Y. Y. Macheret

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.

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.

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...

Geophysical Survey of Johnsons Glacier (Antarctica): comparing seismic and RES data

Seismic and radio-echo sounding data have been acquired along coincident profiles at the temperate Johnsons Glacier (Livingston Island, South Shetland Islands, Antarctica). Seismic data have been processed and the results provide information about ice-thickness and bedrock topography. Preliminary results of the radio-echo sounding survey also show clear bedrock reflections, except in some highlycrevassed areas. Diffraction from englacial bodies and bottom irregularities are observed in many places. Further processing of seismic and radar data sets will allow us to compare the ice-thickness determined from both methods and to extract additional information about the internal structure and physical parameters of temperate ice.