Changes in accumulation-area firn stratigraphy and meltwater flow during a period of climate warming: Devon Ice Cap, Nunavut, Canada

To document climate-driven changes in firn stratigraphy and their implications for meltwater flow patterns within firn on the Devon Ice Cap, Nunavut, during the 21st century summer warming, 500MHz ground-penetrating radar (GPR) surveys were conducted along a 40km transect in each spring from 2007 to 2012. These linear GPR surveys were supplemented by four 190m by 100m GPR grid surveys and 36 firn cores. Increased meltwater percolation and infiltration ice formation associated with high surface melt rates since 2005 modified the firn stratigraphy substantially over a horizontal distance of nearly 30km. The most dramatic change involved the growth of a thick ice layer within the firn body. This layer grew primarily by upward accretion over an initial widespread ice layer formed during summer 2005. It thickened by between 0.5 and 4.5m over the study period and filled much of the pore volume in the upper part of the firn, reducing vertical percolation of meltwater into deeper sections of the firn and thus the water storage potential of much of the firn reservoir. Heterogeneous percolation of surface meltwater promoted by rolling topography played an important role in meltwater infiltration and drainage, encouraging lateral flow at the tops of small hills and ponding and refreezing of meltwater beneath surface depressions.

为记录21世纪夏季变暖期间努纳武特德文冰帽内积雪地层因气候驱动而发生的变化及其对融水流动模式的影响，2007年至2012年每年春季沿着一条40千米的样带进行了500兆赫兹地面穿透雷达（GPR）勘测。这些线性的GPR勘测由四次190米×100米的GPR网格勘测以及36个积雪芯加以补充。自2005年以来，与高地表融化速率相关的融水渗滤增加以及渗透冰的形成，在近30千米的水平距离内极大地改变了积雪地层。最显著的变化是积雪体内一个厚冰层的增长。该冰层主要通过在2005年夏季形成的一个最初广泛分布的冰层上向上增生而增长。在研究期间，它增厚了0.5米至4.5米，填充了积雪上部的大部分孔隙空间，减少了融水向积雪更深处的垂直渗滤，从而降低了大部分积雪储层的储水潜力。起伏地形促使地表融水的非均匀渗滤在融水渗透和排泄中起重要作用，促使小山顶上的侧向流动以及地表洼地下方融水的汇集和再冻结。