Distribution of transparent exopolymer particles (TEP) across an organic carbon gradient in the western North Atlantic Ocean

In this study, the abundance of transparent exopolymer particles (TEP) is examined across a surface water gradient of organic carbon from a phytoplankton bloom region in the western North Atlantic to oligotrophic waters in the Sargasso Sea, including a coastal region sampled near Cape Cod. TEP are macrogels that reach up to millimeters in size and abiotically assemble from dissolved acidic polysaccharides secreted by phytoplankton. Due to their great stickiness, TEP self aggregate and also form aggregates with non-TEP particulate organic carbon (POC). Aggregation enhances ballasting, thereby mutually facilitating export and subsequent sedimentation of both TEP and POC, increasing the efficiency of the biological pump. Here, four distinct regions with varying chlorophyll a concentrations, temperature, and salinity were sampled in the upper column, at the surface, and from the sea surface microlayer (SML). While TEP in seawater shows no correlation to chlorophyll a, nutrients, or total organic carbon (TOC) concentration, a strong correlation exists between TEP and TOC in the SML; and concentrations of both variables are inversely proportional to surface productivity as indicated by chlorophyll a concentrations. As open ocean regions show greater enrichments of TEP and TOC in the SML compared to the coastal region, we suggest that the role of the SML in organic carbon cycling is dependent on regional biogeochemistry and productivity. We hypothesize that a lower abundance of particles in oligotrophic regions compared to bloom regions limits TEP export by sinking, thus increasing the residence time of TEP in the upper water column and the SML.