Dana Floricioiu

Mass changes of outlet glaciers along the Nordensjköld Coast, northern Antarctic Peninsula, based on TanDEM-X satellite measurements

We analyzed volume change and mass balance of outlet glaciers of the northern Antarctic Peninsula over the period 2011 to 2013, using topographic data of high vertical accuracy and great spatial detail, acquired by bistatic radar interferometry of the TanDEM-X/TerraSAR-X satellite formation. The study area includes glaciers draining into the Larsen-A, Larsen Inlet, and Prince-Gustav-Channel embayments. After collapse of buttressing ice shelves in 1995 the glaciers became tidewater calving glaciers and accelerated, resulting in increased ice export. Downwasting of most glaciers is going on, but at reduced rates compared to previous years in accordance with deceleration of ice flow. The rate of mass depletion is 4.2 ± 0.4 Gt a−1, with the largest contribution by Drygalski Glacier amounting to 2.2 ± 0.2 Gt a−1. On the technological side, the investigations demonstrate the capability of satellite-borne single-pass radar interferometry as a new tool for accurate and detailed monitoring of glacier volume change.

Mass, volume and velocity of the Antarctic Ice Sheet: present-day changes and error effects

This study examines present-day changes of the Antarctic ice sheet (AIS) by means of different data sets. We make use of monthly gravity field solutions acquired by the Gravity Recovery and Climate Experiment (GRACE) to study mass changes of the AIS for a 10-year period. In addition to ‘standard’ solutions of release 05, solutions based on radial base functions were used. Both solutions reveal an increased mass loss in recent years. For a 6-year period surface-height changes were inferred from laser altimetry data provided by the Ice, Cloud, and land Elevation Satellite (ICESat). The basin-scale volume trends were converted into mass changes and were compared with the GRACE estimates for the same period. Focussing on the Thwaites Glacier, Landsat optical imagery was utilised to determine ice-flow velocities for a period of more than two decades. This data set was extended by means of high-resolution synthetic aperture radar (SAR) data from the TerraSAR-X mission, revealing an accelerated ice flow of all parts of the glacier. ICESat data over the Thwaites Glacier were complemented by digital elevation models inferred from TanDEM-X data. This extended data set exhibits an increased surface lowering in recent times. Passive microwave remote sensing data prove the long-term stability of the accumulation rates in a low accumulation zone in East Antarctica over several decades. Finally, we discuss the main error sources of present-day mass-balance estimates: the glacial isostatic adjustment effect for GRACE as well as the biases between laser operational periods and the volume–mass conversion for ICESat.

Velocities of Major Outlet Glaciers of the Patagonia Icefield Observed by TerraSAR-X

The capabilities of TerraSAR-X data for feature tracking by amplitude correlation over glacier surfaces are investigated. Methodical aspects of the amplitude correlation approach are described. The TerraSAR-X based velocity fields are compared with former InSAR derived velocities and field measurements on three outlet glaciers on the South Patagonia ice field.

Surface elevation changes of glaciers derived from SRTM and TanDEM-X DEM differences

We compare ice elevation from TanDEM-X DEMs of 2011/2012 and SRTM DEM of 2000 over the Southern Patagonia Icefield (SPI) in order to quantify the volume loss of the icefield over the last decade. The map of elevation change rate is discussed. Detailed results are shown for two glaciers: Jorge Montt and Pio XI, exhibiting opposite trends in elevation and front position.

Surface velocity and variations of outlet glaciers of the Patagonia Icefields by means of TerraSAR-X

An incoherent amplitude correlation approach is used to derive ice motion fields of three major outlet glaciers of the Patagonia Icefields. High resolution repeat pass TerraSAR-X data of 2008 and 2009 were analyzed. The strong gradients in ice velocity of the terminus of San Rafael glacier, ranging from 2 to 16 m d-1, were captured well. Significant acceleration of the ice flow and losses in mass were observed for Upsala glacier.

Rift in Antarctic Glacier: A Unique Chance to Study Ice Shelf Retreat

It happened again, but this time it was caught in the act. During the last week of September 2011 a large transverse rift developed across the floating terminus of West Antarcticas Pine Island Glacier, less than 5 years after its last large calving event, in 2007 (Figure 1). Pine Island Glaciers retreat has accelerated substantially in the past 2 decades, and it is now losing 50 gigatons of ice per year, or roughly 25% of Antarcticas total annual contribution to sea level rise [Rignot et al., 2008]. The glaciers recent accelerated retreat is likely triggered by ocean warming and increased submarine melting. As such, it is of significant interest to glaciologists and of heightened societal relevance.

Dynamics of fast glaciers in the Patagonia Icefields derived from TerraSAR-X and TanDEM-X data

Observations of ice flow velocity with TerraSAR-X were carried out over main outlet glaciers of the Southern Patagonia Icefield (SPI) since 2008 by means of amplitude correlation technique. Velocity data are required to estimate the ice export due to calving. Furthermore we compare ice elevation from a TanDEM-X DEM of 2011 and from an SRTM DEM of 2000 in order to quantify the volume loss of these glaciers over the last decade. Results are shown for three glaciers of the central section of SPI, exhibiting distinct differences in the observed trends for surface topography and ice velocity.

TerraSAR-X observations of the recovery glacier system, Antarctica

We present a comparison of 1997 RADARSAT Antarctic Mapping Project (RAMP) SAR data with 2008–09 TerraSAR-X observations of a tributary glacier that is part of the Recovery Glacier drainage network in Coates Land Antarctica. The Recovery Glacier system is of scientific interest because of its role in discharging East Antarctic ice to the sea and because it has been subsequently learned that the flow of the glacier is likely controlled by the presence of subglacial lakes near the onset of faster glacier flow.

Retrieval of 3D-glacier movement by high resolution X-band SAR data

Observations of the 3D ice velocity field are important for studies of glacier hydraulics and for modeling the dynamic response of glaciers to changing boundary conditions. A method for 3D ice velocity retrieval from repeat pass SAR data of crossing orbits applying offset tracking in amplitude images is presented. In contrast to the conventional technique for ice motion mapping which assumes surface-parallel flow, this method delivers the true velocity vector. The procedure is validated using in-situ GPS data on an outlet glacier of the Vatnajökull ice cap in Iceland.

Seasonal and interannual variabilities in terminus position, glacier velocity, and surface elevation at Helheim and Kangerlussuaq Glaciers from 2008 to 2016

The dynamic response of Greenland tidewater glaciers to oceanic and atmospheric change has varied both spatially and temporally. While some of this variability is likely related to regional climate signals, glacier geometry also appears to be important. In this study, we investigated the environmental and geometric controls on the seasonal and interannual evolution of Helheim and Kangerlussuaq Glaciers, Southeast Greenland, from 2008 to 2016, by combining year-round, satellite measurements of terminus position, glacier velocity, and surface elevation. While Helheim remained relatively stable with a lightly grounded terminus over this time period, Kangerlussuaq continued to lose mass as its grounding line retreated into deeper water. By summer 2011, Kangerlussuaqs grounding line had retreated into shallower water, and the glacier had a ~5-km-long floating ice tongue. We also observed seasonal variations in surface velocity and elevation at both glaciers. At Helheim, seasonal speedups and dynamic thinning occurred in the late summer when the terminus was most retreated. At Kangerlussuaq, we observed summer speedups due to surface-melt-induced basal lubrication and winter speedups due to ice-shelf retreat. We suggest that Helheim and Kangerlussuaq behaved differently on a seasonal timescale due to differences in the spatial extent of floating ice near their termini, which affected iceberg-calving behavior. Given that seasonal speedups and dynamic thinning can alter this spatial extent, these variations may be important for understanding the long-term evolution of these and other Greenland tidewater glaciers.