Ph.D. candidate Morgan Schaller presented his thesis Large Igneous Provinces and Earth's Carbon Cycle: Lessons from the Late Triassic and Rapidly Emplaced Central Atlantic Magmatic Province (11/21/2011). Morgan defended his thesis with flying colors and his committee commented on the completion of a superb dissertation. Morgan will be in short, filing his dissertation with the graduate school. Congratulations Morgan, job well done!
Using stable isotopes of soil carbonates, I demonstrate that the eruption of the Central Atlantic Magmatic Province (CAMP) resulted in a transient perturbation of atmospheric pCO2 in the Late Triassic. I show evidence of a discrete pCO2 pulse (roughly a doubling) immediately after the first CAMP flow-unit preserved in the Newark rift basin, followed by a ~200 kyr falloff toward pre-eruptive concentrations, a pattern repeated above the second and third flow-units. Observations from the Hartford basin indicate that pCO2 had fallen to concentrations well below background by 400 kyr after the final eruptions in the earliest Jurassic. I use a simple geochemical model to demonstrate that this decrease below pre-eruptive background is most easily accomplished by the extrusion of ~1.12 x 107 km2 of basalt into the equatorial humid belt, which effectively amplified the increase in global continental weathering rate by perhaps as much as 50%. These results indicate that LIPs can be overall net sinks for CO2. A test of the Late Triassic equilibrium state from a 33-My record of pCO2, broadly shows a ~3-fold decrease in pCO2 from the Carnian through the Rhaetian. This decrease is most consistent with the hypothesis that a Late-Triassic increase in continental area within the tropical humid belt, as a result of the slow northward migration of the Pangean Supercontinent, lead to increased rates of continental weathering and CO2 consumption. A significant implication of this finding is that changes in degassing rates from variable ocean crust production are not driving this long-term decrease in pCO2 since crustal production rates show little variability through the Late Triassic. Together the results of this work lay the foundation for a revision of our understanding regarding the driving mechanisms behind Earth’s long-term carbon cycle toward a greater emphasis on weathering processes.