Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling
Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling
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DOI：
10.5194/tc-12-1851-2018
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发表时间：
2018-06-04
期刊：
影响因子：
5.2
通讯作者：
Fettweis, Xavier
中科院分区：
文献类型：
--
作者：
Heilig, Achim;Eisen, Olaf;Fettweis, Xavier
在过去几年中记录的格陵兰冰盖（GrIS）的融化增加导致了冰盖渗滤制度的显着变化。目前尚不清楚格陵兰的渗滤区是否会在不久的将来通过逐渐填满所有孔隙空间而充当融水缓冲区，或者近地表的重新冻结是否会导致形成不渗透层，从而引发侧向径流。在多年积雪中观察到均匀的冰层，以及在积雪芯中观察到几米厚的近地表冰层。由于积雪取芯是一种破坏性的方法，推导积雪的地层变化和夏季融化事件的分配具有挑战性。为了克服这一缺陷，并为雪和积雪密度、液态水含量的时间变化和水渗透深度的模型评估提供连续数据，我们于2016年5月在2120 m a.s.l.的Raven营地（66.4779度N，46.2856度W）附近的雪面以下3.4 m处安装了一个上视雷达系统（upGPR）。该雷达能够准连续地监测天线上方积雪和积雪地层的变化。在2016年夏天，我们观察到四次主要的融化事件，这些事件将液态水引导到地表以下的不同深度。8月中旬的最后一次事件导致最深的渗透到地表以下约2.3米。与区域气候模式MAR的模拟比较，在积累的季节性变化和融化开始的时间方面非常一致。然而，无论是近地表层的体积密度，也不是液态水的量和渗透深度MAR预测与upGPR数据相对应。相比之下，雷达数据和附近热敏电阻串的记录在温度变化的时间和深度以及观察到的水蒸发方面都非常匹配。所有四次融化事件将56 kg m（-2）的累积质量转移到2015年夏季地表下的积雪中。我们发现，连续观测的液态水含量，渗透深度和速率的季节性质量通量是足够准确的模型方法的验证提供有价值的信息，并有助于开发一个更好地了解液态水的保留和渗透在常年积雪。
Increasing melt over the Greenland Ice Sheet (GrIS) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779 degrees N, 46.2856 degrees W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m(-2) into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.