ATMOSPHERIC CO2 RESPONSE TO RAPID ERUPTION OF THE CENTRAL ATLANTIC MAGMATIC PROVINCE

Recent evidence from the ~201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark Rift Basin demonstrates that this Large Igneous Province (LIP) produced a transient doubling of atmospheric pCO₂, followed by a ~300 kyr falloff to near pre-eruptive concentrations after each major episode of eruption (Schaller, Wright and Kent; Science, 2011). Here we use pedogenic carbonates to test the million-year effects of the CAMP volcanism on Early Jurassic pCO₂ in the corollary Hartford Basin of Eastern North America. In both basins we find a pre-CAMP pCO₂ background of ~2000 ± 700 ppm, increasing to ~4500 ± 1600 ppm immediately above the first flow unit, followed by 300 kyr post-extrusive decrease to near background concentrations. The longer post-extrusive section of the Hartford Basin shows the same ~300 kyr pCO₂ decrease to pre-eruptive background, and continues to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. We use a geochemical model to demonstrate that the rapidity of the pCO₂ decreases, and the fall to concentrations below background may be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the more highly weatherable CAMP basalts themselves. The effectiveness of this CO₂ sink is attributed specifically to the emplacement of fresh CAMP silicates straddling the equatorial humid belt where they may weather at a rate 10-times greater than the continental crust they cover. This indicates that continental flood basalts capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO₂ to concentrations below pre-eruptive levels.