Amplifying factors leading to the collapse of primary producers during the Chicxulub impact and Deccan Traps eruptions

The latest Cretaceous (K; Maastrichtian) through earliest Paleogene (Pg; Danian) interval is a time marked by one of five major mass extinctions in the Earth’s history. The synthesis of published data permits the temporal correlation of the K-Pg boundary crisis with two major geological events: 1) the Chicxulub impact discovered in the Yucatán peninsula (Mexico) and 2) the Deccan Traps located on the west-central India plateau. In this paper, environmental and biological consequences from the Chicxulub impact and the Deccan continental flood basalts have been explored using a climate-carbon-biodiversity coupled model called the ECO-GEOCLIM model. The novelty of this study is to investigate how abiotic factors (temperature, pH, and calcite saturation state) act on various marine organisms to determine the primary productivity and biodiversity changes in response to a drastic environmental change. This study shows that the combination of the Deccan volcanism with a 10-km impact led to global warming (3.5°C) caused by rising carbon dioxide (CO2) concentration (+470 ppmv), interrupted by a succession of short-term cooling events, provided by a ‘shielding effect’ due to the formation of sulphate aerosols. The consequences related to these climate changes are the decrease of the surface ocean pH by 0.2 (from 8.0 to 7.8), while the deep ocean pH dropped by 0.4 (from 7.8 to 7.4). Without requiring any additional perturbations, these environmental disturbances led to a drastic decrease of the biomass of calcifying species and their biodiversity by about 80%, while the biodiversity of noncalcifying species was reduced by about 60%. We also suggest that the short-lived acidification caused by the Chicxulub impact, when combined with the Deccan traps, may explain the severity of the extinction among pelagic calcifying species.