Analysis of an ice sample with an estimated age of 125 years, from the Antarctic Peninsula, using a scanning electron microscope with a cold stage and an X-ray micro-analysis facility, shows that H2SO4 occurs mainly at triple junctions. Sea salts show no such localization. The different behaviour may be due to the freezing-point behaviour of each chemical substance, and to the effect this has both in the atmosphere and during recrystallization in the ice sheet. If this finding applies generally to other parts of the Antarctic ice sheet, it has major implications for many of the physical properties of Antarctic ice. In particular, it leads to a better understanding of the d.c. electrical conductivity of such ice.

The retreat of the glaciers on Mount Kenya is quantitatively well documented for the intervals 1899–1963 and 1963–1987. The ice recession between 1899 and 1963 was strongly dependent on solar radiation geometry. By contrast, the ice thinning between 1963 and 1987 amounted to about 15 m for all glaciers regardless of topographic location. This suggests that climatic forcings other than solar radiation have become more prominent.

Sensitivity analyses indicate that the energy supply of about 5 W m−2, required to produce the observed ice thinning through melting, can be accounted for by a combination of climatic forcings. The direct effect of changing atmospheric composition (“greenhouse effect”) on the net longwave radiation could have contributed less than 1 W m−2. A warming of 0.0 to 0.2°C would translate into an additional downward-directed sensible heat transfer of 0.0 to 1.4 W m−2. A 0.1 to 0.2 g kg−1 increase in specific humidity would, through savings in the latent heat transfer, contribute 2 to 4 W m−2.

Long-term station records show little warming trend for East Africa itself. However, mid-tropospheric specific humidity trends of about 0.6 g kg−1 over the past two decades in the equatorial belt have been reported in the literature, and considered to be consequences of “global warming” and the “greenhouse effect”.

Viewed in perspective, the ice wastage on Mount Kenya between 1963 and 1987 appears to have been driven primarily by three climatic forcings, conceivably all steered by the “greenhouse effect”: a direct forcing through the net longwave radiation; an indirect forcing through warming and therefore enhanced sensible heat transfer; and another indirect forcing through warming (not necessarily in the region itself), leading to increased (advected) atmospheric moisture, and hence to reduced latent heat transfer, this last line of control being the most important.

During winter 1999 three large avalanche events were triggered by explosives at SLF’s avalanche test site, Vallée de la Sionne, canton Valais, Switzerland. One important goal of these large-scale field experiments was to measure the release and deposition volumes of avalanches by photogrammetric methods. In this paper, the photogrammetric measurements of all three avalanches are summarized. For one avalanche event it was possible to realize the whole measuring procedure as planned, and to obtain volume measurements before and after the avalanche triggering In the other two avalanche events, the photographs before the triggering of the avalanche failed. Nevertheless the photographs taken after the avalanche provide valuable information on the fracture depth at the fracture line. The mean fracture depth of the largest avalanche was about 2.10 m, varying between 1 and 3.5 m over a width of > 1000 m. The total volume of the deposition of all three avalanche events was about 1300 000 m3. The deposits are distributed over a length of > 1000 m with depths up to 30 m. The difference between the released and deposited volumes proved that avalanches entrain a large amount of snow along the avalanche track. Furthermore, the snow distribution in the deposition zone provides important information about the behaviour of a dense flowing avalanche in the runout zone.

Measurements of basal water pressure from 15 boreholes located at both local (tens of meters) and regional (kilometers) length scales were used to elucidate the pressure/sliding relationship during an autumn rapid motion event on Bench Glacier, Alaska, USA. The 8 day event had two distinct phases, each with a ten-fold speed-up with respect to winter velocity. The water pressure in all 15 boreholes varied synchronously during the speed-up. The first phase of rapid sliding began after a peak in basal water pressure and continued while the pressure was elevated and stable, or decreasing. The second phase of rapid sliding occurred when the basal water pressure was low but increasing, and terminated before the pressure peaked. Pressure and velocity do not appear unrelated, but the pressure/sliding relationship was not consistently linked to increasing, decreasing or a critical water pressure. The pressure variations and sliding accelerations are a response to a warm rainstorm, although equally large input events occurred in weeks prior with no apparent response. Drainage system evolution therefore appears to play a key role in both the acceleration and the pressure/velocity relationship. Basal cavity dynamics are likely responsible for three episodes of reverse (up-valley) motion observed after enhanced sliding.

Distinguishing sea-ice-rafted debris (SIRD) from iceberg-rafted debris is crucial to an interpretation of ice-rafting history; however, there are few paleo-sea-ice proxies. This study characterizes quartz grain microfeatures of modern SIRD from the Arctic Ocean, and compares these results with microfeatures from representative glacial deposits to potentially differentiate SIRD from ice-rafted sediments which have been recently subjected to glacial processes. This allows us to evaluate the use of grain microfeatures as a paleo-sea-ice proxy. SIRD grains were largely subrounded, with medium relief, pervasive silica dissolution and a high abundance of breakage blocks and microlayering. The glacial grains were more angular, with lower relief and higher abundances of fractures and striations/gouges. Discriminate analysis shows a distinct difference between SIRD and glacial grains, with ˂7% of the SIRD grains containing typical glacial microtextures, suggesting this method is a useful means of inferring paleo-sea-ice presence in the marine record. We propose that differences in microfeatures of SIRD and glacial ice-rafted debris reflect differences in sediment transport and weathering histories. Sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering, whereas glaciers that calve icebergs would bypass the coastal marine environment, thus preserving their glacial signature.

Recent warming has occurred in near-surface firn in central Greenland, as shown by analysis of a 217 m temperature profile from the GISP2 site. However, this warming falls within the range of natural variability and provides no clear evidence of a greenhouse signal.

The amount of ice growth and ablation are key measures of the thermodynamic state of the ice cover. While ice extent and even ice thickness can be determined using remote-sensing techniques, this is not the case for the mass balance. Mass-balance measurements require an ability to attribute the change, establishing whether a change in the thickness of the ice cover occurs at the top or bottom surface and whether it is a result of growth or ablation. We have developed and implemented a tool that can be used to measure thermodynamic changes in sea-ice mass balance at individual locations: the ice mass-balance buoy (IMB). The primary limitation of the IMB is that it provides a point measurement of the ice mass balance, defined by a particular combination of snow and ice conditions. Determining if, and how, such point measurements can be extrapolated is critical to understanding the large-scale mass balance of the sea-ice cover. We explore the potential for extrapolation using mass-balance observations from the Surface Heat Budget of the Arctic (SHEBA) field experiment. During SHEBA, mass-balance measurements were made at over 100 sites covering a 100 km2 area. Results indicate that individual point measurements can provide reasonable estimates for undeformed and unponded multi-year ice, which represented more than two-thirds of the ice cover at SHEBA and is the dominant ice type in the perennial pack. A key is carefully selecting a representative location for the instrument package. The contribution of these point measurements can be amplified by integrating them with other tools designed to measure ice thickness and assimilating these combined data into sea-ice models.

Meltwater retention by freezing is a highly climate-sensitive term in the mass budget since the cold content is directly controlled by winter climate, which is expected to change most in an anthropogenic-driven climate change. Meltwater released at the surface percolates into dry snow in a pattern with alternating horizontal and vertical water-flow directions, where the processes of pore refreezing (RF) (vertical flow) and superimposed ice (SI) formation (horizontal flow) occur. The flow cannot be forecasted and quantified when water first enters cold, dry snow. However, because the two processes are driven by different physical mechanisms, their potential magnitude can be estimated, which has been done in a transect at 66° N. Results show that SI declines from west to east and inversely correlates with accumulation. From the total retention capacity, theoretical lowest-runoff lines were determined at ∼1400ma.s.l. in the west and ∼1600ma.s.l. in the east. Since the SI potential is high in most places and the warming from SI formation predominately occurs near to the surface, it is argued that winter cooling effectively recharges the cold content of the snow/firn/ice pack, preventing the development of isothermal conditions and subsequent runoff. However, SI formation declines over time, so an extension of the melting season could result in deeper percolation beyond the SI layer.

In order to consider the effect of different ice conditions on the momentum exchange between atmosphere and ocean, a parameterization for variable drag coefficients is introduced. A square dependence on ice concentration is combined with a linear dependence on deformation energy to account for the influence of floe edges as well as for roughness elements in regions with a more compact ice cover. The approach is not regionally specified and is applied over the whole model region. Empirical parameters are optimized via comparison with observed buoy-drift data.

During the 1992–2002 Antarctic expeditions, in the framework of the International Trans-Antarctic Expedition (ITASE) project, about 600 sites were sampled (superficial snow, snow pits and firn cores) along traverses in the northern Victoria Land–Dome C–Wilkes Land region. The sites were characterized by different geographical (distance from the sea, altitude) and climatological (annual mean accumulation rate, temperature) conditions and were affected by air masses from different marine sectors (Ross Sea, Pacific Ocean). Mean anion and cation contents were calculated at each site, in order to evaluate the spatial distribution of chemical impurities in snow. Here we discuss the distribution of non-sea-salt sulphate (nssSO42–) and of methanesulphonic acid (MSA) mainly originating from atmospheric oxidation of biogenic dimethyl sulphide; these compounds play a key role in climate control processes by acting as cloud condensation nuclei. The spatial distribution of nssSO42– and MSA is discussed as a function of distance from the sea, altitude and accumulation rate. Depositional fluxes of nssSO42– and MSA decrease as a function of distance from the sea, with a higher gradient in the first 200km step. There is an analogous trend with the site altitude, and the first 1600m step is relevant in determining the nssSO42– and MSA content in snow. The nssSO42–/MSA ratio depends on the distance from the sea and the biogenic source strength. At coastal sites, where biogenic inputs are dominant, this ratio is ~2. As biogenic input decreases (low MSA content) inland, the ratio increases, indicating the presence of alternative sources of nssSO42– (crustal, volcanic background) or advection of low-latitude air masses. By plotting total flux as a function of accumulation rate, dry depositional contributions were evaluated for nssSO42– and MSA in the Ross Sea and Pacific Ocean sectors. Non-sea-salt sulphate wet deposition prevails at sites where the accumulation rate (expressed as water equivalent) is higher than 70 kgm–2 a–1 (Ross Sea sector) or 370 kgm–2 a–1 (Pacific Ocean sector). MSA threshold values in these sectors are respectively 90 and 220 kgm–2 a–1.

The snowmelt-onset date represents an important transitional point in the Arctic surface energy balance, when albedo decreases and energy absorption increases rapidly in response to the appearance of liquid water. Interannual variations in snowmelt onset are likely related to large-scale variations in atmospheric circulation, such as described by the Arctic Oscillation (AO). This research therefore examines the relationship between monthly-averaged AO values and mean annual snowmelt-onset dates over Arctic sea ice in 13 regions, from 1979 to 1998. The objective is to statistically relate variations in mean annual regional snowmelt-onset dates to variations in the AO. Additionally, monthly-averaged 500 hPa heights and 2 m air temperatures are used to illustrate a physical link between snow-melt onset and a positive AO phase. Regression analyses demonstrate that variations in the AO explain a significant portion of the variations in snowmelt onset in the West Central Arctic, Laptev Sea, East Siberian Sea, Hudson Bay and Baffin Bay. Synoptic analyses suggest earlier (later) than average snowmelt onset occurs where warm (cold) air advection and increased (decreased) cyclonic activity are present.

A glacier-wide ice-thickness distribution and bedrock topography is presented for Starbuck Glacier, Antarctic Peninsula. The results are based on 90 km of ground-based radio-echo sounding lines collected during the 2012/13 field season. Cross-validation with ice-thickness measurements provided by NASA's IceBridge project reveals excellent agreement. Glacier-wide estimates are derived using a model that calculates distributed ice thickness, calibrated with the radio-echo soundings. Additional constraints are obtained from in situ ice flow-speed measurements and the surface topography. The results indicate a reverse-sloped bed extending from a riegel occurring ~ 5 km upstream of the current grounding line. The deepest parts of the glacier are as much as 500 m below sea level. The calculated total volume of 80.7 ± 7.2 km3 corresponds to an average ice thickness of 312 ± 30 m.

The kinematic boundary condition at the glacier surface can be used to provide glacier mass balance at individual points if changes in surface elevation, horizontal and vertical surface velocities and surface slope are known. Vertical ice velocity can in turn be estimated from basal slope, basal ice velocity and surface strain. This relation is applied to reconstruct a 20 year mass-balance curve of Grubengletscher, Swiss Alps, largely using repeated aerial photogrammetry, with only a minimum of fieldwork For individual years the mass-balance distribution on the glacier tongue was modelled with an accuracy of about ±0.9 m a"1. Ice-mechanical assumptions and errors in glacier bed geometry markedly affect discrete mass-balance patterns but are largely eliminated in the calculation of year-to-year mass-balance changes The resulting 1973–92 curve for the Grubengletscher tongue shows reasonable consistency with meteorological data and other glaciologically derived mass-balance series. Large changes in measured ice speed on the glacier tongue (±50%) significantly governed the long-term variability of ice thickness over the observational period.

A long history of research documents that McCall Glacier, Arctic Alaska, USA, continues to lose mass at a rate that is likely increasing with time. We present a photo comparison (1958-2003) that visually documents these volume changes, along with survey measurements that quantify these losses. Measurements of longitudinal profiles initially acquired from airborne laser altimetry, and repeated by ground-based surveys, indicate that the areally averaged rate of thinning increased between 1956-93 and 1993-2002, from 0.35 ± 0.07 m a-1 to 0.47 ± 0.03 m a-1, respectively; total volume loss was (8.3 × 107) ± (1.7 × 107) m3 and (2.7 × 107) ± (0.2 × 107) m3 (all in water equivalent) for these two time periods. These profiles also indicate that a 1 km stretch of the mid-ablation area is behaving differently from this trend, with a rate of thinning that is not changing with time. Lastly we present a comparison of several methods for calculating volume change and assess their relative errors.

Electrical conductivity of melt waters draining from the portal of Gornergletscher, Switzerland, was recorded continuously for extended periods during the 1978‐79 hydrological year. Conductivity was used as a surrogate measure of the total dissolved solids concentration in melt water to describe the seasonal variation of solute, and its relation to discharge, in an attempt to use melt-water hydrochemistry as an indicator of the nature of subglacial processes within an alpine glacier. In winter, conductivity was 2 to 10 times higher than during the summer ablation season. and also showed considerable diurnal and annual variations independent of discharge. The transition from winter to summer discharge regime was preceded by falling solute concentration. A distribution shaped as a “triangle-with-spike” describes the complex relationship between discharge and electrical conductivity for the annual cycle of run-off. Almost all the solute load from beneath Gornergletscher is evacuated during summer. Melt-water hydrochemistry provides some insight into the nature of sub-glacial chemical processes, but, since melt waters do not appear to have access to all areas of the glacier bed, it probably under-estimates total chemical activity.

Chemistry data from 16, 50–115m deep, sub-annually dated ice cores are used to investigate spatial and temporal concentration variability of sea-salt (ss) SO42– and excess (xs) SO42– over West Antarctica and the South Pole for the last 200 years. Low-elevation ice-core sites in western West Antarctica contain higher concentrations of SO42– as a result of cyclogenesis over the Ross Ice Shelf and proximity to the Ross Sea Polynya. Linear correlation analysis of 15 West Antarctic ice-core SO42– time series demonstrates that at several sites concentrations of ssSO42– are higher when sea-ice extent (SIE) is greater, and the inverse for xsSO42–. Concentrations of xsSO42– from the South Pole site (East Antarctica) are associated with SIE from the Weddell region, and West Antarctic xsSO42– concentrations are associated with SIE from the Bellingshausen–Amundsen–Ross region. The only notable rise of the last 200 years in xsSO42–, around 1940, is not related to SIE fluctuations and is most likely a result of increased xsSO42– production in the mid–low latitudes and/or an increase in transport efficiency from the mid–low latitudes to central West Antarctica. These high-resolution records show that the source types and source areas of ssSO42– and xsSO42– delivered to eastern and western West Antarctica and the South Pole differ from site to site but can best be resolved using records from spatial ice-core arrays such as the International Trans-Antarctic Scientific Expedition (ITASE).

With the conclusion of the science phase of the Ice, Cloud and land Elevation Satellite (ICESat) mission in late 2009, and the planned launch of ICESat-2 in late 2015, NASA has recently established the IceBridge program to provide continuity between missions. A major goal of IceBridge is to obtain a sea-ice thickness time series via airborne surveys over the Arctic and Southern Oceans. Typically two laser altimeters, the Airborne Topographic Mapper (ATM) and the Land, Vegetation and Ice Sensor (LVIS), are utilized during IceBridge flights. Using laser altimetry simulations of conventional analogue systems such as ICESat, LVIS and ATM, with the multi-beam system proposed for ICESat-2, we investigate differences in measurements gathered at varying spatial resolutions and the impact on sea-ice freeboard. We assess the ability of each system to reproduce the elevation distributions of two sea-ice models and discuss potential biases in lead detection and sea-surface elevation, arising from variable footprint size and spacing. The conventional systems accurately reproduce mean freeboard over 25 km length scales, while ICESat-2 offers considerable improvements over its predecessor ICESat. In particular, its dense along-track sampling of the surface will allow flexibility in the algorithmic approaches taken to optimize the signal-to-noise ratio for accurate and precise freeboard retrieval.

Crevasse patterns revealing mostly brittle deformation on glacier surfaces are analyzed based on video images collected during systematic overflights of Jakobshavn Isbræ, West Greenland, the Earths continuously fastest moving ice stream, in 1996 and 1997. Crevasse patterns on the surface of the central ice stream are distinct. All crevasses are closed, the surface appears rather smooth. Towards the margins, typical shear patterns with conjugate shears and still-closed crevasses prevail, curved patterns indicate the bending of crevasse lines into the flow direction. Outward from this zone different patterns of open crevasses occur. This suite of patterns is compared to similar data collected over Bering Glacier, Alaska, U.S.A., during its recent surge from 1993–95. There a number of patterns of mostly open crevasses is characteristic: parallel crevasses, two-directional orthogonal open crevasses, arrays of wavy crevasses, en-echelon crevasses. These patterns of the surging glacier are completely different from those of the fast-moving ice stream indicating different underlying kinematics and dynamics.

The disruption of internal layering visible in radio-echo sounding (RES) data from East Antarctica has, to date, been attributed to ice flow around bedrock topography. However, observations of internal layer disruption in the Siple Coast ice streams of West Antarctica have led to the suggestion that increased strain at the margins of ice streams may also be responsible for the disruption of internal layers. Here we present a re-analysis of the extensive RES dataset collected between 1967 and 1979 over a large part of Wilkes Land, East Antarctica, and relate the location of continuous and disrupted internal layers to modelled balance velocities. We show that the mean balance velocity associated with all areas of disrupted layers is 2.5 times higher than that associated with areas of continuous layers. We also demonstrate that disrupted layers are associated not only with ice streams, but also with areas of enhanced ice flow, which penetrate inland from the grounding line up to several hundred kilometres into the interior of East Antarctica. Continuous layers always overlie disrupted layers, suggesting either a depth dependency in the process responsible for layer disruption, or subsequent deposition of continuous layers. In some cases, disrupted layers occur outside fast-flow features, and continuous layers occur within fast-flow features. Such regions are explained by short-term flow patterns, but might also be attributed to inaccuracies in the balance-velocity calculations.

Successful core-drilling to bedrock of both the Greenland and Antarctic ice sheets offers unique opportunities for examining processes acting at the bed. At Byrd Station, Antarctica, penetration of the bed was accompanied by upwelling of glacial meltwater into the drillhole. The nature and disposition of sediment in the 4.83 m thick debris-rich basal ice, together with stable-isotope and gas analyses of the enclosing ice, confirm that incorporation of the debris occurred simultaneously with periodic “freeze-on” of basal meltwater. Currently, the presence of substantial meltwater at the ice/rock interface likely precludes any erosive activity at the bed. At GISP2, Greenland, basal silly ice, 13.1 m thick, is currently frozen to the bed at −9° C. Limited studies of the silty ice at GISP 2, together with results of more comprehensive investigations obtained by GRIP researchers on basal ice at a companion site at Summit indicate that the sediment-bearing basal ice likely formed in the absence of an ice sheet and was therefore unrelated to direct interaction of the present ice sheet with its bed. The fact that the basal ice at Summit is frozen to the bottom also precludes any likelihood of erosive activity at the bed.