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ESS Ph.D. Dissertation Defense - Sverre LeRoy
This talk comprises the public portion of the PhD dissertation defense from approximately 9:00-10:00 AM.
Department: Earth System Science
Graduate Student: Sverre LeRoy
Advisor: Rob Dunbar
Title: Holocene Climate Change From Fjord and Lake Sediment Core and Seismic Records in Southern Patagonia
Abstract: The Southern Hemisphere westerly wind field modulates Earth’s climate by regulating Southern Ocean CO2 ventilation through wind-induced upwelling of Circumpolar Deep Water. However, past changes in the southern westerlies and the extent to which the westerlies influence global atmospheric CO2 concentrations remain relatively unknown. Southern Patagonia, the only major landmass extending into the core of the wind field, is an ideal location for reconstructing past changes in the westerlies. In Chapters 1 and 2, we present the results of sediment cores collected from Lago Sarmiento (51˚S), a large, closed-basin lake, and from Golfo Almirante Montt (GAM; 52˚S), an isolation basin in the Chilean inner-fjord system. We investigate changes in precipitation, relative westerly wind intensity, and Neoglacial events over the last 11 ka using core sedimentology, stable isotope (δ18O, δ13C and δ15N), weight percent carbonate, and elemental concentration (C & N) data. In Chapter 3, we present results of a high resolution seismic survey in GAM. Sediment core data from Lago Sarmiento and GAM identify: (1) low precipitation and weak westerlies during the early Holocene (11 – 9.6 ka), (2) maximum Holocene precipitation and westerly wind strength in the Mid-Holocene (5.4 – 4.1 ka), (3) low precipitation and weakening westerlies between 3.4 – 1.5 ka, (4) and two significant regional Neoglacial events between 9.6 – 9.0 ka and 4.1 – 3.4 ka; we interpret Neoglacial events as a strong pulse of precipitation and strengthening of the westerlies over our field site. Our seismic survey in GAM reveals a sedimentary basin that exceeds a thickness of 100 m. We identify three seismic-stratigraphic facies, which we interpret as: (1) rapidly deposited glacio-lacustrine sediments, (2) outwash as a result of catastrophic ice-dam failure at the termination of the Last Glacial Maximum, and (3) Holocene ice-distal glacio-marine sediment. These data provide important insights into Southern Hemisphere Late Quaternary climatic variability.