SEASONAL VARIABILITY IN DISTRIBUTION AND FLUXES OF METHANE IN THE ARABIAN SEA

Methane, a biogeochemically important gas in Earth's atmosphere was me asured in the water column and air in the Arabian Sea in different sea sons, viz., northeast monsoon, intermonsoon, and southwest monsoon, as part of the Joint Global Ocean Flux Study (India). These observations record its distributions in the water column as well as its fluxes a, nd their seasonal variations. Methane is mainly produced in subsurface water, and its supersaturation occurs in the upper 400 m. The CH4 pea k concentration and its location vary with latitude and season. Below about 400 m, seawater CH4 concentrations, in general, are observed to be undersaturated, suggesting its consumption. Production of CH4 in ox ygenated water appears to be under biological control; however, the pe ak in deep anoxic water does not show any particular relation with any single chemical, biological, or physical variable and rather suggests it to be maintained by the quasi-horizontal transport. The average su rface supersaturations are found to be 140 +/- 37, 173 +/- 54, and 200 +/- 74 in the northeast monsoon, intermonsoon, and southwest monsoon, respectively. Wind speed dependent flux estimation reveals the coasta l region of the Arabian Sea to be a stronger source of methane compare d to the open oceanic region, although a zonal transect along 10(0)N a lso shows higher flux of methane. The effects of the Findlater Jet ind uced downwelling on the distributions of CH4 in the near surface water as well as on its emissions have been discussed. Its annual emission rate of 0.03-0.05 Tg CH4 yr(-1) from the Arabian Sea is nearly the sam e as that observed from the global oceans.