EVALUATING CARBON ISOTOPE AND REDOX RECORDS OF POLAR ENVIRONMENTAL CHANGE DURING THE EARLY JURASSIC

Our planet is currently undergoing major climatic and environmental changes making it imperative to know how it will continue to evolve into the future. We can leverage the geologic record of similar past events in order to understand and make predictions for how the Earth responds to these events. At the Pliensbachian-Toarcian Stage boundary (~183 Ma) in the Early Jurassic Period there was an episode of global warming caused by initial eruptions of the Karoo Ferrar large igneous province that resulted in large-scale deoxygenation, acidification, and mass extinctions in the oceans.

This research explores the Pliensbachian-Toarcian Boundary at two different locations in the Arctic on the North Slope of Alaska: the Walakpa #1 and South Barrow #3 drill cores. Here we present organic carbon isotopes (δ¹³C_org) to reconstruct changes in the carbon cycle and Fe-speciation data to determine local water column redox. Both localities preserve a negative shift in δ¹³C_org that is found elsewhere and likely reflects the increased atmospheric carbon dioxide sourced from volcanic activity. Fe-speciation data suggest deoxygenated (i.e. anoxic) water columns developed across this time period at both localities. The Walakpa #1 core records a shift to higher pyrite abundance in the reactive iron pool whereas South Barrow maintains consistent pyrite contents. These changes in the relative abundance of pyrite may be reflecting more reducing conditions within the sediment. Our data records clear shifts in δ¹³C_org and marine water column deoxygenation associated with atmospheric warming due to volcanically sourced carbon dioxide.