Multi-decadal reduction in glacier velocities and mechanisms driving deceleration at polythermal White Glacier, Arctic Canada
Multi-decadal reduction in glacier velocities and mechanisms driving deceleration at polythermal White Glacier, Arctic Canada
复制标题
加拿大北极地区多温白冰川冰川速度的数十年减少和驱动减速的机制
DOI：
10.1017/jog.2017.3
复制
发表时间：
2017
影响因子：
3.4
通讯作者：
L. Copland
中科院分区：
文献类型：
--
作者：
L. Thomson;L. Copland
白色冰川是一个长14 km、海拔100-1800 m的多温谷冰川，提供了加拿大北极地区最全面的冰动态早期记录。通过与2012年至2016年的差分GPS导出的速度数据进行比较，我们发现在低海拔（600和400 m a.s.l.），平均年速度降低了31%和38%。这些都与减少内部冰变形由于冰变薄和减少的基础运动可能是由于近年来增加水力效率。在较高海拔（约850 m a.s.l.）没有可检测到的变化，在每年的速度和预期的减少，由于冰变薄的内部变形率是抵消了增加的基础运动在夏季和冬季，可能是由于冰上融化访问一个仍然效率低下的冰下排水系统。自20世纪60年代以来，低海拔地区质量通量的减少无法解释观测到的约20米的海拔损失，这意味着冰川主干沿着变薄主要是向下消耗的函数，而不是改变冰的动力学。冰川目前的反应证实了ELA的稳定变薄、速度减慢和上游退缩，但是，由于冰川具有不稳定的几何形状，在1300-1500 m海拔范围内具有相当大的质量，ELA在25-40年内退缩到>1300可能会引发失控的浪费。
ABSTRACT Annual and seasonal surface velocities measured continuously from 1960 to 1970 at White Glacier, a 14 km long polythermal valley glacier spanning ~100–1800 m a.s.l., provide the most comprehensive early record of ice dynamics in the Canadian Arctic. Through comparison with differential GPS-derived velocity data spanning 2012–16, we find reductions in mean annual velocity by 31 and 38% at lower elevations (600 and 400 m a.s.l.). These are associated with decreased internal ice deformation due to ice thinning and reduced basal motion likely due to increased hydraulic efficiency in recent years. At higher elevation (~850 m a.s.l.) there is no detectable change in annual velocity and the expected decrease in internal deformation rates due to ice thinning is offset by increased basal motion in both summer and winter, likely attributable to supraglacial melt accessing a still inefficient subglacial drainage system. Decreases in mass flux at lower elevations since the 1960s cannot explain the observed elevation loss of ~20 m, meaning that ice thinning along the glacier trunk is primarily a function of downwasting rather than changing ice dynamics. The current response of the glacier exemplifies steady thinning, velocity slowdown and upstream retreat of the ELA but, because the glacier has an unstable geometry with considerable mass in the 1300–1500 m elevation range, a retreat of the ELA to >1300 plausible within 25–40 years, could trigger runaway wastage.