Rapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2

a r t i c l e i n f o Keywords: Large Igneous Province atmospheric carbon dioxide Triassic–Jurassic CO 2 chemical weathering Recent evidence from the ~201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO 2 , followed by a falloff to pre-eruptive concentrations over ~300 kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO 2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO 2 levels for pre-CAMP background of 2000 ±700 ppm (at S(z) = 3000 ± 1000 ppm), increasing to ~5000 ± 1700 ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO 2 to ~4500 ± 1200 ppm, about 240 kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of vol-canism, and revise the main CAMP duration to 840 ± 60 kyr. The Portland also records a post-eruptive decrease in pCO 2 reaching pre-eruptive background concentrations of ~2000 ppm in only ~300 kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO 2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt 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 pCO 2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps. Covering millions of square kilometers of continental area, continental flood basalts are Large Igneous Provinces (LIPs) that may produce in excess of several million cubic kilometers of lava (Coffin and Eldholm, 1993). The great volume and aerial extent of these eruptions , and their intriguing association with mass extinction events throughout earth history (Courtillot and Renne, 2003; Wignall, 2001), has spurred interest in the …