Geodetic Mass Balance of Svalbard glaciers : 1936 - 2004

Glaciers and ice masses are very important components of the earth system both in terms of global water storage and as climate indicators. The amount of water tied up in glaciers and ice caps is equivalent to about 69 meters of sea-level (Church and others, 2001). Recent predictions from global climate models indicate the arctic will experience enhanced changes as compared to the lower latitudes linked to the rise of greenhouse gases in the next 100 years (ACIA report, 2005). Svalbard glaciers and ice masses may therefore experience a rapid response to a change in climate (Hagen and others, 2003a). It is thus beneficial to document both present and the long term past glacier fluctuations to increase the comprehension of climatic changes. Svalbard is a high arctic archipelago, located in a climatically sensitive area at the northern extremity of the warm North Atlantic ocean current. Approximately 36000 km2 is covered by glaciers consisting of ice caps, tidewater, outlet, and smaller cirque and piedmont glaciers (Hagen and others, 1993). In this study, a 54 year geodetic balance of Svalbard glaciers is derived by comparing the oldest topographic map series of Svalbard (1936/38) to modern digital elevation models (DEM) from 1990. The errors of the older maps are assessed where precision is limited, but accuracy is sufficient for glacier studies. Elevation changes are analyzed for 7 regions in Svalbard (~5000 km2), where significant thinning was found at glacier fronts, and elevation increases in the upper parts of the accumulation areas. All regions experience volume losses and negative geodetic balances, although regional variability exists relating to both climate and topography. Many surges are apparent within the elevation change maps. Estimated volume change for the regions is -1.59±0.07 km3a-1 (ice eq.) for a geodetic annual balance of -0.30 m a-1 (w. eq.), and the glaciated area has decreased by 16% in the 54 year time interval. For recent balance estimations, differential GPS (2004) and laser altimetry (1996 & 2002) measurements are compared to the 1990 DEM over four glaciers in northwest Svalbard, and along two 60 km profiles in southern Svalbard. For both regions, the rate of frontal thinning has increased dramatically. The annual geodetic balances have become twice as negative for two smaller glaciers, Midtre and Austre Lovenbreen, while becoming more than three times more negative on the larger Kongsvegen. In southern Svalbard, while the glacier fronts are thinning faster in these recent measurements, complex dynamic behavior is occurring at higher altitudes, which complicate the elevation change signal. A number of dynamical events occurred in Wedel Jarlsberg Land between 1990 and 1996. The glaciers of Svalbard are losing ice volume at a faster rate more recently which can be attributed to a changing climate. The large scale synoptic patterns in atmospheric and oceanic circulation, and possibly temporal changes associate with them, is leading to increased thinning at the glacier fronts and slight increases at higher altitudes. Climate change is not only affecting glacier surface change in the form of temperature, but also in the form of precipitation. These changes progress through the glacier creating complicated dynamic patterns. Nonetheless, the present glacial-climate signal is that of increased volume loss

Quantification and interpretation of glacier elevation changes

Glaciers, ice caps and ice sheets constitute a large reservoir in the global hydrological cycle and provide a coupling between climate and sea-level. Observations of glacial change is important for constraining their contribution to sea-level fluctuations and to better understand the interactions between glaciers and climate. This thesis focuses on glacier observations through measurements of elevation change. The research in this thesis is oriented towards the methodological detection of elevation changes using remote sensing techniques. The quality of glacier elevation change measurements is dependent on controlling the potential errors and biases within the data. Therefore, one aspect is focused on a universal co-registration method for elevation products and further identification and correction of biases that remain, specifically in satellite stereo products. For glaciological studies, elevation changes require conversion into volume and mass changes. This is sometimes complicated when the data available is not spatially continuous and/or temporally consistent. Therefore, another aspect of this thesis explores methods for estimating regional glacier volume change. Specifically, Svalbard glacial contribution to sea-level has been estimated using regionalization techniques from scattered elevation measurements over roughly two time epochs. We observed that Svalbard glaciers over the past few decades have had a negative mass balance, contributing approximately 0.026 mm per year to the oceans. During the past few years, the sea-level contribution from Svalbard glaciers decreased slightly to 0.013 mm per year. Interpretations of elevation changes are convoluted by their dependence on climatic and dynamic forces operating on glacier systems. The last aspect of this thesis experiments with surface mass balance modelling for quantifying the climatic component of an elevation change. Combining this with observed elevation changes using theory of mass continuity can yield estimates of the calving flux of icebergs into the ocean. We observed on one particular fast flowing glacier in Svalbard that the average calving flux in the 1966-1990 epoch increased in the 1990-2007 epoch

Sensitivity of glacier volume change estimation to DEM void interpolation

Glacier mass balance has been estimated on individual glacier and regional scales using repeat digital elevation models (DEMs). DEMs often have gaps in coverage (“voids”), the properties of which depend on the nature of the sensor used and the surface being measured. The way that these voids are accounted for has a direct impact on the estimate of geodetic glacier mass balance, though a systematic comparison of different proposed methods has been heretofore lacking. In this study, we determine the impact and sensitivity of void interpolation methods on estimates of volume change. Using two spatially complete, high-resolution DEMs over southeast Alaska, USA, we artificially generate voids in one of the DEMs using correlation values derived from photogrammetric processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes. We then compare 11 different void interpolation methods on a glacier-by-glacier and regional basis. We find that a few methods introduce biases of up to 20&thinsp;% in the regional results, while other methods give results very close (&lt;1&thinsp;% difference) to the true, non-voided volume change estimates. By comparing results from a few of the best-performing methods, an estimate of the uncertainty introduced by interpolating voids can be obtained. Finally, by increasing the number of voids, we show that with these best-performing methods, reliable estimates of glacier-wide volume change can be obtained, even with sparse DEM coverage.</p

MMASTER: improved ASTER DEMs for elevation change monitoring

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system on board the Terra (EOS AM-1) satellite has been a source of stereoscopic images covering the whole globe at 15-m resolution with consistent quality for over 16 years. The potential of these data in terms of geomorphological analysis and change detection in three dimensions is unrivaled and should be exploited more. Due to uncorrected errors in the image geometry due to sensor motion (“jitter”), however, the quality of the DEMs and orthoimages currently available is often insufficient for a number of applications, including surface change detection. We have therefore developed a series of algorithms packaged under the name MicMac ASTER (MMASTER). It is composed of a tool to compute Rational Polynomial Coefficient (RPC) models from the ASTER metadata, a method that improves the quality of the matching by identifying and correcting jitter-induced cross-track parallax errors and a correction for along-track jitter when computing differences between DEMs (either with another MMASTER DEM or with another data source). Our method outputs more precise DEMs with less unmatched areas and reduced overall noise compared to NASA’s standard AST14DMO product. The algorithms were implemented in the open source photogrammetric library and software suite MicMac. Here, we briefly examine the potential of MMASTER-produced DEMs to investigate a variety of geomorphological changes, including river erosion, seismic deformation, changes in biomass, volcanic deformation and glacier mass balance

From high friction zone to frontal collapse: dynamics of an ongoing tidewater glacier surge, Negribreen, Svalbard

Abstract Negribreen, a tidewater glacier located in central eastern Svalbard, began actively surging after it experienced an initial collapse in summer 2016. The surge resulted in horizontal surface velocities of more than 25 m d −1 , making it one of the fastest-flowing glaciers in the archipelago. The last surge of Negribreen likely occurred in the 1930s, but due to a long quiescent phase, investigations of this glacier have been limited. As Negribreen is part of the Negribreen Glacier System, one of the largest glacier systems in Svalbard, investigating its current surge event provides important information on surge behaviour among tidewater glaciers within the region. Here, we demonstrate the surge development and discuss triggering mechanisms using time series of digital elevation models (1969–2018), surface velocities (1995–2018), crevasse patterns and glacier extents from various data sources. We find that the active surge results from a four-stage process. Stage 1 (quiescent phase) involves a long-term, gradual geometry change due to high subglacial friction towards the terminus. These changes allow the onset of Stage 2, an accelerating frontal destabilization, which ultimately results in the collapse (Stage 3) and active surge (Stage 4)

Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments

Digital elevation model and orthophotographs of Greenland based on aerial photographs from 1978–1987

Digital Elevation Models (DEMs) play a prominent role in glaciological studies for the mass balance of glaciers and ice sheets. By providing a time snapshot of glacier geometry, DEMs are crucial for most glacier evolution modelling studies, but are also important for cryospheric modelling in general. We present a historical medium-resolution DEM and orthophotographs that consistently cover the entire surroundings and margins of the Greenland Ice Sheet 1978–1987. About 3,500 aerial photographs of Greenland are combined with field surveyed geodetic ground control to produce a 25 m gridded DEM and a 2 m black-and-white digital orthophotograph. Supporting data consist of a reliability mask and a photo footprint coverage with recording dates. Through one internal and two external validation tests, this DEM shows an accuracy better than 10 m horizontally and 6 m vertically while the precision is better than 4 m. This dataset proved successful for topographical mapping and geodetic mass balance. Other uses include control and calibration of remotely sensed data such as imagery or InSAR velocity maps

Accelerated global glacier mass loss in the early twenty-first century

Glaciers distinct from the Greenland and Antarctic ice sheets are shrinking rapidly, altering regional hydrology1, raising global sea level2 and elevating natural hazards3. Yet, owing to the scarcity of constrained mass loss observations, glacier evolution during the satellite era is known only partially, as a geographic and temporal patchwork4,5. Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. Using largely untapped satellite archives, we chart surface elevation changes at a high spatiotemporal resolution over all of Earth’s glaciers. We extensively validate our estimates against independent, high-precision measurements and present a globally complete and consistent estimate of glacier mass change. We show that during 2000–2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise6. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately7,8,9. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain10. We anticipate our highly resolved estimates to advance the understanding of drivers that govern the distribution of glacier change, and to extend our capabilities of predicting these changes at all scales. Predictions robustly benchmarked against observations are critically needed to design adaptive policies for the local- and regional-scale management of water resources and cryospheric risks, as well as for the global-scale mitigation of sea-level rise.ISSN:0028-0836ISSN:1476-468

Tidewater Glacier Surges Initiated at the Terminus

TerraSAR-X data were provided by DLR (project OCE1503), and funded by the Conoco Phillips-Lundin Northern Area Program through the CRIOS project (Calving Rates and Impact on Sea level). C.N. acknowledges funding from European Union/ERC (grant 320816) and ESA (project Glaciers CCI, 4000109873/14/I-NB).There have been numerous reports that surges of tidewater glaciers in Svalbard were initiated at the terminus and propagated up‐glacier, in contrast with downglacier‐propagating surges of land‐terminating glaciers. Most of these surges were poorly documented, and the cause of this behavior was unknown. We present detailed data on the recent surges of two tidewater glaciers, Aavatsmarkbreen and Wahlenbergbreen in Svalbard. High‐resolution time‐series of glacier velocities and evolution of crevasse patterns show that both surges propagated up‐glacier in abrupt steps. Prior to the surges, both glaciers underwent retreat and steepening, and in the case of Aavatsmarkbreen, we demonstrate that this was accompanied by a large increase in driving stress in the terminal zone. The surges developed in response to two distinct processes. 1) During the late quiescent phase, internal thermodynamic processes and/or retreat from a pinning point caused acceleration of the glacier front, leading to the development of terminal crevasse fields. 2) Crevasses allowed surface melt‐ and rain‐water to access the bed, causing flow acceleration and development of new crevasses up‐glacier. Upward migration of the surge coincided with stepwise expansion of the crevasse field. Geometric changes near the terminus of these glaciers appear to have led to greater strain heating, water production and storage at the glacier bed. Water routing via crevasses likely plays an important role in the evolution of surges. The distinction between internally triggered surges and externally triggered speed‐ups may not be straightforward. The behavior of these glaciers can be understood in terms of the enthalpy cycle model.Publisher PDFPeer reviewe

Dynamic vulnerability revealed in the collapse of an Arctic tidewater glacier

Abstract Glacier flow instabilities can rapidly increase sea level through enhanced ice discharge. Surge-type glacier accelerations often occur with a decadal to centennial cyclicity suggesting internal mechanisms responsible. Recently, many surging tidewater glaciers around the Arctic Barents Sea region question whether external forces such as climate can trigger dynamic instabilities. Here, we identify a mechanism in which climate change can instigate surges of Arctic tidewater glaciers. Using satellite and seismic remote sensing observations combined with three-dimensional thermo-mechanical modeling of the January 2009 collapse of the Nathorst Glacier System (NGS) in Svalbard, we show that an underlying condition for instability was basal freezing and associated friction increase under the glacier tongue. In contrast, continued basal sliding further upstream increased driving stresses until eventual and sudden till failure under the tongue. The instability propagated rapidly up-glacier, mobilizing the entire 450 km2 glacier basin over a few days as the till entered an unstable friction regime. Enhanced mass loss during and after the collapse (5–7 fold compared to pre-collapse mass losses) combined with regionally rising equilibrium line altitudes strongly limit mass replenishment of the glacier, suggesting irreversible consequences. Climate plays a paradoxical role as cold glacier thinning and retreat promote basal freezing which increases friction at the tongue by stabilizing an efficient basal drainage system. However, with some of the most intense atmospheric warming on Earth occurring in the Arctic, increased melt water can reduce till strength under tidewater glacier tongues to orchestrate a temporal clustering of surges at decadal timescales, such as those observed in Svalbard at the end of the Little Ice Age. Consequently, basal terminus freezing promotes a dynamic vulnerability to climate change that may be present in many Arctic tidewater glaciers