DETERMINATION OF THE DISTRIBUTION OF DISSOLVED ORGANIC-CARBON IN THE INDIAN SECTOR OF THE SOUTHERN-OCEAN

During France JGOFS campaign ANTARES 2 (R.V. Marion Dufresne), samples were taken along a section of the 62 degrees E meridian from 49 degre es to 66 degrees S. The high temperature catalytic oxidation (HTCO) me thod was used to determine the concentration of dissolved organic carb on (DOC). The analyses were conducted both on-board ship and after the cruise in the laboratory. Collecting and storing acidified samples fo r post-cruise analysis induced no significant differences. The use of two separate but identical channels on the carbon analyzer increased t he number of samples analysed per day and allowed independent monitori ng of the instrument blank and the calibration of the detector respons e. The mixed layer concentrations of organic carbon varied from about 52 mu M C in the Antarctic Divergence (64 degrees S) to about 63 mu M C in the Polar Frontal Zone (49 degrees S). Vertical profiles showed a slight, but significant, decrease in organic carbon below the mixed l ayer, to about 42 mu M C below 2000 m across the transect. The homogen eity and low concentration of organic carbon in deep water is consiste nt with values recently reported for the equatorial Atlantic and Pacif ic Ocean and supports the evidence for a constant deep water DOC conce ntration. In addition, this provides a verification of the instrument performance, thus validating observed DOC data trends and allowing a c omparison with the 'modern' DOC literature. In general, the organic ca rbon concentration in the mixed layer was lower than previously publis hed data of the main ocean basins, which might -reflect the low chloro phyll a concentration (< 0.5 mu g/l) encountered in this region. Along the 62 degrees E meridian section, organic carbon showed a trend with corresponding measurements of phytoplankton biomass and bacterial pro duction, underlining the dependence of bacterial growth on a pool of ' freshly' produced DOG. Organic carbon was found to exhibit a weak inve rse trend versus apparent oxygen utilization (AOU). This suggests that only a small part of the oxygen consumption is due to the mineralisat ion of DOG. (C) 1998 Elsevier Science B.V. All rights reserved.