Suzanne Bevan

Over the last decades, improvements in remote sensing methods, especially new satellite systems, have revealed accelerating mass loss, increased melt rates, thinning of the ice sheet margins, and increased discharge from many outlet glaciers due to rapid changes in ice dynamics. However, the lack of an historical context for these recent changes makes it difficult to determine whether they are a response to a warming trend or simply a reflection of the ice sheet's natural variability. We use historical stereo photography and modern lidar surveys to create a time series of digital elevation models (DEMs) and ice margin positions for glaciers in GRACE anomaly regions in both the north and south-east of Greenland. The earliest stereo photographs date from the 1940s making these timeseries up to 70 years long. All of this work has been carried out with the support of NASA's Airborne Thematic Mapper (ATM) missions to collect data to control the historical photography from which high resolution DEMs are generated.

ABSTRACT Remote sensing data show that over the last decade the greatest mass loss from the Greenland Ice Sheet (GrIS) has been from the south-east (SE) region, primarily due to synchronous acceleration, thinning and retreat of marine-terminating outlet glaciers. These large dynamic changes have raised concerns about the future stability of the GrIS. We present an 80-year time-series of glacier margin positions for SE Greenland from the 1930s to 2010, together with snapshots of glacial thicknesses from trimlines and DEMs. Calving fronts were digitised from satellite imagery (Landsat, DISP, SAR), aerial photographs, as well as maps and oblique photographs from various expeditions. To extend the time-series beyond the observational record we additionally infer maximum Little Ice Age (LIA; 1150-1850) dimensions from vegetational trimlines. The two largest glaciers in the SE, Helheim and Kangerdlugssuaq, behave very differently over this timescale: Kangerdlugssuaq Glacier has gradually retreated ~20 km, whereas Helheim Glacier's August 2010 margin is within 2 km of the August 1933 position. Over the 80-year period Helheim was most retreated in 2005 and most advanced in 1985. From trimline evidence, the 1980s extent is comparable with the Little Ice Age maximum. Based on these data it is unlikely that Helheim Glacier has contributed to overall mass loss from the ice sheet since the LIA, whereas Kangerdlugssuaq has exhibited significant steady retreat. We compare the frontal positions of other glaciers in the SE including Gyldenlove, Bernstorff and Ikertivaq to determine whether the regionally widespread 2000s mass loss in SE Greenland is indicative of a longer-term contribution to sea-level rise from the region, or simply a rapid but short-lived fluctuation.

ABSTRACT We use sequences of TanDEM-X acquisitions over 'supersites' Helheim and Kangerdlugssuaq glaciers in south-east Greenland to generate interferometric digital elevation models (DEMs) and to feature-track surface displacement between image acquisitions. The high spatial resolution, day/night, and cloud-penetrating capabilities of the X-band SAR system enabled the production of more than 20 DEMs for each glacier with a spatial resolution of 8 m or better. The DEMs span the period June 2011 to March 2012, at 11-day intervals, with a few breaks. Time-lapse animations of Helheim DEMs reveal the development of troughs in surface elevation close to the front. The troughs propagate down flow and develop into the rifts from which calving takes place. On both glaciers, regions of high variance in elevation can be identified caused by the transit of crevasses. In addition, on Helheim, a 1 km wide band of high variance adjacent to the calving front may be interpreted as the response to tidal forcing of a partially floating tongue. In addition to the DEMs we will also present featured tracked high-quality surface velocity fields at a spatial resolution of 2 m coincident with the DEMs. On Helheim these velocity fields indicate a winter deceleration of less than 10% at a point 4 km behind the calving front.

Determining whether increasing temperature or precipitation will dominate the cryospheric response to climate change is key to forecasting future sea-level rise. The volume of ice contained in the ice caps and glaciers of the Arctic archipelago of Svalbard is small compared with that of the Greenland or Antarctic ice sheets, but is likely to be affected much more rapidly in

... 2-3, 30 November 2007, Pages 172-181 Remote Sensing of the Cryosphere Special Issue. ... The interferogram reflects changes across the scene in the distance between the radar and the ... In the Himalaya, where surface velocities are only a fraction of those found in Greenland ...

Determining whether increasing temperature or precipitation will dominate the cryospheric response to climate change is key to forecasting future sea-level rise. The volume of ice contained in the ice caps and glaciers of the Arctic archipelago of Svalbard is small compared with that of the Greenland or Antarctic ice sheets, but is likely to be affected much more rapidly in

We present results of global aerosol retrieval from the ESA ATSR instrument series on ERS-2 and ENVISAT (1995-2010), and initial testing of a new algorithm developed for Sentinel-3, with planned operation 2014-2030. The ATSR instruments on ERS-2 and ENVISAT together ...

ABSTRACT The region of greatest mass loss from the Greenland Ice Sheet is the south-east, where iceberg calving from marine-terminating outlet glaciers dominates mass loss. Helheim Glacier is the third largest catchment of the Greenland Ice Sheet and discharges into Sermilik Fjord on the SE coast, a 90 km long fjord up to 900 m deep. During July 2009 and 2010, we repeated a 60 km profile along Sermilik Fjord measuring water temperature and salinity. The results show warming of up to 4°C of the fjord waters. We report on this interannual variability of fjord waters, adding results from the same profile to be collected in September 2010, and investigate the origin of these warmer waters and their impact on the calving rate and flow dynamics of Helheim Glacier. In July 2009, the fjord waters were strongly stratified, with an upper cold and relatively fresh layer of 150-180 m of water colder than 0°C, below which was warmer (up to 4°C), more saline Subtropical Water (STW) (>34 p.s.u.) originating from the Irminger Current. In July 2010, the upper layer was significantly warmer and saltier, with maximum differences of ~3.2-4°C concentrated at depths between 85-125 m, probably reflecting the influx of new STW. Waters deeper than ~460 m were also warmer by ~1°C. There was some cooling of waters at depths between 180-460 m between the two profiles, but the maximum cooling is 0.3°C, and typically the cooling at this depth is 0-0.2°C. Overall the results suggest a significant increase in the heat available for melting at the glacier front margin. We would therefore expect increased underwater melting, and hence enhanced calving and ice flow rates. During 2009, Helheim Glacier retreated and advanced repeatedly ~1.2 km, ending the year some 0.75 km retreated overall. In 2010, the glacier has retreated 1.3 km to 20 August: in the same period in 2009 it had retreated 0.8-1.0 km. Ice flow rates close to the margin from tracking optical and SAR imagery varied from 18-24 m/d in 2009, and to 26 July 2010 from 18-23 m/d. Despite significant warming of the fjord waters these results do not yet show the glacier's calving front behaving significantly differently between the two years. At the conference we will update these time-series: 2009-2010 seems to be a strong test of the hypothesis that the glacier's calving front dynamics are controlled by the temperature of the fjord waters.

ABSTRACT It has been widely reported that the Greenland Ice Sheet (GrIS) is losing mass to the oceans at an accelerating rate due to increased ice sheet runoff and changes in ice dynamics. This will have important implications on global sea level, ocean circulation and regional climate. Evidence from GRACE and satellite and airborne altimetry shows that change in the island's southeast sector, especially where losses are dynamically driven, is the principal component of overall GrIS mass loss. Central to dynamic mass loss are calving processes, which although responsible for about 50% of the annual mass discharge from the GrIS, remain largely unquantified and poorly understood. This is due in large part to the complex nature of calving mechanisms and their occurrence in highly dynamic environments that are remote, large in scale and difficult to access and observe. However, understanding these processes are critical for tying down estimates of future sea level contributions from the GrIS. Here we present a time-series of hourly stereo terrestrial photographs of the near-terminus surface, calving front and proglacial ice mélange of Helheim Glacier in southeast Greenland collected during July 2010. From these data we have generated daily high resolution digital elevation models (DEMs) over a 21 day period from which measurements of calving volume loss, glacier velocity and ice mélange displacement can be made. From these images we have thus far measured volume loss from a number of major calving events such as the July 12th event that measured 1.30 ± 0.01 km^3 in total volume including a 0.250 ± 0.001 km^3 contribution to sea level. Our methodology provides a low-cost and low-tech approach to monitoring and quantifying calving processes that will contribute to improving predictions of future sea level contributions from the GrIS.