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P/Ca in Carbonates as a Proxy for Alkalinity and Phosphate Levels

Author(s): Ingalls, Miquela; Blättler, Clara L; Higgins, John A; Magyar, John S; Eiler, John M; et al

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Abstract: Understanding mechanisms, rates, and drivers of past carbonate formation provides insight into the chemical evolution of Earth's oceans and atmosphere. We paired geological observations with elemental and isotope geochemistry to test potential proxies for calcium‐to‐alkalinity ratios (Ca:ALK). Across diverse carbonate facies from Pleistocene closed‐basin lakes in Owens Valley, CA, we observed less δ44/40Ca variation than theoretically predicted (>0.75‰) for the very low Ca:ALK in these systems. Carbonate clumped isotope disequilibria implied rapid carbonate growth—kinetic isotope effects, combined with the diverse carbonate minerals present, complicated the interpretation of δ44/40Ca as a paleoalkalinity proxy. In contrast, we observed that the high phosphate concentrations are recorded by shoreline and lake bottom carbonates formed in 11 Pleistocene lakes at orders of magnitude greater concentrations than in marine carbonates. Because the maximum phosphate content of water depends on Ca:ALK, we propose that carbonate P/Ca can inform phosphate levels and thereby Ca:ALK of aqueous environments in the carbonate record.
Publication Date: 19-Oct-2020
Citation: Ingalls, Miquela, Clara L. Blättler, John A. Higgins, John S. Magyar, John M. Eiler, and Woodward W. Fischer. "P/Ca in carbonates as a proxy for alkalinity and phosphate levels." Geophysical Research Letters 47, no. 21 (2020). doi:10.1029/2020GL088804.
DOI: doi:10.1029/2020GL088804
ISSN: 0094-8276
EISSN: 1944-8007
Type of Material: Journal Article
Journal/Proceeding Title: Geophysical Research Letters
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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