183 research outputs found

    Glaciers and ice caps

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    Mass-balance parameters derived from a synthetic network of mass-balance glaciers

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    Glacier mass-balance parameters such as the equilibrium-line altitude (ELA) play an important role when working with large glacier samples. While the number of observational mass-balance series to derive such parameters is limited, more and more modeled data are becoming available. Here we explore the possibilities of analyzing such ‘synthetic’ mass-balance data with respect to mass-balance parameters. A simplified energy-balance model is driven by bias-corrected regional climate model output to model mass-balance distributions for 94 glaciers in the Swiss Alps over 15 years. The modeling results in realistic interannual variability and mean cumulative mass balance. Subsequently model output is analyzed with respect to 18 topographic and mass-balance parameters and a correlation analysis is performed. Well-known correlations such as for ELA and median elevation are confirmed from the synthetic data. Furthermore, previously unreported parameter relationships are found such as a correlation of the balance rate at the tongue with the accumulation–area ratio (AAR) and of the glacier elevation range with the AAR. Analyzing modeled data complements in situ observations and highlights their importance: the small number of accurate mass-balance observations available for validation is a major challenge for the presented approach

    Modeling glacier thickness distribution and bed topography over entire mountain ranges with GlabTop: Application of a fast and robust approach

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    The combination of glacier outlines with digital elevation models (DEMs) opens new dimensions for research on climate change impacts over entire mountain chains. Of particular interest is the modeling of glacier thickness distribution, where several new approaches were proposed recently. The tool applied herein, GlabTop (Glacier bed Topography) is a fast and robust approach to model thickness distribution and bed topography for large glacier samples using a Geographic Information System (GIS). The method is based on an empirical relation between average basal shear stress and elevation range of individual glaciers, calibrated with geometric information from paleoglaciers, and validated with radio echo soundings on contemporary glaciers. It represents an alternative and independent test possibility for approaches based on mass-conservation and flow. As an example for using GlabTop in entire mountain ranges, we here present the modeled ice thickness distribution and bed topography for all Swiss glaciers along with a geomorphometric analysis of glacier characteristics and the overdeepenings found in the modeled glacier bed. These overdeepenings can be seen as potential sites for future lake formation and are thus highly relevant in connection with hydropower production and natural hazards. The thickest ice of the largest glaciers rests on weakly inclined bedrock at comparably low elevations, resulting in a limited potential for a terminus retreat to higher elevations. The calculated total glacier volume for all Swiss glaciers is 75 ± 22 km3 for 1973 and 65 ± 20 km3 in 1999. Considering an uncertainty range of ±30%, these results are in good agreement with estimates from other approaches

    Integrated monitoring of mountain glaciers as key indicators of global climate change: the European Alps

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    The internationally recommended multi-level strategy for monitoring mountain glaciers is illustrated using the example of the European Alps, where especially dense information has been available through historical times. This strategy combines in situ measurements (mass balance, length change) with remote sensing (inventories) and numerical modelling. It helps to bridge the gap between detailed local process-oriented studies and global coverage. Since the 1980s, mass balances have become increasingly negative, with values close to –1 m w.e. a–1 during the first 5 years of the 21st century. The hot, dry summer of 2003 alone caused a record mean loss of 2.45 m w.e., roughly 50% above the previous record loss in 1998, more than three times the average between 1980 and 2000 and an order of magnitude more than characteristic long-term averages since the end of the Little Ice Age and other extended periods of glacier shrinkage during the past 2000 years. It can be estimated that glaciers in the European Alps lost about half their total volume (roughly 0.5% a–1) between 1850 and around 1975, another 25% (or 1% a–1) of the remaining amount between 1975 and 2000, and an additional 10–15% (or 2–3% a–1) in the first 5 years of this century

    An experiment for the measurement of the bound-beta decay of the free neutron

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    The hyperfine-state population of hydrogen after the bound-beta decay of the neutron directly yields the neutrino left-handedness or a possible right-handed admixture and possible small scalar and tensor contributions to the weak force. Using the through-going beam tube of a high-flux reactor, a background free hydrogen rate of ca. 3 s1^{-1} can be obtained. The detection of the neutral hydrogen atoms and the analysis of the hyperfine states is accomplished by Lamb shift source type quenching and subsequent ionization. The constraints on the neutrino helicity and the scalar and tensor coupling constants of weak interaction can be improved by a factor of ten.Comment: 9 pages, 5 figures. Submitted to EPJ

    The influence of ground ice distribution on geomorphic dynamics since the Little Ice Age in proglacial areas of two cirque glacier systems

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    International audienceHolocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrostenvironments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution undercondition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age(LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial beltof the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioningsystems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolutionin time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internalstructure and dynamics. The studied sites are a complex assemblage of debris-covered glacier, ice-rich frozen debris and unfrozendebris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specificzones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debriscoveredupper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciatedmoraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation hasoccurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde.Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply.In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers actmostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because ofthe slope angle weakness

    Perennial snow and ice variations (2000–2008) in the Arctic circumpolar land area from satellite observations

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    Perennial snow and ice (PSI) extent is an important parameter of mountain environments with regard to its involvement in the hydrological cycle and the surface energy budget. We investigated interannual variations of PSI in nine mountain regions of interest (ROI) between 2000 and 2008. For that purpose, a novel MODIS data set processed at the Canada Centre for Remote Sensing at 250 m spatial resolution was utilized. The extent of PSI exhibited significant interannual variations, with coefficients of variation ranging from 5% to 81% depending on the ROI. A strong negative relationship was found between PSI and positive degree‐days (threshold 0°C) during the summer months in most ROIs, with linear correlation coefficients (r) being as low as r = −0.90. In the European Alps and Scandinavia, PSI extent was significantly correlated with annual net glacier mass balances, with r = 0.91 and r = 0.85, respectively, suggesting that MODIS‐derived PSI extent may be used as an indicator of net glacier mass balances. Validation of PSI extent in two land surface classifications for the years 2000 and 2005, GLC‐2000 and Globcover, revealed significant discrepancies of up to 129% for both classifications. With regard to the importance of such classifications for land surface parameterizations in climate and land surface process models, this is a potential source of error to be investigated in future studies. The results presented here provide an interesting insight into variations of PSI in several ROIs and are instrumental for our understanding of sensitive mountain regions in the context of global climate change assessment

    Historically unprecedented global glacier decline in the early 21st century

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    Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (⇠42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (⇠5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable

    Potential climatic transitions with profound impact on Europe

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    We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/
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