ALBERT

Description: Clouds play an important role in the Arctic surface radiative budget, impacting the seasonal evolution of Arctic sea-ice cover. We explore the large-scale impacts of springtime and early summer (March through July) cloud and radiative fluxes on sea ice by comparing these fluxes to seasonal ice volume losses over the central Arctic basin, calculated for available observational years 2004–2007 (ICESat) and 2011–2017 (CryoSat-2). We also supplement observation data with sea-ice volume computed from the Pan-Arctic Ice–Ocean Modeling and Assimilation System (PIOMAS) during summer months. We find that the volume of sea ice lost over the melt season is most closely related to observed downwelling longwave radiation in March and early summer (June and July) longwave cloud radiative forcing, which together explain a large fraction of interannual variability in seasonal sea-ice volume loss (R2 = 0.71, p = 0.007). We show that downwelling longwave fluxes likely impact the timing of melt onset near the sea-ice edge, and can limit the magnitude of ice thickening from March to April. Radiative fluxes in June and July are likely critical to seasonal volume loss because modeled data show the greatest ice volume reductions occur during these months.

Description: Two satellite datasets are used to characterize winter landfast first-year sea-ice (FYI), deformed FYI (DFYI) and multiyear sea-ice (MYI) roughness in the Canadian Arctic Archipelago (CAA): (1) optical Multi-angle Imaging SpectroRadiometer (MISR) and (2) synthetic aperture radar Sentinel-1. The Normalized Difference Angular Index (NDAI) roughness proxy derived from MISR, and backscatter from Sentinel-1 are intercompared. NDAI and backscatter are also compared to surface roughness derived from an airborne LiDAR track covering a subset of FYI and MYI (no DFYI). Overall, NDAI and backscatter are significantly positively correlated when all ice type samples are considered. When individual ice types are evaluated, NDAI and backscatter are only significantly correlated for DFYI. Both NDAI and backscatter are correlated with LiDAR-derived roughness (r = 0.71 and r = 0.74, respectively). The relationship between NDAI and roughness is greater for MYI than FYI, whereas for backscatter and ice roughness, the relationship is greater for FYI than MYI. Linear regression models are created for the estimation of FYI and MYI roughness from NDAI, and FYI roughness from backscatter. Results suggest that using a combination of Sentinel-1 backscatter for FYI and MISR NDAI for MYI may be optimal for mapping winter sea-ice roughness in the CAA.

Description: A Fast Ice Prediction System (FIPS) was constructed and is the first regional land-fast sea-ice forecasting system for the Antarctic. FIPS had two components: (1) near-real-time information on the ice-covered area from MODIS and SAR imagery that revealed, tidal cracks, ridged and rafted ice regions; (2) a high-resolution 1-D thermodynamic snow and ice model (HIGHTSI) that was extended to perform a 2-D simulation on snow and ice evolution using atmospheric forcing from ECMWF: either using ERA-Interim reanalysis (in hindcast mode) or HERS operational 10-day predictions (in forecast mode). A hindcast experiment for the 2015 season was in good agreement with field observations, with a mean bias of 0.14 ± 0.07 m and a correlation coefficient of 0.98 for modeled ice thickness. The errors are largely caused by a cold bias in the atmospheric forcing. The thick snow cover during the 2015 season led to modeled formation of extensive snow ice and superimposed ice. The first FIPS operational service was performed during the 2017/18 season. The system predicted a realistic ice thickness and onset of snow surface melt as well as the area of internal ice melt. The model results on the snow and ice properties were considered by the captain of R/V Xuelong when optimizing a low-risk route for on-ice transportation through fast ice to the coastal Zhongshan Station.

Description: The evolution of melt ponds on Arctic sea ice in summer is one of the main factors that affect sea-ice albedo and hence the polar climate system. Due to the different spectral properties of open water, melt pond and sea ice, the melt pond fraction (MPF) can be retrieved using a fully constrained least-squares algorithm, which shows a high accuracy with root mean square error ~0.06 based on the validation experiment using WorldView-2 image. In this study, the evolution of ponds on first-year and multiyear ice in the Canadian Arctic Archipelago was compared based on Sentinel-2 and Landsat 8 images. The relationships of pond coverage with air temperature and albedo were analysed. The results show that the pond coverage on first-year ice changed dramatically with seasonal maximum of 54%, whereas that on multiyear ice changed relatively flat with only 30% during the entire melting period. During the stage of pond formation, the ponds expanded rapidly when the temperature increased to over 0°C for three consecutive days. Sea-ice albedo shows a significantly negative correlation (R = −1) with the MPF in melt season and increases gradually with the refreezing of ponds and sea ice.

Description: Quantifying the rate of wave attenuation in sea ice is key to understanding trends in the Antarctic marginal ice zone extent. However, a paucity of observations of waves in sea ice limits progress on this front. We deployed 14 waves-in-ice observation systems (WIIOS) on Antarctic sea ice during the Polynyas, Ice Production, and seasonal Evolution in the Ross Sea expedition (PIPERS) in 2017. The WIIOS provide in situ measurement of surface wave characteristics. Two experiments were conducted, one while the ship was inbound and one outbound. The sea ice throughout the experiments generally consisted of pancake and young ice

Description: 〈div data-abstract-type="normal"〉〈p〉We recorded the ice motion and icequakes on the floating part of Langhovde Glacier in East Antarctica to better understand the dynamic behavior of ice shelves and floating tongues. Diurnal and semi-diurnal variations in ice motion and seismicity were simultaneously observed at all four global navigation satellite system and three seismic stations over 2 weeks. The short-term along-flow ice motion is explained by the elastic response of the glacier to ocean tide-induced hydrostatic stress variations, which decayed at a rate of 0.8 km〈span〉−1〈/span〉 toward the grounding line. We observed a large number of icequakes during mid-rising and high tides that covered a broad frequency range and formed two major groups of events centered at 10 and 120 Hz, respectively. The hourly occurrence rates were ~500 events h〈span〉−1〈/span〉, with the observed seismicity consistent with fracture due to floating tongue bending. We also observed minor secondary peaks at high ice speeds, which could reflect surface cracking due to stretching or basal friction. Our observation demonstrates that tidal-modulation was the main factor to fracture the floating tongue of Langhovde Glacier.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Changing rates of water input can affect both the flow of glaciers and ice sheets and their propensity to crevasse. Here we examine geodetic and seismic observations during two substantial (10–18-times background velocity) rain-induced glacier accelerations at Haupapa/Tasman Glacier, New Zealand. Changes in rain rate result in glacier acceleration and associated uplift, which propagate down-glacier. This pattern of acceleration results in a change to the strain rate field, which correlates with an order of magnitude increase in the apparent seismicity rate and an overall down-glacier migration in located seismicity. After each acceleration event the apparent seismicity rate decreases to below the pre-acceleration rate for 3 days. This suggests that seismic events associated with surface crevasse growth occur early during phases of glacier acceleration due to elevated extensional stresses, and then do not occur again until stresses recover.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉We compared elastic moduli in polar firn derived from diving wave refraction seismic velocity analysis, firn-core density measurements and microstructure modelling based on firn-core data. The seismic data were obtained with a small electrodynamic vibrator source near Kohnen Station, East Antarctica. The analysis of diving waves resulted in velocity–depth profiles for different wave types (P-, SH- and SV-waves). Dynamic elastic moduli of firn were derived by combining P- and S-wave velocities and densities obtained from firn-core measurements. The structural finite-element method (FEM) was used to calculate the components of the elastic tensor from firn microstructure derived from X-ray tomography of firn-core samples at depths of 10, 42, 71 and 99 m, providing static elastic moduli. Shear and bulk moduli range from 0.39 to 2.42 GPa and 0.68 to 2.42 GPa, respectively. The elastic moduli from seismic observations and the structural FEM agree within 8.5% for the deepest achieved values at a depth of 71 m, and are within the uncertainty range. Our observations demonstrate that the elastic moduli of the firn can be consistently obtained from two independent methods which are based on dynamic (seismic) and static (tomography and FEM) observations, respectively, for deeper layers in the firn below ~10 m depth.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The evolution of glaciers and ice sheets depends on processes in the subglacial environment. Shear seismicity along the ice–bed interface provides a window into these processes. Such seismicity requires a rapid loss of strength that is typically ascribed to rate-weakening friction, i.e., decreasing friction with sliding or sliding rate. Many friction experiments have investigated glacial materials at the temperate conditions typical of fast flowing glacier beds. To our knowledge, however, these studies have all found rate-strengthening friction. Here, we investigate the possibility that rate-weakening rock-on-rock friction between sediments frozen to the bottom of the glacier and the underlying water-saturated sediments or bedrock may be responsible for subglacial shear seismicity along temperate glacier beds. We test this ‘entrainment-seismicity hypothesis’ using targeted laboratory experiments and simple models of glacier sliding, seismicity and sediment entrainment. These models suggest that sediment entrainment may be a necessary but not sufficient condition for the occurrence of basal shear seismicity. We propose that stagnation at the Whillans Ice Stream, West Antarctica may be caused by the growth of a frozen fringe of entrained sediment in the ice stream margins. Our results suggest that basal shear seismicity may indicate geomorphic activity.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Geophysicists that deploy seismic sensors in ablation zones of glaciers and ice sheets to record glaciogenic signatures can confront recording challenges caused by instrument melt-out or tilt. These challenges often require installing sensors in boreholes to delay melt-out, or securing sensors to structures that improve coupling. We show that some of these structures that were buried near a moulin at a snow-free site in the ablation zone of the Western Greenland Ice Sheet resonated as they became exposed, and caused their geophones to record temporally evolving, narrowband signals that mimic features of glaciogenic sources like moulin tremor. We quantify these artifacts with a mechanical model that shows instruments undergo structural resonance as they melt-out, at exposure rates that we predict from an ablation model (RACMO). These models reproduce general spectral features in our data, and enable us to estimate what instrument exposure reduces ice-to-sensor coupling enough to prevent icequake detection. Last, we use our resonance data to quantitatively measure how narrowband signals that originate from either artificial or glaciogenic sources will reduce the ability of certain waveform detectors (correlators) to capture transient seismic events, even if sensors remain coupled.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉GPS measurements of tidal modulation of ice flow and seismicity within the grounding zone of Beardmore Glacier show that tidally induced fluctuations of horizontal flow are largest near the grounding line and decrease downstream. Seismic activity is continuous, but peaks occur on falling and rising tides. Beamforming methods reveal that most seismic events originate from two distinct locations, one on the grid-north side of the grounding zone, and one on the grid-south side. The broad pattern of deformation generated as Beardmore Glacier merges with the Ross Ice Shelf results in net extension along the grid-north side of the grounding zone and net compression along the grid-south side. During falling tides, seismic activity peaks on both sides because of increased vertical flexure across the grounding line. During rising tides, seismic activity in the region of extension on the grid-north side is relatively low because the tidal influence on both horizontal strain rate and vertical flexure is small. On the grid-south side during rising tides, however, tidally induced horizontal strain rates promote increased seismicity in regions of long-term compressional flow paths. Our study highlights how concurrent geodetic and seismic measurements provide insight into grounding-zone mechanics and their influence on ice-shelf buttressing.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Englacial hydrology plays an important role in routing surface water to the glacier's bed and it consequently affects the glacier's dynamics. However, it is often difficult to observe englacial conduit conditions on temperate glaciers because of their short-lived nature. We acquired repeated active surface seismic data over the Rhone Glacier, Switzerland to monitor and characterise englacial conduit conditions. Amplitude-versus-angle analysis suggested that the englacial conduit is water filled and between 0.5 and 4 m thick. A grid of GPR profiles, acquired during the 2018 melt season, showed the englacial conduit network persisting and covering ~ 14,000 m〈span〉2〈/span〉. In late summer 2018, several boreholes were drilled into the conduit network. We observed generally stable water pressure, but there were also short sudden increases. A borehole camera provided images of a fast flowing englacial stream transporting sediment through the conduit. From these observations, we infer that the englacial conduit network is fed by surface meltwater and morainal streams. The surface and morainal streams merge together, enter the glacier subglacially and flow through subglacial channels along the flank. These subglacial channels flow into highly efficient englacial conduits traversing the up-glacier section of the overdeepening before connecting with the subglacial drainage system.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Icequakes at or near the bed of a glacier have the potential to allow us to investigate the interaction of ice with the underlying till or bedrock. Understanding this interaction is important for studying basal sliding of glaciers and ice streams, a critical process in ice dynamics models used to constrain future sea-level rise projections. However, seismic observations on glaciers can be dominated by seismic energy from surface crevassing. We present a method of automatically detecting basal icequakes and discriminating them from surface crevassing, comparing this method to a commonly used spectrum-based method of detecting icequakes. We use data from Skeidararjökull, an outlet glacier of the Vatnajökull Ice Cap, South-East Iceland, to demonstrate that our method outperforms the commonly used spectrum-based method. Our method detects a higher number of basal icequakes, has a lower rate of incorrectly identifying crevassing as basal icequakes and detects an additional, spatially independent basal icequake cluster. We also show independently that the icequakes do not originate from near the glacier surface. We conclude that the method described here is more effective than currently implemented methods for detecting and discriminating basal icequakes from surface crevassing.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Hydraulic processes within and beneath glacial bodies exert a far-reaching control on ice flow through their influence on basal sliding. Within the subglacial system, rapid changes in these processes may excite resonances whose interpretation requires an understanding of the underlying wave mechanics. Here, we explore these mechanics using observations from a kHz-sampled pressure sensor installed in a borehole directly above the hard granite bedrock of a temperate mountain glacier in Switzerland. We apply a previously established theory of wave propagation along thin, water-filled structures such as water-filled voids, basal water layers, or hydraulic fractures. Within such structures, short-wavelength waves experience restoring forces due to compressibility and are composed of sound waves. Long-wavelength resonances, in contrast, experience restoring forces due to elasticity and are composed of anomalously dispersed crack waves or Krauklis waves. Our borehole observations confirm the occurrence of both sound and crack waves within the basal water layer. Using both the resonance frequencies and attenuation of recorded crack waves we estimate thickness, aperture and length of the resonating basal water layer patch into which we drilled. We demonstrate that high-frequency observations of subglacial hydraulic processes provide new insights into this evolving dynamic system.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Forced ice-shelf vibration modeling is performed using a full 3-D finite-difference elastic model, which also takes into account sub-ice seawater flow. The sea water flow is described by the wave equation. Ice-shelf flexure therefore results from hydrostatic pressure perturbations in the sub-ice seawater layer. Numerical experiments were undertaken for idealized rectangular ice-shelf geometry. The ice-plate vibrations were modeled for harmonic incoming pressure perturbations and for a wide range of incoming wave frequencies. The spectra showed distinct resonant peaks, which demonstrate the ability of the model to simulate a resonant-like motion. The spectra obtained by the full 3-D model are compared with exact solutions for the elastic thin plate with two fixed edges and two free edges. The spectra are also compared with the spectra modeled by the thin-plate Holdsworth and Glynn model (1978).〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉We conducted a 9-d seismic experiment in October 2015 at Laohugou Glacier No. 12. We identified microseismic signals using the short-term/long-term average trigger algorithm at four stations and classified them as long and short-duration events based on waveform, frequency, duration and magnitude characteristics. Both categories show systematical diurnal trends. The long-duration events are low-frequency tremor-like events that mainly occurred during the daytime with only several events per day. These events lasted tens of seconds to tens of minutes and are likely related to resonance of daytime meltwater. The dominant short-duration events mostly occurred during the night time with a peak occurrence frequency of ~360 h〈span〉−1〈/span〉. Their short-duration (〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Passive seismology allows measurement of the structure of glaciers and ice sheets. However, most techniques used so far in this context are based on horizontally homogeneous media where parameters vary only with depth (1-D approximations), which are appropriate only for a subset of glaciers. Here, we analyze seismic noise records from three different types of glaciers (plateau, valley and avalanching glacier) to characterize the influence of the glacier geometry on the seismic wavefield. Using horizontal-to-vertical spectral ratios, polarization analysis and modal analysis, we show that the plateau glacier and the valley glacier can be seen as 1-D, whereas the relatively small avalanching glacier shows 3-D effects due to its bed topography and the deep crevasses. In principle, the techniques proposed here might allow monitoring such crevasses and their depth, and thus to constrain a key parameter of avalanching and calving glacier fronts.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Crevasses and englacial fracture networks route meltwater from a glacier's surface to the subglacial drainage system and thus influence glacial hydraulics. However, rapid fracture growth may also lead to sudden and potentially hazardous structural failure of unstable glaciers and ice dams, rifting of ice shelves, or iceberg calving. Here, we use passive seismic recordings to investigate the englacial fracture network on Glacier de la Plaine Morte, Switzerland. Glacier dynamics and the drainage of an ice-marginal lake give rise to numerous icequakes, the majority of which generate dispersed, high-frequency Rayleigh waves. A wide distribution of events allows us to study azimuthal anisotropy between 10 and 30 Hz in order to extract englacial seismic velocities in regions of preferentially oriented crevasses. Beamforming applied to a 100-m-aperture array reveals azimuthal anisotropy of Rayleigh-wave phase velocities reaching a strength of 8% at high frequencies. In addition, we find that the fast direction of wave propagation coincides with the observed surface strike of the narrow crevasses. Forward modeling and inversion of dispersion curves suggest that the azimuthal anisotropy is induced by a 40-m-thick crevassed layer at the surface of the glacier with 8% anisotropy in shear-wave velocity.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Seismograms acquired on the McMurdo Ice Shelf, Antarctica, during an Austral summer melt season (November 2016–January 2017) reveal a diurnal cycle of seismicity, consisting of hundreds of thousands of small ice quakes limited to a 6–12 hour period during the evening, in an area where there is substantial subsurface melting. This cycle is explained by thermally induced bending and fracture of a frozen surface superimposed on a subsurface slush/water layer that is supported by solar radiation penetration and absorption. A simple, one-dimensional model of heat transfer driven by observed surface air temperature and shortwave absorption reproduces the presence and absence (as daily weather dictated) of the observed diurnal seismicity cycle. Seismic event statistics comparing event occurrence with amplitude suggest that the events are generated in a fractured medium featuring relatively low stresses, as is consistent with a frozen surface superimposed on subsurface slush. Waveforms of the icequakes are consistent with hydroacoustic phases at frequency 〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20190807170601246-0716:S0260305518000290:S0260305518000290_inline1.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉 and flexural-gravity waves at frequency 〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20190807170601246-0716:S0260305518000290:S0260305518000290_inline2.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉. Our results suggest that seismic observation may prove useful in monitoring subsurface melting in a manner that complements other ground-based methods as well as remote sensing.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The response of the atmospheric boundary layer (ABL) to subgrid-scale variations of sea ice properties and fracturing is poorly understood and not taken into account in mesoscale Numerical Weather Prediction (NWP) model parametrizations. In this paper we analyze three-dimensional air circulation within the ABL over fragmented sea ice. A series of idealized high-resolution simulations with the Weather Research and Forecasting (WRF) model is performed for several spatial distributions of ice floes and leads for two values of sea ice concentration (0.5 and 0.9) and several ambient wind speed profiles. The results show that the convective circulation within the ABL is sensitive to the subgrid-scale spatial distribution of sea ice. Considerable variability of several domain-averaged quantities – cloud liquid water content, surface turbulent heat flux (THF) – is found for different arrangements of floes. Moreover, the organized structure of air circulation leads to spatial covariance of variables characterizing the ABL. Based on the example of THF, it is demonstrated that this covariance may lead to substantial errors when THF values are estimated from area-averaged quantities, as it is done in mesoscale NWP models. This suggests the need for developing suitable parametrizations of ABL effects related to subgrid-scale sea ice features for these models.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Significant salinity anomalies have been observed in the Arctic Ocean surface layer during the last decade. Our study is based on an extensive gridded dataset of winter salinity in the upper 50 m layer of the Arctic Ocean for the periods 1950–1993 and 2007–2012, obtained from ~20 000 profiles. We investigate the interannual variability of the salinity fields, identify predominant patterns of anomalous behavior and leading modes of variability, and develop a statistical model for the prediction of surface-layer salinity. The statistical model is based on linear regression equations linking the principal components of surface-layer salinity obtained through empirical orthogonal function decomposition with environmental factors, such as atmospheric circulation, river runoff, ice processes and water exchange with neighboring oceans. Using this model, we obtain prognostic fields of the surface-layer salinity for the winter period 2013–2014. The prognostic fields generated by the model show tendencies of surface-layer salinification, which were also observed in previous years. Although the used data are proprietary and have gaps, they provide the most spatiotemporally detailed observational resource for studying multidecadal variations in basin-wide Arctic salinity. Thus, there is community value in the identification, dissemination and modeling of the principal modes of variability in this salinity record.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉In this paper an algorithm for ice/water classification of C- and L-band dual polarization synthetic aperture radar data is presented. A comparison of the two different frequencies is made in order to investigate the potential to improve classification results with multi-frequency data. The algorithm is based on backscatter intensities in co- and cross-polarization and autocorrelation as a texture feature. The mapping between image features and ice/water classification is made with a neural network. Accurate ice/water maps for both frequencies are produced by the algorithm and the results of two frequencies generally agree very well. Differences are found in the marginal ice zone, where the time difference between acquisitions causes motion of the ice pack. C-band reliably reproduces the outline of the ice edge, while L-band has its strengths for thin ice/calm water areas within the icepack. The classification shows good agreement with ice/water maps derived from met.no ice-charts and radiometer data from AMSR-2. Variations are found in the marginal ice zone where the generalization of the ice charts and lower accuracy of ice concentration from radiometer data introduce deviations. Usage of high-resolution dual frequency data could be beneficial for improving ice cover information for navigation and modelling.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Sea-ice thickness in the Sea of Okhotsk is estimated for 2004–2008 from ICESat derived freeboard under the assumption of hydrostatic balance. Total ice thickness including snow depth (〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉) averaged over 2004–2008 is 95 cm. The interannual variability of 〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉 is large; from 77.5 cm (2008) to 110.4 cm (2005). The mode of 〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉 varies from 50–60 cm (2007 and 2008) to 70–80 cm (2005). Ice thickness derived from ICESat data is validated from a comparison with that observed by Electromagnetic Induction Instrument (EM) aboard the icebreaker 〈span〉Soya〈/span〉 near Hokkaido, Japan. Annual maps of 〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉 reveal that the spatial distribution of 〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉 is similar every year. Ice volume of 6.3 × 10〈span〉11〈/span〉 m〈span〉3〈/span〉 is estimated from the ICESat derived 〈span〉h〈/span〉〈span〉〈span〉t〈/span〉〈span〉o〈/span〉〈span〉t〈/span〉〈/span〉 and AMSR-E derived ice concentration. A comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely, despite the fact that the area has been used as a proxy of the volume in the Sea of Okhotsk. The ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations. This also supports the validity of the estimation of sea-ice thickness and volume using ICESat data.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The presence of leads with open water or thin ice is an important feature of the Arctic sea ice cover. Leads regulate the heat, gas and moisture fluxes between the ocean and atmosphere and are areas of high ice growth rates during periods of freezing conditions. Here, an algorithm providing an automatic lead detection based on synthetic aperture radar images is described that can be applied to a wide range of Sentinel-1 scenes. By using both the HH and the HV channels instead of single co-polarised observations the algorithm is able to classify more leads correctly. The lead classification algorithm is based on polarimetric features and textural features derived from the grey-level co-occurrence matrix. The Random Forest classifier is used to investigate the importance of the individual features for lead detection. The precision–recall curve representing the quality of the classification is used to define threshold for a binary lead/sea ice classification. The algorithm is able to produce a lead classification with more that 90% precision with 60% of all leads classified. The precision can be increased by the cost of the amount of leads detected. Results are evaluated based on comparisons with Sentinel-2 optical satellite data.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Pressure ridges impact the mass, energy and momentum budgets of the sea-ice cover and present an obstacle to transportation through ice-infested waters. Quantifying ridge characteristics is important for understanding total sea-ice mass and for improving the representation of sea-ice dynamics in high-resolution models. Multi-sensor measurements collected during annual Operation IceBridge (OIB) airborne surveys of the Arctic provide new opportunities to assess the sea ice at the end of winter. We present a new methodology to derive ridge sail height from high-resolution OIB Digital Mapping System (DMS) visible imagery. We assess the efficacy of the methodology by mapping the full sail height distribution along 12 pressure ridges in the western and central Arctic. Comparisons against coincident Airborne Topographic Mapper (ATM) elevation anomalies are used to demonstrate the methodology and evaluate DMS-derived sail heights. Sail heights and elevation anomalies were correlated at 0.81 or above. On average mean and maximum sail height agreed with ATM elevation to within 0.11 and 0.49 m, respectively. Of the ridges mapped, mean sail height ranged from 0.99 to 2.16 m, while maximum sail height ranged from 2.1 to 4.8 m. DMS also delivered higher sampling along ridge crests than coincident ATM data.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Large discrepancies have been observed between satellite-derived sea-ice concentrations(IC) from passive microwave remote sensing and those derived from optical images at several locations in the East Antarctic, between February and April 2014. These artefacts, that resemble polynyas in the IC maps, appear in areas where optical satellite data show that there is landfast sea ice. The IC datasets and the corresponding retrieval algorithms are investigated together with microwave brightness temperature, air temperature, snowfall and bathymetry to understand the failure of the IC retrieval. The artefacts are the result of the application of weather filters in retrieval algorithms. These filters use the 37 and 19 GHz channels to correct for atmospheric effects on the retrieval. These channels show significant departures from typical ranges when the artefacts occur. A melt–refreeze cycle with associated snow metamorphism is proposed as the most likely cause. Together, the areas of the artefacts account for up to 0.5% of the Antarctic sea-ice area and thus cause a bias in sea-IC time series. In addition, erroneous sea ICs can adversely affect shipping operations.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Knowledge of Arctic sea-ice conditions is of great interest for Arctic residents, as well as for commercial usage, and to study the effects of climate change. Information gained from analysis of satellite data contributes to this understanding. In the course of using in situ data in combination with remotely sensed data, the question of how representative local scale measurements are of a wider region may arise. We compare in situ total sea-ice thickness measurements from the Norwegian young sea ICE expedition in the area north of Svalbard with airborne-derived total sea-ice thickness from electromagnetic soundings. A segmented and classified synthetic aperture radar (SAR) quad-pol ALOS-2 Palsar-2 satellite scene was grouped into three simplified ice classes. The area fractions of the three classes are: 11.2% ‘thin’, 74.4% ‘level’, and 14.4% ‘deformed’. The area fractions of the simplified classes from ground- and helicopter-based measurements are comparable with those achieved from the SAR data. Thus, this study shows that there is potential for a stepwise upscaling from in situ, to airborne, to satellite data, which allow us to assess whether in situ data collected are representative of a wider region as observed by satellites.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Research on young thin sea ice is essential to understand the changes in the Arctic. But it is also the most challenging to investigate, both in situ and from satellites. If satellite remote-sensing techniques are developing rapidly, fieldwork remains crucial for the mandatory validation of such data. In April 2016, an Arctic fieldwork campaign was conducted at Kongsfjorden, Svalbard. This campaign provided an opportunity to combine various techniques to record the fjord ice properties ranging from local field sampling to broader ground-based and satellite radar remote sensing of the fjord. Tracking the boat used to access the field sites with hand-held GPS devices offered a good opportunity to map fjord ice and assess the limits of radar identification of small icebergs and thin ice. During 1 week, 17 icebergs and the thin ice edges in two different locations were mapped. The GPS tracks present a good agreement with the Radarsat-2 data analysis for one of the two ice edges. The second ice edge track only partly corresponds to the radar scene. Ice movement, recorded by a ground-based radar, is likely to explain this result. Grounded icebergs could be identified in both Radarsat-2 and ground-based radar.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Changing Arctic sea-ice extent and melt season duration, and increasing economic interest in the Arctic have prompted the need for enhanced marine ecosystem studies and improvements to dynamical and forecast models. Sea-ice melt pond fraction 〈span〉f〈/span〉〈span〉p〈/span〉 has been shown to be correlated with the September minimum ice extent due to its impact on ice albedo and heat uptake. Ice forecasts should benefit from knowledge of 〈span〉f〈/span〉〈span〉p〈/span〉 as melt ponds form several months in advance of ice retreat. This study goes further back by examining the potential to predict 〈span〉f〈/span〉〈span〉p〈/span〉 during winter using backscatter data from the commonly available Sentinel-1 synthetic aperture radar. An object-based image analysis links the winter and spring thermodynamic states of first-year and multiyear sea-ice types. Strong correlations between winter backscatter and spring 〈span〉f〈/span〉〈span〉p〈/span〉, detected from high-resolution visible to near infrared imagery, are observed, and models for the retrieval of 〈span〉f〈/span〉〈span〉p〈/span〉 from Sentinel-1 data are provided (〈span〉r〈/span〉〈span〉2〈/span〉 ≥ 0.72). The models utilize HH polarization channel backscatter that is routinely acquired over the Arctic from the two-satellite Sentinel-1 constellation mission, as well as other past, current and future SAR missions operating in the same C-band frequency. Predicted 〈span〉f〈/span〉〈span〉p〈/span〉 is generally representative of major ice types first-year ice and multiyear ice during the stage in seasonal melt pond evolution where 〈span〉f〈/span〉〈span〉p〈/span〉 is closely related to spatial variations in ice topography.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The Arctic marine environment is undergoing a transition from thick multi-year to first-year sea-ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade〈span〉−1〈/span〉 earlier from 1979 to 2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013. (~6〈span〉σ〈/span〉 below the 1981–2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI). The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI 〉+1 on 〉75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt ~50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉With rapid and accelerated Arctic sea-ice loss, it is beneficial to update and baseline historical change on the regional scales from a consistent, intercalibrated, long-term time series of sea-ice data for understanding regional vulnerability and monitoring ice state for climate adaptation and risk mitigation. In this paper, monthly sea-ice extents (SIEs) derived from a passive microwave sea-ice concentration climate data record for the period of 1979–2015, are used to examine Arctic-wide and regional temporal variability of sea-ice cover and their decadal trends for 15 regions of the Arctic. Three unique types of SIE annual cycles are described. Regions of vulnerability within each of three types to further warming are identified. For the Arctic as a whole, the analysis has found significant changes in both annual SIE maximum and minimum, with −2.41 ± 0.56% per decade and −13.5 ± 2.93% per decade change relative to the 1979–2015 climate average, respectively. On the regional scale, the calculated trends for the annual SIE maximum range from +2.48 to −10.8% decade〈span〉−1〈/span〉, while the trends for the annual SIE minimum range from 0 to up to −42% decade〈span〉−1〈/span〉.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉We present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h〈span〉−1〈/span〉) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a ~ 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Ice shelves regulate the rate of ice-sheet discharge along much of the Antarctic coastline. Pinning points, sites of localised grounding within floating ice, can in turn, regulate the flow and thickness of an ice shelf. While the net resistive effect of ice shelves has been quantified in a systematic way, few extant pinning points have been examined in detail. Here, complete force budgets are calculated and examined for ice rises and rumples in the Ross Ice Shelf, West Antarctica. The diverse features have different effects on ice shelf mechanics that do not depend simply on their size but may, we conclude, depend on the properties of seafloor materials.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Measurements of a sample from ~580 m depth in the WAIS Divide (WDC06A) ice core reveal that bubbles are preferentially elongated in the basal plane of their parent grain, as expected if bubble shape preserves the record of dominant basal glide. This suggests that a method using bubbles as strain gauges could provide insights to grain-scale ice deformation. We introduce a technique using fabric and image analyses of paired thin and thick sections. Comparison of the crystallographic orientations of 148 grains and the shape orientations of 2377 intragrain bubbles reveals a strongly preferred elongation of bubbles in the grain basal planes (〈span〉R〈/span〉〈span〉2〈/span〉 = 0.96). Elongation magnitudes are consistent with a balance between ice flow deformation and diffusive restoration, with larger bubbles more elongated. Assuming bubbles record ice strain, grains with greater resolved stress on their basal planes from the far-field ice flow stresses show greater deformation, but with large variability suggesting that heterogeneity of the local stress field causes deformation even in unfavorably oriented grains. A correlation is also observed among bubble elongation, grain size, and bubble size, explaining a small but significant fraction of the variance ( 〈span〉P〈/span〉〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Over a year of seismic observations, ~5000 short duration icequakes were detected by a permanent broadband station installed at the Princess Elisabeth base, located ~180 km inland in eastern Dronning Maud Land, East-Antarctica. Icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events, totalizing ~1500 icequakes. The corresponding icequake locations point towards two distinct zones of outcropping blue ice areas (BIAs) located respectively at 4 and 1 km from the seismic station, both on the leeward side of a nunatak protruding through the ice sheet. The temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled, in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes. Further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change. Besides providing information on the ice fracture mechanics and rheology, investigations of thermal icequakes may be regarded as a ground-based proxy for the monitoring of the thermal state of BIAs, and characterization of ice-sheet ablation zones.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Glacial seismicity provides important insights into glacier dynamic processes. We study the temporal distribution of cryogenic seismic signals (icequakes) at Holtedahlfonna, Svalbard, between April and August 2016 using a single three-component sensor. We investigate sources of observed icequakes using polarization analysis and waveform modeling. Processes responsible for five icequake categories are suggested, incorporating observations of previous studies into our interpretation. We infer that the most dominant icequake type is generated by surface crevasse opening through hydrofracturing. Secondly, bursts of high-frequency signals are presumably caused by repeated near-surface crevassing due to high strain rates during glacier fast-flow episodes. Furthermore, signals related to resonance in water-filled cracks, fracturing or settling events in dry firn or snow before the melt season, and processes at the glacier bed are observed. Amplitude of seismic background noise is clearly related to glacier runoff. We process ambient seismic noise to invert horizontal-to-vertical spectral ratios for a sub-surface seismic velocity model used to model icequake signals. Our study shows that a single seismic sensor provides useful information about seasonal ice dynamics in case deployment of a network is not feasible.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Fast ice flow is associated with the deformation of subglacial sediment. Seismic shear velocities, Vs, increase with the rigidity of material and hence can be used to distinguish soft sediment from hard bedrock substrates. Depth profiles of Vs can be obtained from inversions of Rayleigh wave dispersion curves, from passive or active-sources, but these can be highly ambiguous and lack depth sensitivity. Our novel Bayesian transdimensional algorithm, MuLTI, circumvents these issues by adding independent depth constraints to the inversion, also allowing comprehensive uncertainty analysis. We apply MuLTI to the inversion of a Rayleigh wave dataset, acquired using active-source (Multichannel Analysis of Surface Waves) techniques, to characterise sediment distribution beneath the frontal margin of Midtdalsbreen, an outlet of Norway's Hardangerjøkulen ice cap. Ice thickness (0–20 m) is constrained using co-located GPR data. Outputs from MuLTI suggest that partly-frozen sediment (Vs 500–1000 m s〈span〉−1〈/span〉), overlying bedrock (Vs 2000–2500 m s〈span〉−1〈/span〉), is present in patches with a thickness of ~4 m, although this approaches the resolvable limit of our Rayleigh wave frequencies (14–100 Hz). Uncertainties immediately beneath the glacier bed are −1, implying that MuLTI cannot only distinguish bedrock and sediment substrates but does so with an accuracy sufficient for resolving variations in sediment properties.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Since the 2000s, Greenland ice sheet mass loss has been accelerating, followed by increasing numbers of glacial earthquakes (GEs) at near-grounded glaciers. GEs are caused by calving of km-scale icebergs which capsize against the terminus. Seismic record inversion allows a reconstruction of the history of GE sources which captures capsize dynamics through iceberg-to-terminus contact. When compared with a catalog of contact forces from an iceberg capsize model, seismic force history accurately computes calving volumes while the earthquake magnitude fails to uniquely characterize iceberg size, giving errors up to 1 km〈span〉3〈/span〉. Calving determined from GEs recorded ateight glaciers in 1993–2013 accounts for up to 21% of the associated discharge and 6% of the Greenland mass loss. The proportion of discharge attributed to capsizing calving may be underestimated by at least 10% as numerous events could not be identified by standard seismic detections (Olsen and Nettles, 2018). While calving production tends to stabilize in East Greenland, Western glaciers have released more and larger icebergs since 2010 and have become major contributors to Greenland dynamic discharge. Production of GEs and calving behavior are controlled by glacier geometry with bigger icebergs being produced when the terminus advances in deepening water. We illustrate how GEs can help in partitioning and monitoring Greenland mass loss and characterizing capsize dynamics.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Seasonal lake Gornersee forms at the confluence of Gornergletscher and Grenzgletscher, Switzerland, and experiences outburst floods annually in midsummer. To study the interplay between lake drainage, glacier movement and crevasse activity, high-frequency seismometers and GPS receivers were deployed in networks near Gornersee during the summer ablation seasons of 2004, 2006 and 2007. We use a Rayleigh wave coherence method to locate 3289, 7939 and 4087 icequakes, respectively, primarily along well-defined surface crevasses. We calculate two-dimensional strains from triads of GPS stations and find mean differential strain rates of ~300 × 10〈span〉−6〈/span〉 d〈span〉−1〈/span〉 with diurnal variations up to 800 × 10〈span〉−6〈/span〉 d〈span〉−1〈/span〉. Crevasse icequake activity and glacial velocity are highest during early season, then decrease as meltwater channels erode and subglacial water pressure decreases. Glacial response to Gornersee drainage varied year-to-year, with icequake activity promoted at some crevasses and inhibited at others, suggesting syn-drainage icequakes may be indicative of local drainage patterns and small-scale features of the stress field. Diurnal pulses in icequake activity exhibit peak activity at different times of day in different locations, coincident with a southeast-to-northwest trending concentrated shear zone near the Gornergletscher–Grenzgletscher confluence, likely due to differences in the timing of peak strain rate in these regions.〈/p〉〈/div〉

Description: This work is a collection of radar equations for low-frequency radar sounding and radar in general that emphasize the form of the radar equation for different target and source geometries. This is meant as a handbook for scientists and engineers that work with or analyze radar sounder systems and interpret radar sounding echoes. Lookup tables summarize the results and derivations are provided for each equation.

Description: 〈div data-abstract-type="normal"〉〈p〉This paper presents new insights into the global carbon cycle related to CO〈span〉2〈/span〉 consumption from chemical denudation in heavily glacierised Himalayan catchments. Data from previous studies of solute concentrations from glacierised catchments were reprocessed to determine the regional scale of CO〈span〉2〈/span〉 consumption and solute hydrolysis. The results show that ~90% of the SO〈span〉4〈/span〉〈span〉2−〈/span〉 is derived from crustal sulphide oxidation and ~10% from aerosols and sea salts. However, HCO〈span〉3〈/span〉〈span〉−〈/span〉 flux calculation estimates contribution from sulphide oxidation to carbonate dissolution (SO-CD) (~21%), similar to the contributions from silicate dissolution and simple hydrolysis (~21 and ~20%, respectively). Furthermore, the atmospheric CO〈span〉2〈/span〉 consumption estimations suggests 10.6 × 10〈span〉4〈/span〉 mole km〈span〉−2〈/span〉 a〈span〉−1〈/span〉 (19%) through silicate weathering, 15.7 × 10〈span〉4〈/span〉 mole km〈span〉−2〈/span〉 a〈span〉−1〈/span〉 (28%) through simple hydrolysis, 9.6 × 10〈span〉4〈/span〉 mole km〈span〉−2〈/span〉 a〈span〉−1〈/span〉 (17%) through SO-CD reaction and 5.9 × 10〈span〉4〈/span〉 mole km〈span〉−2〈/span〉 a〈span〉−1〈/span〉 (11%) through carbonate carbonation reaction. Our solute provenance calculations clearly indicate that HCO〈span〉3〈/span〉〈span〉−〈/span〉 production and CO〈span〉2〈/span〉 consumption via silicate weathering reactions is balanced by the simple hydrolysis and coupled SO-CD process. This shows a counter mechanism operating in subglacial environments of the Himalaya as a source of CO〈span〉2〈/span〉 to runoff rather than a sink.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Recent greening of vegetation across the Arctic is associated with warming temperatures, hydrologic change and shorter snow-covered periods. Here we investigated trends for a subset of arctic vegetation on the island of Greenland. Vegetation in Greenland is unique due to its close proximity to the Greenland Ice Sheet and its proportionally large connection to the Greenlandic population through the hunting of grazing animals. The aim of this study was to determine whether or not longer snow-free periods (SFPs) were causing Greenlandic vegetation to dry out and become less productive. If vegetation was drying out, a subsequent aim of the study was to determine how widespread the drying was across Greenland. We utilized a 15-year time-series obtained by the MODerate Resolution Imaging Spectroradiometer (MODIS) to analyze the Greenland vegetation by deriving descriptors corresponding with the SFP, the number of cumulative growing degree-days and the time-integrated Normalized Difference Vegetation Index. While the productivity of most vegetated areas increased in response to longer growing periods, there were localized regions that exhibited signs consistent with the drying hypothesis. In these areas, vegetation productivity decreased in response to longer SFPs and more accumulated growing degree-days.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Cryoconite holes are small depressions of the glacier surface filled with melting water and with a wind-blown debris on the bottom. These environments are considered hot spots of biodiversity and biological activities on glaciers and host communities dominated by bacteria. Most of the studies on cryoconite holes assume that their communities are stable. However, evidence of seasonal variation in cryoconite hole ecological communities exists. We investigated the variation of the bacterial communities of cryoconite holes of Forni Glacier (Central Italian Alps) during the melting seasons (July–September) 2013 and 2016, for which samples at three and five time-points, respectively were available. Bacterial communities were characterized by high-throughput Illumina sequencing of the hypervariable V5−V6 regions of 16S rRNA gene, while meteorological data were obtained by an automatic weather station. We found consistent trends in bacterial communities, which shifted from cyanobacteria-dominated communities in July to communities dominated by heterotrophic orders in late August and September. Temperature seems also to affect seasonal dynamics of communities. We also compared bacterial communities at the beginning of the melting season across 4 years (2012, 2013, 2015 and 2016) and found significant year-to-year variability. Cryoconite hole communities on temperate glaciers are therefore not temporally stable.〈/p〉〈/div〉

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Description: 〈div data-abstract-type="normal"〉〈p〉In January 2016, static GPS measurements were carried out in a 30 × 30 km〈span〉2〈/span〉 area centered around Kunlun station at Dome Argus (Dome A), East Antarctica, to acquire high-precision 3-D geodetic coordinates at 49 sites. By comparing the coordinates with previous GPS measurements in 2008 and 2013 at the same sites, we constructed a detailed and long-term record of the ice-surface velocity field, 2008–2016, around Dome A. During this time span, the estimated ice-surface velocity ranges from 0.8 ± 0.3 to 28.7 ± 1.6 cm a〈span〉−1〈/span〉, with a mean of 10.4 ± 0.3 cm a〈span〉−1〈/span〉. From 2013 to 2016, the surface elevation of most Dome A areas exhibits a rising trend, and the maximum increase of snow surface elevation is 84.8 cm. The mean snow surface elevation change rate at Dome A is estimated to be 6.6 ± 0.7 cm a〈span〉−1〈/span〉. The difference of 1.0 cm a〈span〉−1〈/span〉 between the snow surface change rate derived from GPS and pole-height change rate from surface mass balance is suspected to be a result of a combination of firn densification and basal melt under Dome A.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉This survey presents the first high-throughput characterisation of fungal distribution based on ITS2 Illumina sequencing of uncultured microbiome from a 1500 years old perennial ice deposit in Scărișoara Ice Cave, Romania. Of the total of 1 751 957 ITS2 sequences, 64% corresponded to 182 fungal operational taxonomic units, showing a low diversity, particularly in older ice strata, and a distinct temporal distribution pattern. Ascomycota was the major phylum in all ice samples, dominating the 400 and 1500 years old ice strata deposited during the cold Little Ice Age (LIA) and Dark Ages Cold Period, while Basidiomycota was mostly present in 900-years old ice formed during the Medieval Warm Period (MWP). Chytridiomycota and Mucoromycota phyla were present in recently formed and 400-years old ice, respectively. Among the 80 identified genera, 〈span〉Cryptococcus victoriae〈/span〉, commonly found in glacial habitats, was identified in all strata. A positive correlation between fungal distribution and ice conductivity, Ca, Na and Sr concentrations was observed across the ice block, with pH values trailing climate variations during LIA and MWP, respectively. Our record highlighted the presence of a complex climate and environmental-driven fungal community in perennial ice strata accumulated during the last 1500 years in Scărișoara Ice Cave.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Full snow-pit observations were performed on a monthly basis over ten winter seasons from 1995 to 2004, at 15 study plots spaced at 100 m elevation intervals (1300–2700 m a.s.l.) in the mountainous forest of the Japanese Central Alps. We observed 514 pits with an average depth of 1.12 m. Density measurements were taken in 2610 snow layers in total. Monthly trends indicate that snow depth has a strong linear correlation with elevation and that the mean density of snow cover has a moderate linear correlation with elevation in midwinter. Snow water equivalent can increase as a quadratic function of elevation in January and February. For this reason, the influence of overburden load and wind packing is elevation-dependent from January to February, a period when a facet-prominent snowpack existed on account of low snow and air temperatures. The density of depth hoar is greater at higher elevations than it is for rounded grains in midwinter due to densification. On forested slopes, with increasing elevation, snowfall frequency and the impact of wind upon snow increases while air temperature decreases, causing elevational variance in grain shapes.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Although the disaster reduction effects of forest braking have long been known empirically, they have not been known in detail down to recent. In this study, we ascertained forest braking effect by numerical simulations using the avalanche dynamics program, TITAN2D, to model large-scale avalanches. One of these avalanches occurred in the Makunosawa valley, Myoko, and damaged a cedar forest; the others occurred on Mt. Iwate and damaged a subalpine forest. All avalanches damaged many trees and terminated within the forests. In our simulations, the resistance of the forests to avalanches is simulated using a larger bed friction angle. Fitting the observations from the Makunosawa avalanche by trial and error, a bed friction angle of 13–14° in the non-forested area and of 25° in the forested area is obtained. We conducted simulations of the Mt. Iwate avalanches using the same method as for the Makunosawa valley avalanche, and obtained good agreement between observations and simulations. Simulations reveal that without the forest, the avalanche would have traveled at least 200 m farther than the forest's actual end in the Makunosawa valley, and at least 200 m and possibly up to 600 m farther on Mt. Iwate. This study therefore clearly shows that forests provide a braking effect for avalanches.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Snow can be considered an independent ecosystem that hosts active microbial communities. Snow microbial communities have been extensively investigated in the Arctic and in the Antarctica, but rarely in mid-latitude mountain areas. In this study, we investigated the bacterial communities of snow collected in four glacierized areas (Alps, Eastern Anatolia, Karakoram and Himalaya) by high-throughput DNA sequencing. We also investigated the origin of the air masses that produced the sampled snowfalls by reconstructing back-trajectories. A standardized approach was applied to all the analyses in order to ease comparison among different communities and geographical areas. The bacterial communities hosted from 25 to 211 Operational Taxonomic Units (OTUs), and their structure differed significantly between geographical areas. This suggests that snow bacterial communities may largely derive from ‘local’ air bacteria, maybe by deposition of airborne particulate of local origin that occurs during snowfall. However, some evidences suggest that a contribution of bacteria collected during air mass uplift to snow communities cannot be excluded, particularly when the air mass that originated the snow event is particularly rich in dust.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉To understand the geological origins of minerals in cryoconite and the nutrients sources for microbes on glaciers, we analyzed the Sr–Nd isotopic ratios of the four mineral fractions in cryoconites including saline, carbonate, phosphate, silicate and the organic fraction obtained from Gulkana Glacier in Alaska. The isotopes in the silicate mineral fraction exhibited spatial variation within the glacier (〈span〉87〈/span〉Sr/〈span〉86〈/span〉Sr: 0.704533–0.709563, 〈span〉ε〈/span〉Nd (0): −16.0 to 0.5), which can be explained by the different mixing ratios of the two distinct sources: one of the sources is lateral and terminal moraines or soil, and the other is the medial moraine of the glacier. The minerals in the cryoconite at the lower sites in the glacier are likely derived from the former source, whereas those at the upper sites are from latter sources. The mineralogical and elemental compositions also support mixing of the silicate minerals from the two local sources. The Sr isotopic ratios of the organic fraction also showed spatial variation on the glacier in the middle sites – a trend similar to those of the phosphate fraction. The results suggest that the organic matter is mostly the byproducts of microbes using the phosphate minerals as a nutrient source.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Proglacial environments are ideal for studying the development of soils through the changes of rocks exposed by glacier retreat to weathering and microbial processes. Carbon (C) and nitrogen (N) contents as well as soil pH and soil elemental compositions are thought to be dominant factors structuring the bacterial, archaeal and fungal communities in the early stages of soil ecosystem formation. However, the functional linkages between C and N contents, soil composition and microbial community structures remain poorly understood. Here, we describe a multivariate analysis of geochemical properties and associated microbial community structures between a moraine and a glaciofluvial outwash in the proglacial area of a High Arctic glacier (Longyearbreen, Svalbard). Our results reveal distinct differences in developmental stages and heterogeneity between the moraine and the glaciofluvial outwash. We observed significant relationships between C and N contents, 〈span〉δ〈/span〉〈span〉13〈/span〉C〈span〉org〈/span〉 and 〈span〉δ〈/span〉〈span〉15〈/span〉N isotopic ratios, weathering and microbial abundance and community structures. We suggest that the observed differences in microbial and geochemical parameters between the moraine and the glaciofluvial outwash are primarily a result of geomorphological variations of the proglacial terrain.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Glaciers retreating in response to climate warming are progressively exposing primary mineral substrates to surface conditions. As primary production is constrained by nitrogen (N) availability in these emerging ecosystems, improving our understanding of how N accumulates with soil formation is of critical concern. In this study, we quantified how the distribution and speciation of N, as well as rates of free-living biological N fixation (BNF), change along a 2000-year chronosequence of soil development in a High Arctic glacier forefield. Our results show the soil N pool increases with time since exposure and that the rate at which it accumulates is influenced by soil texture. Further, all N increases were organically bound in soils which had been ice-free for 0–50 years. This is indicative of N limitation and should promote BNF. Using the acetylene reduction assay technique, we demonstrated that microbially mediated inputs of N only occurred in soils which had been ice-free for 0 and 3 years, and that potential rates of BNF declined with increased N availability. Thus, BNF only supports N accumulation in young soils. When considering that glacier forefields are projected to become more expansive, this study has implications for understanding how ice-free ecosystems will become productive over time.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Cryoconite holes play a significant role in the nutrient cycling on glaciers and can be regarded as a storehouse of nutrients that are generated through microbial and photochemical activities. In this work, the chemical characteristics of hydrologically connected and isolated cryoconite holes from three geographically distinct regions of coastal Antarctica, namely Larsemann Hills, Amery Ice Shelf and central Dronning Maud Land were studied. Major ions (Na〈span〉+〈/span〉, K〈span〉+〈/span〉, Mg〈span〉2+〈/span〉, Ca〈span〉2+〈/span〉, Cl〈span〉−〈/span〉, SO〈span〉4〈/span〉〈span〉2−〈/span〉 and NO〈span〉3〈/span〉〈span〉−〈/span〉) and total organic carbon in the hydrologically isolated, closed cryoconite holes showed significantly higher enrichment (6–26 times and 9 times, respectively) over the conservative tracer ion Cl〈span〉−〈/span〉 possibly due to sediment dissolution and microbial synthesis during isolation period. In contrast, depletion of major ions and organic carbon were observed in the open, hydrologically connected holes due to their discharge from the cryoconite holes through interconnected streams. This study suggests that the contribution of cryoconite holes to the nutrient and microbial transport to downstream environments may vary with the extent of hydrological connectivity by virtue of the fact that nutrients and organic carbon which accumulate in the isolated cryoconite holes during isolation could get washed to downstream environments in the event that they get connected through surface or subsurface melt channels.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉The medium-high mountain ranges of Western Europe are undergoing rapid socio-environmental changes. The aim of this study is to show that their landscape can be strongly shaped by the actions of avalanche activity, humans and climate. The study area is the Rothenbachkopf-Rainkopf complex, a site representative of avalanche-prone areas of the Vosges Mountains (France). A geo-historical approach documents regular avalanche activity over more than 200 years on 13 paths. A diachronic analysis of historical maps and photographs demonstrates substantial afforestation (from 60 to 80% of the total surface since 1832). LIDAR data and field surveys highlight the existence of a longitudinal and transversal structure of trees. Hence, the avalanche, human and climate activity footprints are retained by the landscape, which rapidly adapts to these changing drivers. Specifically, the pattern of tree species and heights results from a near equilibrium with regular avalanche activity sometimes disturbed by major avalanches that induce quasi-cyclic changes in the landscape mosaic. The afforestation trend is attributable to profound changes in silvo-pastoral practices, supplemented by the impact of climate change. The wider relevance of the results in relation to the local context is discussed, as well as outlooks that can refine our understanding of this complex system.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Cryoconite holes are water-filled cylindrical holes formed on ablation ice surfaces and commonly observed on glaciers worldwide. Temporal changes of cryoconite holes characteristically −2, 40–55% of the incoming flux). In contrast, holes developed in sunny conditions correspond to high solar radiation (186–278 W m〈span〉−2〈/span〉, 63–88%). Results suggest that the dimensions of holes drastically changed depending on the weather conditions and that frequent cloudy, warm and windy conditions would cause a decay of holes and weathering crust, inducing an increase in the cryoconite coverage on the ice, consequently darkening the glacier surface.〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Snowmelt was measured on a daily basis for 17 days at the open site and 18 days at three Japanese cedar sites with canopy closure of 17.8% (cedar stand A), 5.2% (B) and 2.4% (C) in April. Measured daily snowmelt at each site was reproduced by heat-balance calculation with an accuracy of 〈/p〉〈/div〉

Description: 〈div data-abstract-type="normal"〉〈p〉Dissolved organic matter (DOM) in mountain glaciers is an important source of carbon for downstream aquatic systems, and its impact is expected to increase due to the increased melting rate of glaciers. We present a comprehensive study of Laohugou glacier no. 12 (LHG) at the northern edge of the Tibetan Plateau to characterize the DOM composition and sources by analyzing surface fresh snow, granular ice samples, and snow pit samples which covered a whole year cycle of 2014/15. Excitation–emission matrix fluorescence spectroscopy analysis of the DOM with parallel factor analysis (EEM-PARAFAC) identified four components, including a microbially humic-like component (C1), two protein-like components (C2 and C3) and a terrestrial humic-like component (C4). The use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) showed that DOM from all these samples was dominated by CHO and CHON molecular formulas, mainly corresponding to lipids and aliphatic/proteins compounds, reflecting the presence of significant amounts of microbially derived and/or deposited biogenic DOM. The molecular compositions of DOM showed more CHON compounds in granular ice than in fresh snow, likely suggesting newly formed DOM from microbes during snowmelting.〈/p〉〈/div〉

Description: We present simulation results from a version of the Regional Ocean Modeling System modified for ice shelf/ocean interaction, including the parameterisation of basal melting by molecular diffusion alone. Simulations investigate the differences in melting for an idealised ice shelf experiencing a range of cold to hot ocean cavity conditions. Both the pattern of melt and the location of maximum melt shift due to changes in the buoyancy-driven circulation, in a different way to previous studies. Tidal forcing increases both the circulation strength and melting, with the strongest impact on the cold cavity case. Our results highlight the importance of including a complete melt parameterisation and tidal forcing. In response to the 2.4°C ocean warming initially applied to a cold cavity ice shelf, we find that melting will increase by about an order of magnitude (24 × with tides and 41 × without tides).

Description: Aerial photography was conducted in the high Arctic Ocean during a Chinese research expedition in summer 2010. By partitioning the images into three distinct surface categories (sea ice/snow, water and melt ponds), the areal fraction of each category, ice concentration and the size and geometry of individual melt ponds, are determined with high-spatial resolution. The ice concentration and melt pond coverage have large spatial deviations between flights and even between images from the marginal ice zone to the pack ice zone in the central Arctic. Ice concentration and pond coverage over high Arctic (from 84°N to north) was ~75% and ~6.8%, respectively, providing ‘ground truth’ for the unusual transpolar reduction strip of ice indicated concurrently by AMSR-E data and for the regions (north of 88°N) where no passive microwave sensors can cover. Melt pond size and shape distributions are examined in terms of pond area (S), perimeter (P), mean caliper dimension (MCD) (L), roundness (R), convex degree (C), the ratio of P/S and fractal dimension (D). Power-law relationships are developed between pond size and number. Some general trends in geometric metrics are identified as a function of pond area including R, C, P/S and D. The scale separation of pond complexity is demonstrated by analyzing area-perimeter data. The results will potentially help the modelling of melt pond evolution and the determination of heterogeneity of under-ice transmitted light fields.

Description: Neighboring tidewater glaciers often exhibit asynchronous dynamic behavior, despite relatively uniform regional atmospheric and oceanic forcings. This variability may be controlled by a combination of local factors, including glacier and fjord geometry, fjord heat content and circulation, and glacier surface melt. In order to characterize and understand contrasts in adjacent tidewater glacier and fjord dynamics, we made coincident ice-ocean-atmosphere observations at high temporal resolution (minutes to weeks) within a 10 000 km2 area near Uummannaq, Greenland. Water column velocity, temperature and salinity measurements reveal systematic differences in neighboring fjords that imply contrasting circulation patterns. The observed ocean velocity and hydrography, combined with numerical modeling, suggest that subglacial discharge plays a major role in setting fjord conditions. In addition, satellite remote sensing of seasonal ice flow speed and terminus position reveal both speedup and slow-down in response to melt, as well as differences in calving style among the neighboring glaciers. Glacier force budgets and modeling also point toward subglacial discharge as a key factor in glacier behavior. For the studied region, individual glacier and fjord geometry modulate subglacial discharge, which leads to contrasts in both fjord and glacier dynamics.

Description: The Institute Ice Stream (IIS) rests on a reverse-sloping bed, extending 〉150 km upstream into the ~1.8 km deep Robin Subglacial Basin, placing it at the threshold of marine ice-sheet instability. Understanding IIS vulnerability has focused on the effect of grounding-line melting, which is forecast to increase significantly this century. Changes to ice-flow dynamics are also important to IIS stability, yet little is known about them. Here we reveal that the trunk of the IIS occurs downstream of the intersection of three discrete subglacial features; a large ‘active’ subglacial lake, a newly-discovered sharp transition to a zone of weak basal sediments and a major tectonic rift. The border of IIS trunk flow is confined by the sediment on one side, and by a transition between basal melting and freezing at the border with the Bungenstock Ice Rise. By showing how basal sediment and water dictate present-day flow of IIS, we reveal that ice-sheet stability here is dependent on this unusual arrangement.

Description: Geothermal heat flux (GHF) is one of the key thermal boundary conditions for ice-sheet models. We assess the sensitivity of the Lambert-Amery glacial system in East Antarctica to four different GHF datasets using a regional ice-sheet model. A control solution of the regional model is initialised by minimising the misfit to observations through an optimisation process. The Lambert-Amery glacial system simulation contains temperate ice up to 150 m thick and has an average basal melt of 1.3 mm a−1, with maximum basal melting of 504 mm a−1. The simulations which use a relatively high GHF compared to the control solution increase the volume and area of temperate ice, which causes higher surface velocities at higher elevations, which leads to the advance of the grounding line. The grounding line advance leads to changes in the local flow configuration, which dominates the changes within the glacial system. To investigate the difference in spatial patterns within the geothermal datasets, they were scaled to have the same median value. These scaled GHF simulations showed that the ice flow was most sensitive to the spatial variation in the underlying GHF near the ice divides and on the edges of the ice streams.

Description: High-latitude atmospheric warming is impacting freshwater cycling, requiring techniques for monitoring the hydrology of sparsely-gauged regions. The submarine runoff of tidewater glaciers presents a particular challenge. We evaluate the utility of Moderate Resolution Imaging Spectroradiometer (MODIS) imagery for monitoring turbid meltwater plume variability in the glacier lagoon Jökulsárlón, Iceland, for a short interval before the onset of the main melt season. Total Suspended Solids concentrations (TSS) of surface waters are related to remotely-sensed reflectance via empirical calibration between in-situ-sampled TSS and reflectance in a MODIS band 1-equivalent wavelength window. This study differs from previous ones in its application to an overturning tidewater glacier plume, rather than one derived from river runoff. The linear calibration improves on previous studies by facilitating a wider range of plume metrics than areal extent, notably pixel-by-pixel TSS values. Increasing values of minimum plume TSS over the study interval credibly represent rising overall turbidity in the lagoon as melting accumulates. Plume extent responds principally to consistently-strong offshore winds. Further work is required to determine the temporal persistence of the calibration, but remote plume observation holds promise for monitoring hydrological outputs from ungauged or ungaugeable systems.

Description: At least in conventional hydrostatic ice-sheet models, the numerical error associated with grounding line dynamics can be reduced by modifications to the discretization scheme. These involve altering the integration formulae for the basal traction and/or driving stress close to the grounding line and exhibit lower – if still first-order – error in the MISMIP3d experiments. MISMIP3d may not represent the variety of real ice streams, in that it lacks strong lateral stresses, and imposes a large basal traction at the grounding line. We study resolution sensitivity in the context of extreme forcing simulations of the entire Antarctic ice sheet, using the BISICLES adaptive mesh ice-sheet model with two schemes: the original treatment, and a scheme, which modifies the discretization of the basal traction. The second scheme does indeed improve accuracy – by around a factor of two – for a given mesh spacing, but $lesssim 1$ km resolution is still necessary. For example, in coarser resolution simulations Thwaites Glacier retreats so slowly that other ice streams divert its trunk. In contrast, with $lesssim 1$ km meshes, the same glacier retreats far more quickly and triggers the final phase of West Antarctic collapse a century before any such diversion can take place.

Description: In Northeast Greenland, the Norske Øer Ice Barrier (NØIB) abuts Nioghalvfjerdsfjorden (79N) and Zachariae Isstrøm (ZI), two floating outlets of the Northeast Greenland Ice Stream. NØIB is an extensive region of perennially fast sea ice, which varies in size from year to year, but with complete breakup a rare event in the 20th century. It reportedly broke up in the 1950s and was seen to break up in 1997. Since 2000 the NØIB has broken up during 11 of the last 14 summers. The forcings driving the increased frequency of ice barrier breakup are poorly understood, and it is not clear if the breakup is a purely local phenomenon or an indicator of regional changes in the ocean and atmosphere. Here we use a logistic regression statistical model to show that the odds of breakup are linked to June positive degree days and July wind speeds at a nearby weather station. It is too soon to know if subtle changes detected on 79N and ZI in the last decade are connected to breakups of the NØIB but, if they are, it suggests a complex interaction between the atmosphere, ocean and outlet glaciers in this part of Greenland.

Description: Projections of ice-sheet mass balance require regional ocean warming projections derived from atmosphere-ocean general circulation models (AOGCMs). However, the coarse resolution of AOGCMs: (1) may lead to systematic or AOGCM-specific biases and (2) makes it difficult to identify relevant water masses. Here, we employ a large-scale metric of Antarctic Shelf Bottom Water (ASBW) to investigate circum-Antarctic temperature biases and warming projections in 19 different Coupled Model Intercomparison Project Phase 5 (CMIP5) AOGCMs forced with two different ‘representative concentration pathways’ (RCPs). For high-emissions RCP 8.5, the ensemble mean 21st century ASBW warming is 0.66, 0.74 and 0.58°C for the Amundsen, Ross and Weddell Seas (AS, RS and WS), respectively. RCP 2.6 ensemble mean projections are substantially lower: 0.21, 0.26, and 0.19°C. All distributions of regional ASBW warming are positively skewed; for RCP 8.5, four AOGCMs project warming of greater than 1.8°C in the RS. Across the ensemble, there is a strong, RCP-independent, correlation between WS and RS warming. AS warming is more closely linked to warming in the Southern Ocean. We discuss possible physical mechanisms underlying the spatial patterns of warming and highlight implications of these results on strategies for forcing ice-sheet mass balance projections.

Description: In contrast to the general trend for glaciers of the Southern Patagonia Icefield, Glaciar Pio XI has experienced a large cumulative frontal advance since 1945. In an effort to better understand this advancing behaviour, this paper presents a synoptic analysis of frontal fluctuations (1998–2014), ice velocities (1986–2014), ice-surface elevations (1975–2007) and supraglacial moraines (1945–2014) derived from geospatial datasets. These analyses reveal changes in the ice flow of Glaciar Pio XI's freshwater calving northern terminus and tidewater calving southern terminus over recent decades. Between 1986 and 2000, ice flow speed generally accelerated reaching peaks of 〉15 m d−1 at the frontal edge of the southern terminus. Following this period, flow speed decreased, reducing to 〈1 m d−1 for the central part of the southern terminus in 2014, despite advancing to a neoglacial maximum. From 2000 to 2014 the reduction in speed was accompanied by a shift in maximum velocity away from the southern terminus, towards the central glacier trunk. As a result, the northern terminus, which accelerated during this period, represented the new primary flow path in 2014. Notably, the moraine maps presented highlight surges occurring around 1981 and again between 1997 and 2000, marked by arcuate moraine features on the southern terminus.

Description: The Seal Nunataks ice shelf (SNIS, ~743 km2 in 2013) is an unofficial name for a remnant area between the former Larsen A and Larsen B ice shelves off the northeastern Antarctic Peninsula. Analyses using Landsat 7 ETM+ and Terra ASTER images from 2001 to 13 and ICESat altimetry from 2003 to 09 show it has retreated and thinned following the Larsen A (1995) and Larsen B (2002) disintegrations. Despite some regional cooling and more fast ice since 2008, SNIS continues to lose ice along its margins and may be losing contact with some nunataks. Detailed analysis of data from four ICESat tracks indicates that ice shelf thinning rates range between 1.9 and 2.7 m a−1, and generally increase from west to east. An ICESat repeat track crossing the adjacent Robertson Island shows a mean elevation loss of 1.8 m a−1. Two tracks crossing the SNIS's remaining tributary, Rogosh Glacier, show sub-meter elevation losses. Comparing shelf remnant and grounded ice thinning rates implies that basal ocean melting augments SNIS thinning by ~1 m a−1, a rate that is consistent with other estimates of ocean-driven shelf thinning in the region.

Description: We describe changes in glaciers of the Balkhash-Alakol basin, central Asia, and analyse unified glacier inventories of the Zailiyskiy-Kungei and Jungar glacier systems and the Chinese part of the Ili river basin, as well as mass-balance monitoring data from Tsentralniy Tuyuksu glacier for the period 1957-2014. In spite of significant inter-basin differences, glaciation of the three glacial systems in the Ili river basin within Kazakhstan as well as within Chinese territory is changing simultaneously and similarly. Differences in the rates of glacier degradation are small and are affected primarily by the orientation of the flanks of the mountain ridges. Since the mid-1950s, glaciation of the region has remained degraded and, on average over the period examined, glaciers shrank at a rate of about 0.8% a(-1) in area and about 1% a(-1) in ice volume. Glacial systems in large basins such as Balkhash-Alakol change simultaneously, linearly and at similar rates. The average rates of glacier reduction of the Zailiyskiy-Kungei, Jungar and upper Ili glacier systems for the period 1955/56-2008 amounted to 0.76%, 0.75% and 0.73% a(-1) respectively.

Description: Photogrammetric measurements of powder-cloud surfaces from large avalanches enable the observation of cloud evolution and dispersion as well as quantification of cloud velocities and powder volumes. Since 2002, a total of six large powder avalanches have been recorded at the test site, Valle de la Sionne, Switzerland. The high-spatial-resolution photographs, acquired from two different observation angles, allow us to measure the velocity and height of plume-and-cleft structures on the powder-cloud surface. The photogrammetric measurements are supplemented by airborne laser scans of release, entrainment and deposition zones before and after the artificial avalanche release. Even though the precision of the photogrammetric measurements is limited, they are the best data available to test models of powder snow avalanche dynamics. The laser scan data capture initial and boundary conditions while time series of photogrammetric measurements provide insight into mechanisms driving blow-out formation and inertial propagation of the cloud. In this paper we present the experimental measurements and make direct comparisons with model simulations.

Description: Water stored as ice and snow at high elevations is a resource that plays an important role in the hydrologic cycle, particularly in the timing and volume of downstream discharge. Here we use geochemical and isotopic values of water samples to evaluate relative contributions of melting glacier ice and groundwater to discharge in Bhutan. River water samples were collected between 3100 and 4500m in the Chamkar Chhu (river) watershed of central Bhutan's Himalaya. Glacier ice and snow were sampled in the ablation zone of Thanagang glacier. Groundwater was parameterized from spring water at elevations of 3100 and 3600 m. Synoptic sampling was carried out in separate expeditions in July, August and late September 2014, to characterize monsoon and post-monsoon conditions. Results from a two-component hydrologic mixing model using isotopic and geochemical (sulphate) values show that the glacier outflow contributions decrease from similar to 76% at 4500m to 31% at 3100 m. A four-component hydrologic mixing model using end-member mixing analysis shows glacier ice melt increasing as a proportion of discharge over the 3 month sampling period, and consistently decreasing with distance downstream of Thanagang glacier terminus. These results indicate that isotopic and geochemical tracers can provide a quantitative evaluation of the source water contributions to streamflow in Bhutan.

Description: We present the updated glaciological mass balance (MB) of Chhota Shigri Glacier, the longest continuous annual MB record in the Hindu-Kush Karakoram Himalaya (HKH) region. Additionally, 4 years of seasonal MBs are presented and analyzed using the data acquired at an automatic weather station (AWS-M) installed in 2009 on a lateral moraine (4863ma.s.l.). The glaciological MB series since 2002 is first recalculated using an updated glacier hypsometry and then validated against geodetic MB derived from satellite stereo-imagery between 2005 (SPOT5) and 2014 (Pléiades). Chhota Shigri Glacier lost mass between 2002 and 2014 with a cumulative glaciological MB of –6.72mw.e. corresponding to a mean annual glacier-wide MB (Ba) of –0.56mw.e. a–1. Equilibrium-line altitude (ELA0) for the steady-state condition is calculated as ~4950ma.s.l., corresponding to an accumulation–area ratio (AAR0) of ~61%. Analysis of seasonal MBs between 2009 and 2013 with air temperature from AWS-M and precipitation from the nearest meteorological station at Bhuntar (1050ma.s.l.) suggests that the summer monsoon is the key season driving the interannual variability of Bafor this glacier. The intensity of summer snowfall events controls the Baevolution via controlling summer glacier-wide MB (Bs).

Description: We use numerical modelling of glacier mass balance combined with recent and past glacier extents to obtain information on Little Ice Age (LIA) climate in southeastern Tibet. We choose two glaciers that have been analysed in a previous study of equilibrium-line altitudes (ELA) and LIA glacier advances with remote-sensing approaches. We apply a physically based surface energy-and mass-balance model that is forced by dynamically downscaled global analysis data. The model is applied to two glacier stages mapped from satellite imagery, modern (1999) and LIA. Precipitation scaling factors (PSF) and air temperature offsets (ATO) are applied to reproduce recent ELA and glacier mass balance (MB) during the LIA. A sensitivity analysis is performed by applying seasonally varying gradients of precipitation and air temperature. The calculated glacier-wide MB estimate for the period 2000-12 is negative for both glaciers (-992 +/- 366 kgm(-2) a(-1) and -1053 +/- 258 kgm(-2) a(-1)). Relating recent and LIA PSF/ATO sets suggests a LIA climate with similar to 8-25% increased precipitation and similar to 1-2.5 degrees C lower mean air temperature than in the period 2000-12. The results only provide an order of magnitude because deviations in other input parameters are not considered.

Description: A temperature reconstruction in the glacierized Himalaya over the past centuries using glacial length fluctuation records is challenging due to the abundance of debris-covered glaciers and a scarcity of glacial length fluctuation data. Using idealized flowline model simulations, we show that supraglacial debris cover significantly alters the length fluctuations only when the debris cover is very thick. An expanded database of length fluctuation records for 43 glaciers in the Himalaya and Karakoram is compiled and a standard linear inversion procedure is applied to a subset of 34 glaciers in this database. The reconstructed temperature anomaly during 1860-2010 indicates a continued warming of the region with a total temperature change of ~1.6 K. A close resemblance of the regional temperature anomaly to global trends is seen.

Description: We have compiled and analysed available records and data on the shrinkage of Satopanth (SPG) and Bhagirath Kharak (BKG) Glaciers, Uttarakhand, India, during the period 1936-2013. We estimate the mean retreat rates of the snouts of SPG and BKG for this period at 9.7. +/- 0.8 m a(-1) and 7.0 +/- 0.6 m a(-1) respectively. We have also revised the estimates of the area vacated during the period 1956-2013 to be 0.27 +/- 0.05 km(2) and 0.17 +/- 0.04 km(2) for SPG and BKG respectively, corresponding to front-averaged retreat rates of 5.7 +/- 0.6 m a(-1) and 6.0 +/- 0.9 m a(-1). The study revealed an average thinning of glacial ice in the lower ablation zone of SPG of 9 +/- 11m in the past 51 years. We observed that while the fronts of SPG and BKG depicted in the Survey of India topographic map published in 1962 are inconsistent with other available records, the elevation contours are consistent with them.

Description: We estimate all the individual glacier area and volume changes in High Mountain Asia (HMA) by 2050 based on Randolph Glacier Inventory (RGI) version 4.0, using different methods of assessing sensitivity to summer temperatures driven by a regional climate model and the IPCC A1B radiative forcing scenario. A large range of sea-level rise variation comes from varying equilibrium-line altitude (ELA) sensitivity to summer temperatures. This sensitivity and also the glacier mass-balance gradients with elevation have the largest coefficients of variability (amounting to similar to 50%) among factors examined. Prescribing ELA sensitivities from energy-balance models produces the highest sea-level rise (9.2 mm, or 0.76% of glacier volume a(-1)), while the ELA sensitivities estimated from summer temperatures at Chinese meteorological stations and also from 1 degrees x 1 degrees gridded temperatures in the Berkeley Earth database produce 3.6 and 3.8 mm, respectively. Different choices of the initial ELA or summer precipitation lead to 15% uncertainties in modelled glacier volume loss. RGI version 4.0 produces 20% lower sea-level rise than version 2.0. More surface mass-balance observations, meteorological data from the glaciated areas, and detailed satellite altimetry data can provide better estimates of sea-level rise in the future.

Description: Glacier responses to future climate change will affect hydrology at sub-basin scales. The main goal of this study is to assess glaciological and hydrological sensitivities of sub-basins throughout the Hindu Kush-Himalaya region. We use a simple geometrical analysis based on a full glacier inventory and digital elevation model to estimate sub-basin equilibrium-line altitudes (ELAs) from assumptions of steady-state accumulation area ratios. The ELA response to an increase in temperature is expressed as a function of mean annual precipitation, derived from a range of high-altitude studies. Changes in glacier contributions to streamflow in response to increased temperatures are examined for scenarios of both static and adjusted glacier geometries. On average, glacier contributions to streamflow increase by similar to 50% for a + 1 K warming based on a static geometry. Large decreases(-60% on average) occur in all basins when glacier geometries are instantaneously adjusted to reflect the new ELA. Finally, we provide estimates of sub-basin glacier response times that suggest a majority of basins will experience declining glacier contributions by 2100.

Description: Estimates of melt from debris-covered glaciers require distributed estimates of meteorological variables and air temperature in particular. Meteorological data are scarce for this environment, and spatial variability of temperature over debris is poorly understood. Based on multiple measurements of air and surface temperature from three ablation seasons (2012-14) we investigate the variability of temperature over Lirung Glacier, Nepal, in order to reveal how air temperature is affected by the debris cover and improve ways to extrapolate it. We investigate how much on-glacier temperature deviates from that predicted from a valley lapse rate (LR), analyse on-glacier LRs and test regression models of air temperature and surface temperature. Air temperature over the debris-covered glacier tongue is much higher than what a valley LR would prescribe, so an extrapolation from off-glacier stations is not applicable. An on-glacier LR is clearly defined at night, with strong correlation, but not during the day, when the warming debris disrupts the elevation control. An alternative to derive daytime air temperature is to use a relationship between air and surface temperature, as previously suggested. We find strong variability during daytime that should be accounted for if these regressions are used for temperature extrapolation.

Description: Radio-echo sounding techniques are very useful for fast profiling of seasonal snowpack. Ground-penetrating radar (GPR) is used widely for various cryospheric applications, such as snow/glacier depth estimation, snow layer identification and snow water equivalent assessment. The dielectric constant of snow is an important input parameter for the acquisition and interpretation of GPR data from the snowpack. In this study, snow dielectric constant was measured along with physical properties of snow using a snow fork operating at 1GHz frequency. Experiments were conducted at field observatories of the Snow and Avalanche Study Establishment located in different Himalayan ranges: Patseo (Greater Himalayan range), Dhundhi and Solang (Pir Panjal range). Interseasonal spatial and temporal variations in snow dielectric constant and associated snowpack properties were analysed for five winter seasons (2010-14). The mean seasonal snow dielectric constant is higher at Dhundhi (1.82 +/- 0.02) than at Patseo (1.69 +/- 0.02). The measured snow dielectric constant was used to derive snow density and liquid-water content (LWC). A better correlation between snow dielectric constant and LWC is observed for high-density snow (〉 300 kgm(-3); R-2 = 0.95) than for low-density snow (〈 200 kgm(-3); R-2 = 0.73). Snow-fork-derived snow density was in good agreement with manually measured values. The snow dielectric constant database generated during this study can be used as a reference for various field applications of GPR in snow-related studies.

Description: This study presents the first decadal mass-balance record of a small debris-free glacier in the Bhutan Himalaya, where few in situ measurements have been reported to date. Since 2003 we have measured the mass balance of Gangju La glacier, which covers an area of 0.3 km(2) and extends from 4900 to 5200 ma.s.l., using both differential GPS surveys (geodetic method) and stake measurements (direct method). The observed mass balance ranged from -1.12 to -2.04 mw.e.a(-1) between 2003 and 2014. The glacier exhibited much greater mass loss than neighbouring glaciers in the eastern Himalaya and southeastern Tibet, which are expected to be sensitive to climate change due to the monsoon-influenced humid climate. Observed mass-balance profiles suggest that the equilibrium-line altitude has been higher than Gangju La glacier since 2003, implying that the entire glacier has experienced net ablation for at least the past decade.

Description: An assessment of glacier shrinkage (reduction of area) for all of High Mountain Asia requires a complete compilation of measured rates of change and also a methodology for objective comparison of rates. I present a compilation from 155 publications reporting glacier area changes, and also a methodology that overcomes the main obstacles hindering comparison. Glacier areas are not always assigned uncertainties, and this problem is addressed with an error model derived from published estimates. The problem of discordant survey dates is addressed by interpolating measured areas to fixed dates at pentadal intervals. Interpolation error depends only incoherently on the time span between measurements, but strongly on glacier size: smaller glaciers, in addition to changing more rapidly on average, exhibit more variable rates of change. The overlapping boundaries of study regions are reconciled by mapping all of the information to a 0.5 degrees geographical grid. When coupled with glacier area information from the Randolph Glacier Inventory, the widely observed inverse dependence of shrinkage rates on glacier size shows promise as a tool for treating incomplete spatial coverage. Over High Mountain Asia as a whole from 1960 to 2010, the unweighted average shrinkage rate is -0.57% a(-1), but corrections for variable glacier size raise the average to -0.34% a(-1), and filling unmeasured gridcells with rates based on size dependence alters the latter estimate to -0.40% a(-1). The uncertainties in these rates are large. The Karakoram anomaly is found to be a zonal feature extending well to the east of the Karakoram proper.

Description: The Qinghai-Tibetan Plateau (QTP) is characterized by a cold climate and a large number of lakes. The long ice season necessitates study of the widespread ice covers in the region. An unprecedented multidisciplinary field campaign was conducted on lake ice processes in the central QTP during the period 2019-13. The study lake generally froze up in late October or early November, and broke up in mid or late April, with a maximum ice thickness of 50-70 cm. The mass balances at both ice surface and bottom were measured continuously. Significant ice surface sublimation/ablation was detected and accounted for up to 40% of the whole ice thickness over the ice season. A simple heat-transfer model was developed for the surface ice loss. The calculated values were in good agreement with the observations. They also indicated that atmospheric conditions, including low air humidity and prevailing strong winds, are the primary drivers of the ice surface sublimation.

Description: Air temperature is a key control of processes affecting snow and glaciers in high-elevation catchments, including melt, snowfall and sublimation. It is therefore a key input variable to models of land-surface-atmosphere interaction. Despite this importance, its spatial variability is poorly understood and simple assumptions are made to extrapolate it from point observations to the catchment scale. We use a dataset of 2.75 years of air temperature measurements (from May 2012 to November 2014) at a network of up to 27 locations in the Langtang River, Nepal, catchment to investigate air temperature seasonality and consistency between years. We use observations from high elevations and from the easternmost section of the basin to corroborate previous findings of shallow lapse rates. Seasonal variability is strong, with shallowest lapse rates during the monsoon season. Diurnal variability is also strong and should be taken into account since processes such as melt have a pronounced diurnal variability. Use of seasonal lapse rates seems crucial for glacio-hydrological modelling, but seasonal lapse rates seem stable over the 2-3 years investigated. Lateral variability at transects across valley is high and dominated by aspect, with south-facing sites being warmer than north-facing sites and deviations from the fitted lapse rates of up to several degrees. Local factors (e.g. topographic shading) can reduce or enhance this effect. The interplay of radiation, aspect and elevation should be further investigated with high-elevation transects.

Description: Correlations between a 1000 year record of the major ions in a 108.83m ice core from East Rongbuk Glacier (28 degrees 01' N, 86 degrees 58' E; 6518 ma.s.l.) on the northeast slope of Qomolangma (Mount Everest) and the Southern Oscillation Index (SOI) were examined to investigate possible links between the ice-core records of the southern Tibetan Plateau (TP) and El Nino Southern Oscillation (ENSO). The results show that years with the highest crustal ion concentrations and lowest marine ion concentrations corresponded with a low SOI, and vice versa. Cross wavelet and wavelet coherence analysis between major ion time series and the SOI indicated that there were significant sections with high common power between the major ion time series and the SOI, suggesting a correlation between the ion records of the Qomolangma ice core and ENSO. Further investigation indicated that the higher SOI years corresponded with weaker continental air masses and stronger south Asian monsoons over the southern TP, leading to increased marine ions and decreased continental ions transported to the southern TP. The in-phase surface pressure anomalies of the southern TP and Darwin, Australia, link ENSO and ion transport over the southern TP, and thus suggest a link between aerosol transport over the southern TP and ENSO.

Description: A glacierized terrain comprises different land covers, and their mapping using satellite data is challenged by their spectral similarity. We propose a hierarchical knowledge-based classification (HKBC) approach for differentiation of glacier terrain classes and mapping of glacier boundaries, using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery and Global Digital Elevation Model (GDEM). The methodology was tested over Kolahoi Glacier, Kashmir Himalaya. For the sequential extraction of various glacier terrain classes, several input layers were generated from the primary datasets by applying image-processing techniques. Noticeable differences in temperature and spectral response between supraglacial debris and periglacial debris facilitated the development of a thermal glacier mask and normalized-difference debris index, which together with slope enabled their differentiation. These and the other layers were then used in several discrete tests in HKBC, to map various glacier terrain classes. An ASTER visible near-infrared image and 42 field points were used to validate results. The proposed approach satisfactorily classified all the glacier terrain classes with an overall accuracy of 89%. The Z-test reveals that results obtained from HKBC are significantly (at 95% confidence level) better than those from a maximum likelihood classifier (MLC). Glacier boundaries obtained from HKBC were found to be plausibly better than those obtained from MLC and visual interpretation.

Description: This study presents a reconstruction of the seasonal mass balance of Glacier No. 354, located in the Akshiirak range, Kyrgyzstan, from 2003 to 2014. We use a distributed accumulation and temperature-index melt model driven by daily air temperature and precipitation from a nearby meteorological station. The model is calibrated with in situ measurements of the annual mass balance collected from 2011 to 2014. The snow-cover depletion pattern observed using satellite imagery provides additional information on the dynamics of mass change throughout the melting season. Two digital elevation models derived from high-resolution satellite stereo images acquired in 2003 and 2012 are used to calculate glacier volume change for the corresponding period. The geodetic mass change thus derived is used to validate the modelled cumulative glacier-wide balance. For the period 2003-12 we find a cumulative mass balance of -0.40. +/- 10 m w.e.a(-1). This result agrees well with the geodetic balance of -0.48. +/- 0.07 m w.e.a(-1) over the same period.

Description: High-resolution δ18O records from a Geladaindong mountain ice core spanning the period 1477-1982 were used to investigate past temperature variations in the Yangtze River source region of the central Tibetan Plateau (TP). Annual ice-core δ18O records were positively correlated with temperature data from nearby meteorological stations, suggesting that the δ18O record represented the air temperature in the region. A generally increasing temperature trend over the past 500 years was identified, with amplified warming during the 20th century. A colder stage, spanning before the 1850s, was found to represent the Little Ice Age with colder periods occurring during the 1470s–1500s, 1580s–1660s, 1700s–20s and 1770s–1840s. Compared with other temperature records from the TP and the Northern Hemisphere, the Geladaindong ice-core record suggested that the regional climate of the central TP experienced a stronger warming trend during the 20th century than other regions. In addition, a positive relationship between the Geladaindong δ18O values and the North Atlantic Oscillation index, combined with a wavelet analysis of δ18O records, indicated that there was a potential atmospheric teleconnection between the North Atlantic and the central TP.

Description: Lakes beneath the Antarctic Ice Sheet are known to decrease traction at the ice base and therefore can have a great impact on ice dynamics. However, the total extent of Antarctic subglacial lakes is still unknown. We address this issue by combining modeling and remote-sensing strategies to predict potential lake locations using the general hydraulic potential equation. We are able to reproduce the majority of known lakes, as well as predict the existence of many new and so far undetected potential lakes. To validate our predictions, we analyzed ice-penetrating radar profiles from radio-echo sounding flights acquired over 1994-2013 in Dronning Maud Land, East Antarctica, and this led to the identification of 31 new subglacial lakes. Based on these findings, we estimate the total number of Antarctic subglacial lakes to be similar to 1300, a factor of three higher than the total number of lakes discovered to date. We estimate that only similar to 30% of all Antarctic subglacial lakes and similar to 65% of the total estimated lake-covered area have been discovered, and that lakes account for 0.6% of the Antarctic ice/bed interface.

Description: We investigated glacier changes in the Karatal river basin, the largest basin in Zhetysu (Dzhungar) Alatau, Kazakhstan, for the periods 1956-89, 1989-2001 and 2001-12, based on Landsat TM/ETM+ data analysis. In 1989, we found 243 glaciers with a total area of 142.8km(2); by 2012 these had shrunk to 214 glaciers with a total area of 109.3km(2), a decrease of 33.5km(2) over 23 years (1.02% a(-1)). This very high shrinkage rate is likely connected with a general trend of increasing temperatures, and small glaciers being situated at the relatively low altitude of the outer Zhetysu Alatau ranges. We also analyzed the shrinkage rate of glaciers based on their differences in size, altitude and aspect of slopes, as well as other topographic parameters, in four sub-basins where glacier shrinkage varied between 18% and 39%. Weather-station climate data showed a significant temperature increase and stable precipitation trends over the study period. We conclude that glacierized areas of the Karatal river basin are located in the most unfavorable conditions for glaciation, and as a result showed a higher shrinkage rate than other glacierized areas of the Tien Shan from 1956 to 2012.

Description: Virkisjokull is a rapidly retreating outlet glacier draining the western flanks of Oraefajokull in SE Iceland. Since 2011 there have been continuous measurements of flow in the proglacial meltwater channel and regular campaigns to sample stable isotopes delta H-2 and delta O-18 from the river, ice, moraine springs and groundwater. The stable isotopes provide reliable end members for glacial ice and shallow groundwater. Analysis of data from 2011 to 2014 indicates that although ice and snowmelt dominate summer riverflow (mean 5.3-7.9 m(3) s(-1)), significant flow is also observed in winter (mean 1.6-2.4 m(3) s(-1)) due primarily to ongoing glacier icemelt. The stable isotope data demonstrate that the influence of groundwater discharge from moraines and the sandur aquifer increases during winter and forms a small (15-20%) consistent source of baseflow to the river. The similarity of hydrological response across seasons reflects a highly efficient glacial drainage system, which makes use of a series of permanent englacial channels within active and buried ice throughout the year. The study has shown that the development of an efficient year round drainage network within the lower part of the glacier has been coincident with the stagnation and subsequent rapid retreat of the glacier.

Description: With the exception of northern India, there are few, if any, consistent data records relating to avalanche activity in the high mountains of Asia. However, records do exist of avalanche fatalities in the region, contained in mountaineering expedition reports. In this paper, I review and analyze statistics of avalanche fatalities (both snow and ice) in the high mountains of Asia (Himalaya, Karakoram, Pamir, Hindu Kush, Tien Shan, Dazu Shan) from 1895 to 2014. The data are stratified according to accident cause, geographical region (Nepal-Tibet (Xizang), Pakistan, India, China, Central Asia), mountain range, personnel (hired or expedition members) and terrain. The character of the accidents is compared with data from North America and Europe. The data show that the important risk components are the temporal and spatial exposure probabilities. It is shown that human actions and decisions govern the pattern of fatal avalanches in the high mountains of Asia.

Description: The retention and release of liquid water in glacierized basins was modelled with a conceptual, semi-distributed model of the water and ice balance designed for long-term averages with monthly resolution for 100 m elevation bands. Here we present the components of the liquid water balance of 86 mostly glacierized basins on either side of the main Alpine divide between 10 and 13 degrees E in the period 1998-2006 and compare them with the records of 30 basins monitored from 1970 to 1997. Basin average of liquid water retention has maxima in excess of 100 mm per month in May, often followed by maximum release when the retaining snow matrix melts. Glacier storage peaks in August partly due to ice melt and the ensuing filling of the englacial reservoirs and partly on account of a precipitation maximum. These two components combined to a common maximum of storage in summer in the first period 1970-97 and developed two distinct maxima in the warmer period 1998-2006. A further maximum of liquid water storage that was often found in October is most likely due to a peak in precipitation in the southern part of the study region.