Pore water profiles and authigenic mineralization in shallow marine sediments above the methane-charged system on Umitaka Spur, Japan Sea

Department of Earth Sciences, Rice University, Houston, TX, USA
Deep Sea Research Part II Topical Studies in Oceanography (Impact Factor: 2.19). 06/2007; 54(11):1216-1239. DOI: 10.1016/j.dsr2.2007.04.001


Umitaka Spur, situated on an unusual collisional plate boundary along the eastern margin of the Japan Sea, hosts gas seeps, pock-marks, collapse structures, and gas hydrates. Piston cores were recovered from this ridge to understand carbon cycling, pore fluid gradients and authigenic mineralization above a methane-charged system. We present the chemistry of fluids and solids from three cores adjacent to seep locations. High fluxes of CH4 and alkalinity transport carbon from a deep zone of methanogenesis toward the seafloor. Methane, however, reacts with across a shallow sulfate–methane transition (SMT), which generates additional alkalinity and HS−. A fraction of these CH4 oxidation products form authigenic carbonate and pyrite. These minerals are not readily apparent from visual inspection of split cores, because they exist as micritic coatings on microfossils or as framboidal pyrite. They are, however, readily observed in chemical analyses as peaks of “labile” Ca, Sr, Ba or S in sediment at or near the SMT. Carbon inputs and outputs nicely balance across the SMT in all three cores if one considers four relevant fluxes: loss of alkalinity to the seafloor, addition of methane from below, addition of alkalinity from below, and carbonate precipitation. Importantly, in all cores, the magnitude of the fluxes decreases in this order. Although some carbon rising from depth forms authigenic carbonate, most (>80%) escapes to the ocean as alkalinity. Nonetheless, authigenic fronts in sediment on Umitaka Spur are a significant reservoir of inorganic carbon. Given calculated pore fluid fluxes for Ca and Sr, the fronts require tens of thousands of years to form, suggesting that the present state and loss of carbon represent long-lived processes.


Available from: Gerald Dickens
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    • "The remaining fraction of organic matter in underlying sulfatedepleted deposits is further decomposed by microbial methanogenesis , the principal products being 13 C-depleted methane and 13 C-enriched bicarbonate or dissolved inorganic carbon (DIC) (Fig. 1; Conrad, 2005), both of which diffuse upward toward the sediment-water interface (SWI) (Chatterjee et al., 2011). At shallow depth, however, generally within the upper 25 m of the sediment column (Riedinger et al., 2006; Snyder et al., 2007a), downward diffusing seawater sulfate meets upward migrating methane along the sulfate-methane transition (SMT) zone, a thin (generally less than 2 m) fundamental biogeochemical boundary separating microbial sulfate reducers above from methanogens below (Fig. 1; Barnes and Goldberg, 1976; Reeburgh, 1976; Alperin et al., 1988; Borowski et al., 1997, 1999, 2013; Aloisi et al., 2000; Rodriguez et al., 2000; Dickens, 2001; Niemann et al., 2006; Knittel and Boetius, 2009). Within the SMT, a consortium of sulfate-reducing bacteria and methanotrophic archea consumes the sulfate and methane per the following net reaction: E-mail address: Lash@fredonia.edu. "
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    • ") , which were similar to those observed in the sediments at Kattegat and Ska - gerrak ( Denmark ) , Sannich Inlet , Long Island ( America ) and the methane hydrates area ( Martens and Berner , 1977 ; Devol , 1983 ; Iversen and Jørgensen , 1985 ; Borowski et al . , 1999 ; Joye et al . , 2004 ; Snyder et al . , 2007 ; Hu et al . , 2010 ) . Sulfate profiles that Fig . 6 . Depth profiles of the pore water DIC and δ 13 C - DIC at all of the stations in May , 2012 . Fig . 7 . Plots of the sulfate ( a ) and DIC ( b ) vs . the Cl À for the pore water of the dilution - mixing layer in the wet season at all of the sampling cores . have linearity indicate t"
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    • "ic matter was lower than in the upper layers , have been observed in acidic pitlands ( Cadillo - Quiroz et al . , 2006 ) . Although methane can be oxidized aerobically by methano - trophic bacteria , anoxic oxidation of methane in association with sulfate reduction and H 2 S production ( see reaction 3 ) has been observed in deep - sea sediments ( Snyder et al . , 2007 ) . Three archaeal groups able to oxidize methane under anoxic conditions ( AMNE - 1 , AMNE - 2 and AMNE - 3 ) have been identified so far ( Knittel et al . , 2005 ) ."
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