Direct coupling between carbon release and weathering during the Toarcian oceanic anoxic event.

• Published in: Geology
• Main Authors: Kemp, David B., Selby, David, Izumi, Kentaro
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Geological Society of America 2020
• Subjects: Methane hydrate
• Online Access: http://dro.dur.ac.uk/30977/; http://dro.dur.ac.uk/30977/1/30977.pdf; http://dro.dur.ac.uk/30977/2/30977.pdf; https://doi.org/10.1130/G47509.1

Silicate weathering represents a major feedback mechanism in the Earth’s climate system, helping to stabilize atmospheric CO2 levels and temperature on million-year time scales. On shorter time scales of greater relevance to understanding the fate of anthropogenic CO2, the efficacy and responsiveness of weathering is less clear. Here, we present high-resolution osmium-isotope data that reflect global chemical weathering from a stratigraphically thick record of the early Toarcian oceanic anoxic event (T-OAE; ca. 182 Ma). A pronounced decrease in the carbon-isotope composition of exogenic carbon reservoirs during this event has been linked to the large-scale release of 12C-enriched carbon. Our data indicate that the flux of radiogenic osmium to the oceans increased in lockstep with the decrease in carbon-isotope values, demonstrating a geologically synchronous coupling between massive carbon release and enhanced global continental crust weathering. We show that abrupt shifts in carbon isotopes, previously interpreted as millennial-scale methane hydrate melting or terrestrial carbon-release events, are coeval with rapid increases in weathering. Global weathering may have increased by >40% across each of these intervals of rapid carbon injection. Our results help to reconcile previous estimates of weathering change during the T-OAE, and support the view that, overall, global weathering rates may have increased six-fold through the entire event.