Contribution of zooplankton fecal pellets to deep ocean particle flux in the Sargasso Sea assessed using quantitative image analysis

Abstract

Fecal pellet flux and size distribution at 500, 1500 and 3200 m depths were measured in sediment trap samples collected by the Oceanic Flux Program time-series off Bermuda, December 2006-November 2007. During the study, three mesoscale eddies passed through: a cyclonic eddy in bloom stage (February through mid-April), a decaying post-bloom mode-water eddy (late April through May), and an anticyclonic eddy (August through October). Variability associated with eddy passage masked any seasonal trends in flux or size distributions. At a depth of 1500 m, the fecal pellet flux ranged from a minimum of 100 pellets m-2 day-1 to a maximum of 500 pellets m-2 day-1 during the cyclonic eddy passage, corresponding to ranges in the fecal pellet mass and the carbon flux of 0.5-1.7 mg m-2 day -1 and 0.07-0.25 mg C m-2 day-1, respectively. Fecal pellets averaged 7 ± 3% of the organic carbon flux, a minimum estimate as disassociated pellets were not quantifiable. Size distribution shifts indicated small zooplankton and immature stages were more abundant within the cyclonic eddy, whereas larger zooplankton were present within the mode water and anticyclonic eddies. The fecal pellet number, flux and size distributions showed no consistent depth trends and indicated extensive fecal pellet reprocessing within the water column. © 2012 The Author. Published by Oxford University Press. All rights reserved.