Radiocarbon and Th-230 data reveal rapid redistribution and temporal changes in sediment focussing at a North Atlantic drift

TitleRadiocarbon and Th-230 data reveal rapid redistribution and temporal changes in sediment focussing at a North Atlantic drift
Publication TypeJournal Article
Year of Publication2011
AuthorsMollenhauer, G, McManus, JF, Wagner, T, I. McCave, N, Eglinton, TI
Date PublishedJAN 3
Type of ArticleArticle
Keywordsalkenones, compound-specific radiocarbon dating, drift sediments, focussing factors, Th-230(xs)

In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (Th-230(xs)) measurements on four sediment cores retrieved in 1649-2879 m water depth from two such high accumulation drift deposits in the Northeast Atlantic, Bjorn and Gardar Drifts. While Th-230(xs), inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results show that although focussing factors calculated from bulk sediment Th-230(xs) inventories may allow useful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing. (C) 2010 Elsevier B.V. All rights reserved.