Simultaneous disintegration of outlet glaciers in Porpoise Bay (Wilkes Land), East Antarctica, driven by sea ice break-up

The floating ice shelves and glacier tongues which fringe the Antarctic continent are important because they help buttress ice flow from the ice sheet interior. Dynamic feedbacks associated with glacier calving have the potential to reduce buttressing and subsequently increase ice flow into the ocean. However, there are few high temporal resolution studies on glacier calving, especially in East Antarctica. Here we use remote sensing to investigate monthly glacier terminus change across six marine-terminating outlet glaciers in Porpoise Bay (−76° S, 128° E), Wilkes Land (East Antarctica), between November 2002 and March 2012. This reveals a large simultaneous calving event in January 2007, resulting in a total of ~ 2900 km2 of ice being removed from glacier tongues. Our observations suggest that sea-ice must be removed from glacier termini for any form of calving to take place, and we link this major calving event to a rapid break-up of the multi-year sea-ice which usually occupies Porpoise Bay. Using sea-ice concentrations as a proxy for glacier calving, and by analysing available satellite imagery stretching back to 1963, we reconstruct the long-term calving activity of the largest glacier in Porpoise Bay: Holmes (West) Glacier. This reveals that its present-day velocity (~ 1450 m a−1) is approximately 50 % faster than between 1963 and 1973 (~ 900 m a−1). We also observed the start of a large calving event in Porpoise Bay in March 2016 that is consistent with our reconstructions of the periodicity of major calving events. These results highlight the importance of sea-ice in modulating outlet glacier calving and velocity in East Antarctica

Glacier facies of Vestfonna (Svalbard) based on SAR images and GPR measurements

The warming climate of the Arctic affects the mass budget of glaciers, and changes in the distribution of glacier facies are indicative of their response to climate change. The glacial mass budget over large land ice masses can be estimated by remote sensing techniques, but selecting an efficient remote sensing method for recognizing and mapping glacier facies in the Arctic remains a challenge. In this study, we compared several methods of distinguishing the facies of the Vestfonna ice cap, Svalbard, based upon Synthetic Aperture Radar (SAR) images and terrestrial high frequency Ground Penetrating Radar (GPR) measurements. Glacier zones as determined using the backscattering coefficient (sigma0) of SAR images were compared against GPR data, and an alternative application of Internal Reflection Energy (IRE) calculated from terrestrial GPR data was also used for differentiating the extent of glacier facies. The IRE coefficient was found to offer a suitable method for distinguishing glacier zones and for validating SAR analysis. Furthermore, results of analysis of fully polarimetric Phased Array type Lband Synthetic Aperture Radar (ALOS PALSAR) and European Remote Sensing Synthetic Aperture Radar (ERS-2 SAR) images were compared with the IRE coefficient classification. Especially promising method is H-α segmentation, where the glacier zone boundaries corresponded very well with both GPR visual interpretation and IRE classification results. The IRE coefficient's simplicity of calculation makes it a good alternative to the subjective GPR visual interpretation method, where results strongly depend on the operator's level of experience. We therefore recommend for GPR profiles to be used for additional validation of SAR image analysis in studies of glacier facies on the High Arctic ice masses

The drivers of inter-annual outlet glacier terminus change in Victoria Land, Oates Land and George V Land, East Antarctica (1972-2013)

Recent work has highlighted the potential sensitivity of marine-terminating outlet glaciers to decadal-scale changes in the ocean-climate system in some regions of East Antarctica. However, compared to Greenland and West Antarctica (including the Antarctic Peninsula), very little is known about the drivers of shorter-term inter-annual variation of outlet glaciers in East Antarctica. In this thesis, the terminus positions of 135 glaciers along the coastline of Victoria Land, Oates Land and George V Land were mapped from 1972 to 2013. These three regions span a range of climatic and oceanic conditions and contain a variety of different glacier types, including both land- and marine-terminating glaciers. Over the longest time step (1972-2013), 36% of glacier termini in the study area advanced, 25% of glacier termini retreated, with the remainder showing no discernible change. However, glacier terminus positions fluctuated at inter-annual time-scales, and the magnitude of these changes varied between regions. George V Land exhibited the most extreme fluctuations in terminus positions and Victoria Land exhibited the least. While potential links were found between sea-ice concentrations and glacier change on inter-annual time-scales, there was little correlation between air temperatures and short-term glacier behaviour. Marine-terminating glaciers experienced larger changes in terminus position compared with terrestrial glaciers, and within marine-terminating glaciers, glaciers with a floating unconstrained tongue exhibited the largest variations in terminus position. It is concluded that unlike in Greenland, West Antarctica, the Antarctic Peninsula and localised regions of East Antarctica (e.g. Wilkes Land), there is no clear trend of glacier retreat in the study area and most of the variations are more closely linked to glacier size and terminus type

Remote Sensing of Snow Cover Using Spaceborne SAR: A Review

The importance of snow cover extent (SCE) has been proven to strongly link with various natural phenomenon and human activities; consequently, monitoring snow cover is one the most critical topics in studying and understanding the cryosphere. As snow cover can vary significantly within short time spans and often extends over vast areas, spaceborne remote sensing constitutes an efficient observation technique to track it continuously. However, as optical imagery is limited by cloud cover and polar darkness, synthetic aperture radar (SAR) attracted more attention for its ability to sense day-and-night under any cloud and weather condition. In addition to widely applied backscattering-based method, thanks to the advancements of spaceborne SAR sensors and image processing techniques, many new approaches based on interferometric SAR (InSAR) and polarimetric SAR (PolSAR) have been developed since the launch of ERS-1 in 1991 to monitor snow cover under both dry and wet snow conditions. Critical auxiliary data including DEM, land cover information, and local meteorological data have also been explored to aid the snow cover analysis. This review presents an overview of existing studies and discusses the advantages, constraints, and trajectories of the current developments

Spaceborne monitoring of Arctic lake ice in a changing climate

Lake ice phenology (timing of ice-on and ice-off) and thickness are changing in response to generally warmer climate conditions at high northern latitudes observed during recent decades. Monitoring changes in the lake ice cover provides valuable evidence in assessing climate variability in the Arctic. To enhance our understanding of the role of lake ice in the Arctic cryosphere and to evaluate the extent to which Arctic lakes have been impacted by the contemporary changing climate, development of a lake ice monitoring system at pan-Arctic scale is needed. While large lakes across the Arctic are currently being monitored through satellite observations, there are extremely sparse and mostly non-existent records tracking the changes in small high-latitude lakes. Employing a combination of spaceborne observations from synthetic aperture radar (SAR) and optical sensors, and simulations from the Canadian Lake Ice Model (CLIMo), this researched aimed to investigate changes in winter ice growth and ice phenology of lakes across the Arctic, focus being given to smaller lakes on the North Slope of Alaska (NSA) and lakes of various sizes in the Canadian Arctic Archipelago (CAA). To determine the changes in the fraction of lakes that freeze to bed (grounded ice) in late winter on the NSA from 1991 to 2011, a time series of ERS-1/2 was analysed. Results show a trend toward increasing floating ice fractions from 1991 to 2011, with the greatest change occurring in April, when the grounded ice fraction declined by 22% (α = 0.01). This finding is in good agreement with the decrease in ice thickness simulated with CLIMo, a lower fraction of lakes frozen to the bed corresponding to a thinner ice cover. Model simulations over the same period as SAR acquisitions (1991-2011) indicate a trend toward thinner ice covers by 18-22 cm (no-snow and 53% snow depth scenarios, α = 0.01). The results emphasize the regime shifts that these lakes are currently undergoing, including shorter ice seasons. The longer-term trends (1950-2011) derived from model simulations show a decrease in the ice cover duration by ~ 24 days consequent to later freeze-up dates by 5.9 days (α = 0.1) and earlier break-up dates by 17.7-18.6 days (α = 0.001). The temporal evolution of backscatter (σ0) from two C-band SAR sensors – Advanced Synthetic Aperture Radar (ASAR) Wide Swath and RADARSAT-2 ScanSAR Wide Swath – was then used to investigate the potential of high temporal-frequency SAR for determining lake ice phenological events (e.g. freeze onset, melt onset and water-clear-of-ice). Results show that combined SAR observations are generally suitable for detection of important lake ice events timing. However, the wide range of incidence angles and to a certain extent the orbit differences between the observations, the wind effect, particularly during fall freeze-up, the low differences in σ0 during transition from a grounded-ice cover to melt onset of ice in early spring, complicate the detection of lake ice phenological events. In order to order to document the response of ice cover of lakes in the Canadian High Arctic to climate conditions during recent years, a 15-year time series (1997-2011) of RADARSAT-1/2 ScanSAR Wide Swath, ASAR Wide Swath and Landsat acquisitions were analyzed. Results show that earlier melt onset occurred earlier for all 11 polar-desert and polar-oasis lakes that were investigated. With the exception of Lower Murray Lake, all lakes experienced earlier ice-minimum and water-clear-of-ice dates, with greater changes being observed for polar-oasis lakes (9-23.6 days earlier water-clear-of-ice for lakes located in polar oases and 1.6-20 days earlier water-clear-of-ice for polar-desert lakes). Additionally, results suggest that some lakes may be transitioning from a perennial to a seasonal ice regime, with only a few lakes maintaining a perennial ice cover on occasional years. Aside Lake Hazen and Murray Lakes that preserved their ice cover during the summer of 2009, no residual ice was observed on any of the other lakes from 2007 to 2011. This research provides the foundation of a lake-ice monitoring network that can be built on with the newly launched and future SAR and multispectral missions. Additionally, this study shows that in response to warmer climate conditions, Arctic lakes are experiencing regime shifts with overall shorter ice seasons, thinner ice covers, fewer lakes that freeze to the bottom and more lakes that lose the perennial ice cover and experience a seasonal ice regime

Detection of iceberg calving events in Prydz Bay, East Antarctica during 2013 – 2015 using LISS-IV/IRS-P6 satellite data

This study discusses the calving event took place in Prydz Bay of East Antarctica during the epoch of 2013–2015 using high resolution multispectral data from Indian Linear Imaging Self Scanning Sensor (LISS-IV) aboard IRS-P6 satellite. The present study has been conducted on Larsemann Hills, Prydz Bay, East Antarctica. The two LISS-IV images (5.8 m spatial resolution) acquired specifically 384 days apart (December 31, 2013 and January 19, 2015) were utilized to study the significant changes that have occurred in icebergs during this short epoch. A total of 369 common icebergs present in both images were identified for analysing the changes in their dimensions because of surface melting. All of these icebergs were found to have lost mass because of surface melting and ocean forced base melting; therefore, they have reduced in dimension depicted by 12.51% lapse in terms of surface area. In addition, the coastline was visually observed to have retracted, instigated by calving events from the polar ice sheet and generation of new icebergs in Prydz Bay. The average drift distance of these newly formed icebergs from the coastline was found to be 51.59 m. Our analysis estimates that the total number of icebergs decreased by 70, suggesting either the complete disintegration or significant drifting of these icebergs away from the coast during 2013–2015 period