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.