Figure 2. A. Downcore in situ gas quantities at Sites 995 (circles) and 997 (squares) (Dickens et al., 1997). B. Downcore pore-water chloride concentrations at Site 994 (Paull, Matsumoto, Wallace, et al., 1996). The independent records have been used to estimate the abundance of gas hydrate in sediment on the crest of the Blake Ridge (Paull, Matsumoto, Wallace, et al., 1996; Dickens et al., 1997). Both records show that there are two zones where gas hydrate is concentrated.