Near‐shore talik development beneath shallow water in expanding thermokarst lakes, Old Crow Flats, Yukon
Near‐shore talik development beneath shallow water in expanding thermokarst lakes, Old Crow Flats, Yukon
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育空地区老克罗平原不断扩大的热喀斯特湖浅水区近岸塔里克开发
DOI：
10.1002/2016jf004022
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Christopher R. Burn
中科院分区：
文献类型：
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作者：
P. Roy;Christopher R. Burn
人们通常认为，北美西部北极的浅湖和池塘下保存着永久冻土，那里的水深不到冬末湖冰厚度的三分之二。在这里，我们提供了在YT的老Crow Flats(OCF)，尽管湖冰厚度为1.5米，但在浅至0.2米的水下的塔里克发展的现场观测。通过海岸侵蚀速率、水深、冰层厚度、积雪和湖底温度的现场测量，研究了浅水潜流形成和发展的条件。然后用数值方法研究了塔里克的发育对湖底热力状况变化的敏感性。在冰到达湖底的地方，塔里克的发育受湖底冰冻天数与融化天数的比率(FDDlb/TDDlb)控制。在某些情况下，冰上积雪深度的空间变化对年平均湖底温度(TLb)的影响很小，但会导致FDDlb/TDDlb的充分变化，从而影响塔里克的发展。在TLb接近但大于0°C的情况下，模拟表明，热偏移量允许在特定条件下发生永久冻土堆积，导致不规则的近岸塔利克几何形状。这一结果突显了永冻土对湖底热条件微小变化的敏感性，在初冬水柱冻结的湖底，表明北极池塘和湖泊近岸地区的极浅水域下发生了永冻土退化。
It is generally assumed that permafrost is preserved beneath shallow lakes and ponds in the Western North American Arctic where water depth is less than about two thirds of the late‐winter lake ice thickness. Here we present field observations of talik development beneath water as shallow as 0.2 m despite a lake ice thickness of 1.5 m, in Old Crow Flats (OCF), YT. Conditions leading to the initiation and development of taliks beneath shallow water were investigated with field measurements of shore erosion rates, bathymetry, ice thickness, snow accumulation, and lake bottom temperature near the shores of two expanding lakes in OCF. The sensitivity of talik development to variations in lake bottom thermal regime was then investigated numerically. Where ice reached the lake bottom, talik development was controlled by the ratio of freezing degree days to thawing degree days at the lake bottom (FDDlb/TDDlb). In some cases, spatial variations in on‐ice snow depth had a minimal effect on annual mean lake bottom temperature (Tlb) but caused sufficient variations in FDDlb/TDDlb to influence talik development. Where Tlb was close to but greater than 0°C simulations indicated that the thermal offset allowed permafrost aggradation to occur under certain conditions, resulting in irregular near‐shore talik geometries. The results highlight the sensitivity of permafrost to small changes in lake bottom thermal conditions where the water column freezes through in early winter and indicate the occurrence of permafrost degradation beneath very shallow water in the near‐shore zone of Arctic ponds and lakes.