PaleopH reconstruction across the Middle Eocene Climatic Optimum (MECO) using boron isotopes (d11B)

Lead PI: Dr. Baerbel Hoenisch

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

April 2015 - March 2016
Global ; South Atlantic ; Southern Ocean
Project Type: Research

DESCRIPTION: The Middle Eocene Climatic Optimum (MECO) at ~40 Ma is an event characterized by rapid global warming and ocean acidification. This stuy aimed to quantify warming and acidification using the boron isotope proxy in planktic foraminifer shell selected from two sediment cores in the South Atlantic and Southern Ocean.

OUTCOMES: Our records indicate a substantial acidification on the surface ocean during the MECO interval. Similar to the temperature evolution of the event it occurred in two phases, moderate acidification associated with the initial gradual warming and more severe acidification associated with peak warming. Our calculations, while subject to significant uncertainties, suggests a maximum pH decrease of ~0.4 pH units, resulting in an estimated increase in atmospheric CO2 concentrations of ca. 1000 µatm. Notably, the d11B excursion (and thus, pH and pCO2) is tightly coupled to exciting carbonate MAR records documenting deep-sea carbonate dissolution. The d18O record, and consequently temperature evolution, slightly lack behind the increase in pCO2, confirming the causal relationship between increasing greenhouse gases and the inferred global warming. A few more data need to be collected to verify data interpretation, a manuscript is in preparation.


Max Kade Foundation, Inc.




Iris Möbius


Ruprecht-Karls University Heidelberg


middle eocene climatic optimum paleopH boron isotopes


Modeling and Adapting to Future Climate