Carbon dioxide and nitrous oxide in the Arabian Sea

Abstract

This review concentrates on some aspects of biogeochemical cycling of carbon and nitrogen in the Arabian Sea with emphasis on the atmospheric fluxes of CO sub(2) and N sub(2)O. The Arabian Sea appears to serve as a net sink for combined nitrogen of approx 3 x 10 sup(13) gN y sup(-1). Inflow of deep and bottom waters should make up this deficit providing a net carbon input of approx 1.75 x 10 sup(15) g y sup(-1). This appears to sustain high atmospheric fluxes of CO sub(2) observed particularly during the summer monsoon. The distribution of dissolved organic carbon (DOC) reveals significant gradients corresponding to changes in total carbon dioxide (TCO sub(2)), oxygen consomption and nitrate deficits, suggesting an important role for DOC in the oceanic biogeochemical cycles. The results on the activity of the respiratory electron transport system reinforce this view. Steady northward increases in TCO sub(2) are observed at all depths due to regeneration from biogenic debris which also seems to increase from west to east. Large regional variations occur in the regeneration of soft tissue and skeletal material. The Arabian Sea appears to be a significant source for atmospheric N sub(2)O. The N sub(2)O distribution suggests substantial losses to reducing zones, implying a very rapid tumover of N@l2)O within the region