The effect of meter-scale lateral oxygen gradients at the sediment-water interface on selected organic matter based alteration, productivity and temperature proxies

[摘要] A valid assessment of selective aerobic degradation on organic matter (OM)and its impact on OM-based proxies is vital to produce accurateenvironmental reconstructions. However, most studies investigating theseeffects suffer from inherent environmental heterogeneities. In this study,we used surface samples collected along two meter-scale transects and onelonger transect in the northeastern Arabian Sea to constrain initial OMheterogeneity, in order to evaluate selective aerobic degradation ontemperature, productivity and alteration indices at the sediment-waterinterface. All of the studied alteration indices, the higher plant alkaneindex, alcohol preservation index, and diol oxidation index, demonstratedthat they are sensitive indicators for changes in the oxygen regime. Severalexport production indices, a cholesterol-based stanol/stenol index anddinoflagellate lipid- and cyst-based ratios, showed significant (more than20%) change only over the lateral oxygen gradients. Therefore, these compoundsdo not exclusively reflect surface water productivity, but are significantlyaltered after deposition. Two of the proxies, glycerol dibiphytanyl glyceroltetraether-based TEX₈₆ sea surface temperature indices and indicesbased on phytol, phytane and pristane, did not show any trends related tooxygen. Nevertheless, unrealistic sea surface temperatures were obtainedafter application of the TEX₈₆, TEX₈₆^L, and TEX₈₆^Hproxies. The phytol-based ratios were likely affected by the sedimentaryproduction of pristane. Our results demonstrate the selective impact ofaerobic organic matter degradation on the lipid and palynomorph compositionof surface sediments along a short lateral oxygen gradient and suggest thatsome of the investigated proxies may be useful tracers of changing redoxconditions at the sediment-water interface.

[学科分类] 地球化学与岩石