BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Landsat 7 and RADARSAT‐1/RADARSAT‐2 satellite images are used to produce the most comprehensive record of glacier motion in the Canadian High Arctic to date and to characterize spatial and temporal variability in ice flow over the past ~15 years. This allows us to assess whether dynamically driven glacier change can be attributed to “surging” or “pulsing,” or whether other mechanisms are involved. RADAR velocity mapping allows annual regional dynamic discharge (iceberg calving) to be calculated for 2000 and the period 2011–2015 (yielding a mean regional discharge of 2.21 ± 0.68 Gt a−1), and velocities derived from feature tracking of optical imagery allow for annual dynamic discharge to be calculated for select glaciers from 1999 to 2010. Since ~2011, several of the major tidewater‐terminating glaciers within the region have decelerated and their dynamic discharge has decreased. Trinity and Wykeham Glaciers (Prince of Wales Icefield) represent a notable departure from this pattern as they have generally accelerated over the study period. The resulting increase in dynamic discharge from these glaciers entirely compensates (within error limits) for the decrease in discharge from the other tidewater glaciers across the study region. These two glaciers accounted for ~62% of total regional dynamic discharge in winter 2015 (compared to ~22% in 2000), demonstrating that total ice discharge from the Canadian High Arctic can be sensitive to variations in flow of just a few tidewater glaciers.

A systematic review of 1959/60 aerial photography, and 1999/2000 Landsat 7 imagery, has identified 51 surge-type polythermal glaciers in the Canadian High Arctic. These were identified from the presence of features such as looped medial moraines, intense folding visible at the surface, rapid terminus advance, heavy surface crevassing, and high surface velocities. These observations suggest that surging glaciers are much more common than previously believed in the Canadian High Arctic, where only six surge-type glaciers have previously been described. Of the 51 surge-type glaciers identified in this study, 15 were observed in the active phase in the 1959/60 and/or 1999/2000 imagery. The most dramatic advances have occurred on western Axel Heiberg Island, where Iceberg,“Good Friday Bay” and Airdrop Glaciers have all advanced by 4–7 km between1959 and 1999. For glaciers with repeat Landsat 7 coverage from 1999 and 2000, image correlation software was used to determine the magnitude and spatial distribution of surge velocities. For example,“Mittie” Glacier on Manson Icefield was moving at a rate of up to 1 kma–over a distance of at least 25 km back from its terminus. The terminus of this glacier has advanced by at least 4 km since 1959, and the glacier was observed to be heavily crevassed during overflights in April 2000, with clear signs of surface lowering of 10–25 m indicated by a strandline.

Spatial patterns in residual bed reflection power (BRPr), derived from ground-based radio-echo sounding, were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high-Arctic polythermal glacier (John Evans Glacier, Ellesmere Island, Canada). BRPr is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier. We identified three types of thermal structure: (a) Positive BRPr and an internal reflecting horizon occur over the glacier terminus. The reflecting horizon is interpreted as the boundary between warm and cold ice, and suggests the presence of a warm basal layer. (b) Positive BRPr occurs without an internal reflector in the upper part of the ablation zone. This suggests that ice is at the pressure-melting point only at the bed. (c) Negative BRPr without an internal reflector occurs in all other regions, suggesting cold ice at the bed. Where BRPr is positive, its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface. This suggests that hydrological conditions at the glacier bed are a major control on BRPr, probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials.

ABSTRACT. The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris-covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers.We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock-glacier morphologies.

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[1] On August 13, 2005, almost the entire Ayles Ice Shelf (87.1 km 2 ) calved off within an hour and created a new 66.4 km 2 ice island in the Arctic Ocean. This loss of one of the six remaining Ellesmere Island ice shelves reduced their overall area by $7.5%. The ice shelf was likely weakened prior to calving by a long-term negative mass balance related to an increase in mean annual temperatures over the past 50+ years. The weakened ice shelf then calved during the warmest summer on record in a period of high winds, record low sea ice conditions and the loss of a semipermanent landfast sea ice fringe. Climate reanalysis suggests that a threshold of >200 positive degree days year À1 is important in determining when ice shelf calving events occur on N. Ellesmere Island.

Recent studies indicate an increase in glacier mass loss from the Canadian Arctic Archipelago as a result of warmer summer air temperatures. However, no complete assessment of dynamic ice discharge from this region exists. We present the first complete surface velocity mapping of all ice masses in the Queen Elizabeth Islands and show that these ice masses discharged~2.6 ± 0.8 Gt a À1 of ice to the oceans in winter2012. Approximately 50% of the dynamic discharge was channeled through non surge-type Trinity and Wykeham Glaciers alone. Dynamic discharge of the surge-type Mittie Glacier varied from 0.90 ± 0.09 Gt a À1during its 2003 surge to 0.02 ± 0.02 Gt a À1 during quiescence in 2012, highlighting the importance of surge-type glaciers for interannual variability in regional mass loss. Queen Elizabeth Islands glaciers currently account for~7.5% of reported dynamic discharge from Arctic ice masses outside Greenland.