A blast of gas in the latest Paleocene: Simulating first-order effects of massive dissociation of oceanic methane hydrate

Carbonate and organic matter deposited during the latest Paleocene thermal maximum is characterized by a remarkable ‐2.5‰ excursion in δ 13 C that occurred over ~10 4 yr and returned to near initial values in an exponential pattern over ~2 〈 10 5 yr. It has been hypothesized that this excursion signifies transfer of 1.4 to 2.8 〈 10 18 g of CH 4 from oceanic hydrates to the combined ocean-atmosphere inorganic carbon reservoir. A scenario with 1.12 〈 10 18 g of CH 4 is numerically simulated here within the framework of the present-day global carbon cycle to test the plausibility of the hypothesis. We find that (1) the δ 13 C of the deep ocean, shallow ocean, and atmosphere decreases by ‐2.3‰ over 10 4 yr and returns to initial values in an exponential pattern over ~2 〈 10 5 yr; (2) the depth of the lysocline shoals by up to 400 m over 10 4 yr, and this rise is most pronounced in one ocean region; and (3) global surface temperature increases by ~2 °C over 10 4 yr and returns to initial values over ~2 〈 10 6 yr. The first effect is quantitatively consistent with the geologic record; the latter two effects are qualitatively consistent with observations. Thus, significant CH 4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum. This conclusion is of broad interest because the flux of CH 4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present-day anthropogenic CH 4 sources.