¹W. Rapin,^1,2B. L. Ehlmann,³G. Dromart,⁴J. Schieber,¹N. H. Thomas,¹W. W. Fischer,¹V. K. Fox,¹N. T. Stein,⁵M. Nachon,⁶B. C. Clark,⁷L. C. Kah,⁸L. Thompson,¹H. A. Meyer,⁹T. S. J. Gabriel,⁹C. Hardgrove,¹⁰ N. Mangold,¹¹F. Rivera-Hernandez,¹²R. C. Wiens,¹³A. R. Vasavada
Nature Geoscience 12, 889-895 Link to Article [https://doi.org/10.1038/s41561-019-0458-8]
¹California Institute of Technology, Pasadena, CA, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Laboratoire de Géologie de Lyon, Université de Lyon, Lyon, France
⁴Indiana University, Bloomington, IN, USA
⁵Texas A&M University, College Station, TX, USA
⁶Space Science Institute, Boulder, CO, USA
⁷University of Tennessee, Knoxville, TN, USA
⁸University of New Brunswick, Fredericton, Canada
⁹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
¹⁰Laboratoire de Planétologie et Géodynamique, UMR6112, CNRS,
Université Nantes, Université Angers, Nantes, France
¹¹Dartmouth College, Hanover, NH, USA
¹²Los Alamos National Laboratory, Los Alamos, NM, USA
¹³Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

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^1,2Michael J. Henehan,^3,4Andy Ridgwell,^1,5Ellen Thomas,¹Shuang Zhang,⁶Laia Alegret,⁷Daniela N. Schmidt,⁸James W. B. Rae,^9,10James D. Witts,⁹Neil H. Landman,¹¹Sarah E. Greene,¹²Brian T. Huber,¹James R. Super,¹Noah J. Planavsky,¹Pincelli M. Hull
Proceedings of the National Academy of Sciences of teh United States of America (PNAS) (in Press) Link to to Article [https://doi.org/10.1073/pnas.1905989116]
¹Department of Geology & Geophysics, Yale University, New Haven, CT 06520;
²Section 3.3, Deutsches GeoForschungsZentrum GFZ, 14473 Potsdam, Germany;
³School of Geographical Sciences, Bristol University, Bristol BS8 1SS, United Kingdom;
⁴Department of Earth Sciences, University of California, Riverside, CA 92521;
⁵Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459;
⁶Instituto Universitario de Investigación en Ciencias Ambientales de Aragón, Departamento de Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain;
⁷School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;
⁸School of Earth & Environmental Sciences, University of St. Andrews, St. Andrews KY16 9AL, United Kingdom;
⁹Division of Paleontology, American Museum of Natural History, New York, NY 10024;
¹⁰Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131;
¹¹School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom;
¹²Department of Paleobiology, Smithsonian Institution, Washington, DC 20560

Mass extinction at the Cretaceous–Paleogene (K-Pg) boundary coincides with the Chicxulub bolide impact and also falls within the broader time frame of Deccan trap emplacement. Critically, though, empirical evidence as to how either of these factors could have driven observed extinction patterns and carbon cycle perturbations is still lacking. Here, using boron isotopes in foraminifera, we document a geologically rapid surface-ocean pH drop following the Chicxulub impact, supporting impact-induced ocean acidification as a mechanism for ecological collapse in the marine realm. Subsequently, surface water pH rebounded sharply with the extinction of marine calcifiers and the associated imbalance in the global carbon cycle. Our reconstructed water-column pH gradients, combined with Earth system modeling, indicate that a partial ∼50% reduction in global marine primary productivity is sufficient to explain observed marine carbon isotope patterns at the K-Pg, due to the underlying action of the solubility pump. While primary productivity recovered within a few tens of thousands of years, inefficiency in carbon export to the deep sea lasted much longer. This phased recovery scenario reconciles competing hypotheses previously put forward to explain the K-Pg carbon isotope records, and explains both spatially variable patterns of change in marine productivity across the event and a lack of extinction at the deep sea floor. In sum, we provide insights into the drivers of the last mass extinction, the recovery of marine carbon cycling in a postextinction world, and the way in which marine life imprints its isotopic signal onto the geological record.

¹Yves Marrocchi,¹Johan Villeneuve,²Emmanuel Jacquet,¹Maxime Piralla,³Marc Chaussidon
Proceedings of the National Academy of Sciences of the United States of America (PNAS) (in Press) Link to Article [DOI:https://doi.org/10.1073/pnas.1912479116]
¹Centre de Recherches Pétrographiques et Géochimiques (CRPG), CNRS, Université de Lorraine, UMR 7358, 54501 Vandoeuvre-lès-Nancy, France;
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), CNRS & Muséum national d’Histoire naturelle, UMR 7590, 75005 Paris, France;
³Institut de Physique du Globe de Paris, Université de Paris, CNRS, 75238 Paris, France

Chondritic meteorites are composed of primitive components formed during the evolution of the Solar protoplanetary disk. The oldest of these components formed by condensation, yet little is known about their formation mechanism because of secondary heating processes that erased their primordial signature. Amoeboid Olivine Aggregates (AOAs) have never been melted and underwent minimal thermal annealing, implying they might have retained the conditions under which they condensed. We performed a multiisotope (O, Si, Mg) characterization of AOAs to constrain the conditions under which they condensed and the information they bear on the structure and evolution of the Solar protoplanetary disk. High-precision silicon isotopic measurements of 7 AOAs from weakly metamorphosed carbonaceous chondrites show large, mass-dependent, light Si isotope enrichments (–9‰ < δ³⁰Si < –1‰). Based on physical modeling of condensation within the protoplanetary disk, we attribute these isotopic compositions to the rapid condensation of AOAs over timescales of days to weeks. The same AOAs show slightly positive δ²⁵Mg that suggest that Mg isotopic homogenization occurred during thermal annealing without affecting Si isotopes. Such short condensation times for AOAs are inconsistent with disk transport timescales, indicating that AOAs, and likely other high-temperature condensates, formed during brief localized high-temperature events.