Palaeomonsoon History During the Late Quaternary: Results of a Pilot Study on Sediments from the Laccadive Trough, Southeastern Arabian Sea

Stratigraphic sections of carbonate-free sediments at 5-10 cm intervals of a 1.2 m core (CA 3800) from the Laccadive Trough (water depth: 1724m) were analyzed for organic carbon (OC), nitrogen (N), OC/N, δ¹³C and δ¹⁵N, using a continuous flow stabte isotope mass spectrometer. Data on CaCO₃ were also used. The generally high concentrations of OC (0.9-2.16%) and CaCO₃ (32.2-54.4%) presumably reflect high productivity at the core site. The predominantly marine origin of the OC is indicated by the -19.6 to -18.2 δ¹³C values.

Significantly higher carbonate is recorded in the Holocene than in the late Glacial, presumably reflecting increased Holocene productivity resulting from enhanced upwelling and summer monsoon during the Interglacial than Glacial. The late Glacial to Holocene increase in the mean OC/N from about 13 to 16 and δ¹⁵N by 2‰, presumably mirrors a relative increase in denitrification in the oxygen-deficient zone coinciding with enhanced Holocene productivity in the southeastern Arabian Sea. Our interpretation on the paleoproductivity is consistent with those for the western Arabian Sea proposed by earlier workers for the above time period.