Figure 6. In situ methane quantities at Sites 995 (circles) and 997 (squares) shown with respect to water depth (mbsl) and sediment depth (mbsf). Methane hydrate occurs in sediment from 190 to 450 mbsf, whereas free methane gas occurs in sediment below 450 mbsf. In situ methane quantities (mol/dm3 pore space) indicate the total volume of gas released from the PCS (Dickens et al., Chap. 11 and Chap. 43, both this volume). A smoothed curve through all in situ methane quantities (bold), a saturation curve (dashed line) for methane in seawater with methane hydrate, or in seawater with free methane gas, is shown.
