Australia: The Land Where Time Began

A biography of the Australian continent 

PETM – Rapid, Sustained Acidification of the Ocean Surface

The PETM has been associated with the release of carbon as methane and/or carbon dioxide in amounts of up to several thousand petagrams of carbon (PgC) into the ocean-atmosphere system within about 10,000 years, on the basis of a co-occurrence of a carbon isotope excursion (CIE), widespread dissolution of deep sea carbonates, and global warming. This rapid release of carbon should have, in theory, severely acidified the surface water of the ocean, though there is no geochemical evidence that has been previously presented. In this paper Penman et al. present the first observational evidence of a lowering of the pH of surface and thermohaline seawater during the PETM, their study being based on boron-based proxies for carbonate chemistry in surface waters. A drill site in the North Pacific Ocean (Ocean Drilling Program Site 1209) produced planktonic foraminifers that show a decrease of about 0.8‰ at the onset of the event in the boron isotope composition (δ11B), as well as a 30-40% reduction in shell B/Ca. Similar trends of δ11B were found in 2 records of lower resolution from the South Atlantic and Equatorial Pacific. Penman et al. suggest these observations are consistent with signification acidification on a global scale of the surface of the ocean that lasted at least 70,000 years which required sustained carbon release. They also say the anomalies in the boron records are consistent with an initial drop of surface pH of about 0.3 units, at the upper range of model-based estimates of acidification.

Sources & Further reading

  1. Penman, D. E., B. Hönisch, R. E. Zeebe, E. Thomas and J. C. Zachos (2014). "Rapid and sustained surface ocean acidification during the Paleocene-Eocene Thermal Maximum." Paleoceanography 29(5): 2014PA002621.


Author: M. H. Monroe
Last updated 28/01/2015 
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