Numerical evaluation of mechanisms driving Early Jurassic changes in global carbon cycling

The Early Jurassic (early Toarcian, ca. 183 Ma) carbon cycle perturbation is characterized by an similar to-5 parts per thousand delta C-13 excursion in the exogenic carbon reservoirs, a 1000 ppm rise in atmospheric CO2, and a 6-7 degrees warming. Two proposed explanations for this presumed global carbon cycle perturbation are the liberation of massive amounts of isotopically light CH4 from (1) Gondwanan coals by heating during the intrusive eruption of the Karoo-Ferrar large igneous province (LIP) or (2) the thermal dissociation of gas hydrates. Carbon cycle modeling indicates that the release of CH4 from Gondwanan coals synchronous with the eruption of the Karoo-Ferrar LIP fails to reproduce the magnitude or timing of the CO2 and delta C-13 excursions. However, sensitivity analyses constrained by a marine cyclostratigraphically dated delta C-13 record indicate that both features of geologic record can be explained with the huge input of similar to 15,340-24,750 Gt C over similar to 220 k.y., a result possibly pointing to the involvement of hydrothermal vent complexes in the Karoo Basin. The simulated release of > 6000 Gt C from gas hydrates also reproduces aspects of the early Toarcian rock record, but the large mass involved raises fundamental questions about its formation, storage, and release.