RECONSTRUCTING SEA-SURFACE TEMPERATURE AND SALINITY USING DELTA-O-18 AND ALKENONE RECORDS

THE oxygen isotope (deltaO-18) composition of foraminiferal tests from deep-sea sediments is widely used as a palaeoclimate proxy, but it in cludes contributions from sea surface temperature, global ice volume a nd local salinity, which are difficult to separate. Recently a new tec hnique for deriving palaeotemperatures has been developed which is bas ed on the abundance ratios of unsaturated alkenones in phytoplankton a lgae1,2. Here we use a combination of oxygen isotope and alkenone reco rds in a deep-sea core from the juncture of the Arabian Sea and the Ba y of Bengal to extract the salinity signal from the former record. Var iations in salinity are related to the balance between evaporation and precipitation3, and are thus a sensitive indicator of climate change. Our 170-kyr salinity record enables us to reconstruct changes in the Indian monsoon over this period, considerably extending earlier studie s (which reached back to 18 kyr ago)4-8. Like these previous studies, we find that large variations in the monsoon occurred during the trans ition from the last glacial period to the present interglacial, but ou r results also provide a view of the monsoon throughout the last glaci al and demonstrate the potential of this approach for reconstructing p alaeosalinity.