Paleocene-Eocene Thermal Maximum Benthic Adaptations in

Surviving rapid climate change in the deep sea during the Paleogene hyperthermals

Authors:

1. Laura C. Foster (a)
2. Daniela N. Schmidt (a)
3. Ellen Thomas (b,c)
4. Sandra Arndt (d)
5. Andy Ridgwell (d)

Affiliations:

a. Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;

b. Department of Geology and Geophysics, Yale University, New Haven, CT 06520;

c. Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459; and

d. School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, United Kingdom

Abstract:

Predicting the impact of ongoing anthropogenic CO2 emissions on calcifying marine organisms is complex, owing to the synergy between direct changes (acidification) and indirect changes through climate change (e.g., warming, changes in ocean circulation, and deoxygenation). Laboratory experiments, particularly on longer-lived organisms, tend to be too short to reveal the potential of organisms to acclimatize, adapt, or evolve and usually do not incorporate multiple stressors. We studied two examples of rapid carbon release in the geological record, Eocene Thermal Maximum 2 (∼53.2 Ma) and the Paleocene Eocene Thermal Maximum (PETM, ∼55.5 Ma), the best analogs over the last 65 Ma for future ocean acidification related to high atmospheric CO2 levels. We use benthic foraminifers, which suffered severe extinction during the PETM, as a model group. Using synchrotron radiation X-ray tomographic microscopy, we reconstruct the calcification response of survivor species and find, contrary to expectations, that calcification significantly increased during the PETM. In contrast, there was no significant response to the smaller Eocene Thermal Maximum 2, which was associated with a minor change in diversity only. These observations suggest that there is a response threshold for extinction and calcification response, while highlighting the utility of the geological record in helping constrain the sensitivity of biotic response to environmental change.