Publication Date:
2022-05-25
Description:
This paper is not subject to U.S. copyright. The definitive version was published in Chemical Geology 339 (2013): 242-250, doi:10.1016/j.chemgeo.2012.09.033.
Description:
As a consequence of contemporary or longer term (since 15 ka) climate warming, gas hydrates in some settings may presently be dissociating and releasing methane and other gases to the ocean–atmosphere system. A key challenge in assessing the impact of dissociating gas hydrates on global atmospheric methane is the lack of a technique able to distinguish between methane recently released from gas hydrates and methane emitted from leaky thermogenic reservoirs, shallow sediments (some newly thawed), coal beds, and other sources. Carbon and deuterium stable isotopic fractionation during methane formation provides a first-order constraint on the processes (microbial or thermogenic) of methane generation. However, because gas hydrate formation and dissociation do not cause significant isotopic fractionation, a stable isotope-based hydrate-source determination is not possible. Here, we investigate patterns of mass-dependent noble gas fractionation within the gas hydrate lattice to fingerprint methane released from gas hydrates. Starting with synthetic gas hydrate formed under laboratory conditions, we document complex noble gas fractionation patterns in the gases liberated during dissociation and explore the effects of aging and storage (e.g., in liquid nitrogen), as well as sampling and preservation procedures. The laboratory results confirm a unique noble gas fractionation pattern for gas hydrates, one that shows promise in evaluating modern natural gas seeps for a signature associated with gas hydrate dissociation.
Description:
Partial support for this research was provided by Interagency Agreements
DE-FE0002911 and DE-NT0006147 between the U.S. Geological
Survey Gas Hydrates Project and the U.S. Department of Energy's Methane
Hydrates Research and Development Program.
Keywords:
Gas hydrate
;
Noble gas
;
Methane
;
Stable isotopes
;
Mass-fractionation
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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