Orbital to millennial-scale variability of the Southern Hemisphere Westerlies over the last glacial cycle

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The Southern Hemisphere westerly winds are a crucial component of the global climate system, playing an important role in controlling the weather of the Southern Hemisphere mid-latitudes through the seasonal transmission of precipitation-generating storm systems, as well as through their influence on the circulation of the Southern Ocean. It has been hypothesized that past changes in the position and strength of the westerlies may have also impacted the global carbon cycle through their influence on storage of carbon dioxide in the deep ocean, with impacts on global climate. Models also suggest that future warming will also result in changes in the westerlies, with the potential to drive changes in the storage or release of carbon dioxide from the Southern Ocean. However, the westerlies respond to a number of factors including regional, hemispheric and global patterns of warming, ocean circulation and Southern Ocean sea ice cover. In order to better understand how these factors influence the westerlies and their potential role in changing in the carbon cycle, this research project will generate a new reconstruction of the westerly wind response to a range of natural climate factors over the past ~140,000 years. In combination with the results of climate model simulations, the results of this study will provide a better understanding of how and why the westerlies change, and will thus provide a perspective from the geological past on how the westerlies will respond to future changes in global climate. The impacts of this research on society will be presented to the public through venues such the University of Texas Geoforce program, local community organizations, ongoing activities and outreach at local K-12 schools, through programs such as Girls Start and the Boy Scouts. This research will focus on the generation of a new high-resolution record of past westerly wind behavior using the laminated sediment record from Lake Orakei, a volcanic crater lake located on the North Island of New Zealand. Reconstructions will use the hydrogen isotope composition of sedimentary leaf waxes as a proxy for the position of the westerlies, an approach that is grounded in a study of modern isotope dynamics in this region. The reconstructions will be complemented by temperature reconstructions based on the MBT’5ME paleotemperature proxy and will focus on understanding the timing and nature of the westerly response to orbital forcing, the growth and retreat of the ice sheets and, over targeted intervals, the response to millennial-scale variability during Dansgaard-Oeschger and Heinrich stadials. A robust proxy-model comparison approach will be used to better understand the underlying climate dynamics driving the westerly wind response to these forcing mechanisms. This award is cofunded by the Division of Earth Sciences and the Division of Atmospheric and Geospace Sciences by way of the Paleo Perspectives on Climate Change Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.