Tracking eolian dust with helium and thorium: Impacts of grain size and provenance

MCGEE, D; SERNO, S.; BORUNDA, A.; BORY, A.; RECASENS, C.; MR KAPLAN; JACCARD, S.; SUN, Y; REVEL, M.; G WINCKLER,; ANDERSON, R.; GAIERO, D.; MC MANUS, J

GEOCHIMICA ET COSMOCHIMICA ACTA

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2016 vol. 175 p. 47 - 67

0016-7037

Reconstructions of the deposition rate of windblown mineral dust in ocean sedimentsoffer an important means of tracking past climate changes and of assessing the radiative andbiogeochemical impacts of dust in past climates. Dust flux estimates in ocean sediments havecommonly been based on the operationally defined lithogenic fraction of sediment samples.More recently, dust fluxes have been estimated from measurements of helium and thorium, asrare isotopes of these elements (He-3 and Th-230) allow estimates of sediment flux, and thedominant isotopes (He-4 and Th-232) are uniquely associated with the lithogenic fraction ofmarine sediments. In order to improve the fidelity of dust flux reconstructions based on He andTh, we present a survey of He and Th concentrations in sediments from dust source areas in EastAsia, Australia and South America. Our data show systematic relationships between He and Thconcentrations and grain size, with He concentrations decreasing and Th concentrationsincreasing with decreasing grain size. We find consistent He and Th concentrations in the finefraction (38˚S). In the equatorial Pacific, He/Th ratios are much lower than in extratropicalPacific sediments or potential source areas measured as a part of this study (East Asia, SouthAmerica, Australia) for reasons that are at present unclear, complicating their use as provenancetracers in this region.