Processes governing meltwater penetration into cold firn remain poorly constrained. Here, in situ experiments are used to develop a grain-scale model to investigate physical limitations on meltwater infiltration in firn. At two sites in Greenland, drilling pumped water into cold firn to >75 m depth, and the thermo-hydrologic evolution of the firn column was measured. Rather than filling all available pore space, the water formed perched aquifers with downward penetration halted by thermal and density conditions. The two sites formed deep aquifers at ~40 m depth and at densities considerably less than the air pore close-off density (~725 kg m−3 at −18°C, and ~750 kg m−3 at −14°C), demonstrating that some pore space at depth remains inaccessible. A geometric grain-scale model of firn is constructed to quantify the limits of a descending fully saturated wetting front in cold firn. Agreement between the model and field data implies the model includes the first-order effects of water and heat flow in a firn lattice. The model constrains the relative importance of firn density, temperature and grain/pore size in inhibiting wetting front migration. Results imply that deep infiltration, including that which leads to firn aquifer formation, does not have access to all available firn pore space.

中文翻译：

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融水在冷杉中渗透的物理限制

控制融水渗入冷地层的过程仍然受到很少的约束。在这里，原位实验用于开发颗粒尺度模型，以研究对融水入渗的物理限制。在格陵兰岛的两个地点，钻探将水抽入冷冰层深度 > 75 m，并测量了冰层柱的热水文演变。水并没有填满所有可用的孔隙空间，而是形成了栖息的含水层，其向下渗透会因热力和密度条件而停止。这两个地点在约 40 m 深度处形成了深层含水层，其密度远低于气孔封闭密度（约 725 kg m-3在 -18°C 和 ~750 kg m-3在-14°C），表明深度的一些孔隙空间仍然无法进入。构建了一个几何颗粒尺度模型来量化冷杉中下降的完全饱和润湿锋的极限。模型和现场数据之间的一致性意味着该模型包括水流和热流在冰晶格中的一阶效应。该模型限制了杉木密度、温度和晶粒/孔径在抑制润湿前沿迁移中的相对重要性。结果表明，深层渗透，包括导致冰层含水层形成的渗入，无法进入所有可用的冰层孔隙空间。