Mary I. Scranton

Professor Emeritus

Ph.D., 1977, Massachusetts Institute of Technology/ Woods Hole Oceanographic Institution

mary.scranton@stonybrook.edu

Marine geochemistry, biological-chemical interactions in seawater

Research Interests

One of the most important problems in marine geochemistry is the transformation and fate of organic matter produced by phytoplankton and other organisms in the water column. We have been studying the carbon cycle in the Cariaco Basin, a large permanently anoxic basin on the continental shelf of Venezuela, because the sediments in the Cariaco preserve a high resolution record of deposition of material, including organic carbon, over more than 100,000 years. The value of the sediment record is enhanced if we understand the origin and transformations that sinking material experiences in the system. Another SoMAS faculty member, David Black, uses sediments from the Cariaco Basin and other similar sites for paleoceanographical studies.

In the CARIACO (Carbon Retention in a Colored Ocean) program, I am collaborating with Gordon Taylor of SoMAS, Frank Muller-Karger of the University of South Florida and Robert Thunell of the University of South Carolina, along with scientists from the Fundación la Salle and the Universidad de Oriente in Venezuela. The SoMAS component of the study is using a variety of techniques, including measurements of potential oxidants such as sulfur species (elemental sulfur, thiosulfate, sulfite) and forms of manganese and iron (Scranton and students), and measurements of bacterial abundance and production and chemosynthesis (Taylor and students) to determine how biological activity and carbon cycling under suboxic conditions is influenced by carbon supply, and oxygen content. The CARIACO program has been underway for 13 years, and we will be continuing this important time series until 2013.

Our results show that respiration and fermentation are elevated both in surface waters and near the oxic/anoxic interface, and that these processes respond to changes in carbon supply caused by changing fluxes of carbon from the surface waters. However although chemoautotrophic production (dark fixation of carbon) results in large inputs of organic matter at mid-depth, it does not seem to respond directly to changes in surface productivity. Rather, intrusions of oxygenated water from outside the basin seem to strongly influence carbon cycling at the interface. Most recently we have been examining the linkages between the specific microbial groups present and the sulfur species found in the water.

I also continue a long-standing interest in methane geochemistry. We have studied methane within the Hudson River, in seasonally and permanently anoxic basins, and most recently in the waters of the North Atlantic on and near the US North-East continental shelf. In this latter study, we are investigating the role of seeps and vents in controlling water-column methane concentrations. The methane concentrations in a number of areas over the shelf and slope are elevated, suggesting flux of fluids containing methane (and probably other important chemical species) from the sediments. This modest project has included participation in cruises on the R/V Atlantis as well as the NOAA ships Ron Brown and Henry Bigelow and a dive in the ALVIN.

Selected Publications

Li, X.N., G.T. Taylor, Y. Astor and M.I. Scranton. 2008-in press. Relationship of sulfur speciation to hydrographic conditions and chemoautotrophic production in the Cariaco Basin. Marine Chemistry, doi:10.1016/j.marchem.2008.06.002

Thunell, R. C. Benitez-Nelson, F. Muller-Karger, L. Lorenzoni, K. Fanning, M. Scranton, R. Varela and Y. Astor. 2008. The Si Cycle in the Cariaco Basin, Venezuela: Seasonal Variability in Silicate Availability and the Si:C:N Composition of Sinking Particles. Global Biochemical Cycles, 22, GB4001, doi:10.1029/2007GB003096.

Percy, D., X. Li, G.T. Taylor, Y. Astor, and M. I. Scranton. 2008. Controls on iron, manganese and intermediate oxidation state sulfur compounds in the Cariaco Basin. Marine Chemistry, 111, 47-62.

Scranton, M.I., M. McIntyre, G.T. Taylor, F. Muller-Karger, K. Fanning, and Y. Astor. 2006. Temporal Variability in the Nutrient Chemistry of the Cariaco Basin. In: Past and Present Marine Water Column Anoxia. L.N. Neretin, ed. NATO Science Series: IV. Volume 64, Springer Press, pp 139-160.

Hayes, M.K., G.T. Taylor, Y. Astor and M.I. Scranton. 2006. Vertical distributions of thiosulfate and sulfite in the Cariaco Basin. Limnology and Oceanography, 51, 280-287.

Astor, Y. M. , M.I. Scranton, F. Muller-Karger, R. Bohrer, and J. García. 2005. Seasonal and interannual fCO2 variability in a tropical coastal upwelling system. Marine Chemistry, 97, 245-261.

Ho, T.-Y., G.T. Taylor, Y. Astor, R. Varela, F. Muller-Karger and M.I. Scranton. 2004. Vertical and temporal variability of redox zonation in the water column of the Cariaco Basin: implications for organic carbon oxidation pathways. Marine Chemistry, 86, 89-104.

Astor, Y, F. Muller-Karger and M.I. Scranton. 2003. Seasonal and interannual variation in the hydrography of the Cariaco Basin, Venezuela: Implications for basin ventilation. Continental Shelf Research, 23, 125-144.

Scranton, M.I., Y. Astor, R. Bohrer, T.-H. Ho and F. Muller-Karger. 2001. Controls on temporal variability of the geochemistry of the deep Cariaco Basin. Deep-Sea Research, 48, 1605-1625.