The influence of surface melt on the flow of Greenland's largest outlet glaciers remains poorly known and in situ observations are few. We use field observations to link surface meltwater forcing to glacier-wide diurnal velocity variations on East Greenland's Helheim Glacier over two summer melt seasons. We observe diurnal variations in glacier speed that peak ~6.5 h after daily maximum insolation and extend from the terminus region to the equilibrium line. Both the amplitude of the diurnal speed variation and its sensitivity to daily melt are largest at the glacier terminus and decrease up-glacier, suggesting that the magnitude of the response is controlled not only by melt input volume and temporal variability, but also by background effective pressure, which approaches zero at the terminus. Our results provide evidence that basal lubrication by meltwater drives diurnal velocity variations at Greenland's marine-terminating glaciers in a similar manner to alpine glaciers and Greenland's land-terminating outlet glaciers.

中文翻译：

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由表面熔体强迫驱动的赫尔海姆冰川日速度波动

地表融化对格陵兰岛最大出口冰川流动的影响仍然鲜为人知，现场观测也很少。我们使用实地观测将表面融水强迫与两个夏季融化季节东格陵兰赫尔海姆冰川的冰川范围内的日速度变化联系起来。我们观察到冰川速度的昼夜变化，在每日最大日照后约 6.5 小时达到峰值，并从终点区域延伸到平衡线。昼夜速度变化的幅度及其对每日融化的敏感性在冰川终点处最大并且在冰川上方降低，这表明响应的幅度不仅受融化输入量和时间变化的控制，而且还受背景有效压力，在终点处接近零。