Carbon Cycling During Oceanic Anoxic Event 2: Compound‐Specific Carbon Isotope Evidence From the Western Interior Seaway. Issue 9 (9th September 2021)

• Record Type: Journal Article
• Authors: Boudinot, F. Garrett; Kopf, Sebastian; Dildar, Nadia; Sepúlveda, Julio
• Is Part Of: Paleoceanography and paleoclimatology. Volume 36:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-09
• Subjects: Oceanic Anoxic Event 2 -- carbon isotopes -- lipid biomarkers -- Western Interior Seaway -- carbon cycle -- Smokey Hollow #1 core; Paleoceanography -- Periodicals; Paleoclimatology -- Periodicals; 551.46
• DOI: 10.1029/2021PA004287
• Languages: English
• ISSNs: 2572-4517

Abstract

Abstract: The Cenomanian‐Turonian Oceanic Anoxic Event 2 (OAE2, ∼94 Ma) was a period of widespread ocean deoxygenation and marine organic carbon burial. Increased CO2 and nutrient flux before OAE2 are generally considered the main drivers of ocean anoxia and carbon burial, though some evidence has suggested multiple phases of CO2 input and burial throughout the event. To test hypotheses about the nature of carbon cycle perturbations before and during OAE2, we analyzed stable carbon isotopes in marine‐derived and terrestrial‐derived biomarkers from an expanded sedimentary record of OAE2 from the western margin of the Western Interior Seaway. Biomarker carbon isotope data were used to estimate the concentration and carbon isotopic composition of aqueous and atmospheric CO2, as well as changes in marine productivity, through OAE2. While complicated by biological and environmental uncertainties, our p CO2 reconstructions generally agree with estimates from other locations and proxies around the world. High‐resolution sampling revealed several short‐lived carbon cycle perturbations before and during OAE2 that may reflect fluctuations in the global carbon cycle, including several pulses of isotopically light carbon before OAE2, during the onset of OAE2, and during the Plenus event. This study provides new constraints on carbon cycle dynamics during OAE2 that highlight the complex nature of the event and its causes. Plain Language Summary: Oceanic Anoxic Event 2 (OAE2) was a period of dramatic climate change ∼94 million years ago, characterized by high atmospheric CO2, warm temperatures, and changes in ocean chemistry. While decades of research have identified the climate and ecological impacts of OAE2, there are still questions about how much, and how fast, the carbon cycle changed. We analyzed the carbon chemistry of biomolecules from plants, algae, and bacteria that lived during OAE2, and were preserved in ancient seafloor sediments found in modern‐day Utah. We used our results to estimate important metrics for understanding the carbon cycle during the event, including the composition of carbon in the oceans and atmosphere, and the concentration of atmospheric CO2 . Our results show that there were multiple increases in atmospheric CO2 throughout OAE2. This study paints a more refined picture of how the global carbon cycle was impacted during climate change in Earth's history, which can be used to strengthen our understanding of climate change today and in the future. Key Points: Oceanic Anoxic Event 2 was characterized by multiple carbon cycle perturbations before and during the event The carbon isotopic composition of marine CO2, and p CO2 is estimated using carbon isotopes in carbonate and marine biomarkers The carbon isotopic composition of atmospheric CO2 is estimated using the carbon isotopic composition of terrestrial biomarkers