The upwelling record in the sediments of the western continental margin of India

Abstract

Analysis of 63 sediment samples from the western continental margin of India for planktonic foraminifera, organic carbon, biogenic silica and calcium carbonate content showed higher frequency (30–40%) of Globigerina bulloides and high organic carbon (>3%) coinciding with higher primary productivity (>1 g C m −2 day −1) in the south compared to lesser (20–30%) abundance of G. bulloides and organic carbon (1–2%) and moderate productivity (0.5–0.75 g C m −2 day −1) in the north. This is suggestive of relatively intense upwelling in the south compared to the north. The gradual decrease in abundance of G. bulloides and organic carbon content from upper slope to lower slope similarly reflects a greater intensity of upwelling on the upper slope. The positive correlation between organic carbon and G. bulloides suggests that G. bulloides can be used as an indicator of productivity in the areas of coastal upwelling. Rich occurrences of most sensitive species for dissolution ( Globigerinoides ruber, Orbulina universa, Globigerinella aequilateralis, Globigerinoides sacculifer and Globigerinita glutinata) and less biogenic silica content in the sediments along with more diatoms (538.10–672.50) × 10 3 1 −1 in the water column indicate the preservation of calcium carbonate and dissolution of siliceous constituents.