Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic

Highlights

  • Conodont δ44/40Ca curve is established for the latest Permian to Middle Triassic.
  • Three episodes of decreasing δ44/40Ca (0.16–0.23‰) occurred in the Early Triassic.
  • Negative δ44/40Ca shift in the PTB suggests a CO2-driven ocean acidification event.
  • Negative δ44/40Ca shifts in SSB & OAB suggest upwelling-driven shelf acidification.

Abstract

The marine calcium (Ca) cycle is controlled by rates of continental weathering, seawater pH, and carbonate deposition on the seafloor and is linked to atmospheric CO2, climate change, and marine biotic evolution. Here, we provide the first continuous seawater Ca isotope profile from conodont apatite in South China for the latest Permian to early Middle Triassic, revealing major fluctuations in the Early Triassic calcium cycle. Three episodes of decreasing conodont δ44/40Ca (by 0.16–0.23‰) occurred around the Permian-Triassic, Smithian-Spathian, and Olenekian-Anisian boundaries. The first episode, coincident with a negative excursion of carbonate carbon isotopes, global warming, oceanic anoxia, enhanced weathering, and sea-level fall, was likely caused by a combination of volcanic CO2 release, ocean acidification, a reduced skeletal carbonate sink, and enhanced weathering of shelf carbonates. The latter two episodes, coincident with positive excursions of carbon isotopes, global cooling, and oceanic anoxia, possibly resulted from upwelling-driven shelf acidification and reduced skeletal carbonate burial. All three events were associated with marine biotic diversity losses, demonstrating a link between the calcium cycle and mass extinctions.

Song Ha., Song Hu., Tong J., Gordon G. W., Wignall P. B., Tian L., Zheng W., Algeo T. J., Liang L., Bai R., Wu K. & Anbar A. D., in press. Conodont calcium isotopic evidence for multiple shelf acidification events during the early Triassic. Chemical Geology. Article (subscription required).
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