[B-BG01] 地球惑星科学　生命圏フロンティア

[BBG01-08] The end-Triassic Mass Extinction Event: Insights from compound-specific nitrogen isotopes

*Calum Peter Fox¹、Yuta Isaji¹、Nanako O. Ogawa¹、Jessica H. Whiteside²、Aisha Al Suwaidi³、Naohiko Ohkouchi¹ (1.Japanese Agency for Marine-Earth Science and Technology, Japan、2.San Diego State University, USA、3.Khalifa University of Science and Technology, UAE)

キーワード：Mass Extinction, Triassic, Compound-specific isotopes, Biomarker, Nitrogen

Since complex life emerged 500 million years ago and flourished throughout the Phanerozoic, episodes of massive environmental perturbations have led to five major extinction events that affected many forms of life in terrestrial and marine realms. These events were essential for driving evolution and building the world we see today, however, due to continued anthropogenic activity we find ourselves in the sixth mass extinction event driven by massive increases in atmospheric CO₂. Characterizing previous extinction events, particularly those associated with similar CO₂ increases as observed today, can help us understand how future ecosystems and environments may change and adapt. Massive, pulsed, increases in atmospheric CO₂ on short geological time scales during the end-Triassic mass extinction (that occurred ~201 million years ago) serve as an ancient analogue to the rapid increases in atmospheric CO₂ observed today. A powerful paleo proxy to investigate perturbations to environments, ecologies, and biogeochemical cycles during mass extinction events are biomarkers (molecular-sized fossils from once living organisms) and their isotopic composition. The most often used compound-specific isotopes during mass extinction studies are carbon isotopes. However, investigating other novel isotopes can give further information on shifts in other biogeochemical cycles and the micro-organisms that regulate such cycles.
Since complex life emerged 500 million years ago and flourished throughout the Phanerozoic, episodes of massive environmental perturbations have led to five major extinction events that affected many forms of life in terrestrial and marine realms. These events were essential for driving evolution and building the world we see today, however, due to continued anthropogenic activity we find ourselves in the sixth mass extinction event driven by massive increases in atmospheric CO₂. Characterizing previous extinction events, particularly those associated with similar CO₂ increases as observed today, can help us understand how future ecosystems and environments may change and adapt. Massive, pulsed, increases in atmospheric CO₂ on short geological time scales during the end-Triassic mass extinction (that occurred ~201 million years ago) serve as an ancient analogue to the rapid increases in atmospheric CO₂ observed today. A powerful paleo proxy to investigate perturbations to environments, ecologies, and biogeochemical cycles during mass extinction events are biomarkers (molecular-sized fossils from once living organisms) and their isotopic composition. The most often used compound-specific isotopes during mass extinction studies are carbon isotopes. However, investigating other novel isotopes can give further information on shifts in other biogeochemical cycles and the micro-organisms that regulate such cycles.
We investigated the nitrogen isotopes of porphyrin biomarkers during the end-Triassic mass extinction from a focal locality (St. Audrie’s Bay, UK). Porphyrin compounds preserved in ancient sediments originate exclusively from the chlorophylls in once-living phototrophic eukaryotes and bacteria. We find shifts in the nitrogen isotopic composition of the porphyrin C₃₂ deoxophylloerythroetioporphyrin (DPEP) that can be related to an emergence of microbial mat communities and increases in cyanobacterial activity during perturbations in the bulk organic carbon isotope record and the major period of extinction, respectively. Such a novel approach utilizing compound-specific nitrogen isotopes is severely lacking for the end-Triassic mass extinction but highlights the need for similar investigations at other geographically diverse sections to help tease apart global versus regional differences in compound-specific nitrogen isotopic record.