Air-sea interactions and exchanges

Abstract

To support the idea that the Arabian Sea makes a significant contribution to biogeochemical ocean-atmosphere transfer processes, quantification of parameters such as carbon dioxide, nitrous oxide, methane, ammonia and dimethylsulphide was carried out during JGOFS and related cruises. The results of these studies have conclusively established that the Arabian Sea is indeed a source of CO sub(2) to the atmosphere at almost all places during all seasons, but with very large seasonal and geographical variability. The seasonal contrasts in pCO sub(2) and in the air-sea flux are best marked in coastal waters, but large seasonality in the open ocean is also observed in the Southern Indian Ocean. The Arabian Sea appears to account for at least one-third of the global oceanic water column denitrification. The Arabian Sea also makes significant contribution in terms of nitrogen budget by the efflux of N sub(2) O from the sea surface. JGOFS studies have led to a better quantification of this efflux. Very high surface saturations (greater than 300 percent) in the upwelling zones off Oman, Somalia and SW India were observed. Most of the removal of ammonia and methylamines was found to occur through wet deposition, contributing little (less than 1 percent) to the new production. The experiments also suggest that the atmospheric NO super(-) sub(3) and methane deposition plays an insignificant role in fuelling new production in the region. The results underline that the delicate biogeochemical balance in the Arabian Sea, can have potentially large impacts on chemical fluxes, especially greenhouse gases. Therefore the Arabian Sea is regarded as a sensitive ocean scale barometer of global climate change. It is therefore; continuous monitoring of the processes in this area is essential.