MEPS 223:27-38 (2001)  -  doi:10.3354/meps223027

ABSTRACT: 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 ŒBio Hespérides¹ 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 (≤2 wk) of this material, except in the Polar Front Zone (>5 were deduced from measured primary/bacterial production rates. Maximum contributions of this potentially bioreactive organic carbon pool (TOC_B) 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 TOC_B, in these regions, respectively. In contrast, TOC_B comprised ≤20% of TOC in the less productive open-ocean waters of the Weddell Sea and Drake Passage, where DOC made up ≥65% of TOC_B. The Subantarctic Zone constituted an exception, with high chl a levels and a shallow upper (due to marked temperature gradients): 29% of the organic carbon in the upper mixed layer was TOC_B, 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.

KEY WORDS: Dissolved and suspended organic carbon · Primary and bacterial production · Carbon renewal time · Drake Passage · Southern Ocean