Abstract
Abstract. Oxygen isotope analyses of different size fractions of Pliocene diatoms (δ18Odiatom) from the Bering Sea show no evidence of an isotope offset and support the use of bulk diatom species samples for palaeoceanographic reconstructions. Additional samples containing concentrations of sponge spicules produce δ18O values several per mille (‰) lower than δ18Odiatom with a calculated mean offset of 3.9‰ ± 1.5. This difference is significantly greater than modern-day variations in water δ18O through the regional water column. Despite the potential for oxygen isotope disequilibrium within δ18Osponge, there appears to be some similarity between δ18Osponge and a global stacked benthic δ18Oforam record. This highlights the potential for δ18Osponge in palaeoenvironmental research at sites where carbonates are not readily preserved.
Highlights
The use of oxygen isotopes in palaeoenvironmental research is well documented for both lacustrine and marine environments, predominantly from carbonate fossils, but more recently from siliceous microfossils (Emiliani, 1955; Duplessy et al, 1988; Leng and Marshall, 2004; Lisiecki and Raymo, 2007)
The majority of this work has shown that there are few, or no, intra- or inter-species isotope offsets in diatoms (e.g. Shemesh et al, 1995; Schmidt et al, 2001; Moschen et al, 2005; Dodd and Sharp, 2010), Swann et al (2007, 2008) have shown offsets of up to 3.5‰ between different size fractions of Plioceneand Quaternary-age diatoms from the subarctic North Pacific Ocean. Another form of biogenic silica commonly found in sediments is siliceous sponge spicules
All analysed samples were free of mineral and organic matter contamination, as shown by scanning electron microscope (SEM) (Fig. 2) and verified by X-ray fluorescence (XRF) analyses, with aluminium concentrations in the range of 0.23–0.40 %
Summary
The use of oxygen isotopes in palaeoenvironmental research is well documented for both lacustrine and marine environments, predominantly from carbonate fossils, but more recently from siliceous microfossils (Emiliani, 1955; Duplessy et al, 1988; Leng and Marshall, 2004; Lisiecki and Raymo, 2007). Shemesh et al, 1995; Schmidt et al, 2001; Moschen et al, 2005; Dodd and Sharp, 2010), Swann et al (2007, 2008) have shown offsets of up to 3.5‰ between different size fractions of Plioceneand Quaternary-age diatoms from the subarctic North Pacific Ocean. Another form of biogenic silica commonly found in sediments is siliceous sponge spicules (structural elements which support the skeleton of the animal; phylum Porifera, classes Demospongiae and Hexactinellida). The use of oxygen isotope analysis of sponge spicules (δ18Osponge) is rare, and those studies that have been carried out suggest that oxygen isotope fractionation between sponge spicules and seawater is not systematically reliable, Published by Copernicus Publications on behalf of the European Geosciences Union
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