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Constraints on the sources of branched tetraether membrane lipids in distal marine sediments
Weijers, J.W.H.; Schefuß, E.; Kim, J.-H.; Sinninghe Damsté, J.; Schouten, S. (2014). Constraints on the sources of branched tetraether membrane lipids in distal marine sediments. Org. Geochem. 72: 14-22. dx.doi.org/10.1016/j.orggeochem.2014.04.011
In: Organic Geochemistry. Elsevier: Oxford; New York. ISSN 0146-6380, more
Peer reviewed article  

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Author keywords
    Branched tetraether; Dust; Marine surface sediment

Authors  Top 
  • Weijers, J.W.H.
  • Schefuß, E.
  • Kim, J.-H., more
  • Sinninghe Damsté, J., more
  • Schouten, S., more

Abstract
    Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input. Their abundance relative to marine-derived crenarchaeol, quantified in the BIT index, generally decreases offshore. However, in distal marine sediments, low relative amounts of brGDGTs can often still be observed. Sedimentary in situ production as well as dust input have been suggested as potential, though as yet not well constrained, sources. In this study brGDGT distributions in dust were examined and compared with those in distal marine sediments. Dust was sampled along the equatorial West African coast and brGDGTs were detected in most of the samples, albeit in low abundance. Their degree of methylation and cyclisation, expressed in the MBT' (methylation index of branched tetraethers) and DC (degree of cyclisation) indices, respectively, were comparable with those for African soils, their presumed source. Comparison of DC index values for brGDGTS in global soils, Congo deep-sea river fan sediments and dust with those of distal marine sediments clearly showed, however, that distal marine sediments had significantly higher values. This distinctive distribution is suggestive of sedimentary in situ production as a source of brGDGTs in marine sediments, rather than dust input. The presence of in situ produced brGDGTs in marine sediments means that caution should be exercised when applying the MBT'–CBT palaeothermometer to sediments with low BIT index values, i.e. < 0.1, based on our dataset.

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