Dissolved and suspended organic carbon in the Atlantic sector of the Southern Ocean. Stock dynamics in upper ocean waters

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 'Bio Hespérides' 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 wk), 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 mixed layer (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.

Dynamics of bacterioplankton activities after a summer phytoplankton bloom period in Terra Nova Bay

“…2). Particulate organic carbon (POC) and dissolved organic carbon (DOC) were abundant during a post bloom period (Poutanen & Morris 1983, Fabiano & Pusceddu 1998, Doval et al 2001 which can support an increase in some bacterial ectoenzymatic activities, as observed in Fig. 2.…”

Chemotactic response of marine bacteria to the extracellular products of Synechococcus and Prochlorococcus

“…In our experiments, the mean DOC concentration in the Synechococcus and Prochlorococcus culture filtrates was 279 and 133 µM, respectively. While these DOC values are about 3-to 5-fold higher than open ocean bulk concentrations (Wiebinga & de Baar 1998, Doval et al 2001, they are well within the range of DOC concentrations observed during phytoplankton blooms (Gobler et al 2004, Packard et al 2000. In the environment, associations between heterotrophs and cyanobacteria occur in a microenvironmental scenario, where the concentrations of exudates near the surfaces of cells will be substantially higher than in the bulk phase.…”

Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

“…In addition to the significant increase in surface DOC concentration north of the PF (Doval et al, 2001; this study: p = 0.0066), the observed shift of DOM towards younger average age highlights the role of the ACC as a geo-ecological boundary (Longhurst, 2007). However, especially in surface waters with high productivity, large temporal (daily and seasonal) variations in DO 14 C can occur, as observed for the eastern North Pacific Beaupré and Druffel, 2009).…”