Life cycle of eddies along the western boundary of the Bay of Bengal and their implications

Analysis of vertical thermohaline structure along the western boundary of the Bay of Bengal revealed many undulations during April–May 2003. A prominent feature noticed was a dome in the northwestern boundary of the Bay of Bengal, which was found to be a cyclonic eddy (NCE). This eddy altered the ambient temperature by 6 °C and salinity by 0.8 psu. NCE was formed from a meander generated out of an instability due to cross-shore density gradient in the northeastward flowing western boundary current during early February. The cross-shore density gradient was developed under the influence of cyclonic (upwelling)/anticyclonic (downwelling) wind stress curl along the western boundary/open ocean region and the westward propagating Rossby wave. EOFs of SLA showed that annual cycle (EOFs 1 and 2) accounts for 39% of the total variance, while meso-scale eddies contributed up to 25% of the variance. Meso-scale eddies dominate the BOB circulation and are able to enhance the surface chlorophyll whenever the stratification is weak as in the case of intermonsoon 2003.

► Mesoscale processes are dominant in the Bay of Bengal, a region influenced by monsoons.
► High levels of chlorophyll were sustained in the cyclonic eddy observed throughout its life during spring intermonsoon.
► Eddies mostly fertilize subsurface ocean except during intermonsoon and in the southwestern Bay of Bengal.