Carbon system recovery and planktonic foraminifera ecology after the end Cretaceous mass extinction Seminar

Abstract

The end Cretaceous mass extinction profoundly affected the marine ecosystem. Surface-to-deep-ocean carbon isotope (δ13C) gradients and carbonate accumulation records suggest that pelagic extinctions coincided with a breakdown in marine biological pumping, which was followed by a long (3Myr) delay in recovery, but the apparent lack of response by benthic foraminifera has questioned the extent of this perturbation. Existing reconstructions of K/Pg carbon pumping are based on the difference between δ13C in the calcitic tests of benthic and surface living foraminifera. One problem with this however, is our limited understanding of δ13C disequilibrium effects in fast evolving early Paleocene planktonic foraminifera that diversified rapidly after decimation (~90% extinction) of late Cretaceous stocks at the K/Pg. Positive or negative δ13C disequilibrium effects that are a known feature of fossil and planktonic foraminifera could significantly over or underestimate the measured planktonic-benthic δ13C gradient.
 
To help address this problem we present new multispecies foraminiferal stable isotope data size trends from ODP Site 1262. Our results suggest that all small specimens <150 mm, which includes typical post-K/Pg Danian opportunists and extinction survivors, as well as small/ pre-adult forms of other species, likely underestimate water column DIC δ13C by 0.3-0.5‰ because of a pronounced metabolic vital effect. Our results also lend support to the hypothesis that foraminiferal photosymbiosis evolved in the Praemurica lineage but the new data provide further constraints on the timing of development of this ecology, which is associated with a positive disequilibrium δ13C effect, pin-pointing its appearance to the Pr. pseudoinconstans - Pr. inconstans morphogroup by 63.5Ma. All photosymbiotic species should, therefore, be expected to have artificially enriched δ13C (by up to 1.0‰), especially species above 200mm. By applying these new constraints to our down core records we are able to produce revised estimates of K/Pg changes in surface-to-deep δ13C gradients and carbon cycling.

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This talk is open to all staff and students in NOCS.

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