Palaeoproductivity and associated changes in the north-eastern Indian Ocean since the last glacial: Evidence from benthic foraminifera and stable isotopes

摘要

Here we present the first detailed planktonic and benthic delta C-13 records and benthic foraminiferal assemblage records from the north-eastern Indian Ocean to decipher the palaeoceanographic changes during the last 56 kyr. We identified three different palaeoceanographic stages, clearly differentiated by significant variations in the benthic foraminiferal assemblages and delta C-13 records. The results of this study indicate that productivity was generally higher during the glacial periods than during the Holocene. Comparison of the benthic foraminiferal assemblage distributions and planktonic and benthic delta C-13 records show a significant correlation between productivity and the bottom water oxygenation on glacial-interglacial timescales. Productivity gradually increased during the period between 56 and 27.5 kyr. During this period, the dominance of Melonis spp. and Oridosalis umbonatus were correlated with conditions of intermediate to high surface productivity and moderate bottom water oxygenation. Increased higher equatorial productivity and low bottom water oxygenation during the period between 27.5 and 15 kyr are supported by planktonic delta C-13 and faunal records. During this period, the dominance of benthic foraminifera assemblages characterised by Uvigerina peregrina indicates sustained continuous phytodetritus flux to the seafloor from enhanced surface water productivity and relatively low bottom water oxygenation. The absence or minimal occurrences of high productivity indicating U. peregrina, the dominance of intermediate to low productivity indicating fauna, and relatively low planktonic delta C-13 records suggest low productivity and active deep-water oxygenation after 15 kyr. Concurrent river discharge and rising sea levels during this period are indicated by negative delta O-18 of G. ruber at the site.