Complex Basal Thermal Transition Near the Onset of Petermann Glacier, Greenland
Complex Basal Thermal Transition Near the Onset of Petermann Glacier, Greenland
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DOI：
10.1029/2017jf004561
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发表时间：
2018-05-01
影响因子：
3.9
通讯作者：
Bell, R. E.
中科院分区：
文献类型：
--
作者：
Chu, W.;Schroeder, D. M.;Bell, R. E.
冰盖的基底热状态对冰盖的稳定性和快速流动的开始起着强有力的控制作用。然而，这种滑动开始的热转变的性质在很大程度上不受地球物理观测的约束。在格陵兰冰盖，地形槽或升高的地热热通量通常定义了出口冰川的开始。相比之下，格陵兰岛北方的彼得曼冰川没有任何明显的河床槽或与其发病相关的局部地热加热，使其成为研究基底热状态和研究其在彼得曼冰川发病中的作用的理想场所。在这里，我们使用雷达床的反射率和冰盖热力学模型，以研究彼得曼冰川下的基础热制度。我们的研究结果揭示了一个复杂的热转变彼得曼冰川的发病附近。随着床从大部分冻结到大部分解冻的冰鸿沟的距离增加，我们的研究结果表明，这种热转变发生通过交替带的冻结和解冻带。整个发病地区的复杂的热状态表明，侧向融水注入和当地融水生产确定彼得曼冰川的位置。由于在起始位置缺乏地形钉扎，彼得曼冰川的上游边缘很容易迁移，这取决于对流冷却和冰盖内部融水供应的结合。简单的语言摘要彼得曼冰川是格陵兰岛北方最大的出口冰川之一。它的快速流动的冰深入冰的内部，每年从分水岭到海岸的冰大约有13公里（3）。但是，是什么决定了这个神秘冰川的开始呢？与格陵兰其他大型出口冰川不同，彼得曼冰川的冰川头并不位于任何明显的冰下盆地。在没有地形强迫的情况下，与冰盖底部温度有关的其他内部过程可能是控制彼得曼冰川位置的关键因素。然而，目前，对这种基本热条件的观测很少。使用一种新的冰穿透雷达分析技术，我们提出了第一个详细的观测彼得曼冰川的基本热条件。我们的研究结果表明，随着冰盖床开始变暖，冰移近海岸，床从冻结到解冻的条件下多次转移之前，它达到一个持久的解冻条件。这些结果解释了为什么假设一个简单的，单一的冻融床过渡的冰盖模型难以准确地再现彼得曼冰川的上游边缘。
The basal thermal regime of ice sheets exerts a strong control on ice-sheet stability and the onset of rapidly streaming flow. However, the nature of this thermal transition where sliding initiates is largely unconstrained by geophysical observations. In the Greenland Ice Sheet, topographic troughs or elevated geothermal heat fluxes typically define the onset of outlet glaciers. In contrast, Petermann Glacier in Northern Greenland does not have any distinct bed troughs or localized geothermal heating associated with its onset, making it an ideal site to investigate the basal thermal state and examine its role in the onset of Petermann Glacier. Here we use radar bed reflectivity and an ice-sheet thermomechanical model to examine the basal thermal regime beneath Petermann Glacier. Our results reveal a complex thermal transition near the onset of Petermann Glacier. As the bed shifts from largely frozen to largely thawed with increasing distances from the ice divide, our results show that this thermal transition happens through alternating bands of frozen and thawed bands. The complex thermal state across the onset region suggests that lateral meltwater injection and local meltwater production determine the location of Petermann Glacier. Given the lack of topographic pinning at the onset location, the upstream margin of Petermann is vulnerable to migrate depending on a combination of advective cooling and meltwater supply from the interior of the ice sheet.Plain Language Summary Petermann Glacier is one of the largest outlet glaciers in Northern Greenland. Its fast-flowing ice reaches deep into the ice interior, drawing similar to 13km(3) of ice every year from the divide to the coast. But what determines the onset of this enigmatic glacier? Different from other large outlet glaciers in Greenland, the head of Petermann Glacier does not sit in any distinct subglacial basins. Without this topographic forcing to promote its ice velocity, other internal process related to the temperature of ice sheet base could be the critical factor that controls the location of Petermann Glacier. However, currently, there are very few observations on this basal thermal condition. Using a novel ice-penetrating radar analysis technique, we present the first detailed observations on the basal thermal condition of Petermann Glacier. Our results reveal that as the ice sheet bed begins to warm up as the ice moves closer to the coast, the bed shifts from a frozen to a thawed condition multiple times before it reaches a persistent thawed condition. These results explain why ice sheet models that assume a simple, single frozen-to-thawed bed transition struggle to reproduce the upstream margin of Petermann Glacier accurately.