A STUDY OF THE CARBON-DIOXIDE SYSTEM IN THE NORTHERN INDIAN-OCEAN DURING PREMONSOON

Extensive data sets on the carbon dioxide system in the northern India n Ocean have been obtained during the premonsoon season. A marked incr ease (approximately 50 muM) in the total carbon dioxide (TCO2) content is observed in deep (greater-than-or-equal-to 1 km) waters of the nor thern Arabian Sea between approximately 10 and 20-degrees-N; contribut ions from soft tissue decomposition and skeletal solution to the obser ved increase are about the same. In the Bay of Bengal, the correspondi ng increase in TCO2 observed from 11 to 19-degrees-N is relatively sma ll (17.5 muM). Significantly, the contribution of the organic decompos ition in this region is only 1/7 of the increase in TCO2. This, togeth er with the earlier reports on large sinking fluxes of particulate org anic carbon and pronounced near-bottom anomalies, suggests rapid sinki ng of organic matter with little decomposition in the water column due to the immense fluvial inputs of lithogenic matter into the Bay of Be ngal. The greater extent of organic decomposition in subsurface waters of the Arabian Sea is reflected by generally lower pH and higher pCO2 levels. This also causes the deep waters in the Arabian Sea to be mor e corrosive to CaCO3 than those in the Bay of Bengal. However, the TCO 2 concentrations in the deep Bay of Bengal are slightly higher as comp ared to those in the Arabian Sea, presumably due to the greater CaCO3 dissolution in deep waters en route the Bay of Bengal. The atmospheric fluxes of CO2 are found to be larger in the Arabian Sea (2.9 mmol/m2/ d) than in the Bay of Bengal (0.33 mmol/m2/d) during the premonsoon se ason. The overall annual evasion rate of CO2 from the Arabian Sea and Bay of Bengal has been estimated as greater-than-or-equal-to 50 Tg C. These results confirm that the northern Indian Ocean serves as a signi ficant source of atmospheric CO2.