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

Abstract

Abstract.A valid assessment of selective aerobic degradation on organic matter (OM) and its impact on OM-based proxies is vital to produce accurate environmental reconstructions. However, most studies investigating these effects suffer from inherent environmental heterogeneities. In this study, we used surface samples collected along two meterscale transects and one longer transect in the northeastern Arabian Sea to constrain initial OM heterogeneity, in order to evaluate selective aerobic degradation on temperature, productivity and alteration indices at the sediment-water interface. All of the studied alteration indices, the higher plant alkane index, alcohol preservation index, and diol oxidation index, demonstrated that they are sensitive indicators for changes in the oxygen regime. Several export production indices, a cholesterol-based stanol/stenol index and dinoflagellate lipid-and cyst-based ratios, showed significant (more than 20 %) change only over the lateral oxygen gradients. Therefore, these compounds do not exclusively reflect surface water productivity, but are significantly altered after deposition. Two of the proxies, glycerol dibiphytanyl glycerol tetraether-based TEX 86 sea surface temperature indices and indices based on phytol, phytane and pristane, did not show any trends related to oxygen. Nevertheless, unrealistic sea surface temperatures were obtained after application of the TEX 86 , TEX L 86 , and TEX H 86 proxies. The phytol-based ratios were likely affected by the sedimentary production of pristane. Our results demonstrate the selective impact of aerobic organic matter degradation on the lipid and palynomorph composition of surface sediments along a short lateral oxygen gradient and suggest that some of the investigated proxies may be useful tracers of changing redox conditions at the sediment-water interface.

I/Ca ratios in benthic foraminifera from the Peruvian oxygen minimum zone: analytical methodology and evaluation as a proxy for redox conditions

“…These results suggest that a careful distinction of the analysed species is essential for the application of this proxy, at least for the infaunal species. Nevertheless, since the species dependency of I / Ca ratios appears to be higher than the oxygenation dependency, bulk analyses might provide information about oxygenation in a different way: the species composition of a foraminiferal assemblage is often oxygen dependent (Bernhard, 1986;Sen Gupta and Machain-Castello, 1993;Bernhard and Sen Gupta, 1999;Mallon et al, 2012). Thus, bulk I / Ca ratios might be dominated by the species composition, which is affected by oxygen availability.…”

“…This difference might either be related to a strong vital effect or to a species-dependent difference in calcification depths. Oxygen gradients in the pore waters of a comparable OMZ off Pakistan are quite steep under suboxic conditions (Bogus et al, 2012), and IO − 3 probably follows this gradient. Thus, a difference in calcification depth might have a severe influence on the I / Ca ratio.…”

The impact of oxygen exposure on long-chain alkyl diols and the long chain diol index (LDI) – a long-term incubation study

“…Only a few studies have considered the impact of diagenesis on the abundance and distribution of LCDs (Ferreira et al, 2001;Versteegh et al, 2010;Bogus et al, 2012). As shown by various studies, biomarker distributions can be altered substantially by oxygen exposure (Sun and Wakeham, 1994;Hoefs et al, 1998;Prahl et al, 2003;Rontani et al, 2009Rontani et al, , 2013, but only Sinninghe , Hoefs et al (2002) and Rodrigo-Gámiz et al (2016) analyzed the impact of oxic degradation on LCD distributions.…”

An ocean–ice coupled response during the last glacial: a view from a marine isotopic stage 3 record south of the Faeroe Shetland Gateway

“…Versteegh et al, 2012), but their preservation potential is still high, even if the assemblages can be altered by oxidation processes in some specific environments (e.g. Zonneveld et al, 2007;Bogus et al, 2012). They are among the rare proxies offering access to past hydrological conditions of polar and/or glacial extreme environments (e.g.…”