PALEOPRODUCTIVITY VARIATIONS IN THE EQUATORIAL ARABIAN SEA: IMPLICATIONS FOR EAST AFRICAN AND INDIAN SUMMER RAINFALLS AND THE EL NINO FREQUENCY

摘要

We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian Ocean Equatorial Westerlies (IEW). The IEW in turn are positively correlated to the Southern Oscillation Index (SOI), which is a measure of El Nino, Southwest monsoon (SWM), and east African rainfall (EAR). The productivity data show that Indian and east African rainfalls declined from 35,000 calendar yr BP up to the last glacial maximum (LGM), with the maximum El Nino frequency during the last glacial period. From approx 14,500 to approx 2000 calendar yr BP (i.e. core top), we find strengthening SWM and EAR along with declining El Nino frequency.