Postimpact earliest Paleogene warming shown by fish debris oxygen isotopes (El Kef, Tunisia)

Abstract

Greenhouse warming is a predicted consequence of the Chicxulub impact, but supporting data are sparse. This shortcoming compromises understanding of the impact's effects, and it has persisted due to an absence of sections that both contain suitable material for traditional carbonate- or organic-based paleothermometry and are complete and expanded enough to resolve changes on short time scales. We address the problem by analyzing the oxygen isotopic composition of fish debris, phosphatic microfossils that are relatively resistant to diagenetic alteration, from the Global Stratotype Section and Point for the Cretaceous/Paleogene boundary at El Kef, Tunisia. We report an ~1 per mil decrease in oxygen isotopic values (~5°C warming) beginning at the boundary and spanning ~300 centimeters of section (~100,000 years). The pattern found matches expectations for impact-initiated greenhouse warming.

No Evidence for a Large Atmospheric CO2 Spike Across the Cretaceous‐Paleogene Boundary

“…If we assume an Earth system sensitivity of 3°C or higher per CO 2 doubling (Royer, 2016), these records imply-at most-one CO 2 doubling. One exception is a~5°C warming within~100,000 years after the K-Pg boundary at the global stratotype El Kef, Tunisia (~20°N paleolatitude; MacLeod et al, 2018). This subtropical temperature record appears incompatible with our record, suggesting that either CO 2 directly before the K-Pg boundary was substantially lower (<400 ppm) than what our and most other reconstructions imply (Zhang et al, 2018; see also Figure S17) or local changes in ocean chemistry biased the temperature estimates.…”

“…After a brief "impact winter" (months to decades; Bardeen et al, 2017;Brugger et al, 2017;Taylor et al, 2018;Vellekoop et al, 2014Vellekoop et al, , 2015Vellekoop et al, , 2016, temperatures increased between~1 and 6°C depending on paleolatitude and geographic location, with the largest increases often at higher paleolatitudes (MacLeod et al, 2018;Taylor et al, 2018;Vellekoop et al, 2014;Zhang et al, 2018). After a brief "impact winter" (months to decades; Bardeen et al, 2017;Brugger et al, 2017;Taylor et al, 2018;Vellekoop et al, 2014Vellekoop et al, , 2015Vellekoop et al, , 2016, temperatures increased between~1 and 6°C depending on paleolatitude and geographic location, with the largest increases often at higher paleolatitudes (MacLeod et al, 2018;Taylor et al, 2018;Vellekoop et al, 2014;Zhang et al, 2018).…”

“…Among marine records and most relevant to our study, Taylor et al (2018) document a 2.5-4°C warming during the fern spike interval in the southern midlatitudes (present-day New Zealand). One exception is a~5°C warming within~100,000 years after the K-Pg boundary at the global stratotype El Kef, Tunisia (~20°N paleolatitude; MacLeod et al, 2018). If we assume an Earth system sensitivity of 3°C or higher per CO 2 doubling (Royer, 2016), these records imply-at most-one CO 2 doubling.…”

“…Temperature records spanning the first 10 2 -10 3 years after the K-Pg boundary are sparse, but most modeling and high-resolution marine data are not consistent with a large change in CO 2 . After a brief "impact winter" (months to decades; Bardeen et al, 2017;Brugger et al, 2017;Taylor et al, 2018;Vellekoop et al, 2014Vellekoop et al, , 2015Vellekoop et al, , 2016, temperatures increased between~1 and 6°C depending on paleolatitude and geographic location, with the largest increases often at higher paleolatitudes (MacLeod et al, 2018;Taylor et al, 2018;Vellekoop et al, 2014;Zhang et al, 2018). Terrestrial temperature trends inferred from leaf fossils are somewhat ambiguous and model dependent (Upchurch et al, 2007).…”

Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure

“…The effects of impact cratering have long been recognised as drivers of climate change 2,53 . Many studies have described the atmospheric effects of the end-Cretaceous Chicxulub impact structure in Mexico 49,54,55 , which resulted in global cooling of oceans and production of widespread acidic rains 56,57 . While the Yarrabubba structure dated at 2229 ± 5 Ma represents the Earth's oldest dated impact crater, its coincidence with termination of Palaeoproterozoic glacial conditions prompts further consideration of the ability of meteorite impacts to trigger climate change.…”