Organic carbon partitioning during spring phytoplankton blooms in the Ross Sea polynya and the Sargasso Sea

Abstract

In this study we evaluate the partitioning of organic carbon between the particulate and dissolved pools during spring phytoplankton blooms in the Ross Sea, Antarctica, and the Sargasso Sea. As part of a multidisciplinary project in the Ross Sea polynya we investigated the dynamics of the dissolved organic carbon (DOC) pool and the role it played in the carbon cycle during the 1994 spring phytoplankton bloom. Phytoplankton biomass during the bloom was dominated by an Antarctic Phaeocystis sp. We determined primary productivity (PP; via H14CO3-incubations), particulate organic carbon (POC), bacterial productivity (BP; via [3H]thymidine incorporation), and DOC during two occupations of 76°30'S from 175°W to 168°E. Results from this bloom are compared to blooms observed in the Sargasso Sea in the vicinity of the Bermuda Atlantic Time-Series Study station (BATS). We present data that demonstrate clear differences in the production, biolability, and accumulation of DOC between the two ocean regions. Despite four- to fivefold greater PP in the Ross Sea, almost an order of magnitude less DOC (mmol m-2) accumulated during the Ross Sea bloom compared to the Sargasso Sea blooms. In the Ross Sea 89% (~ 1 mol C m-2) of the total organic carbon (TOC) that accumulated during the bloom was partitioned as POC, with the remaining 11% (~ 0.1 tool C m-2) partitioned as DOC. In contrast, a mean of 86% (0.75-1.0 mol m-2) of TOC accumulated as DOC during the 1992, 1993, and 1995 blooms in the Sargasso Sea, with as little as 14% (0.08-0.29 mol C m-2) accumulating as POC. Although a relatively small portion of the fixed carbon was produced as DOC in the Ross Sea, the bacterial carbon demand indicated that a qualitatively more labile carbon was produced in the Ross Sea compared to the Sargasso Sea. There are fundamental differences in organic carbon partitioning between the two systems that may be controlled by plankton community structure and food-web dynamics.