Articles de revues : « Minimal model glacier »

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Oerlemans, J., et F. M. Nick. « A minimal model of a tidewater glacier ». Annals of Glaciology 42 (2005) : 1–6. http://dx.doi.org/10.3189/172756405781813023.

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AbstractWe propose a simple, highly parameterized model of a tidewater glacier. The mean ice thickness and the ice thickness at the glacier front are parameterized in terms of glacier length and, when the glacier is calving, water depth. We use a linear relation between calving rate and water depth. The change in glacier length is determined by the total change in the mass budget (surface balance and calving flux), but not by the details of the glacier profile and the related velocity field. We show that this may still yield relatively rapid rates of retreat for an idealized bed geometry with a smooth overdeepening. The model is able to simulate the full cycle of ice-free conditions, glacier terminus on land, tidewater glaciers terminus, and backwards. We study two cases: (i) a glacier with a specific balance (accumulation) that is spatially uniform, and (ii) a glacier in a warmer climate with the specific balance being a linear function of altitude. Equilibrium states exhibit a double branching with respect to the climatic forcing (equilibrium-line altitude). One bifurcation is related to the dependence of the calving process on the bed profile; the other bifurcation is due to the height–mass-balance feedback. We discuss the structure of the solution diagram for different values of the calving-rate parameter. The model results are similar to those of Vieli and others (2001), who combined a fairly sophisticated two-dimensional (vertical plane) numerical ice-flow model with the modified flotation criterion suggested by Van der Veen (1996). With regard to the global dynamics of a tidewater glacier, we conclude that the details of the glacier profile or velocity field are less significant than the bed profile and the relation between the water depth and the calving rate.

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Peano, D., M. Chiarle et J. von Hardenberg. « Glacier dynamics in the Western Italian Alps : a minimal model approach ». Cryosphere Discussions 8, n^o 2 (6 mars 2014) : 1479–516. http://dx.doi.org/10.5194/tcd-8-1479-2014.

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Abstract. We study the response of a set of glaciers in the Western Italian Alps to climate variations using the minimal glacier modeling approach, first introduced by Oerlemans. The mathematical models are forced over the period 1959–2009, using temperature and precipitation recorded by a dense network of meteorological stations and we find a good match between the observed and modeled glacier length dynamics. Forcing the model with future projections from a state-of-the-art global climate model in the RCP 4.5 and RCP 8.5 scenarios, we obtain a first estimate for the "expiration date" of these glaciers.

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Masiokas, M. H., D. A. Christie, C. Le Quesne, P. Pitte, L. Ruiz, R. Villalba, B. H. Luckman et al. « Reconstructing glacier mass balances in the Central Andes of Chile and Argentina using local and regional hydro-climatic data ». Cryosphere Discussions 9, n^o 5 (17 septembre 2015) : 4949–80. http://dx.doi.org/10.5194/tcd-9-4949-2015.

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Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass balance record, available for glaciar Echaurren Norte in the Andes at ~34° S, to develop a minimal glacier surface mass balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass balance record over the 1978–2013 calibration period. An attribution assessment indicates that precipitation variability constitutes the most important forcing modulating annual glacier mass balances at this site. A regionally-averaged series of mean annual streamflow records from both sides of the Andes is then used to estimate, through simple linear regression, this glacier's annual mass balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend totaling almost −42 m w.eq. over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass balance series suggest the glaciar Echaurren Norte reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

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Oerlemans, J., J. Jania et L. Kolondra. « Application of a minimal glacier model to Hansbreen, Spitsbergen ». Cryosphere Discussions 4, n^o 3 (13 juillet 2010) : 949–79. http://dx.doi.org/10.5194/tcd-4-949-2010.

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Abstract. Hansbreen is a well studied tidewater glacier in the southwestern part of Spitsbergen, currently about 16 km long. Since the end of the 19th century it has been retreating over a distance of 2.7 km. In this paper the global dynamics of Hansbreen are studied with a minimal glacier model, in which the ice mechanics are strongly parameterised and a simple law for iceberg calving is used. The model is calibrated by reconstructing a climate history in such a way that observed and simulated glacier length match. In addition, the calving law is tuned to reproduce the observed mean calving flux for the period 2000–2008. Equilibrium states are studied for a wide range of values of the equilibrium line altitude. The dynamics of the glacier are strongly nonlinear. The height-mass balance feedback and the water depth – calving flux feedback give rise to cusp catastrophes in the system. For the present climatic conditions Hansbreen cannot survive. Depending on the imposed climate change scenario, in AD 2100 Hansbreen is predicted to have a length between 10 and 12 km. The corresponding decrease in ice volume (relative to the volume in AD 2000) is 45 to 65%. Finally the late-Holocene history of Hansbreen is considered. We quote evidence from dated peat samples that Hansbreen did not exist during the Holocene Climatic Optimum. We speculate that at the end of the mid-Holocene Climatic Optimum Hansbreen could advance because the glacier bed was at least 50 m higher than today, and because the tributary glaciers on the western side may have supplied a significant amount of mass to the main stream. The excavation of the overdeepening and the formation of the shoal at the glacier terminus probably took place during the Little Ice Age.

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Oerlemans, J., J. Jania et L. Kolondra. « Application of a minimal glacier model to Hansbreen, Svalbard ». Cryosphere 5, n^o 1 (3 janvier 2011) : 1–11. http://dx.doi.org/10.5194/tc-5-1-2011.

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Abstract. Hansbreen is a well studied tidewater glacier in the southwestern part of Svalbard, currently about 16 km long. Since the end of the 19th century it has been retreating over a distance of 2.7 km. In this paper the global dynamics of Hansbreen are studied with a minimal glacier model, in which the ice mechanics are strongly parameterised and a simple law for iceberg calving is used. The model is calibrated by reconstructing a climate history in such a way that observed and simulated glacier length match. In addition, the calving law is tuned to reproduce the observed mean calving flux for the period 2000–2008. Equilibrium states are studied for a wide range of values of the equilibrium line altitude. The dynamics of the glacier are strongly nonlinear. The height-mass balance feedback and the water depth-calving flux feedback give rise to cusp catastrophes in the system. For the present climatic conditions Hansbreen cannot survive. Depending on the imposed climate change scenario, in AD 2100 Hansbreen is predicted to have a length between 10 and 12 km. The corresponding decrease in ice volume (relative to the volume in AD 2000) is 45 to 65%. Finally the late-Holocene history of Hansbreen is considered. We quote evidence from dated peat samples that Hansbreen did not exist during the Holocene Climatic Optimum. We speculate that at the end of the mid-Holocene Climatic Optimum Hansbreen could advance because the glacier bed was at least 50 m higher than today, and because the tributary glaciers on the western side may have supplied a significant amount of mass to the main stream. The excavation of the overdeepening and the formation of the shoal at the glacier terminus probably took place during the Little Ice Age.

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Marzeion, B., M. Hofer, A. H. Jarosch, G. Kaser et T. Mölg. « A minimal model for reconstructing interannual mass balance variability of glaciers in the European Alps ». Cryosphere Discussions 5, n^o 5 (19 octobre 2011) : 2799–839. http://dx.doi.org/10.5194/tcd-5-2799-2011.

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Abstract. We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements, and cross validated using the 15 glaciers above, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

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Marzeion, B., M. Hofer, A. H. Jarosch, G. Kaser et T. Mölg. « A minimal model for reconstructing interannual mass balance variability of glaciers in the European Alps ». Cryosphere 6, n^o 1 (17 janvier 2012) : 71–84. http://dx.doi.org/10.5194/tc-6-71-2012.

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Abstract. We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements. We cross validated the model again by withholding the mass balance information from each of the 15 glaciers above during the model training, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in the extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

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Nick, F. M., et J. Oerlemans. « Dynamics of tidewater glaciers : comparison of three models ». Journal of Glaciology 52, n^o 177 (2006) : 183–90. http://dx.doi.org/10.3189/172756506781828755.

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AbstractA minimal model of a tidewater glacier based solely on mass conservation is compared with two one-dimensional numerical flowline models, one with the calving rate proportional to water depth, and the other with the flotation criterion as a boundary condition at the glacier terminus. The models were run with two simplified bed geometries and two mass-balance formulations. The models simulate the full cycle of length variations and the equilibrium states for a tidewater glacier. This study shows that the branching of the equilibrium states depends significantly on the bed geometry. The similarity between the results of the three models indicates that if there is a submarine undulation at the terminus of a tidewater glacier, any model in which the frontal ice loss is related to the water depth yields qualitatively the same non-linear behaviour. For large glaciers extending into deep water, the flotation model causes unrealistic behaviour.

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Adhikari, S., et S. J. Marshall. « Influence of high-order mechanics on simulation of glacier response to climate change : insights from Haig Glacier, Canadian Rocky Mountains ». Cryosphere 7, n^o 5 (25 septembre 2013) : 1527–41. http://dx.doi.org/10.5194/tc-7-1527-2013.

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Abstract. Evolution of glaciers in response to climate change has mostly been simulated using simplified dynamical models. Because these models do not account for the influence of high-order physics, corresponding results may exhibit some biases. For Haig Glacier in the Canadian Rocky Mountains, we test this hypothesis by comparing simulation results obtained from 3-D numerical models that deal with different assumptions concerning physics, ranging from simple shear deformation to comprehensive Stokes flow. In glacier retreat scenarios, we find a minimal role of high-order mechanics in glacier evolution, as geometric effects at our site (the presence of an overdeepened bed) result in limited horizontal movement of ice (flow speed on the order of a few meters per year). Consequently, high-order and reduced models all predict that Haig Glacier ceases to exist by ca. 2080 under ongoing climate warming. The influence of high-order mechanics is evident, however, in glacier advance scenarios, where ice speeds are greater and ice dynamical effects become more important. Although similar studies on other glaciers are essential to generalize such findings, we advise that high-order mechanics are important and therefore should be considered while modeling the evolution of active glaciers. Reduced model predictions may be adequate for other glaciologic and topographic settings, particularly where flow speeds are low and where mass balance changes dominate over ice dynamics in determining glacier geometry.

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Masiokas, Mariano H., Duncan A. Christie, Carlos Le Quesne, Pierre Pitte, Lucas Ruiz, Ricardo Villalba, Brian H. Luckman et al. « Reconstructing the annual mass balance of the Echaurren Norte glacier (Central Andes, 33.5° S) using local and regional hydroclimatic data ». Cryosphere 10, n^o 2 (26 avril 2016) : 927–40. http://dx.doi.org/10.5194/tc-10-927-2016.

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Abstract. Despite the great number and variety of glaciers in southern South America, in situ glacier mass-balance records are extremely scarce and glacier–climate relationships are still poorly understood in this region. Here we use the longest (> 35 years) and most complete in situ mass-balance record, available for the Echaurren Norte glacier (ECH) in the Andes at ∼ 33.5° S, to develop a minimal glacier surface mass-balance model that relies on nearby monthly precipitation and air temperature data as forcing. This basic model is able to explain 78 % of the variance in the annual glacier mass-balance record over the 1978–2013 calibration period. An attribution assessment identified precipitation variability as the dominant forcing modulating annual mass balances at ECH, with temperature variations likely playing a secondary role. A regionally averaged series of mean annual streamflow records from both sides of the Andes between ∼ 30 and 37° S is then used to estimate, through simple linear regression, this glacier's annual mass-balance variations since 1909. The reconstruction model captures 68 % of the observed glacier mass-balance variability and shows three periods of sustained positive mass balances embedded in an overall negative trend over the past 105 years. The three periods of sustained positive mass balances (centered in the 1920s–1930s, in the 1980s and in the first decade of the 21st century) coincide with several documented glacier advances in this region. Similar trends observed in other shorter glacier mass-balance series suggest that the Echaurren Norte glacier reconstruction is representative of larger-scale conditions and could be useful for more detailed glaciological, hydrological and climatological assessments in this portion of the Andes.

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Adhikari, S., et S. J. Marshall. « Influence of high-order mechanics on simulation of glacier response to climate change : insights from Haig Glacier, Canadian Rocky Mountains ». Cryosphere Discussions 7, n^o 2 (24 avril 2013) : 1707–48. http://dx.doi.org/10.5194/tcd-7-1707-2013.

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Abstract. Evolution of glaciers in response to climate change has mostly been simulated using simplified dynamical models. Because these models do not account for the influence of high-order physics, corresponding results may exhibit some biases. For Haig Glacier in the Canadian Rocky Mountains, we test this hypothesis by comparing simulation results obtained from 3-D numerical models that deal with different assumptions concerning ice-flow physics, ranging from simple shear-deformation to comprehensive Stokes flow. In glacier retreat scenarios, we find a minimal role of high-order mechanics in glacier evolution, as geometric effects at our site (the presence of an overdeepened bed) result in limited horizontal movement of ice (flow speed on the order of a few meters per year). Consequently, high-order and reduced models all predict that Haig Glacier ceases to exist by ca. 2080 under ongoing climate warming. The influence of high-order mechanics is evident, however, in glacier advance scenarios, where ice speeds are greater and ice dynamical effects become more important. To generalize these findings for other glacier applications, we advise that high-order mechanics are important and therefore should be considered while modelling the evolution of active glaciers. Reduced model predictions may, however, be adequate for other glaciologic and topographic settings, particularly where flow speeds are low.

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Guðmundsson, Snævarr, Hrafnhildur Hannesdóttir et Helgi Björnsson. « Post-Little Ice Age (1891–2011 AD) volume loss of Kotárjökull glacier, southeastern Iceland, as established from historical photography ». Jökull 62, n^o 1 (15 décembre 2012) : 97–110. http://dx.doi.org/10.33799/jokull2012.62.097.

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Kotárjökull is one of several outlet glaciers draining the ice-covered central volcano Öræfajökull in SE-Iceland. We estimate the average annual specific mass loss of the glacier, to be 0.22 m (water equivalent) over the post Little Ice Age period 1891–2011. The glacial recession corresponds to an areal decrease of 2.7 km² (20\%) and a volume loss of 0.4 km³ (30\%). A surface lowering of 180 m is observed near the snout decreasing to negligible amounts above 1700 m elevation. This minimal surface lowering at high altitudes is supported by a comparison of the elevation of trigonometrical points on Öræfajökull’s plateau from the Danish General Staff map of 1904 and a recent LiDAR-based digital elevation model. Our estimates are derived from a) three pairs of photographs from 1891 and 2011, b) geomorphological field evidence delineating the maximum glacier extent at the end of the Little Ice Age, and c) the high-resolution digital elevation model from 2010–2011. The historical photographs of Frederick W.W. Howell from 1891 were taken at the end of the Little Ice Age in Iceland, thus providing a reference of the maximum glacier extent.

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Adhikari, Surendra, et Philippe Huybrechts. « Numerical modelling of historical front variations and the 21st-century evolution of glacier AX010, Nepal Himalaya ». Annals of Glaciology 50, n^o 52 (2009) : 27–34. http://dx.doi.org/10.3189/172756409789624346.

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AbstractDue to the lack of measurements of ice velocity, mass balance, glacier geometry and other baseline data, model-based studies of glacial systems in the Nepal Himalaya are very limited. Here a numerical ice-flow model has been developed for glacier AX010 in order to study its relation to local climate and investigate the possible causes of its general retreat since the end of the Little Ice Age. First, an attempt is made to simulate the historical front variations, considering each climatic parameter separately. Good agreement between the observations and model projections can be obtained under the assumption that variations in glacier front position are a response to changes in temperature alone. The same assumption is made about future changes to explore the 21st-century evolution of the glacier. Under a no-change scenario, the glacier will retreat by another ∽600m by AD 2100, whereas it is projected to vanish completely during this century for all trends with a temperature rise larger than +2.5˚C by AD 2100 with respect to the 1980–99 mean. With constant precipitation at the 1980–99 mean, the model predicts that the glacier will cease to exist at AD 2083, 2056 or 2049 if the temperature rises linearly by 3˚C, 4.5˚C or 6˚C respectively by the end of this century. With an additional range of precipitation changes between –30% and +30%, the life expectancy of glacier AX010 varies by 18, 6 and 2 years for the respective temperature rises. Thus the role of precipitation becomes minimal for the higher trends of temperature rise.

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Campbell, Seth, Karl Kreutz, Erich Osterberg, Steven Arcone, Cameron Wake, Douglas Introne, Kevin Volkening et Dominic Winski. « Melt regimes, stratigraphy, flow dynamics and glaciochemistry of three glaciers in the Alaska Range ». Journal of Glaciology 58, n^o 207 (2012) : 99–109. http://dx.doi.org/10.3189/2012jog10j238.

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AbstractWe used ground-penetrating radar (GPR), GPS and glaciochemistry to evaluate melt regimes and ice depths, important variables for mass-balance and ice-volume studies, of Upper Yentna Glacier, Upper Kahiltna Glacier and the Mount Hunter ice divide, Alaska. We show the wet, percolation and dry snow zones located below ~2700ma.s.l., at ~2700 to 3900ma.s.l. and above 3900ma.s.l., respectively. We successfully imaged glacier ice depths upwards of 480 m using 40-100 MHz GPR frequencies. This depth is nearly double previous depth measurements reached using mid-frequency GPR systems on temperate glaciers. Few Holocene-length climate records are available in Alaska, hence we also assess stratigraphy and flow dynamics at each study site as a potential ice-core location. Ice layers in shallow firn cores and attenuated glaciochemical signals or lacking strata in GPR profiles collected on Upper Yentna Glacier suggest that regions below 2800ma.s.l. are inappropriate for paleoclimate studies because of chemical diffusion, through melt. Flow complexities on Kahiltna Glacier preclude ice-core climate studies. Minimal signs of melt or deformation, and depth-age model estimates suggesting ~4815 years of ice on the Mount Hunter ice divide (3912ma.s.l.) make it a suitable Holocene-age ice-core location.

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Sinclair, K. E., et S. J. Marshall. « Post-depositional modification of stable water isotopes in winter snowpacks in the Canadian Rocky Mountains ». Annals of Glaciology 49 (2008) : 96–106. http://dx.doi.org/10.3189/172756408787814979.

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AbstractTo assess the seasonal stability of the δ18O stratigraphy in winter snowpacks in the Canadian Rocky Mountains, snow pits were sampled over three accumulation seasons at two field sites. These sites, Opabin and Haig Glaciers, are ~160km apart at similar elevations and represent windward and lee-slope environments respectively. At both sites, snow pits were sampled at one glacier and one forefield location throughout each accumulation season. Intra-seasonal changes in δ18O at each site were examined to determine the extent of post-depositional modification of isotope stratigraphies. At both glacier sites, there was minimal temporal change before the onset of spring melt in all years. In addition, the similar structure of δ18O profiles from both glacier sites suggests that regional controls govern the isotopic composition of solid-phase precipitation across the study area. At forefield locations, the absence of an insulating layer of ice at the base of the snowpack allowed for vapour transport and post-depositional modification of the seasonal δ18O signal. This did not result in consistent changes to the mean δ18O, deuterium excess and δD–δ18O regression line slopes in the lower layers of snow, and the observed smoothing of δ18O profiles was less than that simulated by applying a diffusion model to these snowpacks.

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Kislov, A. V., et A. F. Glazovsky. « Simulation of the dynamics of the Hansbreen tidal glacier (Svalbard) based on the stochastic model ». Ice and Snow 59, n^o 4 (1 décembre 2019) : 452–59. http://dx.doi.org/10.15356/2076-6734-2019-4-441.

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The dynamics of the Hansbreen tidal glacier (Svalbard) is manifested at different time scales. In addition to the long-term trend, there are noticeable inter-annual fluctuations. And the last ones are precisely the subject of this work. Based on general conclusions of the theory of temporal dynamics of the massive inertial objects, the observed inter-annual changes in the length of the glacier can be explained as a result of the accumulation of anomalies of the heat fluxes and water flows. In spite the fact that the initial model of glacier dynamics is deterministically based on the physical law of conservation of ice mass (the so-called the «minimal model» was used), the model of length change is interpreted as stochastic. From this standpoint, it is the Langevin equation, which includes the effect of random temperature anomalies that can be interpreted as a white noise. From a mathematical point of view, this process is analogous to Brownian motion, i.e. the length of the Hansbreen glacier randomly fluctuates in the vicinity of its stable equilibrium position. Based on the Langevin equation, we passed to the Fokker–Planck equation, the solution of which allowed us to obtain the distribution function of the probabilities of interannual fluctuations of glacier length, which is close to the normal law. It was shown that the possible range of the variability covers the observed interval of the length fluctuations. The pdf is close to normal distribution.

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Marzeion, B., et A. Nesje. « Spatial patterns of North Atlantic Oscillation influence on mass balance variability of European Glaciers ». Cryosphere Discussions 6, n^o 1 (3 janvier 2012) : 1–35. http://dx.doi.org/10.5194/tcd-6-1-2012.

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Abstract. We present and validate a set of minimal models of glacier mass balance variability. The most skillful model is then applied to reconstruct 7735 individual time series of mass balance variability for all glaciers in the European Alps and Scandinavia. Subsequently, we investigate the influence of atmospheric variability associated with the North Atlantic Oscillation (NAO) on the glaciers' mass balances. We find a spatial coherence in the glaciers' sensitivity to NAO forcing which is caused by regionally similar mechanisms relating the NAO forcing to the mass balance: In Southwestern Scandinavia, winter precipitation causes a correlation of mass balances with the NAO. In Northern Scandinavia, temperature anomalies outside the core winter season cause an anti-correlation between NAO and mass balances. In the Western Alps, both temperature and winter precipitation anomalies lead to a weak anti-correlation of mass balances with the NAO, while in the Eastern Alps, the influences of winter precipitation and temperature anomalies tend to cancel each other, and only on the southern side a slight anti-correlation of mass balances with the NAO prevails.

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Marzeion, B., et A. Nesje. « Spatial patterns of North Atlantic Oscillation influence on mass balance variability of European glaciers ». Cryosphere 6, n^o 3 (14 juin 2012) : 661–73. http://dx.doi.org/10.5194/tc-6-661-2012.

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Abstract. We present and validate a set of minimal models of glacier mass balance variability. The most skillful model is then applied to reconstruct 7735 individual time series of mass balance variability for all glaciers in the European Alps and Scandinavia. Subsequently, we investigate the influence of atmospheric variability associated with the North Atlantic Oscillation (NAO) on the glaciers' mass balances. We find a spatial coherence in the glaciers' sensitivity to NAO forcing which is caused by regionally similar mechanisms relating the NAO forcing to the mass balance: in southwestern Scandinavia, winter precipitation causes a correlation of mass balances with the NAO. In northern Scandinavia, temperature anomalies outside the core winter season cause an anti-correlation between NAO and mass balances. In the western Alps, both temperature and winter precipitation anomalies lead to a weak anti-correlation of mass balances with the NAO, while in the eastern Alps, the influences of winter precipitation and temperature anomalies tend to cancel each other, and only on the southern side a slight anti-correlation of mass balances with the NAO prevails.

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Oerlemans, Johannes, Jack Kohler et Adrian Luckman. « Modelling the mass budget and future evolution of Tunabreen, central Spitsbergen ». Cryosphere 16, n^o 5 (1 juin 2022) : 2115–26. http://dx.doi.org/10.5194/tc-16-2115-2022.

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Abstract. The 26 km long tidewater glacier Tunabreen is the most frequently surging glacier in Svalbard, with four documented surges in the past 100 years. We model the evolution of this glacier with a minimal glacier model (MGM), in which ice mechanics, calving, and surging are parameterized. The model geometry consists of a flow band to which three tributaries supply mass. The calving rate is set to the mean observed value for the period 2012–2019 and kept constant. For the past 120 years, a smooth equilibrium line altitude (ELA) history is reconstructed by finding the best possible match between observed and simulated glacier length. There is a modest correlation between this reconstructed ELA history and an ELA history based on meteorological observations from Longyearbyen. Runs with and without surging show that the effect of surging on the long-term glacier evolution is limited. Due to the low surface slope and associated strong height–mass-balance feedback, Tunabreen is very sensitive to changes in the ELA. For a constant future ELA equal to the reconstructed value for 2020, the glacier front will retreat by 8 km during the coming 100 years. For an increase in the ELA of 2 m a−1, the retreat is projected to be 13 km, and Tunabreen becomes a land-terminating glacier around 2100. The calving parameter is an important quantity: increasing its value by 50 % has about the same effect as a 35 m increase in the ELA, with the corresponding equilibrium glacier length being 17.5 km (as compared to 25.8 km in the reference state). Response times vary from 150 to 400 years, depending on the forcing and on the state of the glacier (tidewater or land-terminating).

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Farías-Barahona, David, Ryan Wilson, Claudio Bravo, Sebastián Vivero, Alexis Caro, Thomas E. Shaw, Gino Casassa et al. « A near 90-year record of the evolution of El Morado Glacier and its proglacial lake, Central Chilean Andes ». Journal of Glaciology 66, n^o 259 (18 août 2020) : 846–60. http://dx.doi.org/10.1017/jog.2020.52.

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AbstractUsing an ensemble of close- and long-range remote sensing, lake bathymetry and regional meteorological data, we present a detailed assessment of the geometric changes of El Morado Glacier in the Central Andes of Chile and its adjacent proglacial lake between 1932 and 2019. Overall, the results revealed a period of marked glacier down wasting, with a mean geodetic glacier mass balance of −0.39 ± 0.15 m w.e.a−1 observed for the entire glacier between 1955 and 2015 with an area loss of 40% between 1955 and 2019. We estimate an ice elevation change of −1.00 ± 0.17 m a−1 for the glacier tongue between 1932 and 2019. The increase in the ice thinning rates and area loss during the last decade is coincident with the severe drought in this region (2010–present), which our minimal surface mass-balance model is able to reproduce. As a result of the glacier changes observed, the proglacial lake increased in area substantially between 1955 and 2019, with bathymetry data suggesting a water volume of 3.6 million m3 in 2017. This study highlights the need for further monitoring of glacierised areas in the Central Andes. Such efforts would facilitate a better understanding of the downstream impacts of glacier downwasting.

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Skidmore, Mark L., Julia M. Foght et Martin J. Sharp. « Microbial Life beneath a High Arctic Glacier ». Applied and Environmental Microbiology 66, n^o 8 (1 août 2000) : 3214–20. http://dx.doi.org/10.1128/aem.66.8.3214-3220.2000.

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ABSTRACT The debris-rich basal ice layers of a high Arctic glacier were shown to contain metabolically diverse microbes that could be cultured oligotrophically at low temperatures (0.3 to 4°C). These organisms included aerobic chemoheterotrophs and anaerobic nitrate reducers, sulfate reducers, and methanogens. Colonies purified from subglacial samples at 4°C appeared to be predominantly psychrophilic. Aerobic chemoheterotrophs were metabolically active in unfrozen basal sediments when they were cultured at 0.3°C in the dark (to simulate nearly in situ conditions), producing 14CO2from radiolabeled sodium acetate with minimal organic amendment (≥38 μM C). In contrast, no activity was observed when samples were cultured at subfreezing temperatures (≤−1.8°C) for 66 days. Electron microscopy of thawed basal ice samples revealed various cell morphologies, including dividing cells. This suggests that the subglacial environment beneath a polythermal glacier provides a viable habitat for life and that microbes may be widespread where the basal ice is temperate and water is present at the base of the glacier and where organic carbon from glacially overridden soils is present. Our observations raise the possibility that in situ microbial production of CO2 and CH4beneath ice masses (e.g., the Northern Hemisphere ice sheets) is an important factor in carbon cycling during glacial periods. Moreover, this terrestrial environment may provide a model for viable habitats for life on Mars, since similar conditions may exist or may have existed in the basal sediments beneath the Martian north polar ice cap.

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Oerlemans, Johannes. « Modelling the late Holocene and future evolution of Monacobreen, northern Spitsbergen ». Cryosphere 12, n^o 9 (21 septembre 2018) : 3001–15. http://dx.doi.org/10.5194/tc-12-3001-2018.

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Abstract. Monacobreen is a 40 km long surge-type tidewater glacier in northern Spitsbergen. During 1991–1997 Monacobreen surged and advanced by about 2 km, but the front did not reach the maximum Little Ice Age (LIA) stand. Since 1997 the glacier front is retreating at a fast rate (∼125 m a−1). The questions addressed in this study are as follows: (1) Can the late Holocene behaviour of Monacobreen be understood in terms of climatic forcing?, and (2) What will be the likely evolution of this glacier for different scenarios of future climate change? Monacobreen is modelled with a minimal glacier model, including a parameterization of the calving process as well as the effect of surges. The model is driven by an equilibrium-line altitude (ELA) history derived from lake sediments of a nearby glacier catchment in combination with meteorological data from 1899 onwards. The simulated glacier length is in good agreement with the observations: the maximum LIA stand, the front position at the end of the surge, and the 2.5 km retreat after the surge (1997–2016) are well reproduced (the mean difference between observed and simulated glacier length being 6 % when scaled with the total retreat during 1900–2016). The effect of surging is limited. Directly after a surge the initiated mass balance perturbation due to a lower mean surface elevation is about -0.13mw.e.a-1, which only has a small effect on the long-term evolution of the glacier. The simulation suggests that the major growth of Monacobreen after the Holocene climatic optimum started around 1500 BCE. Monacobreen became a tidewater glacier around 500 BCE and reached a size comparable to the present state around 500 CE. For the mid-B2 scenario (IPCC, 2013), which corresponds to a ∼2ma-1 rise of the ELA, the model predicts a volume loss of 20 % to 30 % by the year 2100 (relative to the 2017 volume). For a ∼4ma-1 rise in the ELA this is 30 % to 40 %. However, much of the response to 21st century warming will still come after 2100.

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Haq, Mateeul, Muhammad Jawed Iqbal, Khan Alam, Zhongwei Huang, Thomas Blaschke, Salman Qureshi et Sher Muhammad. « Assessment of Runoff Components of River Flow in the Karakoram Mountains, Pakistan, during 1995–2010 ». Remote Sensing 15, n^o 2 (9 janvier 2023) : 399. http://dx.doi.org/10.3390/rs15020399.

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Glaciers are generally believed to be subjugating by global warming but the Karakoram glaciers are reportedly maintaining their balance. Earlier studies in the Karakoram and its sub-basins have mostly addressed a short span of time and used complex models to understand the phenomenon. Thus, this study is based on a long-term trend analysis of the computed runoff components using satellite data with continuous spatial and temporal coverage incorporated into a simple degree day Snowmelt Runoff Model (SRM). The trends of melt runoff components can help us understanding the future scenarios of the glaciers in the study area. The SRM was calibrated against the recorded river flows in the Hunza River Basin (HRB). Our simulations showed that runoff contribution from rain, snow, and glaciers are 14.4%, 34.2%, and 51.4%, respectively during 1995–2010. The melting during the summer has slightly increased, suggesting overall but modest glacier mass loss which consistent with a few recent studies. The annual stream flows showed a rising trend during the 1995–2010 period, while, rainfall and temperatures showed contrasting increasing/decreasing behavior in the July, August, and September months during the same period. The average decreasing temperatures (0.08 °C per annum) in July, August, and September makes it challenging and unclear to explain the reason for this rising trend of runoff but a rise in precipitation in the same months affirms the rise in basin flows. At times, the warmer rainwater over the snow and glacier surfaces also contributed to excessive melting. Moreover, the uncertainties in the recorded hydrological, meteorological, and remote sensing data due to low temporal and spatial resolution also portrayed contrasting results. Gradual climate change in the HRB can affect river flows in the near future, requiring effective water resource management to mitigate any adverse impacts. This study shows that assessment of long-term runoff components can be a good alternative to detect changes in melting glaciers with minimal field observations.

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Rodriguez, M., N. Ohlanders et J. McPhee. « Estimating glacier and snowmelt contributions to stream flow in a Central Andes catchment in Chile using natural tracers ». Hydrology and Earth System Sciences Discussions 11, n^o 7 (29 juillet 2014) : 8949–94. http://dx.doi.org/10.5194/hessd-11-8949-2014.

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Abstract. This paper presents a methodology for hydrograph separation in high elevation watersheds, which aims at identifying individual flow sources such as snow- and ice melt, rainfall and soil water. Daily summer and bi-daily spring water samples from the outlet of the Juncal River were analyzed for all major ions as well as stable water isotopes, δ18O and δ2H. Additionally, various water sources such as rain, springs, snow- and glacial melt were sampled throughout the catchment. A principal component analysis (PCA) was performed in order to reduce the dimensionality of the problem. Potential sources were identified in a two-component U space that explains 77% of variability. Hydrograph separation (HS) was performed through three models: (i) Isotopic model, (ii) Mixing–PCA model, and (iii) Informative–Bayesian model, with very similar results in each case. At the Juncal River outlet, summer flows were composed by at least 50% of water originating in highly glaciarized headwaters in 2011–2012 (a dry period in the Central Andes). Autumn and winter flows were highly influenced by soil water and affect total annual discharge. Before the high flow season, snow melt accounted for approximately 25% of streamflow, However during summer, when streamflow was highest, snowmelt contribution was minimal, while glacier melt and soil water were the most important sources.

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Lindstrom, D. R. « Formation of the West Antarctic Ice Sheet ». Annals of Glaciology 11 (1988) : 71–76. http://dx.doi.org/10.3189/s0260305500006352.

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A numerical ice-shelf model is employed to observe the inception of the West Antarctic ice sheet (WAIS) from a thin (20 m thick) floating ice cover under the following conditions: (i) a lower sea-level than at present, due to ice-sheet formation in the Northern Hemisphere, (ii) surface and basal temperature and accumulation rates approximately equal to those of present Antarctic ice shelves, and (iii) ice flow from East Antarctica into West Antarctica is neglected. The model determines the flow and thickness of floating ice and assumes that grounded ice is stagnant. Under these constraints, all regions except the Ross Sea, the Filchner region (east of Berkner Island), and up-stream of Thwaites Glacier ground within 4000 years. Ice readily grounds in the Ronne region (west of Berkner Island), forcing ice from Ellsworth Land to flow east toward the Filchner region. It is suggested that grounding over the Ross Sea, the Filchner region, and up-stream of Thwaites Glacier occurs only after grounded-ice flow is established. Grounded-ice flow is also a prerequisite of bed erosion and sediment deposition, which leave historical records of the actual ice-sheet formation. It is suggested that erosion and sediment deposition is minimal over the Ronne region and considerable along the path from Ellsworth Land to the Filchner region, because more ice flows toward the Filchner region than the Ronne region. It is probably difficult for ice to ground over the Ross region, so this region should have a high proportion of glacial marine sediments.

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Lindstrom, D. R. « Formation of the West Antarctic Ice Sheet ». Annals of Glaciology 11 (1988) : 71–76. http://dx.doi.org/10.1017/s0260305500006352.

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A numerical ice-shelf model is employed to observe the inception of the West Antarctic ice sheet (WAIS) from a thin (20 m thick) floating ice cover under the following conditions: (i) a lower sea-level than at present, due to ice-sheet formation in the Northern Hemisphere, (ii) surface and basal temperature and accumulation rates approximately equal to those of present Antarctic ice shelves, and (iii) ice flow from East Antarctica into West Antarctica is neglected. The model determines the flow and thickness of floating ice and assumes that grounded ice is stagnant. Under these constraints, all regions except the Ross Sea, the Filchner region (east of Berkner Island), and up-stream of Thwaites Glacier ground within 4000 years. Ice readily grounds in the Ronne region (west of Berkner Island), forcing ice from Ellsworth Land to flow east toward the Filchner region. It is suggested that grounding over the Ross Sea, the Filchner region, and up-stream of Thwaites Glacier occurs only after grounded-ice flow is established. Grounded-ice flow is also a prerequisite of bed erosion and sediment deposition, which leave historical records of the actual ice-sheet formation. It is suggested that erosion and sediment deposition is minimal over the Ronne region and considerable along the path from Ellsworth Land to the Filchner region, because more ice flows toward the Filchner region than the Ronne region. It is probably difficult for ice to ground over the Ross region, so this region should have a high proportion of glacial marine sediments.

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Yasunari, T. J., P. Bonasoni, P. Laj, K. Fujita, E. Vuillermoz, A. Marinoni, P. Cristofanelli, R. Duchi, G. Tartari et K. M. Lau. « Estimated impact of black carbon deposition during pre-monsoon season from Nepal Climate Observatory – Pyramid data and snow albedo changes over Himalayan glaciers ». Atmospheric Chemistry and Physics 10, n^o 14 (19 juillet 2010) : 6603–15. http://dx.doi.org/10.5194/acp-10-6603-2010.

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Abstract. The possible minimal range of reduction in snow surface albedo due to dry deposition of black carbon (BC) in the pre-monsoon period (March–May) was estimated as a lower bound together with the estimation of its accuracy, based on atmospheric observations at the Nepal Climate Observatory – Pyramid (NCO-P) sited at 5079 m a.s.l. in the Himalayan region. A total BC deposition rate was estimated as 2.89 μg m−2 day−1 providing a total deposition of 266 μg m−2 for March–May at the site, based on a calculation with a minimal deposition velocity of 1.0×10−4 m s−1 with atmospheric data of equivalent BC concentration. Main BC size at NCO-P site was determined as 103.1–669.8 nm by correlation analyses between equivalent BC concentration and particulate size distributions in the atmosphere. The BC deposition from the size distribution data was also estimated. It was found that 8.7% of the estimated dry deposition corresponds to the estimated BC deposition from equivalent BC concentration data. If all the BC is deposited uniformly on the top 2-cm pure snow, the corresponding BC concentration is 26.0–68.2 μg kg−1, assuming snow density variations of 195–512 kg m−3 of Yala Glacier close to NCO-P site. Such a concentration of BC in snow could result in 2.0–5.2% albedo reductions. By assuming these albedo reductions continue throughout the year, and then applying simple numerical experiments with a glacier mass balance model, we estimated reductions would lead to runoff increases of 70–204 mm of water. This runoff is the equivalent of 11.6–33.9% of the annual discharge of a typical Tibetan glacier. Our estimates of BC concentration in snow surface for pre-monsoon season is comparable to those at similar altitudes in the Himalayan region, where glaciers and perpetual snow regions begin, in the vicinity of NCO-P. Our estimates from only BC are likely to represent a lower bound for snow albedo reductions, because we used a fixed slower deposition velocity. In addition, we excluded the effects of atmospheric wind and turbulence, snow aging, dust deposition, and snow albedo feedbacks. This preliminary study represents the first investigation of BC deposition and related albedo on snow, using atmospheric aerosol data observed at the southern slope in the Himalayas.

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Salamatin, Andrey N., Vladimir Ya Lipenkov et Paul Duval. « Bubbly-ice densification in ice sheets : I. Theory ». Journal of Glaciology 43, n^o 145 (1997) : 387–96. http://dx.doi.org/10.3189/s0022143000034961.

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AbstractDry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn. Bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure. This stage extends to the transition zone where, due to high pressures and low temperatures. air trapped in bubbles and ice begins to form the mixed air clathrate hydrates, while the gas phase progressively disappears. Here we develop a model of bubbly-ice rheology and ice-sheet dynamics taking into account glacier-ice compressibility. The interaction between hydrostatic compression of air bubbles, deviatoric (uniaxial) compressive deformation of the ice matrix and global deformations of the glacier body is considered. The ice-matrix pressure and the absolute-load pressure are distinguished. Similarity theory and scale analysis are used in examine the resultant mathematical model of bubbly-ice densification. The initial rate of bubble compression in ice sheets appears to be relatively high, so that the pressure (density) relaxation process takes place only 150-200 m in depth (below pore close-off) to reach its asymptotic phase, wherein the minimal drop between bubble and ice pressures is governed by the rate of loading (ice accumulation). This makes it possible to consider densification under stationary (present-day) conditions of ice formation as a special case of primary interest. The computational tests performed with the model indicate that both ice-porosity and bubble-pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice. However, only the bubble-pressure distinguishes between the rheological properties at low and high stresses. The porosity profile at the asymptotic phase is mostly determined by the air content in the ice. In the companion paper (Lipenkov and others, 1997), we apply the model to experimental data from polar ice cores and deduce, through an inverse procedure, the rhelogical properties of pure ice as well as the mean air content in Holocene and glacial ice sediments at vostok Station (Antarctica).

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Salamatin, Andrey N., Vladimir Ya Lipenkov et Paul Duval. « Bubbly-ice densification in ice sheets : I. Theory ». Journal of Glaciology 43, n^o 145 (1997) : 387–96. http://dx.doi.org/10.1017/s0022143000034961.

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AbstractDry snow on the surface of polar ice ice sheets is first densified and metamorphosed to produce firn. Bubbly ice is the next stage of the transformation process which takes place below the depth of pore closure. This stage extends to the transition zone where, due to high pressures and low temperatures. air trapped in bubbles and ice begins to form the mixed air clathrate hydrates, while the gas phase progressively disappears. Here we develop a model of bubbly-ice rheology and ice-sheet dynamics taking into account glacier-ice compressibility. The interaction between hydrostatic compression of air bubbles, deviatoric (uniaxial) compressive deformation of the ice matrix and global deformations of the glacier body is considered. The ice-matrix pressure and the absolute-load pressure are distinguished. Similarity theory and scale analysis are used in examine the resultant mathematical model of bubbly-ice densification. The initial rate of bubble compression in ice sheets appears to be relatively high, so that the pressure (density) relaxation process takes place only 150-200 m in depth (below pore close-off) to reach its asymptotic phase, wherein the minimal drop between bubble and ice pressures is governed by the rate of loading (ice accumulation). This makes it possible to consider densification under stationary (present-day) conditions of ice formation as a special case of primary interest. The computational tests performed with the model indicate that both ice-porosity and bubble-pressure profiles in ice sheets are sensitive to variations of the rheological parameters of pure ice. However, only the bubble-pressure distinguishes between the rheological properties at low and high stresses. The porosity profile at the asymptotic phase is mostly determined by the air content in the ice. In the companion paper (Lipenkov and others, 1997), we apply the model to experimental data from polar ice cores and deduce, through an inverse procedure, the rhelogical properties of pure ice as well as the mean air content in Holocene and glacial ice sediments at vostok Station (Antarctica).

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Damsgaard, A., D. L. Egholm, J. A. Piotrowski, S. Tulaczyk, N. K. Larsen et C. F. Brædstrup. « A new methodology to simulate subglacial deformation of water-saturated granular material ». Cryosphere 9, n^o 6 (20 novembre 2015) : 2183–200. http://dx.doi.org/10.5194/tc-9-2183-2015.

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Abstract. The dynamics of glaciers are to a large degree governed by processes operating at the ice–bed interface, and one of the primary mechanisms of glacier flow over soft unconsolidated sediments is subglacial deformation. However, it has proven difficult to constrain the mechanical response of subglacial sediment to the shear stress of an overriding glacier. In this study, we present a new methodology designed to simulate subglacial deformation using a coupled numerical model for computational experiments on grain-fluid mixtures. The granular phase is simulated on a per-grain basis by the discrete element method. The pore water is modeled as a compressible Newtonian fluid without inertia. The numerical approach allows close monitoring of the internal behavior under a range of conditions. Our computational experiments support the findings of previous studies where the rheology of a slowly deforming water-saturated granular bed in the steady state generally conforms to the rate-independent plastic rheology. Before this so-called critical state, deformation is in many cases accompanied by volumetric changes as grain rearrangement in active shear zones changes the local porosity. For previously consolidated beds porosity increases can cause local pore-pressure decline, dependent on till permeability and shear rate. We observe that the pore-water pressure reduction strengthens inter-granular contacts, which results in increased shear strength of the granular material. In contrast, weakening takes place when shear deformation causes consolidation of dilated sediments or during rapid fabric development. Both processes of strengthening and weakening depend inversely on the sediment permeability and are transient phenomena tied to the porosity changes during the early stages of shear. We find that the transient strengthening and weakening in turn influences the distribution of shear strain in the granular bed. Dilatant strengthening has the ability to distribute strain during early deformation to large depths, if sediment dilatancy causes the water pressure at the ice–bed interface to decline. Oppositely, if the ice–bed interface is hydrologically stable the strengthening process is minimal and instead causes shallow deformation. The depth of deformation in subglacial beds thus seems to be governed by not only local grain and pore-water feedbacks but also larger-scale hydrological properties at the ice base.

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Berg, Brandon, et Jeremy Bassis. « Brief communication : Time step dependence (and fixes) in Stokes simulations of calving ice shelves ». Cryosphere 14, n^o 9 (22 septembre 2020) : 3209–13. http://dx.doi.org/10.5194/tc-14-3209-2020.

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Abstract. The buoyancy boundary condition applied to floating portions of ice sheets and glaciers in Stokes models requires special consideration when the glacier rapidly departs from hydrostatic equilibrium. This boundary condition can manifest in velocity fields that are unphysically (and strongly) dependent on time step size, thereby contaminating diagnostic stress fields. This can be especially problematic for models of calving glaciers, where rapid changes in geometry cause configurations that suddenly depart from hydrostatic equilibrium and lead to inaccurate estimates of the stress field. Here we show that the unphysical behavior can be cured with minimal computational cost by reintroducing a regularization that corresponds to the acceleration term in the stress balance. This regularization provides consistent velocity solutions for all time step sizes.

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Cutler, Paul M., et D. Scott Munro. « Visible and near-infrared reflectivity during the ablation period on Peyto Glacier, Alberta, Canada ». Journal of Glaciology 42, n^o 141 (1996) : 333–40. http://dx.doi.org/10.1017/s0022143000004184.

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AbstractModels for calculating glacier mass balance are sensitive to surface reflectivity variation. Fieldwork carried out on Peyto Glacier, Alberta, Canada, contributes to the data set available for ice-reflectivity parameterization in such models. Hemispherical reflectivity in the visible and near-infrared parts of the solar spectrum was obtained for rock, snow and three contrasting glacier surfaces to examine temporal and spatial variations. Glacier-ice near-infrared reflectivity displays only minor spatial variation (0.12–0.17) in comparison with the visible range (0.23–0.40), the latter being influenced primarily by surface impurity content. Surface roughness is of minor importance compared with impurities. Temporal variation of reflectivity was weak at all glacier-ice and rock locations; slight variations observed were due to changes in either solar zenith angle or cloud amount. Snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover. The minimal temporal variation in glacier-ice reflectivity simplifies its parameterization. This behaviour is additionally useful for satellite-based measurements of the reflectivity field on larger glaciers, as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2–3% of daily mean values.

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Cutler, Paul M., et D. Scott Munro. « Visible and near-infrared reflectivity during the ablation period on Peyto Glacier, Alberta, Canada ». Journal of Glaciology 42, n^o 141 (1996) : 333–40. http://dx.doi.org/10.3189/s0022143000004184.

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AbstractModels for calculating glacier mass balance are sensitive to surface reflectivity variation. Fieldwork carried out on Peyto Glacier, Alberta, Canada, contributes to the data set available for ice-reflectivity parameterization in such models. Hemispherical reflectivity in the visible and near-infrared parts of the solar spectrum was obtained for rock, snow and three contrasting glacier surfaces to examine temporal and spatial variations. Glacier-ice near-infrared reflectivity displays only minor spatial variation (0.12–0.17) in comparison with the visible range (0.23–0.40), the latter being influenced primarily by surface impurity content. Surface roughness is of minor importance compared with impurities. Temporal variation of reflectivity was weak at all glacier-ice and rock locations; slight variations observed were due to changes in either solar zenith angle or cloud amount. Snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover. The minimal temporal variation in glacier-ice reflectivity simplifies its parameterization. This behaviour is additionally useful for satellite-based measurements of the reflectivity field on larger glaciers, as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2–3% of daily mean values.

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Wilson, L., et J. W. Head. « Heat transfer in volcano–ice interactions on Earth ». Annals of Glaciology 45 (2007) : 83–86. http://dx.doi.org/10.3189/172756407782282507.

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AbstractThe very high temperature contrast between magma/ lava and water ice commonly leads to the assumption that significant melting will take place immediately upon magma/ lava ice contact, yet observations of active flows show little evidence of voluminous melting upon contact. We use analytical thermal models to reassess the efficiency with which heat can be transferred from magma to ice in three situations: lava flows erupted on top of glacial ice, sill intrusions beneath glacial ice evolving into subglacial lava flows and dyke intrusions into the interiors of glaciers. We find that the maximum ratios of thickness of ice that can be melted to the thickness of magmatic heat source are likely to be ∽2–5 for subaerial lava flows encroaching onto glaciers, ∽6–7 for subglacial lava flows and ∽10 for dykes intruded into glacial ice. Rates of ice melt production are not linear functions of time and flow thickness, however, and this may account for the observations of minimal immediate water release from beneath advancing lava flows. Field observations during future eruptions should be directed at measuring the temperature of released water.

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Ioli, Francesco, Alberto Bianchi, Alberto Cina, Carlo De Michele, Paolo Maschio, Daniele Passoni et Livio Pinto. « Mid-Term Monitoring of Glacier’s Variations with UAVs : The Example of the Belvedere Glacier ». Remote Sensing 14, n^o 1 (22 décembre 2021) : 28. http://dx.doi.org/10.3390/rs14010028.

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Recently, Unmanned Aerial Vehicles (UAV) have opened up unparalleled opportunities for alpine glacier monitoring, as they allow for reconstructing extensive and high-resolution 3D models. In order to evaluate annual ice flow velocities and volume variations, six yearly measurements were carried out between 2015 and 2020 on the debris-covered Belvedere Glacier (Anzasca Valley, Italian Alps) with low-cost fixed-wing UAVs and quadcopters. Every year, ground control points and check points were measured with GNSS. Images acquired from UAV were processed with Structure-from-Motion and Multi-View Stereo algorithms to build photogrammetric models, orthophotos and digital surface models, with decimetric accuracy. Annual glacier velocities were derived by combining manually-tracked features on orthophotos with GNSS measurements. Velocities ranging between 17 m y−1 and 22 m y−1 were found in the central part of the glacier, whereas values between 2 m y−1 and 7 m y−1 were found in the accumulation area and at the glacier terminus. Between 2 × 106 m3 and 3.5 × 106 m3 of ice volume were lost every year. A pair of intra-year measurements (October 2017–July 2018) highlighted that winter and spring volume reduction was ∼1/4 of the average annual ice loss. The Belvedere monitoring activity proved that decimetric-accurate glacier models can be derived with low-cost UAVs and photogrammetry, limiting in-situ operations. Moreover, UAVs require minimal data acquisition costs and allow for great surveying flexibility, compared to traditional techniques. Information about annual flow velocities and ice volume variations of the Belvedere Glacier may have great value for further understanding glacier dynamics, compute mass balances, or it might be used as input for glacier flow modelling.

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Mayewski, Paul A., W. Berry Lyons, M. J. Spencer, Mark S. Twickler, Pieter M. Grootes et Minze Stuiver. « A Climatic Record Using An Ice Core from the Transantarctic Mountains, Antarctica (Abstract) ». Annals of Glaciology 10 (1988) : 211. http://dx.doi.org/10.3189/s0260305500004572.

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The production of climatic-change records using glaciochemical time series has seen minimal application in the Transantarctic Mountains. This is true despite the fact that glacial geologic studies in this area are the primary basis for understanding the glacial history of East Antarctica and thus provide an excellent potential framework for the more detailed records obtainable from glaciochemical studies. Numerous sites within the Transantarctic Mountains fit the requirements necessary for the retrieval of ice cores, and pilot studies have been conducted in both southern Victoria Land (Mayewski and Lyons 1982) and northern Victoria Land (Allen and others 1985). These pilot studies have validated the hypothesis that glaciochemical records retrieved from appropriately chosen ice-core sites in the Transantarctic Mountains can be used for: (1) assessing the current stability of the East Antarctic ice sheet, (2) validating models concerning the recent glacial history of the Transantarctic Mountains, (3) searching for relatively high-frequency (1–100 year) climatic signals, (4) determining changes in the relative geography (ocean – land – ice) of a region, and (5) defining the relative importance of the chemical species source areas (i.e. volcanic, biogenic, anthropogenic, marine, crustal) that provide precipitation to the Transantarctic Mountains.During the 1984–85 austral summer, a combined University of New Hampshire – Polar Ice Coring Office effort resulted in the recovery of a 201 m long core from a 2800 m high snow massif atop the Dominion Range (85°15'S, 166°10'E), close to the confluence of the Mill and Beardmore glaciers. Chemical and physical data sets to be developed from this ice core, which is estimated to span a period of approximately 1000 years, include: a detailed 6 m snow pit, several shallow snow pits, and fresh and aged surface snow, in combination with a radio echo-sounding survey of the general area, which will be used to provide three-dimensional control. Chemical and physical analyses conducted as part of the study include: stratigraphy, density, sulfate, nitrate, fluoride, chloride, phosphate, sodium, reactive silicate, total beta activity and oxygen isotopes. The oxygen-isotope analyses are being provided by P. Grootes and M. Stuiver (University of Washington), and all other analyses are being conducted by the Glacier Research Group (University of New Hampshire).

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Mayewski, Paul A., W. Berry Lyons, M. J. Spencer, Mark S. Twickler, Pieter M. Grootes et Minze Stuiver. « A Climatic Record Using An Ice Core from the Transantarctic Mountains, Antarctica (Abstract) ». Annals of Glaciology 10 (1988) : 211. http://dx.doi.org/10.1017/s0260305500004572.

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The production of climatic-change records using glaciochemical time series has seen minimal application in the Transantarctic Mountains. This is true despite the fact that glacial geologic studies in this area are the primary basis for understanding the glacial history of East Antarctica and thus provide an excellent potential framework for the more detailed records obtainable from glaciochemical studies. Numerous sites within the Transantarctic Mountains fit the requirements necessary for the retrieval of ice cores, and pilot studies have been conducted in both southern Victoria Land (Mayewski and Lyons 1982) and northern Victoria Land (Allen and others 1985). These pilot studies have validated the hypothesis that glaciochemical records retrieved from appropriately chosen ice-core sites in the Transantarctic Mountains can be used for: (1) assessing the current stability of the East Antarctic ice sheet, (2) validating models concerning the recent glacial history of the Transantarctic Mountains, (3) searching for relatively high-frequency (1–100 year) climatic signals, (4) determining changes in the relative geography (ocean – land – ice) of a region, and (5) defining the relative importance of the chemical species source areas (i.e. volcanic, biogenic, anthropogenic, marine, crustal) that provide precipitation to the Transantarctic Mountains. During the 1984–85 austral summer, a combined University of New Hampshire – Polar Ice Coring Office effort resulted in the recovery of a 201 m long core from a 2800 m high snow massif atop the Dominion Range (85°15'S, 166°10'E), close to the confluence of the Mill and Beardmore glaciers. Chemical and physical data sets to be developed from this ice core, which is estimated to span a period of approximately 1000 years, include: a detailed 6 m snow pit, several shallow snow pits, and fresh and aged surface snow, in combination with a radio echo-sounding survey of the general area, which will be used to provide three-dimensional control. Chemical and physical analyses conducted as part of the study include: stratigraphy, density, sulfate, nitrate, fluoride, chloride, phosphate, sodium, reactive silicate, total beta activity and oxygen isotopes. The oxygen-isotope analyses are being provided by P. Grootes and M. Stuiver (University of Washington), and all other analyses are being conducted by the Glacier Research Group (University of New Hampshire).

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Adhikari, S., E. R. Ivins et E. Larour. « ISSM-SESAW v1.0 : mesh-based computation of gravitationally consistent sea level and geodetic signatures caused by cryosphere and climate driven mass change ». Geoscientific Model Development Discussions 8, n^o 11 (10 novembre 2015) : 9769–816. http://dx.doi.org/10.5194/gmdd-8-9769-2015.

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Abstract. A classical Green's function approach to computing gravitationally consistent sea level variations, following mass redistribution on the earth surface, employed in contemporary state-of-the-art sea-level models naturally suits the spectral methods for numerical evaluation. The capability of these methods to resolve high wave number features such as small glaciers is limited by the need for large numbers of pixels and high-degree (associated Legendre) series truncation. Incorporating a spectral model into (components of) earth system models that generally operate on an unstructured mesh system also requires cumbersome and repetitive forward and inverse transform of solutions. In order to overcome these limitations of contemporary models, we present a novel computational method that functions efficiently on a flexible mesh system, thus capturing the physics operating at kilometer-scale yet capable of simulating geophysical observables that are inherently of global scale with minimal computational cost. The model has numerous important geophysical applications. Coupling to a local mesh of 3-D ice-sheet model, for example, allows for a refined and realistic simulation of fast-flowing outlet glaciers, while simultaneously retaining its global predictive capability. As an example model application, we provide time-varying computations of global geodetic and sea level signatures associated with recent ice sheet changes that are derived from space gravimetry observations.

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Zhao, Hang, Meimei Zhang et Fang Chen. « GAN-GL : Generative Adversarial Networks for Glacial Lake Mapping ». Remote Sensing 13, n^o 22 (22 novembre 2021) : 4728. http://dx.doi.org/10.3390/rs13224728.

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Remote sensing is a powerful tool that provides flexibility and scalability for monitoring and investigating glacial lakes in High Mountain Asia (HMA). However, existing methods for mapping glacial lakes are designed based on a combination of several spectral features and ancillary data (such as the digital elevation model, DEM) to highlight the lake extent and suppress background information. These methods, however, suffer from either the inevitable requirement of post-processing work or the high costs of additional data acquisition. Signifying a key advancement in the deep learning models, a generative adversarial network (GAN) can capture multi-level features and learn the mapping rules in source and target domains using a minimax game between a generator and discriminator. This provides a new and feasible way to conduct large-scale glacial lake mapping. In this work, a complete glacial lake dataset was first created, containing approximately 4600 patches of Landsat-8 OLI images edited in three ways—random cropping, density cropping, and uniform cropping. Then, a GAN model for glacial lake mapping (GAN-GL) was constructed. The GAN-GL consists of two parts—a generator that incorporates a water attention module and an image segmentation module to produce the glacial lake masks, and a discriminator which employs the ResNet-152 backbone to ascertain whether a given pixel belonged to a glacial lake. The model was evaluated using the created glacial lake dataset, delivering a good performance, with an F1 score of 92.17% and IoU of 86.34%. Moreover, compared to the mapping results derived from the global–local iterative segmentation algorithm and random forest for the entire Eastern Himalayas, our proposed model was superior regarding the segmentation of glacial lakes under complex and diverse environmental conditions, in terms of accuracy (precision = 93.19%) and segmentation efficiency. Our model was also very good at detecting small glacial lakes without assistance from ancillary data or human intervention.

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Bocchiola, D., G. Diolaiuti, A. Soncini, C. Mihalcea, C. D'Agata, C. Mayer, A. Lambrecht, R. Rosso et C. Smiraglia. « Prediction of future hydrological regimes in poorly gauged high altitude basins : the case study of the upper Indus, Pakistan ». Hydrology and Earth System Sciences 15, n^o 7 (4 juillet 2011) : 2059–75. http://dx.doi.org/10.5194/hess-15-2059-2011.

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Abstract. In the mountain regions of the Hindu Kush, Karakoram and Himalaya (HKH) the "third polar ice cap" of our planet, glaciers play the role of "water towers" by providing significant amount of melt water, especially in the dry season, essential for agriculture, drinking purposes, and hydropower production. Recently, most glaciers in the HKH have been retreating and losing mass, mainly due to significant regional warming, thus calling for assessment of future water resources availability for populations down slope. However, hydrology of these high altitude catchments is poorly studied and little understood. Most such catchments are poorly gauged, thus posing major issues in flow prediction therein, and representing in fact typical grounds of application of PUB concepts, where simple and portable hydrological modeling based upon scarce data amount is necessary for water budget estimation, and prediction under climate change conditions. In this preliminarily study, future (2060) hydrological flows in a particular watershed (Shigar river at Shigar, ca. 7000 km2), nested within the upper Indus basin and fed by seasonal melt from major glaciers, are investigated. The study is carried out under the umbrella of the SHARE-Paprika project, aiming at evaluating the impact of climate change upon hydrology of the upper Indus river. We set up a minimal hydrological model, tuned against a short series of observed ground climatic data from a number of stations in the area, in situ measured ice ablation data, and remotely sensed snow cover data. The future, locally adjusted, precipitation and temperature fields for the reference decade 2050–2059 from CCSM3 model, available within the IPCC's panel, are then fed to the hydrological model. We adopt four different glaciers' cover scenarios, to test sensitivity to decreased glacierized areas. The projected flow duration curves, and some selected flow descriptors are evaluated. The uncertainty of the results is then addressed, and use of the model for nearby catchments discussed. The proposed approach is valuable as a tool to investigate the hydrology of poorly gauged high altitude areas, and to project forward their hydrological behavior pending climate change.

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Bocchiola, D., G. Diolaiuti, A. Soncini, C. Mihalcea, C. D'Agata, C. Mayer, A. Lambrecht, R. Rosso et C. Smiraglia. « Prediction of future hydrological regimes in poorly gauged high altitude basins : the case study of the upper Indus, Pakistan ». Hydrology and Earth System Sciences Discussions 8, n^o 2 (15 avril 2011) : 3743–91. http://dx.doi.org/10.5194/hessd-8-3743-2011.

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Abstract. In the mountain regions of the Hindu Kush, Karakoram and Himalaya (HKH) the "third polar ice cap" of our planet, glaciers play the role of "water towers" by providing significant amount of melt water, especially in the dry season, essential for agriculture, drinking purposes, and hydropower production. Recently, most glaciers in the HKH have been retreating and losing mass, mainly due to significant regional warming, thus calling for assessment of future water resources availability for populations down slope. However, hydrology of these high altitude catchments is poorly studied and little understood. Most such catchments are poorly gauged, thus posing major issues in flow prediction therein, and representing in facts typical grounds of application of PUB concepts, where simple and portable hydrological modeling based upon scarce data amount is necessary for water budget estimation, and prediction under climate change conditions. In this preliminarily study, future (2060) hydrological flows in a particular watershed (Shigar river at Shigar, ca. 7000 km2), nested within the upper Indus basin and fed by seasonal melt from major glaciers, are investigated. The study is carried out under the umbrella of the SHARE-Paprika project, aiming at evaluating the impact of climate change upon hydrology of the upper Indus river. We set up a minimal hydrological model, tuned against a short series of observed ground climatic data from a number of stations in the area, in situ measured ice ablation data, and remotely sensed snow cover data. The future, locally adjusted, precipitation and temperature fields for the reference decade 2050–2059 from CCSM3 model, available within the IPCC's panel, are then fed to the hydrological model. We adopt four different glaciers' cover scenarios, to test sensitivity to decreased glacierized areas. The projected flow duration curves, and some selected flow descriptors are evaluated. The uncertainty of the results is then addressed, and use of the model for nearby catchments discussed. The proposed approach is valuable as a tool to investigate the hydrology of poorly gauged high altitude areas, and to project forward their hydrological behavior pending climate change.

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Christensen, Steen. « Hydrological Model for the Tude Å Catchment ». Hydrology Research 25, n^o 3 (1 juin 1994) : 145–66. http://dx.doi.org/10.2166/nh.1994.0001.

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A numerical hydrological model has been developed for a 450 km2 Danish catchment using comprehensive field data. The model integrates a simple evapotranspiration model, a lumped flow model for a phreatic aquifer found in till, and a traditional two-dimensional groundwater model for a confined fluvio-glacial aquifer. A minimal but adequate number of model parameters were calibrated by trial and error to make the model fit 29-year time series of hydraulic head and stream runoff data. By simulating a “semi-natural” hydrological situation unaffected by withdrawals it is demonstrated that groundwater development can change the water balance considerably. In the actual case withdrawals induce a 25% increase in leakage from the phreatic to the confined aquifer, and reduce stream base flow by up to 30% in normal years, and up to 35% in dry years. On the other hand the reduction in base flow is considerably smaller for the upper stream catchments.

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Adhikari, Surendra, Erik R. Ivins et Eric Larour. « ISSM-SESAW v1.0 : mesh-based computation of gravitationally consistent sea-level and geodetic signatures caused by cryosphere and climate driven mass change ». Geoscientific Model Development 9, n^o 3 (18 mars 2016) : 1087–109. http://dx.doi.org/10.5194/gmd-9-1087-2016.

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Abstract. A classical Green's function approach for computing gravitationally consistent sea-level variations associated with mass redistribution on the earth's surface employed in contemporary sea-level models naturally suits the spectral methods for numerical evaluation. The capability of these methods to resolve high wave number features such as small glaciers is limited by the need for large numbers of pixels and high-degree (associated Legendre) series truncation. Incorporating a spectral model into (components of) earth system models that generally operate on a mesh system also requires repetitive forward and inverse transforms. In order to overcome these limitations, we present a method that functions efficiently on an unstructured mesh, thus capturing the physics operating at kilometer scale yet capable of simulating geophysical observables that are inherently of global scale with minimal computational cost. The goal of the current version of this model is to provide high-resolution solid-earth, gravitational, sea-level and rotational responses for earth system models operating in the domain of the earth's outer fluid envelope on timescales less than about 1 century when viscous effects can largely be ignored over most of the globe. The model has numerous important geophysical applications. For example, we compute time-varying computations of global geodetic and sea-level signatures associated with recent ice-sheet changes that are derived from space gravimetry observations. We also demonstrate the capability of our model to simultaneously resolve kilometer-scale sources of the earth's time-varying surface mass transport, derived from high-resolution modeling of polar ice sheets, and predict the corresponding local and global geodetic signatures.

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Krapp, Mario, Alexander Robinson et Andrey Ganopolski. « SEMIC : an efficient surface energy and mass balance model applied to the Greenland ice sheet ». Cryosphere 11, n^o 4 (3 juillet 2017) : 1519–35. http://dx.doi.org/10.5194/tc-11-1519-2017.

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Abstract. We present SEMIC, a Surface Energy and Mass balance model of Intermediate Complexity for snow- and ice-covered surfaces such as the Greenland ice sheet. SEMIC is fast enough for glacial cycle applications, making it a suitable replacement for simpler methods such as the positive degree day (PDD) method often used in ice sheet modelling. Our model explicitly calculates the main processes involved in the surface energy and mass balance, while maintaining a simple interface and requiring minimal data input to drive it. In this novel approach, we parameterise diurnal temperature variations in order to more realistically capture the daily thaw–freeze cycles that characterise the ice sheet mass balance. We show how to derive optimal model parameters for SEMIC specifically to reproduce surface characteristics and day-to-day variations similar to the regional climate model MAR (Modèle Atmosphérique Régional, version 2) and its incorporated multilayer snowpack model SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer). A validation test shows that SEMIC simulates future changes in surface temperature and surface mass balance in good agreement with the more sophisticated multilayer snowpack model SISVAT included in MAR. With this paper, we present a physically based surface model to the ice sheet modelling community that is general enough to be used with in situ observations, climate model, or reanalysis data, and that is at the same time computationally fast enough for long-term integrations, such as glacial cycles or future climate change scenarios.

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PIASECKI, Adam, Jakub JURASZ et Rajmund SKOWRON. « FORECASTING SURFACE WATER LEVEL FLUCTUATIONS OF LAKE SERWY (NORTHEASTERN POLAND) BY ARTIFICIAL NEURAL NETWORKS AND MULTIPLE LINEAR REGRESSION ». Journal of Environmental Engineering and Landscape Management 25, n^o 4 (21 décembre 2017) : 379–88. http://dx.doi.org/10.3846/16486897.2017.1303498.

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The aim of this study is to assess the possibility of forecasting water level fluctuations in a relatively small (<100 km2), post-glacial lake located in a temperate climate zone by means of artificial neural networks and multiple linear regression. The area of study was Lake Serwy, located in northeastern Poland. Two artificial neural network (ANN) multilayer perceptron (MLP) and multiple linear regression (MLR) models were built. The following explanatory variables were considered: maximal and minimal temperature (Tmax, Tmin) wind speed (WS), vertical circulation (VC) and water level from previous periods (WL). Additionally, a binary variable describing the period of the year (winter, summer) has been considered in one of the two MLP and MLR models. The forecasting models have been assessed based on selected criteria: mean absolute percentage error (MAPE), root mean squared error (RMSE), coefficient of determination (R2) and mean biased error. Considering their values and absolute deviations from observed values it was concluded that the ANN model using an additional binary variable (MLP_B+) has the best forecasting performance. Absolute deviations from observed values were the determining factor which made this model the most efficient. In the case of the MLP_B+ model, those values were about 10% lower than in other models. The conducted analyses indicated good performance of ANN networks as a forecasting tool for relatively small lakes located in temperate climate zones. It is acknowledged that they enable water level forecasting with greater precision and lower absolute deviations than the use of multiple linear regression models.

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Kreuzer, Moritz, Ronja Reese, Willem Nicholas Huiskamp, Stefan Petri, Torsten Albrecht, Georg Feulner et Ricarda Winkelmann. « Coupling framework (1.0) for the PISM (1.1.4) ice sheet model and the MOM5 (5.1.0) ocean model via the PICO ice shelf cavity model in an Antarctic domain ». Geoscientific Model Development 14, n^o 6 (22 juin 2021) : 3697–714. http://dx.doi.org/10.5194/gmd-14-3697-2021.

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Abstract. The past and future evolution of the Antarctic Ice Sheet is largely controlled by interactions between the ocean and floating ice shelves. To investigate these interactions, coupled ocean and ice sheet model configurations are required. Previous modelling studies have mostly relied on high-resolution configurations, limiting these studies to individual glaciers or regions over short timescales of decades to a few centuries. We present a framework to couple the dynamic ice sheet model PISM (Parallel Ice Sheet Model) with the global ocean general circulation model MOM5 (Modular Ocean Model) via the ice shelf cavity model PICO (Potsdam Ice-shelf Cavity mOdel). As ice shelf cavities are not resolved by MOM5 but are parameterized with the PICO box model, the framework allows the ice sheet and ocean components to be run at resolutions of 16 km and 3∘ respectively. This approach makes the coupled configuration a useful tool for the analysis of interactions between the Antarctic Ice Sheet and the global ocean over time spans of the order of centuries to millennia. In this study, we describe the technical implementation of this coupling framework: sub-shelf melting in the ice sheet component is calculated by PICO from modelled ocean temperatures and salinities at the depth of the continental shelf, and, vice versa, the resulting mass and energy fluxes from melting at the ice–ocean interface are transferred to the ocean component. Mass and energy fluxes are shown to be conserved to machine precision across the considered component domains. The implementation is computationally efficient as it introduces only minimal overhead. Furthermore, the coupled model is evaluated in a 4000 year simulation under constant present-day climate forcing and is found to be stable with respect to the ocean and ice sheet spin-up states. The framework deals with heterogeneous spatial grid geometries, varying grid resolutions, and timescales between the ice and ocean component in a generic way; thus, it can be adopted to a wide range of model set-ups.

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Stuiver, Minze, Thomas F. Braziunas, Bernd Becker et Bernd Kromer. « Climatic, Solar, Oceanic, and Geomagnetic Influences on Late-Glacial and Holocene Atmospheric 14C/12C Change ». Quaternary Research 35, n^o 1 (janvier 1991) : 1–24. http://dx.doi.org/10.1016/0033-5894(91)90091-i.

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AbstractLate-glacial and Holocene 14C/12C ratios of atmospheric CO2 vary in magnitude from a few per mil for annual/decadal pertubations to more than 10% for events lasting millennia. A data set illuminating 10- to 104-yr variability refines our understanding of oceanic (climatic) versus geomagnetic or solar forcing of atmospheric 14C/12C ratios. Most of the variance in the Holocene atmospheric 14C/12C record can be attributed to the geomagnetic (millennia time scale) and solar (century time scale) influence on the flux of primary cosmic rays entering the atmosphere. Attributing the observed atmospheric 14C/12C changes to climate alone leads to ocean circulation and/or global wind speed changes incompatible with proxy records. Climate-(ocean-)related 14C redistribution between carbon reservoirs, while evidently playing a minor role during the Holocene, may have perturbed atmospheric 14C/12C ratios measurably during the late-glacial Younger Dryas event. First-order corrections to the radiocarbon time scale (12,000–30,000 14C yr B.P.) are calculated from adjusted lake-sediment and tree-ring records and from geomagnetically defined model 14C histories. Paleosunspot numbers (100–9700 cal yr B.P.) are derived from the relationship of model 14C production rates to sunspot observations. The spectral interpretation of the 14C/12C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.

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Hodgson, Dominic A., Elie Verleyen, Koen Sabbe, Angela H. Squier, Brendan J. Keely, Melanie J. Leng, Krystyna M. Saunders et Wim Vyverman. « Late Quaternary climate-driven environmental change in the Larsemann Hills, East Antarctica, multi-proxy evidence from a lake sediment core ». Quaternary Research 64, n^o 1 (juillet 2005) : 83–99. http://dx.doi.org/10.1016/j.yqres.2005.04.002.

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AbstractLittle is known about the response of terrestrial East Antarctica to climate changes during the last glacialâ€“interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.

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Rej, Julie E., et T. Andrew Joyner. « Niche modeling for the genus Pogona (Squamata : Agamidae) in Australia : predicting past (late Quaternary) and future (2070) areas of suitable habitat ». PeerJ 6 (17 décembre 2018) : e6128. http://dx.doi.org/10.7717/peerj.6128.

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Background As the climate warms, many species of reptiles are at risk of habitat loss and ultimately extinction. Locations of suitable habitat in the past, present, and future were modeled for several lizard species using MaxEnt, incorporating climatic variables related to temperature and precipitation. In this study, we predict where there is currently suitable habitat for the genus Pogona and potential shifts in habitat suitability in the past and future. Methods Georeferenced occurrence records were obtained from the Global Biodiversity Information Facility, climate variables (describing temperature and precipitation) were obtained from WorldClim, and a vegetation index was obtained from AVHRR satellite data. Matching climate variables were downloaded for three different past time periods (mid-Holocene, Last Glacial Maximum, and Last Interglacial) and two different future projections representative concentration pathways (RCPs 2.6 and 8.5). MaxEnt produced accuracy metrics, response curves, and probability surfaces. For each species, parameters were adjusted for the best possible output that was biologically informative. Results Model results predicted that in the past, there was little suitable habitat for P. henrylawsoni and P. microlepidota within the areas of their current range. Past areas of suitable habitat for P. barbata were predicted to be similar to the current prediction. Pogona minor and P. nullarbor were predicted to have had a more expansive range of suitable habitat in the past, which has reduced over time. P. vitticeps was predicted to have less suitable habitat in the past when examining the region of their known occurrence; however, there was predicted growth in suitable habitat in Western Australia. Both 2070 models predict a similar distribution of habitat; however, the model produced using the 2070 RCP 8.5 climate change projection showed a larger change, both in areas of suitable habitat gain and loss. In the future, P. henrylawsoni and P. microlepidota might gain suitable habitat, while the other four species could possibly suffer habitat loss. Discussion Based on the model results, P. henrylawsoni and P. microlepidota had minimal areas of suitable habitat during the Last Glacial Maximum, possibly due to changes in tolerance or data/model limitations, especially since genetic analyses for these species suggest a much earlier emergence. The predicted late Quaternary habitat results for all species of Pogona are conservative and should be compared to the fossil record which is not possible at the moment due to the current inability to identify fossil Pogona to the species level. P. nullarbor and P. vitticeps future models predict substantial habitat loss. P. nullarbor could potentially be considered vulnerable in the present since it already has a restricted range, and a conservation plan may need to be considered.

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Sümegi, Pál, Dávid Molnár, Sándor Gulyás, Thomas Stevens, László Makó, Péter Cseh, Mihály Molnár et al. « Comparison of High-Resolution 14C and Luminescence-Based Chronologies of the MIS 2 Madaras Loess/Paleosol Sequence, Hungary : Implications for Chronological Studies ». Quaternary 5, n^o 4 (10 novembre 2022) : 47. http://dx.doi.org/10.3390/quat5040047.

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Numerous loess/paleosol sequences (LPS) in the Carpathian Basin span the period of Marine Isotope Stage (MIS) 2 and the last glacial maximum (LGM). Nevertheless, only two known records—Madaras and Dunaszekcső—preserve highly resolved records with absolute chronologies with minimal uncertainties, which enable the meaningful assessment of feedbacks and short-term climatic fluctuations over this period. The Madaras profile is located at the northern margin fringe of the Bácska loess plateau; Dunaszekcső, located on the Danube to its west, yields a chronology built on over 100 14C dates yet spans only part of MIS 2, missing half of the LGM including its peak. Here, we add to the previously published 14C chronology for Madaras (15 dates) with an additional 17 14C and luminescence ages. Resulting age models built solely on quartz OSL and feldspar pIRIRSL data underestimate the 14C based chronology, which is likely based on inaccuracies related to luminescence signal behavior; we observe age underestimations associated with unusual quartz behavior and significant signal loss, a phenomenon also observed in Serbian and Romanian loess, which may relate to non-sensitized grains from proximal sources. Our new chronology provides higher resolution than hitherto possible, yielding consistent 2 sigma uncertainties of ~150–200 years throughout the entire sequence. Our study indicates that the addition of further dates may not increase the chronological precision significantly. Additionally, the new age model is suitable for tackling centennial-scale changes. The mean sedimentation rate based on our new age-depth model (10.78 ± 2.34 years/cm) is the highest yet recorded in the Carpathian Basin for MIS 2. The resolution of our age model is higher than that for the Greenland NGRIP ice core record. The referred horizons in our profile are all characterized by a drop in accumulation and a higher sand input, the latter most likely deriving from nearby re-exposed sand dunes.

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