Grain size effects on Th-230(xs) inventories in opal-rich and carbonate-rich marine sediments

S Kretschmer, W Geibert, M R van der Loeff, G Mollenhauer

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Excess Thorium-230 (Th-230(xs)) as a constant flux tracer is an essential tool for paleoceanographic studies, but its limitations for flux normalization are still a matter of debate. In regions of rapid sediment accumulation, it has been an open question if (230)T(hx)x-normalized fluxes are biased by particle sorting effects during sediment redistribution. In order to study the sorting effect of sediment transport on 'Thxs, we analyzed the specific activity of (230)Thxs in different particle size classes of carbonate-rich sediments from the South East Atlantic, and of opal-rich sediments from the Atlantic sector of the Southern Ocean. At both sites, we compare the Th-230(xs) distribution in neighboring high vs. low accumulation settings. Two grain-size fractionation methods are explored. We find that the (230)Thx, distribution is strongly grain size dependent, and 50-90% of the total (230)Thx, inventory is concentrated in fine material smaller than 10 pm, which is preferentially deposited at the high accumulation sites. This leads to an overestimation of the focusing factor psi, and consequently to an underestimation of the vertical flux rate at such sites. The distribution of authigenic uranium indicates that fine organic-rich material has also been re-deposited from lateral sources. If the particle sorting effect is considered in the flux calculations, it reduces the estimated extent of sediment focusing. In order to assess the maximum effect of particle sorting on qr, we present an extreme scenario, in which we assume a lateral sediment supply of only fine material (
Original languageEnglish
Pages (from-to)131-142
Number of pages12
JournalEARTH PLANET SC LETT
Volume294
Issue number1-2
DOIs
Publication statusPublished - 2010

Keywords

  • Geochemistry & Geophysics
  • ORGANIC-CARBON
  • ATLANTIC SECTOR
  • SEA-FLOOR
  • INTERGLACIAL CHANGES
  • DEEP-SEA
  • TRANSPORT
  • PARTICLE COMPOSITION
  • BASIN
  • THORIUM ISOTOPES
  • SOUTHERN-OCEAN

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