Affiliation:
1. Lamont‐Doherty Earth Observatory Columbia University Palisades NY USA
2. Department of Earth and Environmental Sciences Columbia University New York NY USA
3. Now at Vassar College Poughkeepsie NY USA
4. Research School of Earth Sciences The Australian National University Canberra Australia
5. Department of Marine and Coastal Sciences and Department of Earth and Planetary Sciences Rutgers University New Brunswick NJ USA
Abstract
AbstractForaminiferal Mg/Ca has proven to be a powerful paleothermometer for reconstructing past sea‐surface temperature, which, among other applications, is a critical parameter for boron isotope reconstructions of past surface ocean pH and PCO2. However, recent laboratory culture studies indicate seawater pH and the total dissolved inorganic carbon content (DIC) may both exert a significant additional control on foraminiferal Mg/Ca, likely influencing paleotemperature records as a result of seawater chemistry evolution on geologic timescales. In addition, the seawater Mg/Ca composition (Mg/Casw) has been shown to reduce the sensitivity of foraminiferal Mg/Ca to temperature and possibly its sensitivity to the carbonate system as well. Here we present new Mg/Ca data from laboratory culture experiments with living planktic foraminifera— Globigerinoides ruber (p), Trilobatus sacculifer, and Orbulina universa— grown under a range of different pH and/or seawater DIC conditions and in low Mg/Casw to mimic the chemical composition of the Paleocene ocean. We also conducted targeted [Ca] experiments to help define Mg/Cacalcite–Mg/Casw relationships for each species and conducted new pH experiments with G. bulloides. We find that pH effects on foraminiferal Mg/Ca are reduced or absent at Mg/Casw = 1.5 mol/mol in all three species, and that T. sacculifer is generally insensitive to variable DIC and pH, making it the ideal species for Mg/Ca SST reconstructions back to 20 Ma. We apply our new T. sacculifer calibration to a Middle Miocene Mg/Ca record and provide recommendations for interpreting Mg/Ca records from extinct species.
Funder
National Science Foundation
Publisher
American Geophysical Union (AGU)
Subject
Paleontology,Atmospheric Science,Oceanography
Cited by
2 articles.
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