Six Decades of Glacial Mass Loss in the Canadian Arctic Archipelago

The Canadian Arctic Archipelago comprises multiple small glaciers and ice caps, mostly concentrated on Ellesmere and Baffin Islands in the northern (NCAA, Northern Canadian Arctic Archipelago) and southern parts (SCAA, Southern Canadian Arctic Archipelago) of the archipelago, respectively. Because these glaciers are small and show complex geometries, current regional climate models, using 5- to 20-km horizontal resolution, do not properly resolve surface mass balance patterns. Here we present a 58-year (1958-2015) reconstruction of daily surface mass balance of the Canadian Arctic Archipelago, statistically downscaled to 1km from the output of the regional climate model RACMO2.3 at 11km. By correcting for biases in elevation and ice albedo, the downscaling method significantly improves runoff estimates over narrow outlet glaciers and isolated ice fields. Since the last two decades, NCAA and SCAA glaciers have experienced warmer conditions (+1.1 degrees C) resulting in continued mass loss of 28.2 11.5 and 22.0 4.5Gt/year, respectively, more than doubling (11.9Gt/year) and doubling (11.9Gt/year) the pre-1996 average. While the interior of NCAA ice caps can still buffer most of the additional melt, the lack of a perennial firn area over low-lying SCAA glaciers has caused uninterrupted mass loss since the 1980s. In the absence of significant refreezing capacity, this indicates inevitable disappearance of these highly sensitive glaciers. Plain Language Summary Outside the ice sheets of Greenland and Antarctica, the Canadian Arctic Archipelago is home to 14% of the world's ice-covered area. Ice caps can be found on Ellesmere and Baffin Islands in the north and south of the archipelago. Here we present a novel daily, 1 km surface mass balance product for the period 1958-2015 that allows us to quantify the contemporary mass loss of Canadian ice caps and identify the acting processes. The high-resolution product realistically resolves local patterns of mass change over narrow glaciers and confined ice fields that are often found in the Canadian Arctic. We show that these ice caps have been losing mass for decades and that mass loss accelerated in 1996. This followed a significant warming (+1.1 degrees C), which increased the production of meltwater. While the snow covering the interior of the northern ice caps can still buffer most of this additional melt through refreezing, the lack of a perennial snow cover over low-lying southern ice caps caused uninterrupted mass loss since the 1980s. If this trend is not reversed, these southern ice caps might disappear within 400years.