Collaborative Research: An Eocene Perspective on Future Recovery Rates of Climate

Lead PI: Dr. Baerbel Hoenisch

Unit Affiliation: Geochemistry, Lamont-Doherty Earth Observatory (LDEO)

March 2017 - February 2020
Project Type: Research

DESCRIPTION: This projects provides a case study of a past climate event, called the Eocene Thermal Maximum-2 to constrain natural recovery rates of climate and ocean chemistry following massive carbon input into Earth's surface reservoirs. The study will allow new insight into past climate and ocean acidification processes that were hitherto unexplored, hence promoting the progress of science and advancing the field of climatology. Such insight is essential to providing the public, scientific leaders, and policy makers with a better understanding of the consequences of unabated CO2 emissions for global climate, ocean carbonate chemistry, and marine ecosystems. Moreover, the project integrates research and educational activities by introducing this information directly into secondary school and college curricula and popular journals. The project fosters education for graduate and undergraduate students from ethnically diverse populations, while conducting cutting-edge research at the same time. The outcome of this study will advancethe understanding of the Earth system and hence improve forecasts of future climate change, which is beneficial to society. Specifically, proxy records will be generated and used (d13C, d18O, %CaCO3, B/Ca, d11B) in combination with numerical modeling to determine natural recovery times for carbon cycle processes, temperature, and surface ocean acidification. The study will (1) provide fundamental insight into negative climate-carbon cycle feedbacks, (2) address important gaps in data coverage and understanding of Eocene hyperthermals, and (3) constrain critical parameter values needed for future climate-carbon cycle simulations.

OUTCOMES: The ETM-2 is characterized by warming of 2-4°C at both mid-latitude sites and an increase in sea surface salinity of 1-3 units, consistent with simulations of early Paleogene hydroclimate that suggest an increase in low- to mid-latitude aridity due to an intensification of moisture transport to high-latitudes. Furthermore, the magnitude of the carbon isotope excursion (CIE) and warming for ETM-2 scales with the CIE and warming for the PETM.

The d11B samples suggest a pH decrease across the event that is similar in magnitude to the PETM, which is characterized by much larger excursions in carbon isotopes, Mg/Ca (i.e. warming) and B/Ca than ETM-2. In addition, although we find a long-term decrease in d11B that parallels the previously documented decrease in d13C from the Paleocene into the Eocene, at both core sites the d11B data increase just before ETM-2 again, suggesting an oceanwide shift in seawater boron chemistry or a shift in the foraminiferal vital effects. To obtain a pH decrease within error of proxy-based reconstructions, LOSCAR model simulations require twice the carbon flux than previously estimated for ETM-2. Additional data are being collected to verify these findings.


National Science Foundation (NSF)





Harper, D.T., R. Zeebe, B. Hönisch, C. Schrader, L. Lourens, J. Zachos, “Subtropical sea surface warming and increased salinity during Eocene Thermal Maximum 2”, Geology, Vol. 6, p. 187-190, 2017. Harper, D.T., B. Hönisch, R.E. Zeebe, G. Schaffer, *L. Haynes, E. Thomas, J.C. Zachos, “The Magnitude of Surface Ocean Acidification and Carbon Release During Eocene Thermal Maximum 2 (ETM-2) compared to the Paleocene-Eocene Thermal Maximum”, subm. to Paleoceanography and Paleoclimatology.


climate-carbon cycle feedback eocene thermal maximum-2 hyperthermals carbon cycle perturbation ocean acidification


Modeling and Adapting to Future Climate