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An asteroid impact in the Yucatán Peninsula set off a sequence of events that led to the Cretaceous–Paleogene (K–Pg) mass extinction of 76% species, including the nonavian dinosaurs. The impact hit a carbonate platform and released sulfate aerosols and dust into Earth’s upper atmosphere, which cooled and darkened the planet—a scenario known as an impact winter. Organic burn markers are observed in K–Pg boundary records globally, but their source is debated. If some were derived from sedimentary carbon, and not solely wildfires, it implies soot from the target rock also contributed to the impact winter. Characteristics of polycyclic aromatic hydrocarbons (PAHs) in the Chicxulub crater sediments and at two deep ocean sites indicate a fossil carbon source that experienced rapid heating, consistent with organic matter ejected during the formation of the crater. Furthermore, PAH size distributions proximal and distal to the crater indicate the ejected carbon was dispersed globally by atmospheric processes. Molecular and charcoal evidence indicates wildfires were also present but more delayed and protracted and likely played a less acute role in biotic extinctions than previously suggested. Based on stratigraphy near the crater, between 7.5 × 10¹⁴and 2.5 × 10¹⁵g of black carbon was released from the target and ejected into the atmosphere, where it circulated the globe within a few hours. This carbon, together with sulfate aerosols and dust, initiated an impact winter and global darkening that curtailed photosynthesis and is widely considered to have caused the K–Pg mass extinction. 

Abstract The Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ¹³C) ofn‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ¹³C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chainn‐alkanes (nC₁₉; marine algae/bacteria) with a ∼−5‰ CIE in long‐chainn‐alkanes (nC₂₉andnC₃₁; plant waxes) during the peak of the PETM. Although δ¹³C_n‐alkanesvalues were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ¹³C_n‐alkanesremain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ¹³C_TOCrecords. The CIE magnitude of both δ¹³C_n‐C19and δ¹³C_n‐C29can be explained by the elevated influence of¹³C‐depleted respired CO₂in the water column and increased water availability on land, elevatedpCO₂in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ¹³C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossiln‐alkanes in the Arctic region.