H

ffi Q

Distance from the coast (km)

along the west coast of India since the oceano-graphic conditions are similar.

Zonal variations of DMS in the Bay of Bengal are shown in Fig. 7. Near Paradip (86.87°E, 19.98°N), DMS concentrations varied between 0.5 and 3.3 nM in coastal waters but showed little change with increasing distance from the coast. Similar features were noticed off Chennai as well. Here, DMS varied from 0.5 to 3.2 nM. Thus the zonal variability trends of DMS were contrasting between the Arabian Sea (with clear inshore-offshore gradients) and the Bay of Bengal (with no significant variation).

In the central Indian Ocean a different scenario was found. Figure 8 depicts the variation of DMS in the central Indian Ocean observed during the INDOEX cruises of 1998 and 1999. High DMS concentrations (0.1-13.9 nM) were observed between 5°S and 15°S in 1999. These were observed as pockets between surface and 75 m with detectable concentrations down to 100-150 m. While away from these latitudes viz. between 0° and 5°S, and

Distance from the coast (km)

15°S and 20°S DMS concentrations, in the same depth range, as mentioned above varied between 1 and 5 nM. DMS levels were lower in 1998 with strong latitudinal gradients.

Thus DMS in the Indian Ocean exhibits very high spatial variability in which higher concentrations were observed near to the coast and lower concentrations in the open Ocean. Further, DMS concentrations (MLD average) showed a gradual increase from the central Indian Ocean (2.7 nM) and the Bay of Bengal (2.8 nM) to the Arabian Sea (7.8 nM).

Discussion

DMS at sea surface and its emission Variations in surface DMS

The envisaged indirect global cooling by DMS products depends on its emission from the ocean.

Fig. 7 Variations in DMS and DMSPt off Paradip (a) and (b) during SK147A and (c) during SK147B and off Chennai (d) during SK147B

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