EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Variations of the Indian Ocean Walker circulation since the Last Glacial Maximum revealed by reconstructed and simulated zonal wind intensity

Xinquan Zhou1, Stéphanie Duchamp-Alphonse1, Masa Kageyama2, Franck Bassinot2, Xiaoxu Shi3, Luc Beaufort4, and Gerrit Lohmann3
Xinquan Zhou et al.
  • 1Université Paris-Saclay, CNRS, Géosciences Paris Sud, Orsay, France
  • 2Le Laboratoire des Sciences du Climat et de l'Environnement, CEA, CNRS, Université de Versailles Saint-Quentin, Gif-sur-Yvette, France
  • 3Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany
  • 4Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement, CNRS/IRD/Aix-Marseille Université, Aix-en-Provence, France

Today, precipitation and wind patterns over the equatorial Indian Ocean and surrounding lands are paced by monsoon and Walker circulations that are controlled by the seasonal land-sea temperature contrast and the inter-annual convection over the Indo-Pacific Warm Pool, respectively. The annual mean surface westerly winds are particularly tied to the Walker circulation, showing interannual variability coupled with the gradient of Sea Surface Temperature (SST) anomaly between the tropical western and southeastern Indian Ocean, namely, the Indian Ocean Dipole (IOD). While the Indian monsoon pattern has been widely studied in the past, few works deal with the evolution of Walker circulation despite its crucial impacts on modern and future tropical climate systems. Here, we reconstruct the long-term westerly (summer) and easterly (winter) wind dynamics of the equatorial Indian Ocean (10°S−10°N), since the Last Glacial Maximum (LGM) based on i) primary productivity (PP) records derived from coccolith analyses of sedimentary cores MD77-191 and BAR94-24, retrieved off the southern tip of India and off the northwestern tip of Sumatra, respectively and ii) the calculation of a sea surface temperature (SST) anomaly gradient off (south) western Sumatra based on published SST data. We compare these reconstructions with atmospheric circulation simulations obtained with the general coupled model AWI-ESM-1-1-LR (Alfred Wegener Institute Earth System Model).

Our results show that the Indian Ocean Walker circulation was weaker during the LGM and the early/middle Holocene than present. Model simulations suggest that this is due to anomalous easterlies over the eastern Indian Ocean. The LGM mean circulation state may have been comparable to the year 1997 with a positive IOD, when anomalously strong equatorial easterlies prevailed in winter. The early/mid Holocene mean circulation state may have been equivalent to the year 2006 with a positive IOD, when anomalously strong southeasterlies prevailed over Java-Sumatra in summer. The deglaciation can be seen as a transient period between these two positive IOD-like mean states.

How to cite: Zhou, X., Duchamp-Alphonse, S., Kageyama, M., Bassinot, F., Shi, X., Beaufort, L., and Lohmann, G.: Variations of the Indian Ocean Walker circulation since the Last Glacial Maximum revealed by reconstructed and simulated zonal wind intensity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12762,, 2021.


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