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Theses Doctoral

Tracing dust in the Southern Hemisphere over the last glacial cycle

Borunda, Alejandra

Mineral dust both influences and is influenced by climate on many timescales, from seconds to epochs. Its complex interactions with the climate system are still being unraveled. For example, dust fluxes change in tandem with other records of past changes in climate, and dust source is often presumed to change as well, in response to shifts in climate conditions in source regions; changes in wind regimes; or changes in atmospheric transport pathways. In this work, I investigate dust records from the Southern Hemisphere from ice core and marine sediment core climate archives, looking at both flux and provenance in order elucidate the conditions that allowed for those particles to travel from source to sink. Using multiple radiogenic isotope systems as tracers (87Sr/86Sr, εNd(0), 206Pb/207Pb, and 208Pb/207Pb), I geochemically “fingerprint” of dust particles from Southern Hemisphere climate archives over the last glacial cycle. I compare the dust fingerprints to potential source areas (PSA’s) from across the Southern Hemisphere in order to identify the sources of dust found in the WAIS Divide and Taylor Glacier ice cores from West Antarctica, as well as from marine sediment core ELT39.75 in the Tasman Sea. I use endmember mixing theory to determine the relative contribution of different sources to the climate archives over time. In West Antarctica, I geochemically identify specific local volcanoes from Marie Byrd Land as significant particle contributors to the WAIS Divide ice core during the previous glacial period. In the Tasman Sea, I identify a specific region of southeastern Australia as primary the dust source over the past glacial cycle, with the source remaining constant across glacial-interglacial climate transitions. This clarifies that the “fingerprint” of Australian dust is relatively invariant over time and allows a single Australian signature to be used as an endmember for identifying dust provenance in climate archives downwind. I also identify the dust sources in the WAIS Divide during the Last Glacial Maximum and through the early deglacial, identifying southern South America as the predominant source during cold stages. WAIS Divide and Taylor Glacier dust records do not record dust source changes across millennial-scale climate events, suggesting that a) the source regions did not change, b) the transport pathways remained pinned, or c) the proxy is not sensitive to changes in these variables. Contributions from local volcanoes are also inferred from the WAIS dust record using mixing theory. In summary, I find that the radiogenic isotope fingerprint of dust samples from the archives analyzed show subtle or no changes in source over climate transitions, and therefore the strategy of dust particles as a tracer of past atmospheric circulation pathways should be approached cautiously.

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More About This Work

Academic Units
Earth and Environmental Sciences
Thesis Advisors
Winckler, Gisela
Degree
Ph.D., Columbia University
Published Here
September 27, 2019
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