooplankton abundance in the N.E. Atlantic. Oceanol.Acta 3, 145-149.

The enormous increase in our knowledge of oceanographic processesin the Pacific Ocean over the past decade has documented largetemporal variations in the carbon cycle. For example, chlorophyllconcentration in the Equatorial Pacific underwent factor of 20changes associated with the 1997-1998 El Niño and subsequentrecovery to La Nina conditions. The ecosystem in this region is nowbelieved to shift states abruptly depending on the availability ofiron. Studies at the subtropical Pacific time-series station suggestthe food web dynamics and productivity in this location shifted toone strongly influenced by nitrogen fixation and phosphoruslimitation sometime in the 1980s. SeaWifs ocean color observationsfrom 1997 and 1998 show the presence of meso-scale coccolithophoreblooms in the Bearing sea that were never noted in older Coastal ZoneColor Scanner data (1978-1986). Forcings that control these changesand the mechanisms that link them to carbon fluxes must be understoodand incorporated into basin-scale coupled biological and physicalmodels to accurately predict the response to natural andanthropogenically induced variability.

The questions listed below have all grown out of the synthesis ofexisting data and summarize our view of the most important unknownsin the processes that control variability in Pacific Ocean carbonfluxes.

• How are ecological dynamics and carbon cycling affected by the basin scale differences between nitrogen fixation and denitrification?

Nitrogen fixation creates reactive nitrogen which is thenavailable to the rest of the life in the sea. Denitrification removesthis reactive nitrogen as part of the metabolism of a specific groupof micro-organisms. The balance of these two processes controls thetotal pool of reactive nitrogen, primarily nitrate, in the ocean. ThePacific Ocean contains one of the largest areas of water column andsediment denitrification in the world. Nitrogen fixation iswidespread over the oligotrophic surface waters of the Pacific andapparently fluctuates on interannual and decadal time-scales,although the absolute rates over the whole basin are unclear. Thecreation of reactive nitrogen by diazotrophs will result in the netuptake of atmospheric CO₂, and denitrification will causethe return of CO₂ to the atmosphere, modulated by theresidence time of the nitrate in the ocean. If these two rates areexactly in balance, the net exchange of CO₂ with theatmosphere will be zero; imbalances between these two rates willresult in a net ocean uptake or outgassing of CO₂.

The nitrogen fixation-denitrification balance has the potential tohave an effect on the concentration of carbon in the atmosphere.Current estimates of the global denitrification rate are over 300Tg/y, and Pacific rates may be greater than half of this total.Estimates of the global rates of nitrogen fixation are only about 100Tg/y, again with approximately half of this in the Pacific Ocean.Given these estimates, either the ocean is wildly out of balance orone or both of the rates is in error. An imbalance implies aconcomitant trend in atmospheric CO₂ change. Ice core dataindicate that since about 8000 years before the industrial revolutionthe atmospheric pCO₂ increased slowly by about 20 ppm. Oneof the goals of nitrogen cycle studies is to determine its role inthe air-sea partitioning and variability in atmosphericCO₂.

• What controls the east-west variation in carbon fluxes in the subarctic Pacific Ocean?

Observations of nitrate draw-down, ¹⁴C primaryproductivity and ¹⁵N uptake incubation experiments in theCanadian and Japanese JGOFS time-series sites indicate that the ratesof carbon export and new production in the western subarctic Pacificare about twice that of the eastern part of this basin. The reasonsfor this difference are unknown given that both sides of this basinare nutrient replete, year-round. Since the western subarctic Pacifichas been identified by global surface CO₂ maps as one ofthe important regions of net CO₂ flux into the oceans, aninvestigation into the reasons for this asymmetry is warranted. Keypossibilities for the difference are: (1) differences in Fe fluxbetween the eastern and the western basin because of prevailing windpatterns; (2) physical processes of seasonal mixed layer deepeningand mechanisms controlling exchange between the euphotic zone andnutrient-enriched upper thermocline; and (3) hydrological cycledifferences in the two basins with emphasis on the influence offreshwater input to the upper ocean on physical mixing processes. Tounderstand the effect of natural decadal-scale oscillations andanthropogenically-induced climate changes on the rates of physicallyand biologically induced CO₂ exchanges, one must know theimportance of these mechanisms in the subarctic Pacificocean.

• How much does the interannual and decadal variability in oceanic ventilation and regional heat storage change the uptake/partitioning of ocean/atmosphere carbon?

Many lines of evidence exist that show past variability in theventilation of the upper ocean on interannual to decadal time scales.For example decadal variability of the climate mean state shiftoccurred abruptly in 1976. After this time, more frequent, severe ElNiño events occurred. These changes in the climate mean stateare associated with large variability of the wind field and regionalheat storage in the upper ocean. This significant variation from yearto year in the ventilation of the Pacific waters is large and likelyaffects carbon fluxes in profound ways. Local manifestations of thedecadal shifts likely include changes in mixing, convection, gasexchange and upwelling. All would contribute to the changes in thesolubility pump. Further, each has an impact on nutrient supply andproductivity leading to changes in the biological pump. Given thegrand size of the North Pacific basin, interannual (ENSO) and decadal(PDO) scale variability in ventilation is likely important in upperocean control of atmospheric pCO₂. Whether recent changesare a result of global warming or natural variability due toatmospheric forcing or interactions between circulation in thetropical and extratropical Pacific can be resolved with a combinationof paleoceanographic and instrumental data. A boost in the number andlocation of moorings and/or the use of drifters or ships ofopportunity are strategies to be considered for increasing spatialand temporal instrumental data coverage.

• How important are margins to C pathways on basin to global-scale, at annual, decadal, and centennial time scales?

Margin processes are not marginal in the context of global carboncycling on decadal to centennial time scales. Continental marginsprovide Fe both to the overlying water and to the open ocean, aresites of a major portion of global denitrification, and are thegateway for terrestrial carbon input to the ocean. Primaryproductivity measurements, from S. California, central California,and the Washington margin indicate strong seasonality in primaryproductivity, and average values are >100 mmolC/m²d.New production is on the order of 50 mmolC/m²d which is 10times greater than new production at BATS, HOT and Sta. P and 7 timesgreater than new production in the Equatorial Pacific (JGOFS EqPac).Margins represent approximately 10% of the area of ocean basins,hence global new production should be about evenly divided betweenthe margins and the open ocean.

Important reasons to study continental margins in carbon cycleresearch are mainly their role in carbon export and preservation andtheir susceptibility to anthropogenic perturbations. Variability inthe recycling of exported carbon and its remineralization lengthscales should affect global CO₂ budgets on decadal tocentennial time scales. Carbon burial in margin environments is amuch more important removal term than burial in the deep oceanbecause of the high flux and relatively shallow water column. Burialrates on river-dominated and narrow margins are not well documented.Organic mater preservation rates in margin areas are subject to largevariations in time and space because of physical (floods, coastalerosion) and anthropogenic (eutrophication) forcing. Margins areparticularly sensitive to anthropogenic perturbations (trawling,pollution, coastal building) and many elements of coastal ecosystemshave been documented to track changes in physical forcing (PDO,ENSO).

• How are ecosystem dynamics and carbon cycling in the North and South Pacific affected by the source of Fe from above and below (dust, upwelling, margins, hydrothermal sources)?

Iron is now considered to play a crucial role in oceanic nutrientcycles. It may control the biological activity in high-nutrient, lowchlorophyll areas like the North Pacific, Equatorial Pacific and theSouthern Ocean. It may also control the rate of nitrogen fixation inthe oligotrophic gyres. Both of these processes may influence theair-sea partitioning of CO₂, and they determine theecosystem structure of these basins. The sources of iron are muchmore diverse than previously thought, and an understanding of each isrequired to determine the overall controls on biogeochemistry. Inopen ocean areas, atmospheric deposition of dust is the primarysource of iron. These fluxes are closely tied to terrestrial sourcesand their dynamics and tend to decline with distance from the source.Upwelling of subsurface, regenerated iron is important in areas wherethe primary macronutrients are brought up from below. This cycleoperates in rough concert with the macronutrient cycles. Near land,margin sediments are a third source of iron, both as a dissolved fluxand a particulate, resuspended flux. As iron is mobilized fromsediments, it spreads into the interior and becomes available throughupwelling. Finally, active volcanoes emit large amounts of iron andphosphate and could be local airborne sources.

• How do carbon fluxes and ecosystem structure in the equatorial Pacific respond to physical variability on ENSO and PDO timescales?

Upwelling of waters enriched in nutrients and carbon dioxidecreates a tongue of cold surface water along the equator, from thecoast of South America to the international dateline in theequatorial Pacific Ocean. The vast area involved makes this regionthe largest natural oceanic source of atmospheric CO₂.Physical processes and biological production determine the strengthof this source. During normal or cool conditions, high concentrationsof nitrate in the equatorial Pacific lead to unexpectedly smallincreases in chlorophyll. This low productivity contributes directlyto the loss of upwelled CO₂ to the atmosphere. Small-scaleiron fertilization experiments have shown that the low productivitycan result from iron limitation. The upwelled water originates fromthe EUC, which flows eastward across the basin at a depth of 20 to200m and is enriched in iron.

Every 3 to 7 years the central and eastern equatorial Pacificwarms dramatically as El Niño develops. On decadal scales thePacific Decadal Oscillation (PDO) is an important source ofvariability. Early conceptual models suggested that during ElNiño, Kelvin waves were the primary agents affectingbiological productivity, since upwelling-favorable winds weremaintained in the eastern Pacific. The waters upwelled were low innutrients and degassing of CO₂ to the atmosphere, andproductivity was hence reduced. During weak to moderate events, zonalwind anomalies are restricted to the western Pacific. However, duringthe strong 1997-98 event the zonal wind anomalies extended into theeastern equatorial Pacific, shutting down local upwelling anddegassing of CO₂ to the atmosphere in the centralequatorial Pacific for several months. After recovery from the1997-98 El Niño the equatorial Pacific again became a sourceof CO₂ to the atmosphere and an unprecedented large bloomwas observed, presumably the result of an enhanced supply of iron.While most think that the equatorial Pacific air-sea flux ofCO₂ is physically driven, the role of the biological pumphas yet to be adequately resolved for both particulate and dissolvedorganic carbon and particulate inorganic carbon. Further, theavailable field data is from the warm phase of the PDO. How theequatorial Pacific will respond to the projected cool phase of thePDO or to global warming is uncertain.

• What controls the fate of material that leaves the zone of net carbon production?

Organic matter respiration below the sun-lit surface ocean is adominant factor controlling chemical transformations and biologicalcommunities of the subsurface ocean. The rate of respiration anddownward transport of organic material (both particulate anddissolved) influence the depth scales of the chemical and biologicalchanges, which determines the response time of sequestration ofcarbon in the ocean by the biological pump and ocean circulation.Tracers in the euphotic zone (including ¹³C, the threeoxygen isotopes, and N isotopes) can make a big impact on ourunderstanding of production rates and hence also export processes.Rates of respiration in the sub-euphotic zone have been determined bymodeling apparent oxygen utilization and transient and short-livedtracers, because they are too slow to measure directly in most cases.A more complete understanding of the rates of respiration andtransport processes will help oceanographers determine the responsetime of the carbon cycle to climate change, should help close themass balance inferred from upper ocean tracers, and bear on questionsof spatial variability of inputs. A better understanding of theseprocesses will also aid in our attempt to use tracers of metabolicprocesses as indicators of decadal scale changes in the strength ofthe carbon pump. Specific areas that are ripe for improvedunderstanding are: (1) the rates and mechanisms of particulate anddissolved organic matter degradation, including the differing ratesof remineralization of micronutrients, P, N, and C; (2) the rates andmechanisms of particulate inorganic carbon (PIC) production anddissolution; (3) rates of mixing and subduction in the upper ocean,and (4) the influence of different amounts and types of organic materballast (in the form of calcium carbonate and opal) on its sinkingand degradation characteristics.

Major Features of the Southern Ocean

The Southern Ocean, defined for the purposes of this study as theregion south of, and including, the Subtropical Convergence, coversnearly 20% of the global ocean area. The Antarctic CircumpolarCurrent has the largest volume flux of any major ocean current (~130Sverdrups). It is the only continuous circumglobal current, withoutbeginning or end, and it is responsible for mixing of the deep watersof the other major oceans. Because of the absence of land masses toimpede its flow, a large component of the flow is barotropic. Most ofthe ventilation of deep-sea water masses takes place in the SouthernOcean; that is, deep water masses exchange gaseous components,including CO₂, with the atmosphere. Furthermore, most deepwaters derive their physical, chemical, and biologicalcharacteristics in the regions of the Southern Ocean where isopycnalsoutcrop at the sea surface and where mixing, cooling, and sea iceformation produce new water masses which sink into the ocean interiorand renew the intermediate and deep waters of the world’s oceans.

Associated with deep-sea ventilation is a series of frontalsystems that encircle Antarctica. From north to south the majorfronts include the Subtropical Convergence, the Subantarctic Front,and the Antarctic Convergence (Polar Front). These three fronts occurunder permanently ice-free conditions, and represent the sites offormation of mode waters in the north and Antarctic IntermediateWater in the south. Further south, under conditions of seasonal icecover, deep waters are drawn to the surface to the north of the SouthACC Front, the southern boundary of the ACC, bringing with themexcess metabolic CO₂ and inorganic nutrients – theproducts of centuries of deep-sea respiration in regions to thenorth. Finally, the densest bottom waters, spreading out over theworld’s oceans, originate from restricted areas near the Antarcticcoast, primarily in the Weddell and Ross Seas.

The extensive regular seasonal advance and retreat of sea ice,oscillating between a maximum coverage of ~20 (10)⁶km² and a minimum of ~4 (10)⁶ km²,represents the largest seasonal signal of changing environmentalboundary conditions in the global ocean. This surface feature, too,can be thought of as a frontal system, one that migrates north andsouth many hundreds of km annually. Biological productivity ofsurface waters is strongly influenced by the presence, and melting,of sea ice. Ice-edge productivity supports an abundance of life athigher trophic levels, including mammals and birds as well aszooplankton and fish.

The Southern Ocean is the ocean’s largest High-NutrientLow-Chlorophyll region. Roughly 90% of the phosphate and nitrate isocean surface waters resides in the Southern Ocean. The potential foraltering the partitioning of CO₂ between the atmosphereand the deep sea as the result of a perturbation of the efficiency ofnutrient utilization in the Southern Ocean has been widelypublicized. Some have even constructed schemes to fertilize theSouthern Ocean with iron as a geoengineering strategy to reduce thelevel of anthropogenic CO₂ in the atmosphere. Theecological consequences of such an endeavor have yet to beexplored.

An organized pattern of atmospheric circulation over the SouthernOcean known as the “Annular Mode” has recently been recognized.Broadly analogous to the North Atlantic Oscillation, the Annular Mode(AM) is characterized by changes in atmospheric pressure gradientsbetween high and temperate latitudes. Wind patterns associated withthe AM may exhibit teleconnections to the tropics, and may furtherexplain some of the interannual variability in the Southern Oceanassociated with the Antarctic Circumpolar Wave (ACW). The ACW is awave-number two feature that circles Antarctica with a period ofabout 8 years, and represents systematic changes in air pressure, airtemperature, meridional wind stress, and sea ice extent. Neither thenature of the teleconnections between these features and the tropics,nor the implications for ocean ecology and carbon fluxes, have beenstudied quantitatively.

Paleoclimate records show strong correlations betweenenvironmental conditions in the Southern Ocean and changes in theCO₂ content of the atmosphere, as recorded in air bubblestrapped in the polar ice caps. Past atmospheric CO₂concentrations are correlated not only with air temperature overAntarctica, but with sea surface temperature, sea ice extent, and theflux of dust from the atmosphere as well. These correlated featuresprecede the manifestations of climate change in other parts of theworld, implicating processes within the Southern Ocean as causalfactors regulating natural changes in atmospheric CO2. Because of theunique physical, chemical and biological features of the SouthernOcean described above, perturbation of physical and biogeochemicalprocesses in the region by future climate change may substantiallyalter the partitioning of CO₂ between the ocean and theatmosphere. While the potential for significant feedbacks in theSouthern Ocean in response to the rise in anthropogenicCO₂ is well recognized, our understanding of the processesin the Southern Ocean regulating carbon fluxes, and of theirsensitivity to perturbation, remains insufficient to predict with anyconfidence the consequences of global warming.

Critical Processes in the Southern Ocean

Superimposed on the large-scale barotropic flow of the ACC is anabundance of mesoscale activity, including eddies, the intensity ofwhich is regulated to some extent by bottom topography. Eddiescontribute significantly both to the meridional transport of heat andnutrients as well as to the vertical fluxes of limiting nutrientssuch as iron and, in some cases, silicon. Meandering of the majorfrontal features in the Southern Ocean represents another form ofmesoscale variability. Vertical displacement of waters influenced bymeandering fronts can be on the order of tens of meters per day.Vertical transport of this magnitude affects both the supply ofnutrients from below as well as the light regime experienced byphytoplankton.

Although major nutrients such as N and P are rarely depleted fromsurface waters, nutrient limitation by Fe and, sometimes, by Si aswell as by other essential elements, is believed to be common. Theimplications for ecosystem structure and, hence, for carbon fluxes ofaltering the supply of Fe and other limiting nutrients is onlybeginning to be explored.

Changes in stratification of the Southern Ocean, both throughnatural seasonal and interannual variability of physical conditionsas well as due to climate change, are likely to have substantialimpacts on carbon fluxes. South of the Polar Front, upper watercolumn stratification is largely determined by cold water of reducedsalinity residing over warmer, saltier circumpolar deep water. Warmsalty deep waters derive their characteristics by mixing with thedeep waters of the Atlantic, Pacific and Indian Oceans. Ventilationof deep waters in the Southern Ocean is directly dependent on therate of exchange between surface waters and deep waters and this, inturn, is dependent on the strength of the thermohaline stratificationof the upper water column. The static stability between the mixedlayer and deep water is quite weak, and small perturbations of thesalinity budget can upset the stability, thereby leading to a changein the rate of deep convection. Sea ice is maintained in a metastablestate through a network of negative feedbacks. Perturbation ofthermohaline stratification, and hence of the dependent features ofthe Southern Ocean such as sea ice distributions and deep-waterventilation, by greenhouse-gas-induced global change will depend,then, in large part on the effect of global change on the fresh waterbalance of the Southern Ocean.

Paleoclimate records indicate that the mean position of thewesterlies shifted meridionally in response to past climate changes,and it is conceivable that future climate change will likewise induceshifts in the position of the winds. Surface wind stress and Ekmandivergence are tied to the zero-line of wind stress curl, so it wouldbe expected that these features would shift with any change in thewinds. The major fronts, on the other hand, are believed to be lockedinto their position through interaction with bottom topography. Thepotential impact on carbon fluxes of a change in the physicalrelationship between the zero-line of wind stress curl and theAntarctic Polar Front have not been investigated. In addition,regional wind patterns are known to follow the Antarctic CircumpolarWave as it migrates around Antarctica. Divergence of the westerliesfrom seasonal sea ice boundaries may well have impacts on oceanecology and carbon fluxes, although these, too, have yet to beexplored.

Anticipated Perturbations of the Modern Carbon Cycle

With increased levels of atmospheric CO₂, there will beless need for phytoplankton to pump bicarbonate ions to fill theirneed for CO₂ in support of photosynthesis. This effect islikely to be less significant in the Southern Ocean compared to lowerlatitudes, however, because the low temperatures of Southern Oceanwaters lead to higher concentrations of aqueous CO₂, at agiven level of pCO₂, reducing the potential severity ofCO₂ limitation during phytoplankton blooms.

A general concern is that the acid titration of the ocean byrising atmospheric CO₂ will endanger calciumcarbonate-secreting organisms through the reduction of theconcentration of dissolved carbonate ion. A widely-held view is thatcarbonate-secreting plankton are rare in the Southern Ocean, and thatone need not consider this perturbation for this region. However, theanalysis of sinking particles collected by sediment traps deployed bythe U.S. JGOFS Southern Ocean program showed that the export flux ofCaCO₃ in the Southern Ocean, throughout the region northof the SACCF, is nearly as large as in the central equatorial PacificOcean. Ecological changes resulting from reduced carbonate ionconcentration in the Southern Ocean cannot be neglected.

General circulation models have predicted an increased flux offresh water to polar latitudes as a consequence of global warming. Asnoted above, stratification of the Southern Ocean is weak andprecariously balanced. A minor perturbation of the freshwater budgetcould lead to a radical alteration of the nature and rates ofconvection and deep water formation, as well as to changes in sea iceextent and seasonality (see below).

The abundance of major nutrients that exists in surface waters ofthe Southern Ocean reflects the limited capacity of phytoplankton toconsume these nutrients due to other factors, such as theavailability of iron. Both positive and negative impacts of dust (Fe)supply to the Southern Ocean, as the result of global warming, can beenvisioned. Increased temperatures over land may lead to reduced soilmoisture and, hence, to increased supply of dust. On the other hand,increased water vapor transport from warmer tropics to the poles willlead to enhanced washout of dust, thereby limiting the effectivenessof poleward atmospheric transport of dust. The net impact of globalwarming on the supply of dust to the Southern Ocean remainsunknown.

Seasonal advance and retreat of sea ice over the Southern Oceanrepresents one of the largest sources of environmental variability onearth. Much of the heat driving the seasonal melt-back of sea ice isprovided from below by upwelling of warm deep water. An increasedflux of freshwater (precipitation) to the Southern Ocean would leadto increased stratification and, consequently, to a reduction in theupward flux of heat. Therefore, the net effect of global warmingcould be an increase in sea ice cover of the Southern Ocean. Theconsequences for ocean ecology and carbon fluxes of thiscounterintuitive response to global warming remains untested.

As noted in the preceding section, wind patterns are expected tochange in response to global warming, and this may lead to a dominoeffect with changes in upwelling, mixed layer depths, sea ice extent,storminess, etc. Each of these, in turn, can affect ecosystemstructure and carbon fluxes.

Critical Questions/Hypotheses

The working group discussed a number of questions and hypothesesconcerning the role of the Southern Ocean in the global carbon cycle,as well as potential responses to global warming that may impartsignificant feedbacks into the rise in atmospheric CO₂levels. Physical, biogeochemical and ecological issues pertaining tothe Southern Ocean, jointly afforded high priority for future study,include:

• How do ecosystem structure and carbon fluxes respond to:

1. Changes in stratification, mixed layer depth?
2. Changes in sea ice extent and seasonality?
3. The mean and variance in the supply of iron?
4. Variability about the mean in the position of the fronts?
5. Changes in ventilation processes; for example, at sites of bottom water formation (shelf) and intermediate and mode water formation?
6. Changes in wind stress curl/Ekman divergence; for example, distance between zero line of the wind stress curl and the mean position of the Polar Front?
7. Changes in large-scale atmospheric circulation; for example, upwelling and Ekman transport?

• Does variability in carbon fluxes associated with the ACW contribute significantly to interannual variability in net air/sea CO₂ flux?
• Is Si limitation common in the modern Southern Ocean, and would it be reduced in a dustier world?

1. Recent studies have shown that the degree of silicification of diatoms, the dominant phytoplankton in the Southern Ocean, as well as the Si/N uptake ratio of diatoms, depends on Fe availability. Silica and nitrate are supplied by upwelling at a Si/N ratio of roughly three, whereas Fe-replete diatoms consume Si and N at a molar ratio of about one. Under Fe stress, Si/N uptake ratios rise significantly, although C/N ratios remain relatively constant and close to the traditional Redfield ratio. Observations made during the U.S. JGOFS program found Si limitation of diatoms in Antarctic waters, where less than half of the initial nitrate had been consumed. With increased supply of Fe, it is possible that all of the upwelled nitrate could be consumed without exhausting Si. Under these conditions, the system would shift to nitrogen limitation and, because of increased efficiency of nitrate consumption, there would be a net increase in the amount of carbon exported to the deep sea.

• Can we reconcile low measured inventories of anthropogenic CO₂ in the Southern Ocean with model predictions of high uptake at high southern latitudes? Doing so requires:

1. Improved techniques for estimating anthropogenic CO₂;
2. More direct CO₂ flux measurements and techniques for evaluating large-scale net flux;
3. Improved model parameterizations for Southern Ocean processes.

General Strategy to Advance our Understanding of the SouthernOcean

Given the high degree of spatial and temporal variability in theSouthern Ocean, it is necessary to extrapolate from discreteobservations to obtain basin-scale estimates of fluxes and changes inecosystem structure. Successful extrapolation will requirecoordinated efforts in the following areas.

Process Studies. Meaningful extrapolation requires amechanistic understanding of the processes regulating ecosystemstructure and carbon fluxes, as well as the response of theseprocesses to changes in physical forcing. Acquisition ofprocess-level information will require intensive dedicated studies,similar in some ways to those conducted by JGOFS, but also with somesignificant distinctions. For example, process studies may involvepurposeful manipulations to test hypotheses concerning ecological andbiogeochemical responses to physical and chemical perturbations.Process studies will also exploit natural temporal and spatialvariability to explore responses to changing environmentalconditions. For example, investigators may study regions “downstream”from islands (e.g., Kerguelan) to determine the long-term ecologicalresponse, as well as the net effect on nutrient consumption andexport production, to a sustained supply of iron. Process studieswill also be designed to exploit natural interannual variability, forexample associated with the Antarctic Circumpolar Wave, to determinethe sensitivity of ecosystem structure and carbon fluxes toperturbation by changes in sea ice, wind stress, and other physicalboundary conditions.

Expanded Observations. While process studies enable us toestablish the biogeochemical response to changes in environmentalconditions, they are insufficient in themselves to extrapolate thisunderstanding to basin and global scales. Spatial and temporalcoverage of observations must be expanded through a coordinatedprogram involving volunteer observing ships (VOS) and satellites,together with instrumented moorings and floats. Satellite data willbe used to provide broad synoptic coverage, as well as time-seriesinformation, about surface properties. Volunteer observing shipsprovide platforms to expand the spatial and temporal coverage ofparameters not measurable from space beyond results that can beobtained from dedicated research cruises. While commercial shiptraffic in the Southern Ocean is rare, the frequency of visits bytourist ships is increasing, and data can be collected from researchcruises dedicated to other disciplines. Moorings and floats provideadditional platforms for collecting time-series information aboutparameters not measurable from space, as well as the opportunity forin situ calibration of satellite-derived measurements. Mooredinstrumentation will also provide time-series information aboutsubsurface parameters; for example, to define the stratification ofthe upper water column, together with critical information aboutconcentrations and fluxes dependent on stratification.

Models. Parameterization of the understanding derived fromprocess studies, and incorporation of that information into regionalmodels, should take place concurrently with the observationalactivities described above. High-resolution coupled models of theSouthern Ocean, incorporating essential components of ecosystemstructure and biogeochemistry, need to be developed. . Moreover,models with realistic thermodynamics (e.g., linking sea ice modelswith GCMs, convective processes on the continental shelves, etc.)also must be developed and tested. Model development should be aniterative process, with repeated tests against observational data andsequential improvements as new information becomes available.Modeling will serve the broader community, both by developingcredible predictions of the response of the Southern Ocean to risinglevels of atmospheric CO₂ and through an improvedunderstanding of the contribution by Southern Ocean processes tonatural variability of atmospheric CO₂ associated withpast climate changes.

Development and Use of Sensor Systems

The distributions of inorganic and organic carbon pools in theocean are driven by temporally and spatially varying process thatcannot be efficiently examined solely with expeditionary ship basedobservations. It is well recognized that programs based solely onexpeditionary observations will undersample most biogeochemicalprocesses. Autonomous observing systems, including moored, driftingand profiling platforms, and Volunteer Observing Ships, provide animportant means of describing ocean variability on a range of spatialand temporal scales that are not accessible to observing programsbased solely on research ships. These scales may extend from muchfiner resolution than is available from shipboard sampling to muchlonger term observations. However, autonomous observation platformsmust use suites of sensor systems capable of monitoring many of theparameters that influence and are influenced by carbon-systemprocesses and fluxes. The availability of these sensors (or lackthereof) is a major hindrance in the use of autonomous observingsystems.

At the time the JGOFS program was designed and implemented therewere, with the exception of basic bio-optical instrumentation,relatively few chemical or biological sensor systems with theprecision, accuracy and endurance for useful in-situ analysis. One ofthe early goals of the JGOFS study was development of additionalsensor systems for biogeochemical processes. The long developmentalperiod required to bring new observing systems to an operationalstate (often 10 or more years) prevented these new sensors, includingthe SeaWIFS ocean color imager, from playing the role intended.Autonomous observing systems with bio-optical sensors were usedextensively in the Arabian Sea and Southern Ocean process studies(e.g., Marra et al., 1999) and they have become a key component ofthe BATS and HOT time series stations (e.g. Dickey et al., 1998), butthey did not play as large a role in earlier JGOFS studies.Nevertheless, development of diverse autonomous sensor systems hasbeen an important legacy of JGOFS. These new capabilities includeenhanced satellite-borne views of the global ocean (e.g., SeaWIFS;Chavez et al., 1999), moored determinations of the partial pressureof carbon dioxide (pCO₂; both absolute and air-seadifference; DeGrandpre et al., 1997; Chavez et al., 1999), in-situobservation of nutrient cycles (e.g., observations of eddy inducedchanges in nitrate flux; Johnson and Jannasch, 1994; McGillicuddy etal., 1998) and greatly improved estimates of carbon flux through thewater column (neutrally buoyant sediment traps in the water columnand long time-series observations of benthic respiration; Buesseleret al., 2000; Sayles et al., 1994; Smith et al., 1997).

Autonomous observing systems are now well poised for use in thenext generation of global carbon studies, including OCTET. They willcomplement shipboard measurements in a variety of ways. Autonomousin-situ systems can provide efficient monitoring of temporal changeson scales that are cost prohibitive via ship board measurements.Mobile platforms, such as gliders, drifters and VOS, will give sensorsystems access to broad geographic regions. In addition to acquiringdata on improved spatial and temporal scales, in-situ analysis canpotentially improve data quality by minimizing sample contaminationas well as transformations of metastable seawater constituents.Autonomous observations cannot currently supply the breadth ofspecialized measurements that can be made by shipboard scientists,and problems associated with power requirements, endurance,biofouling and sensor response times also weigh against the strengthsof in-situ observations. Nevertheless, a sufficient diversity ofautonomous sensors is now available to make in-situ biogeochemicalobservations a major part of global studies. Regions of specialinterest that are identified via the wide diversity of shipboardanalyses can be targeted for longer term observations with autonomousobserving systems capable of monitoring major components of thecarbon system.

Development of autonomous sensor systems typically progresses frombench top prototypes, to research systems operated in situ andfinally to production of operational systems that are accessible tothe broad community. The long time frames that have been required tobring new sensor systems to an operational status suggests that nextgeneration observational programs, such as OCTET, will be influencedprimarily by those sensor systems where significant developmentalprogress has already been made. Sensor systems will be useful notonly in OCTET, but also a variety of other programs such as theGlobal Ocean Observing System (GOOS), Climate Variability andPredictability (CLIVAR), ECOHAB (Ecology of Harmful Algal Blooms) andRIDGE (Ridge Interdisciplinary Global Experiment). The following textand tables represent a summary of many sensor systems that are nowoperational or well along in development, as well as a list ofsensors judged to be important but not yet under development. Itwould be useful in the long term to obtain community perspectives onthe significance of various measurement capabilities in furtheringOCTET goals. Which measurements are essential? Which are highlyrecommended, useful, or only of marginal importance?

Current Sensor and Sensor Platform Capabilities

Many biogeochemical sensor systems are under development orcurrently in use. The capability of several of these are described inTables 1-5 with respect to deployment mode (moored, drifting),profiling capability, power requirements and response time. In eachtable, column 1 identifies the sensor type and column 2 indicates thecurrent status of development: (I) if the sensor is currentlyoperational and available commercially; (II) if it has beensuccessfully deployed in the marine environment for extended periods(>1 month) with oceanographically consistent results but notcommercially available; (III) if it is in an early stage ofdevelopment with successful short-term deployments in the marineenvironment; or (IV) if bench top prototypes are in operation. Column3 provides an estimated range for the sensor power consumption with areasonable duty cycle (e.g., 1-10 measurements per day on a mooringor drifter, or one complete vertical profile per day on glider orfloat). Column 4 provides each sensor’s processing time per sample(e.g., seconds, minutes, hours). Column 5 indicates each sensor’scapabilities for moored operations (M) and/or deployment on drifters(D). Finally, column 6 indicates the capability of each sensor forprofiling measurements (P), autonomous shipboard measurements (S) andmanual shipboard measurements (s). Although sensor cost is a veryimportant issue regulating the number of sensors that can be deployedand the types of integrated sensor platforms that can be constructed,sensor costs are likely to be strongly influenced by demand andtherefore are highly transitory. Therefore no attempt has been madeto assess this important issue. Since some sensors currently underdevelopment for seawater analysis will also find applications infreshwater and drinking water investigations, it is anticipated thatsensor commercialization will decrease capital costs per unit.

Sensor Platforms

The sensor systems shown in Table 1 to 5 are appropriate to some,but generally not all, types of sensor platforms. In addition tooceanographic research vessels, potential platforms for sensordeployments include the following:

• Volunteer Observing Ships. VOS observations are generally confined to measurements of sea surface parameters and/or measurements of atmospheric chemistry along major commercial shipping routes. Repeated passages of VOS can provide observations of surface ocean chemical properties over many seasons and years.
• Moorings and Surface Drifters. Observations from moorings can provide high vertical and temporal resolution of processes at a single point via subsurface instruments, vertically profiling packages, or fiber optic links to sensors at depth. The high cost of maintaining moorings generally limits them to a few in number. However, the TAO/TRITON array of some 70 moorings in the Equatorial Pacific (http://www.pmel.noaa.gov:80/toga-tao/home.html) is an example of the effort that can be sustained if observations receive sufficient societal support. Surface drifters are proximate to the sea surface, but they can also be expected to access the mixed layer in general. The very large number of drifters deployed in the WOCE program (http://www.aoml.noaa.gov/phod/dac/gdc.html) illustrates the potential of sampling with low cost packages distributed throughout the ocean.
• Floats and Gliders. Observations from gliders and neutrally buoyant floats are distinct from VOS, mooring and surface drifter observations in allowing access to both surface and mesopelagic zones over broad geographic ranges. A principal advantage of neutrally buoyant floats is low cost and, therefore, an extremely large geographic distribution with reasonable sampling density (http://wfdac.whoi.edu). This is an important and occasionally essential advantage in assessment of biogenic particle fluxes. Gliders share with floats a capacity for substantial observational endurance and resolution on a vertical scale. They are distinct in providing a capacity for observations of parameter gradients along defined horizontal sections. Although gliders are still in development, they hold significant promise.
• CTDs and Towed Vehicles. A principal advantage of CTD based measurements is rapid profiling of selectable depths. Towed, undulating vehicles constitute an important platform for integrating chemical and physical measurements with biological measurements and sample collections over mesoscales. Both platforms require the presence of a research ship.
• Autonomous Underwater Vehicles. AUV operations provide for biogeochemical observations with somewhat reduced constraints on sensor power consumption. Deployment of larger sensor arrays is therefore possible. AUVs potentially have access to all ocean depths, and fuel-cell technology provides a capacity for great measurement endurance. The endurance and spatial coverage of AUV operations could be greatly extended via mid-ocean nodes for AUV deployment and docking. AUVs should, therefore, be capable of multiple autonomous docking and deployment cycles. Finally, it is important to recognize the potential for extending shipboard measurement campaigns via AUV-assisted operations.
• Satellites. Observations obtained via satellite include ocean color (from which chlorophyll concentration is obtained), sea surface height, wind field, temperature, dust and aerosol optical thickness. Satellite observations constitute the most potent capability for integrating global observations of the upper ocean. Although they generally provide little information on the ocean interior, the global extent of coverage greatly outweighs this limitation. The global coverage that is unique to satellite-borne sensors provides a powerful capability for integrating and constraining other observations and model results.
  

Sensors

Table 1 lists sensors for measurement of inorganic carbon systemparameters. Characterization of the carbon system requiresmeasurement of two independent carbon dioxide parameters. The partialpressure of CO₂ (pCO₂) is currently measured insitu (e.g., DeGrandpre et al., 1997) and as a mole fractiondifference between the atmosphere and seawater (from which deltapCO₂ is calculated). Measurements of delta pCO₂have been made continuously for more than 1 year on several of theTAO/TRITON moorings (Chavez et al., 1999). Seawater pH has beenmeasured in situ using spectrophotometric procedures similar to thosethat have been used for in-situ pCO₂ measurements(Kaltenbacher et al., in press). Total dissolved inorganicCO₂ (C_T) measurements and total alkalinity(A_T) measurements are currently obtained only throughshipboard procedures. In-situ C_T measurements are underdevelopment.

Dissolved gas measurements are essential parameters forassessments of net primary production. In-situ oxygen measurementsare currently obtained through amperometry with Clark-type membranecovered electrodes (Wallace and Wirick, 1992; DeGrandpre et al.,1997). A variety of commercially available sensors are available,although long-term stability (>1 month) at the level required foroceanographic studies remains problematic (S. Emerson, personalcommunication). Fluorometric measurements are also possible andshould be amenable to some types of in-situ work, although thesesensors are also subject to stability problems (Demas et al., 1999).Commercially available gas tension devices provide N₂fugacity estimates as a difference between total gas fugacities andthe fugacities of O₂ and Ar. These measurements are neededto assess whether oxygen concentration changes are due to physical orbiological processes. A Membrane Introduction Mass Spectrometerydeveloped for measurements of volatile species has been deployedin-situ and shows promise for observation of a variety of gasesin-situ (Short et al., 1999).

Table 2 summarizes the current measurement capabilities ofnutrient and micronutrient sensors. A more extensive review can befound in Johnson et al. (2000). Nitrate and nitrite can currently bemeasured throughout the water column using several procedures. Avariety of adaptations of the standard colorimetric method fornitrate (reduction on cadmium to nitrite and determination as an azodye) have been developed, and several are available commercially.Colorimetric nitrate analysis systems have been deployed in the openocean for time periods up to 4 months (e.g., McGillicuddy et al.,1998). Sensitive fluorometric procedures are available for all formsof inorganic nitrogen in AUV and ship based operations, but have notundergone extensive field testing. Autonomous PO₄ and Simeasurements are currently available only as shipboardmeasurements.

Trace metals are key regulators of the ocean carbon cycle. Ironcan be measured using both chemiluminescence and colorimetricprocedures. These procedures are potentially robust and amenable toall forms of in-situ analysis. Detection limits must be less than 0.1nM for open ocean applications. Autonomous Mn measurements have beenobtained in situ via fluorescence based measurements (Klinkhammer,1994).

Table 3 lists several developments that are underway on biologicalsensor systems. The response of the ecosystem to chemical andphysical forcing is a key factor in understanding globalbiogeochemical cycles, and sensors that report ecosystem structureand rates of ecosystem processes, such as primary production, arecritical. For example, changes in iron flux that may stimulatenitrogen fixation may dramatically alter the potential capability ofthe biological carbon pump. Biooptical instrumentation such asspectral radiometers, fluorometers and transmissometers make itpossible to assess the stock of particles and their nature bymeasuring changes in the optical properties of seawater. Theseinstruments are generally well developed and commercially available.Key improvements regarding resistance to biofouling are being made.DNA based analyses, driven by the biomedical industry, may shortlymake it feasible to determine phytoplankton speciation at the genusand species level with autonomous observations (e.g., Scholin et al.,2000). Developments of instruments such as the Fast Repetition RateFluorometer now make it possible to remotely study the physiologicalstate of phytoplankton (e.g., Behrenfeld et al., 1996).

Table 4 lists a variety of instruments that operate by collectingsamples for later laboratory analysis. These include instruments thatmeasure vertical particle flux, both from moored or neutrally buoyantplatforms, benthic landers that measure chemical flux across thesediment-water interface and in-situ filtration devices that allowparticles or dissolved chemicals present at ultra-traceconcentrations to be collected from large volumes of seawater. Recentdevelopments include submersible incubation devices that may be usedto perform in-situ ¹⁴C primary production measurements andwater sampling devices that can collect uncontaminated samples fortrace metal analyses, obviating the need for complex, trace metalclean, sampling gear. A novel mooring that allows marine aerosols tobe collected and analyzed is currently being tested.

Finally, Table 5 summarizes some of the satellite sensors that arenow operational or which are in development. Satellite sensorsprovide an unparalleled view of the spatial and temporal variabilityof processes that leave a detectable imprint on the ocean surface.Such processes include the development of phytoplankton blooms whichalter ocean color, and the formation of eddies which may alterseasurface height and temperature and therefore the spectrum ofoutgoing infrared radiation. Sensors for these systems areoperational and relatively well understood. Recent developmentsinclude algorithms to determine concentrations and fluxes ofair-borne aerosol including transport of micro-nutrient iron tophytoplankton. Remote sensors for salinity are in the planningstages. Satellite sensors will play an integral role in the nextgeneration of global studies.

Potential Applications of Autonomous Sensor Systems to OCTETObjectives

Autonomous sensor systems could be applied directly to test anumber of OCTET hypotheses. For example, imagine a profiling gliderequipped with CO₂, oxygen and nitrate sensors, as well asa small suite of bio-optical instrumentation and a CTD. An array of100 such instruments could be used to directly answer questions suchas: How do carbon fluxes in the equatorial Pacific respond tophysical variability on ENSO and PDO time scales? What is themagnitude of the carbon sink (natural and perturbed) in the NorthAtlantic? What is the natural variability of carbon uptake in theSouthern Ocean? How do ecosystem structure and carbon fluxes respondto changes in stratification and mixed layer depth?

Another example includes an autonomous observing system that isbuilt around a moored aerosol sampler (Sholkovitz et al., 1998).Deposition of aerosol iron on the sea surface is an episodic eventthat may stimulate short lived, but important plankton blooms. Suchepisodic events are difficult to sample from a ship, but may be wellresolved by a moored system that measures aerosol concentration,nutrient and trace metal concentrations in the upper ocean andproduction of biomass (determined from biooptical paramters).

Development of such instruments is a reasonable programmatic goal.All of the individual sensors have now been operated for extendedperiods of time in the ocean. The glider platform is now operationalfor at least limited deployments and versions capable of making oceanbasin transects are in development. Moored buoys capable of samplingaerosols have been demonstrated.

Satellite-borne sensors in particular will be useful inmeasuring or inferring biogeochemical variables of interest to OCTETgoals on a basin scale. Several oceanographic processes (andcompartments of the carbon cycle) can be addressed with remotesensing observations. For example, estimates of air-sea gas exchangeand oceanic pCO₂ can be improved using remote sensing. Theair-sea exchange coefficient is usually parameterized using windspeed. Scatterometers provide global observations of wind speed anddirection on a daily basis. Similarly, measurements of surfaceroughness (from which capillary wave height is estimated) from theTOPEX/Poseidon altimeter (Frew et al., 2000) or from scatterometrymay give a more direct value of the exchange rate than wind-basedparameterizations.

Relationships between sea surface temperature and pCO₂are not globally applicable and change in space and time (Lee etal.,1998). Salinity will be measured remotely on European and USsalinity missions in the mid-2000s; this will enable the applicationof local relationships obtained from shipboard and moored or driftingplatforms. Although chlorophyll concentration (obtained from oceancolor) is often invoked as a factor determining pCO₂, thealgorithms that would incorporate it are still under development.

Ocean color measurements have fueled the development of a suite ofprimary production (PP) models that use chlorophyll concentration,irradiance, and SST (all measured remotely). There are several typesof PP models with varying degrees of complexity (Behrenfeld andFalkowski,1997). Although models exist to estimate primaryproduction, a significant level of uncertainty follows from ourestimates of new or export production. Most of these estimates use arelationship between f-ratio and SST or primary production, nitrateor chlorophyll concentration (Sathyendranath et al.,1991). Theseapproaches can be used with satellite-derived measurements, but willonly be as good as the primary production estimate and as theinferred f-ratio, which may vary regionally and with time.

Satellites also provide an unprecedented opportunity to quantifyvariability and processes that are unresolved by coarse models andnecessarily inadequate sampling campaigns. Quasi-synoptic coverage isan amazing benefit, even considering the loss of data due to cloudcoverage for electromagnetic sensors. The TOPEX/Poseidon altimeterenables improved quantification of eddies for biogeochemicalapplications (Siegel et al., 1999) and for ocean circulation models.Coastal processes, which require higher spatial and temporalresolution than is usually possible from sun-synchronous sensors, canbenefit from geostationary platforms and multispectral reflectancemeasurements. The NASA-NOAA Special Events Imager (SEI) willinstrument a GOESS satellite in the early 2000s and will be capableof 300m (few-minute) resolution.

Sensor Wish List

As mentioned above, the development time for sensors is long andsomewhat unpredictable. Efforts to continue sensor development mustbe an important adjunct to global biogeochemical studies. There is aclear need for a variety of additional sensor systems, includingcontinued development of moored sampling equipment for trace metalsand for gases, including inorganic carbon and freons. Sensors capableof monitoring important components of the carbon system on relativelyhigh speed platforms (towed, undulating fish or CTDs) are alsoneeded. Extensive development is needed before measurement of majorcomponents of the organic matter pool, particularly dissolved organiccarbon, nitrogen and phosphorus, is possible. Particulate inorganiccarbon sensors would be an important tool to monitor changes in theratio of organic to inorganic carbon export, a potential control onthe oceans capacity for fossil fuel carbon dioxide. Sensors capableof ultratrace measurements of metals, particularly iron, and metalspeciation would also be valuable.

One of the most important advances in sensor technology is likelyto follow from the development of micro electromechanical systems(MEMS). MEMS devices will provide chemical analyses on a chip.Colorimetric microfluidic MEMS devices are expected to be veryversatile and amenable to mass manufacture. Since many importantorganic measurements are based on absorbance spectroscopy, low costMEMS devices may allow a large number of measurement types within onesmall, inexpensive, robust and widely deployed system.

Refinement of existing sensors is also an important activity thatmust be continued. This includes important efforts to reduce size,power requirements, cost and failure rates of current sensors.Relatively modest improvements will greatly extend the usability ofinstruments.

Conclusions

A variety of sensor systems and platforms are under development.Although the development of measurement protocols is generally along-term process, this is not always the case. Some sensor systemswill be amenable to a wide variety of analyses. Colorimetric analyseshave many attributes in common, with differences based principally onthe timing and sequence of reagent additions to aqueous samples. Assuch, a single spectrophotometric system can be used to access avariety of measurements solely via software and reagent selections.Critical perspectives on sensor/platform efficacy will be gainedthrough long-term in-situ testing and rigorous intercomparisons withship-based sampling. Initial deployments of in-situ devicesconstitute the final stage of sensor development in which field dataare obtained while sensor performance is still under evaluation.Since sensor capabilities are multidimensional with respect to powerrequirements, endurance, detection limits, size, cost, etc.,deployment of suites of sensors for measurement of a single chemicalparameter can provide important insights about not only sensoraccuracy, but also the deployment modes most appropriate for eachsensor design. In some cases, simultaneous deployment of a variety ofsensor types can be used to assess sensor accuracy/efficacy. Thesuite of inorganic carbon-system measurements, total dissolvedinorganic carbon, alkalinity, pCO₂ and pH, are linked viaa robust physical-chemical model. While only two of these fourmeasurements are required for calculation of all system parameters,different types of measurements may be appropriate for differentdepths and locations.

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Chavez F. P., P. G. Strutton, G. E. Friederich, R. A. Feely, G. C.Feldman, D. G. Foley and M. J. McPhaden. 1999. Biological andchemical response of the equatorial Pacific to the 197-98 El Nino.Science 286: 2126-2131.

DeGrandpre, M. D., T. R. Hammar, D. W. R. Wallace and C. D.Wirick. 1997. Simultaneous mooring-based measurements of seawaterCO₂ and O₂ off Cape Hatteras, North Carolina.Limnol. Oceanogr. 42: 21-28.

Demas J. N., B. A. DeGraff and P. B. Coleman. 1999. Oxygen sensorsbased on luminescence quenching. Anal. Chem. 71: 793A-800A.

Dickey, T., D. Frye, H. Jannasch, E. Boyle, D. Manov, D.Sigurdson, J. McNeil, M. Stramska, A. Michaels, N. Nelson, D. Siegel,G. Chang, J. Wu, and A. Knap. 1998. Initial results from the BermudaTestbed Mooring Program, Deep-Sea Res. I, 45: 771-794.

Frew, N.M. et al. 2000. AGU Ocean Sciences Meeting Abstracts, SanAntonio, TX.

Johnson, K. S., and H. W. Jannasch. 1994. Analytical chemistryunder the sea surface: monitoring ocean chemistry in situ. NavalResearch Reviews, XLVI-3: 4-12.

Johnson, K. S., V. A. Elrod, J. L. Nowicki, K. H. Coale and H.Zamzow. 2000. Continuous flow techniques for on site and in situmeasurements of metals and nutrients in sea water. In, In situmonitoring of aquatic systems: chemical analysis and speciation, J.Buffle and G. Horvai, eds. John Wiley.

Kaltenbacher, E., E. T. Steimle and R. H. Byrne. In press. Acompact, in situ spectrophotometric sensor for aqueous environments:Design and applications. IEEE Oceanic Engineering Society. UnderwaterTechnology 2000.

Klinkhmammer G. P. 1994. Fiber optic spectrometers for in situmeasurements in the oceans: the ZAPS probe. Mar. Chem. 47: 13-20.

Lee, K, R. Wanninkhof, T. Takahashi, S.C. Doney and R.A. Feely.1998. Low interannual variability in recent oceanic uptake ofatmospheric carbon dioxide. Nature 396:155-159.

Marra, J., T. D. Dickey, C. Ho., C. S. Kinkade, D. E. Sigurdson,R. Weller, and R. T. Barber. 1999. Variability in primary productionas observed from moored observations in the central Arabian Sea in1995, Deep-Sea Res. II, 45: 2253-2267.

McGillicuddy D. J. Jr., A. R. Robinson, D. A. Siegel, H. W.Jannasch, R. Johnson, T. D. Dickey, J. McNeil, A. F. Michaels, A. H.Knapp. 1998. Influence of mesoscale eddies on new production in theSargasso Sea. Nature 394: 263-266.

Sathyendranath, S. T. Platt, E.P.W. Horne, W.G. Harrison, O.Ulloa, R. Outerbridge and N. Hoepffner. 1991. Estimation of newproduction in the ocean by compound remote-sensing. Nature 353:129-133.

Sayles F. L., W. R. Martin and W. G. Deuser. 1994. Response ofbenthic oxygen demand to particulate organic carbon supply in thedeep sea near Bermuda. Nature 371: 686-689.

Scholin C. A. and 25 others. 2000. Mortality of sea lions alongthe central California coast linked to a toxic diatom bloom. Nature403: 80-84.

Sholkovitz E., G. Allsup, R. Arthur and D. Hosom. 1998. Aerosolsampling from ocean buoys shows promise. EOS Trans. Am. Geophys.Union 79: 29.

Short R. T., D. P. Fries, S. K. Toler, C. E. Lembke and R. H.Byrne. 1999. Development of an underwater mass-spectrometry systemfor in-situ chemical analysis. Meas. Sci. Technol. 10: 1195-1201.

Siegel DA, McGillicuddy DJ, Fields EA. 1999. Mesoscale eddies,satellite altimetry, and new production in the Sargasso Sea. J.Geophys. Res.-Oceans 104: 13359-13379.

Smith, K. L. Jr., R. C. Glatts, R. J. Baldwin, S. E. Beaulieu, A.H. Uhlman, R. C. Horn, and C. E. Reimers. 1997. An autonomous,bottom-transecting vehicle for making long time-series measurementsof sediment community oxygen consumption to abyssal depth. Limnol.Oceanogr. 42: 1601-1612.

Wallace, D. W. R. and C. D. Wirick. 1992. Large air-sea gas fluxesassociated with breaking waves. Nature 356: 694-696.

Table 3a. Summary of autonomous sensors for ecosystemparameters

Table 3b. Summary of autonomous bio-optical sensors forecosystem parameters

Table 5. Summary of satellite borne sensors

The primary focus of OCTET is to improve our understanding ofbiogeochemical processes related to the carbon system that must beknown to estimate future global environmental changes. The primegoals of OCTET encompass a longer time frame than did the goals ofJGOFS. Paleoceanography (the study of the behavior of the ocean inthe past) can contribute to OCTET by extending our understanding ofnatural variability of the ocean to the period before the onset ofmodern instrumental observations. To do this, the tools ofpaleoceanography – which in recent times are dominantly geochemical”proxy” tracers – must be properly calibrated and evaluated. Theobservations made by OCTET will be crucial in establishing andimproving these tracers when they are made in the context of theassessing appropriate paleoceanographic proxies.

How paleoceanography can contribute to OCTET

The scientific community is attempting to predict the consequencesof global anthropogenic perturbations for decades to centuries intothe future. Most observations of the ocean extend only 50-100 yearsinto the past, yet even for that period many observations are sparseand incomplete. It is risky to predict the evolution of even anunperturbed system for periods longer than the interval ofobservations. Many of the global changes anticipated for the futurehave occurred in the past; it behooves us to take advantage of thesepast natural experiments to improve our understanding ofbiogeochemical processes. If glacial/interglacial CO₂cycles cannot be explained, how can we claim to have predictive skillfor the carbon system?

We have already learned much about the carbon system frompaleoclimatic records, particularly with regard to the processes thatgovern natural CO₂ variability. Our geologic andglaciologic records show that the carbon system can undergo largechanges in response to relatively minor shifts in incoming radiation(Milankovich Effect). These data indicate that the sensitivity of thecarbon system may be large, and indicate the presence of largepositive feedbacks to amplify the modest and gradual energy forcingsinto major climate shifts. Evidence suggests that nutrient uptakeefficiency in high latitude, high nutrient regimes has changed, andthat there have been large changes in export flux from the surfaceocean. Large changes in the physical environment of the upper oceanhave been documented (e.g., temperature, salinity, mixed layer depth,thermocline depth); these changes have biogeochemical consequencesthat are documented in the sedimentary record. Scientificunderstanding that the earth is not a fixed unchanging environment isbased on evidence from the past derived from geological studies; wemight be more complacent about the prospects of future change withoutthis geological perspective.

Concretely, paleoceanography can contribute the following to OCTETgoals:

• The study of changes that have occurred in the past can contribute to the understanding of long term natural variability (against which future changes must be judged as natural or due to human perturbations)
• Instrumental time series for the past few decades can be extended into the past, allowing for (a) better judgment of periodic and aperiodic behavior, (b) identification of the long-term mean, and (c) understanding natural extrema.
• Most measurements of the ocean have been made after anthropogenic perturbation began; paleoceanographic tools can assess the state of the ocean before it was perturbed.
• It is convenient to assume that the ocean was in a steady state before human influences, but we cannot know this assumption is true without studies that evaluate the system before the perturbation began.
• In cases where the forcing factors are understood (e.g., orbital influences on insolation; changes in greenhouse gas concentrations), paleoceanographic studies can assess the sensitivity of climate to forced changes and evaluate the positive and negative feedbacks that occur in response to the initial forcing.
• Often the period of modern observations began after the injection of valuable transient tracers such as radiocarbon and tritium. Paleoclimatic studies can help us reconstruct the evolution of transient tracers through studies of tree rings. Examples: the evolution of tritium in tropical oceans may be recoverable from the tritium content of mangroves; corals contain records of some transient radioisotopes [⁹⁰Sr] and trace elements [Pb]; studies of ¹⁴C in surface and deep-sea corals can document the early evolution of the bomb radiocarbon transient; and studies of C in sclerosponges can document the oceanic history of the “Suess Effect”, ¹³C reduction by fossil fuel burning.
  

Several points about time scales should be emphasized in thiscontext:

1. OCTET may not want to consider all processes that operate on glacial/interglacial time scales (and longer).
2. Paleoceanographic measurements can cover both millennial and shorter time scales. Examples: (a) laminated sediments with annual resolution [e.g., diagenetic metals (Mo) in Santa Barbara Basin appear to provide a record of ENSO in recent sediments, and stable isotopes document centennial climate change 25-65 ka], (b) high deposition sediment records with centennial resolution (e.g., the “Little Ice Age” and “Medieval Warm Periods” have been observed in Bermuda Rise cores), and (c) scleractinian corals, deep sea solitary corals, and mollusk records that provide records of bomb ¹⁴C and other chemical changes.
3. Processes that are important to glacial/interglacial CO₂ change can act in many cases on any time scale, even if their natural forcings occur on longer time scales. Example: changes in high latitude nutrient uptake.
4. We must be cautious about pigeon-holing the time scale of some processes. For example, an abrupt change in nitrogen fixation may cause rapid short-term changes in carbon flux before settling into the steady-state millennial response time of the oceanic nitrate inventory.

How OCTET can contribute to paleoceanographic work

At the same time that paleoceanographic work can contribute toOCTET goals, OCTET studies can contribute to the development andrefinement of paleoceanographic tools. OCTET will improve ourunderstanding of the biogeochemical character of the modern ocean,which will provide a context within which proxy tools can be comparedto modern conditions. OCTET refinement of our understanding ofgeochemical processes will contribute to our ability to model pastenvironmental changes, and reduce the uncertainties ofpaleoceanographic proxies. The best paleoceanography is done byiterative forays between proxy development in the modern ocean,investigation of paleo archives, and consideration of theimplications for modern biogeochemistry.

OCTET can contribute the following to paleoceanography:

• Ground-truthing of recorders, proxy testing and development: OCTET can contribute to proxy testing in the context of process studies. For example consider the JGOFS studies of particulate and diagenetic barium fluxes, and process studies of N isotopes and nitrate uptake. In some cases we have major discrepancies between proxies. Proxies can be difficult to measure, so individual investigators may find it necessary to specialize in a limited number of properties; but these measurements should be considered together with other proxies at the same times and places rather than being completely disjoint in time and space. OCTET coordination can ensure that full advantage is taken of the multi-proxy approach.
• Some geochemical tracers have an inadequate global database (e.g., d¹³C in deep and bottom waters, nitrogen and silicon isotopes in the upper ocean, Cd and Fe concentrations in the water column). Future proxy development may depend on the availability of archived samples. A major effort such as OCTET will send biogeochemists to sea in remote locations. It is imperative that we take advantage of this presence to improve our global database of geochemical tracers. As far as is practical, OCTET cruises should archive water, particle, and box-core/multi-core samples with pore water geochemical measurements for future measurements of tracers yet to be developed.
• Paleoceanographic studies rely on the accuracy of time scales provided by radioisotopes such as ¹⁴C and ²³⁰Th. Although our understanding of these tracers is good enough to provide reasonable accuracy, evolving demands for improved precision and accuracy of dating exceed our understanding of the behavior of these radioisotopes in the modern ocean. OCTET will use radioisotope tracers such as ¹⁴C and ²³⁰Th to help constrain rates of processes in the modern carbon system, but OCTET can also use these studies to improve our understanding of the geochemistry of these isotopes so as to provide for more accurate and precise time scales in future paleoceanographic efforts.
  

Paleooceanographic studies appropriate for OCTET

The following examples (with testable hypotheses) indicate some ofthe paleoceanographic studies appropriate for OCTET. The list is notexclusive; the justification for a given paleo/OCTET link is bestdone by individual scientists explaining the relevance of their workto OCTET goals.

1. The relationship between sea surface temperature, salinity, sea ice, and other physical boundary conditions with paleoceanographic indices
   Hypothesis: Stratification changes in the Southern Ocean were forced by changes in the wind-field and associated shifts in Ekman divergence.
2. The relationship between geochemical tracers (e.g., ¹⁴C) and the physical circulation of global and regional oceans, and their role in determining surface ocean processes.
   Hypothesis: Climate change is manifested by the frequency within which recognized states of the modern climate system are occupied. Example: the “bipolar seesaw”, first recognized in paleoclimate records, may affect the carbon and nutrient chemistry of the ocean subsurface, with changes occurring on decadal time scales.
3. The relationship between nutrient concentrations and uptake, and ecological regime in high nutrient areas. Changes in export flux from the surface ocean, and chemical composition of that export.
   Hypotheses: Nutrient uptake in the Antarctic surface was higher during the last ice age and therefore drove glacial/interglacial atmospheric CO₂ change. Export fluxes were several fold lower in the glacial Antarctic and several-fold higher in the glacial Subantarctic.
4. The relationship between Redfield ratios and nitrogen fixation.
   Hypotheses: The oceanic nitrate reservoir was modulated by the size of the inorganic phosphate reservoir. Nitrogen fixation rates were higher in the glacial ocean, and denitrification rates were lower.
5. The relationship between margin environments (high resolution sedimentary records and their contribution to export to the deep ocean), anthropogenic impacts on the ecology and productivity of coastal waters, and the role of rivers and estuaries.
   Hypothesis: Large natural variations have occurred in export production and/or the intensity and depth of the O₂ minimum zone in the California Current system.
6. (The relationship between multi-annual and decadal ocean variability will affect biogeochemical cycles, and the nature of these modes of variability will likely change in the future.
   Hypothesis: The frequencies of ENSO/NAO/PDO events have changed on centennial time scales.

Conclusions

The paleoclimatic record shows that large changes in oceanic”regime” have occurred (glacial/interglacial changes, variations infish populations off Southern California, etc.). Althoughpaleoclimate proxies are always subject to improved quantitativeunderstanding, there is no doubt about the qualitative accuracy ofthese observations of oceanic variability. We must develop a betterunderstanding to accurately interpret these changes.

Although we foresee a symbiotic relationship between OCTET andpaleoceanographic research, paleoceanographic work within OCTETshould focus on the main OCTET goals. OCTET should focus on proxytesting and development through process-related measurements (withbox coring at process stations linking ocean process studies tostudies of the sedimentary record; coral calibration studies nearOCTET time series stations, etc.)

Sociological Issues

A central organizing principle of OCTET should be closecollaboration between modelers and non-modelers, and thiscollaboration should extend (in any particular study) from theformative stage, through the period of data collection and analysis,and into the synthesis and modeling stage. The justification for thisclose collaboration is that an essential output from OCTET will bethe formulation of algorithms that allow better prediction of theeffects of climate change on ocean processes, and of the feedbacks ofthese changes to climate. This goal is likely to be met to a greaterdegree if data collection is designed with algorithm development inmind, so that data is collected in a manner that insures itsusefulness in modeling. Conversely, close collaboration will insurethat any models that are developed will be based on the best currentunderstanding of the ocean carbon system as described bynon-modelers.

To insure this collaborative atmosphere, misperceptions about theplace of modeling in the scientific endeavor must be overcome.”Modelers” create and use analytic and numerical mathematical modelsto understand the implications of mechanisms and empiricalgeneralizations, the goal being both improved understanding andimproved skill at numerical prediction. “Non-modelers” also usemodels, but because these tend to be verbal, pictorial, orstatistical (e.g., regression analysis), they are often notrecognized as such. The distinction between modelers and non-modelersis therefore one of technique, not of goal. Bringing all availabletechniques to bear in all phases of OCTET studies has the potentialto increase substantially the rate of progress in our field

Strategy: Three specific suggestions were made concerningmechanisms for bringing modelers and non-modelers together.

1. Joint participation by both modelers and non-modelers on OCTET proposals should be encouraged. This mechanism was begun in JGOFS SMP and is also strongly encouraged in NSF Biocomplexity proposals, and seems to be leading to a better working relationship between modelers and non-modelers.
2. Participation of modelers in data-gathering exercises, such as cruises, should be encouraged. The inclusion of modelers who use real-time satellite data may directly enhance sampling efficiencies. However, it should also be valuable to include more process-oriented modelers, so that their insights and confusions in using data to construct better algorithmic representations of reality can be confronted in real time.
3. Courses could be created to introduce non-modelers to modeling; this would introduce non-modelers to the requirements and thought processes of modeling, in much the same way that including modelers in data-collection would improve their intuitive appreciation of data.
   

Modeling Issues

The current generation of numerical ocean biogeochemical modelsare based almost entirely on the aggregated N-P-Z (nutrient,phytoplankton, zooplankton) box model framework dating back at leastseveral decades in aquatic ecology. Model advances over the timeperiod of OCTET can be expected through the extension andsophistication of these techniques (e.g., multi-nutrient limitation;plankton functional groups; more explicit dissolved organicmatter/microbial interactions; eddy resolution; data assimilation).Progress may also depend on the implementation of more novel,ecologically based approaches.

The modeling challenges for OCTET will involve issues including(but not limited to):

• Development of improved algorithms for large-scale simulations should be a stated goal, and the success of OCTET should be measured by how much algorithms are improved. This requirement alone will encourage the collaboration of modelers and non-modelers.
• Species compositions may change in response to climate change, altering stoichiometric ratios among biogenic elements; in turn, changes in nutrient abundances will feed back to community structure. Existing food web models have for the most part been developed to represent changes on shorter time scales; a gap exists between these models and models that possess the taxonomic complexity and numerical efficiency to be used on longer time scales, where species replacements may be of paramount importance. Novel approaches are needed to formulate efficient biogeochemical models that incorporate functional diversity (diatoms, coccolithophorids, Phaeocystis, photosynthetic prokaryotes, N-fixers). A key question is the level at which functional taxonomic groups will need to be resolved.
• Physical models must be developed with explicit consideration of their use in biogeochemical simulations. Physical models that seem to work well for temperature and salinity may nonetheless not behave well with biogeochemical tracers. Related problems concern the adequacy of present forcing fields (e.g., winds) and with air/sea and sea/ice couplings.
• A persistent problem facing modelers is one of scale: how can results of small process-oriented studies be extrapolated to larger scales?
  1. Can satellite imagery serve as the basis for this extrapolation?
  2. How must mechanistic parameterizations that make sense on small space and time scales be changed for use in GCMs with large grid boxes, limited vertical resolution, and uncertainty in parameterizations of small-scale physical forcings, such as turbulence?
  3. The ocean is not one-dimensional: how do we analyze data at depth when its source is not the surface directly overhead? At what spatial scales does this matter for large-scale simulation?
• The objective fusion of data and models remains a key issue in oceanography, particularly for biological and biogeochemical models where large-scale data assimilation is still in its infancy. With the expected long-term availability of satellite ocean color imagery and the rapid development of autonomous in-situ samplers, sufficient data may be available to generate reasonable ocean biogeochemical state estimates, at least for key surface ocean properties (e.g., autotrophic biomass, productivity, new production, sea surface pCO₂). Many technical and scientific issues exist, however, including:
  1. What are the time/space scales of biological variability?
  2. What are the tradeoffs between measurements of extensive (e.g., satellite chlorophyll) and intensive (e.g., size class structure; grazing rates) properties?
  3. How best can one define the dynamic relationships among the ecosystem variables such that assimilation of one observable quantity (e.g., chlorophyll) projects onto other, unobserved ecosystem compartments (e.g., bacterial and zooplankton biomass)?
• The biogeochemical modeling treatment of the subsurface water column has until now been primarily empirical in nature (e.g., the Martin et al. particle flux curves). This situation should improve with an increased understanding of the mechanisms involved and the use of inverse modeling.

Participant List:

MarkAbbott
College of Oceanic and Atmospheric Sciences
Oceanogr. Admin. Bldg.104
Oregon State University
Corvallis, OR 97331-5503
541-737-4045
541-737-2064 FAX
mabbott@oce.orst.edu

BobAnderson
Lamont-Doherty Earth Observatory
Columbia University
Route 9
West Palisades, NY 10964
914-365-8508
914-365-8155 FAX
boba@lamont.ldeo.columbia.edu

DavidArcher
Department of Geophysical Sciences
5734 S Ellis Ave
University of Chicago
Chicago, IL 60637
773-702-0823
773-702-9505 FAX
d-archer@uchicago.edu

Rob Armstrong
Marine Sciences Research Center
State University of New York
Stony Brook NY 11794-5000
516-632-3088
516-632-8820 FAX
raa@splash.Princeton.edu

WilliamM. Balch
Bigelow Laboratory for Ocean Sciences
P.O.B. 475; 180 McKown Point Rd
W. Boothbay Harbor, ME 04575
207-633-9600
207-633-9641 FAX
bbalch@bigelow.org

DickBarber
Duke University
NSOE Marine Laboratory
135 Duke Marine Lab Road
Beaufort, NC 28516-9721
252-504-7578
252-504-7648 FAX
rbarber@duke.edu

JackBarth
College of Oceanic and Atmospheric Sciences
104 Ocean Admin Bldg
Oregon State University
Corvallis, OR 97331-5503
541-737-1607
541-737-2064 FAX
barth@oce.orst.edu

MichaelBender
Department of Geosciences
Princeton University
Princeton, NJ 08544
609-258-2936
609-258-5242 FAX
bender@princeton.edu

Ron Benner
Department of Biological Sciences
University of South Carolina
Columbia, SC 29208
803-777-9561
803-777-4002 FAX
benner@biol.sc.edu

WillBerelson
Department of Earth Sciences
University of Southern California
Los Angeles, CA 90089-0740
213-740-5828
213-740-8801 FAX
berelson@usc.edu

JimBishop
EO Lawrence Berkeley National Laboratory
One Cyclotron Road, M/S 90-1116
Berkeley, CA 94720
510-495-2457
510-486-5686
JKBishop@lbl.gov

EdBoyle
Department of Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA 02139
617-253-3388
eaboyle@mit.edu

KenBrink
Mail Stop 21
Woods Hole Oceanographic Institution
Woods Hole, MA 02543
508-289-2535
508-457-2181 FAX
kbrink@whoi.edu

Deborah Bronk
College of William and Mary/ VIMS
Department of Physical Sciences
Route 1208; Greate Rd.
Gloucester Point, VA 23062
804-684-7779
804-684-7789 FAX
bronk@vims.edu

RobertByrne
Department of Marine Sciences
University of South Florida
140 7th Ave. S.
St. Petersburg FL 33701
813-893-9130
byrne@marine.usf.edu

MarkBrzezinski
Dept. of Ecology Evolution and Marine Biology
University of California
Santa Barbara, CA 93106
805-893-8605
805-893-8062 FAX
brzezins@lifesci.ucsb.edu

KenBuesseler
Mail Stop #25, Clark 447
Dept. of Marine Chemistry and Geochemistry
Woods Hole Oceanographic Institution
Woods Hole, MA 02543
508-289-2309
508-457-2193 FAX
kbuesseler@whoi.edu

Mary-ElenaCarr
Jet Propulsion Lab
MS 300-323
4800 Oak Grove Dr
Pasadena, CA 91109
818-354-5097
mec@pacific.jpl.nasa.gov

FranciscoChavez
Monterey Bay Aquarium Research Institute
P.O. BOX 628, 7700 Sandholdt Rd.
Moss Landing, CA 95039-0628
831-775-1709
831-775-1620 FAX
chfr@mbari.org

JonCole
Institute of Ecosystem Studies
Cary Arboretum
Box AB
Millbrook, NY
914-677-5343
914-677-5976 FAX
colej@ecostudies.org

ScottDoney
Climate and Global Dynamics
National Center for Atmospheric Research
P.O. Box 3000
Boulder, CO 80307
303-497-1639
303-497-1700 FAX
doney@ncar.ucar.edu

Ellen R. M. Druffel
Dept. of Earth System Science
222 RH
University of California
Irvine, CA 92697-3100
949-824-2116
949-824-3256 Fax
edruffel@uci.edu

HughDucklow
School of Marine Science
The College of William and Mary
Box 1346
Gloucester Point, VA 23062-1346
804-684-7180
804-684-7293 FAX
duck@vims.edu

SteveEmerson
P.O. 357940
School of Oceanography
University of Washington
Seattle, WA 98195
206-543-0428
206-685-3351 FAX
emerson@u.washington.edu

Dick Feely
Pacific Marine Environmental Laboratory
National Oceanic and Atmospheric Administration
7600 Sand Point Way N.E.
Seattle, WA 98115
206-526-6214
206-526-6744 FAX
feely@pmel.noaa.gov

Christopher Field
Carnegie Institution of Washington
Department of Plant Biology
260 Panama Street
Stanford, CA 94305
650-325-1521, Ext. 213
650-325-3748 FAX
chris@jasper.stanford.edu

MickFollows
54-1412
Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA 02139
617-253 -454
617-253-4464 FAX
mick@plume.mit.edu

AnandGnanadesikan
Program in Atmospheric and Oceanic Sciences
Princeton University
Sayre Hall, Forrestal Campus
Princeton, NJ 08544-0710
609-987-5062
a1g@gfdl.gov
gnana@phoenix.princeton.edu

NicolasGruber
Program in Atmospheric and Oceanic Sciences
Princeton University
Sayre Hall, Forrestal Campus
Princeton, NJ 08544-0710
609-258-1314
609-258-2850 FAX
gruber@splash.Princeton.edu

BurkeHales
College of Oceanic and Atmospheric Sciences
104 Ocean Administration
Oregon State University
Corvallis, OR 97331
541-737-8121
541-737-2064 FAX
bhales@oce.orst.edu

DennisHansell
Bermuda Biological Station for Research, Inc.
17 Biological Lane
St. Georges, GE-01, BERMUDA
441-297-1880, Ext. 210
441-297-8143 FAX
dennis@bbsr.edu

Anitra Ingalls (Student Assistant)
Marine Sciences Research Center
State University of New York
Stony Brook NY 11794-5000
516-632-8749
516-632-8820 FAX
aingalls@ic.sunysb.edu

Rick Jahnke
Skidaway Institute of Oceanography
10 Ocean Science Circle
Savannah, GA 31411
912-598-2491
912-598-2310 FAX
rick@skio.peachnet.edu

Kenneth S. Johnson
Monterey Bay Aquarium Research Institute
7700 Sandholdt Road
Moss Landing, CA 95039
831-775-1985
831-775-1620 fax
johnson@mbari.org

DaveKarl
University of Hawaii
Department of Oceanography
1000 Pope Road
Honolulu, HI 96822
808-956-8964
808-956-5059 FAX
dkarl@soest.hawaii.edu

CindyLee
Marine Sciences Research Center
State University of New York
Stony Brook, NY 11794-5000
631-632-8741
631-632-8820 FAX
cindylee@notes.cc.sunysb.edu

TonyMichaels
USC
Wrigley Institute for Environmental Studies
University of Southern California
AHF 232
Los Angeles, CA 90089-0371
213-740-6780
213-740-6720 FAX
tony@usc.edu

JamesW. Murray
School of Oceanography
Box 357940
University of Washington
Seattle WA 98195-7940
206-543-4730
206-685-3351 FAX
jmurray@u.washington.edu

Mercedes Pascual
Center of Marine Biotechnology
701 East Pratt Street
Baltimore, Maryland 21202
410-234-8847
410-234-8896 FAX
mercedes@pampero.umbi.umd.edu

PaulRobbins
Scripps Institution of Oceanography
Mail Stop 0230
University of California
9500 Gilman Drive
La Jolla, CA 92093-0230
858-534-6366
858-534-9820 FAX
probbins@ucsd.edu

MikeRoman
Horn Point Environmental Lab
Box 775
Cambridge, MD 21613
401-221-8425
401-221-8490 FAX
roman@hpl.umces.edu

ChristopherSabine
Pacific Marine Environmental Laboratory
National Oceanic and Atmospheric Administration
7600 Sand Point Way NE
Seattle, WA 98115
206-526-4809
206-526-6744 FAX
sabine@pmel.noaa.gov

JorgeSarmiento
Program in Atmospheric and Oceanic Sciences
Princeton University
Sayre Hall, Forrestal Campus
P.O. Box CN710
Princeton, NJ 08544-0710
609-258-6585
609-258-2850 FAX
jls@splash.princeton.edu

Daniel Sigman
Deptartment of Geosciences
Princeton University
Princeton, NJ 08544
609-258-2194
609-258-5242 FAX
sigman@princeton.edu

John Southon
Center for AMS, L-397
Lawrence Livermore National Lab
P.O. Box 808, 7000 East Ave
Livermore, CA 94551-9900
925-423-4226
925-423-7884 FAX
southon1@llnl.gov

DeborahSteinberg
Bermuda Biological Station for Research
Ferry Reach, GE01, BERMUDA
441-297-1880 x303
441-297-8143
debbie@bbsr.edu

TaroTakahashi
Lamont-Doherty Earth Observatory
Columbia University
Route 9
West Palisades, NY 10964
914-365-8537
taka@ldeo.columbia.edu

RikWanninkhof
OCD/AOML/NOAA
4301 Rickenbacker Causeway
Miami, FL 33149
305-361-4379
305-361-4392 FAX
wanninkhof@aoml.noaa.gov 

Agency Participants:

Enriqueta Barrera
Geology and Paleontology Program
National Science Foundation
4201 Wilson Boulevard
Arlington, VA 22230
703-306-1551
703-306-0382 FAX
ebarrera@nsf.gov

Kendra Daly
Biological Oceanography Program
Division of Ocean Sciences
National Science Foundation
4201 Wilson Blvd., Suite 725
Arlington, VA 22230
703-306-1587
703-306-0390 FAX
kdaly@nsf.gov

Lisa Dilling
NOAA
Office of Global Programs
1100 Wayne Avenue, Suite 1225
Silver Spring, MD 20910
301-427-2089, Ext. 106
301-427-2073 FAX
dilling@ogp.noaa.gov

Sarah Horrigan
Science and Space Programs
Office of Mangement and Budget
Washington, D.C. 20503
202-395-3534
202-395-4817FAX
Sarah_G._Horrigan@omb.eop.edu

Eric C. Itsweire
Physical Oceanography Program
Division of Ocean Sciences, Room 725
National Science Foundation
4201 Wilson Blvd, Arlington, VA 22230
703-306-1583
703-306-0390 FAX
eitsweir@nsf.gov

Jack A. Kaye
Director, Research Division
NASA Office of Earth Science
NASA HQ – Mail Code YS
Washington, DC 20546
202-358-0757
202-358-2770 FAX
Jack.Kaye@hq.nasa.gov

John Marra, Program Scientist
Oceanography Program
Office of Earth Science/Code YS
NASA Headquarters
300 E Street SW, Room 5P33
Washington, D.C. 20546
202-358-0310
202-358-2770 FAX
jmarra@mail.hq.nasa.gov

Ken Mooney
NOAA
Office of Global Programs
1100 Wayne Avenue, Suite 1225
Silver Spring, MD 20910
301-427-2089, Ext. 104
301-427-2073 FAX
mooney@ogp.noaa.gov

Dr. Anna Palmisano
Environmental Sciences Division
Department of Energy
19901 Germantown Rd.
Germantown, MD 20874
301-903-9963
301-903-8519 FAX
anna.palmisano@science.doe.gov

Don Rice
Chemical Oceanography Program
Division of Ocean Sciences
National Science Foundation
4201 Wilson Boulevard
Arlington VA 22230
703-306-1589, Ext. 7219
703-306-0390 FAX
drice@nsf.gov

Phillip R. Taylor
Biological Oceanography Program
Division of Ocean Sciences
National Science Foundation
4201 Wilson Blvd., Suite 725
Arlington, VA 22230
703-306-1587
703-306-0390 FAX
prtaylor@nsf.gov