CO2 pulses and carbonate and biotic crises in the mesozoic

The Mesozoic is characterized by a number of rapid changes in the mode of global carbon cycling documented as positive excursions in the marine and terrestrial carbon isotope record. Several of these large perturbations are preceeded by a negative carbon isotope spike and they are accompanied by major biotic crises and/or extinction events. Many of these events have been related to massive CO2 inputs to the ocean and atmosphere related to the emplacement of Large Igneous Provinces. The biosphere was affected by massive C-cycle perturbations to a variable degree.
Contrasting response of the biosphere is observed if two of the most extreme C-cycle perturbations in the Mesozoic, the Triassic-Jurassic (T-J) Boundary Event and the Oceanic Anoxic Event 1a (OAE1a) in the Cretaceous are compared. The Triassic-Jurassic boundary C-isotope anomaly is coupled with a major biotic extinction event while the Early Aptian Cisotope excursion coincides with widespread biocalcification crises in neritic and pelagic environments but with no major extinction. New stratigraphic data at high resolution (104 years) from a pelagic T-J boundary section from the Budva Basin in Montenegro allow for the first time to document the sudden termination of carbonate deposition in a pelagic environment, coinciding with the T-J extinction event. A very high-resolution study of OAE1a indicates that the short-lived negative carbon isotope excursion coincides with a biocalcification crisis in nannoconids, which is synchronous to the increase in volcanism-induced pCO2 as revealed by compound-specifc carbon isotope analyses. We propose that ocean acidification following a massive carbon release to the atmosphere and ocean triggered both observed carbonate crises. Differing oceanographic boundary conditions and tempo of perturbation may explain contrasting response of end-Triassic and of Aptian biota to volcanic CO2 pulses.

Bernasconi S, Črne A, Méhay S, Keller C, Hochuli P, Erba E & Weissert H, 2009. CO2 pulses and carbonate and biotic crises in the mesozoic. Awards Ceremony Speeches and Abstracts of the 19th Annual V.M. Goldschmidt Conference, V.M. Goldschmidt Conference. Geochimica et Cosmochimica Acta 73(13)-1: A113. Supplement.

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