This proposal aims to determine the nature of the environmental perturbation at the end-Triassic mass extinction by comparing lipid biomarker and bulk carbon isotopic records from mid-ocean and more restricted marine rift basins. This extinction, at 201.5 million years ago, is one of the "big five" mass extinctions in Earth history, and is associated with multiple, massive increases in CO2 and global warming linked with eruptive pulses of the voluminous Central Atlantic Magmatic Province basalts. PIs study will be the first to examine in detail a mid-ocean record (Panthalassic basaltic plateau of the Queen Charlotte Islands, Canada) and contrast that with records from shallower sections in restricted marine basins in the United Kingdom that have dominated the discussions of the mass extinction. This proposed analysis is of critical importance for understanding this singular moment in Earth history, as well as unraveling the specific cause and effect mechanisms of extinction events in general, by remedying the dearth of studies that utilize taxonomically and environmentally diagnostic compounds that can test specific hypotheses regarding environmental change and extinction mechanisms. In an effort to support emerging scientists from underrepresented groups, this proposal will support one high school summer intern from School District 50 (encompassing the Queen Charlotte archipelago) to assist with lab work and hone geologic skills. Furthermore, PIs will co-lead a summer field trip for tenth grade students of School District 50, and our discoveries will be incorporated into the science curricula and educational programs for 2nd, 4th, 7th, and 10th grades, exposing science to hundreds of students belonging predominantly (65%) to the Haida Nation and other First Nations tribes, highly underrepresented groups in the sciences. New research will be incorporated into the curricula of Brown University and MIT and will be incorporated into K-12 educational outreach programs at schools local to PI institutions, in which multiple undergraduate and graduate students participate.
The end-Triassic mass extinction (ETE; ~201.4 million years ago) decimated biodiversity in Earth’s marine and terrestrial realms. It is one of the ‘big 5’ mass extinction events recognized in the sedimentary rock record. Previous researchers have speculated the ETE was due to one of the aerially extensive large igneous provinces, the Central Atlantic Magmatic Province, through (1) rapid CO2–driven global warming, (2) changes in ocean circulation, and (3) ocean acidification and ocean deoxygenation. Deoxygenation of ocean waters can alter nutrient inventories and lead to eruptions of toxic hydrogen sulfide into the surface waters. This may favor phytoplankton suited to using different nutrients to those normally found such as ammonium. It can also favor bacteria that employ nitrogen fixation. Existing evidence for such conditions across the ETE have previously come from a limited number of sites in marginal marine basins of the Tethys and Central Atlantic. These sites are characterized by shallower and more restricted circulation conditions that are inherently more sensitive to local or regional climatic perturbations, rather than providing a reliable picture of environmental change in the open ocean. To provide a more robust and globally representative characterization of the environmental changes across the ETE, we generated a ~3 million year long record from Haida Gwaii (formerly Queen Charlotte Islands), British Columbia, Canada. We made a large number of measurements of molecular fossils and isotopic values for carbon and nitrogen. We detected molecules that could only have been made by bacteria that use hydrogen sulfide for photosynthesis. We also found major changes to the distributions of steroids that are diagnostic for particular kinds of algae. Our results provide the first conclusive evidence of shallow water sulfide eruptions and disruption to the biogeochemistry in open waters of the northeastern sector of the main ocean basin of that time, the Panthalassic Ocean. The development of sulfidic surface waters was accompanied by a perturbed nitrogen cycle, ecological turnovers among non-calcifying plankton including algae that normally rely on nitrate. We evidence of enhanced cyanobacterial primary production and an elevated methane cycle. If these conditions developed widely elsewhere at this time, they could be regarded as a potent extinction mechanism for animal life in the ocean. Even though the ETE occurred at a similar time to the Central Atlantic Magmatic Province, additional factors must have been in play to trigger the mass extinction. Increasing atmospheric CO2 by burning of fossil fuels has the potential to not only cause climate warming but also expansion of reduced oxygen zones (aka oxygen minimum zones) of the oceans with consequent ecological disruption. The funding from this award supported several early career female researchers as well as two minority junior investigators and, as such, helps promote women and underrepresented groups in science. Since its completion, two of the junior researchers have gained tenure-track faculty positions and an undergraduate working on the project has begun graduate study in a closely related field.
