Current sea-level rise partly stems from increased surface melting and meltwater runoff from the Greenland ice sheet. Multi-year snow, also known as firn, covers about 80% of the ice sheet and retains part of the surface meltwater. Since the firn cold content integrates its physical and thermal characteristics, it is a valuable tool for determining the meltwater-retention potential of firn. We use gap-filled climatological data from nine automatic weather stations in the ice-sheet accumulation area to drive a surface-energy-budget and firn model, validated against firn density and temperature observations, over the 1998–2017 period. Our results show a stable top 20 m firn cold content (CC20) at most sites. Only at the lower-elevation Dye-2 site did CC20 decrease, by 24% in 2012, before recovering to its original value by 2017. Heat conduction towards the surface is the main process feeding CC20 at all nine sites, while CC20 reduction occurs through low-cold-content fresh-snow addition at the surface during snowfall and latent-heat release when meltwater refreezes. Our simulations suggest that firn densification, while reducing pore space for meltwater retention, increases the firn cold content, enhances near-surface meltwater refreezing and potentially sets favourable conditions for ice-slab formation.

中文翻译：

---

1998 年至 2017 年间格陵兰冰盖上 9 个地点的冷含量演变

目前的海平面上升部分源于格陵兰冰盖的地表融化和融水径流增加。多年积雪，也称为冷杉，覆盖了大约 80% 的冰盖，并保留了部分地表融水。由于冰冷含量综合了它的物理和热特性，它是确定冰冷融水潜力的有价值的工具。我们使用来自冰盖堆积区 9 个自动气象站的填空气候数据来驱动表面能量预算和冰层模型，并在 1998 年至 2017 年期间根据冰层密度和温度观测结果进行验证。我们的结果显示稳定的顶部 20 m 冷含量（CC20) 在大多数网站上。只有在海拔较低的 Dye-2 站点进行了 CC202012 年减少了 24%，然后到 2017 年恢复到原来的值。向表面的热传导是供给 CC 的主要过程20在所有九个站点，而 CC20降雪期间通过在地表添加低冷含量的新雪和融水重新冻结时释放潜热来减少冷量。我们的模拟表明，岩层致密化在减少融水滞留的孔隙空间的同时，增加了岩层冷含量，增强了近地表融水的再冻结，并可能为冰板的形成创造有利条件。