Mass‐balance estimates of the polar ice sheets presently rely on static ice masks to identify the area under investigation. However, the vintage of available ice masks can differ by more than a decade, and the resolution of the imagery used to delineate ice extent can differ by an order of magnitude, despite evidence of ongoing ice‐sheet retreat. We show that using a fine‐resolution, time‐varying ice mask significantly improves mass‐balance estimates of the northwestern sector of the Greenland Ice Sheet and affects interpretation of local crustal uplift. Accounting for ice margin retreat using a time‐varying ice mask between 2003 and 2015 results in 1.0%–6.8% less ice‐sheet mass loss relative to assuming one of several existing static ice masks. This indicates that mass‐balance estimates that use a static ice mask will progressively overestimate mass loss where the ice sheet is predominantly retreating, meaning a negative bias on mass‐balance. This trend is anticipated to be amplified in a future warming scenario unless updated ice masks are incorporated. For altimetry‐derived mass‐balance estimates, this ice‐mask‐induced bias approaches the magnitude of the ice‐sheet‐wide uncertainty presently associated with spatiotemporal variability in modeled firn compaction. Further, at five Greenland GPS Network (GNET) stations, the ice‐mask‐induced bias is equivalent to 5%–15% of the modeled uplift due to elastic deformation. Given present and projected negative trends in Greenland Ice Sheet mass‐balance and areal extent, we conclude that studies of its mass‐balance should begin incorporating dynamic, periodically updated, fine‐resolution ice masks. This methodological refinement will reduce bias in estimates of both ice‐sheet mass‐balance and crustal uplift.

中文翻译：

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时变冰盖面膜：对冰盖质量平衡和地壳隆升的影响

目前，极地冰盖的质量平衡估计依赖于静态冰罩来确定被调查的区域。但是，可用冰面罩的年份可能相差十多年，尽管有证据表明冰盖正在不断退缩，但用来描述冰面范围的图像分辨率可能相差一个数量级。我们表明，使用高分辨率，时变的冰面罩可以大大改善格陵兰冰原西北部的质量平衡估计，并影响对当地地壳隆升的解释。与使用多个现有的静态冰罩之一进行假设相比，在2003年至2015年之间使用时变冰罩对冰缘退缩进行核算，可减少1.0％–6.8％的冰盖质量损失。这表明使用静态冰罩的质量平衡估计将逐渐高估冰原主要后退的质量损失，这意味着质量平衡存在负偏倚。除非并入更新的冰罩，否则这种趋势预计在未来的变暖情况下会加剧。对于基于海拔高度的质量平衡估计，这种冰罩引起的偏差接近模拟的压实模型中当前与时空变化相关的冰盖范围不确定性的大小。此外，在五个格陵兰GPS网络（GNET）站，由于弹性变形，冰罩引起的偏差相当于模拟隆起的5％–15％。考虑到格陵兰冰原质量平衡和面积范围目前和预计的负面趋势，我们得出结论，对其质量平衡的研究应开始纳入动态的，定期更新的，高分辨率的冰罩。这种方法上的改进将减少冰盖质量平衡和地壳隆升估计的偏差。