Vertical distributions of dissolved organic carbon and nitrogen in the Southern Ocean

Detailed vertical profiles of dissolved organic carbon (DOC), nitrogen (DON) and DOC/DON ratios in the Australian sector of the Southern Ocean (56 degrees-65 degrees S around 140 degrees W transect) were obtained by a high-temperature catalytic oxidation method with a modified Shimadzu TOC-5000 unit. The simultaneous analyses of DOC and total dissolved nitrogen (TDN) gave high precision results (+/- 0.7 mu MC and +/- 0.3 mu MN). In surface layers, DOC concentrations were lower (45-55 mu M) than those generally obtained from other oceanic environments (60-90 mu M). The surface concentrations of DON varied from 4 to 9 mu M, but within the range generally reported for other ocean regions. Surface excesses of DOC and DON were calculated against nearly constant subsurface concentrations. A consistent contribution of low C/N ratio (2.7-5.0) was found in the mid-surface layer (30-75 m), suggesting more extensive degradation of carbon-enriched materials and/or enhanced supply of nitrogen-enriched ones. (C) 1999 Elsevier Science Ltd. All rights reserved.