Carbon and nitrogen budgets of the Arabian Sea

Abstract

From the available data, carbon and nitrogen budgets have been estimated for the Arabian Sea (0-25°N, 50-80°E), taking into consideration the possible sources of fluxes. By our model calculations the annual fluxes into and out of the Arabian Sea were estimated to be 446 and 530 trillion grams (Tg) for carbon, and 8.06 and 3.60 Tg for nitrogen, respectively. The carbon budget was found to be negatively balanced by 84 Tg year^-1. A possible source to compensate for this deficit could be from the northward movement of Antarctic Bottom Water in the bottom layers, which are probably enriched with anthropogenic carbon dioxide. Annually, ~74 Tg of carbon in the form of carbon dioxide escaped into the atmosphere from the Arabian Sea; this is higher than the global average fluxes from the tropical oceans. The percentage loss of carbon (14.0%) to the atmosphere was much lower than that of nitrogen (56.9%). Out of the total amount of denitrified nitrogen (29.5 Tg) only ~7% was lost to the atmosphere. This model suggests that ~6 Tg N year^-1 of denitrified nitrogen of the world's oceans could be liberated to the atmosphere through the surface layer of denitrified areas. A quantitative assessment has been made to account for the excess of nitrogen that could result from N₂ fixation by extensive blooms of Trichodesmium in the Arabian Sea. Fluxes from rivers did not seem to contribute significantly to the carbon influx. The burial of carbon through the sedimentation process was not very significant to the total flux. The Arabian Sea was found to be a carbon source for the Persian Gulf and the Red Sea, whereas both of these adjacent seas added nitrogen to the Arabian Sea. Based on the standing crop and net outfluxes, estimated residence times were ~944 and 4.04 × 10⁴ years for carbon and nitrogen, respectively, in the Arabian Sea.