The rare earth element distribution in marine carbonates as a potential proxy for seawater pH on early earth
Data files
Jun 11, 2024 version files 16.58 KB
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Lin_2024_Supplementary_Table_1_AJS.csv
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Lin_2024_Supplementary_Table_2_AJS.csv
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README.md
Abstract
Understanding the marine environment of early Earth is crucial for understanding the evolution of climate and early life. However, the master variable of Archean and Proterozoic seawater, the pH, is poorly constrained, and published ideas about the pH range encompass ~7 pH units from mildly acidic to hyperalkaline. To better infer ancient seawater pH, we examine the possibility of a seawater pH proxy using rare earth elements (REEs) in marine carbonates. The principle is based on increasing concentrations of heavy rare earth elements in solution relative to the light REEs with decreasing pH due to REE complexation and scavenging. We calibrated such an REE pH proxy using pH variability in modern seawater and tested the proxy with ~100 REE measurements from 13 separate carbonate formations. We compared our pH estimates derived from the REE proxy to published pH estimates of Cenozoic and Neoproterozoic seawater that use the established pH proxy of boron isotopes (δ11B). REE-pH estimates agree with the Cenozoic and the Ediacaran δ11B-pH proxy based on the type of carbonate and boron isotopic composition at corresponding times. The uncertainty in our REE-pH proxy can probably be explained by model assumptions, noise from freshwater influence, siliciclastic input, and diagenesis. This proof-of-concept study demonstrates that the REE-pH method provides pH estimates comparable to boron isotope pH estimates within uncertainties, which potentially could constrain changes in Precambrian seawater pH to better understand the coevolution of life and early Earth’s environment.
README: The Rare Earth Element Distribution in Marine Carbonates as a Potential Proxy for Seawater pH on Early Earth
https://doi.org/10.5061/dryad.69p8cz99r
Data and file structure
There are two CSVs and two URLs for supplementary data for Lin and Catling (2024).
Supplementary Tables
Supplementary Table 1: Rare earth element (REE) speciation using the PHREEQC model mentioned in the manuscript. The labels on the data include the pH and REE species. Please refer to the PHREEQC source code mentioned in Supplementary Data below for more instructions on generating the table.
Supplementary Table 2: REE slope and pH estimates of marine carbonate formations mentioned in the manuscript. Data includes the formations, sample label, epoch or period, pH with uncertainty, REE slope with uncertainty, and references.
Supplementary Data
The supplementary data documents include the equation derivations and supplementary figures mentioned in Lin and Catling (2024). The figures and the document that describes the figures here: https://zenodo.org/records/11557285
The source code for the REE-pH proxy and the PHREEQC model is available at https://github.com/PingChunLin/REE_pH.git.