The spatiotemporal variability and driving mechanisms of the Intertropical Convergence Zone at centennial-millennial time scales since the Last Glacial

Abstract

As the most important rainfall belt in the world, the change of the Intertropical Convergence Zone (ITCZ) directly affects the distribution of rainfall between the Northern and Southern Hemispheres and impacts the livelihood of nearly one-third of the global population. Therefore, identifying the spatiotemporal variability of the ITCZ during the geological past is of great significance for understanding future climate change and preventing natural disasters. Understanding the evolution mechanism of the ITCZ is essential for a more accurate prediction of its future changes. The abundance of paleoclimate records and numerical simulations in the Last Glacial and the Holocene renders this period of time optimal for comprehensive multi-proxy comparisons, thereby aiding our understanding of the behavior and impacts of the past ITCZ. The mainstream view is that the changes in the intensity of the Atlantic Meridional Overturning Circulation (AMOC) affect the energy balance and temperature gradient between Hemispheres, leading to the ITCZ moving towards the warmer Hemisphere, thereby altering the climate between the Hemispheres. However, research on the changes in the past ITCZ has mostly focused on the Northern Hemisphere, which likely arises from the large continental exposure and the resultant abundance of summer monsoon rainfall records in the Northern Hemisphere. In contrast, the relatively smaller land exposure in the Southern Hemisphere leads to poorly preserved summer monsoon rainfall records, especially in northwestern Australia at the southernmost edge of the ITCZ. This directly restricts our in-depth understanding of the spatiotemporal variability of the ITCZ in the geological past, especially the climate response mechanisms between the Hemispheres. Thus, there is an urgent need for new high-resolution records in the Southern Hemisphere to constrain the positional changes of the ITCZ and its related monsoon rainfall. In this study, we use the high-resolution sediment core SO257-18567 retrieved by R/V Sonne Cruise 257 offshore northwestern Australia as research material. Through analysis of clay minerals, grain size, elemental and Sr-Nd isotopic geochemistry, we reconstruct the high-resolution summer monsoon rainfall history at the southern edge of the ITCZ since the Last Glacial. We then compared with monsoonal rainfall records in the Northern Hemisphere and integrated other high- and low-latitude paleoclimate reconstructions including the TraCE-21ka model results, eustatic sea-level changes and proxies for the strengths of AMOC and Indonesian Throughflow, thereby exploring the spatiotemporal variability and driving mechanisms of the ITCZ on millennial time scales.