Drainage of Southeast Greenland Firn Aquifer Water through Crevasses to the Bed
Drainage of Southeast Greenland Firn Aquifer Water through Crevasses to the Bed
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DOI：
10.3389/feart.2017.00005
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发表时间：
2017-02
影响因子：
2.9
通讯作者：
K. Poinar;I. Joughin;D. Lilien;L. Brucker;L. Kehrl;S. Nowicki
中科院分区：
文献类型：
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作者：
K. Poinar;I. Joughin;D. Lilien;L. Brucker;L. Kehrl;S. Nowicki
格陵兰东南部黑尔海姆冰川集水区的一个积雪含水层位于一个决口区的正上游。先前的测量表明，2012年春季至2013年春季，3.5公里长的含水层段损失了大量的水（横截面为26 000 - 65 000平方米），而每年的融水累积量为6 000 - 15 000平方米。水被认为已经进入了裂缝，但水是否到达了河床或在冰盖内重新冻结尚不清楚。我们使用了一个热粘弹性模型的裂缝传播计算的深度和体积，这些水填充裂缝。我们将我们的模型输出与机载地形测绘仪（ATM）的数据进行了比较，ATM揭示了特定裂缝的近地表几何形状，WorldView图像捕捉了我们1.5公里研究区域内裂缝的表面表达。我们发现，在我们的研究区域内的剪切模量在0.2和1.5 GPa之间的最佳拟合。我们表明，表面融水可以驱动裂隙的顶部表面的积雪含水层（~20米深），因此它接收水的速率对应于通过含水层的水通量。我们的模型表明，裂缝接收积雪含水层水水力压裂通过床，~1000米以下，在10-40天。在十年的时间里，积雪含水层水的冰川再冻结使当地平均冰温提高了约4°C，与观测到的约200米/年的表面速度相比，这使冰的变形运动增加了约50米/年。基底水对滑动速度的影响尚不清楚。如果没有积雪含水层将地表融水集中到冰隙中，我们发现地表融水不会到达冰床;相反，它会在深度小于500 m的冰隙中每年重新冻结。在我们的研究区域，雪含水层下游的决口场可能允许大部分含水层水到达床。因此，今后的研究应将含水层和裂隙视为共同系统的一部分。这个系统可能会独特地影响冰盖动力学路由大量的水床外的典型径流期。
A firn aquifer in the Helheim Glacier catchment of Southeast Greenland lies directly upstream of a crevasse field. Previous measurements show that a 3.5-km long segment of the aquifer lost a large volume of water (26,000 – 65,000 m2 in cross section) between spring 2012 and spring 2013, compared to annual meltwater accumulation of 6000 – 15,000 m2. The water is thought to have entered the crevasses, but whether the water reached the bed or refroze within the ice sheet is unknown. We used a thermo-visco-elastic model for crevasse propagation to calculate the depths and volumes of these water-filled crevasses. We compared our model output to data from the Airborne Topographic Mapper (ATM), which reveals the near-surface geometry of specific crevasses, and WorldView images, which capture the surface expressions of crevasses across our 1.5-km study area. We found a best fit with a shear modulus between 0.2 and 1.5 GPa within our study area. We show that surface meltwater can drive crevasses to the top surface of the firn aquifer (~20 m depth), whereupon it receives water at rates corresponding to the water flux through the aquifer. Our model shows that crevasses receiving firn-aquifer water hydrofracture through to the bed, ~1000 m below, in 10–40 days. Englacial refreezing of firn-aquifer water raises the average local ice temperature by ~4°C over a ten-year period, which enhances deformational ice motion by ~50 m/yr, compared to the observed surface velocity of ~200 m/yr. The effect of the basal water on the sliding velocity remains unknown. Were the firn aquifer not present to concentrate surface meltwater into crevasses, we find that no surface melt would reach the bed; instead, it would refreeze annually in crevasses at depths <500 m. The crevasse field downstream of the firn aquifer likely allows a large fraction of the aquifer water in our study area to reach the bed. Thus, future studies should consider the aquifer and crevasses as part of a common system. This system may uniquely affect ice-sheet dynamics by routing a large volume of water to the bed outside of the typical runoff period.