Meeting Abstract

S3-2.2  Jan. 4  Elevated Zooplankton Biomass in Mid-Ocean Eddies GOLDTHWAIT, S.*; STEINBERG, D.; MCGILLICUDDY, D.; Humboldt State University; Virginia Institute of Marine Science; Woods Hole Oceanographic Institute sg65@humboldt.edu

Physical factors ultimately determine the course of biological events in the ocean because processes such as mixing, advection, turbulence, and diffusion affect the distribution, production, and behavior of pelagic organisms. Physics influences biology on many scales, from ocean basin circulation to turbulence affecting single cells. The currents, fronts, and eddies that comprise the oceanic mesoscale are energetic and ubiquitous features of ocean circulation. As mesozooplankton play a fundamental role in food web interactions and the flux of material out of the surface waters, changes in mesozooplankton community composition due to physical perturbation by eddies could affect biogeochemical cycling. As part of the Eddy Dynamics, mIxing, Export, and Species composition (EDDIES) project we followed the evolution of 2 distinct features in the Sargasso Sea, a cold-core eddy and a mode-water eddy. Zooplankton biomass in the upper 150 m was enhanced for both eddies at 752 mg m^-2 and 674 mg m^-2, respectively, compared with an average of 462 mg m^-2 for summer samples collected near Bermuda. Zooplankton biomass was enhanced on the periphery of the cold-core eddy, with a 1.5 fold increase in vertical migrators such as euphausiids and shrimp. In the mode-water eddy, peak zooplankton biomass occurred at eddy center but was highly variable over time. Copepods and euphausiids inside both eddies had elevated gut chlorophyll concentrations. Shifts in zooplankton community composition and grazing rates were also reflected in sedimenting fecal pellets. Zooplankton fecal pellets are a primary mechanism of carbon transport from surface waters into the ocean interior. Inside the eddy features, the number of zooplankton fecal pellets sinking out of the euphotic zone was up to 2 fold higher than background, accounting for 20-35% of total carbon flux.