Impact of Indian Ocean surface temperature gradient reversals on the Indian Summer Monsoon

Syee Weldeab, Carsten Rühlemann, Qinghua Ding, Vyacheslav Khon, Birgit Schneider, William R. Gray

Research output: Contribution to journalArticlepeer-review

Abstract

Indian Summer Monsoon (ISM) precipitation is the main determinant of livelihood in a densely populated world region. The interannual variability of the ISM is influenced by several modes of climate variability, including anomalous seasonal sea surface temperature (SST) gradient reversals between the eastern, western, and northeastern Indian Ocean. With global warming, the frequency of zonal and meridional Indian Ocean's SST gradient changes is projected to increase but its impact on the ISM is debated. Here we present a 25,000-year proxy record of SST and inferred Ganges-Brahmaputra-Meghna (GBM) River runoff that provides a spatially integrated measure of ISM precipitation changes. This record indicates a monotonic deglacial strengthening of the ISM system when the SST gradient between the Bay of Bengal surface water and the eastern equatorial Indian Ocean was reversed. We posit that the reversal in the meridional SST gradient reduced the impact of Heinrich Event 1 and Younger Dryas on the low elevation part of the ISM domain. Furthermore, the proxy record shows that the strongest Holocene ISM strengthening occurred between 7900±470 and 5700±360 years before present, coinciding with and causally linked to the reversal of the Indian Ocean zonal SST gradient and ensuing changes in the wind fields, a sequence of events that is inferred from and supported by the results of our climate simulation. Our study demonstrates that changes in the Indian Ocean's zonal and meridional thermal gradient strongly shaped the timing of Holocene monsoon strengthening and the response of ISM to the last deglacial freshwater forcing.
Original languageEnglish
Article number117327
JournalEarth and Planetary Science Letters
Volume578
Early online date17 Dec 2021
DOIs
Publication statusPublished - 15 Jan 2022

Keywords

  • Impact of zonal and meridional SST gradient reversal on Indian Summer Monsoon
  • Reversal of zonal SST gradient across the equatorial Indian Ocean
  • Spatially heterogeneous response of Indian Summer Monsoon during YD, HE1 mid Holocene

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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