DISTRIBUTION OF NITROUS-OXIDE AND METHANE IN THE ARABIAN SEA

Measurements of the two important biogenic gases N2O and CH4 have been made both in the water column and in air of the Arabian sea during Ap ril-May 1994 and February-March 1995, as part of the JGOFS (India) pro gramme, The average abundances of N2O and CH4 in the air are 313 +/- 7 ppbv and 1.69 +/- 0.05 ppmv respectively. During both the periods, th e vertical profiles of N2O in the water column show a double peak stru cture with the dominant peak in the 500-1000 m depth region with conce ntrations of 70-80 nmol, The entire water column is supersaturated wit h respect to N2O and in the major peak region it is supersaturated by as much as 600-800%, suggesting this region of the Arabian sea to be a n important reservoir of N2O. During February-March 1995, sea-air flux of N2O is calculated to be about 0.26 pg cm(-2) s(-1), while the flux calculated for April-May 1994 is not significantly different from zer o, Methane concentrations were measured only down to 400 m depth, Its distribution shows a peak concentration of 6-8 nmol in the 100-200 m d epth region, Supersaturation (up to 200-400% at the peak) is found for CH4 in most of the profiles. Average sea-air flux of methane during A pril-May 1994 and February-March 1995 is 0.0001 and 0.033 pg cm(-2) s( -1), respectively.