Because progress was made toward most of the leg's objectives, Leg 164 has to be viewed as very successful. However, with any large operation there are inevitably a few shortcomings, which we outline here.
Obtaining unequivocal data on the chemical composition of in situ pore-water values is critical for making assessments of gas hydrate composition. Amounts of gas hydrate can be calculated very accurately if the true in situ values are known. Although numerous attempts were made to sample the in situ pore waters using two ODP tools (water sampling temperature probe and the Fisseler Water Sampler), all the samples were seriously contaminated and of little or no value.
Site 994 was located less than a kilometer to the south of an area that displays a well-developed BSR. The site was intended as a background site. However, Site 994 was very similar to Sites 995 and 997, and contained similar amounts of gas and gas hydrate. However, the lack of a BSR is believed to indicate that there was insufficient gas to saturate the pore waters immediately beneath the base of the gas hydrate stability zone at Site 994. Whereas Site 994 provided very important information concerning the nature of the BSR and gas hydrate distribution, it does not serve as a gas-hydrate-free reference site.
Direct measurements of the amounts of gas and gas hydrate(?) that occur within the upper 200 m of the seafloor were not obtained. Thus, a major ambiguity exists about the nature of the top of the gas hydrate-bearing zone. Unfortunately, appropriate techniques to make these measurements have yet to be developed.
Leg 164 was designed to make a static description of a gas hydrate deposit. However, it is increasingly clear that these are dynamic reservoirs. Establishing the rates at which these deposits evolve is a major challenge for future gas hydrate researchers.