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Monday, May 16, 2011

Mea S. Cook et al., PaleoRepeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea

Paleoceanography, 26 (2011) PA2210; doi: 10.1029/2010PA001993
Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea
Key Points
  • There are multiple episodes of intense vertical methane flux in MIS3 sediments
  • The episodes have similar timing and duration as D-O events
  • These sites are too cold and deep for the Clathrate Gun Hypothesis
Mea S. Cook (Geosciences Department, Williams College, Williamstown, MA, USA), Lloyd D. Keigwin (Geology and Geophysics Department, Woods Hole Oceanographic Institution, Woods Hole, MA, USA), and Daniel Birgel and Kai-Uwe Hinrichs (MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany)


There is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard-Oeschger events. The episodes are marked by horizons of sediment containing 13C-depleted authigenic carbonate minerals; 13C-depleted archaeal and bacterial lipids, which resemble those found in ANME-1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region-wide increase in the upward flux of methane-bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the “Clathrate Gun Hypothesis” (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean's sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal-rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.
Received 19 May 2010; accepted 25 January 2011; published 11 May 2011.
Citation: Cook, M. S., L. D. Keigwin, D. Birgel, and K.-U. Hinrichs (2011), Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering SeaPaleoceanography26, PA2210, doi:10.1029/2010PA001993.

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