OCE-PRF Unraveling Southern Hemisphere westerly wind variability through the last ~150 ky using Tasman Sea sediments

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

The Southern Hemisphere westerly winds, commonly referred to as the “westerlies”, play a crucial role in regional and global climate. Modern observations suggest that these winds are moving towards Antarctica and becoming stronger in response to anthropogenic warming. Shifts in the position and intensity of these winds can potentially impact ocean circulation, the distribution of natural and anthropogenic aerosols, and the carbon cycle.

As such, developing a better understanding of how the westerly winds change when conditions on Earth were different from today is critical to enhancing our constraints on their future variability. The research proposed here seeks to reconstruct the characteristics of the Southern Hemisphere westerlies during climate states both colder and warmer than today over the last 150,000-years.

To accomplish this, PI Abell will develop records of dust fluxes, sea-surface temperatures, and Australian vegetation regimes utilizing marine sediments from several cores in the Tasman Sea. It is the combination of these independent proxies related to the westerly winds, along with sampling multiple cores that cover an ~10° north-south transect, that will allow for information on both the position and strength of the Southern Hemisphere westerlies to be ascertained.

As an NSF Postdoctoral Fellow, PI Abell will mentor high school and undergraduate students through several programs. One of these is the Southern Arizona Research, Science, and Engineering Foundation S.T.A.R Labs Program, where he will guide a local high school student through developing and executing a research project related to this proposed research.

Additionally, PI Abell will work with a University of Arizona undergraduate student to prepare them for graduate school through the Ronald E. McNair Achievement Program.

The proposed project will focus on reconstructing the characteristics of the Southern Hemisphere westerly winds during various climate states over the last ~150 ky. PI Abell will utilize samples from three marine sediment cores spanning ~10° latitude in the Tasman Sea, along with four independent (organic and inorganic) geochemical methods, to investigate shifts in the position and intensity of the westerlies.

Specifically, PI Abell will 1) produce constant flux proxy-derived dust flux records based on inorganic dust proxies, 2) use n-alkanes as a dust proxy to develop additional records of dust fluxes that are not influenced by volcanic inputs, 3) generate records of plant-wax carbon isotopes to gain information on C3/C4 vegetation boundaries, and in turn precipitation seasonality, in Australia, and 4) reconstruct shifts in the Subtropical and Tasman Fronts by utilizing the alkenone UK’37 SST proxy. Combined, information from these various proxies will allow for the reconstruction of both the position and intensity of the Southern Hemisphere westerlies during key climatic intervals such as the Holocene, the Last Glacial Maximum, and the last interglacial period.

These datasets will be useful to the climate modeling community, as they will provide constraints on the natural variability of the westerlies to changes in potential driving mechanisms such as ice volume and atmospheric temperature gradients, thus aiding essential modeling of future changes in the westerly winds. Interpretations and conclusions drawn from this work will be brought to the public via non-technical settings such as public talks and presentations/activities at The Science Center at the Tucson Festival of Books.

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.