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Revealing their true stripes: Mg/Ca banding in the Paleogene planktonic foraminifera genus Morozovella and implications for paleothermometry

John, Eleanor H., Staudigel, Philip T., Buse, Benjamin, Lear, Caroline H. ORCID:, Pearson, Paul N. ORCID: and Slater, Sophie M. 2023. Revealing their true stripes: Mg/Ca banding in the Paleogene planktonic foraminifera genus Morozovella and implications for paleothermometry. Paleoceanography and Paleoclimatology 38 (9) , e2023PA004652. 10.1029/2023PA004652

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The Mg/Ca ratio of foraminiferal calcite is a widely used empirical proxy for ocean temperature. Foraminiferal Mg/Ca-temperature relationships are based on extant species and are species-specific, introducing uncertainty when applying them to the fossil tests of extinct groups. Many modern species show remarkable heterogeneity in their intra-test Mg distributions, typically due to the presence of high Mg bands, which have a biological origin. Importantly, banding patterns differ between species, which could affect Mg/Ca-temperature relationships. Few studies have looked at intra-test variability in Mg/Ca ratios in extinct species of foraminifera, despite the obvious implications for paleothermometry. We used electron probe microanalysis (EPMA) to investigate intra-test Mg distributions in the fossil tests of two species of planktonic foraminifera from the extinct muricate mixed-layer-dwelling genus Morozovella, commonly used in Paleogene sea surface temperature reconstructions. Both M. aragonensis and M. crater show striking Mg banding patterns with multiple high and low Mg/Ca band pairs throughout the test wall in all chambers. The intra-test Mg variability in M. aragonensis and M. crater is similar to that in modern species widely used in paleoclimate reconstructions and banding patterns are consistent with published growth models for modern forms, albeit with subtle differences. The presence of Mg bands supports the application of Mg/Ca-palaeothermometry in extinct Morozovella species as well as the utility of EPMA for examining preservation of foraminifera tests in paleoclimatological studies. However, we emphasize the importance of rigorous assessments of inter- and intra-test Mg variability when using microanalytical techniques for foraminiferal Mg/Ca paleothermometry.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: American Geophysical Union
ISSN: 2572-4517
Funders: NERC
Date of First Compliant Deposit: 25 August 2023
Date of Acceptance: 9 August 2023
Last Modified: 06 Oct 2023 18:44

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