Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland
Physical Conditions of Fast Glacier Flow: 1. Measurements From Boreholes Drilled to the Bed of Store Glacier, West Greenland
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DOI：
10.1002/2017jf004529
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发表时间：
2018-02-01
影响因子：
3.9
通讯作者：
Hubbard, A.
中科院分区：
文献类型：
--
作者：
Doyle, S. H.;Hubbard, B.;Hubbard, A.
格陵兰冰盖的海洋末端出口冰川对全球海平面上升做出了重大贡献，但由于缺乏数据，促进其快速流动的条件仍然很差。我们在格陵兰岛的Store Glacier上钻了七个钻孔，用来监测冰层下的水压、温度、电导率、浊度以及冰层的温度和变形。这些观测得到了表面速度和气象测量的补充，以深入了解快速冰川流动的条件和机制。每个钻孔距离崩解前沿30公里，在达到大约600米深时迅速排干，这表明与活跃的冰川下水文系统有直接联系。持续较高的冰下水压表明有效压力较低(180-280kPa)，小幅度变化与地表速度的显著峰值相关，这些峰值是由昼夜融化周期和较长的融化和降雨周期驱动的。由钻孔倾角测量确定的冰川形变剖面表明，63-71%的冰运动发生在冰床上，其余的29%-37%主要归因于冰柱最低50-100m处的强化变形。我们认为这个最低的100米是由温暖的前全新世冰盖在一层较薄的(0-8米)温带基冰层上形成的。我们的观察结果与空间上广泛且持续低效的冰下排水系统是一致的，我们假设该系统包括冰-沉积物界面和通过冰下沉积物的排水。这种形态与动态相似的南极冰流、阿拉斯加潮水冰川和汹涌的冰川下面的解释有相似之处。简单来说，格陵兰快速流动的潮水冰川对海平面上升做出了重要贡献，但人们对它们内部和下面的条件知之甚少。我们在Store Glacier的床上钻了几个钻孔，用传感器测量冰的温度和变形，以及冰层下的水的性质。这些数据表明，Store Glacier的快速流动主要是由高压冰下水和基底沉积物驱动的冰床界面运动造成的，同时有很大一部分冰变形集中在末次冰期沉积的最低80m冰层上。冰下条件，包括高压下无效的冰下排水，类似于在快速流动的南极冰流、阿拉斯加潮水冰川和激增的冰川下观察到的情况。
Marine-terminating outlet glaciers of the Greenland Ice Sheet make significant contributions to global sea level rise, yet the conditions that facilitate their fast flow remain poorly constrained owing to a paucity of data. We drilled and instrumented seven boreholes on Store Glacier, Greenland, to monitor subglacial water pressure, temperature, electrical conductivity, and turbidity along with englacial ice temperature and deformation. These observations were supplemented by surface velocity and meteorological measurements to gain insight into the conditions and mechanisms of fast glacier flow. Located 30km from the calving front, each borehole drained rapidly on attaining approximate to 600m depth indicating a direct connection with an active subglacial hydrological system. Persistently high subglacial water pressures indicate low effective pressure (180-280kPa), with small-amplitude variations correlated with notable peaks in surface velocity driven by the diurnal melt cycle and longer periods of melt and rainfall. The englacial deformation profile determined from borehole tilt measurements indicates that 63-71% of total ice motion occurred at the bed, with the remaining 29-37% predominantly attributed to enhanced deformation in the lowermost 50-100m of the ice column. We interpret this lowermost 100m to be formed of warmer, pre-Holocene ice overlying a thin (0-8m) layer of temperate basal ice. Our observations are consistent with a spatially extensive and persistently inefficient subglacial drainage system that we hypothesize comprises drainage both at the ice-sediment interface and through subglacial sediments. This configuration has similarities to that interpreted beneath dynamically analogous Antarctic ice streams, Alaskan tidewater glaciers, and glaciers in surge.Plain Language Summary Greenland's fast flowing tidewater glaciers account for significant contributions to sea level rise, yet little is known about the conditions within and beneath them. We instrumented boreholes drilled to the bed of Store Glacier with sensors to measure ice temperature and deformation, and subglacial water properties. These data reveal that the fast flow of Store Glacier is mainly caused by motion at the ice bed interface driven by highly pressurized subglacial water and basal sediments, together with a significant component of ice deformation concentrated in the lowermost 80m of ice deposited in the last glacial period. The subglacial conditions, including inefficient subglacial drainage at high pressure, are similar to those observed beneath fast-flowing Antarctic ice streams, Alaskan tidewater glacier, and glaciers in surge.