Project: Establishing The Magnitude Of Sea-Surface Acidification During The Paleocene-Eocene Thermal Maximum

Extracted from the NSF award abstract:

At projected rates of anthropogenic carbon emissions, the pH of the surface ocean is expected to decline by 0.3 pH units by the end of this century, and 0.7 pH units by 2300. The only other time the ocean might have experienced a similar change in pH in the past is during the Paleocene-Eocene Thermal Maximum (PETM; 56 Mya) as a consequence of a massive carbon release, which also warmed the planet. The mass of carbon released is estimated to have been as large as that projected for the future but over thousands of years rather than centuries, thus allowing for greater buffering of the saturation state of the surface ocean. Nonetheless, planktonic calcifiers and coral reefs both experienced significant reductions in diversity, likely in response to a combination of factors, including pH and carbonate saturation state. Efforts to quantify changes in carbonate chemistry, however, have relied on indirect methods, that is with numerical models of the carbon cycle constrained by observations of changes in ocean carbonate chemistry such as carbon isotopes and the distribution of carbonate sediments. In computing the mass and rate of carbon release, the models also simulate changes in ocean pH and saturation state. While the range of model estimates continues to narrow, testing has been limited by the lack of more direct information on ocean carbonate chemistry, specifically changes in the pH and/or carbonate ion concentration.

To address this deficiency, a team of scientists from the University of California at Santa Cruz, the Lamont-Doherty Earth Observatory of Columbia University, and the University of Hawaii are conducting a 3-year study to quantify changes in the sea-surface carbonate chemistry during the PETM. The project will focus on the application of two boron-based proxies, B/Ca and B isotopes as recorded in planktonic foraminifera, to quantify pH and possibly carbonate ion concentration. The team will develop detailed proxy records for a number of globally distributed locations, with the goal of establishing regional anomalies in surface ocean carbonate chemistry relative to longer-term trends. The data will be interpreted with numerical models utilizing information from laboratory-based calibration studies of modern foraminifera, and compared with plankton assemblage records. The results will also provide an independent means of testing model simulations of the rate and duration of carbon release, and ultimately the rise in atmospheric CO2.

Data from this project are published in:

Penman, D. E., B. Honisch, R. E. Zeebe, E. Thomas, J. C. Zachos. Rapid and sustained surface ocean acidification during the Paleocene-Eocene Thermal Maximum. Paleoceanography Volume 29(5),357–369, 2014. DOI: 10.1002/2014PA002621