The JGOFS - INDIA Arabian Sea Process Study brought in a few new scientific insights from the area:

1. Winter Blooms Driven by Winter Cooling

During Winter (November - February), the cool, dry continental air brought by the prevailing northeast trade winds intensifies evaporation leading to surface cooling. This combined with reduced solar insolation and high ambient salinity ( about 36 psu ) leads to densification of the surface waters in the Northern Arabian Sea. The consequent sinking initiates the convection processes that leads to the upward transport of nutrient into the surface layers from the top of the thermocline. This leads to enhanced primary productivity throughout the northern Arabian Sea.

Schematic representation of winter cooling mechanism in the northern Arabian sea. The yellow layer indicates the shallow, uniform mixed layer ( < 30 m) during inter-monsoon ( April-May ) under the influence of increased solar insolation ( SST in excess of 28 ° C ) when the upper layer is highly stratified. The pink layer represents deep variable mixed layer ( in excess of 100m ) under winter ( SST ~25 ° C ) convection. Straight arrows into the box ( left ) indicates reduced incoming solar radiation on the sea surface during winter while the curved arrows out of the box ( right ) represents the enhanced evaporation under the influence of the dry continental air from the north brought by the prevailing northerly trade winds ( average 5m/ s ). The resulting cooling and convection introduces about 2-4 µM nitrate into the surface layers from the top of the thermocline.

With the onset of southwesterly winds in summer ( June - September ), upwelling starts off Somalia and propagates with time towards north. Upwelling enhances the nutrient levels in the coastal waters of Somalia and Arabia. Lateral Advection of fluid in the Ekman layer transports nutrient rich waters into the interior Arabian Sea. This leads to biological production south of the Findlater jet. In the north, lateral advection from the Arabian coast ( Ekman divergence ) as well as Ekman pumping in the offshore region ( open ocean upwelling ) leads to the high biological production.

Schematic representation of the flow regime and the physical forcing that fertilizes the central Arabian Sea during summer. Open arrows show the lateral advection from the Somalia and Arabia upwelling systems which transports nutrient rich waters to the central Arabian Sea. The green arrows show the prevailing flow in summer. The broad red arrow with bold face is the atmospheric Findlater jet which extends from the tip of Somalia ( 12 °N , 51 °E ) to Gujarat ( 21 °N , 71 °E) , India. The positive wind stress curl north of this jet drives the cyclonic circulation in the sea indicated by anticlockwise arrow and the dark short arrows out of it show the divergence associated with them. The negative wind stress curl south of the jet drives the anticyclonic circulation in the sea indicated by clockwise arrow and the dark short arrows into it show the convergence. The right hand side of the box shows the climatological mean thermal structure for August along 64 deg E based on Levitus ( 1982 ) data.

3. Microbial Loop

In the entire Arabian Sea, phtoplankton biomass and primary production is very low during the inter-monsoon ( May - June ). However, the mesozooplankton biomass remains fairly high, constituting of small herbivores. This `paradox' of the Arabian Sea presumably happens through a microbial loop. The bacteria and microzooplankton increase during this period through the Dissolved Organic Carbon ( DOC ) pool.

4. Transparent exopolymer particles (TEP) could significantly contribute to subsurface bacterial demands

The possible sinking carbon fluxes at 100 m were calculated from sediment traps (also using Th-disequilibria) and  colorimetric measurements of TEP. The results suggest that even at the least density gradient, between TEP and surrounding seawater, of 10^-6 kg/l the export in the form of TEP is more significant than of POC. Hence, TEP plays an important role in sustaining the subsurface bacterial activities in the Arabian Sea. The flux of DOC is still unknown.

5. Perennial emission of Carbon Dioxide

The surface Arabian Sea is found to be supersaturated with respect to atmospheric carbon dioxide in all the seasons. This enrichment leads to the perennial emission of 45 Tg Cy^-1 from about one quarter of the Arabian Sea (central and eastern parts).

6. Air - Sea flux of nitrate and methane

The role of atmospheric deposition of nutrients in contributing to biological productivity in the eastern & central Arabian Sea by determining the air-sea flux of nitrate during different seasons show an annual nitrate flux of about 1mg/m²/day, orders of magnitude lower than that fixed by primary productivity in the region. Concentration-depth profiles of methane in the water column show that it is generally supersaturated in the upper 400m water column.This leads to an annual sea-air flux of 0.03-0.05Tg methane from the Arabian Sea.