Southern Hemisphere Westerly Winds and Holocene climate variability on sub-Antarctic South Georgia

Abstract

<p>The Southern Hemisphere Westerly Winds play a major role in the global climate system. By driving circulation in the Southern Ocean and its subsequent effect on the upwelling of carbon-rich deep water, the Westerlies affect the oceans ability to take up atmospheric CO<sub>2</sub>. Furthermore, by impacting temperature conditions and moisture availability, the Westerlies act as a first-order control on local environmental conditions. Uncovering long term natural climatic variability in the sub-Antarctic is therefore crucial to understand how the global system might react under future climate changes. Due to the lack of land mass on the Southern Hemisphere, sub-Antarctic islands are essential for studying climate variability in this region; terrestrial records provide valuable insights into both local and regional surface climate conditions. We use a pollen record from Lake Diamond to provide detailed reconstructions of vegetation and climate on sub-Antarctic South Georgia for the last ~9900 years. Westerly Wind strength and position is inferred from long-distance transport of pollen from South America, Africa, and New Zealand. Additionally, changes in relative pollen abundance of native taxa occupying either upland (cold) or lowland (warm) environments are used to infer local climatic variation, supported by additional sedimentological proxies. On South Georgia we find long-distance transported pollen from several South American taxa, mainly Nothofagus, Ephedra and Asteraceae. They show a general increase in abundance throughout the Holocene, with peak influx between 2800 and 1500 cal yr BP, most likely caused by changes in the strength of the Southern Hemisphere Westerly Winds. In both our record and others, this interval is seen as the end of the Neoglacial period.</p>