Edward T. Peltzer
Monterey Bay Aquarium Research Institute
Moss Landing, California, USA
Journal of Geophysical Research (2001) 106: 26,413-26,423.
24 May 2000.
Revised: 27 April 2001.
Accepted: 14 May 2001.
Published: 10 November 2001.
We investigate the response of a methane hydrate layer in marine sediments to cyclic seafloor perturbations of temperature and pressure in order to determine the change in seafloor methane flux resulting from gas hydrate dissociation or accumulation. By using a one-dimensional model describing mass, energy, and methane transport through porous sediments, we show that seafloor pressure changes have negligible effect on methane transport to the seafloor. The effect of seafloor temperature perturbations is more pronounced than that of pressure. With an initial seafloor temperature of 3°C, which corresponds to current conditions on Earth, a + 4°C temperature perturbation occurring over 104 years does not significantly affect methane transport. Thus such a perturbation is not likely to have a significant impact on the current global climate or to give rise to an event such as the del13C excursion during the late Paleocene thermal maximum (LPTM). If the initial seafloor temperature is assumed to be 11°C, which corresponds to the conditions of the late Paleocene, a + 4°C temperature perturbation over a period of 104 years could result in complete dissociation of methane hydrate layers situated at water depths areound 1200m. In this case, the calculations show that the change in methane flux might be able to explain the del13C excursion of marine carbonate fossils during the LPTM. This result is weakened because the simplifications in the model tend to yield overestimates of the change in methane flux. The principal point is that strong coupling between methane transport and seafloor temperature occurs because significant hydrate accumulation and dissociation take place near the seafloor only when the seafloor temperature is relatively high. This was the case during the late Paleocene, but is not the case at present.
The authors wish to thank reviewers Keith Kvenvolden and Bruse Buffet and the Associate Editor Earl Davis for their comments on the original version of this manuscript. The paper has greatly improved as a result. This work was supported in part by NSF grant OCE-9730846.