Dissolved and suspended organic carbon (DOC and POC) distributions were studied in the undersampled Atlantic sector of the Southern Ocean during Cruise HE052 of the 'Bio Hesperides' in December 1998, The coastal waters of the ice edge, the Gerlache Strait, and the open-ocean waters of the Weddell Sea and the Drake Passage were sampled. The high correlation between chlorophyll a (chl a), DOC and POC suggest that a considerable fraction (estimated at 15 to 30%) of the organic matter available in the upper mixed layer of the different study regions is the product of synthesis and early degradation of planktonic primary production. Relatively low renewal times (less than or equal to2 wk) of this material, except in the Polar Front Zone (>5 wk), were deduced from measured primary/bacterial production rates Maximum contributions of this potentially bioreactive organic carbon pool (TOCB) to the total organic carbon (TOC) were observed in the highly productive waters of the ice edge (24%) and Gerlache Strait (30%) regions, where high chl a levels and shallow upper mixed layers (due to marked salinity gradients) occurred. DOC represented 42 and 56% of TOCB, in these regions, respectively. In contrast, TOCB comprised less than or equal to20% of TOC in the less productive open-ocean waters of the Weddell Sea and Drake Passage, where DOC made up greater than or equal to65% of TOCB. The Subantarctic Zone constituted an exception, with high chl a levels and a shallow upper mixed layer (due to marked temperature gradients): 29% of the organic carbon in the upper mixed layer was TOCB, 68% of which was in the dissolved fraction. Accumulation of DOC in the study regions points to a reduction in bacterial activity through mechanisms other than substrate limitation.