HR: 0830h
AN: OS51B-0840    [PDF]
TI: Thermal Conductivity of THF Hydrate Between -25 \deg C and +4 \deg C
AU: * Waite, W F
EM: wwaite@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Winters, W J
EM:
AF: U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Mason, D H
EM:
AF: U.S. Geological Survey, 384 Woods Hole Rd., Woods Hole, MA 02543 United States
AB: We observe two temperature dependencies in the thermal conductivity of tetrahydrofuran (THF) hydrate at atmospheric pressure between -25 and +4$\deg$ C. After accounting for 4$ \pm$ 2% H$_{2}$O in our sample, the thermal conductivity of THF hydrate between -25 and -4$\deg$ C rises only 0.2%, from .507 to .508 W/mK. As temperature approaches +4$\deg$ C, thermal conductivity rises nonlinearly to 1.822 W/mK, 350% of its value at -4$\deg$ C. We attribute the rapid thermal conductivity rise to THF hydrate dissociation. Close to its stability temperature of +4$\deg$ C at atmospheric pressure, heat absorption for dissociation dominates heat conduction through the hydrate structure. As a result, heat is transferred to hydrate much more efficiently in this temperature range, increasing the measured thermal conductivity. THF hydrate has been used as a laboratory analog for estimating physical properties of natural methane hydrate, despite differences in the water molecule arrangement and cage occupant species. Because thermal conductivity appears to depend only weakly on these parameters, our THF hydrate results suggest thermal conductivity in methane hydrate should be nearly constant with temperature until the hydrate is within 8$\deg$ C of its stability temperature. Based on a marine geothermal gradient of 25$\deg$ C/km, this 8$\deg$ C range corresponds to the lowest 320 m of the hydrate stability zone. At a local scale, increased heat transfer efficiency in this zone may facilitate heat input schemes for recovering methane as a resource. At regional and global scales, efficient heat transfer to gas hydrates has both geohazard and climate change implications. Along upper continental slopes (400--1000 m water depth) with normal geothermal gradients, the entire hydrate stability zone occupies only the upper 300 to 400 m of the sediment column. In the late Quaternary, these water depths were exposed to warmer bottom water, which could efficiently transfer heat to near surface hydrates. The resulting hydrate dissociation would destabilize the hydrate-bearing sediment, initiating submarine landslides and potentially releasing vast quantities of methane into the atmosphere. This rapid methane transfer, a potent greenhouse gas, from the marine subsurface to the atmosphere provides a rapid response mechanism for tying bottom water warming to observed rapid global warmings in the late Quaternary.
DE: 3022 Marine sediments--processes and transport
DE: 5134 Thermal properties
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting