Department of Electrical Engineering, Stanford University, Stanford, CA, USA.
Department of Geophysics, Stanford University, Stanford, CA, USA.
Nat Commun. 2021 Apr 20;12(1):2336. doi: 10.1038/s41467-021-22656-5.
Surface meltwater runoff dominates present-day mass loss from the Greenland Ice Sheet. In Greenland's interior, porous firn can limit runoff by retaining meltwater unless perched low-permeability horizons, such as ice slabs, develop and restrict percolation. Recent observations suggest that such horizons might develop rapidly during extreme melt seasons. Here we present radar sounding evidence that an extensive near surface melt layer formed following the extreme melt season in 2012. This layer was still present in 2017 in regions up to 700 m higher in elevation and 160 km further inland than known ice slabs. We find that melt layer formation is driven by local, short-timescale thermal and hydrologic processes in addition to mean climate state. These melt layers reduce vertical percolation pathways, and, under appropriate firn temperature and surface melt conditions, encourage further ice aggregation at their horizon. Therefore, the frequency of extreme melt seasons relative to the rate at which pore space and cold content regenerates above the most recent melt layer may be a key determinant of the firn's multi-year response to surface melt.
地表融水径流是目前格陵兰冰原质量损失的主要原因。在格陵兰内陆，多孔的积雪可能会通过保留融水来限制径流，除非形成低渗透性的悬空地层，如冰板，并限制渗透。最近的观测表明，在极端融雪季节，这种地层可能会迅速发育。在这里，我们提出了雷达探测的证据，表明在 2012 年极端融雪季节之后，形成了一个广泛的近地表融雪层。在海拔高达 700 米以上、比已知冰板更内陆 160 公里的地区，2017 年仍存在这种融雪层。我们发现，除了平均气候条件外，融雪层的形成还受到当地短期热和水文过程的驱动。这些融雪层减少了垂直渗透途径，并在适当的积雪温度和地表融雪条件下，鼓励在其层面进一步聚集冰。因此，相对于最近一次融雪层之上的孔隙空间和冷含量再生的速度，极端融雪季节的频率可能是积雪对地表融雪多年反应的关键决定因素。
