T80 Global Change: Evolution and Extinctions in the Triassic

Monday, 5 November 2018
8:00 AM - 12:00 PM
Room 136-137

CALCIUM ISOTOPE EVIDENCE OF AN EPISODE OF OCEAN ACIDIFICATION ACROSS THE SMITHIAN-SPATHIAN BOUNDARY

Paper number: T80-8
Program: Technical Sessions
Time: 9:55 AM – 10:10 AM

Authors

Abstract

The Smithian-Spathian boundary (SSB) transition was an interval characterized by a major global carbon cycle perturbation, climatic cooling from a late Smithian hyperthermal condition, and a major setback in the recovery of marine biotas from the end-Permian mass extinction. Previous studies have provided evidence that these events were interconnected. The marine Ca cycle is closely related to marine alkalinity and atmospheric CO2, playing an important role in the Earth’s climate system. The Ca isotopic composition (δ44/40Ca) of seawater provides a proxy for changes in the global Ca cycle. Here, to explore perturbations to the global marine Ca cycle across the SSB, we generated a high-resolution Ca isotope profile from the upper Smithian to the lower Spathian of Jiarong section (South China). Our δ44/40Ca profile shows a negative shift from ~+1.0 ‰ in the early late Smithian to ~+0.5 ‰ at the SSB, followed by a positive shift to ~+1.1 ‰ in the early Spathian. Traditional carbonate diagenetic indicators suggest that our Ca isotope record was not systematically altered by post-depositional diagenesis. We thus interpret these δ44/40Ca trends as secular variations in the Ca isotopic composition of Early Triassic global seawater. Using a simple Ca isotope mass balance model, we infer a rapid increase in seawater Ca2+ concentrations during the late Smithian, coincident with the Smithian Thermal Maximum, and a subsequent decrease in Ca2+ concentrations across the SSB that was coincident with climatic cooling. This pattern may reflect an episode of ocean acidification that contributed to end-Smithian marine biodiversity losses. Our study highlights the potential influence of paleo-ocean acidification events on marine organisms and communities.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321794

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