A Multi-Proxy Isotope Approach to Reconstruct Seawater Oxygenation

Rhodes, Felicity Sarah Amy (2019). A Multi-Proxy Isotope Approach to Reconstruct Seawater Oxygenation. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00011559


The isotopic composition of redox sensitive metals in marine sedimentary rocks have been used to provide insights into the degree and extent of oceanic anoxia during environmental changes such as oceanic anoxic events (OAEs). In this study a new method has been developed to determine the isotope composition (δ187Re = [[(187Re/185Re)sample / (187Re/185Re)SRM 3143]-1]*1000) of the redox sensitive element rhenium in sedimentary deposits. The method requires 1.5 – 6.0 ng Re per analysis and utilises a two-stage chromatographic separation and MC-ICP-MS analysis. The accuracy was tested using matrix test samples (δ187Re = 0) that have an average δ187Re of -0.035 ± 0.112 ‰; and column processed aliquots of standard SRM 3143 of δ187Re = -0.042 ± 0.108 ‰. The long-term reproducibility of standard analyses is 0.082 ‰ (2 SD). The reference sample SDO-1 had 187Re = -0.163 ± 0.113 ‰. The total measured range in δ187Re was -1.087 ± 0.084 ‰ between a sediment sample from the Baltic Sea and SRM 3143.

The δ187Re of marine mudrocks from the Toarcian OAE in Yorkshire, UK have a range of 0.699‰ from -0.019 ± 0.080 ‰ to -0.756 ± 0.085 ‰. During the OAE onset δ187Re increases by 0.219 ‰. The main event is synchronous with a - 0.596 ‰ 187Re excursion. Minimum δ187Re values correspond to the maximum global extent of anoxia indicated by other proxies. The 187Re decrease is interpreted to indicate a decrease in δ187Re of contemporaneous seawater due to a progressive increase in the global extent of anoxia.

Recent sediments from the Gotland Deep, Baltic Sea have a 187Re range of 0.826 ‰ from 0.261 ± 0.084 to -1.087 ± 0.084 ‰. The cause of changes in δ187Re is inconclusive and could include changes in local anoxia, the basin-wide extent of anoxia, anthropogenic Re, runoff variation and diagenesis.

Viewing alternatives

Download history


Public Attention

Altmetrics from Altmetric

Number of Citations

Citations from Dimensions

Item Actions