Organic carbon and apparent oxygen utilization in the western South Pacific and the central Indian Oceans

Ž . Ž . Samples for total organic carbon TOC analysis were collected on WOCE Line P15S 08 to 678S along 1708W and from Ž . 538 to 678S along 1708E in the western South Pacific, and on Line I8 58N to 438S along 808r908E in the central Indian Ocean. TOC concentrations in the upper ocean varied greatly between the regions studied. Highest surface TOC Ž . Ž . concentrations 81–85 mM C and 68–73 mM C were observed in the warmest waters )278C of the western South Pacific Ž . and central Indian Oceans, respectively. Lowest surface TOC concentrations 45–65 mM C were recorded in the Ž . Ž . southernmost waters occupied )508S along 1708W and 1708E . Deep water )1000 m TOC concentrations were uniform Ž . across all regions analyzed, averaging between 42.3 and 43 mM C SD: "0.9 mM C . Mixing between TOC-rich surface Ž 2 waters and TOC-poor deep waters was indicated by the strong correlations between TOC and temperature r )0.80, north . Ž 2 . of 458S and TOC and density r )0.50, southernmost regions . TOC was inversely correlated with apparent oxygen Ž . Ž . utilization AOU along isopycnal surfaces north of the Polar Frontal Zone PFZ and at depths -500 m. The TOC:AOU molar ratios at densities of s 23–27 ranged from y0.15 to y0.34 in the South Pacific and from y0.13 to y0.31 in the T Indian Ocean. These ratios indicate that TOC oxidation was responsible for 21%–47% and 18%–43% of oxygen consumption in the upper South Pacific and Indian Oceans, respectively. At greater depths, TOC did not contribute to the development of AOU. There was no evidence for significant export of dissolved and suspended organic carbon along isopycnal surfaces that ventilate near the PFZ. q 2000 Elsevier Science B.V. All rights reserved.