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

Ingalls, Miquela and Blättler, Clara L. and Higgins, John A. and Magyar, John S. and Eiler, John M. and Fischer, Woodward W. (2020) P/Ca in Carbonates as a Proxy for Alkalinity and Phosphate Levels. Geophysical Research Letters, 47 (21). Art. No. e2020GL088804. ISSN 0094-8276.

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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 δ^(44/40)Ca 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 δ^(44/40)Ca 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ingalls, Miquela0000-0002-7451-2944
Blättler, Clara L.0000-0003-4843-3625
Magyar, John S.0000-0002-3586-8286
Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2020 American Geophysical Union. Issue Online: 30 October 2020; Version of Record online: 30 October 2020; Accepted manuscript online: 19 October 2020; Manuscript accepted: 14 October 2020; Manuscript revised: 07 October 2020; Manuscript received: 09 May 2020. The authors would like to thank Christine Chen, Adam Hudson, Dan Ibarra, Max Lloyd, and Theodore Present for contributing sample material from other paleolakes and marine carbonates, two anonymous reviewers for greatly improving this manuscript, and the International Geobiology Course (supported by the Agouron Institute, Simons Foundation, NASA, and Caltech) for access to Mono Lake sediment cores. Funding for the work was provided by the Simons Foundation Collaboration on the Origins of Life (WWF) and Barr Foundation Postdoctoral Fellowship to M. I. Data Availability Statement: Supporting information detailing methods and all data may be found in the supporting information and were archived in the Open Science Framework ( Samples collected as a part of this study were registered with IGSNs, listed in Table S1.
Funding AgencyGrant Number
Agouron InstituteUNSPECIFIED
Simons FoundationUNSPECIFIED
Barr FoundationUNSPECIFIED
Subject Keywords:phosphate; alkalinity; closed‐basin lakes; Ca isotopes; clumped isotopes
Issue or Number:21
Record Number:CaltechAUTHORS:20201021-084310520
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Official Citation:Ingalls, M., Blättler, C. L., Higgins, J. A., Magyar, J. S., Eiler, J. M., & Fischer, W. W. (2020). P/Ca in carbonates as a proxy for alkalinity and phosphate levels. Geophysical Research Letters, 47, e2020GL088804.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106182
Deposited By: Tony Diaz
Deposited On:21 Oct 2020 16:28
Last Modified:02 Jun 2021 19:48

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