Effects of ocean acidification on the marine calcium isotope record at the Paleocene–Eocene Thermal Maximum

• Published in: Earth and Planetary Science Letters
• Main Authors: Griffith, Elizabeth M., Fantle, Matthew S., Eisenhauer, Anton, Paytan, Adina, Bullen, Thomas D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2015
• Subjects: Pacific; Ocean acidification
• Online Access: https://oceanrep.geomar.de/id/eprint/28871/; https://oceanrep.geomar.de/id/eprint/28871/1/Griffith%20et.al.pdf; https://doi.org/10.1016/j.epsl.2015.03.010

Highlights • δ44Ca was measured in bulk carbonate and barite at two sites over the PETM. • Diagenetic effects on δ44Ca are observed associated with ocean acidification. • Multiple sites and proxy archives necessary to reconstruct the past accurately. Abstract Carbonates are used extensively to reconstruct paleoclimate and paleoceanographic conditions over geologic time scales. However, these archives are susceptible to diagenetic alteration via dissolution, recrystallization and secondary precipitation, particularly during ocean acidification events when intense dissolution can occur. Despite the possible effects of diagenesis on proxy fidelity, the impacts of diagenesis on the calcium isotopic composition (δ44Ca) of carbonates are unclear. To shed light on this issue, bulk carbonate δ44Ca was measured at high resolution in two Pacific deep sea sediment cores (ODP Sites 1212 and 1221) with considerably different dissolution histories over the Paleocene–Eocene Thermal Maximum (PETM, ∼55 Ma∼55 Ma). The δ44Ca of marine barite was also measured at the deeper Site 1221, which experienced severe carbonate dissolution during the PETM. Large variations (∼0.8‰∼0.8‰) in bulk carbonate δ44Ca occur in the deeper of the two sites at depths corresponding to the peak carbon isotope excursion, which correlate with a large drop in carbonate weight percent. Such an effect is not observed in either the 1221 barite record or the bulk carbonate record at the shallower Site 1212, which is also less affected by dissolution. We contend that ocean chemical changes associated with abrupt and massive carbon release into the ocean–atmosphere system and subsequent ocean acidification at the PETM affected the bulk carbonate δ44Ca record via diagenesis in the sedimentary column. Such effects are considerable, and need to be taken into account when interpreting Ca isotope data and, potentially, other geochemical proxies over extreme climatic events that drive sediment dissolution.