FROZEN HEAT | Volume 1

Box 1.1 Gas Hydrate and the Deep Sea Drilling Project

The Deep Sea Drilling Project (DSDP) (1968-1983, Legs 1-96) introduced R/V Glomar Challenger, the first international drilling platform for global studies of gas hydrates in the marine environment (Figure TB1.1). Over the course of several DSDP legs, scientists obtained the first tangible proof that gas hydrates exist in a variety of geologic settings, evidence that gas hydrates could be nearly ubiquitous in continental-margin and slope sediment around the world. An objective of DSDP Leg 11 in 1970 was to investigate the nature of the anomalous acoustic reflections (called Bottom Simulating Reflectors or BSRs) that parallel the sea floor. They had been observed on seismic profiles of the passive margin along the Blake Outer Ridge in the Atlantic Ocean. The expedition recovered sediment cores with methane concentrations so high that, in many cases, gas expansion was sufficient to extrude sediment from core liners. Although no obvious gas hydrates were recovered on Leg 11, the high gas concentrations and presence of the BSR were suggestive enough for the R/V Glomar Challenger to return in 1980 (DSDP Leg 76) with an objective of recovering gas hydrates. This objective was met with the recovery and testing of a gas hydrate specimen with a high concentration of methane. A year earlier, in 1979, gas hydrates were recovered in the active margin setting along the landward wall of the Middle America Trench during DSDP Leg 66 off Mexico and Leg 67 off Guatemala. The primary gas from hydrate specimens at both sites was methane, which was confirmed by a massive gas- hydrate specimen recovered in 1983 during Leg 84 near the Leg 66 sites. Although a BSR was present at the Leg 66 hydrate-

recovery sites, the Leg 67 hydrate recoveries were in vitric, or glass-like, sands with no associated BSR.

Yet another hydrate-bearing geologic setting was discovered in 1983, when DSDP Leg 96 recovered gas-hydrate nodules and crystals in Gulf of Mexico mud. Taken together, these sites provided a particularly significant result of the Deep Sea Drilling Project by showing how gas hydrates were present in sediments from a wide range of geologic environments. Extrapolation of these results suggests that gas hydrates are ubiquitous in continental-margin and slope sediment around the world, and this assumption has been confirmed by subsequent investigations.

Figure TB-1.1: The R/V Glomar Challenger (Courtesy of the U.S. Geological Survey).

marine discoveries made in the early 1980s during scientific expeditions by the Deep Sea Drilling Program’s R/V Glomar Challenger (see Text Box 1.1), however, that gas hydrates were recognized as a significant part of the natural environment. It

was soon realized that such a large, and previously unappre- ciated, storehouse of organic carbon and its inherent energy potential could have profound implications for society and our understanding of Earth (Kvenvolden 1988a, b; 2000).

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 13