Oxygen isotope evidence for a stronger winter monsoon current during the last glaciation

Abstract

A variety of palaeoclimate data from the northern Indian Ocean has shown that the Asian summer monsoon was weaker during the Last Glacial Maximum (~18,000 years ago) than it is today. It has also been inferred from these data that the winter monsoon was stronger at that time. Here we present evidence that the transport of low-salinity water from the Bay of Bengal to the Arabian Sea, caused by the winter monsoon6 was higher during the Last Glacial Maximum. This inference is based on a negative excursion, up to about 1‰ in magnitude, in the oxygen isotope ratios of three planktonic foraminiferal species, detected in a sediment core from the Arabian Sea by high-resolution (1-2 cm) sampling. Our results place an upper limit of about 4,000 years on the length of time during which the winter monsoon was stronger than today.