Sundarvel,
Ragasakthi S.S.
School of Ecology, Pondicherry University, Pondicherry 605 014, India, Tel: 0091 – 413 – 2655 513, Fax: 0091 - 413 - 2655 265, E-mail: ragasakthi@yahoo.co.in, Sundar1956@satyam.net.in
The surface waters of coastal and upwelling regions tend to be rich in nutrients, whereas the extensive central regions of the oceans are nutrient–deficient. This pattern is reflected in the pattern of plant productivities. But sunshine is the other important ingredient in photosynthesis and it causes important seasonal and geographic variations in the pattern of productivities. Due to thermocline that separates warm surface waters from cool deeper waters in temperate and tropical latitudes, nutrients are lost from the surface and do not get recycled, as organic detritus sinks into colder deeper water. And thus, though sunshine is plentiful, scarcity of nutrients keep plant productivities quite low as in most of the tropical oceans.
The Indonesian throughflow crosses the Indian ocean near 12°S within the south equatorial current. The throughflow stream acts to isolate the thermocline and intermediate water masses of the monsoon regime to the north from those of the subtropical regime to the south. North of this equatorial flow is the low salinity thermocline of the Bay of Bengal. It is suggested that downward flux of low salinity surface water is a product of the tidally active eastern Bay of Bengal. The oxygen is low throughout the Bay of Bengal water column below the surface layer, however, in the southern Bay of Bengal and in the equatorial zone, there is a weak oxygen maximum, coupled with a salinity maximum .
However there are few regions of the Bay of Bengal, where nutrients are plentiful. The combination of nutrients and sunlight make these regions very productive. There is a oxygen and nutrient rich benthic boundary layer, BBL rather in a limited area in the western Bay of Bengal (Edmond et al. 1979 and Broecker et al. 1980). While the Arabian Sea has strong upwelling that supports high surface productivity, the Bay of Bengal upwelling is much weaker. High productivity may not be supported by upwelling, but rather by the enormous amount of dissolved and particulate material that enters the Bay of Bengal with the river water. Also high productivities are observed in the following limited areas: equatorial upwelling areas, reefs and rises (which force deeper currents to the surface), and continental shelves (because decaying detritus can not sink so deep). But away from these limited regions, the Bay of Bengal is relatively barren.
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