Doc dynamics in eddies of the sargasso sea

摘要

Bacterial productivity and size-fractioned rates of dissolved organic carbon (DOC) excretion from primary and secondary producers were measured in two eddy types, one anti-cyclonic (February 2012) and one cyclonic eddy (July 2012), in the Sargasso Sea. Bacterial productivity (BP) rates in the cyclonic eddy were highest in the center (9.2 mg C m-2 d-1) and edge (10.4 mg C m-2 d-1) of the eddy compared to the anti-cyclone center (2.2 mg C m-2 d-1) and edge (5.1 mg C m-2 d-1). Rates of DOC excretion from 14C-tracer experiments were not significantly higher than background; lack of accumulation of labeled material indicated very fast uptake of DOC by the bacterial community. Since rates were not measureable in the field, an inverse modeling approach was used to estimate flows to and from the DOC pool for three stations (center, edge, and outside) in the cyclonic eddy sampled in 2012. DOC excretion rates by phytoplankton were between 10.1 and 14.5 mg C m-2 d-1. These values on average were 11.7 % of the total primary production. Generally, DOC excretion was higher inside the eddy compared to the edge and outside the eddy. Modeling results indicated that one of the largest potential fates of DOC in this ecosystem was advection out of the euphotic zone. The highest rates of DOC advection were seen inside the eddy center, decreasing moving to the edge and then outside of the hydrodynamic influences of the cyclonic eddy.