@article{4e7f007134594416b28cf7b293e16554,
title = "P/Ca in Carbonates as a Proxy for Alkalinity and Phosphate Levels",
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.",
keywords = "Ca isotopes, alkalinity, closed-basin lakes, clumped isotopes, phosphate",
author = "Miquela Ingalls and Bl{\"a}ttler, {Clara L.} and Higgins, {John A.} and Magyar, {John S.} and Eiler, {John M.} and Fischer, {Woodward W.}",
note = "Funding Information: 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. Funding Information: 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. Publisher Copyright: {\textcopyright}2020. American Geophysical Union. All Rights Reserved.",
year = "2020",
month = nov,
day = "16",
doi = "10.1029/2020GL088804",
language = "English (US)",
volume = "47",
journal = "Geophysical Research Letters",
issn = "0094-8276",
publisher = "American Geophysical Union",
number = "21",
}