Carbon isotope records across the Latest Palaeocene Thermal Maximum (LPTM) display by a remarkable delta 13 C excursion of at least -2.5 per mil that occurred within 10X10 3 yrs. Thermal dissociation of marine gas hydrate and release of massive quantities of CH 4 to the exogenic carbon cycle appears to be the only plausible explanation for this geochemical perturbation. Three numerical simulations of the scenario are compared here. Each simulation involved release of 1.12X10 18 g of CH 4 over 10X10 3 yrs into the pre-industrial steady-state exogenic carbon cycle. The only difference between the simulations is whether CH 4 was oxidized in the atmosphere, deep Atlantic Ocean, or deep Pacific Ocean. Important conclusions from this work are that massive CH 4 release into any carbon reservoir will cause a negative delta 13 C excursion, increased atmosphere pCO 2 , elevated global surface temperature, and pelagic carbonate dissolution, but that the timing and magnitude of these responses depends on the location of CH 4 oxidation. Oxygen deficiency must also occur if significant quantities of CH 4 are oxidized in an ocean reservoir. Release and oxidation of massive quantities of CH 4 in the deep Atlantic Ocean is consistent with several observations from the geological record across the LPTM. However key data sets and additional modeling are needed before geochemical perturbations during this extraordinary time interval can be well understood.

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