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The article presents a reply to the article "Glacier velocities and dynamic discharge from the ice masses of Baffin Island and Bylot Island, Nunavut, Canada," that was published in a previous issue of the journal.

The article presents a reply to the article "Glacier velocities and dynamic discharge from the ice masses of Baffin Island and Bylot Island, Nunavut, Canada," that was published in a previous issue of the journal.

In spring 2018, two firn cores (21 and 36 m in length) were extracted from the accumulation zone of Kaskawulsh Glacier, St. Elias Mountains, Yukon. The cores were analyzed for ice layer stratigraphy and density and compared against historical measurements made in 1964 and 2006. Deep meltwater percolation and refreezing events were evident in the cores, with a total ice content of 2.33±0.26 m in the 36 m core and liquid water discovered below a depth of 34.5 m. Together with the observed ice content, surface energy balance and firn modelling indicate that Kaskawulsh Glacier firn retained about 86 % of its meltwater in the years 2005–2017. For an average surface ablation of 0.38 m w.e. yr -1 over this period, an estimated 0.28 m w.e. yr -1 refroze in the firn, 0.05 m w.e. yr -1 was retained as liquid water, and 0.05 m w.e. yr -1 drained or ran off. The refrozen meltwater is associated with a surface lowering of 0.73±0.23 m between 2005 and 2017 (i.e., surface drawdown that has no associated mass loss). The firn has become denser and more ice-rich since the 1960s and contains a perennial firn aquifer (PFA), which may have developed over the past decade. This illustrates how firn may be evolving in response to climate change in the St. Elias Mountains, provides firn density information required for geodetic mass balance calculations, and is the first documented PFA in the Yukon–Alaska region. [ABSTRACT FROM AUTHOR]

The climate of high midlatitude mountains appears to be warming faster than the global average, but evidence for such elevation-dependent warming (EDW) at higher latitudes is presently scarce. Here, we use a comprehensive network of remote meteorological stations, proximal radiosonde measurements, downscaled temperature reanalysis, ice cores, and climate indices to investigate the manifestation and possible drivers of EDW in the St. Elias Mountains in subarctic Yukon, Canada. Linear trend analysis of comprehensively validated annual downscaled North American Regional Reanalysis (NARR) gridded surface air temperatures for the years 1979–2016 indicates a warming rate of 0.028°C a−1 between 5500 and 6000 m above mean sea level (MSL), which is ~1.6 times larger than the global-average warming rate between 1970 and 2015. The warming rate between 5500 and 6000 m MSL was ~1.5 times greater than the rate at the 2000–2500 m MSL bin (0.019°C a−1), which is similar to the majority of warming rates estimated worldwide over similar elevation gradients. Accelerated warming since 1979, measured by radiosondes, indicates a maximum rate at 400 hPa (~7010 m MSL). EDW in the St. Elias region therefore appears to be driven by recent warming of the free troposphere. MODIS satellite data show no evidence for an enhanced snow albedo feedback above 2500 m MSL, and declining trends in sulfate aerosols deposited in high-elevation ice cores suggest a modest increase in radiative forcing at these elevations. In contrast, increasing trends in water vapor mixing ratio at the 500-hPa level measured by radiosonde suggest that a longwave radiation vapor feedback is contributing to EDW. [ABSTRACT FROM AUTHOR]

Abstract: Mass movement constitutes an important process in the evolution of landscapes in mountain regions. However, the role of massive slope failures in denudational unloading and landscape evolution has not been extensively studied. Large-scale mass movements in one of the greatest mountain ranges on Earth, the Central Karakoram in Pakistan, were therefore examined to help evaluate their role in landscape evolution in high mountains. Specifically, four major mass-movement complexes (Ghoro Choh rock avalanche, Busper sackung and slope failure, Gomboro slope failure, and Urdokas rockslide), each comprising 106 m3 of debris, were assessed and mapped in detail. Two of these mass-movement complexes, the Ghoro Choh rock avalanche and Gomboro slope failure, were dated using terrestrial cosmogenic nuclides. The ages of occurrence of the mass-movement complexes studied in the Central Karakoram date from the late Pleistocene to the Holocene. The four major mass-movement complexes all involved the removal of mass from the tops of mountain ridges and peaks that failed and were subsequently transported towards the bottom of their respective valleys. Such massive movement of mass is anomalous compared to other forms of mass movement and is generally spatially coincident with exposed deeply buried gneiss-dome structures. These large-scale movements appear to be part of a coupled system involving river incision and glacial debuttrussing, although earthquakes might have triggered these mass movements. This study illustrates the role of climate forcing, which is part of a coupled system of denudational unloading, but it is unclear whether high-magnitude, low-frequency events such as these initiate the isostatic and tectonic influx of mass, or if sustained high-magnitude denudation resulting from a coupled system is responsible for the exhumation of buried structures. [Copyright &y& Elsevier]

Abstract: Basin-wide rockwall retreat rates are estimated using cosmogenic 10Be concentrations in supraglacial debris from the Baltoro Glacier basin in K2 region of the Central Karakoram, Pakistan. Total cosmogenic 10Be concentrations of the supraglacial debris were measured using accelerator mass spectrometry to determine 10Be concentrations inherited from the rockwalls within the glaciated basin. Given that rockfall induced by periglacial weathering and snow and ice avalanches is the most important source of supraglacial debris production in the high mountain glaciated basin, the erosion rate of the bare bedrock can be considered to be the rate of rockwall retreat. The rate of the rockwall erosion, converted from the calculated inheritance of 10Be concentrations, using the maximum velocity of the active glacier, places an upper limit ranging from 0.65 mm/year to 2.48 mm/year. This rate of rockwall retreat is in the same order of magnitude reported in other high Himalayan mountains. The rate, however, is an order of magnitude higher than erosion rates inferred from sediment budget studies and half that of the fluvial incision rate and exhumation rate for the same region. The difference between rates of basin-wide rockwall retreat and fluvial incision rates over the Late Quaternary suggests that in this glaciated basin fluvial incision is likely enhanced by localized/differential tectonism and/or isostatic uplift. [Copyright &y& Elsevier]

Abstract: The Central Karakoram, which includes K2 in Pakistan, is one of the most rapidly rising areas on Earth and exhibits complex topography and extreme relief. Impressive valley fills and glacial landforms are present throughout the valleys. The dynamics of landscape evolution of the region are currently not well understood. Consequently, the landforms were mapped and assessed in the Skardu, Shigar, and Braldu valleys, to elucidate the spatio-temporal scale dependencies of surface processes active in the region. These valleys were examined using geomorphic field methods, remote sensing, geomorphometry, and terrestrial cosmogenic nuclides (TCNs) surface exposure dating. The glaciers in this region have oscillated considerably throughout the Late Quaternary, and four glacial stages have been recognized including at least six glacial advances. Surface processes readjusted after glacier retreat, and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms, while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley. Glacier geochronology and late Holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late Quaternary. [Copyright &y& Elsevier]

Glacier mass loss affects sea level rise, water resources, and natural hazards. We present global glacier projections, excluding the ice sheets, for shared socioeconomic pathways calibrated with data for each glacier. Glaciers are projected to lose 26 ± 6% (+1.5°C) to 41 ± 11% (+4°C) of their mass by 2100, relative to 2015, for global temperature change scenarios. This corresponds to 90 ± 26 to 154 ± 44 millimeters sea level equivalent and will cause 49 ± 9 to 83 ± 7% of glaciers to disappear. Mass loss is linearly related to temperature increase and thus reductions in temperature increase reduce mass loss. Based on climate pledges from the Conference of the Parties (COP26), global mean temperature is projected to increase by +2.7°C, which would lead to a sea level contribution of 115 ± 40 millimeters and cause widespread deglaciation in most mid-latitude regions by 2100.

In the Northern Hemisphere, ~1500 glaciers, accounting for 28% of glacierized area outside the Greenland Ice Sheet, terminate in the ocean. Glacier mass loss at their ice-ocean interface, known as frontal ablation, has not yet been comprehensively quantified. Here, we estimate decadal frontal ablation from measurements of ice discharge and terminus position change from 2000 to 2020. We bias-correct and cross-validate estimates and uncertainties using independent sources. Frontal ablation of marine-terminating glaciers contributed an average of 44.47 ± 6.23 Gt a -1 of ice to the ocean from 2000 to 2010, and 51.98 ± 4.62 Gt a -1 from 2010 to 2020. Ice discharge from 2000 to 2020 was equivalent to 2.10 ± 0.22 mm of sea-level rise and comprised approximately 79% of frontal ablation, with the remainder from terminus retreat. Near-coastal areas most impacted include Austfonna, Svalbard, and central Severnaya Zemlya, the Russian Arctic, and a few Alaskan fjords., (© 2022. The Author(s).)

The Canadian Arctic Archipelago contains >300 glaciers that terminate in the ocean, but little is known about changes in their frontal positions in response to recent changes in the ocean-climate system. Here, we examine changes in glacier frontal positions since the 1950s and investigate the relative influence of oceanic temperature versus atmospheric temperature. Over 94% of glaciers retreated between 1958 and 2015, with a region-wide trend of gradual retreat before ~2000, followed by a fivefold increase in retreat rates up to 2015. Retreat patterns show no correlation with changes in subsurface ocean temperatures, in clear contrast to the dominance of ocean forcing in western Greenland and elsewhere. Rather, significant correlations with surface melt indicate that increased atmospheric temperature has been the primary driver of the acceleration in marine-terminating glacier frontal retreat in this region.