Oceanography of marginal seas
Abstract
The North Indian Ocean consists of three marginal seas; The Persian Gulf and the Red Sea in the west and the Andaman Sea in the east. Oceanographic features of these semi-enclosed basins have been discussed in this article. While circulation in the first two shallow seas are driven by surface densification following evaporation that in the latter is largely influenced by freshwater discharge from Irrawaddy and inflows across the Andaman Ridge from east Bay of Bengal. Biological productivity in the marginal seas is low since the inflowing surface waters from the Arabian Sea are oligotrophic. High evaporative conditions in the Persian Gulf facilitate a carbonate precipitation of 125 mu mole kg-1 near the Trucial coast. The partial pressure of carbon dioxide in intermediate layers falls from approx. 1000 mu atm in the southern end to approx. 500 mu atm in the northern Red Sea. Temperature in Atlantis II deep and brine level in Discovery deep in the Red Sea seem to be increasing in recent years. The Andaman Sea remains the least studied basin in this region. Physical and chemical signatures suggest that the deep basin of the Andaman Sea are largely influenced by intermediate circulation. Deep waters are warmer and low in oxygen than those at similar depths in the eastern Bay of Bengal. Intermediate waters in this basin contain signatures of denitrification and provide evidence for the Arabian Sea high salinity waters influence on circulation at intermediate depths in the rest of the Indian Ocean. Carbon dioxide chemistry in surface waters of the Andaman Sea are significantly influenced by large inflow of run-off from Irrawaddy.
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