Methane in shallow subsurface sediments at the landward limit of the gas hydrate stability zone offshore western Svalbard
Methane in shallow subsurface sediments at the landward limit of the gas hydrate stability zone offshore western Svalbard
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DOI：
10.1016/j.gca.2016.11.015
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发表时间：
2017-02-01
影响因子：
5
通讯作者：
Connelly, Douglas P.
中科院分区：
文献类型：
--
作者：
Graves, Carolyn A.;James, Rachael H.;Connelly, Douglas P.
近海西部Svalbard气泡的气泡从海底上升到气体水合物稳定区域（LLGHSZ；类似于400 m的水深）的海底。假设这种甲烷可能部分来自在近期海洋底部水域变暖的基础沉积物中气体水合物的解离。为了评估气体水合物在向浅的地下沉积物供应中的潜在作用，以及厌氧氧化在调节沉积物水界面跨压缩甲烷通量中的作用，我们表征了气体和沉淀物孔隙水的化学和同位素组成。气泡羽流中气体的分子和同位素特征（C1/C2+ = 1 x 10（4）； Delta C -13 -CH4 = -55至-51零件每千； delta d -Ch4 = -187至-184零件的delta d -ch4 = -184至-184零件类似于与与30 km ex extements lach secements相似的气体水合物的相似之处。孔硫酸盐谱的建模表明，地下甲烷通量在很大程度上处于LLGHSZ附近的稳态状态，没有证据表明由于气体水合解离而导致的甲烷供应发生任何变化。但是，在更大的水深处，在GHSZ内，有一些证据表明，甲烷向浅层沉积物的供应最近增加了，这与GHSZ的下坡撤退是由于底部水变暖而导致的，尽管其他解释是可能的。我们估计，向上向上扩散的甲烷通量进入靠近LLGHSZ的浅地下沉积物为30,550 mmol m（-2）yr（-1），但它是
Offshore western Svalbard plumes of gas bubbles rise from the seafloor at the landward limit of the gas hydrate stability zone (LLGHSZ; similar to 400 m water depth). It is hypothesized that this methane may, in part, come from dissociation of gas hydrate in the underlying sediments in response to recent warming of ocean bottom waters. To evaluate the potential role of gas hydrate in the supply of methane to the shallow subsurface sediments, and the role of anaerobic oxidation in regulating methane fluxes across the sedimentseawater interface, we have characterised the chemical and isotopic compositions of the gases and sediment pore waters. The molecular and isotopic signatures of gas in the bubble plumes (C1/C2+ = 1 x 10(4); delta C-13-CH4 = -55 to -51 parts per thousand; delta D-CH4 = -187 to -184 parts per thousand) are similar to gas hydrate recovered from within sediments similar to 30 km away from the LLGHSZ. Modelling of pore water sulphate profiles indicates that subsurface methane fluxes are largely at steady state in the vicinity of the LLGHSZ, providing no evidence for any recent change in methane supply due to gas hydrate dissociation. However, at greater water depths, within the GHSZ, there is some evidence that the supply of methane to the shallow sediments has recently increased, which is consistent with downslope retreat of the GHSZ due to bottom water warming although other explanations are possible. We estimate that the upward diffusive methane flux into shallow subsurface sediments close to the LLGHSZ is 30,550 mmol m(-2) yr(-1), but it is