Glacial to Holocene climate variability in the southern mid latitudes

The Southern Hemisphere westerly winds play an important role in global climate, by influencing the weather in the mid latitudes, transmitting climate changes between high and low latitudes, and have been proposed to influence the carbon storage in the Southern Ocean. Changes in the position and intensity of the westerlies are anticipated to have a large impact in the future and have also been proposed to play significant role in past climate changes. Paleoclimate proxy records of past variation in the westerlies, however, are controversial, and models suggest that they may depend on a complex interplay between high and low latitude drivers as well as factors such as the mean state of the climate system. This dissertation seeks to improve our understanding of the Southern Hemisphere westerly wind and climate variations. To do so, I generate a 45,000-year record of Southern Hemisphere westerly wind and temperature variability on the North Island of New Zealand using compound-specific hydrogen isotope in sedimentary leaf waxes and branched GDGT-derived temperature using lake records. To improve our interpretations of the hydrogen isotope data in proxy records, I first examine climatic controls on the modern isotopic composition of rainfall on the North Island of New Zealand. This work indicates that isotopic ratios of precipitation mainly reflect regional-scale changes in the atmospheric circulation, with higher δ¹⁸Oₚ values reflecting an increased influence of the tropical anticyclonic circulation and lower δ¹⁸Oₚ ratios reflecting a greater contribution from the Southern Hemisphere westerly winds. Based on our improved understanding of isotopic controls, our multi-proxy record shows that Northern Hemisphere climate exerts a dominant control over the westerlies, irrespective of the changes in the southern Hemisphere mid to high latitude climate conditions. Finally, I examine the distribution of isoprenoid GDGT lipids and elemental ratios from the same lake to provide a complimentary set of proxies of lake stratification and mixing.Geological Science