An In Situ Experiment of Methane Sequestration as Gas Hydrate, Authigenic Carbonate, and Loss to the Water Column and/or Atmosphere

: A one year in situ experiment to quantify the flux of carbon, primarily as methane, from an overpressured thrust fault at the Cascadia convergent margin (ODP Site 892B) is described. Most of the expelled carbon is sequestered in two solid phases, methane hydrate and authigenic carbonates and an unknown portion is lost in the water column and/or atmosphere.14 ages of clam shells from the vicinity of the site suggest active methane venting for at least 21–24 kyrs. The water column chemistry provides information on the potential effects of global warming on rapid massive gas hydrate dissociation and on the effects of microbial oxidation of the released methane on the local oceanic oxygen and CO2 contents. The local and global implications of these processes for the oceanic carbon cycle are being assessed.