Mertz Glacier, East Antarctica, is characterized by a 140 km long, 25 km wide floating ice tongue. In this paper, we combine a large number of remotely sensed datasets, including in situ global positioning system measurements, satellite radar altimetry, airborne radio-echo sounding and satellite synthetic aperture radar imagery and interferometry. These various datasets allow us to study the interaction of the ice tongue with the tides and currents. However, the inverse barometer effect needs to be applied to sea-level variations affecting the tongue. We find that the tide-induced currents exert a small lateral pressure on the tongue which, when integrated over the large surface of the tongue, induce a flexure of up to 2 m amplitude per day. Simple elastic modelling of the flexure confirms the observations and helps validate the boundary conditions necessary to explain different eastward and westward tongue deflections. In addition, the along-flow velocity of the tongue does vary daily from 1.9 to 6.8 m d À1 depending on the tidal current.When the current pushes the tongue toward the eastern boundary of the fjord, the tongue is retarded by the drag and the velocity decreases. The accumulated stress is released, allowing the tongue to flow very rapidly when the current pushes the tongue westward. These forcing and boundary conditions on the floating ice flow are important and must be taken into account when studying glacier discharge and calving.

ABSTRACT. Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM

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Abstract. The Antarctic Peninsula is one of the world's regions most affected by climate change. Several ice shelves have retreated, thinned or completely disintegrated during recent decades, leading to acceleration and increased

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Surge-type glaciers are characterised by relatively short phases of enhanced ice transport and mass redistribution after a comparatively long quiescent phase when the glacier is virtually inactive. This unstable behaviour makes it difficult to assess the influence of climate change on those glaciers. We describe the evolution of the most recent surge of Bivachny Glacier in the Pamir Mountains, Tajikistan between 2011 and 2015 with respect to changes in its topography and dynamics. For the relevant time span, nine digital elevation models were derived from TanDEM-X data; optical satellite data (Landsat 5, 7 and 8, EO-1) as well as synthetic aperture radar data (TerraSAR-X and TanDEM-X) were used to analyse ice flow velocities. The comparison of the topography at the beginning of the surge with the one observed by the Shuttle Radar Topography Mission in 2000 revealed a thickening in the upper part of the ablation area of the glacier and a thinning further down the glacier as is typically observed during the quiescent phase. During the active phase, a surge bulge measuring up to around 80 m developed and travelled downstream for a distance of 13 km with a mean velocity of 4400 m year −1 . Ice flow velocities increased from below 90 m year −1 duringthe quiescent phase in 2000 to up to 3400 m year −1 in spring 2014. After reaching the confluence with Fedchenko Glacier, the surge slowed down until it completely terminated in 2015. The observed seasonality of the glacier velocities with a regular speed-up during the onset of the melt period suggests a hydrological control of the surge related to the effectiveness of the subglacial drainage system.

S U M M A R YIn the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.The derived ice flow velocity for Vostok Station is 2.00 m a −1 ± 0.01 m a −1 . Along the flowline of Vostok Station an extension rate of about 10 −5 a −1 (equivalent to 1 cm km −1 a −1 ) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a −1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.

S U M M A R YLake Vostok is the largest subglacial lake in Antarctica. We show that as a result of its size tidal and atmospheric pressure forcings are large enough to induce vertical displacements of the ice surface above the lake. These effects have been modelled assuming equilibrium tides and an inverse barometer response based on mass conservation. Differences in the tidal potential on the area of the lake result in height changes with amplitudes of a few millimetres for the largest diurnal and semidiurnal tides with maximum values at the southern end of the lake. Air pressure differences above the lake cause a differential inverse barometer effect (IBE) with resulting height changes of up to 40 mm on timescales from days to weeks. Both effects could be verified by differential Global Positioning System (GPS) observations in the southern part of the lake during the 2001/2002 and 2002/2003 summer seasons. The measured amplitudes and phases of the main constituents correspond to the respective values of the differential equilibrium tides. ERS-1& 2 tandem interferograms of 1996 were used to analyse the spatial pattern of the surface displacement. For the southern part of the lake, these measurements reveal a bulge with a wide flexure zone of varying amplitude but a similar geometry. A quasi-simultaneous pair of interferograms from the northern and the southern part of the lake respectively, demonstrates surface height changes of opposite sign in both areas. Therefore, it can be concluded that the associated water redistribution as a result of tides and changing atmospheric pressure forms an additional component of the overall water circulation in the lake.