Collaborative Research-The East Siberian Arctic Shelf as a Source of Atmospheric Methane: First Approach to Quantitative Assessment

Six investigators from three institutions propose to study methane release over the East Siberian Arctic shelf (ESAS), the largest (about 10% of the world ocean shelf area) and the shallowest (mean depth less than 50 m) continental shelf of the world ocean. The ESAS stores the world?s largest hydrocarbon stocks, mostly as shallow Arctic hydrates, and thus represents a large potential methane atmospheric source that could result from global warming-triggered permafrost degradation. Increased methane fluxes could occur as numerous weak seeps or as strong bubble plumes over large areas. Due to the shallow depth of the ESAS, it is possible that the majority of methane released avoids oxidation and escapes to the atmosphere. The PIs will investigate the migration pathway characteristics and identify the controlling factors of methane flux from the seabed, in the water column, and to the atmosphere. The central hypothesis is that seabed methane fluxes are significant year-round sources while atmospheric fluxes are only significant during ice-free periods. The questions of methane sources, sinks, spatial and temporal variations in fluxes will be addressed through summer and winter expeditions to sample the water column and seabed, and helicopter surveys to sample the atmosphere. The PIs will also assess seafloor direct bubble flux over 6 control and 2 test sites on a nested range of sonar scales and using a combination of bubble video imaging and bubble modeling. Modeling will aim to develop a regional flux model. Broader impacts of the proposed activity include international collaboration, graduate and undergraduate student training, and public outreach.来自三家研究机构的六名研究者提议针对东西伯利亚北极大陆架（East Siberian Arctic Shelf，以下简称ESAS）开展甲烷释放相关研究。该大陆架是全球海洋大陆架中面积最大（约占全球海洋大陆架总面积的10%）且最浅（平均水深不足50米）的区域。东西伯利亚北极大陆架储存着全球规模最大的碳氢化合物储量，其中大部分以浅层北极水合物形式存在，因此其可能成为全球变暖引发多年冻土退化后，甲烷释放进入大气的巨大潜在来源。甲烷通量的增加可能以大范围分布的多处弱渗漏，或是强烈气泡羽流的形式出现。由于该大陆架水深较浅，绝大多数释放出的甲烷有望避开氧化过程，直接逸散进入大气。本项目的首席研究员（Principal Investigators，以下简称PIs）将研究甲烷迁移路径特征，并明确甲烷从海底、水体直至大气的通量控制因素。本次研究的核心假设为：海底甲烷通量是全年持续的重要排放源，而大气甲烷通量仅在无冰期才具有显著影响。针对甲烷的源与汇、通量的时空变化等问题，研究团队将通过夏季与冬季的科考航次对水体及海底进行采样，并借助直升机航测开展大气采样工作。首席研究员还将在嵌套式声呐尺度范围内，结合气泡视频成像与气泡模拟技术，对6个对照位点与2个试验位点的海底直接气泡通量进行评估。模拟工作将致力于构建区域甲烷通量模型。本项目的拓展价值与社会影响包括开展国际协作、培养研究生与本科生人才，以及面向公众开展科普推广活动。