Upwelling along the western Indian continental margin and its geological record - a summary

Abstract

Upwelling along the western Indian continental margin is recorded each year from Cape Comorin to Cochin and further north up to Goa from June to September during the southwest monsoon. During this upwelling heavy phytoplankton blooms develop which contribute to the sediment compositions along the western continental margin. Here, under the influence of coastal upwelling and the resulting intense midwater oxygen minimum, a belt of laminated dark organic-carbon-rich muds is deposited along the upper slope. These laminations are believed to represent the response of the depositional environment to the annually recurring upwelling events. Distributions of organic carbon, opaline silica, benthic and planktonic faunas, and the preservation of biogenic sediment components can be correlated to the characteristics of the water masses and, thereby, to the intensity and magnitude of upwelling. Benthic and planktonic foraminifers are particularly useful indicators; e.g., the invasion of immigrant populations of @iGlobigerina bulloides@@, and of dextrally coiled @iNeogloboquadrina pachyderma typica@@ through upwelling leave a record of the presence of such water masses in the sediments of that region. The very occurrence of @iG. bulloides@@ and the absence or irregular occurrence of @iGloborotalia menardii@@ also imply upwelling in that region, as does the presence of benthic foraminifers @iHyalinea balthica@@ and @iEhrenbergina@@ sp.