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Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/Tertiary boundary

James Zachos·M.A. Arthur·Walter E. Dean
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Abstract

The normal, biologically productive ocean is characterized by a gradient of the 13 C/ 12 C ratio from surface to deep waters. Here we present stable isotope data from planktonic and benthic micro-fossils across the Cretaceous/Tertiary boundary in the North pacific, which reveal a rapid and complete breakdown in this biologically mediated gradient. The fluxes of barium (a proxy for organic carbon) and CaCO 3 also decrease significantly at the time of the major marine plankton extinctions. The implied substantial reduction in oceanic primary productivity persisted for ∼ 0.5 Myr before the carbon isotope gradient was gradually re-established. In addition, the stable isotope and preservational data indicate that environmental change, including cooling, began at least 200 kyr before the Cretaceous/Tertiary boundary, and a peak warming of ∼ 3 °C occurred 600 kyr after the boundary event.

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James Zachos, M.A. Arthur, Walter E. Dean. 1989. Geochemical evidence for suppression of pelagic marine productivity at the Cretaceous/Tertiary boundary. https://doi.org/10.1038/337061a0

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