Abstract
Ocean acidification (OA) during the Paleocene-Eocene thermal maximum (PETM) likely caused a biocalcification crisis. The calcium isotope composition (δ44/40Ca) of primary carbonate producers may be sensitive to OA. To test this hypothesis, we constructed the first high-resolution, high-precision planktic foraminiferal δ44/40Ca records before and across the PETM. The records employ specimens of Morozovella spp. collected from Ocean Drilling Program Sites 1209 (Shatsky Rise, Pacific Ocean) and 1263 (Walvis Ridge, Atlantic Ocean). At Site 1209, δ44/40Ca values start at -1. 33%c during the Upper Paleocene and increase to a peak of -1.15%o immediately before the negative carbon isotope excursion (CIE) that marks the PETM onset. Values remain elevated through the PETM interval and decrease into the earliest Eocene. A shorter-term record for Site 1263 shows a similar trend, although δ44/40Ca values are on average 0.22%o lower and decrease shortly after the CIE onset. The trends support neither diagenetic overprinting, authigenic carbonate additions, nor changes in the δ44/40Ca value of seawater. Rather, they are consistent with a kinetic isotope effect, whereby calcite 844/40Ca values inversely correlate with precipitation rate. Geologically rapid Ca isotope shifts appear to reflect the response of Morozovella to globally forced changes in the local carbonate geochemistry of seawater. All data combined suggest that the PETM-OA event occurred near the peak of a gradual reduction in seawater carbonate ion concentrations during a time of elevated atmospheric pCO2, potentially driven by North Atlantic igneous province emplacement.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 723-727 |
| Number of pages | 5 |
| Journal | Geology |
| Volume | 49 |
| Issue number | 6 |
| DOIs | |
| State | Published - 2021 |
Funding
We thank Alain Potrel, who assisted with data collection, along with Meagan E. Ankney and Gregory O. Lehn for laboratory oversight. We also thank Tirzah Abbot for assisting with scanning electron microscope training and imaging, and Clay Kelly for confirming species analyzed in this study. Members of the Jacobson Laboratory Group at Northwestern University (Illinois, USA) provided many useful discussions, and we also appreciate efforts made by the shipboard scientists of Ocean Drilling Program Legs 198 and 208. Matthew Fantle and other anonymous reviewers provided thoughtful feedback that improved the presentation. This work was supported by an National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP) grant (DGE-1842165) awarded to Kitch, as well as a David and Lucile Packard Foundation Fellowship (2007-31757) and an NSF grant (EAR 0723151) awarded to Jacobson. We thank Alain Potrel, who assisted with data collection, along with Meagan E. Ankney and Gregory O. Lehn for laboratory oversight. We also thank Tirzah Abbot for assisting with scanning electron microscope training and imaging, and Clay Kelly for confirming species analyzed in this study. Members of the Jacobson Laboratory Group at Northwestern University (Illinois, USA) provided many useful discussions, and we also appreciate efforts made by the shipboard scientists of Ocean Drilling Program Legs 198 and 208. Matthew Fantle and other anonymous reviewers provided thoughtful feedback that improved the presentation. This work was supported by an National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP) grant (DGE-1842165) awarded to Kitch, as well as a David and Lucile Packard Foundation Fellowship (2007–31757) and an NSF grant (EAR 0723151) awarded to Jacobson.
ASJC Scopus subject areas
- Geology
