Influence of the Indian Walker Circulation on δ $\delta $ 18OP and Hydroclimate Variability in the Indian Ocean Basin

Abstract

The Indian Ocean plays a crucial role in water cycle dynamics around the Indian Ocean Basin, yet the relationships between the Indian Walker Circulation (IWC) and hydroclimate variability remain poorly understood. We examine the IWC-hydroclimate linkages throughout the Indian Ocean Basin during two study periods (instrumental era and the last millennium), using the ECHAM5-wiso, iCESM-iLME, and ERA5 global data products. We leverage the stable isotopic composition of precipitation ($\delta$¹⁸O_P) as an integrative water cycle tracer to elucidate the link between large-scale atmospheric processes and regional hydroclimate characteristics. We find a strong statistical relationship between the East African short rain $\delta$¹⁸O_P and IWC in Eastern Africa and Horn of Africa. In Indonesia, the relationship is weaker due to the strong influence of the Pacific Walker Circulation (PWC). These patterns arise over multiple time scales and are consistent with the strong tie between the IWC and precipitation variability during the short rain season in Eastern Africa and Horn of Africa that had previously been reported in the instrumental era but not yet for the last millennium. We document strong fluctuations in the strength of the IWC during the last millennium, with periods of stronger or weaker interactions with the PWC that influenced $\delta$¹⁸O_P variability. Finally, our study underscores the ability of $\delta$¹⁸O_P to capture major atmospheric circulation signals, demonstrating its potential to examine the impact of interacting Walker Circulations on regional hydroclimate even during periods of low precipitation.