Sub-permafrost methane seepage from open-system pingos in Svalbard
Sub-permafrost methane seepage from open-system pingos in Svalbard
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DOI：
10.5194/tc-14-3829-2020
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发表时间：
2020-11
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通讯作者：
A. Hodson;A. Nowak;M. T. Hornum;K. Senger;K. Redeker;H. Christiansen;S. Jessen;P. Betlem;S. Thornton;A. Turchyn;S. Olaussen;A. Marca
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作者：
A. Hodson;A. Nowak;M. T. Hornum;K. Senger;K. Redeker;H. Christiansen;S. Jessen;P. Betlem;S. Thornton;A. Turchyn;S. Olaussen;A. Marca
摘要。从低地永久冻土下释放的甲烷是北极温室气体收支中一个重要的不确定因素。我们目前的知识可以说是在永久冻土被海平面上升淹没的情况下发展得最好，这意味着大部分甲烷在到达大气之前就在水柱中被氧化了。在这里，我们提供了一个不同的过程视角，适用于北极峡湾山谷，在那里，局部冰川消融导致均衡隆起，以超过海平面上升的速度。我们描述了隆起是如何引起前海洋沉积物的永久冻土恶化的，其加压导致甲烷通过地下水泉直接逃逸到大气中。在斯匹次卑尔根中部的Adventdalen，我们展示了泉水是如何成为开放系统pingo形成的历史特征，并能够排放富含高浓度生物甲烷（平均18 mg L−1）的咸淡水。热力学计算表明，在0°C （41 mg L−1）下，甲烷的浓度有时会略微超过甲烷在水中的溶解度极限。书中描述了萍果全年的排放量。在冬季，随着冰疱下面的爆发事件，甲烷迅速流失到大气中。在夏季，由于渗流点的复杂地表过程及其被地表径流淹没而发生高度变化的排放。尽管存在这种复杂性，但我们的观测结果证实，在改进北极温室气体排放预测方面，永久冻土下的甲烷迁移值得更多关注。
Abstract. Methane release from beneath lowland permafrost represents an important uncertainty in the Arctic greenhouse gas budget. Our current knowledge is arguably best developed in settings where permafrost is being inundated by rising sea level, which means much of the methane is oxidised in the water column before it reaches the atmosphere. Here we provide a different process perspective that is appropriate for Arctic fjord valleys where local deglaciation causes isostatic uplift to out pace rising sea level. We describe how the uplift induces permafrost aggradation in former marine sediments, whose pressurisation results in methane escape directly to the atmosphere via groundwater springs. In Adventdalen, central Spitsbergen, we show how the springs are historic features responsible for the formation of open-system pingos and capable of discharging brackish waters enriched with high concentrations of mostly biogenic methane (average 18 mg L−1). Thermodynamic calculations show that the methane concentrations sometimes marginally exceed the solubility limit for methane in water at 0 ∘C (41 mg L−1). Year-round emissions from the pingos are described. During winter, rapid methane loss to the atmosphere occurs following outburst events from beneath an ice blister. During summer, highly variable emissions occur due to complex surface processes at the seepage point and its inundation by surface runoff. In spite of this complexity, our observations confirm that sub-permafrost methane migration deserves more attention for the improved forecasting of Arctic greenhouse gas emissions.