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Investigating the use of 232Th/230Th as a dust proxy using co-located seawater and sediment samples from the low-latitude North Atlantic

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)143-156
Number of pages14
JournalGeochimica et Cosmochimica Acta
Volume214
Early online date27 Jul 2017
DOIs
DateAccepted/In press - 19 Jul 2017
DateE-pub ahead of print - 27 Jul 2017
DatePublished (current) - 1 Oct 2017

Abstract

The thorium isotope ratio 232Th/230Th can be measured in seawater and sediment samples, and has been used as a proxy to reconstruct lithogenic fluxes to the oceans for the modern day and the Pleistocene. There has not yet been a systematic study testing the proxy using the 232Th/230Th ratio in seawater and the ratio recorded in the underlying sediment. In this study we use co-located core-top sediments and seawater samples from five seamount sites spanning the tropical North Atlantic to investigate the link between seawater and sediment 232Th/230Th ratios across a range of water depths. Our results indicate that a broad correlation exists between seawater and sedimentary 232Th/230Th ratios. Both seawater and sedimentary 232Th/230Th ratios record a signal consistent with decreasing lithogenic input east to west, from Africa to South America. However, calculated 232Th fluxes for the core-top sediment samples indicate a strong dependence on depth, with up to a factor of ∼4 difference from shallow (<600 m) to deep sites (>2900 m). This depth dependence is likely caused by either a deficit of 230Th burial at depth compared to the production in the overlying water column, through addition of 232Th, or by a combination of the two. By comparing seawater and sedimentary 232Th/230Th ratios we derive an apparent fractional solubility of 232Th of 29 ± 3%, in reasonable agreement with the upper end of existing estimates.

    Research areas

  • Thorium, Dust, Sediment, Seawater, Isotope

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  • Full-text PDF (accepted author manuscript)

    Rights statement: This is the accepted author manuscript (AAM). The final published version (version of record) is available online via Elsevier at DOI: 10.1016/j.gca.2017.07.033. Please refer to any applicable terms of use of the publisher.

    Accepted author manuscript, 5.6 MB, PDF document

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