The oceans cover more than 70% of Earth’s surface. Any wind driven waves result in the generation of sea spray aerosol (SSA). As such, SSA represents one of the main contributors to particles in the atmosphere with important implications for atmospheric composition and cloud formation. In recent years, it has been shown that SSA consist of complex chemical mixtures including inorganic compounds such as salts and organic matter, primary or secondary in nature.

The left hand side figure exemplifies the complex physical and biochemical processes that define the composition of SSA and its possible interactions in the atmosphere. This figure is from Laskin et al., (2016).

Dissolved organic carbon (DOC) can transform into gel-like particles, also termed transparent exoploymers (TEP) and enter the atmosphere. Rising air bubbles can scavenge organic matter during ascending in the water column or when interacting with the sea surface microlayer which is highly enriched in organic matter. As the bubble bursts at the ocean-atmosphere interface, biogenic matter is released to the atmosphere.

In our group, in collaboration with Prof. Josephine Aller, our research questions revolve around which biological processes determine the DOC pool and subsequently the organic matter in SSA and does the ocean serve as a source of ice-nucleating particles?

We have recently shown during a cruise in the western North Atlantic, that nascent SSA particles in all sizes contain significant amounts of TEP (Aller et al., 2017). To gain a better understanding of these processes our group conducts micro- and mesocosm experiments in which we simulate ocean conditions in the laboratory making full use of the expertise available in SoMAS which is New York State’s Marine Science Research Center.

The right hand side shows a home-buitl 1000L mesocosm to simulate a phytoplankton bloom over two weeks. Also shown is the change in aerosol size distribution as the biological processes involving phytoplankton microorganism evolve (from Alpert et al., 2015).

Inspired by previous work of Russ Schnell and colleagues, we revisited the the question if and how the ocean can serve as a source of ice-nucleating particles. We have demonstrated that phytoplankton cells and their fragments can serve as a substrate that efficiently nucleate ice (Knopf et al. 2011; Alpert et al., 2011a, 2011b). In recent years, it became more evident that even the exudate material only, polysaccharidic in nature, can act as ice-nucleating particle (Ladino et al., 2016) and that the same material is found in the sea surface microlayer (Wilson et al., 2015).

The left hand side shows exemplary immersion freezing results from three different kinds of phytoplankton species (Knopf et al. 2011; Alpert et al., 2011a, 2011b). Whole and fragemented cells of T. Pseudonana and N. Atomus enhanced the immersion freezing compared to the homogeneous freezing limit. E. Huxleyi did not enhance freezing in micrometer sized droplets.

 

In our group we investigate the formation, characteristics, and ice nucleation capability of SSA particles via careful laboratory experiments and field studies including sampling in the surf zone of beaches and abroad research vessels. Long Island provides many opportunities to sample ocean water and SSA particles from our SoMAS research vessels and from the northern and southern shores, the latter shown below as the Knopf group conducted SSA particle sampling in the field.