Abrupt climate change events during the last glacial period and the Last Interglacial resulted from changes in the Atlantic Meridional Overturning Circulation (AMOC). Over the last 50 years, the AMOC has weakened and is projected to weaken further or even collapse this century due to freshwater influx from melting glaciers driven by climate warming. Despite numerous modelling studies investigating the impacts of an AMOC shutdown, little is known about its impact on Australasian hydroclimate, particularly under a climate warmer than the pre-industrial (PI). Using the ACCESS-ESM1.5 model, we assess the processes impacting seasonal hydroclimate in the Australasian region in response to an AMOC shutdown under PI and Last Interglacial (LIG) climatic conditions. While the broad hydroclimate response to an AMOC shutdown is similar in both experiments, notable regional differences emerge, highlighting the influence of background climate states. During austral summer (DJF), the AMOC shutdown leads to drier conditions over the Maritime Continent and increased precipitation over northern Australia under both PI and LIG conditions. However, the precipitation increase over Australia is weaker under PI than LIG. During austral winter (JJA), mid to high southern latitude regions of Australia and New Zealand experience drying in response to the AMOC shutdown under PI boundary conditions, while under LIG boundary conditions, only southeastern Australia and New Zealand exhibit drier conditions, with northwestern Australia displaying wetter conditions. These results underscore the complex and region-specific responses of Australasian hydroclimate to AMOC disruptions, highlighting the importance of considering background climate states when assessing such impacts.

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.

Long, continuous palaeoclimate records provide an opportunity to extend knowledge of decadal to multi-decadal scale climate variability beyond the limit of instrumental records. In this study, quality-controlled proxy records from southeastern Australia are examined for coherent variability during the Common Era, with age uncertainty for each record estimated using iterative age modeling. Site-level empirical orthogonal functions (EOFs) are derived from multivariate records for the purpose of objective comparison of climate signals between sites without selection bias. A regional Monte Carlo EOF (MCEOF) analysis is conducted on combined time-uncertain single-proxy records and site-level EOFs. The analysis identifies two robust vectors, which are inferred to represent hydroclimate changes. The first regional MCEOF suggests an increase in effective moisture between 900 – 1750 CE. Agreement between regional MCEOF1 and Australian temperature reconstructions suggests suppressed evaporation was a significant influence on regional effective moisture during this time. Regional MCEOF2 exhibits shorter, centennial-scale oscillations that show some similarity with rainfall reconstructions based on remote high-resolution proxies. We interpret MCEOF2 to represent regional-scale rainfall patterns driven by changes in seasonal rainfall and the influence of the Southern Annular Mode over southern Australian rainfall. This study presents the first quantitative regional synthesis of southeastern Australian hydroclimate reconstructions from multivariate sedimentary archives covering the last 1200 years. The resulting MCEOFs demonstrate the utility of low-resolution climate records from this region, but also highlight the limitations of the existing data network, which must be resolved through the generation of new records.