Bakaninbreen, Svalbard, started surging in 1985 and developed a steep surge front where fast-moving ice impinged on stagnant non-surging ice. This front, which was 20- 25 m high in 1985, became a steep and heavily crevassed feature about 60 m high. The surge continued through 1986-95. Annual surge-front propagation rate was 1.0 1.8 km a−1during 1985-89; this rate dropped considerably during 1989 95 and the front became less steep. Front propagation occurred largely by longitudinal compression and vertical extension of the ice and the effects of over-riding appear minor. Ice velocities were slower than the average propagation rate of the front. The surge affected Bakaninbreen in four zones: (1)Upper regionwhere extensive flow, fast propagation rates and negative vertical strain occurred, resulting in widespread crevassing and stranded blocks tens of metres above the post-surge ice surface, (2)Mid-glacierregion where initial strong compression was associated with ice thickening which started before the arrivai of the surge front. Horizontal strain rates were very low but vertical strain rates were tip to 300 mmd−1. As (he front passed, the horizontal velocity increased and about 500 m behind it became extensive. Negative vertical strain and ice down-draw occurred as ice velocities dropped, (3)Surge frontwhere ice velocity was high but vertical strain remained positive associated with compression. (4)Lower regionbelow the iront where only compression occurred, resulting in the formation of a fore bulge, a thickening of the ice of up to 50 m above pre-surge levels. The fore bulge affected the whole 1.7 km below the, now halted, surge front. The glacier has not advanced, Bakaninbreen’s surge was characterized by a long active phase, approximately 10 years, low ice velocities and low basal shear stresses compared to glaciers in lower latitudes, and an indistinct surge termination.

No abstract

Airborne geophysical investigations of the previously little-studied Nordaustlandet ice caps (11 150 km 2 ) took place in 1983, using SPRI 60 MHz radio echo-sounding (RES) equipment of 160 dB system performance. RES and navigational data were recorded digitally . Navigation used a ranging system (accurate to ±30 m) from aircraft to ground-based transponders, located by satellite geoceivers, supplemented by the aircraft's navigational instruments and timed crossings of known features . Ice surface and bedrock elevations were measured, using aircraft pressure altitude, terrain clearance , and ice thickness data. The mean error of 251 crossing points on Austfonna was II m. The reduced geophysical data are stored on a direct-access computer 2 database . During 3400 km of flying, Austfonna (8105 km ) was covered by traverses a nominal 5 km apart, whereas a 15 km-spaced grid was flown over Vestfonna (2510 km 2 ). Maps of ice surface morphology and subglacial, bedrock topography were produced for Austfonna and Vestfonna, along with an ice thickness map of Austfonna. Austfonna reaches a maximum surface elevation of 791 m and ice thickness of 583 m. 28% of the bedrock area beneath Austfonna lies below sea level. RES yielded bedrock echoes for 91 % of track over Austfonna, but only 52% over Vestfonna. This was probably due to warmer conditions on Vestfonna, resulting in greater absorption and scattering of electro-magnetic energy.Ice surface elevations are a principal data source in the revision of official Norwegian maps of Nordaustlandet.

A vertically stable, step-like thermohaline structure is observed throughout a continuous, 400 m conductivity-temperature-depth (CTD) profile taken near the Erebus Glarer Tongue, McMurdo Sound, Antarctica. The pattern is best developed between the sea surface and 250 m depth, the interval corresponding to that of the irregular underwater profile of the Glacier Tongue. The steps average 17 m in thickness and typically display discontinuities of 0.1 øC in temperature, 0.04 %o in salinity and 3.5 x 10 -4 g cm -3 in density. The observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water. At this location, subsurface seawater is inferred to remain above the in situ freezing point year-round, and contains sufficient heat to account for much of the Glacier Tongue thinning by basal melting. An adequate volume of meltwater would result to produce the measured salinity steps. We discuss related observations and some implications of this process for ocean circulation and biological productivity in the Antarctic. identified on nearby station 218, but the relative importance of spatial versus temporal changes could not be determined, as these stations were taken on an opportunity basis. The CTD records are relatively noisy, possibly due to system response time and slow sensor descent rate. The differing descent and ascent profiles, and turbulence near the large local gradients also suggest actively evolving, not remnant features. OCEANOGRAPHIC OBSERVATIONSOn and near the Antarctic continental shelf we have frequently recorded thermohaline staircases of varying dimensions at intermediate depths. Some were of the variety generafly ascribed to double-diffusive processes, e.g., cold fresh over warm salty water beneath the Antarctic Surface Water temperature minimum, or warm salty over cold fresh water below the Circumpolar Deep Water that intrudes onto the continental shelf. At other times, steps were barely discernible, or not much greater than the resolution of the instrumentation then being used. Station 217 is unlike any of the above, but graphically displays a statically stable configuration of relatively warm fresh over cold salty water. This is analogous to the homogeneous summer surface layer that overlies the temperature minimum (steps also occur at that transition), but here the stairs are more uniform and descend to greater depths.The step structure observed here differs in an important respect from that reported, e.g., by Neal et al. [1969], under a drifting ice island in the Arctic. In that case the steps were formed by the one-dimensional process of cooling from Paper number 1C0546.

Results of airborne radio echo-sounding (RES) i n Antarctica are presented. F l i g h t tracks covering 50% of the Antarctic 1ce sheet on a 50 to 100 km square g r i d , flown using I n e r t i a ! navigation, have errors « 5 km. Ice thicknesses determined from 35, 60, and 300 MHz RES records are accurate to 10 m or 1.5% thickness (whichever i s g r e a t e r). A l t i m e t r y , determining surface and sub-surface elevations, a f t e r corrections have errors <<50 m. An up-to-date coast-l i n e compiled from s a t e l l i t e imagery and a l l recent sources has frequencies f o r various coastal types of: 1ce shelves (44%), ice streams/outlet glaciers (132), Ice walls (38%), and rocks (5%). A new map of the Ice sheet surface has been compiled from 101 000 RES data points, 5 000 Tropical Wind, Energy conversion and Reference Level Experiment (TWERLE) balloon altimetry points, geodetic s a t e l l i t e and selected traverse elevations. The volume of the Antarctic ice sheet Including 1ce shelves has been calculated p r i n c i p a l l y from RES data using various techniques as 30.11±2.5 x 10 6 km 3. Frequency d i s t r i b u t i o n s for subgladal bedrock elevations f o r East and West Antarctica are presented. They conform approximately to Gaussian (normal) functions.

Results of airborne radio echo-sounding (RES) i n Antarctica are presented. F l i g h t tracks covering 50% of the Antarctic 1ce sheet on a 50 to 100 km square g r i d , flown using I n e r t i a ! navigation, have errors « 5 km. Ice thicknesses determined from 35, 60, and 300 MHz RES records are accurate to 10 m or 1.5% thickness (whichever i s g r e a t e r ) . A l t i m e t r y , determining surface and sub-surface elevations, a f t e r corrections have errors <<50 m. An up-to-date coastl i n e compiled from s a t e l l i t e imagery and a l l recent sources has frequencies f o r various coastal types of: 1ce shelves (44%), ice streams/outlet glaciers (132), Ice walls (38%), and rocks (5%). A new map of the Ice sheet surface has been compiled from 101 000 RES data points, 5 000 Tropical Wind, Energy conversion and Reference Level Experiment (TWERLE) balloon altimetry points, geodetic s a t e l l i t e and selected traverse elevations.

Glaciomarine sediments (GMS) comprise detrital, biogenic, and authigenic materials of two principal facies: laminated deposits and massive aqueous till. The processes governing sedimentation of the ice-rafted debris (IRD) component of GMS are investigated in the marine zone around Antarctica.Four controlling factors are identified: nature and disposition of sediments at the grounding line, transition from grounded to floating ice (ice shelves, outlet glaciers, and ice cliffs), processes of under-side melting and freezing of these ice masses, and, finally, mechanisms of iceberg calving, fragmentation, and melt-release of debris in the open ocean. Modelling studies of Brunt and Ross ice shelves suggest two main conclusions.(1) Ice shelves are of major importance for sedimentation on the continental shelf. Bulk ·debris release occurs within the grounding-line zone which may frequently oscillate, producing pronounced diachronism. Bottom melting removes all debris prior to calving at the ice front so that ice shelves do not playa part in deposition in the open ocean.(2) Outlet glaciers, in contrast, have high sediment content, calve rapidly, and produce debris-rich icebergs which contribute the major portion of IRD in the ocean.

Airborne radio echo-sounding of Spitsbergen glaciers during 1980 used 60 MHz SPR1 Mk IV equipment. On several glaciers results showed unambiguous bottom returns at depths 2–3 times those reported in previous Soviet echo-sounding at 440 and 620 MHz. Comparison of 60 MHZ records and independent gravity-surveyed ice thickness for two glaciers agreed to within 10%, whereas Soviet ice thicknesses were only 30–60% of gravity depths. Soviet bed echoes often coincided closely with an internal reflecting horizon recorded by the SPRI Mk IV system, and it is shown that Soviet U.H.F. equipment failed to penetrate to the true glacier bed on a number of ice masses (e.g. Finsterwalderbreen, Kongsvegen, Negribreen). This was probably due to increased absorption and scattering at higher radio frequencies, related to the inhomogeneous nature of Spitsbergen glaciers, which are often at or near the pressure-melting point. Both 60 MHz and U.H.F. equipment seldom recorded bed echoes in ice-cap accumulation areas (e.g. Isachsenfonna), where firn soaking during summer and 10 m temperatures of zero degrees have been observed. An isolated internal reflecting horizon was recorded on many glaciers. It is unlikely to be a moraine layer, but may be related to ice with a water content of 1–2% observed at a similar depth (115 m) in a drill core from Fridtjovbreen.