Gabriel J. Wolken

Sharply increased mass loss from glaciers and ice caps in the Canadian Arctic Archipelago

Mountain glaciers and ice caps are contributing significantly to present rates of sea level rise and will continue to do so over the next century and beyond. The Canadian Arctic Archipelago, located off the northwestern shore of Greenland, contains one-third of the global volume of land ice outside the ice sheets, but its contribution to sea-level change remains largely unknown. Here we show that the Canadian Arctic Archipelago has recently lost 61 ± 7 gigatonnes per year (Gt yr−1) of ice, contributing 0.17 ± 0.02 mm yr−1 to sea-level rise. Our estimates are of regional mass changes for the ice caps and glaciers of the Canadian Arctic Archipelago referring to the years 2004 to 2009 and are based on three independent approaches: surface mass-budget modelling plus an estimate of ice discharge (SMB+D), repeat satellite laser altimetry (ICESat) and repeat satellite gravimetry (GRACE). All three approaches show consistent and large mass-loss estimates. Between the periods 2004–2006 and 2007–2009, the rate of mass loss sharply increased from 31 ± 8 Gt yr−1 to 92 ± 12 Gt yr−1 in direct response to warmer summer temperatures, to which rates of ice loss are highly sensitive (64 ± 14 Gt yr−1 per 1 K increase). The duration of the study is too short to establish a long-term trend, but for 2007–2009, the increase in the rate of mass loss makes the Canadian Arctic Archipelago the single largest contributor to eustatic sea-level rise outside Greenland and Antarctica.

End‐of‐winter snow depth variability on glaciers in Alaska

A quantitative understanding of snow thickness and snow water equivalent (SWE) on glaciers is essential to a wide range of scientific and resource management topics. However, robust SWE estimates are observationally challenging, in part because SWE can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes. In spring 2013, we measured snow accumulation on several glaciers around the Gulf of Alaska using both ground- and helicopter-based ground-penetrating radar surveys, complemented by extensive ground truth observations. We found that SWE can be highly variable (40% difference) over short spatial scales (tens to hundreds of meters), especially in the ablation zone where the underlying ice surfaces are typically rough. Elevation provides the dominant basin-scale influence on SWE, with gradients ranging from 115 to 400 mm/100 m. Regionally, total accumulation and the accumulation gradient are strongly controlled by a glaciers distance from the coastal moisture source. Multiple linear regressions, used to calculate distributed SWE fields, show that robust results require adequate sampling of the true distribution of multiple terrain parameters. Final SWE estimates (comparable to winter balances) show reasonable agreement with both the Parameter-elevation Relationships on Independent Slopes Model climate data set (9–36% difference) and the U.S. Geological Survey Alaska Benchmark Glaciers (6–36% difference). All the glaciers in our study exhibit substantial sensitivity to changing snow-rain fractions, regardless of their location in a coastal or continental climate. While process-based SWE projections remain elusive, the collection of ground-penetrating radar (GPR)-derived data sets provides a greatly enhanced perspective on the spatial distribution of SWE and will pave the way for future work that may eventually allow such projections.

Remote sensing of recent glacier changes in the Canadian Arctic

The Canadian Arctic contains the largest area of land ice (~150,000 km2) on Earth outside the ice sheets of Greenland and Antarctica and is a potentially significant contributor to global sea level change. The current ice cover includes large ice caps that are remnants of the Wisconsinan Laurentide and Innuitian ice sheets, and many smaller ice caps and valley glaciers that formed during the late Holocene. Most of these ice masses have decreased in area over the past century as a result of climate warming in the first half of the 20th century and since the mid-1980s. In general, smaller ice masses have lost a higher proportion of their area, but the largest total area losses have come from the larger ice caps. Both iceberg calving and negative surface mass balances have contributed to this episode of glacier shrinkage. Long-term calving rates are not well known, however, and many tidewater glaciers exhibit velocity variability on a range of timescales that may affect calving rates. Floating ice shelves in northern Ellesmere Island have lost over 90 % of their area in the 20th century, with the most recent phase of disintegration occurring since 2000. Some fjords in the region are now ice free for the first time in over 3000 years. Regional rates of mass loss have accelerated strongly since 2005, and Canadian Arctic glaciers and ice caps have emerged as the most significant non–ice sheet contributor to the nonsteric component of global sea level rise.

Helicopter-borne radar imaging of snow cover on and around glaciers in Alaska

Abstract During spring 2013, we performed 500 MHz, helicopter-borne impulsive ground-penetrating radar surveys of several glaciers and glacier forelands in south-central Alaska, USA. These surveys were designed to obtain spatially distributed measurements of snow accumulation spanning a broad range of continental and maritime climatic zones. Visual assessment of radar images shows that data quality varied with the terrains and was optimal for snow that covered smooth glacier ice and firn, smooth debris-covered areas and moraines, freshwater lake and river ice, tundra, and taiga. Conversely, returns from the base of the snowpack were unrecognizable over rough debris-covered glacier termini, icefalls and some high-altitude accumulation basins. Optimal flying speed was 15-20ms–1 (30–40kt). At these speeds, which are two to three times faster than previously reported for such surveys, we could still identify snow-depth data with confidence, at a point spacing of ~1.5-2.0m. Data quality on glaciers decreased with increased air speed, though useful echoes from the base of the snowpack were still obtained at 40-45 ms–1 (87 kt; data point spacing of 6-8 m). Similar high-speed surveys over non-glacial terrains were unsuccessful, as basal reflections were no longer recognizable.