Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic–Jurassic transition

A sharp negative δ13C excursion coincides with the end-Triassic mass extinction. This is followed by a protracted interval of 13C enrichment. These isotopic events occurred simultaneously with the emplacement of the Central Atlantic Magmatic Province (CAMP). Here we use a carbon cycle box model to explore the effects of episodic carbon release – constrained by recently developed high-resolution chronology – on atmospheric pCO2, ocean chemistry and the δ13C of the ocean–atmosphere carbon pool. Our results are consistent with previous modelling efforts in suggesting that the sharp negative δ13C excursion and acidification event associated with the extinction are best explained by the rapid release (<20 ka) of highly 13C-depleted carbon (−70‰). However, our model also indicates that the likely short duration of the excursion requires organic carbon burial to have closely followed carbon injection. The age within the Hettangian of the large positive δ13C excursion which follows is currently uncertain. If early Hettangian in age, then our modelling indicates that the interval of 13C enrichment was closely associated with the volcanic CO2 pulses and pCO2 peaks. If late Hettangian in age, then the 13C enrichment must have lagged the carbon input substantially (by hundreds of thousands of years) and was associated with CO2 drawdown and over-cooling. Our modelling highlights the need for improved age constraints on Hettangian stratigraphic sections in order to test between two distinct and contrasting possibilities: continuing carbon cycle instability due to recurrent perturbations from CAMP activity or a delayed recovery arising from internal biosphere dynamics.

Bachan A. & Payne J. L., 2016. Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic–Jurassic transition. Geological Magazine 153(02):252-270. Article (subscription required).

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