Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization
Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization
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DOI：
10.1002/2015jf003602
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发表时间：
2015-11-01
影响因子：
3.9
通讯作者：
Koch, J.
中科院分区：
文献类型：
--
作者：
Jorgenson, M. T.;Kanevskiy, M.;Koch, J.
在整个北极地区的永久冻土层上部，有大量的地面冰，从根本上影响着地形对气候变暖的反应。冰楔形成于地表附近，是北极主要的大块冰类型，特别容易受到变暖的影响。然而，控制冰楔退化和稳定的过程知之甚少。在这里，我们量化冰楔体积和降解率，比较地面冰的特性和热制度在一个序列的五个退化和稳定化阶段，并评估生物物理反馈控制永久冻土稳定性附近的普鲁德霍湾，阿拉斯加。多年冻土顶部3m的平均冰楔体积为21%。1949年至2012年的图像显示，热岩溶范围（充水槽的面积）从1949年（0.9%）到1988年（1.5%）相对较小，到2004年（6.3%）突然增加，到2012年（7.5%）略有增加。年平均地表温度在退化和稳定阶段之间变化4.9摄氏度，从多边形中心到深湖底变化9.9摄氏度。活动层、贫冰过渡层、富冰中间层、热溶洞冰和楔形冰的平均厚度在各阶段之间变化很大。在早期阶段，融化沉降导致水蓄积在热岩溶槽中，产生正反馈，增加净辐射，土壤热通量和土壤温度。退化槽中的植物生长和有机物积累提供了负反馈，使地面冰淤积并隆起表面，从而减少了后期的地表水深度和土壤温度。地面冰动力学和生态反馈大大复杂化的努力，以评估多年冻土对气候变化的反应。
Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet processes controlling ice wedge degradation and stabilization are poorly understood. Here we quantified ice wedge volume and degradation rates, compared ground ice characteristics and thermal regimes across a sequence of five degradation and stabilization stages and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. Mean ice wedge volume in the top 3m of permafrost was 21%. Imagery from 1949 to 2012 showed thermokarst extent (area of water-filled troughs) was relatively small from 1949 (0.9%) to 1988 (1.5%), abruptly increased by 2004 (6.3%) and increased slightly by 2012 (7.5%). Mean annual surface temperatures varied by 4.9 degrees C among degradation and stabilization stages and by 9.9 degrees C from polygon center to deep lake bottom. Mean thicknesses of the active layer, ice-poor transient layer, ice-rich intermediate layer, thermokarst cave ice, and wedge ice varied substantially among stages. In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. Plant growth and organic matter accumulation in the degraded troughs provided negative feedbacks that allowed ground ice to aggrade and heave the surface, thus reducing surface water depth and soil temperatures in later stages. The ground ice dynamics and ecological feedbacks greatly complicate efforts to assess permafrost responses to climate change.