On the relation between organic and inorganic carbon in the Weddell Sea

Carbon cycling in the Weddell Sea was investigated during the ANT X/7 cruise with 'FS Polarstern' Dec. 1992 - Jan. 1993. Samples were taken on a cross section from Kapp Norvegia to Joinville Island, and on a section from the Larsen Ice Shelf to the north-east. The following quantities were measured: total carbon dioxide (TCO2), fluorescence from humic substances and total organic carbon. The distribution of TCO2 was strongly positively correlated to the time elapsed since the various water masses were last ventilated. In general, humic substance fluorescence was positively correlated with TCO2, with the exception of the productive part of the western Weddell Sea, where the correlation was negative in the surface mixed layer. The increased fluorescence at the surface is suggested to be a result of biological production. The distribution of total organic carbon showed less structure, since this quantity includes a particulate component, which is subject to dispersion processes different from those of the dissolved components TCO2 and humic substances. The mean total organic carbon concentration below the surface mixed layer was 50 µmol l1. At some stations, a steep maximum around 2000 m depth was observed. This was interpreted to result from mass sinking of phytoplankton blooms. Total organic carbon had a maximum in surface water and, at some stations also a second subsurface maximum. In the Warm Deep Water, TCO2 and fluorescence had their maximum values, while total organic carbon tended to be low. In low productivity surface water in the eastern part of the Kapp Norvegia - Joinville Island section, the lowest fluorescence was found. Surface water is eventually formed from Warm Deep Water, which had the highest fluorescence values, and therefore it is concluded that humic substances were removed in situ from surface water. In the central area of the Weddell Sea, TCO2 and fluorescence showed their highest Warm Deep Water maxima, while total organic carbon was low. The Warm Deep Water in this area, close to the axis of the Weddell Gyre, is part of the so-called Central Intermediate Water which circulates for a long time within the Gyre. Reduced total organic carbon, which coincides with the most pronounced Central Intermediate Water characteristics, and high TCO2 can thus both be accounted for by continued degradation of organic matter in this water mass. The associated fluorescence maximum implies that humic substances are also produced during mineralisation. Recently formed bottom water, by contrast, could be seen as patches of low TCO2, low fluorescence and high total organic carbon along the western slope of the Weddell Sea

Spring distribution of dissolved organic matter in a system encompassing the Northeast Water Polynya: Implications for early-season sources and sinks

This study addresses sources and diagenetic state of early-season dissolved organic matter (DOM) in the Northeast Water Polynya (NEWP) area northeast of Greenland from distributions of humic substance fluorescence (HSfl), dissolved organic carbon (DOC), and dissolved organic nitrogen (DON) in the water column inside and outside the NEWP area. The water masses of the polynya area had acquired their spring/summer temperature-salinity characteristics at the time of sampling, and also had individual, different DOM signatures. DOC concentrations were variable within and among water masses in the polynya area, indicating patchy local sources and sinks of DOC. PySW and polynya intermediate water (PyIW) had higher average DON concentrations and average lower C:N ratios than polynya bottom water (PyBW), indicating a larger fraction of fresh DOM in PySW and PyIW than in PyBW. Ice-covered, polynya area surface waters (PySW) had higher DOC concentrations (113 +/- 14 mu M, n=68) than surface water (SW) outside the polynya area (96 +/- 18 mu M, n=6). The DOM C:N ratios in a low-salinity, ice-melt subgroup of PySW samples indicate labile material, and these low-salinity surface waters appeared to have a local DOC and DON source. In contrast, HSfl was significantly lower inside than outside the NEWP area. Despite the lower HSfl values within the NEWP area, the PySW values were high when compared to open-ocean water. There were no local terrestrial sources for HSfl to the NEWP area and the East Greenland Current is therefore proposed as a likely source of allochtonous HSfl. When HSfl was used as a conservative tracer, up to similar to 70% of the water in PySW and PyIW was found to be derived from SW, which contains a high fraction of water from the East Greenland Current. Similarly, a mixing model based on HSfl indicated that similar to 80% of early-season DOC and 90-100% of early-season DON in PySW and PyIW were derived from SW, indicating a potentially high fraction of terrestrially-derived, relatively refractory DOM in the early-season NEWP area. (c) 2005 Elsevier B.V. All rights reserved

Research cruise of the Scandinavian/South African Antarctic expedition, December 1997 to February 1998

Focuses on the Scandinavian/South African Antarctic expedition conducted between December 4, 1997 to February 6, 1998 which determined the role of Southern Ocean in the global carbon cycle in physical and biological oceanographic studies. Aims of the expedition; Underway sampling conducted; Biological results of the expedition; Conclusions