Abstract
The impact of an asteroid at the end of the Cretaceous caused mass extinctions in the oceans. A rapid collapse in surface to deep-ocean carbon isotope gradients suggests that transfer of organic matter to the deep sea via the biological pump was severely perturbed. However, this view has been challenged by the survival of deep-sea benthic organisms dependent on surface-derived food and uncertainties regarding isotopic fractionation in planktic foraminifera used as tracers. Here we present new stable carbon (δ13C) and oxygen (δ18O) isotope data measured on carefully selected planktic and benthic foraminifera from an orbitally dated deep-sea sequence in the southeast Atlantic. Our approach uniquely combines δ18O evidence for habitat depth of foraminiferal tracer species with species-specific δ13C eco-adjustments, and compares isotopic patterns with corresponding benthic assemblage data. Our results show that changes in ocean circulation and foraminiferal vital effects contribute to but cannot explain all of the observed collapse in surface to deep-ocean foraminiferal δ13C gradient. We conclude that the biological pump was weakened as a consequence of marine extinctions, but less severely and for a shorter duration (maximum of 1.77 m.y.) than has previously been suggested.
Highlights
The Cretaceous-Paleogene (K-Pg, 66.02 Ma) boundary is defined by a major mass extinction of terrestrial and marine life (Schulte et al, 2010)
Stable isotope results were calibrated to the Vienna Peedee belemnite (VPDB) scale by international standard NBS19 and analytical precision was better than ±0.05‰ for d18O and ±0.03‰ for d13C
The selection of species was guided by previous work on early Paleo cene planktic foraminifera isotopic depth ecologies (Birch et al, 2012) (Fig. 1): thermocline dwellers—Subbotina trivalis to S. triloculinoides; mixed-layer dwellers—Praemurica taurica to Pr
Summary
The Cretaceous-Paleogene (K-Pg, 66.02 Ma) boundary is defined by a major mass extinction of terrestrial and marine life (Schulte et al, 2010). Analyzing isotopic patterns across this extinction event using depth-stratified foraminifera has special challenges: (1) the planktic foraminifera used as dissolved inorganic carbon (DIC) tracers are mostly lost to extinction (>90% taxonomic loss of Smit, 1982), such that no continuous single-species planktic d13C record crossing the K-Pg boundary has been generated; (2) the new species that evolved in the aftermath are typically small and have strong d13C vital effects resulting in test calcite that deviates from the DIC d13C (Alegret and Thomas, 2009); and (3) there may have been changes in ocean circulation patterns across the K-Pg boundary (Alegret and Thomas, 2009; Hull and Norris, 2011; MacLeod et al, 2011), which could have affected the foraminiferal d13C signal. A comparison of our data with benthic assemblage records for the first time reveals commonalities between proxy observations that help harmonize perspectives on the pelagic ecosystem response
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
