Subglacial Drainage Evolution Modulates Seasonal Ice Flow Variability of Three Tidewater Glaciers in Southwest Greenland
Subglacial Drainage Evolution Modulates Seasonal Ice Flow Variability of Three Tidewater Glaciers in Southwest Greenland
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DOI：
10.1029/2019jf005492
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发表时间：
2020-09-01
影响因子：
3.9
通讯作者：
Nienow, P. W.
中科院分区：
文献类型：
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作者：
Davison, B. J.;Sole, A. J.;Nienow, P. W.
来自地表的融水可以进入格陵兰冰盖的底部，造成季节性的速度变化。这些季节性扰动的大小、时间和对年平均冰流量的净影响取决于冰下排水系统的水力效率。我们研究排水系统效率和冰速度之间的关系，在格陵兰岛西南部的三个对比鲜明的冰川在2014年至2019年期间，使用高分辨率遥感冰速度，模拟表面融化，冰下放电在终点，从浮力羽建模的结果。所有的冰川都经历了季节性的加速，这通常与表面融化的开始相吻合，随后的减速，这通常遵循推断的冰下通道化。这些速度变化的幅度和时间在冰川之间不同，在我们最快的研究冰川中，速度增加更大，时间更长。然而，在所有冰川，冰流量的季节变化与冰下排水系统水力效率的推断变化一致，并定性地表明了一种流动状态，即年平均冰速对融水供应的年际变化相对不敏感，即所谓的“冰流量自我调节”。这些发现表明，冰下水道的形成可能对季节性冰流的变化有很强的控制作用，即使在快速流动的冰川上也是如此。简明语言摘要每年夏天，格陵兰冰盖表面产生的融水到达并润滑其底部，导致上覆的冰加速融化。在夏季的几个月里，持续的水流融化了水力有效的排水通道（管道）进入基底冰，使水能够快速排出，并使覆盖的冰减速。在快速流动的冰川上，就像这里研究的那些，基底管道的形成被认为是中断的，从而抵消了它的制动作用。我们测试这个想法，通过检查冰流和融水排放在三个海洋终止冰川，不同的速度，超过5年。每一年，每个冰川最初加速响应表面融化，然后减速后推断基底导管形成。在平均流速更快的冰川上，加速更大，减速更小。然而，在我们研究的所有冰川中，我们发现底部管道的形成导致了冰流的减速。这表明，即使在非常快的冰川，基底导管可以形成，并施加一个强大的控制冰川速度在季节性的时间尺度。
Surface-derived meltwater can access the bed of the Greenland ice sheet, causing seasonal velocity variations. The magnitude, timing, and net impact on annual average ice flow of these seasonal perturbations depend on the hydraulic efficiency of the subglacial drainage system. We examine the relationships between drainage system efficiency and ice velocity, at three contrasting tidewater glaciers in southwest Greenland during 2014-2019, using high-resolution remotely sensed ice velocities, modeled surface melting, subglacial discharge at the terminus, and results from buoyant plume modeling. All glaciers underwent a seasonal speed-up, which usually coincided with surface melt onset, and subsequent slow-down, which usually followed inferred subglacial channelization. The amplitude and timing of these speed variations differed between glaciers, with the speed-up being larger and more prolonged at our fastest study glacier. At all glaciers, however, the seasonal variations in ice flow are consistent with inferred changes in hydraulic efficiency of the subglacial drainage system and qualitatively indicative of a flow regime in which annually averaged ice velocity is relatively insensitive to interannual variations in meltwater supply-so-called "ice flow self-regulation." These findings suggest that subglacial channel formation may exert a strong control on seasonal ice flow variations, even at fast-flowing tidewater glaciers.Plain Language Summary Each summer, meltwater produced at the surface of the Greenland ice sheet reaches and lubricates its base, causing the overlying ice to accelerate. Continual water flow during the summer months melts hydraulically efficient drainage pathways (conduits) into the basal ice, enabling rapid evacuation of water and causing the overlying ice to decelerate. At fast-flowing glaciers, like those studied here, basal conduit formation is thought to be disrupted, thereby negating its braking effect. We test this idea by examining ice flow and meltwater discharge at three ocean-terminating glaciers, of varying velocities, over 5 years. Every year, each glacier initially accelerated in response to surface melting, then decelerated following inferred basal conduit formation. The acceleration was greater, and deceleration smaller, at glaciers that were faster flowing on average. At all our studied glaciers, however, we found that the formation of basal conduits caused ice flow deceleration. This suggests that, even at very fast glaciers, basal conduits can form and exert a strong control on glacier velocity at seasonal timescales.