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Mg isotope fractionation in the bivalve Glycymeris

The Cenozoic cooling that occurred over the past 50 Ma is accompanied by an increase of Mg/Ca in seawater. How this change in seawater chemistry is linked to climate change is still disputed. Mg isotope ratios of seawater could distinguish several possible causes including dolomitization, authigenic clay formation and changes in rates of silicate- and carbonate weathering. Previous reconstructions of Mg isotope ratios of paleo-seawater were based on foraminifera, corals or carbonate muds, which however yielded conflicting results. Here we assess the suitability of bivalves from genus Glycymeris as archives for paleo-seawater δ26Mg (the standardized 26Mg/24Mg). Their potential advantage over other archives arises from their strong evolutionary conservatism, thick shells and a fossil record dating back to the Lower Cretaceous. We established a new method to analyze δ26Mg for samples with a very low Mg/Ca ratio. We report Mg isotope signatures from ventral margins of shells of three recent Glycymeris species from the Adriatic Sea that show an increasing fractionation with increasing ontogenetic age. Similar isotope signatures were observed across single shells, a property that we are going to exploit in the future for reconstructions of paleo-seawater δ26Mg from specimens of fossil Glycymeris.

Details

Author
Niklas Keller1, Eric Otto Walliser2, Melita Peharda3, Michael Tatzel1
Institutionen
1University of Göttingen, Germany; 2Hessisches Landesmuseum für Kunst und Natur, Wiesbaden, Germany; 3Institute of Oceanography and Fisheries, Split, Croatia
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/dsea-0r51