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Pb-210-Ra-226-Th-230 systematics in very low sedimentation rate sediments from the Mendeleev Ridge (Arctic Ocean)
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2008 (English)In: Canadian journal of earth sciences (Print), ISSN 0008-4077, E-ISSN 1480-3313, Vol. 45, no 11, 1207-1219 p.Article in journal (Refereed) Published
Abstract [en]

U-series isotope behaviour in subsurface sediment of the Arctic Ocean is investigated based on high resolution measurements of natural radionuclides (Ph-210, Ra-226, Th-230) and a few analyses of anthropogenic Cs-137 in cores collected during the 2005 Healy-Oden Trans-Arctic Expedition (HOTRAX). Cores from the Mendeleev Ridge, representing distinct bathymetric settings, are analyzed in more detail as a means to assess the dating potential of such radionuclides at sites characterized by very low sedimentation rates (similar to 3 mm ka(-1)). The sediment consists of variable proportions of fine-grained carbonates, clays, and ice-rafted debris and shows excesses in (210)pb (Pb-210(xs)) over parent Ra-226 content, down to similar to 1 cm below core top. This Pb-210(xs) distribution is due to shallow mixing by benthic organisms and (or) diffusion from the sediment-water interface, as also indicated by Cs-137 activities. From similar to 1 to 7 cm downcore, Pb-210 activities closely follow Ra-226 activities. Below 7 cm downcore, Ra-226 activities are controlled by variable excesses in parent Th-230 ((230)Thx) resulting from its scavenging in the overlying water column. Ra-226 diffusion is observed towards the water column occuring from the upper similar to 7 cm of sediment below the seafloor (with a flux of similar to 0.043 disintegrations per minute (dpm) cm(-2) a(-1)) and deeper in the sediment below Th-230(xs) peaks but with lesser fluxes. Both cores show identical Pb-210 profiles despite their I kin bathymetric difference. This suggests negligible Th-230 and Pb-210 scavenging below water depths of similar to 1.6 km, i.e., the bathymetry of the shallower core. In such settings where sedimentation rates are very low and vertical particle rain is the major sediment source, estimates of the actual Pb-210(xs) require precise knowledge of the Ra-226-supported fraction, which is controlled by Th-230(xs), Ra diffusion, and thus sedimentation rates and porosity.

Place, publisher, year, edition, pages
2008. Vol. 45, no 11, 1207-1219 p.
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Natural Sciences
Research subject
SWEDARCTIC 2005, Beringia 2005
Identifiers
URN: urn:nbn:se:polar:diva-3123DOI: 10.1139/E08-047OAI: oai:DiVA.org:polar-3123DiVA: diva2:1050090
Available from: 2016-11-28 Created: 2016-11-21 Last updated: 2016-11-28

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  • apa
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  • modern-language-association-8th-edition
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