Impact-driven ocean acidification as a mechanism of the Cretaceous-Palaeogene mass extinction

Friday, 19 December 2014
Sohsuke Ohno1, Toshihiko Kadono2, Kosuke Kurosawa1, Taiga Hamura3, Tatsuhiro Sakaiya4, Keisuke Shigemori4, Yoichiro Hironaka4, Takayoshi Sano4, Takeshi Watari4, Kazuto Otani5, Takafumi Matsui1 and Seiji Sugita3, (1)Chiba Institute of Technology, Chiba, Japan, (2)University of Occupational and Environmental Health Japan, Kitakyusyu, Japan, (3)University of Tokyo, Bunkyo-ku, Japan, (4)Osaka University, Osaka, Japan, (5)Institut national de la recherche scientifique, Montreal, Canada
The Cretaceous-Paleogene (K-Pg) mass extinction event at 66 Ma triggered by a meteorite impact is one of the most drastic events in the history of life on the Earth. Many hypotheses have been proposed as killing mechanisms induced by the impact, including global darkness due to high concentrations of atmospheric silicate dust particles, global wildfires, greenhouse warming due to CO2 release, and global acid rain. However, the actual mechanism of extinction remains highly controversial. One of the most important clues for understanding the extinction mechanism is the marine plankton record, which indicates that plankton foraminifera, living in the near-surface ocean, suffered very severe extinction in contrast to the high survival ratio of benthic foraminifera. No proposed extinction mechanism can account for this globally observed marine extinction pattern. Here, we show that SO3-rich impact vapor was released in the K-Pg impact and resulted in the occurrence of global acid rain and sudden severe ocean acidification at the end of the Cretaceous, based on the new results of impact experiments at velocities much higher than previous works (> 10 km/s) and theoretical calculations on aerosol coagulation processes. Sudden severe ocean acidification can account for many of the features of various geologic records at the K?Pg boundary, including severe extinction of plankton foraminifera. This extinction mechanism requires impact degassing of SO3-rich vapor, which is not necessarily found at impact sites other than Chicxulub, suggesting that the degree of mass extinction was controlled greatly by target lithology.