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Geodetic methods have been relied on heavily to quantify the response of glaciers and ice caps to warmingover the past few decades (e.g. Abdalati et al., 2004; Gardner et al., 2011; Gardner et al., 2012). Typicallyin such studies, the observed surface elevation change of a glacier or ice cap over a given time interval is used to directly calculate its mass loss. However, there can be a change elevation due to a change in firndensification rate or ice dynamics without actual mass loss. For example, at the summit of Penny Ice Cap,Baffin Island, the firn density increased due to the formation of infiltration ice layers, resulting in a 6%increase in cumulative ice‐equivalent thickness between 1995 and 2010 (Zdanowicz et al., 2012).To our knowledge no studies have previously measured the vertical component of ice motion (firncompaction and/or ice dynamics) or adjusted geodetic data over an entire ice cap in the Canadian Arctic. Inthis study we use NASA Airborne Topographic Mapper (ATM) laser altimetry data, ICESat data, as well as insitu geodetic and surface mass balance measurements, to determine surface elevation changes over Penny Ice Cap from 2005‐2013, and correct these data to account for the effects of vertical motion due to ice dynamics and firn densification. Our results show that failure to account for vertical ice motion and firn densification would result in an~19% overestimation of mass loss for this ice cap.

This study presents the first reanalysis of a long-term glacier mass-balance record in the Canadian Arctic. The reanalysis is accomplished through comparison of the 1960–2014 glaciological mass-balance record of White Glacier, Axel Heiberg Island, Nunavut, with a geodetically derived mass change over the same period. The corrections applied to homogenize the two datasets, including adjusting for changes in hypsometry over the period of record and the generic differences between methods, are discussed along with the associated systematic and random errors of the two forms of mass-balance measurement. Statistical comparison of the two datasets reveals that within the error margin there is no significant difference between the average annual glaciological balance (–213 ± 28 mm w.e. a−1) and geodetic balance (–178 ± 16 mm w.e. a−1) at White Glacier over the 54 year record. The validity of this result, and the assumptions made in implementing the glaciological method, are critically assessed.

Glaciers in the Wrangell and St. Elias Mountains (Alaska and Yukon) are presently experiencing some of thehighest regional wastage rates worldwide. While the effect of regional temperatures on glacier melt rates in thisregion has been investigated, comparatively little is known about how synoptic climate variations, for example inthe position and strength of the Aleutian Low, modulate snow accumulation on these glaciers. Such informationis needed to accurately forecast future wastage rates, glacier-water resource availability, and contributions tosea-level rise. Starting in 2000, automated weather stations (AWS) were established in the central St-EliasMountains (Yukon) at altitudes ranging from 1190 to 5400 m asl, to collect climatological data in support ofglaciological research. These data are the longest continuous year-round observations of surface climate everobtained from this vast glaciated region. Here we present an analysis of snowfall events in the icefields of theSt-Elias Mountains based on a decade-long series of AWS observations of snow accumulation. Specifically,we investigated the synoptic patterns and air mass trajectories associated with the largest snowfall events (> 25cm/12 hours) that occurred between 2002 and 2012. Nearly 80% of these events occurred during the cold season(October-March), and in 74 % of cases the precipitating air masses originated from the North Pacific south of50N. Zonal air mass advection over Alaska, or from the Bering Sea or the Arctic Ocean, was comparativelyrare (20%). Somewhat counter-intuitively, dominant surface winds in the St. Elias Mountains during highsnowfall events were predominantly easterly, probably due to boundary-layer frictional drag and topographicfunneling effects. Composite maps of sea-level pressure and 700 mb winds reveal that intense snowfall eventsbetween 2002 and 2012 were associated with synoptic situations characterized by a split, eastwardly-shifted orlongitudinally-stretched Aleutian Low (AL)

Recent observations of accelerated glacier wastage in Greenland and Alaska haveprompted reassessments of mass balance trends and volume changes on Cana-dian Arctic glaciers and ice caps. While long surface mass balance measurementsare available from glaciers and ice caps in the Queen Elizabeth Islands (e.g., WhiteGlacier, Devon Ice Cap, Meighen Ice Cap), no such records exist for Baffin Islandglaciers. In the absence of such data, air- and space-borne measurements canbe used in combination with in situ data to evaluate historical and recent trendsin ice cover changes. Here, we use repeat laser airborne altimetry surveys con-ducted in 2005 and 2013 by NASA to estimate recent volume and mass changesof Penny Ice Cap, the southernmost large ice cap on Baffin Island ( 66N). Thesedata are validated against in-situ surface mass balance measurements from 2013and IceSat derived elevation change from 2003-2009. Once validated, surface el-evation changes along altimetry lines are extrapolated to the entire ice cap usinga digital elevation model (DEM). Changes in areal extent of the ice cap are con-strained using satellite imagery (e.g. Landsat). From these data we estimate thetotal mass wastage of the ice cap and its recent contribution to sea level rise. Thiswork builds on previous surveys for the period 1995-2005 (Abdalati et al.,2004;Gardneret al.,2012).

On 4 August 2010, about one fifth of the floating ice tongue of Petermann Glacier (also known as “Petermann Gletscher”) in northwestern Greenland calved (Figure 1). The resulting “ice island” had an area approximately 4 times that of Manhattan Island (about 253±17 square kilometers). The ice island garnered much attention from the media, politicians, and the public, who raised concerns about downstream implications for shipping, offshore oil and gas operations, and possible connections to Arctic and global warming. Does this event signal a change in the glacier's dynamics? Or can it be characterized as part of the glacier's natural variability? Understanding the known historical context of this event allows scientists and the public to judge its significance.