A. F. Glazovsky

Glaciers dominate eustatic sea-level rise in the 21st century

Ice loss to the sea currently accounts for virtually all of the sea-level rise that is not attributable to ocean warming, and about 60% of the ice loss is from glaciers and ice caps rather than from the two ice sheets. The contribution of these smaller glaciers has accelerated over the past decade, in part due to marked thinning and retreat of marine-terminating glaciers associated with a dynamic instability that is generally not considered in mass-balance and climate modeling. This acceleration of glacier melt may cause 0.1 to 0.25 meter of additional sea-level rise by 2100.

Estimation of absolute water content in Spitsbergen glaciers from radar sounding data

Field data available on radio-wave velocities and power reflection coefficients from the cold/temperate ice boundary have been used to estimate the absolute water content and its variations in the temperate ice of two-layered galciers on Spitsbergen. The data have been interpreted with certain assumptions concerning radio-wave propagation and reflection models. The study shows that in cold periods, the average total water content in the upper part of the temperate ice varies in different glaciers from 2.8 to 9.1%. Macro inclusions might contain the major part of the total water content volume. Within one glacier, the spatial variability of water content in the upper part of the temperate ice varies in different galciers from 2.8 to 9.1%. Macro inclusions might contain the major part of the total water volume. Within one glacier, the spatial variability of water content in the upper part of the temperature ice is 1.7 - 11.9%. Seasonal variation of the total water content in the temperate layer reaches 2.3% (from 0.1% in spring to 2.4% in summer). Water content distribution with depth can vary: either it has a maximum up to 5.0% (even in spring) in the upper 30–60 m of the temperate ic, then decreases downward: or it is more uniform. Water content in the upper part of temperate ice and bedrock reflection coefficients reveal a rather close relation with surficial melting rate at the ELA and with ice facies zones. Water storage in the temperate layer is enough to feed englacial run-off during the whole cold period.

Evidence for Floating Ice Shelves in Franz Josef Land, Russian High Arctic

Examination of digital Landsat TM and MSS imagery of Franz Josef Land, Russian High Arctic, reveals a number of ice caps with apparently very low surface gradients at their seaward margins. The largest of these low gradient areas is 45 km2. The areas are dynamically a part of the parent ice mass, and have a marked break of slope at their inner margins. They generally occur in protected embayments and often have relatively deep water offshore. The presence of deep inter-island channels (up to 600 m) in the archipelago also suggests that deglaciation after the last glaciation may have proceeded rapidly due to enhanced iceberg calving. Tabular icebergs (maximum observed length 2.3 km) are produced from several of the low gradient ice cap margins today. Ice surface profiles, derived from analysis of vertical aerial photographs, show slopes of 0.50 on these features, as compared with 3.5 to 50 on other ice caps. At least some are likely to be floating ice shelves. They have similar ice surface gradients to a known ice shelf on Severnaya Zemlya. There is no requirement for deep water to occur beneath these features, but simply that they become buoyant over a significant part of their base. Glacier thinning, due to reduced mass balance since the termination of the Little Ice Age, may have contributed to the presence of these features. An origin for some of these low gradient margins by deformation of an unlithified substrate cannot be ruled out. Field radio-echo experiments could be used to test the interpretation of these features as ice shelves.

Quantifying the Mass Balance of Ice Caps on Severnaya Zemlya, Russian High Arctic. I: Climate and Mass Balance of the Vavilov Ice Cap

Abstract Due to their remote location within the Russian High Arctic, little is known about the mass balance of ice caps on Severnaya Zemlya now and in the past. Such information is critical, however, to building a global picture of the cryospheric response to climate change. This paper provides a numerical analysis of the climate and mass balance of the Vavilov Ice Cap on October Revolution Island. Mass balance model results are compared with available glaciological and climatological data. A reference climate was constructed at the location of Vavilov Station, representing average conditions for the periods 1974–1981 and 1985–1988. The site of the station has a mean annual temperature of −16.5°C, and an annual precipitation of 423 mm water equivalent. The mass balance model was calibrated to the measured mass balance, and tested against the time-dependent evolution of the englacial temperatures (to a depth of 15 m). The mass balance model was then converted to a distributed model for the entire Vavilov Ice Cap. Model results predict the spatial distribution of mass balance components over the ice cap. Processes involving refreezing of water are found to be critical to the ice caps state of health. Superimposed ice makes up 40% of the total net accumulation, with the remaining 60% coming from firn that has been heavily densified by refreezing.

Ice-volume changes (1936–1990) and structure of Aldegondabreen, Spitsbergen

Abstract Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50–80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936–90 has been estimated: a glacier tongue retreat of 930 m, a decrease in area from 8.9 to 7.6 km2, in average ice thickness from 101 to 73 m and in ice volume from 0.950 to 0.558 km3, which are equivalent to an average annual balance of –0.7 mw.e. This is comparable with the only available data of net mass balance for Aldegondabreen (–1.1 and –1.35m w.e. for the balance years 1976/77 and 2002/03) and consistent with the 0.27˚C increase in mean summer air temperature in this zone during 1936–90, as well as the warming in Spitsbergen following the end of the Little Ice Age (LIA), and the general glacier recession trend observed in this region.

Temporal changes in the radiophysical properties of a polythermal glacier in Spitsbergen

Abstract In order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiophysical investigations were made at Hansbreen, a polythermal glacier in Spitsbergen, in July– August 2003 and April 2004. These investigations included repeated radar profiling (20 and 25 MHz) along a transverse profile, repeated common-midpoint measurements, continuous radar measurements during 8 days at a fixed site, meteorological observations, and continuous ice surface velocity monitoring by differential GPS. Seasonal and inter-seasonal RWV changes in the temperate ice layer are attributed, respectively, to rapid water redistribution within it during the summer, and to variations in water content from 2.1% in summer to 0.4% in spring. The reflection properties of the temperate ice layer correlate well with the air temperature, with a nearly semi-diurnal time lag. The temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon. Repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography. The spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems.

Geometric Changes in a Tidewater Glacier in Svalbard during its Surge Cycle

Abstract Fridtjovbreen, Svalbard, is a partially tidewater-terminating glacier that started a 7-year surge during the 1990s. Flow peaked during 1996 and no surge front was apparent. We use two pre-surge (1969 and 1990) and a post-surge (2005) digital elevation models (DEMs) together with a bed DEM to quantify volume changes and iceberg calving during the surge, calculate the changes in glacier hypsometry, and investigate the surge trigger. Between 1969 and 1990, the glacier lost 5% of its volume, retreated 530 m and thinned by up to 60 m in the lower elevations while thickening by up to 20 m in its higher elevations. During the surge, the reservoir zone thinned by up to 118 m and the receiving zone thickened by ∼140 m. Fridtjovbreens ice divide moved ∼500 m, incorporating extra ice into its catchment. Despite this volume gain, during 1990–2005 the glacier lost ∼ 10% of its volume through iceberg calving and 7% through surface melt. The surge occurred in a climate of decreasing overall ice volume, so we need to revise the notion that surging is triggered by a return to an original geometry, and we suggest Fridtjovbreens surge was triggered by increasing shear stresses primarily caused by increases in surface slope.

Ice thickness, internal structure and subglacial topography of Bowles Plateau ice cap and the main ice divides of Livingston Island, Antarctica, by ground-based radio-echo sounding

Abstract We present the results of low-frequency (20 MHz) radio-echo sounding (RES) carried out in December 2000 and December 2006 on the main ice divides of Livingston Island, South Shetland Islands (SSI), Antarctica, and Bowles Plateau, Antarctica, respectively, as well as high-frequency (200 MHz) RES on the latter, aimed at determining the ice thickness, internal structure and subglacial relief. Typical ice thickness along the main ice divides is ~150 m, reaching maxima of ~200 m. On Bowles Plateau the ice is much thicker, with an average of 265 m and maxima of ~500 m. The bed below the main ice divides is above sea level, while part of the outlet glaciers from Bowles Plateau lies significantly below sea level, down to –120 m. The strong scattering of the radio waves in the areas under study constitutes further evidence that the ice in the accumulation area of the ice masses of the SSI is temperate. Typical thickness of the firn layer in Bowles Plateau is 20–35 m, similar to that found in King George ice cap. A strong internal reflector within the firn layer, interpreted as a tephra layer from the 1970 eruption at Deception Island, has allowed a rough estimate of the specific mass balances for Bowles Plateau within 0.20–0.40ma–1w.e., as average values for the period 1970–2006.

High resolution imagery from the Russian KATE-200 satellite camera: morphology and dynamics of ice masses in the European high Arctic

Abstract Imagery from Russian Cosmos series near-polar orbiting satellites has recently become more widely available. We have obtained KATE-200 photographic imagery of ice caps in the European high Arctic archipelagos of Franz Josef Land and Svalbard, and from the Greenland Ice Sheet. This visible-band imagery is of high spatial resolution (nominal 15 m) and each image covers a large ground segment (approximately 59 000km2). KATE-200 products are first generation film positives, first generation film negatives, and prints. No calibration standards or grey scales are provided. A number of ice-surface topographic features can be extracted from these high resolution photographic products. Examples include flow directions in the Greenland Ice Sheet and drainage-basin ice divides on Svalbard ice caps. The large area covered by each KATE-200 image, almost twice that of a Landsat scene, and over 15 times that of SPOT, is an advantage when monitoring the occurrence of glacier surges. The 15 m resolution clearly d...

Speed of radio wave propagation in dry and wet snow

In recent years, ground-penetrating radars are widely used for measuring thickness and liquid water content in snow cover on land and glaciers. The measurement accuracy depends on radio wave velocity (RWV) adopted for calculations. The RWV depends mainly on density, water content and structure of the snow cover and ice layers in it. The density and wetness of snow, and its structure can be estimated from data on RWV, using the available experimental and theoretical relations. Satisfactory results can be obtained using the Looyenga’s (1965) equations to estimate the density and wetness of snow cover, and equations of van Beek’s (1967) showing the distinction between RWV speeds velocities in snow cover and ice layers with different prevailing orientation and sizes of air or water inclusions. RWV in dry snow with density 300 kg/m3 may vary by 32 m/μs, depending on whether the vertical or horizontal orientation of the air inclusions prevails therein. In ice with density 700 kg/m3 effect of air inclusions orientation on differences in RWV is reduced to 5 m/μs. If the inclusions are not filled with air but with water, the difference in RWV in snow is 21 m/μs, and in ice is 24 m/μs. The RWV is affected not only by orientation of the inclusions, but their elongation. Twofold elongation of ellipsoidal air and water inclusions increases the difference in RWV in snow (with a density 300 kg/m3) to 23 m/μs and 22 m/μs. These estimates show a noticeable influence of snow structure on RWV in snow cover. The reliability of the above RWV estimates depends significantly on a thermal state of the snow cover, and decreases during snowmelt and increases in the cold period. It strongly depends on accuracy of measurements of the RWV in snow cover and its separate layers. With sufficiently high accuracy of the measurements this makes possible to detect and identify loose layers of deep hoar and compact layers of infiltration and superimposed ice, which is important for studying the liquid water storage of snow cover and a glacier mass balance. Therefore, considerable attention should be given to accuracy of the RWV measurements in dry and wet snow cover and its individual layers. With sufficiently high accuracy of measurements of the RWV, this should allow revealing such layers and estimating their thickness and average density.