Earth and Planetary Science Letters, 2011, Vol.310(1), pp.105-112
Sea floor methane vents and seeps direct methane generated by microbial and thermal decompositions of organic matter in sediment into the oceans and atmosphere. Methane vents contribute to ocean acidification, global warming, and providing a long-term (e.g. 500–4000 years; ) life-sustaining role for unique chemosynthetic biological communities. However, the role methane vents play in both climate change and chemosynthetic life remains controversial primarily because we do not understand long-term methane flux and the mechanisms that control it ( ). Vents are inherently dynamic and flux varies greatly in magnitude and even flow direction over short time periods (hours-to-days), often tidally-driven ( ). But, it remains unclear if flux changes at vents occur on the order of the life-cycle of various species within chemosynthetic communities (months, years, to decades ) and thus impacts their sustainability. Here, using repeat high-resolution 3D seismic surveys acquired in 2000 and 2008, we demonstrate in 4D that Hydrate Ridge, a vent off the Oregon coast has undergone significant reduction of methane flow and complete interruption in just the past few years. In the subsurface, below a frozen methane hydrate layer, free gas appears to be migrating toward the vent, but currently there is accumulating gas that is unable to reach the seafloor through the gas hydrate layer. At the same time, abundant authigenic carbonates show that the system has been active for several thousands of years. Thus, it is likely that activity has been intermittent because gas hydrates clog the vertical flow pathways feeding the seafloor vent. Back pressure building in the subsurface will ultimately trigger hydrofracturing that will revive fluid-flow to the seafloor. The nature of this mechanism implies regular recurring flow interruptions and methane flux changes that threaten the viability of chemosynthetic life, but simultaneously and enigmatically sustains it. ► Collocated 3D seismic surveys compare seafloor methane vent system in 2000 and 2008. ► Reflectivity changes between surveys reveal rapid gas migration toward the vent. ► Methane hydrate temporarily blocks flow causing backpressure to build. ► Seafloor chemosynthetic communities have adapted to flow interruptions.
Gas Hydrate ; Seafloor Methane Vents ; Chemosynthetic Communities ; 4d Seismics ; Geology ; Physics
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