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Barite accumulation, ocean productivity, and Sr/Ba in barite across the Paleocene–Eocene Thermal Maximum

¹ Institute of Marine Science, University of California–Santa Cruz, Santa Cruz, California 95064, USA
² Intergovernmental Panel on Climate Change, Working Group I Support Unit, 325 Broadway, Boulder, Colorado 80305, USA
³ Environmental Sciences, Mills College, 5000 MacArthur Boulevard, Oakland, California 94613, USA
⁴ Geological and Environmental Science Department, Stanford University, Stanford, California 94305-2115, USA
⁵ Department of Geology & Geophysics, Yale University, P.O. Box 208109, New Haven, Connecticut 06520-8109, USA, and Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut 06459, USA

The Paleocene–Eocene Thermal Maximum (PETM), ca. 55 Ma, was a period of extreme global warming caused by rapid emission of greenhouse gases. It is unknown what ended this episode of greenhouse warming, but high oceanic export productivity over thousands of years (as indicated by high accumulation rates of barium, Ba) may have been a factor in ending this warm period by carbon sequestration. However, Ba has a short oceanic residence time (10 k.y.), so a prolonged global increase in Ba accumulation rates requires an increase in input of Ba to the ocean, increasing barite saturation. We use a novel proxy for barite saturation (Sr/Ba in marine barite) to demonstrate that the seawater saturation state with respect to barite did not change across the PETM. The observations of increased barite burial, no change in saturation, and the short residence time can be reconciled if Ba burial decreased at continental margin and shelf sites due to widespread occurrence of suboxic conditions, leading to Ba release into the water column, combined with increased biological export production at some pelagic sites, resulting in Ba sink reorganization.

Key Words: Paleocene–Eocene Thermal Maximum • barite • paleoproductivity • carbon sequestration