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Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification


The mass extinction event at the Cretaceous/Palaeogene boundary 65.5 Myr ago has been widely attributed to the Chicxulub impact1,2, but the mechanisms of extinction remain debated1,3,4,5,6. In the oceans, near-surface planktonic foraminifera suffered severe declines, in contrast to the relatively high survival rates of bottom-dwelling benthic foraminifera7. The vapour produced by an impact into Chicxulub’s target rocks, which include sulphate-rich anhydrite, could have led to global acid rain, which can explain the pattern of oceanic extinctions4,5. However, it has been suggested that most of the sulphur in the target rocks would have been released as sulphur dioxide and would have stayed in the stratosphere for a long time6. Here we show, from impact experiments into anhydrite at velocities exceeding 10 km s−1, that sulphur trioxide dominates over sulphur dioxide in the resulting vapour cloud. Our experiments suggest that the Chicxulub impact released a huge quantity of sulphur trioxide into the atmosphere, where it would have rapidly combined with water vapour to form sulphuric acid aerosol particles. We also find, using a theoretical model of aerosol coagulation following the Chicxulub impact, that larger silicate particles ejected during the impact efficiently scavenge sulphuric acid aerosol particles and deliver the sulphuric acid to the surface within a few days. The rapid surface deposition of sulphuric acid would cause severe ocean acidification and account for preferential extinction of planktonic over benthic foraminifera.

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Figure 1: Schematic diagram of the experimental set-up.
Figure 2: The SO3/SO2 ratios of impact-induced vapours as a function of impact velocities and peak shock pressures for impacts involving Murchison meteorite and anhydrite, obtained from the mass spectra of vapours using a QMS.
Figure 3: Modelled temporal trends in the oceanic CO32− concentrations at a water depth of 60 m, following the impact.

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The authors thank the GXII technical crew for their support. This research was supported in part by the Japanese Ministry of Education, Science, Sports and Culture (MEXT) and by a joint research project of the Institute of Laser Engineering, Osaka University. This study has been supported by Grant-in-Aid 2424407 and 25120006. The authors also thank late G. Igarashi for discussions during the early phase of this study.

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S.O., T.K., T.M. and S.S. conceived the study and wrote the paper. S.O., T.K., K.K., T.H., T. Sakaiya, K.S., Y.H., T. Sano, T.W., K.O. and S.S. carried out the experimental work using the GXII and analysed the results. S.O. and S.S. created the sweeping out model and carried out the calculations.

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Correspondence to Sohsuke Ohno.

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Ohno, S., Kadono, T., Kurosawa, K. et al. Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification. Nature Geosci 7, 279–282 (2014).

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