Biogeochemical ocean-atmosphere transfers in the Arabian Sea

Abstract

Transfers of some important biogenic atmospheric constituents, carbon dioxide (CO₂), methane (CH₄), molecular nitrogen (N₂), nitrous oxide (N₂O), nitrate (NO^-₃), ammonia (NH₃), methylamines (MAs) and dimethylsulphide (DMS), across the air-sea interface are investigated using published data generated mostly during the Arabian Sea Process Study (1992-1997) of the Joint Global Ocean Flux Study (JGOFS). The most important contribution of the region to biogeochemical fluxes is through the production of N₂ and N₂O facilitated by an acute, mid-water deficiency of dissolved oxygen (O₂); emissions of these gases to the atmosphere from the Arabian Sea are globally significant. For the other constituents, especially CO₂, even though the surface concentrations and atmospheric fluxes exhibit extremely large variations both in space and time, arising from the unique physical forcing and associated biogeochemical environment, the overall significance in terms of their global fluxes is not much because of the relatively small area of the Arabian Sea. Distribution and air-sea exchanges of some of these constituents are likely to be greatly influenced by alterations of the subsurface O₂ field forced by human-induced eutrophication and/or modifications to the regional hydrography.