A23C-0309
K/Ar geochronology as a tool for tracing dust provenance in the Southern Hemisphere

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Judy Pu1, Bess G Koffman2, Cristina Recasens3, Sidney R Hemming4, Michael R Kaplan5, Joel H Gombiner6, Steven Boswell4 and Trevor Williams7, (1)Massachusetts Institute of Technology, Earth, Atmospheric, and Planetary Sciences, Cambridge, MA, United States, (2)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (3)Columbia University, Palisades, NY, United States, (4)Columbia University of New York, Palisades, NY, United States, (5)Lamont-DohertyEarthObservatory, Palisades, NY, United States, (6)Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (7)Lamont Doherty Earth Obs, Palisades, NY, United States
Abstract:
Determining the sources and transport pathways of dust can provide a better understanding of past atmospheric circulation and give insight into nutrient and radiative effects on the climate system. Mineralogy and radiogenic isotope chemistry using strontium (Sr) and neodymium (Nd) have been able to constrain sources of dust but are not sufficient to distinguish among important potential source areas in the Southern Hemisphere. The K/Ar isotope system can improve our ability to infer dust provenance because it can discriminate between sources that have similar crustal residence ages but different subsequent tectonothermal histories. To assess K/Ar ages as a provenance tool, we measured radiogenic argon concentrations of samples from potential dust sources such as glaciogenic sediments in Patagonia and New Zealand. Provenance ages from Patagonian sediments cluster around 70 Ma with a range from 33.2 ± 0.4 Ma to 120 ± 3 Ma, and those from New Zealand sediments cluster around 160 Ma with a range from 125 ± 1 Ma to 191 ± 2 Ma, showing that K/Ar geochronology can discriminate between these two source areas and improve upon previous provenance studies.

In addition, as a proof of concept we made a case study of a sedimentary time series from core TN057-6 on the Agulhas Ridge in the southeast Atlantic Ocean as well as a set of Holocene and glacial samples from four cores along the SE African margin. We found that K/Ar provenance ages of the <5μm terrigenous material from TN057-6 are best explained as the result of mixing of sediments transported from Patagonia and Africa-derived sediments delivered by the Agulhas Current. The K/Ar method was also able to show different sediment provenance between glacial and interglacial times, with a dominant Patagonian signature during glacial intervals. Ongoing work aims to characterize additional Southern Hemisphere dust sources, including the ice-free regions of Antarctica, and apply the K/Ar provenance tool to dust in Antarctic ice cores.

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