Distribution of nitrous oxide and methane in the Arabian Sea
Shyam Lal, Prabir K. Patra, S. Venkataramani and M. M. Sarin
Physical Research Laboratory, Ahmedabad 380 009, India
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 April-May 1994 and February-March
1995, as part of the JGOFS (India) programme. The average abundances of
N2O and CH4
in the air are 313±7ppbv and 1.69±0.05 ppmv respectively.
During both the periods, the vertical proriles of N2O
in the water column show a double peak structure with the dominant peak
in the 500-1000 m depth region with concentrations of 70-80 nmol. The entire
water column is supersaturated with 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 an 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 zero. 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 depth region. Supersaturation (up to 200400% at the peak) is found for
CH4 in most of the profiles. Average sea-air
flux of methane during April-May 1994 and February-March 1995 is 0.0001
and 0.033 pg cm-2 s-1
, respectively.