Reconstruction of Indian summer monsoon winds and precipitation over the past 10,000 years using equatorial pacific SST proxy records

Abstract

Using a multiproxy reduced dimension methodology, we reconstruct fields of Arabian Sea summer wind stress curl and Indian monsoon rainfall anomalies since early Holocene using sea surface temperature (SST) proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind stress curl reveal positive anomalies of ∼30% greater than present day off the coastlines of Oman and Yemen at 10 ka, suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time. Positive wind stress curl anomalies in these regions continued but weakened to ∼12% greater than present day at 6 ka. Wind stress curl anomalies increased by about 8% from 6 to 4 ka but declined again until 2 ka. Positive anomalies in wind stress curl during the early to middle Holocene are consistent with greater early Holocene abundances of the upwelling indicator Globigerina bulloides in the western Arabian Sea, which accumulates most rapidly in present climates during periods of marked upwelling. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region (∼20–60% greater than present day) and concurrently the greatest deficit in rainfall in North East India and on the eastern side of the Western Ghats (∼10–30% less than present day). Specifically, reconstructions for 10 ka reveal 40–60% greater rainfall than present day over northwest India. These findings advance the hypothesis that teleconnections from the equatorial Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, and discharge) paleoclimate proxies throughout the monsoon region.