The Bighorn Basin Coring Project will collect ~200 meters of core from each of three sites (Polecat Bench, Gilmore Hill, Basin Substation) in the Bighorn Basin of Wyoming to better constrain the causes and effects of Paleogene hyperthermal events. Hyperthermals are abrupt, large-magnitude global warming events associated with extreme perturbations to the Earth's carbon cycle. Two events in particular will be targeted - the Paleocene-Eocene Thermal Maximum (PETM, ETM1) and the Elmo (ETM2) event. The PETM is the best documented hyperthermal and involved the release of 2,000-6,800 gigatons (Gt) of carbon from an unknown reservoir over less than 10 thousand years (ky) causing the earth to warm by 5-9ºC for a period of 100-200 ky. For comparison, the entire fossil fuel resource base on earth today is estimated to be ~5,000 Gt. Elmo is a smaller amplitude event that occurs after the PETM and just below the Chron C24N/C24R polarity reversal in marine records but remains poorly documented in continental sections. By applying a variety of sedimentological, geochemical, and palynological methods to the proposed cores we hope to better understand what caused these events, study the biogeochemical and ecological feedbacks that operated during them, and reveal precisely how they impacted continental environments. The Bighorn Basin preserves the most expanded stratigraphic records of the PETM and Elmo yet known, so these cores will provide an opportunity to study hyperthermals at unprecedented resolution.
This research led to improved understanding of global carbon cycle and climate change at the Paleocene-Eocene boundary, ~55 million years ago, through geochemical study ~1 km of newly obtained drill core from terrestrial sedimentary rocks of the Bighorn Basin (Wyoming). The P-E boundary event has been long studied as a potential analogue for ongoing anthropogenic environmental change, but significant questions have remained unanswered, including: How much carbon was released to the atmosphere and oceans during the P-E event, and how quickly? Where did carbon added to the ocean/atmosphere system during the P-E event come from, and what triggered its release? What were the impacts of the event on storage of carbon in terrestrial ecosystems? The new cores obtained here preserve an exceptional record of terrestrial environmental change through this major event in Earth’s history, and provide research samples that were used to address these questions in the current project and will support a range of future research activities. The Intellectual Merit of this project consisted of significant contributions to understanding the P-E boundary global change event by addressing the questions posed above. New, highly-resolved records of the carbon isotope chemistry of fossil soils preserved in the Bighorn Basin cores revealed that carbon was released at the beginning of the event in two, rapid pulses. The rate of carbon input to the ocean/atmosphere system during these pulses may have approached, but likely did not exceed, current rates of release associated with fossil fuel burning by humans. This suggests that the intensity of carbon cycle change and climate forcing during the P-E event may have been comparable to ongoing and future changes driven by humans. Our discovery of repeated and rapid carbon input during the event cannot in and of itself pinpoint the source and cause of carbon release, but it eliminates several previously proposed ideas that are not consistent with the new observations. Melting of seafloor methane hydrates or generation of methane through igneous intrusion into organic-rich rocks remain among the potential candidate causes for the P-E event carbon releases. Lastly, we showed through a series of studies that organic carbon storage in Bighorn Basin soils decreased dramatically during the P-E warming event, likely due to enhanced seasonal drying of soils, and that the small amount of organic carbon preserved in soils forming during the peak warming was mostly derived from weathering of ancient rocks. Conversely, storage of inorganic (limestone) carbon in these soils increased during the peak of the event. These changes, if widespread across the global land surface, may have constituted a positive feedback on P-E climate change, releasing more carbon to the atmosphere and slowing the climate’s recovery from the event. This pattern is consistent with the results of global carbon cycle modeling work conducted during our project, and would help to explain features of the geologic record of the P-E event that have previously challenged researchers. The Broader Impacts of our research include development of research infrastructure, training of STEM researchers, and contributions to society. The cores and data obtained here are archived through the facilities of the International Ocean Drilling Program, and are freely available to the research community in support of future investigations. In addition, this research was a component of a large, collaborative project in which strong research ties were established between researchers from 7 institutions representing a range of Earth science disciplines, and these organization ties continue to support ongoing and new research. Two students, both women, were employed and trained in geoscience research through the project. Both completed their degree (one MS, one BS) during the course of the project and are currently employed (the MS graduate) or enrolled in graduate school (BS graduate) in the geoscience field. Lastly, the work conducted here directly addressed the question of whether, and in what ways, global change at the P-E boundary could serve as a valuable analogue for ongoing anthropogenic climate change. The results of our work establish the P-E event as a strong analogue, in many senses, providing a wide range of opportunities for scientists and the public to learn from this ancient event about potential changes and challenges that will affect our future. One of our research papers, published shortly after the conclusion of the grant period, made this case and attracted significant media attention, and the PI conducted a number of interviews to communicate the scope and importance of what we can learn from the P-E event and how it might influence research and decision making centered on human-induced global change.
