Unravelling the Holocene history of the Southern Westerlies: driver of global climate and the carbon cycle

Earth’s climate is undergoing significant changes due to global warming. Geographically well-dispersed climate reconstructions from natural archives are crucial for understanding climate change beyond the period of instrumental and historical data. So far, most of these reconstructions were focussed on the Northern Hemisphere but recently it has been recognised that the Southern Hemisphere (SH) plays a crucial, yet understudied, role in global climate. SH mid- to high latitude climate is dominated by the rain-bearing Southern Hemisphere Westerly winds (SHW). Changes in the intensity and position of the SHW and their impact on the oceanic Antarctic Circumpolar Current, affect both upwelling and uptake of CO2 in the Southern Ocean (SO), the main area on the planet where the deep ocean is connected to the atmosphere and where about 40% of the global oceanic uptake of anthropogenic CO2 takes place. Furthermore, a poleward shift of the SHW during a number of successive austral winters recently caused severe drinking water shortages in Cape Town (South Africa), highlighting the societal impact of such changes. Understanding natural SHW variability is essential for further testing climate models, as these are not yet able to accurately simulate the position and strength of the modern SHW, hampering comprehensive future projections of SO behaviour. Yet, knowledge on past SHW behaviour is still fragmentary. A prerequisite for reconstructing changes in the SHW (35° to 60°S), is the availability of well-dated terrestrial records that reflect atmospheric conditions and are situated on a latitudinal transect covering the SHW. Here we propose a novel approach to study the pre-anthropogenic (Holocene) history of the SHW, by reconstructing a latitudinal transect of peat bogs on a series of sub-Antarctic islands in the Indian sector of the SO. By targeting islands we avoid the bias that is implicit in South American SHW (precipitation) records, caused by the SHW obstruction by the Andes mountain range and/or unclear relations between precipitation and SHW strength. We will assess past SHW dynamics through wind intensity, humidity/precipitation and temperature reconstructions, based on a novel combination of well-established and recently developed proxies. Predicting potential future latitudinal SHW shifts is crucial for forecasting prolonged drought periods, impacting densely populated regions.