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In situ Raman‐based measurements of high dissolved methane concentrations in hydrate‐rich ocean sediments
Author(s) -
Zhang Xin,
Hester Keith C.,
Ussler William,
Walz Peter M.,
Peltzer Edward T.,
Brewer Peter G.
Publication year - 2011
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl047141
Subject(s) - methane , clathrate hydrate , geology , sediment , in situ , dissolved organic carbon , pore water pressure , hydrate , environmental science , cold seep , deep sea , raman spectroscopy , carbon cycle , environmental chemistry , oceanography , mineralogy , chemistry , geomorphology , physics , organic chemistry , optics , ecology , geotechnical engineering , ecosystem , biology
Ocean sediment dissolved CH 4 concentrations are of interest for possible climate‐driven venting from sea floor hydrate decomposition, for supporting the large‐scale microbial anaerobic oxidation of CH 4 that holds the oceanic CH 4 budget in balance, and for environmental issues of the oil and gas industry. Analyses of CH 4 from recovered cores near vent locations typically show a maximum of ∼1 mM, close to the 1 atmosphere equilibrium value. We show from novel in situ measurement with a Raman‐based probe that geochemically coherent profiles of dissolved CH 4 occur rising to 30 mM ( p CH 4 = 3 MPa) or an excess pressure ∼3× greater than CO 2 in a bottle of champagne. Normalization of the CH 4 Raman ν 1 peak to the ubiquitous water ν 2 bending peak provides a fundamental internal calibration. Very large losses of CH 4 and fractions of other gases (CO 2 , H 2 S) must typically occur from recovered cores at gas rich sites. The new data are consistent with observations of microbial biomass and observed CH 4 oxidation rates at hydrate rich sites and support estimates of a greatly expanded near surface oceanic pore water CH 4 reservoir.