Temperature [C

Figure 8. Temperature and pressure conditions for DSDP Site 995 on the Blake Ridge. Equilibrium stability conditions were calculated with Multiflash (—); the thermal gradients of 32.7°C/km (—-)and 38.6°C/km (--) are from Ruppel (1997) and the Initial Reports from ODP Leg 164.

BSR since there are no guarantees that the geothermal gradients must remain constant. Indeed, given that the BSR may coincide with a phase change, we should expect to find, at the very least, a change in the geothermal gradient in the region of the BSR. At the same time, given the effects that we saw earlier (Fig. 6), the importance of in situ measurements of the pore-water salinity, gas composition and pressure regarding predictions of the P-T stability conditions at this site can not be over-stated. Only then can we determine whether sufficient methane is present in the pore-spaces to achieve saturation relative to methane hydrate solubility (Xu and Ruppel, 1999). At present, the conundrum exists because of conflicts among extrapolations, not in situ observations; and it is only through additional observations that the solution to the riddle will be found.

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