The Impacts of an AMOC Slowdown on Southern Hemisphere and Australian Climates at 8.2 ka in ACCESS-ESM1.5 Model

Abstract

Greenland ice cores reveal an abrupt cooling of up to 3.3°C 8.2 kyr ago (8.2 ka), lasting for roughly 160 years. The event was likely caused by a weakening of the Atlantic Meridional Overturning Circulation (AMOC) due to freshwater drainage into the North Atlantic. It was associated with a global-scale climate change but is recorded in very few high-resolution paleoclimatic time series from the Southern Hemisphere (SH). In this study, we investigate the 8.2 ka event in the SH, particularly the Australian climate response to a weakened AMOC. Five North Atlantic meltwater experiments are conducted with the Australian Earth System Model, ACCESS-ESM1.5, to evaluate the sensitivity of AMOC responses to freshwater perturbations under early Holocene conditions as well as their climate impact. Our results suggest a 100 year freshwater pulse reproduces a global climate change that best matches existing proxy records for the 8.2 ka event. Australian surface air temperatures show significant cooler conditions in the northern half of the continent but warmer anomalies in the south in response to a weakened AMOC. Australian hydroclimate displays a more complex response at 8.2 ka. Northern Australian precipitation is influenced by a southward shift in the mean position of the Intertropical Convergence Zone and a strengthened Indo-Australian summer monsoon, while the southern part of the continent is more sensitive to weakening of the winter westerly winds. These results highlight the importance of understanding the Australian climate response to a weakened AMOC under different background climate in order to better predict potential future impacts.