Characterization of a stratigraphically constrained gas hydrate system along the western continental margin of Svalbard from ocean bottom seismometer data
Characterization of a stratigraphically constrained gas hydrate system along the western continental margin of Svalbard from ocean bottom seismometer data
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DOI：
10.1029/2011jb008211
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发表时间：
2011-12-10
影响因子：
3.9
通讯作者：
Sarkar, Sudipta
中科院分区：
文献类型：
--
作者：
Chabert, Anne;Minshull, Tim A.;Sarkar, Sudipta
预计北极地区底水的持续变暖会破坏浅海沉积物中存在的某些气体水合物的稳定，从而可能导致甲烷从将水合分离到海洋和大气中的释放。海底地震仪（OBS）实验沿西部Svalbard的大陆边缘进行了实验，以量化海床下水合物或气体的甲烷量。使用Ray-Trace向前建模，对沿大陆边缘的五个位点进行了P-和S波速度。两个南部地点位于30公里长的区域的附近，在巡航过程中观察到甲烷气泡从海底逃脱。其余的三个位置位于边缘北部的E-W取向线。在最深的北部部位，V-P异常表明在沉积物中存在水合物，该沉积物立即上覆盖了一个含有100米厚的自由气体的区域。这两个区域之间的声阻抗对比形成了一个底部的反射器（BSR），在海底下方约195 m。气体水合物稳定区（GHSZ）中的其他两个位置未显示BSR或气体水合物的清晰存在。但是，对两个地点的自由气体的存在异常低的V-P，表明存在游离气体。使用有效的中等理论从V-P和V-S估算水合物含量。在最深的北部地点，建模表明，如果形成水合物作为连接框架的一部分，则孔隙空间水合物浓度为7-12％，如果孔隙填充孔，则约为22％。在位于GHSZ最深的地点和地面限制之间的其他两个北部地点，我们建议在沉积物中存在水合物作为夹杂物。水合物可能以少量数量存在于孔隙空间的这两个位置（4-5％）。高分辨率地震曲线指示的三个位点的岩性变化可能控制水合物和游离气体的分布，浓度和形成。
The ongoing warming of bottom water in the Arctic region is anticipated to destabilize some of the gas hydrate present in shallow seafloor sediment, potentially causing the release of methane from dissociating hydrate into the ocean and the atmosphere. Ocean-bottom seismometer (OBS) experiments were conducted along the continental margin of western Svalbard to quantify the amount of methane present as hydrate or gas beneath the seabed. P- and S-wave velocities were modeled for five sites along the continental margin, using ray-trace forward modeling. Two southern sites were located in the vicinity of a 30 km long zone where methane gas bubbles escaping from the seafloor were observed during the cruise. The three remaining sites were located along an E-W orientated line in the north of the margin. At the deepest northern site, V-p anomalies indicate the presence of hydrate in the sediment immediately overlying a zone containing free gas up to 100-m thick. The acoustic impedance contrast between the two zones forms a bottom-simulating reflector (BSR) at approximately 195 m below the seabed. The two other sites within the gas hydrate stability zone (GHSZ) do not show the clear presence of a BSR or of gas hydrate. However, anomalously low V-p, indicating the presence of free gas, was modeled for both sites. The hydrate content was estimated from V-p and V-s, using effective-medium theory. At the deepest northern site, modeling suggests a pore-space hydrate concentration of 7-12%, if hydrate forms as part of a connected framework, and about 22% if it is pore-filling. At the two other northern sites, located between the deepest site and the landward limit of the GHSZ, we suggest that hydrate is present in the sediment as inclusions. Hydrate may be present in small quantities at these two sites (4-5%) of the pore space. The variation in lithology for the three sites indicated by high-resolution seismic profiles may control the distribution, concentration and formation of hydrate and free gas.