Two hundred fifty years of reconstructed South Asian summer monsoon intensity and decadal-scale variability

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(7) (2019): 3927-3935, doi: 10.1029/2018GL081593.Climate model simulations of the summer South Asian monsoon predict increased rainfall in response to anthropogenic warming. However, instrumental data show a decline in Indian rainfall in recent decades, underscoring the critical need for additional, independent records of past monsoon variability. Here, we present new reconstructions of annual summer South Asian Monsoon circulation over the past 250 years, based on the geochemical barium‐calcium signature of dust present in Red Sea corals. These records reveal how monsoon circulation has evolved with warming climate and indicate a significant multi‐century long monsoon intensification, with decreased multidecadal variance. Stronger monsoon circulation would have increased the moisture transport from the Arabian Sea and Bay of Bengal over the Indian subcontinent. If these trends continue, the monsoon circulation and associated moisture transport and precipitation will remain strong and stable for several decades.We thank Editor Valerie Trouet and two anonymous reviewers for their constructive comments. We gratefully acknowledge Justin Ossolinski for assistance during core drilling; Maureen Auro, Laura Robinson, and Tom Marchitto for use of lab space and for technical advice; Margaret Sulanowska for providing XRD analysis of dust samples; and Sujata Murty and Ryan Davis for assistance in the lab. We thank Falmouth Hospital for use of X‐ray equipment. We acknowledge the use of the NSF‐supported WHOI ICP‐MS facility and thank Scot Birdwhistell for his assistance. This research was supported by grants to K. A. H. from NSF award OCE‐1031288 and KAUST award USA00002, and by a WHOI Postdoctoral Fellowship awarded to S. P. B. All data presented in this manuscript will be made publicly available online through the NOAA NCDC Paleoclimatology data archive (https://www.ncdc.noaa.gov/data‐access/paleoclimatology‐data/).2019-09-2