Award: OCE-1030345

This award funded an investigation of planktonic food webs in the Sargasso Sea. It combined field work at sea (4 cruises, 2 in 2011 and 2 in 2012) with numerical models (simulations) of carbon cycling through food webs. For each cruise we compiled a dataset of all carbon flow rates measured at sea. These included size-fractionated primary productivity, size-fractionated grazing, bacterial production, and rates of carbon export. These known values were incorporated into an inverse food web model that simulated a food web that included flows we could not measure during our time at sea. Due to the mesoscale and sub-mesoscale variability we observed, we performed separate food web models for each station, rather than averaging data over the approximately 200 km transects. In the summer of 2014, a student was assigned the task of running models for our spring and summer 2011 cruise data. She found that export in the center of anticyclone AC1 (spring 2011) was greater than in the center of cyclone C1 (summer 2011). The model showed these differences could be attributed to decreased detrital export in C1. In C1 the microzooplankton grazed nearly exclusively on detritus (dead organic matter), thus reducing the pool available for export. In AC1 microzooplankton grazed nearly equally on detritus and small phytoplankton, and total grazing rates were lower. Currently, an undergraduate at USC is conducting an independent research project on the 2012 dataset. Using data from literature sources we are analyzing the modelÆs sensitivity to zooplankton grazing rates. Once we have finalized the 2012 models we will perform network analyses on the model outputs. This will allow us to directly compare each set of modeled flows and determine how the ecosystem varies spatially (along a transect), and temporally (between seasons). Last Modified: 04/10/2015 Submitted by: Tammi L Richardson