Near-surface firn temperatures were measured in 22 steam-drilled boreholes in the summit region of Mont Blanc (France and Italy) at 3800 –4800ma.s.l. in June 1998 and in 31 boreholes in the Monte Rosa area (Italy and Switzerland) at 3900– 4500ma.s.l. in May–July 1999. Borehole temperatures were logged to 22 m depth. the temperatures at 18 m depth ranged between temperate conditions and approximately –15˚C. In a small altitude band, the observed distribution pattern suggests a strong influence of shortwave radiation and turbulent heat exchange (being generally more effective at wind-exposed sites). These two energy fluxes mainly determine the melt-energy input into the snow and firn during summer and, thereby, the measured near-surface temperatures. A statistical analysis of the measured firn temperatures revealed altitude-dependent firn temperature gradients of –1.48 and of –2.36˚C (100m)–1 for the Mont Blanc and Monte Rosa areas, respectively. the high lapse rates, as compared to the air-temperature lapse rate, are the result of englacial latent-heat contribution. the parameters elevation, potential direct solar radiation, slope and accumulation explain 480% of the variation of the mean annual firn temperatures. Aspect-dependent lower boundaries for the cold-firn occurrence in the two areas ranged between 3500 and 4100 ma.s.l.

The accumulation rate on Potsdam Glacier, East Antarctica, and its spatial and temporal variations are examined using ground-penetrating radar, snow samples and firn-core studies. Physical properties in snow samples and along firn cores provide distributions of density with depth, showing only small spatial variation. Counting of peaks in δ18O along the firn cores yields an age–depth distribution that is transferred to the stratigraphy of isochronal internal layers observed with radar. From two radar horizons we determine the spatial accumulation pattern, averaged over the periods 1970–80 and 1980–2004. The shape of internal layers indicates an ablation area at the eastern margin of the investigation area. Accumulation rates show a very high spatial variability, with a mean value of 141 kgm–2 a–1 for the period 1970–2004 and a standard deviation of almost 50%. Mean temporal variation of only a few per cent throughout the investigated area for the observed time interval is much less than the spatial variations. The mean accumulation values are somewhat less than values reported before from this region. Accumulation pattern and surface topography are linked in a way indicating that wind-borne redistribution of snow significantly contributes to the observed spatial variations of accumulation rates. The accumulation data and their variability complement and validate present and future satellite studies of Antarctica’s mass balance.

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 km3. 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.

Despite their importance as freshwater reservoirs for downstream river systems, few glaciers in central Chile have been comprehensively surveyed. This study presents ground-penetrating radar (GPR) and field-based observations for characterizing the englacial and basal conditions of Glaciar Olivares Alfa (33°110 S, 70°130 W), central Chilean Andes. Using a 50 MHz radar mounted onto a helicopter platform, data were collected covering large portions of the glacier accumulation and ablation zones. The radar data revealed boundaries of a temperate-ice layer at the base of the eastern body of Glaciar Olivares Alfa which appears to be covered by colder ice that extends throughout large parts of the glacier. The thickness of the temperate ice layer is highly variable across the glacier, being on average 40% of the total ice thickness. Radar data analyses reveal regions of cold ice at the bottom/base of the glacier and also patterns of highly saturated sediments beneath the glacier. Using GPR data, this study represents the most exhaustive analysis of glacier ice structure performed in the central Chilean Andes. The results will enable improved estimations of the glacier’s mass balance and ice dynamics, helping us to understand its further development and its impact on water availability.

Floe size within the Antarctic pack ice is an important parameter that affects both the ocean-ice-atmosphere energy exchange and the mechanical properties of pack ice. In this paper we present a computer-based algorithm to extract floe-size distribution information from digital aerial photographs of Antarctic sea ice. The algorithm segments digital images of sea ice into distinct floes from which the size of each floe is calculated and floe-size distributions are derived. Through a recursive application of the morphological erosion operator, each floe is eroded towards its centre while each pixel’s erosion number is recorded. This ensures no information is lost while individual floes are identified. The algorithm combines image-processing techniques with some manual input to accurately identify the boundaries of individual floes within an image. To demonstrate the functionality of the algorithm, six images, representing regions along a 22 km south-to-north transect through a transitional zone of pack ice near 65° S, 140° E, have been processed. Regional variations in the floe-size distributions show an increase in the number of smaller floes relative to larger floes and a decrease in the dominant floe size (in terms of areal coverage) from south to north. These results are consistent with ship-based observations.

Macropores - large open channels that can conduct water - have been found within snowpacks of the Sierra Nevada of California. Extensive networks of channels as well as apparently isolated single channels have been documented. These openings, which are usually found near the base of the snowpack, were recognized at several widespread sites. Such basal channels may be an important means of draining liquid water from the snowpack. The presence of open conduits in snow helps to explain such phenomena as rapid streamflow response to percolating rain and melt water.

Explosive seismic reflection data from Halvfarryggen, a 910 m thick local ice dome of the Antarctic ice sheet, show numerous laterally continuous reflections within the ice between 300 and 870 m depth. We compare the quality of data obtained with explosive sources with that obtained using a vibroseis source for detecting englacial reflections with a snowstreamer, and investigate the origin of englacial reflections. We find vibroseis in combination with a snowstreamer is ten times more productive than explosive seismics. However, englacial reflections are more clearly visible with explosives, which have a broader bandwidth signature, than the vibroseis, which is band-limited at the high-frequency end to 100 Hz. Only the strongest and deepest englacial reflection is detected with vibroseis. We interpret the majority of englacial reflections to originate from changes in the crystal orientation fabric in closely spaced layers, less than the vibro-seismic tuning thickness of 13.5 m. Phase analysis of the lowermost englacial reflector, 40 m above the bed, indicates a sharp increase in seismic wave speed. We interpret this reflector as a transition to a vertical single-maximum fabric. Our findings support current results from anisotropic ice-flow models, that crystal fabric is highly anisotropic at ice domes, both laterally and vertically.

Creep tests carried out on specimens of isotropic ice containing a monocrystalline inclusion allow us to observe some strain heterogeneities that develop during the deformation of polycrystalline ice. Different kinds of heterogeneities, some of them leading to strain localization, are observed and described, and mechanisms are proposed to explain how they arise. However, when the inclusion has a very regular shape with no geometric singularity (e.g. circular shape) and is embedded in a fine-grained isotropic matrix, the observations lead us to assume homogeneous deformation of the inclusion, with no strain localization except that associated with basal glide.

The spatial distribution of surface mass balance on the Greenland ice sheet is mapped on a 50 km grid using a combination of methods depending on a zonal characterization of the diagenetic snow fades. In the zones of dry snow and upper percolation fades, the accumulation rate is calculated from microwave emissivities derived from satellite measurements using a model that is calibrated with field accumulation data. In the lower percolation zone, accumulation rates are obtained from visual interpolation of previously compiled field data, with some modification so the balance is zero at the equilibrium line In the ablation zone, ablation rates are calculated as a function of ice-surface elevation and latitude. Average values of the surface balance are 263 kg m–2a–1 in the accumulation zone, (-) 1259 kg m–2 a–1 in the ablation zone and 1286 kg m–2 a–1 overall. Compared to the findings of a previous study using practically the same approach but different models, our bulk estimate of balance (216 Gt a–1) is 57% smaller, but the differences in the estimates of net accumulation and net ablation are, respectively, 30% and 172% larger. In this and other comparisons, there is evidence that the differences in estimates are primarily due to differences in the delineation of the equilibrium line and the estimate of ablation, and secondarily to the estimate of accumulation and interpolation of field data. The differences noted with six other estimates reported in the last two decades are all of a size close to the composite variation of the difference (±50Gtσ–1) . Our surface balance is smaller than three estimates, larger than one and in agreement with two. If substituted in the latest mass-budget estimate that indicates equilibrium, our surface balance estimate would suggest a negative budget of 55 Gt a–1 and thus a positive contribution to sea-level change of 0.15 mm a–1.

The aim of this study is to investigate spatial and temporal variations of meteorological variables known to control glacier mass-balance processes, and to demonstrate their relevance in High Asia. The study uses the NCEP/NCAR reanalysis database (US National Centers for Environmental Prediction and US National Center for Atmospheric Research), which is global and continuous since 1 January 1948. A positive degree-day (PDD) model of annual glacier-wide summer surface balance, Bs, uses upper-air temperatures at NCEP/NCAR gridpoints near each of six glaciers between 40 and 45° N and between 71 and 87°E and two others near 50° N, 87° E. Model error ranged between 0.19 and 0.41 mw.e., comparable with the observational accuracy of Bs. Sensitivity to temperature change, dBs=dT, ranges between –0.5 and –0.2 m w.e. a–1 °C–1 for these glaciers.

We present the analysis of global sympagic primary production (PP) from 300 years of pre-industrial and historical simulations of the E3SMv1.1-BGC model. The model includes a novel, eight-element sea ice biogeochemical component, MPAS-Seaice zbgc, which is resolved in three spatial dimensions and uses a vertical transport scheme based on internal brine dynamics. Modeled ice algal chlorophyll-a concentrations and column-integrated values are broadly consistent with observations, though chl-a profile fractions indicate that upper ice communities of the Southern Ocean are underestimated. Simulations of polar integrated sea ice PP support the lower bound in published estimates for both polar regions with mean Arctic values of 7.5 and 15.5 TgC/a in the Southern Ocean. However, comparisons of the polar climate state with observations, using a maximal bound for ice algal growth rates, suggest that the Arctic lower bound is a significant underestimation driven by biases in ocean surface nitrate, and that correction of these biases supports as much as 60.7 TgC/a of net Arctic PP. Simulated Southern Ocean sympagic PP is predominantly light-limited, and regional patterns, particularly in the coastal high production band, are found to be negatively correlated with snow thickness.

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.

A so-called ‘warm and wet transition’ of climate has occurred in the arid part of northwestern China since the late 1980s. A result of this climatic transition is an increase in runoff in Xinjiang and neighboring regions. In a warming and wetting change-of-climate scenario, we attempt to evaluate the impact of glacier meltwater and precipitation on the increase in outlet discharge (runoff) from Keqicar Baqi glacier, southwestern Tien Shan, China. In our research we have applied a degree-day model which is one of the most widely used methods of ice- and snowmelt computations for a multitude of purposes such as hydrological modeling, ice-dynamic modeling and climate sensitivity studies. It is concluded that under the warming and wetting scenario, the primary supply for the runoff in this catchment is glacier meltwater, with precipitation being the dominant secondary source; 84% and 8% of total runoff, respectively.

We used internal ice layers from a radio-echo sounding profile between the Kohnen and Dome Fuji deep drilling sites to infer the spatio-temporal pattern of accumulation rate in this sector of Dronning Maud Land, East Antarctica. Continuous internal reflection horizons can be traced to about half of the ice thickness and have a maximum age of approximately 72.7 ka BP. To infer palaeo-accumulation rates from the dated layers, we derived the thinning functions from a flow calculation with a high-resolution higher-order model of Dronning Maud Land embedded into a three-dimensional thermomechanical model of the Antarctic ice sheet. The method takes into account complex ice-flow dynamics and advection effects that cannot be dealt with using traditional local approaches. We selected seven time intervals over which we determine the average accumulation rate and average surface temperature at the place and time of origin of the layer particles. Our results show lower accumulation rates along eastern parts of the profile for the late Holocene (0–5 ka BP) than are shown by existing maps, which had no surface control points. During the last glacial period we find a substantially lower accumulation rate than predicted by the usual approach linking palaeo-accumulation rates to the condensation temperature above the surface inversion layer. These findings were used to fine-tune the relation between accumulation rate and temperature.

The present work addresses the urgent demand for methods of quantifying the uncertainties inherent in the current procedures for avalanche hazard assessment. A Monte Carlo approach to hazard mapping is proposed for this purpose. This statistical sampling-analysis method allows us to evaluate the probability distributions of the relevant variables for avalanche hazard assessment –– essentially runout distance and impact pressure-once the release variables and the model parameters are expressed in terms of suitable probability distributions. In this way it is possible to explicitly account for uncertainties both in the input-data definition of the dynamic models and in the mapping results. The overall methodology is presented in detail and applied to a real-world avalanche mapping problem. The one-dimensional version of the VARA models is used for avalanche dynamics simulations.

The United States National Ice Center (NIC) provides weekly ice analyses of the Arctic and Antarctic using information from ice reconnaissance, ship reports and high-resolution satellite imagery. In cloud-covered areas and regions lacking imagery, the higher-resolution sources are augmented by ice concentrations derived from Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) passive-microwave imagery. However, the SSM/I-derived ice concentrations are limited by low resolution and uncertainties in thin-ice regions. Ongoing research at NIC is attempting to improve the utility of these SSM/I products for operational sea-ice analyses. The refinements of operational algorithms may also aid future scientific studies. Here we discuss an evaluation of the standard operational ice-concentration algorithm, Cal/Val, with a possible alternative, a modified NASA Team algorithm. The modified algorithm compares favorably with Cal/Val and is a substantial improvement over the standard NASA Team algorithm in thin-ice regions that are of particular interest to operational activities.

This study outlines a consistent methodology for identifying glacier surfaces from Landsat 5, 7 and 8 imagery that is applied to map all mainland North Asian glaciers, providing the first methodologically consistent and complete glacier inventory for the region ~2010. We identify 5065 glaciers covering a planimetric area of 2326 ± 186 km2, most of which is located in the Altai mountain subregion. The total glacier count is 15% higher, but the total glacier area is 32 ±11.6% lower, than the estimated glacier coverage provided in version 4.0 of the Randolph Glacier Inventory. We investigate the distribution of glacier size within North Asia and find that the majority of glaciers (82%) are smaller than 0.5 km2 but only account for a third of the total glacier area, with the largest 1 % (60 glaciers ≥ 5 km2 ) accounting for 28% of the total area. We present hypsometric characterizations of North Asian glaciers, largely substantiating existing findings that glaciers in this region are dominated by cold, relatively dry conditions. We provide a detailed assessment of errors and determine the uncertainty in our area estimate to be ±8.0%, with snow-cover uncertainty the largest contributing factor. Based on this assessment, the new glacier inventory presented here is more complete and of higher quality than other currently available data sources.

Although satellite data are useful for obtaining ice-thickness distribution for perennial sea ice or in stable thin-sea-ice areas, they are still largely an unresolved issue for the seasonal ice zone (SIZ). We address this problem using L-band synthetic aperture radar (SAR). In the SIZ, ice-thickness growth is closely related to deformation, so surface roughness is expected to correlate with ice thickness. L-band SAR, suitable for detecting such surface roughness, is a promising tool for obtaining thickness distribution. This idea was supported by an airborne polarimetric and interferometric SAR (Pi-SAR) validation. To extend this result to spaceborne L-band SAR with coarser resolution, we conducted in situ measurements of ice thickness and surface roughness in February 2008 in the southern Sea of Okhotsk with an icebreaker in coordination with the Advanced Land Observing Satellite (ALOS)/Phased Array-type L-band SAR (PALSAR) orbit. A helicopter-borne laser profiler was used to improve the estimation of surface roughness. It was found that backscatter coefficients (HH) correlated well with ice thickness (R = 0.86) and surface roughness (R = 0.70), which confirms the possibility of determining ice-thickness distribution in the SIZ. the interannual variation of PALSAR-derived ice-thickness distribution in the southern Sea of Okhotsk is also discussed.

Water level fluctuations of inland lakes are related to regional-scale climate changes, and reflect variations in evaporation, precipitation and glacier meltwater flowing into the lake area in its catchment. In this paper, Ice, Cloud and land Elevation Satellite (ICESat) altimeter data and Landsat imagery (2002-09) are used to estimate Nam Co lake (Nyainqentanglha range, Tibetan Plateau) water elevation changes during 2002-09. In 2003 Nam Co lake covered an area of ~1998.8 ± 4.2 km2 and was situated at 4723 m a.s.l. Over such inland water bodies, ICESat altimeter data offer both wide coverage and spatial and temporal accuracy. We combine remote-sensing and GIS technology to map and reconstruct lake area and increased volume changes during a 7 year time series. Nam Co lake water level increased by 2.4±0.12m (0.33ma–1) between 23 February 2003 and 1 October 2009, and lake volume increased by 4.9 ±0.5 km3. In the past 7 years, Nam Co lake area has increased from 1998.78 ±5.4 to 2023.8 ±3.4 km2, the glacier-covered area has decreased from 832.34 to 821.0 km2 and the drainage basin area has decreased from 201.1 ±4.2 to 196.1 ±2.3 km2. However, the most spectacular feature is the continual water level rise from 2003 to 2009 without an obvious associated increase in precipitation. Based on digital elevation models (DEMs) from Shuttle Radar Topography Mission (SRTM) DEM data and corrected ICESat elevation data, significant changes to glacier mass balance in the western Nyainqentanglha mountains are indicated. Nyainqentanglha mountain glacier surface elevations decreased by 8.39 ± 0.45 m during 2003-09. Over the same period, at least 1.01 km3 of glacial meltwater flowed into Nam Co lake, assuming a glacial runoff coefficient of 0.6. The mean glacier mass-balance value is -490mmw.e. over the corresponding period, indicating that glacier meltwater in the catchment contributes to lake level rise. The contribution rate of glacial meltwater to lake water volume rise is 20.75%. The temporal lake level fluctuation correlates with temperature variations over the same time span.

This study examines precipitation samples collected at the Yushu meteorological station on the eastern Tibetan Plateau from November 2000 to November 2002. Results show that air-temperature effects control δ18O in precipitation in this area. Values of δ18O in precipitation positively correlate with air temperature, especially for monthly averages. Our data also show δ18O values in precipitation positively correlate with dew point and surface pressure in the Yushu region. Similar to other stations (Tuotuohe, Nagqu, Gaize and Shiquanhe) lying in the transition zone between the regions in the south dominated by the monsoon and those in the north dominated by the westerlies, because of the effect of monsoon precipitation, precipitation rates are high, and heavy isotopes are more depleted in summer at the Yushu station. Accordingly, values of δ18O in precipitation correlate more strongly with air temperature and dew point before the monsoon onset and after the monsoon retreat than during the monsoon period. That is, intense monsoon activities weaken the correlations between δ18O and air temperature and dew point. Clearly, dew point, surface pressure and the monsoon intensity contribute to controlling the δ18O values in precipitation at the Yushu station.