The clumped isotope composition of carbonates can be directly related to their formation temperature in the environment, but a robust temperature calibration for siderite is still lacking, and thus limits the applicability of this tool. Here, we present a new calibration for the clumped isotope composition of siderites precipitated with two different techniques between 8.5 and 62 °C: Δ 47 =0.0428±0.002∗[Formula presented]+0.0683±0.022±95%CL,TinKelvinR 2 =0.92 The slope of our calibration obtained at an acid digestion temperature of 115 °C is statistically indistinguishable from recently published calcite and dolomite clumped isotope calibrations. The intercept differs from calcite at phosphoric acid digestion temperatures of 70 and 115 °C due to a difference in phosphoric acid fractionation, highlighting the necessity of a siderite specific calibration. We performed the first survey of the clumped isotope compositions of siderites from different environmental settings at ambient temperatures including two permanently waterlogged swamp sites as modern analogues for pedogenic siderite formation in the geologic record. We conclude that pedogenic siderites form at temperatures between the Mean Annual Air Temperature (MAAT) and the summer air temperature highlighting the strong potential of siderites for paleoclimate reconstructions in continental environments.
Bibliographical noteFunding Information:
We thank Madalina Jaggi and Felix Marxer for assistance in the laboratory and Dani Or for help with the soil temperature modelling. JD and SB acknowledge financial support through ETH project ETH-3314-1 and SNF projects 200020_160046 and 200021_169849. SGD and GAL gratefully acknowledge financial support through grant NSF EAR064334 . AK acknowledges support from the Russian Foundation for Basic Research (RFBR) grant RFBR-16-05-00979 . CW acknowledges support from the US National Science Foundation (NSF) grant NSF-1462297 and the National Lacustrine Core Facility (LacCore), Department of Earth Sciences, University of Minnesota-Twin Cities for storing the Otter Lake sample. Field work in the Norfolk Salt Marsh was funded through an ERC StG to AVT 3075842 CARBONSINK. All raw data can be received from SB upon request. We thank Jens Fiebig and three anonymous reviewers for providing constructive feedback that significantly improved the manuscript.
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- Clumped isotope thermometry
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