Presenter: Shavonna Bent (Woods Hole Oceanographic Institution)

Description:
Despite their prevalence in the oceans, the effects of mesoscale eddies on the biogeochemical cycling of carbon and nutrients remains largely uncategorized, especially as it relates to export. A more detailed understanding of how eddies of different polarity alter community structure, including the biochemical response of marine communities to the mesoscale uplift and depression of deep water layers will help to determine the fate of phosphorus and carbon in these systems. A pair of adjacent eddies of opposite polarity was sampled in 2017 near Station ALOHA, allowing for the unique opportunity to study how these eddies perturb the environment around them. Lipidomic analysis of these samples probed how the altered community structure reflected different levels of nutrient stress, and how these changes trickled down into increased export of rapidly sinking, ballasted, eukaryotic phytoplankton particulate matter. The combination of water column sampling and sediment trap data allowed for a time-integrated approach to understanding how each eddy impacted phytoplankton. Our data suggests that the cyclonic eddy delivered phosphate to the lower euphotic zone, alleviating nutrient stress for eukaryotic microbes at the deep chlorophyll maximum. This contrasts the response of the cyanobacterial population, which did not demonstrate any response to increased phosphate, perhaps due to the larger, rapidly growing (r-selected) eukaryotic phytoplankton outcompeting them for the new nutrients while they are adapted to the highly oligotrophic environment (k-selected). This study demonstrates even minute changes in nutrient delivery can affect lipid export and highlights the importance of looking at intracellular nutrient partitioning to produce a better understanding of export. Determining if these changes are mechanistically related to eddy dynamics will allow for improved modeling of carbon cycling in the oligotrophic ocean.