Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, 10964, USA
Global warming and ocean acidification are widely discussed to impact marine life, but evidence from laboratory experiments and observations of reduced calcification in modern and historic records is challenged by the short duration and limited complexity of experimental work, as well as potential preservation bias of original calcification signals. The geological record provides opportunities to study the long-term response of marine organisms to ocean acidification, warming and deoxygenation, in particular when supported by independent geochemical evidence. However, translating geochemical proxies to past environmental conditions requires sound knowledge of the elemental and isotopic composition of seawater, in addition to constraints on vital effects in proxy carrier organisms that may now be extinct. Furthermore, it is important to realize that for paleocean acidification to impact marine calcification, CO2 release must have been massive and rapid, but constraining the duration of such events in Earth distant history is fraught with uncertainty.
I will provide an overview of these challenges, using the Paleocene-Eocene Thermal Maximum as an example, but also raise questions about how well we understand fundamental proxy systematics, and the temptation to infer physiological processes from geochemical proxy relationships in foraminifers and corals.