Physical Conditions of Fast Glacier Flow: 3. Seasonally-Evolving Ice Deformation on Store Glacier, West Greenland.
Physical Conditions of Fast Glacier Flow: 3. Seasonally-Evolving Ice Deformation on Store Glacier, West Greenland.
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快速冰川流动的物理条件：3.西格陵兰岛存储冰川上季节性变化的冰变形。
DOI：
10.1029/2018jf004821
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Young TJ
中科院分区：
文献类型：
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作者：
Young TJ
冰盖流动的时间变化通过冰盖变形直接影响冰盖内部结构。冰盖内垂直地层学的大规模变化以前是在百年到千年的时间尺度上进行的；然而，内部层形态的年内变化还有待探索。在两年的时间里，我们使用自主相敏无线电回波测深来跟踪西格陵兰岛Store Glacier的内部层的每日位移，精度达到毫米级。在距离崩解终点30公里处的一个地点，那里的冰厚为∼600米，流速为∼700米/年，我们测量了两年期间垂直速度和垂直应变率的明显季节变化。在融化季节(3-6月)之前，我们观察到冰柱上半部冰柱上半部分的非线性变形越来越严重，垂直应变率约为负−0.03a−1，而冰柱下方的冰在垂直应变高达+0.16a−1的情况下增厚。在融化季节早期(6-7月)，随着冰川的加厚，垂直变薄逐渐停止。在夏末到冬至(8-2月)，整个冰柱的垂直增厚呈线性变化，平均应变率为0.016 a−1。我们发现，这种复杂的变化与地形背景和局部的基面滑动无关，并假设这种季节性是由冰川力平衡中的远场扰动所驱动的，在这种情况下，冰川末端附近的基面水文变化产生，并通过瞬变的基面润滑纵向耦合向上游传播数十公里。
Temporal variations in ice sheet flow directly impact the internal structure within ice sheets through englacial deformation. Large‐scale changes in the vertical stratigraphy within ice sheets have been previously conducted on centennial to millennial timescales; however, intra‐annual changes in the morphology of internal layers have yet to be explored. Over a period of 2 years, we use autonomous phase‐sensitive radio‐echo sounding to track the daily displacement of internal layers on Store Glacier, West Greenland, to millimeter accuracy. At a site located ∼30 km from the calving terminus, where the ice is ∼600 m thick and flows at ∼700 m/a, we measure distinct seasonal variations in vertical velocities and vertical strain rates over a 2‐year period. Prior to the melt season (March–June), we observe increasingly nonlinear englacial deformation with negative vertical strain rates (i.e., strain thinning) in the upper half of the ice column of approximately −0.03 a−1, whereas the ice below thickens under vertical strain reaching up to +0.16 a−1. Early in the melt season (June–July), vertical thinning gradually ceases as the glacier increasingly thickens. During late summer to midwinter (August–February), vertical thickening occurs linearly throughout the entire ice column, with strain rates averaging 0.016 a−1. We show that these complex variations are unrelated to topographic setting and localized basal slip and hypothesize that this seasonality is driven by far‐field perturbations in the glacier's force balance, in this case generated by variations in basal hydrology near the glacier's terminus and propagated tens of kilometers upstream through transient basal lubrication longitudinal coupling.