Hydrocode simulation of the Chicxulub impact event and the production of climatically active gases

Abstract

Abstract. We constructed a numerical model of the Chicxulub impact event using the Chart-D Squared (CSQ) code coupled with the ANalytic Equation Of State (ANEOS) package. In the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact-related extinction hypothesis: carbonates (calcite) and evaporites (anhydrite). Simulations explored the effects of different projectile sizes (10 to 30 km in diameter) and porosity (0 to 50%). The effect of impact speed is addressed by doing simulations of asteroid impacts (v•=20 km/s) and comet impacts (¾i=50 km/s). The masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event, ranging from 3 50 to 3 500 Gt for CO2, from 40 to 560 Gt for S, and from 200 to 1400 Gt for water vapor. While our results are in good agreement with those of Ivanov et al. [1996], our estimated CO2 production is 1 to 2 orders of magnitude lower than the results of Takata and Ahrens [1994], indicating that the impact event enhanced the end-Cretaceous atmospheric CO2 inventory by, at most, 40%. Consequently, sulfur may have been the most important climatically active gas injected into the stratosphere. The amount of S released by the impact is several orders of magnitude higher than any known volcanic eruption and, with H20, is high enough to produce a sudden and significant perturbation of Earth's climate.

Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary

“…The initial cooling was followed by a long-term warming trend (41), also observed in our TEX 86 record (Fig. 2) and in previously reported stable isotope analyses (43), that most likely is associated with greenhouse gasses released into the atmosphere from the vaporization of carbonate target rock, the mass mortality, and forest fires (6,8,10,41). Our study reveals a combination of environmental and climatological events that is compatible with the pattern of extinction of many biological clades, including most species of planktic foraminifera and many coccolithophorids but also larger marine taxa like ammonites and marine reptiles, in addition to the dinosaurs and flying reptiles (1, 2, 16).…”

“…This included asteroid-derived trace elements, globally recognized as a peak in platinum group element (PGE; including iridium) concentrations in complete marine and terrestrial successions (14). Crucially, fossil evidence for this impact winter scenario is still missing because this period of reduced solar radiation may only have lasted several months to decades (8,10,15,16), generally too short to be captured in the ancient sedimentary record. In case of the K-Pg boundary this is even more complicated because the traditional proxy carriers for the surface ocean conditions, calcareous microfossils, experienced major extinction (17).…”

“…Impact models suggest that the first hours after the impact were characterized by earthquakes and tsunamis and the so-called "fireball stage," including an intense heat pulse resulting from the return flux of larger ejecta, in turn resulting in global wildfires (7). Next, the dust and sulfur aerosols, originating from the anhydrite target rocks, are predicted to have partially blocked incoming solar radiation, leading to an "impact winter" (8,9), potentially further amplified by soot derived from burning of fossil organic matter in targeted sediments, a strong absorber of short-wave radiation (10). This dark phase is proposed to have temporarily inhibited photosynthesis, causing a global collapse of terrestrial and marine food webs (5,6).…”

Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub

“…An oblique impact would have been much more damaging than a sub-vertical one because the shock wave would be more focused within the near-surface, volatile-rich, sedimentary rocks, and this would cause the release of higher volumes of climatically active carbon-and sulfur-rich gasses. [17][18][19]. The impact size and target chemistry are now reasonably well constrained [e.g.…”

“…The impact would have released dust and climatically active gasses into the atmosphere, and caused a period of extreme temperature change and darkness, but calculations of the nature, extent and duration of these changes differ [e.g. [14][15][16][17]. Estimates of climatic effects are dependent, in part, upon knowledge of the energy of impact, the chemistry of the target rocks, and the obliquity of impact.…”