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Benthic foraminifera as paleoceanographic proxies : core-top element/calcium ratios and stable isotope data

  • Author(s): Harper, Dustin T.
  • Harper, Dustin T.
  • et al.
Abstract

This thesis examined the reliability and potential paleoceanographic applications of multiple chemical and isotopic proxies in a variety of benthic foraminifera species. The selected proxies are known to resolve organic matter flux and bottom water oxygenation, simultaneously allowing for examination of microhabitat effects in species with diverse depths of calcification. Globally distributed core-top samples from 19 different sites yielded a total of 17 varieties of benthic foraminifera. Samples were analyzed for [delta]¹³C and [delta]¹⁸O values to determine species depth distributions and interspecies vital differences in [delta]¹⁸O. A Mg-cleaning method was employed before samples were analyzed for the elemental ratios; U/Ca, Mn/Ca, B/Ca, and Mg/Ca to elucidate species elemental incorporation differences in various locations. Modeled [delta]¹³C pore water curves were applied in two different sites to determine calcification depth distribution of benthic foraminifera. [delta]¹³C offset differences between C. wuellerstorfi and Oridorsalis spp., were determined at every possible site and evaluated as a potential carbonate chemistry proxy, showing notable success. Positive correlations were observed between [delta]¹³C offset, and pH and carbonate ion concentration, with R2 values of 0.67 and 0.67, respectively. Stronger correlations between [delta]¹³C offset differences and temperature were observed (R² of 0.73), suggesting the proxy is being influenced by physical effects, not solely chemical. Epifaunal C. wuellerstorfi showed higher variability in U/Ca test coatings and in Mn/Ca test incorporation when compared to the [delta]¹³C differences between epifaunal and infaunal species, while infaunal Oridorsalis spp. showed tighter interdependence suggesting microhabitat depth plays a significant role in the variability of elemental incorporation

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