ORGANIC-CARBON PARTITIONING DURING SPRING PHYTOPLANKTON BLOOMS IN THEROSS SEA POLYNYA AND THE SARGASSO SEA

In this study we evaluate the partitioning of organic carbon between t he particulate and dissolved pools during spring phytoplankton blooms in the Ross Sea, Antarctica, and the Sargasso Sea. As part of a multid isciplinary project in the Ross Sea polynya we investigated the dynami cs of the dissolved organic carbon (DOC) pool and the role it played i n the carbon cycle during the 1994 spring phytoplankton bloom. Phytopl ankton biomass during the bloom was dominated by an Antarctic Phaeocys tis sp. We determined primary productivity (PP; via (HCO3-)-C-14 incub ations), particulate organic carbon (POC), bacterial productivity (BP; via [H-3]thymidine incorporation), and DOC during two occupations of 76 degrees 30'S from 175 degrees W to 168 degrees E. Results from this bloom are compared to blooms observed in the Sargasso Sea in the vici nity of the Bermuda Atlantic Time-Series Study station (BATS). We pres ent data that demonstrate clear differences in the production, biolabi lity, and accumulation of DOC between the two ocean regions. Despite f our- to fivefold greater PP in the Ross Sea, almost an order of magnit ude less DOC (mmol m(-2)) accumulated during the Ross Sea bloom compar ed to the Sargasso Sea blooms. In the Ross Sea 89% (similar to 1 mol C m-2) of the total organic carbon (TOC) that accumulated during the bl oom was partitioned as POC, with the remaining 11% (similar to 0.1 mol 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 bloo ms 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 deman d indicated that a qualitatively more labile carbon was produced in th e Ross Sea compared to the Sargasso Sea. There are fundamental differe nces in organic carbon partitioning between the two systems that may b e controlled by plankton community structure and food-web dynamics.