Calcium phosphates in Pacific deep-sea sediments as proxies for the REY distribution in pore waters

jessica.volz [ at ]


Rare earth elements and yttrium (REY) are often used as proxies to describe past enviromental conditions or to track element sources. Calcium phosphates are commonly used as archives for REY, but our study of the upper 10 m of deep-sea sediments from the equatorial Pacific, where REY are controlled by Ca phosphates, show that the shale-normalized (SN) REY patterns are heavily impacted by early diagenesis. The Ca phosphates incorporate REY from ambient pore waters without major fractionation, and thus, their REYSN patterns are similar to the pore-water REYSN pattern [1]. Our data from the Clarion Clipperton Zone (CCZ) and from the Peru Basin reveal such incorporation of pore-water REY into the Ca phosphates over long geographical distances and over a rather wide range of oxic to suboxic pore-water conditions. The pore-water REYSN patterns from the Peru Basin show similar features as seawater (e.g., heavy REY enrichment, negative CeSN and positive YSN anomalies), whereas the pore-water REYSN patterns from the CCZ display middle REY enrichment, the development of a negative CeSN-anomaly with depth, and either no or a slightly negative YSN-anomaly [1]. The differing pore-water REYSN patterns are possibly due to different REY sources to the pore water. These results cast doubt on the approach of using marine Ca phosphates as archives for the REY distribution or the Nd isotope composition of seawater, because the REY are derived from pore water and the Ca phosphates therefore do not preserve a primary seawater REY signal.

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GOLDSCHMIDT Conference, 18 Aug 2019 - 23 Aug 2019, Barcelona, Spain.
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Paul, S. A. L. , Bau, M. , Volz, J. B. , Köster, M. , Kasten, S. , Haeckel, M. and Koschinsky, A. (2019): Calcium phosphates in Pacific deep-sea sediments as proxies for the REY distribution in pore waters , GOLDSCHMIDT Conference, Barcelona, Spain, 18 August 2019 - 23 August 2019 .

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