Part of the global DOC versus AOU (dissolved organic carbon/apparent oxygen utilization) data compilation, Indian Ocean

Samples for total organic carbon (TOC) analysis were collected on WOCE Line P15S (0° to 67°S along 170°W) and from 53° to 67°S along 170°E in the western South Pacific, and on Line I8 (5°N to 43°S along 80°/90°E) in the central Indian Ocean. TOC concentrations in the upper ocean varied greatly between the regions studied. Highest surface TOC concentrations (81-85 µM C and 68-73 µM C) were observed in the warmest waters (>27°C) of the western South Pacific and central Indian Oceans, respectively. Lowest surface TOC concentrations (45-65 µM C) were recorded in the southernmost waters occupied (>50°S along 170°W and 170°E). Deep water (>1000 m) TOC concentrations were uniform across all regions analyzed, averaging between 42.3 and 43 µM C (SD: ±0.9 µM C). Mixing between TOC-rich surface waters and TOC-poor deep waters was indicated by the strong correlations between TOC and temperature (r2>0.80, north of 45°S) and TOC and density (r2>0.50, southernmost regions). TOC was inversely correlated with apparent oxygen 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 sigmaT 23-27 ranged from -0.15 to -0.34 in the South Pacific and from -0.13 to -0.31 in the 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.

Concentrations of dissolved organic carbon and particulate organic nitrogen in the Eastern North Pacific

Data are presented on concentration of dissolved organic carbon and particulate organic nitrogen in sea water at four stations, and also of dissolved and particulate amino acids at a deep-sea station above the Japan Trench. Concentration of Corg ranged from 0.79 to 2.00 mg/l, reaching maximum in the upper productive layers, while that of particulate Norg varied from 0.0018 to 0.037 mg/l, the maximum being in the upper layer (0-100 m). Water and particulate matter contained 18 amino acids in concentrations varying from 0.150 to 0.177 mg/l in the former and from 0.010 to 0.048 mg/l in the latter. Amino acid composition is variable. Vertical distribution of dissolved Corg and particulate Norg, as well as of dissolved and particulate amino acids is greatly dependent on water dynamics.

Impact of dissolved inorganic carbon concentrations and pH on growth of the chemolithoautotrophic epsilonproteobacterium GD1

Epsilonproteobacteria have been found globally distributed in marine anoxic/sulfidic areas mediating relevant transformations within the sulfur and nitrogen cycles. In the Baltic Sea redox zones, chemoautotrophic epsilonproteobacteria mainly belong to the Sulfurimonas gotlandica GD17 cluster for which recently a representative strain, S. gotlandica GD1T, could be established as a model organism. In this study, the potential effects of changes in dissolved inorganic carbon (DIC) and pH on S. gotlandica GD1T were examined. Bacterial cell abundance within a broad range of DIC concentrations and pH values were monitored and substrate utilization was determined. The results showed that the DIC saturation concentration for achieving maximal cell numbers was already reached at 800 µmol/l, which is well below in situ DIC levels. The pH optimum was between 6.6 and 8.0. Within a pH range of 6.6-7.1 there was no significant difference in substrate utilization; however, at lower pH values maximum cell abundance decreased sharply and cell-specific substrate consumption increased.