Observed melt-season snowpack evolution on the Greenland ice sheet
Observed melt-season snowpack evolution on the Greenland ice sheet
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观察格陵兰冰盖融化季节积雪的演变
DOI：
10.34194/geusb.v33.4503
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发表时间：
1969
影响因子：
--
通讯作者：
D. As
中科院分区：
文献类型：
--
作者：
Charalampos Charalampidis;D. As
由于格陵兰岛最近出现了温暖且创纪录的温暖夏季（Nghiem 等人，2012 年），冰盖表面的融化和随后的径流正在增加（Shepherd 等人，2012 年）。 2009 年至 2012 年间，格陵兰冰盖约 84% 的质量损失是由于地表径流增加造成的（Enderlin 等人，2014 年）。最大的融化发生在消融区，即冰盖的低边缘区域（Van As et al. 2014），这里的融化量超过了冬季的积累，因此在每个融化季节都会暴露出裸露的冰。在冰盖较高的区域（即积雪区），融化有限，积雪全年持续存在。正是在后一个广阔的领域，模型难以准确计算某些质量通量。更好地了解融水渗透以及雪和冰雪中的再冻结等过程对于更准确地估计格陵兰冰盖总体预算至关重要（Van Angelen 等人，2013 年）。 2012 年 5 月，丹麦和格陵兰地质调查局 (GEUS) 在 KAN_U 自动气象站（北纬 67°0 0，西经 47°1 1；海拔 1840 米）组织了“低积雪带的积雪过程”现场活动，该活动向格陵兰冰盖监测计划（PROMICE；Van As 等人，2013）提供数据，是为数不多的活动之一。气象站位于格陵兰岛下部堆积区（图 1，插图）。在探险期间，我们安装了热敏电阻串、压实度监视器和积雪分析仪；我们钻探了岩心，进行了岩心雷达测量，收集了气象数据，挖了雪坑并进行了染料示踪实验。该活动的一个重要目标是通过高精度温度探头（Campbell Scientific 温度探头，型号 107；精度：在 –24 至 48°C 范围内优于 ± 0.4°C）进行监测，了解融化季节期间积雪的热变化。在去年冬天的积雪中安装了6个温度探头，深度分别为0.05、0.10、0.20、0.30、0.40和0.70 m（图1）。探测器的数据每隔 30 分钟存储在数据记录器上，这还触发了对 1.10 m 处的辐射屏蔽空气温度、表面反照率以及由于累积和消融而导致的表面高度变化的额外测量。还记录了发射的长波辐射，以便能够计算假设雪是黑体辐射体的表面温度。探头相对于表面的垂直位置由于烧蚀和积累而变化，由声波测距仪测量确定。探针浮出水面后记录的温度被丢弃。相对较浅的积雪（0.70~0.80 m）位于前几年积雪密度ρ>500 kg·m-3的积雪之上（图1）。在上层冰层中，我们发现了几米厚的冰晶状体（ρ >800 kg m–3）。积雪内有两层薄冰层，一层为 0.30 m
Due to recent warm and record-warm summers in Greenland (Nghiem et al. 2012), the melt of the ice-sheet surface and the subsequent runoff are increasing (Shepherd et al. 2012). About 84% of the mass loss from the Greenland ice sheet between 2009 and 2012 resulted from increased surface runoff (Enderlin et al. 2014). Th e largest melt occurs in the ablation zone, the low marginal area of the ice sheet (Van As et al. 2014), where melt exceeds wintertime accumulation and bare ice is thus exposed during each melt season. In the higher regions of the ice sheet (i.e. the accumulation area), melt is limited and the snow cover persists throughout the year. It is in the vast latter area that models struggle to calculate certain mass fl uxes with accuracy. A better understanding of processes such as meltwater percolation and refreezing in snow and fi rn is crucial for more accurate Greenland icesheet mass-budget estimates (Van Angelen et al. 2013). In May 2012, the fi eld campaign ‘Snow Processes in the Lower Accumulation Zone’ was organised by the Geological Survey of Denmark and Greenland (GEUS) at the KAN_U automatic weather station (67°0 0 N, 47°1 1 W; 1840 m above sea level), which delivers data to the Programme for Monitoring of the Greenland Ice Sheet (PROMICE; Van As et al. 2013) and is one of the few weather stations located in the lower accumulation area of Greenland (Fig. 1, inset). During the expedition, we installed thermistor strings, fi rn compaction monitors and a snowpack analyser; we drilled fi rn cores, performed fi rn radar measurements, gathered meteorological data, dug snow pits and performed dye-tracing experiments. One important objective of the campaign was to understand the thermal variability in the snowpack during the melt season by monitoring with high-precision temperature probes (Campbell Scientifi c temperature probe, model 107; accuracy: better than ± 0.4°C over the range –24 to 48°C). Six temperature probes were installed in the snowpack of the previous winter at depths of 0.05, 0.10, 0.20, 0.30, 0.40 and 0.70 m below the surface (Fig. 1). Th e data from the probes were stored at 30-minute intervals on data loggers, which also triggered additional measurements of radiation-shielded air temperature at 1.10 m, surface albedo and surface-height change due to accumulation and ablation. Emitted longwave radiation was also recorded to be able to calculate the surface temperature assuming snow to be a black-body radiator. Th e vertical position of the probes relative to the surface, which changes due to ablation and accumulation, was determined by the sonic ranger measurements. Recorded temperatures aft er the probes surfaced were discarded. Th e relatively shallow snowpack (0.70–0.80 m) was on top of fi rn of density ρ >500 kg m-3 which had accumulated in the previous years (Fig. 1). In the upper fi rn we found ice lenses (ρ >800 kg m–3) several metres thick. Within the snowpack, two thin ice layers were present, one at 0.30 m