Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments
Excess Thorium-230 (230Thxs) 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 230Thxs-normalized fluxes are biased by parti...
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ftawi:oai:epic.awi.de:22240 2023-05-15T18:25:57+02:00 Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments Kretschmer, Sven Geibert, W. Rutgers v. d. Loeff, Michiel Mollenhauer, Gesine 2010 https://epic.awi.de/id/eprint/22240/ https://doi.org/10.1016/j.epsl.2010.03.021 https://hdl.handle.net/10013/epic.35388 unknown Kretschmer, S. , Geibert, W. orcid:0000-0001-8646-2334 , Rutgers v. d. Loeff, M. orcid:0000-0003-1393-3742 and Mollenhauer, G. orcid:0000-0001-5138-564X (2010) Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments , Earth and Planetary Science Letters. . doi:10.1016/j.epsl.2010.03.021 <https://doi.org/10.1016/j.epsl.2010.03.021> , hdl:10013/epic.35388 EPIC3Earth and Planetary Science Letters. Article isiRev 2010 ftawi https://doi.org/10.1016/j.epsl.2010.03.021 2021-12-24T15:34:10Z Excess Thorium-230 (230Thxs) 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 230Thxs-normalized fluxes are biased by particle sorting effects during sediment redistribution. In order to study the sorting effect of sediment transport on 230Thxs, we analyzed the specific activity of 230Thxs 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 230Thxs distribution in neighboring high vs. low accumulation settings. Two grain-size fractionation methods are explored. We find that the 230Thxs distribution is strongly grain size dependent, and 5090% of the total 230Thxs inventory is concentrated in fine material smaller than 10 μm, which is preferentially deposited at the highaccumulation sites. This leads to an overestimation of the focusing factor Ψ, 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 isconsidered in the flux calculations, it reduces the estimated extent of sediment focusing. In order to assess the maximum effect of particle sorting on Ψ, we present an extreme scenario, in which we assume a lateralsediment supply of only fine material (b10 μm). In this case, the focusing factor of the opal-rich core would be reduced from Ψ=5.9 to Ψ=3.2. In a more likely scenario, allowing silt-sized material to be transported, Ψ is reduced from 5.9 to 5.0 if particle sorting is taken into consideration. The bias introduced by particle sorting is most important for strongly focused sediments. Comparing 230Thxs-normalized mass fluxes biased by sorting effects with uncorrected mass fluxes, we suggest that 230Thxs-normalization is still a valid tool to correct for lateral sediment redistribution. However,differences in focusing factors between core locations have to be evaluated carefully, taking the grain size distributions into consideration. Article in Journal/Newspaper Southern Ocean Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) Southern Ocean Earth and Planetary Science Letters 294 1-2 131 142 |
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Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) |
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ftawi |
language |
unknown |
description |
Excess Thorium-230 (230Thxs) 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 230Thxs-normalized fluxes are biased by particle sorting effects during sediment redistribution. In order to study the sorting effect of sediment transport on 230Thxs, we analyzed the specific activity of 230Thxs 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 230Thxs distribution in neighboring high vs. low accumulation settings. Two grain-size fractionation methods are explored. We find that the 230Thxs distribution is strongly grain size dependent, and 5090% of the total 230Thxs inventory is concentrated in fine material smaller than 10 μm, which is preferentially deposited at the highaccumulation sites. This leads to an overestimation of the focusing factor Ψ, 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 isconsidered in the flux calculations, it reduces the estimated extent of sediment focusing. In order to assess the maximum effect of particle sorting on Ψ, we present an extreme scenario, in which we assume a lateralsediment supply of only fine material (b10 μm). In this case, the focusing factor of the opal-rich core would be reduced from Ψ=5.9 to Ψ=3.2. In a more likely scenario, allowing silt-sized material to be transported, Ψ is reduced from 5.9 to 5.0 if particle sorting is taken into consideration. The bias introduced by particle sorting is most important for strongly focused sediments. Comparing 230Thxs-normalized mass fluxes biased by sorting effects with uncorrected mass fluxes, we suggest that 230Thxs-normalization is still a valid tool to correct for lateral sediment redistribution. However,differences in focusing factors between core locations have to be evaluated carefully, taking the grain size distributions into consideration. |
format |
Article in Journal/Newspaper |
author |
Kretschmer, Sven Geibert, W. Rutgers v. d. Loeff, Michiel Mollenhauer, Gesine |
spellingShingle |
Kretschmer, Sven Geibert, W. Rutgers v. d. Loeff, Michiel Mollenhauer, Gesine Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
author_facet |
Kretschmer, Sven Geibert, W. Rutgers v. d. Loeff, Michiel Mollenhauer, Gesine |
author_sort |
Kretschmer, Sven |
title |
Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
title_short |
Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
title_full |
Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
title_fullStr |
Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
title_full_unstemmed |
Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments |
title_sort |
grain size effects on 230thxs inventories in opal-rich and carbonate-rich marine sediments |
publishDate |
2010 |
url |
https://epic.awi.de/id/eprint/22240/ https://doi.org/10.1016/j.epsl.2010.03.021 https://hdl.handle.net/10013/epic.35388 |
geographic |
Southern Ocean |
geographic_facet |
Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
EPIC3Earth and Planetary Science Letters. |
op_relation |
Kretschmer, S. , Geibert, W. orcid:0000-0001-8646-2334 , Rutgers v. d. Loeff, M. orcid:0000-0003-1393-3742 and Mollenhauer, G. orcid:0000-0001-5138-564X (2010) Grain size effects on 230Thxs inventories in opal-rich and carbonate-rich marine sediments , Earth and Planetary Science Letters. . doi:10.1016/j.epsl.2010.03.021 <https://doi.org/10.1016/j.epsl.2010.03.021> , hdl:10013/epic.35388 |
op_doi |
https://doi.org/10.1016/j.epsl.2010.03.021 |
container_title |
Earth and Planetary Science Letters |
container_volume |
294 |
container_issue |
1-2 |
container_start_page |
131 |
op_container_end_page |
142 |
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1766207705193644032 |