Permafrost-Associated Gas Hydrate

Abstract

Gas hydrate in onshore arctic environments is typically closely associated with permafrost. It is generally believed that thermal conditions conducive to the formation of permafrost and gas hydrate have persisted in the Arctic since the end of the Pliocene (about 1.88 Ma). Maps of present day permafrost reveal that about 20 percent of the land area of the northern hemisphere is underlain by permafrost (Fig. 1). Geologic studies (MacKay, 1972; Lewellen, 1973; Molochushkin, 1978) and thermal modeling of subsea conditions (Osterkamp and Fej, 1993) also indicate that permafrost and gas hydrate may exist within the continental shelf of the Arctic Ocean. Subaerial emergence of portions of the Arctic continental shelf to current water depths of 120 m (Bard and Fairbanks, 1990) during repeated Pleistocene glaciations, subjected the exposed shelf to temperature conditions favorable to the formation of permafrost and gas hydrate. Thus, it is speculated that “relic” permafrost and gas hydrate may exist on the continental shelf of the Arctic Ocean to present water depths of 120 m. In practical terms, onshore and nearshore gas hydrate can only exist in close association with permafrost, therefore, the map in Figure 1 that depicts the distribution of onshore continuous permafrost and the potential extent of “relic” sub-sea permafrost also depicts the potential limit of onshore and nearshore gas hydrate.