Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node
Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node
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海洋环流促进海王星加拿大巴克利峡谷节点天然气水合物露头的甲烷释放
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发表时间：
2012
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影响因子：
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通讯作者：
J. Vogt
中科院分区：
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作者：
L. Thomsen;C. Barnes;M. Best;R. Chapman;B. Pirenne;R. Thomson;J. Vogt
加拿大海王星有线观测网使移动机器人能够对不列颠哥伦比亚省温哥华岛近海约100公里、水深约870米、面积约1平方公里的小高原上的天然气水合物和海底群落结构进行无损、受控的实验和时间序列观测。利用移动互联网运营的车辆作为仪器平台，对多达2000平方米的泥沙表面进行实时监测和研究。2010年，该机器人的第一个任务是调查振荡的深海洋流对大陆边缘甲烷释放的重要性。此前，其他实验研究表明，天然气水合物露头的甲烷释放是扩散控制的，应该比半渗透沉积物中埋藏的水合物的渗漏要高得多。我们的结果表明，与昼夜陆架波、内部半日潮汐以及风产生的近惯性运动相关的底层流增强周期可以调制甲烷渗漏。当水合物没有被海底生物群或沉积物覆盖时，水合物稳定性区域内的天然气水合物可能会受到增强的底流的依赖于流动的破坏。计算的渗透率在40~400molmolCH4 mμ−2 S−1之间变化，比埋藏水合物在可渗透沉积物中的溶解速率高1~3个数量级，在不同水动力边界条件下露头天然气水合物的实验推导范围内。我们的结论是，由于气候变化而出现的天气模式，表现出高流体动力活动的海底峡谷可能成为渗漏增强的关键区域。
The NEPTUNE Canada cabled observatory network enables non‐destructive, controlled experiments and time‐series observations with mobile robots on gas hydrates and benthic community structure on a small plateau of about 1 km2 at a water depth of 870 m in Barkley Canyon, about 100 km offshore Vancouver Island, British Columbia. A mobile Internet operated vehicle was used as an instrument platform to monitor and study up to 2000 m2of sediment surface in real‐time. In 2010 the first mission of the robot was to investigate the importance of oscillatory deep ocean currents on methane release at continental margins. Previously, other experimental studies have indicated that methane release from gas hydrate outcrops is diffusion‐controlled and should be much higher than seepage from buried hydrate in semipermeable sediments. Our results show that periods of enhanced bottom currents associated with diurnal shelf waves, internal semidiurnal tides, and also wind‐generated near‐inertial motions can modulate methane seepage. Flow dependent destruction of gas hydrates within the hydrate stability field is possible from enhanced bottom currents when hydrates are not covered by either seafloor biota or sediments. The calculated seepage varied between 40–400 μmol CH4 m−2 s−1. This is 1–3 orders of magnitude higher than dissolution rates of buried hydrates through permeable sediments and well within the experimentally derived range for exposed gas hydrates under different hydrodynamic boundary conditions. We conclude that submarine canyons which display high hydrodynamic activity can become key areas of enhanced seepage as a result of emerging weather patterns due to climate change.