Article

Willis MJ, Melkonian AK, Pritchard ME, Ramage JM. Ice loss rates at the northern Patagonian icefield derived using a decade of satellite remote sensing. Remote Sensing of Environment

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Abstract

We use a satellite-based survey of glacier surface elevation changes, speeds and surface melt conditions between 2000 and 2011 to quantify mass loss from the Northern Patagonian Icefield (NPI), Chile. A history of ice elevation change is found by differencing ASTER Digital Elevation Models (DEMs) relative to a void-filled version of the DEM collected by the Shuttle Radar Topography Mission (SRTM) in February 2000. Thinning rates have accelerated at lower elevations, while above the Equilibrium Line Altitude (ELA) recent thinning rates are not significantly different from those observed in previous studies. A volumetric change of − 4.06 ± 0.11 km³/yr is found by summing surface elevation changes over all glaciers in the NPI. This is regarded as a lower bound because volume loss due to frontal retreat and sub-aqueous melting is not included. This volume change is converted to a mass loss of 3.40 ± 0.07 Gt/yr, taking into account density differences above and below the equilibrium line. We find that the NPI is providing at least 0.009 ± 0.0002 mm/yr to ongoing sea level change, in agreement with previous estimates.

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... This elevation band is characterized by a flat and vast plateau, making the icefield surface mass balance particularly sensitive to shifts in the ELA in response to changes in temperature and accumulation. The NPI is formed by 140 units in the Randolph Glacier (RG) inventory (Pfeffer et al., 2014), including 38 main glaciers of different terminus types: one tidewater calving glacier (San Rafael Glacier (SRG) covering 18% of the total surface area of the NPI), 18 freshwater calving glaciers (64% of the total surface area) and 19 land-terminating glaciers (18% of the total surface area) (Rivera et al., 2007;Willis et al., 2012a;Pfeffer et al., 2014). A recent ice velocity mosaic reveals that fast flow regions extend far into the plateau in the accumulation area, making the icefield also potentially sensitive to dynamical changes (Mouginot and Rignot, 2015). ...
... (Aniya, 1988;Rignot et al., 1996;Rivera et al., 2007;Koppes et al., 2011;Schaefer et al., 2013). SRG is among the fastest glaciers in the world with frontal velocities exceeding 7 km a 1 (Willis et al., 2012a;Mouginot and Rignot, 2015). The SPI is located at the south of NPI between 48 S and 51.5 S and centered at 73.5 W ( Fig.1.6). ...
... More recently Rignot et al. (2003) proposed MB values of the icefields over the periods 1968/1975-2000 and 1995-2000 calculations for SPI, which can be due to a 2m correction applied by Willis et al. (2012a) to the SRTM-2000 DEM to consider the penetration of the radar signal within the firn (Foresta et al., 2018). Abdel Jaber ( ...
Thesis
The Northern Patagonia Icefield (NPI) have been losing mass at an accelerated rate during the last decades compared to the mean losses recorded since the Little Ice Age. Here we look for accurate estimates of the mean climate variables, surface mass balance (SMB) and ice dynamics of NPI. Due to the lack of available data in the area, the approach is based on physical models for both the atmosphere and the ice dynamics, in order to properly attribute the components of the glacial mass budget (mass balance, surface mass balance and ice discharge).First, the San Rafael Glacier (SRG) ice dynamics are modelled using the full-Stokes model Elmer/Ice. The flow model is initialised and constrained using the most up-to-date observations of surface velocities and bedrock elevation. The model is forced with several parametrisations of thealtitudinal SMB distribution to obtain consistency between the changes in SMB and ice dynamics. We show that previous studies have proposed excessive accumulation values on the icefield plateau, and that SRG imbalance is largely controlled by a large ice discharge (-0.83 +- 0.08 Gt/a compared to a slightly positive glacier-wide SMB (0.08 +- 0.06 Gt/a). This allows for an estimation of a committed mass loss of 0.34 +- 0.03 Gt/a for the next century. This value likely constitutes a minimum wastage in the future global climate change situation.Second, we model the SMB of the SRG and the NPI using the regional circulation model MAR (Modèle Atmosphérique Regional). This model is forced by the ERA-Interim reanalysis outputs and adapted to accurately reproduce accumulation on the icefield. In addition to accumulation, attention is paid to estimating accurate ablation and albedo values on the plateau. The modelled temperature and precipitation are also validated using data from weather stations in the valleys around the icefield. For the period 1980-2014, the modelled mean SMB of the SRG and the NPI are 0.86 Gt/a and -1.84 Gt/a, respectively, with a large inter-annual variability of 1.4 Gt/a and 6.1 Gt/a, which is induced by temperature and snowfall variability. Due to the hypsometry of the SRG, small changes in the punctual SMB around the ELA have impacts over large areas and have significant consequences on the final glacier-wide SMB. However, in-situ data above the ELA are lacking, leading to important uncertainty in accumulation. Nevertheless, our SMB estimates for the 3 largest non-calving glaciers of the icefield are similar to mass balance values given by geodetic techniques. This validation shows that our estimate of SMB, which is the first negative proposed at the scale of NPI, is accurate. Combined with the ice discharge proposed in the first section of this study, this SMB could have contributed to the observed mass loss from the 1980s.Finally, the study of the surface energy balance given by MAR reveals the key role of the albedo and the shortwave radiation budget in the variations of the SMB. Albedo variations indirectly justify the existing correlations between temperature and melting as air temperature controls the phase of precipitation on the plateau. Thus, changes in solid precipitation explain most of the SMB variations. Consequently, past conditions with higher solid precipitation may have explained larger glaciers in Patagonia. The current instability is possibly a result from the location of glacier fronts which are well below the necessary altitude for equilibrium in the current icefield topography.This study allows us to conclude that well constrained atmospheric and ice dynamic modelling leads to SMB values which are in better agreement with the mass balance of the icefield. Nevertheless, new field data is necessary to better constrain SMB estimates of the SRG and the NPI in order to improve our understanding of past and future climate change impacts on these glaciers.
... and Methods section). Inspired from previous studies Willis et al., 2012;Wang and Kääb, 2015), this methodology was further developed and validated on the Mont-Blanc area in the European Alps . Contrary to earlier studies, we did not rely on DEMs available online (the socalled 14DMO product) but directly calculated more than 50,000 DEMs from L1A ASTER images using the Ames Stereo Pipeline (Shean et al., 2016). ...
... In chapter 3, we processed more than 50 000 individual ASTER DEMs in order to extract time series of elevation, which were then converted into rate of elevation changes. The method was not novel by itself (e.g., Willis et al., 2012;, but it is the first time it was applied over such a large area. My main contribution to this work was the automation of existing procedures (Nuth and Kääb, 2011;Gardelle et al., 2012a;Berthier et al., 2016) and the careful validations against published and unpublished individual glacier geodetic mass balances estimates. ...
... Direction 7: using the ASTER glacier-wide mass balances for model calibration or validation The geodetic method based on timeseries of ASTER DEMs is not a new method (e.g., Willis et al., 2012;Wang and Kääb, 2015), but it is now highly automated (based on the developments made by myself and by Romain Hugonnet) and has the potential to be applied at the scale of the globe. It was recently applied to the Northern Patagonian Icefield (Dussaillant et al., 2018), in Alaska and is currently applied to the entire Andes (PhD project of Ines Dussaillant 2016-2019). ...
Thesis
High Mountain Asia (HMA) hosts the largest glacierized area outside the polar regions. Approximately 15 % of the ~100 000 km² of HMA glaciers is covered by a debris layer of various thickness. The influence of this debris on the HMA glacier response to climate change remains debated. In principle, the presence of a thick layer of debris reduces the melt of the ice beneath it, due to the insulating effect. However, other processes such as ablation of bare ice cliff faces, subaqueous melt of supraglacial ponds and internal ablation due to englacial hydrology could substantially contribute to enhance the debris-covered glacier mass losses. The aim of this PhD work is to assess the impact of the debris on glacier mass balance in HMA. Up to now, the influence of the debris cover has been assessed through glacier front position changes or on a restricted sample of glaciers, and no large scale study of the influence of the debris cover on the glacier-wide mass balance is available.As a starting point, we derived glacier mass changes for the period 2000-2016 for the entire HMA, with an unprecedented resolution, using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) optical satellite imagery. We calculated a total mass loss of -16.3 ± 3.5 Gt yr-1 (-0.18 ± 0.04 m w.e. yr-1) with contrasted rates of regionally-averaged mass changes ranging from -0.62 ± 0.23 m w.e. yr-1 for the eastern Nyainqentanglha to +0.14 ± 0.08 m w.e. yr-1 for the western Kunlun Shan.At the scale of HMA, the pattern of glacier mass changes is not related to the presence of debris, but is linked with the climatology. Consequently, we studied the influence of the debris-cover on mass balance within climatically homogeneous regions. Based on the mass balances of individual glaciers larger than 2 km² (more than 6 500 glaciers, which represent 54% of the total glacierized area), we found that debris-covered glaciers have significantly more negative mass balances for four regions out of twelve, a significantly less negative mass balance for one region and non-significantly different mass balances for the remaining seven regions. The debris-cover is generally a less significant predictor of the mass balance than the slope of the glacier tongue or the glacier mean elevation. The influence of the debris is not completely clear and complicated to untangle from the effect of the other morphological parameters, because heavily debris-covered tongues are situated at lower elevations than debris-free tongues, where ablation is higher.However, such a statistical analysis of the influence of the debris-cover on the glacier-wide mass balance variability is not very informative in terms of glaciological processes. In order to better constrain the contribution of the different ablation processes on debris-covered tongues, work at a finer scale is required. For the debris-covered tongue of Changri Nup Glacier, Everest region, Nepal, we quantified the contribution of ice cliffs to the ablation budget. Using a combination of very high resolution DEMs derived from Pléiades images and an unmanned aerial vehicle, we found that ice cliffs contributed to ~23 ± 5 % of the total net ablation of the tongue, over two contrasted years, although they occupy only 7 to 8 % of its area. Ice cliffs are large contributors to the ablation of a debris-covered tongue, but they cannot alone explain the so-called debris cover anomaly, i.e. the fact that debris free and debris covered tongues have similar thinning rates. This anomaly is probably due to smaller emergence velocity over debris-covered tongues than over debris-free tongues, resulting in similar thinning rates, despite less negative surface mass balance rates. We advocate for more measurements of ice thickness of debris-covered tongues in order to better understand their dynamics.
... Glaciers of the Southern Andes, a region dominated by Patagonian Icefields, are the second-largest mountain-glacier contributors to sea-level rise after Alaskan glaciers; however, uncertainties surrounding their mass budgets remain large (Hock et al., 2019). In addition, the NPI and SPI host several intriguing characteristics and phenomena of interest to the scientific community, which previous studies highlight well: many glaciers interact with lakes and fjords at their termini; the San Rafael Glacier in the NPI is the closest marine-terminating glacier to the equator on Earth (Willis et al., 2012a); HPS-12, a small tidewater glacier of the SPI, has alarmingly high thinning rates (−44 m yr −1 in the 21st century (Dussaillant et al., 2019); Pio XI, a large tidewater glacier on the SPI, has anomalously positive mass balance (Rivera et al., 1997;Wilson et al., 2016); glaciers also span from sea level to several thousand meters above sea level (Dussaillant et al., 2019). These myriad factors contribute to the NPI and SPI being ideal targets for assessing spatial and temporal variability in glacier mass changes over time. ...
... Geodetic mass balance observations are often used to help fill spatial gaps in mass balance data, and provide opportunities to assess model results and statistical evaluations of spatial patterns in glacier mass changes. Many recent studies (Willis et al., 2012a;Willis et al., 2012b;Dussaillant et al., 2018;Malz et al., 2018;Abdel Jaber et al., 2019;Braun et al., 2019;Dussaillant et al., 2019;Cirací et al., 2020;Hugonnet et al., 2021) have quantified geodetic mass balance for the Patagonia region for the 21st century and explored the spatial heterogeneity across the icefields. The global studies (Cirací et al., 2020;Hugonnet et al., 2021) found the Southern Andes to have the highest rate of mass loss after the Canadian Arctic, Alaska, and High-Mountain Asia. ...
... These results are broadly consistent with previous work. Willis et al. (2012a) and Willis et al. (2012b) use SRTM and ASTER to calculate elevation and volume changes of the icefields and show that from 2000-2012, 40% of the SPI volume loss is derived from eastern lake-terminating glaciers retreat. Willis et al. (2012a) find that NPI western glaciers are thinning rapidly from 2000-2011 and hypothesize that this is due to their lower elevation. ...
Article
Full-text available
Southern Andean glaciers contribute substantially to global sea-level rise. Unfortunately, mass balance estimates prior to 2000 are limited, hindering our understanding of the evolution of glacier mass changes over time. Elevation changes over 1976/1979 to 2000 derived from historical KH-9 Hexagon imagery and NASADEM provide the basis for geodetic mass balance estimates for subsets of the Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI), extending current mass balance observations by ∼20 years. Geodetic mass balances were −0.63 ± 0.03 m w.e. yr−1 for 63% of the NPI and −0.33 ± 0.05 m w.e. yr−1 for 52% of the SPI glacierized areas for this historical period. We also extend previous estimates temporally by 25% using NASADEM and ASTER elevation trends for the period 2000 to 2020, and find geodetic mass balances of −0.86 ± 0.03 m w.e. yr−1 for 100% of the NPI and −1.23 ± 0.04 m w.e. yr−1 for 97% of the SPI glacierized areas. 2000–2020 aggregations for the same areas represented in the 1976/1979 to 2000 estimates are −0.78 ± 0.03 m w.e. yr−1 in the NPI and −0.80 ± 0.04 m w.e. yr−1 on the SPI. The significant difference in SPI geodetic mass balance in the modern period for 100% vs. 52% of the glacierized area suggests subsampling leads to significant biases in regional mass balance estimates. When we compare the same areas in each time period, the results highlight an acceleration of ice loss by a factor of 1.2 on the NPI and 2.4 on the SPI in the 21st century as compared to the 1976/1979 to 2000 period. While lake-terminating glaciers show the most significant increase in mass loss rate from 1976/1979–2000 to 2000–2020, mass balance trends are highly variable within glaciers of all terminus environments, which suggests that individual glacier sensitivity to climate change is dependent on a multitude of morphological and climatological factors.
... For the historical period, the mean SMB was negative in the NPI, reaching an annual mean value of − 0.6 ± 2.1 m w.e. yr −1 , in agreement with previously published geodetic mass balances in comparable periods 3,4,6,[8][9][10][11][12] (Fig. 2a, Table S2) and with previously modelled SMBs (e.g. mean of − 0.2 ± 0.7 m w.e. ...
... This shadow area is due to the parametrization of the glacier cooling effect and the method used for the phase partitioning in the total precipitation to define the surface snow accumulation. Green coloured bars indicate previously derived geodetic mass balances and their error range previously estimated in NPI 3,4,6,[8][9][10][11][12] and in the SPI 3,5,7,[9][10][11][12] . Trends with the 95% confidence interval are shown. ...
... We make a key assumption that future rates of frontal ablation will be unchanged from those estimated during past and present conditions, masking the interannual variability as has been estimated, for instance, in Jorge Montt Glacier 31 . We calculate these frontal ablation rates by differencing our modelled SMB and previously published geodetic mass balances [3][4][5][6][7][8][9][10][11][12] (Tables S2 and S3). Since the RCP simulations start in 2005, we used the mean SMB of the two scenarios in order to compare with the geodetic mass balances calculated after this year. ...
Article
Full-text available
The Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI) have increased their ice mass loss in recent decades. In view of the impacts of glacier shrinkage in Patagonia, an assessment of the potential future surface mass balance (SMB) of the icefields is critical. We seek to provide this assessment by modelling the SMB between 1976 and 2050 for both icefields, using regional climate model data (RegCM4.6) and a range of emission scenarios. For the NPI, reductions between 1.5 m w.e. (RCP2.6) and 1.9 m w.e. (RCP8.5) were estimated in the mean SMB during the period 2005–2050 compared to the historical period (1976–2005). For the SPI, the estimated reductions were between 1.1 m w.e. (RCP2.6) and 1.5 m w.e. (RCP8.5). Recently frontal ablation estimates suggest that mean SMB in the SPI is positively biased by 1.5 m w.e., probably due to accumulation overestimation. If it is assumed that frontal ablation rates of the recent past will continue, ice loss and sea-level rise contribution will increase. The trend towards lower SMB is mostly explained by an increase in surface melt. Positive ice loss feedbacks linked to increasing in meltwater availability are expected for calving glaciers.
... The glaciers in Patagonia and Tierra del Fuego have shown one of the largest retreats in the past decades worldwide, with the Northern Patagonia Icefield (NPI) and the Southern Patagonia Icefield (SPI) being the largest contributors to sea-level rise (Willis et al. 2012b;Willis et al. 2012a;Gardner et al. 2013;Braun et al. 2019). The mass loss of the large icefields seems to be mainly caused by long-term warming, but the dynamical adjustment of individual calving glaciers accelerates the mass loss during recent decades (Casassa et al. 1997;Koppes et al. 2011;Rivera et al. 2012;Willis et al. 2012b;Willis et al. 2012a;Sakakibara and Sugiyama 2014;Malz et al. 2018;Braun et al. 2019). ...
... The glaciers in Patagonia and Tierra del Fuego have shown one of the largest retreats in the past decades worldwide, with the Northern Patagonia Icefield (NPI) and the Southern Patagonia Icefield (SPI) being the largest contributors to sea-level rise (Willis et al. 2012b;Willis et al. 2012a;Gardner et al. 2013;Braun et al. 2019). The mass loss of the large icefields seems to be mainly caused by long-term warming, but the dynamical adjustment of individual calving glaciers accelerates the mass loss during recent decades (Casassa et al. 1997;Koppes et al. 2011;Rivera et al. 2012;Willis et al. 2012b;Willis et al. 2012a;Sakakibara and Sugiyama 2014;Malz et al. 2018;Braun et al. 2019). In particular, calving glaciers have the potential to disproportionately contribute to sea level rise due to a possible rapid retreat (Benn et al. 2007). ...
... The number of remote sensing studies, updating the glacier inventories of the Southernmost Andes, assessing glacier area changes for different time periods Meier et al. 2018) and estimating the overall contribution to see level rise (Willis et al. 2012b;Willis et al. 2012a;Malz et al. 2018;Braun et al. 2019;Dussaillant et al. 2019), have increased in the past decade. However, to estimate future changes of glaciers, we need to improve our understanding of the individual spatial and temporal variation of glacier retreat for different glacier catchments and different sets of atmospheric drivers (Schneider et al. 2020a). ...
Thesis
Die Gletscherschmelze in den südlichen Anden trägt maßgeblich zum Anstieg des Meeresspiegels der letzten Jahrzehnte bei und beeinflusst regional die saisonale Wasserverfügbarkeit. In jüngster Zeit wurde eine rapide Zunahme der Massenverluste insbesondere einzelner großer Auslassgletscher des Südlichen Patagonisches Eisfeldes beobachtet. Im Rahmen der Dissertation wurden die rezente Variabilität des Klimas und der klimatischen Massenbilanz für ausgewählte vergletscherte Gebiete in Patagonien und Feuerland untersucht. Die Verbesserung unseres Verständnisses über räumliche und zeitliche Muster der klimatischen Massenbilanz, ihrer atmosphärischen Antriebsfaktoren und ihres Einflusses auf das in jüngster Vergangenheit beobachtete individuelle Gletscherverhalten, sind weitere wichtige Ziele. Da die Klimavariabilität die Hauptursache für lokale Veränderungen in der Kryosphäre der südlichen Anden ist, wurden langjährige meteorologische Beobachtungen im Gebiet der Gran Campo Nevado-Eiskappe im südlichsten Patagonien im Hinblick auf räumliche und zeitliche Variabilität untersucht und der Einfluss mesoskaliger Wettermuster und Modi atmosphärischer Oszillationen auf die Ausprägung des Klimas analysiert. Darüber hinaus wurde die rezente Variabilität der klimatischen Massenbilanz für ausgewählte Gletscher in Südpatagonien und Feuerland durch die Implementierung des Energie- und Massenbilanzmodells COSIMA simuliert. Eine unterschiedliche Ausprägung der Oberflächenmassenbilanz und geodätischer Massenbilanz unterstreicht wie wichtig ein besseres Verständnis über die Prozesse der klimatischen Massenbilanz und Eisdynamik ist. Des Weiteren wurden Simulationen der klimatischen Massenbilanz eingesetzt, um eine ausgeglichene Massenbilanz für rezente und vergangene Ausdehnungen des Gletschers Schiaparelli abzuleiten. Ziel war es, eine modellgestützte Annäherung an die klimatischen Bedingungen während der Kleinen Eiszeit zu simulieren.
... Flow velocities near the calving front of San Rafael Glacier reached magnitudes in excess of 18 m d −1 in April 2007 (Willis et al., 2012a), dropping to 16 m d −1 in May 2012 (Abdel Jaber et al., 2014). Mouginot and Rignot (2015) report a temporal peak in 2005 and a decrease by about 20 % until 2014 for the velocity at 10 km from the ice front. ...
... Our result for NPI during epoch 1 (VCR = −4.26 ± 0.20 km 3 a −1 ) complies with the numbers reported by Abdel Jaber (2016) for the period 2000 to 2014 (−4.40 ± 0.13 km 3 a −1 ) and Willis et al. (2012a) for 2000 to 2011 (−4.06 ± 0.12 km 3 a −1 ), the latter based on SRTM and ASTER DEMs. Willis et al. (2012b) recomputed their previous estimate applying a 2 m offset to the SRTM DEM to account for signal penetration, which results in larger losses (VCR = −4.9 ...
... On glaciers larger than 100 km 2 the SEC rates with both methods applied by Dussaillant et al. (2018) agree with our results within error bars. On two medium-sized glaciers, Exploradores (86 km 2 ) and Grosse (67 km 2 ), the average SECR of their two methods differs by more than 1.0 m a −1 , their ASTER_trend being ∼ 0.8 m a −1 higher than our SECR and ∼ 0.6 m a −1 higher than those of Willis et al. (2012a). ...
Article
Full-text available
The northern and southern Patagonian ice fields (NPI and SPI) have been subject to accelerated retreat during the last decades, with considerable variability in magnitude and timing among individual glaciers. We derive spatially detailed maps of surface elevation change (SEC) of NPI and SPI from bistatic synthetic aperture radar (SAR) interferometry data of the Shuttle Radar Topography Mission (SRTM) and TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X) for two epochs, 2000–2012 and 2012–2016, and provide data on changes in surface elevation and ice volume for the individual glaciers and the ice fields at large. We apply advanced TanDEM-X processing techniques allowing us to cover 90 % and 95 % of the area of NPI and 97 % and 98 % of SPI for the two epochs, respectively. Particular attention is paid to precisely co-registering the digital elevation models (DEMs), accounting for possible effects of radar signal penetration through backscatter analysis and correcting for seasonality biases in case of deviations in repeat DEM coverage from full annual time spans. The results show a different temporal trend between the two ice fields and reveal a heterogeneous spatial pattern of SEC and mass balance caused by different sensitivities with respect to direct climatic forcing and ice flow dynamics of individual glaciers. The estimated volume change rates for NPI are -4.26±0.20 km3 a−1 for epoch 1 and -5.60±0.74 km3 a−1 for epoch 2, while for SPI these are -14.87±0.52 km3 a−1 for epoch 1 and -11.86±1.99 km3 a−1 for epoch 2. This corresponds for both ice fields to an eustatic sea level rise of 0.048±0.002 mm a−1 for epoch 1 and 0.043±0.005 mm a−1 for epoch 2. On SPI the spatial pattern of surface elevation change is more complex than on NPI and the temporal trend is less uniform. On terminus sections of the main calving glaciers of SPI, temporal variations in flow velocities are a main factor for differences in SEC between the two epochs. Striking differences are observed even on adjoining glaciers, such as Upsala Glacier, with decreasing mass losses associated with slowdown of flow velocity, contrasting with acceleration and increase in mass losses on Viedma Glacier.
... Among those studies, mass balance estimates are often based on the geodetic method, 2.3 Introduction which allows calculation of glacier volume changes by differentiation of two or more multi-temporal digital elevation models (DEMs) (e.g., Marzeion et al., 2017;Paul et al., 2015). In particular for the NPI, Willis et al. (2012a) The goal of our study is to produce two new and independent geodetic estimates of the NPI mass balance for the time period 2000-2012 using, on one hand, SRTM and SPOT5 and, on the other hand, ASTER DEMs. Although the NPI mass balance during this time period has already been estimated in two previous studies Willis et al., 2012a) our contribution is justified by: ...
... In particular for the NPI, Willis et al. (2012a) The goal of our study is to produce two new and independent geodetic estimates of the NPI mass balance for the time period 2000-2012 using, on one hand, SRTM and SPOT5 and, on the other hand, ASTER DEMs. Although the NPI mass balance during this time period has already been estimated in two previous studies Willis et al., 2012a) our contribution is justified by: ...
... (i) The use of ASTER DEMs calculated using the Ames Stereo Pipeline (ASP) (Shean et al., 2016). As shown in the supplement of our study, these DEMs have less artefacts than the 14DMO DEM available from LP-DAAC and used in many earlier studies including the one of Willis et al. (2012a) over the NPI. ...
Thesis
Andean glaciers are amongst the fastest shrinking and the largest contributors to sea level rise in the world. They also represent crucial water resources in the vast semi-arid portions of this large Andes Cordillera (10°N-56°S), sustaining river runoff during dry periods and buffering the effects of droughts. Despite the widespread shrinkage of these glaciers, direct measurement of glacier fluctuations in the Andes are sparse, short-termed and in many cases incomplete, preventing the accurate quantification of recent ice loss for the entire mountain range. Comprehensively quantifying the magnitude of this loss at different special scales is crucial to better constrain future economical, ecological and social impacts. First, we evaluated the performance of a methodology to calculate glacier mass changes on Andean glaciers using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Over our validation zone, the Northern Patagonian Icefield, we found strongly negative icefield-wide mass balance rates of -1.06 ± 0.14 m w.e. yr-1 for the period 2000-2012, in good agreement with estimates from earlier studies and with a second independent estimate (-1.02 ± 0.21 m w.e. yr-1) obtained by differencing the better resolved Shuttle Radar Topography Mission (SRTM) DEM with a Satellite pour l'Observation de la Terre 5 (SPOT5) DEM. Importantly, this work permitted us to (i) validate "ASTER monitoring Ice towards eXtinction" (ASTERIX) method over the Andes; (ii) confirm the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a small high altitude region (above 2900 m a.s.l.) with negligible effects on NPI-wide mass balance; and (iii) provide the basis for an analysis of NPI mass balance changes during different sub-periods between 1975 and 2016 using additional DEMs. Then, we processed more than 30000 ASTER DEMs to calculate the integrated volume of ice lost by Andean glaciers during the past two decades. Andes-wide mass loss amounts to -22.9 ± 5.9 Gt yr-1 (-0.72 ± 0.22 m w.e. yr-1) for the entire period (or -26.0 ± 6.0 Gt yr-1 including subaqueous losses). All regions show consistent glacier wastage, with the most negative mass balance rates in the Patagonian Andes (-0.78 ± 0.25 m w.e. yr-1) and Tropical Andes (-0.42 ± 0.24 m w.e. yr-1). Relatively moderate loss (-0.28 ± 0.18 m w.e. yr-1) is measured in the intermediate regions of the Dry Andes. The inter-decadal patterns of glacier mass loss is an important contribution of this work, observed for the first time at an Andes-wide scale. We observe steady thinning rates in the Tropics and south of 45°S. Conversely, glaciers from the Dry Andes were stable during the 2000s, shifting to drastic thinning rates during the 2010s, coinciding with conditions of sustained drought since 2010. The evaluation of the imbalanced glacier contribution to river discharge during these two decades revealed that glaciers partially helped to mitigate the negative impacts of this sustained drought in the Dry Andes. The results obtained in this thesis contribute to the understanding of recent Andean glacier evolution at a local, regional and Andes-wide scale. We provide a high-quality, multi-decadal dataset that will be useful to constrain the diversity of present 21st century Andes-wide mass loss estimates, in the pursuit of the good calibration of glaciological and hydrological models intended to project future glacier changes and to improve water resource management in the Andes.
... The surface mass balance estimates derived from atmospheric modelling [17,21,22], or the changes derived from field glaciological measurements, suffer from a sparse distribution of meteorological stations and sampling sites that do not adequately capture the large variability over very short distances and rugged topography. Remote sensing techniques based on both optical [2,3,[23][24][25] and radar imagery [26][27][28] provide valuable data for quantifying the ice volume and ice mass changes of the SPI and NPI, in spite of having to deal with cloud cover or uncertain radar signal penetration. All of the remote sensing results (Table 1) have a partially reconcilable agreement on the net ice mass loss to both icefields. ...
... First, an SPI and NPI a-priori pattern consisting of 174 point masses was derived from the average ice surface elevation rates for the accumulation and ablation zones of 87 glacier basins [2] (see Appendix A). However, these ice surface elevation rates were based on slightly different imagery acquisition time spans and processing algorithms for NPI [23] and SPI [2]. Therefore, a systematic bias between the icefields cannot be ruled out. ...
... Therefore, the GRACE derived ice mass change rates can be compared only with those remote sensing results, which consistently sum the contributions of both icefields [2,26,28]. Synthetic-aperture radar interferometry (TanDEM-X) [26][27][28], in fact, seems to yield systematically smaller ice mass losses than optical imagery (ASTER, SPOT) [2,23,24]. Our results support the larger trend in ice loss as derived by Willis et al. [2] from the ASTER imagery. ...
Article
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We use the complete gravity recovery and climate experiment (GRACE) Level-2 monthly time series to derive the ice mass changes of the Patagonian Icefields (Southern Andes). The glacial isostatic adjustment is accounted for by a regional model that is constrained by global navigation satellite systems (GNSS) uplift observations. Further corrections are applied concerning the effect of mass variations in the ocean, in the continental water storage, and of the Antarctic ice sheet. The 161 monthly GRACE gravity field solutions are inverted in the spatial domain through the adjustment of scaling factors applied to a-priori ice mass change patterns based on published remote sensing results for the Southern and Northern Patagonian Icefields, respectively. We infer an ice mass change rate of −24.4 ± 4.7 Gt/a for the Patagonian Icefields between April 2002 and June 2017, which corresponds to a contribution to the eustatic sea level rise of 0.067 ± 0.013 mm/a. Our time series of monthly ice mass changes reveals no indication for an acceleration in ice mass loss. We find indications that the Northern Patagonian Icefield contributes more to the integral ice loss than previously assumed.
... The vast majority of alpine glaciers and ice fields globally have been receding in recent decades and a growing body of science suggests Patagonia Icefields are particularly sensitive to climatic changes (Schaefer et al., 2013;Willis et al., 2012). Nearly all of the outlet glaciers on the NPI have a negative mass balance trend for the past 40 years Willis et al., 2012). ...
... The vast majority of alpine glaciers and ice fields globally have been receding in recent decades and a growing body of science suggests Patagonia Icefields are particularly sensitive to climatic changes (Schaefer et al., 2013;Willis et al., 2012). Nearly all of the outlet glaciers on the NPI have a negative mass balance trend for the past 40 years Willis et al., 2012). The region receives exceedingly high precipitation rates, 5-6 m w.e.yr −1 (Sauter, 2020). ...
... Models project a dramatic loss of solid precipitation as a consequence of global climate change (Sauter, 2020;Schaefer et al., 2013Schaefer et al., , 2015, and other surface mass balance studies show that glaciers are concurrently thinning and retreating at accelerating rates (I. Dussaillant et al., 2018;Malz et al., 2018;Meier et al., 2018;Schaefer et al., 2013;Willis et al., 2012). Thinning rates are highest along the western margins of the NPI and are as negative as −10 m yr −1 on lower elevation glacier tongues (I. ...
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Glacial lake outburst floods (GLOFs) pose an increasing hazard to communities living downstream of glaciated areas of the Northern Patagonia Icefield (NPI). The proliferation of GLOF events poses a growing hazard to human development and infrastructure which is rapidly expanding into formerly isolated areas. The outlet glaciers on the eastern flank of the NPI, in particular, have experienced an increase in the frequency of GLOFs, threatening downstream communities with the potential for future events. Using a satellite-derived DEM and UAV imagery , we evaluated flood parameters of a 16 March 1989 GLOF event in the Valle Soler. Calculated flood volume was in excess of 140 × 10 6 m 3 while the peak discharge was approximately 20,000 m 3 /s. This newly calculated flood discharge value distinguishes this event as the largest recorded glacial moraine outburst flood in the literature and is significantly larger than previous estimates (1,800-2,000 m 3 /s) for this incident. ARTICLE HISTORY
... Since 1975, the largest magnitudes of 1°C per decade have been observed in central Brazil (e.g., de Barros Soares et al. 2017). For the same period, in the Andes Mountains of southern Chile (i.e., Patagonia), observed warming has not been statistically significant (e.g., Carrasco et al. 2008;de Barros Soares et al. 2017), but valley glaciers on the flanks of the two major icefields (the Northern Patagonia Ice Field (NPI) and Southern Patagonia Ice Field (SPI)) have been rapidly receding and thinning (e.g., Davies and Glasser 2012;Willis et al. 2012). Combined, the NPI and SPI make up the largest extent of ice in the Southern Hemisphere outside of Antarctica, and their ongoing melting has contributed a Landslides disproportionate amount (9%) to sea-level rise compared to larger icefields in other parts of the world (Ringot et al. 2003). ...
... I selected a bellwether site along the eastern and northern flanks of the rapidly deglaciating NPI (Figs. 2 and 5) because glaciers are rapidly receding and thinning there (e.g., Davies and Glasser 2012;Willis et al. 2012) and because I observed about six large (areas > 0.2 km 2 ), recent rock avalanches in glacier ablation areas in post-2010 satellite imagery (e.g., Fig. 5b). Some of these rock avalanches were previously identified as rock-fall deposits (Glasser et al. 2016). ...
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Permafrost and glaciers are being degraded by the warming effects of climate change. The impact that this degradation has on slope stability in mountainous terrain is the subject of ongoing research efforts. The relatively new availability of high-resolution (≤ 10 m) imagery with worldwide coverage and short (≤ 30 days) repeat acquisition times, as well as the emerging field of environmental seismology, presents opportunities for making remote, systematic observations of landslides in cryospheric mountainous terrain. I reviewed the literature and evaluated landslide activity in existing imagery to select five ~ 5000-km2 sites where long-term, systematic observations could take place. The five proposed sites are the northern and eastern flanks of the Northern Patagonia Ice Field, the Western European Alps, the eastern Karakoram Range in the Himalayan Mountains, the Southern Alps of New Zealand, and the Fairweather Range in Southeast Alaska. Systematic observations of landslide occurrence, triggers, size, and travel distance at these sites, especially if coupled with observations from in situ instrumental monitoring, could lead to a better understanding of changes in slope stability induced by climate change. The suggested sites are not meant to be absolute and unalterable. Rather, they are intended as a starting point and discussion starter for new work in this expanding landslide research frontier.
... 6-7). Some of the slightly higher mass change rates 14,[20][21][22][23] can be attributed to their different methodology and time frames as well as the assumption of 2 m Shuttle Radar Topography Mission (SRTM) radar penetration 21,22 , which was best practice at that time, but now proven to be erroneous for the NPI 23 . For Tierra del Fuego (region 11), our values reveal only about one quarter of the mass change stated in the previous analysis of time series from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) (2000-2011) 24 . ...
... 6-7). Some of the slightly higher mass change rates 14,[20][21][22][23] can be attributed to their different methodology and time frames as well as the assumption of 2 m Shuttle Radar Topography Mission (SRTM) radar penetration 21,22 , which was best practice at that time, but now proven to be erroneous for the NPI 23 . For Tierra del Fuego (region 11), our values reveal only about one quarter of the mass change stated in the previous analysis of time series from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) (2000-2011) 24 . ...
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Excluding the large ice sheets of Greenland and Antarctica, glaciers in South America are large contributors to sea-level rise. Their rates of mass loss, however, are poorly known. Here, using repeat bi-static synthetic aperture radar interferometry over the years 2000 to 2011/2015, we compute continent-wide, glacier-specific elevation and mass changes for 85% of the glacierized area of South America. Mass loss rate is calculated to be 19.43 ± 0.60 Gt a−1 from elevation changes above ground, sea or lake level, with an additional 3.06 ± 1.24 Gt a−1 from subaqueous ice mass loss not contributing to sea-level rise. The largest contributions come from the Patagonian icefields, where 83% mass loss occurs, largely from dynamic adjustments of large glaciers. These changes contribute 0.054 ± 0.002 mm a−1 to sea-level rise. In comparison with previous studies, tropical and out-tropical glaciers — as well as those in Tierra del Fuego — show considerably less ice loss. These results provide basic information to calibrate and validate glacier-climate models and also for decision-makers in water resource management.
... Les séries de MNE sont utilisées par simple différenciation (MNE différentiels) lorsque le jeu de données ne comporte que quelques MNE (e.g. Berthier et al., 2014) ou par analyse statistique de la tendance de chaque pixel lorsque la série est assez dense (Willis et al., 2012a). ...
... Les premières études ont permis de déterminer la tendance de changement de volume des parties basses des glaciers sur des périodes de plusieurs années (Berthier et al., 2004). Le foisonnement de données permet maintenant de traiter des séries pluriannuelles de MNE ce qui renforce la robustesse statistique des tendances observées (Willis et al., 2012a ;Wang et Kääb, 2015 ;Brun et al., 2017 ;Kääb et al., 2018). La forte répétitivité en région polaire, du fait de l'orbite héliosynchrone, assure des séries d'images denses dans les régions arctiques qui rassemblent 58 % des glaciers sur Terre (Pfeffer et al., 2014). ...
Thesis
Le manteau neigeux en montagne est une ressource importante pour les écosystèmes et les activités humaines comme l'irrigation, l'approvisionnement en eau des populations, la production hydroélectrique et l'économie touristique. Il représente aussi un risque dans les zones exposées aux avalanches. L'étude et le suivi du manteau neigeux en montagne s'appuie souvent sur des réseaux de mesure, des observations par télédétection et de la modélisation. Les avancées récentes en photogrammétrie satellite offrent de nouvelles perspectives pour compléter les réseaux de mesures qui sont souvent insuffisants vis-à-vis de la forte variabilité spatiale du manteau neigeux. Une méthode de cartographie de la hauteur de neige à partir d'images stéréoscopiques Pléiades est présentée et appliquée sur plusieurs sites. La comparaison avec une carte de référence par lidar aéroporté fournit une estimation de l'erreur des produits de photogrammétrie satellite sur un bassin versant de Californie (États-Unis). A l'échelle d'un pixel de 3 m, l'erreur standard est de 0,7 m. L'erreur décroît à ~0,3 m lorsque les mesures sont moyennées sur des surfaces supérieures à 103 m². Avec cette précision, les cartes de hauteur de neige par photogrammétrie satellite permettent d'observer les processus modelant le manteau neigeux en montagne (transport par le vent, avalanche), de mesurer le volume de neige sur des zones de plus 100 km² et de décrire la variabilité spatiale du manteau. Une série de cartes de hauteur de neige est assimilée dans la chaine de modélisation SAFRAN-Crocus afin d'évaluer le potentiel de ces données pour améliorer la représentation spatiale des propriétés physiques du manteau neigeux. Un filtre particulaire est utilisé pour assimiler une carte de hauteur de neige par hiver pendant cinq hivers sur un bassin versant des Pyrénées. L'assimilation corrige des biais dans les précipitations initialement sous-estimées à haute altitude et introduit une variabilité spatiale autrement absente des forçages et des processus modélisés. Cette combinaison innovante de produits de télédétection satellite et d'un modèle complexe spatialisé offre de nouvelles perspectives pour l'estimation de la ressource en eau en montagne et du risque avalanche.
... The GRACE-hydrological signal in region five (TWS-5, Figs. 2 and 3) is the melting of the Patagonia ice-field. Consistent with this study, different methods, which includes forward modeling approach have been employed to highlight the continued mass loss in Patagonia (Rodell et al., 2018;Willis et al., 2012;Chen et al., 2007a). This extensive and unabated mass loss in Patagonia ice-field (TWS-5, Fig. 3) is caused by the warming of the climate system, and being the second largest ice body in the Southern Hemisphere, GRACE is a viable tool for the continued monitoring of the impact of rising temperature on Ice fields. ...
... This is particularly true for Patagonia since it is characteristically a dry climate. As shown in region 6 (Figs. 2 and Fig. 3), the Patagonia ice fields are undergoing a contemporary melting and retreating of glacial ice and is consistent with previous studies (e.g., Willis et al., 2012;Chen et al., 2007a). The Andean Plateau (Altiplano) presents a phase lead greater than twelve months for rainfall relative to TWS series and includes part of the Pampas region. ...
Article
The underlying uncertainties in the prediction of freshwater evolutions in some regions can be induced by several unmitigated human actions, multi-scale climatic drivers, and dynamic physical processes. These factors have enduring hydro-ecological effects on the environments and combine to limit our understanding of large-scale hydrological processes and impacts of climate on water availability. Considering the fact that several hydrogeological perturbations and disturbances have been reported during the last decade in South America (SA), a further assessment of continental land water storage is therefore warranted. In this study, a twostep regularization approach that combined the JADE (Joint Approximate Diagonalisation of Eigen matrices) algorithm and PLSR (Partial Least Squares Regression) was employed to assess GRACE (Gravity Recovery and Climate Experiment)-terrestrial water storage (TWS) over SA. Based on the Bartlett’s statistics, significant independent patterns of SST (Sea Surface Temperature) anomalies from the Pacific and Atlantic oceans were used in the PLSR scheme to model the temporal evolutions of TWS (2002-2017) over twelve prominent river basins in SA. From the JADE rotation of TWS over SA, strong inter-annual changes in TWS observed over the Amazon basin and within its floodplain corridors were identified. The unabated mass loss in Patagonia ice-field caused by warming of the climate and other GRACE-hydrological signals were also retrieved from the JADE scheme. The rainfall-TWS relationship is considerably strong (r=0.80 at 0-2 months lag) in much of tropical SA, including the Amazon basin and highlights the influence of climate variability in the region. Medium (r = 0.40) and moderately strong (r = 0.60) rainfall-TWS relationships were also found to be significant (α = 0.05) but with up to 4 months lag and more in some basins. During the 2010-2017 period, estimated TWS trends (α = 0.05) showed a considerable fall in Orinoco (-38.48±7.90 mm/yr) and Sao Francisco (-30.84±4.17) while the strongest rise was found in Uruguay (28.28±3.49 mm/yr). As the rainfall-TWS relationship is not statistically significant (α = 0.05) in some areas, the spatial distribution of trends in TWS and rainfall, especially in some arid regions, which are inconsistent confirm possible impacts resulting from complex hydrogeological processes and/or anthropogenic influence. Further, in the modelling of TWS time series using the JADE-PLSR scheme, several validation skill metrics (e.g., R2, Nash-Sutcliffe Efficiency) confirm the considerable agreements between predicted and observed TWS in the Amazon (R2 = 0.95), Orinoco (R2 = 0.94), Tocantins (R2 = 0.91), and Chobut (R2 = 0.88). However, GRACE-hydrological signals in some regions are somewhat complex given the relatively higher uncertainties in the multivariate models employed in this study.
... The growing availability of submeter resolution satellite imagery, publicly available lidar surveys, and DSMs derived from unmanned aerial vehicles further enhances and expands the applications of these data sets by allowing for both unprecedented spatial resolution and the generation of topographic time series from repeated acquisitions. In response to repeated acquisitions of topographic models, differential topography is emerging as a new geodetic tool for the quantification of vertical surface displacements resulting from earthquakes, landslides, glacier flow, volcanoes, and other processes (e.g., Bessette-Kirton et al., 2018;Borsa & Minster, 2012;Nissen et al., 2014Nissen et al., , 2012Oskin et al., 2012;Scott et al., 2018;Teza et al., 2007;Willis et al., 2015Willis et al., , 2012. These offsets in turn contribute spatially dense measurements of vertical displacements that complement other geodetic observations, such as those from interferometric synthetic aperture radar and subpixel image cross-correlation approaches. ...
... High-resolution (0.3-to 5-m resolution) DSMs derived from commercial satellite optical imagery, such as those from Pleiades, PLANET, and DigitalGlobe sensors, present an enticing alternative source of high-resolution topography for geodetic change detection (Figure 1). The generation of stereogrammetric DSMs from commercial satellite optical imagery is becoming a relatively routine technique (Noh & Howat, 2015;Willis et al., 2012;Willis et al., 2015), and expanding these techniques to broad regions (10 3 -10 7 km 2 ) is now possible through expanded image availability and high-performance computing strategies (Figure 1). The WorldView-1, WorldView-2, and WorldView-3 (WV01, WV02, WV03, respectively), Quickbird, and GEOEYE sensors, each with spatial resolutions of 0.3-0.5 m, regularly acquire land surface imagery in both along-track stereo and off-nadir, nonstereo viewing geometries. ...
Article
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The recent proliferation of high‐resolution (<3‐m spatial resolution) digital topography data sets opens a spectrum of geodetic applications in differential topography, including the quantification of coseismic vertical displacement fields. Most investigations of coseismic vertical displacements to date rely, in part, on preevent or postevent lidar surveys that are intractable or nonexistent in many locales. Stereogrammetric digital surface models (DSMs) derived from high‐resolution satellite optical imagery provide a new avenue for the retrieval of spatially dense vertical coseismic displacements on a global scale. In this study, we generated 2‐m resolution preseismic and postseismic DSMs from satellite optical imagery spanning the 2013 Mw7.7 Baluchistan strike‐slip earthquake that occurred on the Hoshab fault in southern Pakistan. We applied the Iterative Closest Point algorithm to the DSMs to quantify the coseismic vertical displacement field at a spatial resolution of 10–30 m and to generate 3‐D coseismic strain tensors. We found that across‐fault vertical offsets alternated between uplift and subsidence and varied between ~1 and 3 m in a nonsystematic manner along the Hoshab fault. We show that the preexisting topography and near‐fault geomorphology are variably consistent and inconsistent with the displacement kinematics of the 2013 earthquake, and we argue that these relationships highlight varied slip sense history along the Hoshab fault. Notably, topography along the southern extents of the Hoshab fault requires different surface displacement kinematics than occurred in the 2013 earthquake, suggesting that the Hoshab fault accommodates varying senses of slip (bimodal slip) through time.
... PLSR indicates the major contributing factors to be PE, TA, WS and LAI, with declining TWS accompanied by increasing PE and WS (which can promote increases in actual ET). In central Argentina and the Patagonia plateau (R5), dominant factors appear to be DSW, TA, DLW and VPD; along with accelerated melting of the Patagonia glacier ( Willis et al., 2012 ) and significant groundwater depletion due to droughts ( Chen et al., 2010 ), increased TA enhances atmospheric water vapor holding capacity, and the resulting enhanced VPD (and PE) may be responsible for exacerbating the drying trend. Over the Arabian Desert and the Karakum Desert in the Middle East (R8), major explanatory factors appear to be TA, DLW and PE; decreasing TWS can be explained mainly by increasing PE (caused by increasing TA and DLW), especially since 2011. ...
... Here there is a strong coupling of continental and marine systems via continental runoff. These areas are temporally dynamic as they are spatially complex, and moreover sensitive to global and local level drivers such as melting of continental ice (Chen et al., 2007;Milner et al., 2017;Willis et al., 2012), acceleration of the hydrological cycle (Barnett et al., 2005;Syed et al., 2010), changes in large-scale wind patterns (B€ oning et al., 2008;Wyrwoll et al., 2000), changes in atmospheric deposition of nutrients and contaminants (Dentener et al., 2006) as well as vegetation response and feedback to these drivers. Freshening has been identified as a key pathway for climate change in high-latitude ecosystems (Cook et al., 2016;Coupel et al., 2015), not only through the dilution of seawater but also via the addition of bioactive solutes (Klunder et al., 2012;Sedwick and DiTullio, 1997) and colloidal nanoparticles (Hawkings et al., 2018). ...
... The data and methodology (ASTERIX) applied here to the entire Andes was inspired by previous studies [52][53][54] . Below we briefly summarize the processing steps and highlight the specificity for the application to the Andes. ...
Article
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Andean glaciers are among the fastest shrinking and largest contributors to sea level rise on Earth. They also represent crucial water resources in many tropical and semi-arid mountain catchments. Yet the magnitude of the recent ice loss is still debated. Here we present Andean glacier mass changes (from 10° N to 56° S) between 2000 and 2018 using time series of digital elevation models derived from ASTER stereo images. The total mass change over this period was −22.9 ± 5.9 Gt yr⁻¹ (−0.72 ± 0.22 m w.e. yr⁻¹ (m w.e., metres of water equivalent)), with the most negative mass balances in the Patagonian Andes (−0.78 ± 0.25 m w.e. yr⁻¹) and the Tropical Andes (−0.42 ± 0.24 m w.e. yr⁻¹), compared to relatively moderate losses (−0.28 ± 0.18 m w.e. yr⁻¹) in the Dry Andes. Subperiod analysis (2000–2009 versus 2009–2018) revealed a steady mass loss in the tropics and south of 45° S. Conversely, a shift from a slightly positive to a strongly negative mass balance was measured between 26 and 45° S. In the latter region, the drastic glacier loss in recent years coincides with the extremely dry conditions since 2010 and partially helped to mitigate the negative hydrological impacts of this severe and sustained drought. These results provide a comprehensive, high-resolution and multidecadal data set of recent Andes-wide glacier mass changes that constitutes a relevant basis for the calibration and validation of hydrological and glaciological models intended to project future glacier changes and their hydrological impacts.
... Na região Norte da Patagônia Chilena tem sido evidenciado mudanças nas geleiras, como balanço negativo de massa, com a retração glacial e diminuição de volume (Cassassa et al., 2007;Rabatel et al., 2013;Pellicciotti et al., 2014;Mernild et al., 2015;IPCC 2016). As geleiras na Patagônia estão retraindo acentuadamente e em constante desgaste (Rignot et al., 2003;Masiokas et al., 2008;Willis et al., 2012), mas muito pouco se sabe sobre os motivos e como essas alterações são ligadas a mudanças no clima. Masiokas et al. (2008) atribuíram a recessão a uma tendência para condições mais secas e mais quentes detectadas durante o período de 1912-2002. ...
Article
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This work analyzed changes area of glacier Number 6 of the Melimoyu Mont, Chile, 44° 5’S – 72° 51’W and the glaciers Ecology, Sphinx, Baranowski and Tower, in King George Island, Antarctic Peninsula, 62º 12’ – 58° 28’W. The area variations mapping of the glaciers for 2000 – 2017 period was performed using two images of the Sentinel–2 program and the glacier outline manual delineation method applying. The results were compared with GLIMS and Centro Polar e Climático data for glaciers area evolution analyses. The glaciers of both regions showed continuous frontal retreat in the periods analyzed and are compared in frontal retreat dynamic. The loss of area in glacier of Melimoyu Mont was 4.94 km² of the total area in 1970 (13.23 km²). The loss of area in glaciers of King George Island was 3.83 km² of the total area in 1956, of 13.94 km². The results indicate a general retreat process tendency of the glaciers for period. The images of Sentinel–2 have potential for continuity environment changes monitoring in the Cryosphere. Este artigo analisou as alterações de área da Geleira de número 6 do Monte Melimoyu, Chile, 44° 5’S – 72° 51’W e as geleiras Ecology, Sphinx, Baranowski e Tower, na Ilha Rei George, Península Antártica, 62° 12’S - 58° 28’W. Para o mapeamento da variação de área das geleiras entre 2000 e 2017 utilizou-se duas imagens do programa Sentinel–2, aplicando o método de delineamento manual com classificação visual dos alvos. Os resultados foram comparados com dados do GLIMS e do Centro Polar e Climático para a análise da evolução de área no Monte Melimoyu e na Ilha Rei George, respectivamente. As geleiras de ambas as regiões apresentaram contínua retração frontal nos períodos analisados e são comparáveis em dinâmica de retração frontal. A perda de área na geleira do Monte Melimoyu foi de 4,94 km² da área total em 1970 (de 13,23 km²). A perda de área nas geleiras da Ilha Rei George foi de 3,83 km² da área total em 1956 (de 13,94 km²). Os resultados indicaram uma tendência geral das geleiras à retração. As imagens Sentinel–2, com 10 m de resolução espacial, possuem potencial para continuidade do monitoramento das mudanças ambientais da Criosfera.
... The mass balance of Chilean glaciers has been calculated by different methods, ranging from the traditional glaciological method (e.g., [23][24][25]) to remote sensing techniques (e.g., [26]). Additionally, ice cores can be used as mass balance proxies. ...
Article
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The Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service (WGMS) network and has the longest time series of glacier mass balance data in the Southern Hemisphere. The data has been obtained by the direct glaciological method since 1975. In this study, we calculated glacier area changes using satellite images and historical aerial photographs, as well as geodetic mass balances for different periods between 1955 and 2015 for the Echaurren Norte Glacier in the Central Andes of Chile. Over this period, this glacier lost 65% of its original area and disaggregated into two ice bodies in the late 1990s. The geodetic mass balances were calculated by differencing digital elevation models derived from several sources. The results indicated a mean cumulative glacier wide mass loss of −40.64 ± 5.19 m w.e. (−0.68 ± 0.09 m w.e. a−1). Within this overall downwasting trend, a positive mass balance of 0.54 ± 0.40 m w.e. a−1 was detected for the period 2000–2009. These estimates agree with the results obtained with the glaciological method during the same time span. Highly negative mass change rates were found from 2010 onwards, with −1.20 ± 0.09 m w.e. a−1 during an unprecedented drought in Central Andes of Chile. The observed area and the elevation changes indicate that the Echaurren Norte Glacier may disappear in the coming years if negative mass balance rates prevail.
... The ALOS PRISM DEM is another stereoimage-based global DEM, built with data from the PRISM instrument on board the ALOS satellite, active between 2006 and 2011 [14]. These products have a common spatial resolution of 30 m (with SRTM available in 90 m as well) and are commonly used in glaciological change detection studies [15][16][17][18]. ...
Article
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TanDEM-X digital elevation model (DEM) is a global DEM released by the German Aerospace Center (DLR) at outstanding resolution of 12 m. However, the procedure for its creation involves the combination of several DEMs from acquisitions spread between 2011 and 2014, which casts doubt on its value for precise glaciological change detection studies. In this work we present TanDEM-X DEM as a high-quality product ready for use in glaciological studies. We compare it to Aerial Laser Scanning (ALS)-based dataset from April 2013 (1 m), used as the ground-truth reference, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) V003 DEM and SRTM v3 DEM (both 30 m), serving as representations of past glacier states. We use a method of sub-pixel coregistration of DEMs by Nuth and Kääb (2011) to determine the geometric accuracy of the products. In addition, we propose a slope-aspect heatmap-based workflow to remove the errors resulting from radar shadowing over steep terrain. Elevation difference maps obtained by subtraction of DEMs are analyzed to obtain accuracy assessments and glacier mass balance reconstructions. The vertical accuracy (± standard deviation) of TanDEM-X DEM over non-glacierized area is very good at 0.02 ± 3.48 m. Nevertheless, steep areas introduce large errors and their filtering is required for reliable results. The 30 m version of TanDEM-X DEM performs worse than the finer product, but its accuracy, −0.08 ± 7.57 m, is better than that of SRTM and ASTER. The ASTER DEM contains errors, possibly resulting from imperfect DEM creation from stereopairs over uniform ice surface. Universidad Glacier has been losing mass at a rate of −0.44 ± 0.08 m of water equivalent per year between 2000 and 2013. This value is in general agreement with previously reported mass balance estimated with the glaciological method for 2012–2014.
... Similar observations can be found in a number of studies (e.g. Rignot et al. 2003;Rivera et al. 2007;Masiokas et al. 2008;Davies and Glasser 2012;Willis et al. 2012). ...
Article
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This work analysed the application of Sentinel-2 multispectral imagery and GLIMS data for mapping glacier retreat and to estimate glacier area changes of Mount Melimoyu, located in northern Patagonia, Chile for the period between 1970 and 2017. The results showed a decrease of about 35.61% in the area for the period analysed and there is a continuing retreating trend in the region. The decreasing trend in mean annual precipitation may explain the recent glacier changes, which indicates a large sensibility for meteorological variability of glaciers, which is influenced by geomorphometry and glacier area, in the region. Using Sentinel 2 imagery, we provided inventory of rock glaciers in the study area. Glacier outlines obtained through manual delineation showed comparable results with the glacier outlines using Sentinel-2 MSI data in the study area, which shows greater accuracy in glacier mapping using Sentinel-2 data.
... This hydrological regime may be defined as nival with glacial contributions (e.g., Lara et al., 2015). Additionally, the channels receive freshwater from Steffen Fjord, which is fed by meltwaters from Steffen Glacier (the third largest glacier of the NPI; Willis et al., 2012) via Huemules River, and from the calving Jorge Montt Glacier (the northernmost SPI glacier) (Fig. 1). The latter has experienced a rapid retreat during the last decade, with a rate of almost a kilometer per year (Rivera et al., 2012). ...
Article
The Baker-Martínez fjord system (Chile, 48°S) is a transitional environment between the terrestrial ecosystems of Patagonia and the SE Pacific Ocean. This unique setting makes it an ideal system to evaluate land-ocean gradients in sediment composition and in a range of biogeochemical variables. Here, we studied the composition and organic geochemistry of surface sediments deposited in the Baker-Martínez fjord system to assess spatial changes in sediment properties and identify the best tracers of terrestrial input. We determined concentrations in biogenic opal, organic carbon, calcium carbonate, and lithogenic particles, and we measured diatom abundance, bulk elemental and isotopic organic geochemistry, and n-alkanes distribution, on a series of surface sediment samples distributed along two proximal-to-distal transects (one in the Martínez Channel and a second one in the Baker Channel). Results reveal clear proximal-to-distal trends in the proportion of freshwater diatoms and in the fraction of organic carbon of terrestrial origin calculated from the bulk organic δ¹³C measurements. Diatoms are particularly sensitive to freshwater input in proximal environments, whereas bulk organic geochemistry better reflects terrestrial input over long distances across the fjord system. Other terrestrial proxies frequently used in the literature, such as the N/C ratio and the n-alkane-based terrestrial/aquatic ratio, did not show clear variations with distance from the fjord head. Our results suggest that the isotopic composition of bulk organic matter (δ¹³Corg) and the relative proportion of diatoms of freshwater origin are the best-suited proxies to estimate past changes in terrestrial input from fjord sediment archives, irrespective of the glacial status of the fjord and its watershed.
... We selected multiple image pairs of the same locality to maximize the velocity field coverage. The final velocity field is an average of all the valid velocity estimates, a strategy successfully explored by several studies (i.e., [31,71]). In this study, we used the orientations-correlated feature-tracking method, as this method has proven to perform best under most circumstances [33]. ...
Article
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Meltwater from the cryosphere contributes a significant fraction of the freshwater resources in the countries receiving water from the Third Pole. Within the ESA-MOST Dragon 4 project, we ad-dressed in particular changes of glaciers and proglacial lakes and their interaction. In addition, we investigated rock glaciers in permafrost environments. Here, we focus on the detailed investigations which have been performed in the Poiqu River Basin, central Himalaya. We used in particular multi-temporal stereo satellite imagery, including high-resolution 1960/70s Corona and Hexagon spy images and contemporary Pleiades data. Sentinel-2 data was applied to assess the glacier flow. The results reveal that glacier mass loss continuously increased with a mass budget of −0.42 ± 0.11 m w.e.a−1 for the period 2004–2018. The mass loss has been primarily driven by an increase in summer temperature and is further accelerated by proglacial lakes, which have become abundant. The glacial lake area more than doubled between 1964 and 2017. The termini of glaciers that flow into lakes moved on average twice as fast as glaciers terminating on land, indicating that dynamical thinning plays an important role. Rock glaciers are abundant, covering approximately 21 km2, which was more than 10% of the glacier area (approximately 190 km2) in 2015. With ongoing glacier wastage, rock glaciers can become an increasingly important water resource.
... Mass loss of the CDI occurred at an average thinning rate of −1.5 ± 0.6 m w.e. a −1 , which contributed to sea-level rise by 0.001 ± 0.004 mm a −1 between 2000 and 2011 [3]. Similarly to observations at the NPI and SPI [1,14,[16][17][18][19][20][21][22][23], individual glacier responses come along with the long-term demise of the icefield mainly caused by a warming climate and changing precipitation patterns [15]. ...
Article
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The Cordillera Darwin Icefield loses mass at a similar rate as the Northern and Southern Patagonian Icefields, showing contrasting individual glacier responses, particularly between the north-facing and south-facing glaciers, which are subject to changing climate conditions. Detailed investigations of climatic mass balance processes on recent glacier behavior are not available for glaciers of the Cordillera Darwin Icefield and surrounding icefields. We therefore applied the coupled snow and ice energy and mass balance model in Python (COSIPY) to assess recent surface energy and mass balance variability for the Schiaparelli Glacier at the Monte Sarmiento Massif. We further used COSIPY to simulate steady-state glacier conditions during the Little Ice Age using information of moraine systems and glacier areal extent. The model is driven by downscaled 6-hourly atmospheric data and high resolution precipitation fields, obtained by using an analytical orographic precipitation model. Precipitation and air temperature offsets to present-day climate were considered to reconstruct climatic conditions during the Little Ice Age. A glacier-wide mean annual climatic mass balance of −1.8 ± 0.36 m w.e. a −1 was simulated between between April 2000 and March 2017. An air temperature decrease between −0.9 • C and −1.7 • C in combination with a precipitation offset of up to +60% to recent climate conditions is necessary to simulate steady-state conditions for Schiaparelli Glacier in 1870.
... Na região Norte da Patagônia Chilena tem sido evidenciado mudanças nas geleiras, como balanço negativo de massa, com a retração glacial e diminuição de volume (Cassassa et al., 2007;Rabatel et al., 2013;Pellicciotti et al., 2014;Mernild et al., 2015;IPCC 2016). As geleiras na Patagônia estão retraindo acentuadamente e em constante desgaste (Rignot et al., 2003;Masiokas et al., 2008;Willis et al., 2012), mas muito pouco se sabe sobre os motivos e como essas alterações são ligadas a mudanças no clima. Masiokas et al. (2008) atribuíram a recessão a uma tendência para condições mais secas e mais quentes detectadas durante o período de 1912-2002. ...
Article
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This work analyzed changes area of glacier Number 6 of the Melimoyu Mont, Chile, 44° 5’S – 72° 51’W and the glaciers Ecology, Sphinx, Baranowski and Tower, in King George Island, Antarctic Peninsula, 62º 12’ – 58° 28’W. The area variations mapping of the glaciers for 2000 – 2017 period was performed using two images of the Sentinel–2 program and the glacier outline manual delineation method applying. The results were compared with GLIMS and Centro Polar e Climático data for glaciers area evolution analyses. The glaciers of both regions showed continuous frontal retreat in the periods analyzed and are compared in frontal retreat dynamic. The loss of area in glacier of Melimoyu Mont was 4.94 km² of the total area in 1970 (13.23 km²). The loss of area in glaciers of King George Island was 3.83 km² of the total area in 1956, of 13.94 km². The results indicate a general retreat process tendency of the glaciers for period. The images of Sentinel–2 have potential for continuity environment changes monitoring in the Cryosphere.
... Mass loss of the CDI occurred at an average thinning rate of −1.5 ± 0.6 m w.e. a −1 , which contributed to sea-level rise by 0.001 ± 0.004 mm a −1 between 2000 and 2011 [3]. Similarly to observations at the NPI and SPI [1,14,[16][17][18][19][20][21][22][23], individual glacier responses come along with the long-term demise of the icefield mainly caused by a warming climate and changing precipitation patterns [15]. ...
Article
Full-text available
The Cordillera Darwin Icefield loses mass at a similar rate as the Northern and Southern Patagonian Icefields, showing contrasting individual glacier responses, particularly between the north-facing and south-facing glaciers, which are subject to changing climate conditions. Detailed investigations of climatic mass balance processes on recent glacier behavior are not available for glaciers of the Cordillera Darwin Icefield and surrounding icefields. We therefore applied the coupled snow and ice energy and mass balance model in Python (COSIPY) to assess recent surface energy and mass balance variability for the Schiaparelli Glacier at the Monte Sarmiento Massif. We further used COSIPY to simulate steady-state glacier conditions during the Little Ice Age using information of moraine systems and glacier areal extent. The model is driven by downscaled 6-hourly atmospheric data and high resolution precipitation fields, obtained by using an analytical orographic precipitation model. Precipitation and air temperature offsets to present-day climate were considered to reconstruct climatic conditions during the Little Ice Age. A glacier-wide mean annual climatic mass balance of −1.8 ± 0.36 m w.e. a −1 was simulated between between April 2000 and March 2017. An air temperature decrease between −0.9 ° C and −1.7 ° C in combination with a precipitation offset of up to +60% to recent climate conditions is necessary to simulate steady-state conditions for Schiaparelli Glacier in 1870.
... The accumulation area lies below the north face of Mount San Valentin (4,032 m asl). The equilibrium line altitude (ELA) is located at ca. 1,200 m asl (Rivera et al., 2007) and the glacier has an accumulation area ratio of 0.62 (Willis et al., 2012). Also, there is a prominent icefall located in between the accumulation and ablation areas that extends from~500 to 1,500 m asl ( Figure 1A). ...
Article
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Proglacial lakes are ubiquitous features formed during deglaciarization and are currently increasing in number in Patagonia and elsewhere. Proglacial lakes can affect glacier dynamics, catchment hydrology and have the potential to cause glacial lake outburst floods. Therefore, monitoring the onset and development of proglacial lake formation is relevant to understand glacial processes and anticipate glacier response to climate change. In this study, we integrate geomorphological and ice-dynamic information to assess proglacial lake development in Exploradores Glacier, Chilean Patagonia. We monitor recent spatial and temporal changes in the lower trunk of Exploradores Glacier (10 km 2) to provide a 20-year observation record by combining eight uncrewed aerial vehicles (UAV) surveys between 2019 and 2020, with high-medium resolution satellite imagery (Rapid Eye and Landsat) between 2000 and 2018. We use feature tracking techniques, digital surface elevation model analysis and field data to create a multi-temporal scale (inter-annual and seasonal) and a multi-spatial (cm to km) data set. Our analysis shows that surface velocity overall trend has not changed over the last 20 years and that surface velocity near the terminus is significant (>10 m a −1). Moreover, an exceptional advance over moraine deposits was detected. We also found low downwasting rates (<0.5 m a −1) close to the glacier terminus which are attributed to sufficient ice flux and the insulation effect of the debris-covered surface. However, hundreds of supraglacial ponds were observed and are currently coalescing and expanding by ice-cliff backwasting favoring glacier disintegration. Lastly, it was found that calving losses at the east marginal lake equaled ice-flux input into the lake for the UAV monitored period. This study contributes to a better understanding of glacial lake dynamics during proglacial lake development, and our results may help ice modelling efforts to predict glacier response to future climate scenarios.
... The final velocity field is then an average of all the valid velocity estimates, a strategy explored by several studies (i.e. Dehecq et al., 2015;Scherler et al., 2011;Willis et al., 2012). The maximum number of image pairs separated by 1 year was selected for the month of November. ...
Article
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Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are expected to occur in coming decades. About 10 % of the Himalayan glacier population terminates into proglacial lakes, and such lake-terminating glaciers are known to exhibit higher-than-average total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a composite (2017–2019) glacier surface velocity dataset, derived from Sentinel 2 imagery, covering central and eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers (N = 70; umedian: 18.83 m yr−1; IQR – interquartile range – uncertainty estimate: 18.55–19.06 m yr−1) are on average more than double those of land-terminating glaciers (N = 249; umedian: 8.24 m yr−1; IQR uncertainty estimate: 8.17–8.35 m yr−1) and show substantially more heterogeneity than land-terminating glaciers around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which causes about half of the lake-terminating glacier population to accelerate towards the glacier termini. Numerical ice-flow model experiments show that changes in the force balance at the glacier termini are likely to play a key role in accelerating the glacier flow at the front, with variations in basal friction only being of modest importance. The expansion of current glacial lakes and the formation of new meltwater bodies will influence the dynamics of an increasing number of Himalayan glaciers in the future, and these factors should be carefully considered in regional projections.
... Patagonia ice mass loss histories from a number of studies (e.g., Rignot et al., 2003;Chen et al., 2007;Ivins et al., 2011;Willis et al., 2012aWillis et al., , 2012bFig. S1A in the Supplemental Material 1 ) were synthesized by Lange et al. (2014) into a representative ice-loss history (history B), which was translated into a history of uniform ice-thinning rate shown in Figure 2A. ...
Article
The geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12–24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 1018 Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosity.
... The largest temperate ice masses acknowledged in the southern hemisphere are also undergoing this melting process (Warren & Sugden,1993). Both the Northern and Southern Patagonian Icefields (hereafter, NPI and SPI, respectively) and their outlet glaciers, have shown high thinning rates since the second half of the 20 th century (Rignot et al., 2003;Willis et al., 2012a;Willis et al., 2012b). ...
Article
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Despite present efforts to better understand glacier changes and their trends, the satellite gravimetry is a powerful tool still not applied in-depth to study relatively large areas in the Andes of Argentina and Chile. In this work, the Patagonian Icefield mass variations are analyzed together with the decrease trends of the ice layer in the region. The purpose of this study is to demonstrate the GRACE satellite mission (Gravity Recovery and Climate Experiment) ability to detect water storage changes over the glaciers area. Furthermore, the variations of the hydrometric level in some Patagonian lakes were monitored by combining satellite altimetry data and in situ measurements with the observed water mass variations. Data retrieved from GRACE were used to estimate gravity trends; and high-resolution GRACE CSR RL05 mascon solutions were used to analyze the icefields water storage change in the region under study for the 2002-2017 period. Virtual stations from satellite altimetry obtained from a lake database and hydrometric height data from in situ stations, located at Patagonian lakes in Argentina and Chile, were also used in order to compare the TWS from GRACE to the water level of the specific lakes. Additionally, correlation coefficients were determined at each station. The results show a significant water storage decrease in the Icefield area, and they also demonstrate that the ice melt in southern Patagonia (of about 6 cm/year) tends to be more pronounced than in the northern region.
... We selected multiple image pairs of the same locality to maximise velocity field coverage, which is often limited by shadows, 135 cloud cover, low visual contrast, or sensor saturation, and to increase the overall confidence in the velocity estimates. The final velocity field is then an average of all the valid velocity estimates, a strategy explored by several studies (i.e., Dehecq et al., 2015;Scherler et al., 2011;Willis et al., 2012). The maximum number of image pairs separated by one year was selected for the month of November, as this month is associated with low cloud cover and a relatively high snow line. ...
Preprint
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Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to exhibit higher than average total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a composite (2017–2019) glacier surface velocity dataset, derived from Sentinel 2 imagery, covering Central and Eastern Himalayan glaciers larger than 3 km2. We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr−1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Numerical ice-flow model experiments show that changes at the frontal boundary condition are likely to play a key role in accelerating the glacier flow at the front, with variations in basal friction only being of modest importance. The expansion of current glacial lakes, and the formation of new meltwater bodies will influence the dynamics of an increasing number of Himalayan glaciers in the future; a scenario not currently considered in regional ice loss projections.
... One of the most widely used feature tracking algorithms is the amplitude cross-correlator ("ampcor") developed by NASA/JPL. ampcor is an open-source software that has been integrated to NASA/JPL's open-source InSAR processing software, such as ROI_PAC [26] and the InSAR Scientific Computing Environment (ISCE) [27], which were further used to develop various feature tracking software found in the literature [25,[28][29][30][31][32][33]. ...
Article
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In this paper, we build on past efforts with regard to the implementation of an efficient feature tracking algorithm for the mass processing of satellite images. This generic open-source feature tracking routine can be applied to any type of imagery to measure sub-pixel displacements between images. The routine consists of a feature tracking module (autoRIFT) that enhances computational efficiency and a geocoding module (Geogrid) that mitigates problems found in existing geocoding algorithms. When applied to satellite imagery, autoRIFT can run on a grid in the native image coordinates (such as radar or map) and, when used in conjunction with the Geogrid module, on a user-defined grid in geographic Cartesian coordinates such as Universal Transverse Mercator or Polar Stereographic. To validate the efficiency and accuracy of this approach, we demonstrate its use for tracking ice motion by using ESA’s Sentinel-1A/B radar data (seven pairs) and NASA’s Landsat-8 optical data (seven pairs) collected over Greenland’s Jakobshavn Isbræ glacier in 2017. Feature-tracked velocity errors are characterized over stable surfaces, where the best Sentinel-1A/B pair with a 6 day separation has errors in X/Y of 12 m/year or 39 m/year, compared to 22 m/year or 31 m/year for Landsat-8 with a 16-day separation. Different error sources for radar and optical image pairs are investigated, where the seasonal variation and the error dependence on the temporal baseline are analyzed. Estimated velocities were compared with reference velocities derived from DLR’s TanDEM-X SAR/InSAR data over the fast-moving glacier outlet, where Sentinel-1 results agree within 4% compared to 3–7% for Landsat-8. A comprehensive apples-to-apples comparison is made with regard to runtime and accuracy between multiple implementations of the proposed routine and the widely-used “dense ampcor" program from NASA/JPL’s ISCE software. autoRIFT is shown to provide two orders of magnitude of runtime improvement with a 20% improvement in accuracy.
... Glacier lobes in this area have been receding since the end of the LIA (1870 CE), with acceleration of shrinking in the last several decades (Davies and Glasser, 2012). The most pronounced clusters of DSLs are around the Fiero, Leones and Pared Sur outlet glaciers (Fig. 4A), which have experienced kilometre-scale recession since the end of the 19th century (Davies et al., 2020) and approximately 1 m of recent annual thinning (Willis et al., 2012). Some of the major rockslope failures in this area have originated in the last two decades, as reported by Harrison et al. (2006) and Glasser et al. (2016b). ...
Article
Although the dynamics of individual rock-slope failures above recently shrinking glaciers have received increasing study, less is known about the spatial distribution of landslides in paraglacial settings. Here, we present a landslide inventory for large deglaciated area (~100,000 km²) situated within the Last Glacial Maximum (LGM) limits of the Northern Patagonian Icefield (NPI). Using satellite images and the TanDEM-X digital elevation model, we mapped a total of 15,543 landslides, among which 1006 are deep-seated landslides (DSLs) with area ≥0.01 km². The distribution of DSLs is highly asymmetric in a W-E transect of the NPI region, with pronounced clustering along the semi-arid eastern front of the Patagonian Andes. The most strongly affected domain is volcanic tablelands overlying weak Miocene sedimentary rocks, but DSLs tend to also cluster along recently deglaciated (i.e. since the end of the 19th century) eastern margin of the NPI. Compared with other high mountain regions, alpine valleys of the Patagonian Andes are affected by DSLs only in <1% of their area, an order of magnitude lower than in other reported deglaciated mountains. The modest incidence of DSLs in the Patagonian Andes is due to dominance of hard granitoid rocks and relatively weak historical seismic activity. We conclude that 1) geological conditions control the distribution of DSLs and their types in the NPI region; 2) paraglacial effects play secondary (although locally important) roles in the origin of DSLs; 3) local clusters of large DSLs originate due to specifics of the post-LGM landscape evolution, involving drawdowns of glacial lakes and incision of rivers into the unconsolidated deposits; and 4) increased abundance of landslides above the recently shrinking margin of the NPI results from the repeated Holocene fluctuations of glacier snouts around the Little Ice Age (LIA) glacier limits and the spatial coincidence of glacial debuttressing effects with the presence of active faults.
... Large decreases in ice cover in the Northern Patagonian Ice Field (NPIF) have exposed the vast soil surface of the major ice field in the Southern Hemisphere (Rignot, Rivera, and Casass 2003;Willis et al. 2012; Barcaza et al. 2017). These soils have been subject to extensive and prolonged ice cover during the last 100,000 years (Rasmussen, Conway, and Raymond 2007;Masiokas et al. 2015;Mardones et al. 2018). ...
... Large decreases in ice cover in the Northern Patagonian Ice Field (NPIF) have exposed the vast soil surface of the major ice field in the Southern Hemisphere (Rignot, Rivera, and Casass 2003;Willis et al. 2012; Barcaza et al. 2017). These soils have been subject to extensive and prolonged ice cover during the last 100,000 years (Rasmussen, Conway, and Raymond 2007;Masiokas et al. 2015;Mardones et al. 2018). ...
Article
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In recently deglaciated soils, microbial organisms drive soil transformations by increasing carbon (C) and nitrogen (N) pools while depleting available phosphorous (P), thus improving plant colonization and soil development. However, the rate of soil development can vary in response to local environmental conditions that affect microbial abundance and activity. In this contribution we use observational and experimental approaches to evaluate the interplay between soil biogeochemical features and microbial abundance and function after approximately seventy years of soil development in the forefield of the Exploradores Glacier that is located at the northernmost end of the Northern Patagonian Ice Field. Our findings suggest that after approximately seventy years of soil development, microbial abundance and soil C and N accumulation increase with soil age, soil bulk density and pH decreased, and microbial activity measured as soil chlorophyll a and nifH gene abundance increased. In turn, decomposition increased with fungal abundance, showing higher values in the late stages of soil development where the soil C:N ratio was higher and soil pH was lower. Overall, biogeochemical changes along this chronosequence followed the predicted pattern, with gradual increases in soil nutrients and microbial abundance, in addition to decomposition processes.
... Sustained glacier recession is driving the development of proglacial lakes at the termini of glaciers as meltwater accumulates within bedrock basins, behind moraine ridges and outwash fan heads, or is impounded by dead ice (Carrivick & Tweed, 2013). Glaciers in contact with a lake are receding more rapidly than their land-terminating counterparts, for example, in the Himalaya (Maurer et al., 2019;Tsutaki et al., 2019), in Alaska (Larsen et al., 2007;Willis et al., 2012), and in New Zealand (Chinn et al., 2012). Glaciers terminating in proglacial lakes can lose mass by several mechanisms in addition to melt from energy exchanges at the ice surface, namely, calving and subaqueous melting, collectively known as frontal ablation (Maurer et al., 2016;Sakai et al., 2009;Truffer & Motyka, 2016;Watson et al., 2020). ...
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Plain Language Summary Lakes form at the margins of glaciers as meltwater accumulates against hillsides and behind ridges of glacier debris. Lakes at a glacier terminus are known to affect its behavior. However, glaciers terminating into such lakes are usually absent from computer simulations, and the effects of these lakes on the rates of deglaciation and on glacier behavior are poorly quantified. In this study, we tested the effect of a lake on glacier recession under two different scenarios; a land‐terminating versus a lake‐terminating glacier. We used an ice flow model called BISICLES and applied it to what was once the Pukaki Glacier in New Zealand during the end of the last ice age. We found that the presence of a lake caused the glacier to recede more than 4 times further and it accelerated ice flow by up to 8 times when compared to the same glacier that terminated on land under the same climate. Our simulated lake processes predominantly influenced the glacier over decades to centuries rather than over millennia. We suggest, therefore, that simulations of glacier evolution ignoring glacial lakes will likely misrepresent the timing and rate of recession, especially during the transition from a land‐terminating to a lake‐terminating environment.
... Les séries de MNE sont utilisées par simple différenciation (MNE différentiels) lorsque le jeu de données ne comporte que quelques MNE (e. g. Berthier et al. 2004) ou par analyse statistique de la tendance de chaque pixel lorsque la série est assez dense (Willis et al., 2012a(Willis et al., , 2012b (Berthier … Chevallier, 2007.) ou par analyse de la relation entre la différence d'élévation et l'aspect du terrain (Nuth et Kääb, 2011.). ...
... The data and methodology (ASTERIX) applied here to the entire Andes was inspired by previous studies [52][53][54] . Below we briefly summarize the processing steps and highlight the specificity for the application to the Andes. ...
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An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3–4 m in the high accumulation regions. The seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928–2000, resulting in peak values of 1.5 m a ⁻¹ . Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between −0.2 and −0.4 m a ⁻¹ from 2009 to 2016. The estimated glacier-wide mass-balance rates are −0.27 ± 0.05 m w.e. a ⁻¹ for 2000 to 2011 and −0.51 ± 0.04 m w.e. a ⁻¹ between 2011 and 2016.
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The Andean Glacier and Water Atlas provides a state of the art overview of the Andean glaciers, the impacts of climate change on their retreat, and the impact on water security in vulnerable regions of the Andes. An eye-opener.
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Ice caps that are mostly frozen at the bedrock-ice interface are thought to be stable and respond slowly to changes in climate. We use remote sensing to measure velocity and thickness changes that occur when the margin of the largely cold-based Vavilov Ice Cap in the Russian High Arctic advances over weak marine sediments. We show that cold-based to polythermal glacier systems with no previous history of surging may evolve with unexpected and unprecedented speed when their basal boundary conditions change, resulting in very large dynamic ice mass losses (an increase in annual mass loss by a factor of ∼100) over a few years. We question the future long-term stability of cold and polythermal polar ice caps, many of which terminate in marine waters as the climate becomes warmer and wetter in the polar regions. Significance statement: A tipping point is reached as a largely cold-based ice-cap outlet glacier with no previous history of surges advanced over low-friction marine sediments, causing it to accelerate and thin.
Article
Fedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation canges. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3–4 m in the high accumulation regions. The seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928–2000, resulting in peak values of 1.5 m a−1. Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between −0.2 and −0.4 m a−1 from 2009 to 2016. The estimated glacier-wide mass-balance rates are −0.27 ± 0.05 m w.e. a−1 for 2000 to 2011 and −0.51 ± 0.04 m w.e. a−1 between 2011 and 2016.
Thesis
Glaciers on Earth along other components of the cryosphere are important for the climate system. However, it is widely known that the vast majority of glaciers are retreating and thinning since the early part of the 20th century. Additionally, future projections have highlighted that at the end of the 21st century, glaciers are going to lose a considerable part of their remaining mass. These glacier changes have several implications for physical, biological and human systems, affecting the water availability for downstream communities and contribute to sea level rise. Unlike other regions, where glaciers are less relevant for the overall hydrology, glaciers in South America constitute a critical resource since minimum flow levels in headwaters of the Andean mountains are usually sustained by ice melt, especially during late summer and droughts, when the contribution from the seasonal snow cover is depleted. In the last decades, the number of studies has increased considerable, however, in the Southern Andes and the surrounding sub-Antarctic islands glaciers still are less studied in comparison with their counterparts in the Northern Hemisphere. The few studies on glacier mass balance in this region suggest a risk of water scarcity for many Andean cities which freshwater supply depends on glacial meltwater. Additionally, glaciers on sub-Antarctic islands have not been completely assessed and their contribution to the sea level rise has been roughly estimated. Hence, the monitoring of glaciers is critical to provide baseline information for regional climate change adaptation policies and facilitate potential hazard assessments. Close and long-range remote sensing techniques offer the potential for repeated measurements of glacier variables (e.g. glacier mass balance, area changes). In the last decades, the number of sensors and methods has increased considerably, allowing time series analysis as well as new and more precise measurements of glacier changes. The main goal of this thesis is to investigate and provide a detailed quantification of glacier elevation and mass changes of the Southern Andes with strong focus on the Central Andes of Chile and South Georgia. Six comprehensive studies were performed to provide a better understanding of the development and current status of glaciers in this region. Overall, the glacier changes were estimated by means of various remote sensing techniques. For the Andes as a whole, the first continent-wide glacier elevation and mass balance was conducted for 85% of the total glacierized area of South America. A detailed estimation of mass changes using the bi-static synthetic aperture radar interferometry (Shuttle Radar Topography Mission -SRTM- and TerraSAR-X add-on for Digital Elevation Measurements -TanDEM-X- DEMs) over the years 2000 to 2011/2015 was computed. A total mass loss rate of 19.43 ± 0.60 Gt a-1 (0.054 ± 0.002 mm a-1 sea level rise contribution) from elevation changes above ground, sea or lake level was calculated, with an extra 3.06 ± 1.24 Gt a-1 derived from subaqueous ice mass loss. The results indicated that about 83% of the total mass loss observed in this study was contributed by the Patagonian icefields (Northern and Southern), which can largely be explained by the dynamic adjustments of large glaciers. For the Central Andes of Chile, four studies were conducted where detailed times series of glacier area, mass and runoff changes were performed on individual glaciers and at a region level (Maipo River basin). Glaciers in the central Andes of Chile are a fundamental natural resources since they provide freshwater for ecosystems and for the densely populated Metropolitan Region of Chile. The first study was conducted in the Maipo River basin to obtain time series of basin-wide glacier mass balance estimates. The estimations were obtained using historical topographic maps, SRTM, TanDEM-X, and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results showed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, with more negative values between 2000 and 2013. A mean basin-wide glacier mass balance of −0.12 ± 0.06 m w.e. a-1 , with a total mass loss of 2.43 ± 0.26 Gt between 1955–2013 was calculated. For this region, a 20% reduction in glacier ice volume since 1955 was observed with associated consequences for the meltwater contribution to the local river system. Individual glacier studies were performed for the Echaurren Norte and El Morado glaciers. Echaurren Norte Glacier is a reference glacier for the World Glacier Monitoring Service. An ensemble of different data sets was used to derive a complete time series of elevation, mass and area changes. For El Morado Glacier, a continuous thinning and retreat since the 20th century was found. Overall, highly negative elevation and mass changes rates were observed from 2010 onwards. This coincides with the severe drought in Chile in this period. Moreover, the evolution of a proglacial lake was traced. If drained, the water volume poses an important risk to down-valley infrastructure. The glacier mass balance for the Central Andes of Chile has been observed to be highly correlated with precipitation (ENSO). All these changes have provoked a glacier volume reduction of one-fifth between 1955 and 2016 and decrease in the glacier runoff contribution in the Maipo basin. The thesis closes with the first island-wide glacier elevation and mass change study for South Georgia glaciers, one of the largest sub-Antarctic islands. There, glaciers changes were inferred by bi-static synthetic aperture radar interferometry between 2000 and 2013. Frontal area changes were mapped between 2003 and 2016 to roughly estimate the subaqueous mass loss. Special focus was given to Szielasko Glacier where repeated GNSS measurements were available from 2012 and 2017. The results showed an average glacier mass balance of −1.04 ± 0.09 m w.e. a-1 and a mass loss rate of 2.28 ± 0.19 Gt a-1 (equivalent to 0.006 ± 0.001 mm a-1 sea level rise) in the period 2000-2013. An extra 0.77 ± 0.04 Gt a-1 was estimated for subaqueous mass loss. The concurrent area change rate of the marine and lake-terminating glaciers amounts to −6.58 ± 0.33 km2 a-1 (2003–2016). Overall, the highest thinning and retreat rates were observed for the large outlet glaciers located at the north-east coast. Neumayer Glacier showed the highest thinning rates with the disintegration of some tributaries. Our comparison between InSAR data and GNSS measurements showed good agreement, demonstrating consistency in the glacier elevation change rates from two different methods. Our glacier elevation and mass changes assessment provides a baseline for further comparison and calibration of model projection in a sparsely investigated region. Future field measurements, long-term climate reanalysis, and glacier system modelling including ice-dynamic changes are required to understand and identify the key forcing factors of the glacier retreat and thinning.
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El Atlas de Glaciares y Aguas Andinos proporciona una visión general de los glaciares andinos, los impactos del cambio climático en su retirada y el impacto en la seguridad del agua en las regiones vulnerables de los Andes. Una referencia.
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Glacial change is an important part of global change. Its evolutionary process directly reflects global climate change, and its data features high resolutions, a large amount of information, and high fidelity.
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The Southern Patagonia Icefield (SPI) withdrawal in recent decades shows contrasting behaviours between adjacent basins. One of the basins with highest volumetric losses is located at northern- most SPI. We refer to Jorge Montt tidewater glacier (48° 30′S/73° 30′W, 445 km2 in 2018), which retreated 2.7 km between 2011 and 2018 and thinned at rates of up to 21 m a−1 over this period. Based on the retreat record, remote-sensing imagery, field data, a mass-balance model and a calving parameterisation, we attempted to differentiate climatic-induced changes (i.e. surface mass balance) and dynamic responses (i.e. calving fluxes). The surface mass balance reached −4.15 km3 w.e. a−1 between 2012 and 2017. When frontal ablation is included, the net mass bal- ance is −17.79 km3 w.e. a−1. This represents a change of trend compared with modelling estima- tions of positive surface mass balance prior to 2010. This shift is attributed to higher ablation rates given that accumulation is known to have increased between 1980 and 2015. The available evidence, therefore, indicates that frontal ablation is the main factor, supported by observed rates at Jorge Montt as high as 3.81 km3 w.e. a−1 in 2015, with ice velocities peaking at 11 km a−1.
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Most glaciers in South America and on the Antarctic Peninsula are retreating and thinning. They are considered strong contributors to global sea level rise. However, there is a lack of glacier mass balance studies in other areas of the Southern Hemisphere, such as the surrounding Antarctic Islands. Here, we present a detailed quantification of the 21st century glacier elevation and mass changes for the entire South Georgia Island using bi-static synthetic aperture radar interferometry between 2000 and 2013. The results suggest a significant mass loss since the beginning of the present century. We calculate an average glacier mass balance of −1.04 ± 0.09 m w.e.a−1 and a mass loss rate of 2.28 ± 0.19 Gt a−1 (2000–2013), contributing 0.006 ± 0.001 mm a−1 to sea-level rise. Additionally, we calculate a subaqueous mass loss of 0.77 ± 0.04 Gt a−1 (2003–2016), with an area change at the marine and lake-terminating glacier fronts of −6.58 ± 0.33 km2 a−1, corresponding to ~4% of the total glacier area. Overall, we observe negative mass balance rates in South Georgia, with the highest thinning and retreat rates at the large outlet glaciers located at the north-east coast. Although the spaceborne remote sensing dataset analysed in this research is a key contribution to better understanding of the glacier changes in South Georgia, more detailed field measurements, glacier dynamics studies or further long-term analysis with high-resolution regional climate models are required to precisely identify the forcing factors.
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The Tasman Glacier is New Zealand’s largest body of ice comprising several tributary glaciers. Since the early 1990s it has undergone a rapid frontal retreat associated with the expansion of a proglacial lake. In this study, digital photogrammetric processing of vertical aerial photographs were used to derive two high-resolution Digital Elevation Models (DEM) of the Tasman Glacier. Additionally, in order to account for the volume loss due to lake expansion, the subaqueous lake topography was generated from a recent bathymetric survey and appended to the latest DEM. Detailed analysis of the multitemporal DEM enabled the quantification of geodetic surface elevation and mass balance changes. Calculations show that the main Tasman Glacier and its tributaries have lost 19.72 ± 0.05 × 10^8 m^3 of ice between 1986 and 2008. The proglacial Tasman Lake occupied ca. 28% of this volume loss. The glacier-wide volume loss corresponds to a geodetic balance of 0.87 ± 0.002 m w. eq. yr^-1. Differential DEM analysis revealed diverse spatial patterns of thickness and volume change, varying between the tributaries and within and between elevation bins. Furthermore, reworked and transported material from recent rockfall deposits produced localised areas of apparent positive elevation changes. Previous ice volume change estimates may have underestimated mass loss from the Tasman Glacier, partly due to a lack of bathymetric data to account for the glacier-wide volume variation and omission of the tributary glaciers. The methods developed in this study offer a potential way forward for glacier monitoring in New Zealand, where old aerial photographs are available but have not previously been processed in this manner to obtain accurate assessment of geodetic mass balance.
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The Andes Cordillera contains the most diverse cryosphere on Earth, including extensive areas covered by seasonal snow, numerous tropical and extratropical glaciers, and many mountain permafrost landforms. Here, we review some recent advances in the study of the main components of the cryosphere in the Andes, and discuss the changes observed in the seasonal snow and permanent ice masses of this region over the past decades. The open access and increasing availability of remote sensing products has produced a substantial improvement in our understanding of the current state and recent changes of the Andean cryosphere, allowing an unprecedented detail in their identification and monitoring at local and regional scales. Analyses of snow cover maps has allowed the identification of seasonal patterns and long term trends in snow accumulation for most of the Andes, with some sectors in central Chile and central-western Argentina showing a clear decline in snowfall and snow persistence since 2010. This recent shortage of mountain snow has caused an extended, severe drought that is unprecedented in the hydrological and climatological records from this region. Together with data from global glacier inventories, detailed inventories at local/regional scales are now also freely available, providing important new information for glaciological, hydrological, and climatological assessments in different sectors of the Andes. Numerous studies largely based on field measurements and/or remote sensing techniques have documented the recent glacier shrinkage throughout the Andes. This observed ice mass loss has put Andean glaciers among the highest contributors to sea level rise per unit area. Other recent studies have focused on rock glaciers, showing that in extensive semi-arid sectors of the Andes these mountain permafrost features contain large reserves of freshwater and may play a crucial role as future climate becomes warmer and drier in this region. Many relevant issues remain to be investigated, however, including an improved estimation of ice volumes at local scales, and detailed assessments of the hydrological significance of the different components of the cryosphere in Andean river basins. The impacts of future climate changes on the Andean cryosphere also need to be studied in more detail, considering the contrasting climatic scenarios projected for each region. The sustained work of various monitoring programs in the different Andean countries is promising and will provide much needed field observations to validate and improve the analyses made from remote sensors and modeling techniques. In this sense, the development of a well-coordinated network of high-elevation hydro-meteorological stations appears as a much needed priority to complement and improve the many glaciological and hydro-climatological assessments that are being conducted across the Andes.
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Central Tianshan (CTS) plays a prominent role in maintaining the vulnerable ecosystem in Central Asia. Rivers originating from it have high proportions of the runoffs contributed by glacier meltwater. In this study, the glacier mass balance in the catchments of Muzart and Karayulun rivers, CTS, was estimated by a geodetic method based on Advanced Land Observing Satellite/Panchromatic Remote-sensing Instrument for Stereo Mapping images and Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM). The results revealed that at the west and east glacial centers in the study area, the 2000–2011 mass loss rates were −0.03 ± 0.17 and −0.06 ± 0.17 m w.e./a, respectively, considerably lower than other CTS zones. In order to ascertain this stable glacier state, we also performed a geodetic measurement based on TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) images and SRTM DEM (2000–2012), and the results are similar (0.01 ± 0.17 and −0.04 ± 0.17 m w.e./a, respectively). The glacier thickness change around the regional snowline was close to zero. The strong capability of cold storage and the temperature drop in the early 21st century may account for the anomalous mass changes. Despite slight overall mass changes, obvious thinning was observed on many exposed glacier feet. This study indicates that the glacier melting can be effectively controlled if the rising trend of temperatures is reversed; furthermore, the land surface hydrological model should be calibrated with geodetic glacier mass balance measurement when it is used to simulate the streamflow trend in the headwater basin.
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Mass balance variations of Glaciar San Rafael, the most equatorial tidewater glacier in the North Patagonian Icefield, are reconstructed over the period 1950–2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km<sup>3</sup> of ice equivalent. Over that period, except for a short period of cooling from 1998–2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggest that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than changes in balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.
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Earlier reports, maps, aerial photographs, and tree-ring dates for moraines are used to investigate and compare the oscillations of the land-based San Quintin Glacier and the calving, tidewater San Rafael Glacier in Southern Chile. The findings show that these two very different outlet glaciers of the North Patagonian Icefield (NPI) have displayed similar trends of ice front retreat and advance since the end of 'The Little Ice Age'. The similarities imply that these glaciers are chiefly controlled by common climatic factors. A review of the literature suggests that some of the earlier reported positions of the San Rafael Glacier may be in error, but all authors agree on the beginning of the recessional trend in the late nineteenth century. The retreat of the San Rafael Glacier stopped in 1991 and by 1993 the San Quintin glacier was advancing over vegetated ground. This study mapped the San Quintin Glacier moraines and dated them by dendrochronology. Twelve years were added to treering counts for colonization and growth to core height. Dendrochronology is also used to provide minimum rates of ice surface downwasting. Investigation of records from the nearest weather station suggests that precipitation could be the main control of ice front oscillations, with a response time of 20 years. A comparison of records from other weather stations to the north and south shows that these glaciers lie in a highly sensitive area between two climatic regimes, with precipitation and temperature, at present, weakly reflecting northern rather than southern Patagonian weather patterns.
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Version 3.1 of the Generic Mapping Tools (GMT) has been released. More than 6000 scientists worldwide are currently using this free, public domain collection of UNIX tools that contains programs serving a variety of research functions. GMT allows users to manipulate (x,y) and (x,y,z) data, and generate PostScript illustrations, including simple x-y diagrams, contour maps, color images, and artificially illuminated, perspective, and/or shaded-relief plots using a variety of map projections (see Wessel and Smith [1991] and Wessel and Smith [1995], for details.). GMT has been installed under UNIX on most types of workstations and both IBM-compatible and Macintosh personal computers.
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The Patagonian icefields are the largest mid-latitude ice masses and yet few glaciological data exist for them. The presence of the Andes lying athwart the westerlies makes for a dynamic glacial system with steep balance gradients and west-east equilibrium-line altitude gradients. The overall trend during the 20th century has been glacier retreat. However, whereas most eastern outlets retreated consistently from the beginning of the century, recession on the west began later, has been interrupted by readvances, and most recently has accelerated markedly, reaching higher mean rates of retreat than those on the east. This contrast may result from a predominantly precipitation-controlled mass-balance regime in the west and a dominant temperature control in the east. Superimposed on these contrasts is the anomalous behavior of certain calving glaciers, the oscillations of which contrast in magnitude, timing and sign with each other and with noncalving glaciers, and which in many cases do not relate directly to climate change. Two large calving outlets are at or near their Neoglacial maxima. The tantalizing fragments of information that exist suggest that there is a rich glaciological source to be mined in Patagonia yielding insights into glacioclimatic interactions, calving dynamics, Holocene climate change and the role of topography in controlling glacier behavior. 118 refs., 13 figs., 2 tabs.
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Tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour. Near the terminus of the glacier, surface speeds average 17 m d-1 in summer and calving is profuse and continual. Mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 Mm3d-1. Mean annual calving speed and calving flux are about 4500 m a-1 and 2.0 km3a-1, respectively. This calving speed is higher than that predicted by the established empirical relationships between tide-water calving speed and water depth. Daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables, but tidal stage may have some control over the timing of large submarine calving events. The relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates. -from Authors
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Coverage of ice velocities in the central part of the Southern Alps, New Zealand, is obtained from feature tracking using repeat optical imagery in 2002 and 2006. Precise orthorectification, co-registration and correlation is carried out using the freely available software COSI-Corr. This analysis, combined with short times between image acquisitions, has enabled velocities to be captured even in the accumulation areas, where velocities are lowest and surface features ephemeral. The results indicate large velocities for mountain glaciers (i.e. up to ~5 m d–1) as well as dynamic changes in some glaciers that have occurred between 2002 and 2006. For the steep and more responsive Fox and Franz Josef Glaciers the speed increased at the glacier snout during the advance period, while the low-angled and debris-covered Tasman Glacier showed no measurable velocity change. Velocity increases on the steeper glaciers are the result of an observed thickening and steepening of the glacier tongues as they moved from a retreat phase in 2002 to an advance phase in 2006. This contrasting behaviour is consistent with historic terminus position changes. The steeper glaciers have undergone several advance/retreat cycles during the observation period (1894 to present), while the low-angled glacier showed little terminus response until retreat resulting from the accelerating growth of a proglacial lake commenced in 1983.
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We propose a technique for monitoring snowmelt over the Greenland ice sheet between 1992 and 2005 based on the difference between ascending and descending brightness temperatures (DAV) measured either at 19.35- or 37- GHz by the Special Sensor Microwave Imager (SSM/I). Wet snow is detected when both brightness temperatures and DAV values exceed fixed thresholds. Differently from existing techniques, a multi-frequency approach allows detection of wet snow at different depths and intensities, providing a tool for improving climatological and hydrological applications. Air temperature values either recorded by ground based stations or derived from model are used for calibrating and validating the technique. Results are compared with those obtained using backscattering coefficients recorded by the NASA's Quick Scatterometer (QuikSCAT) during an extreme melting event occurring on June 2002. Long-term results show that snowmelt extent has been increasing at a rate of ∼40,000 Km2 per year for the past 14 years.
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Land glacier extent and volume at the northern and southern margins of the Drake Passage have been in a state of dramatic demise since the early 1990s. Here time-varying space gravity observations from the Gravity Recovery and Climate Experiment (GRACE) are combined with Global Positioning System (GPS) bedrock uplift data to simultaneously solve for ice loss and for solid Earth glacial isostatic adjustment (GIA) to Little Ice Age (LIA) cryospheric loading. The present-day ice loss rates are determined to be −26 ± 6 Gt/yr and −41.5 ± 9 Gt/yr in the Southern and Northern Patagonia Ice Fields (NPI+SPI) and Antarctic Peninsula (AP), respectively. These are consistent with estimates based upon thickness and flux changes. Bounds are recovered for elastic lithosphere thicknesses of 35 ≤ h ≤ 70 km and 20 ≤ h ≤ 45 km and for upper mantle viscosities of 4–8 × 1018 Pa s and 3–10 × 1019 Pa s (using a half-space approximation) for NPI+SPI and AP, respectively, using an iterative forward model strategy. Antarctic Peninsula ice models with a prolonged LIA, extending to A.D. 1930, are favored in all χ2 fits to the GPS uplift data. This result is largely decoupled from Earth structure assumptions. The GIA corrections account for roughly 20–60% of the space-determined secular gravity change. Collectively, the on-land ice losses correspond to volume increases of the oceans equivalent to 0.19 ± 0.045 mm/yr of sea level rise for the last 15 years.
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The first near-global high-resolution digital elevation model (DEM) of the Earth has recently been released following the successful Shuttle Radar Topography Mission (SRTM) of 2000. This data set will have applications in a wide range of fields and will be especially valuable in the Earth sciences. Prior to widespread dissemination and use, it is important to acquire knowledge regarding the accuracy characteristics. In this work a comprehensive analysis of the vertical errors present in the data set and the assessment of their effects on different hydrogeomorphic products is performed. In particular, the work consisted of (1) measuring the vertical accuracy of the data set in two areas with different topographic characteristics; (2) characterizing the error structure by comparing elevation residuals with terrain attributes; (3) assessing a wavelet-based filter for removing speckle; and (4) assessing the effects of vertical errors on hydrogeomorphic products and on slope stability modeling. The results indicate that in the two sites, relief has a strong effect on the vertical accuracy of the SRTM DEM. In the high-relief terrain, large errors and data voids are frequent, and their location is strongly influenced by topography, while in the low- to medium-relief site, errors are smaller, although the hilly terrain still produces an effect on the sign of the errors. Speckling generates deviations in the drainage network in one of the investigated areas, but the application of a wavelet filter proved to be an effective tool for removing vertical noise, although further fine tuning is necessary. Vertical errors cause differences in automatically extracted hydrogeomorphic products that range between 4 and 1090.
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Current heuristic laws that relate the motion of glaciers due to sliding along the bed to the subglacial water pressure fail to reproduce variations in sliding speed on timescales of specific hydrologic events, such as lake drainage, rainfall, or surging. This may be due to the importance of subglacial cavity evolution and shifts in the glacier stress field, both of which are not accounted for in typical sliding laws. We use multiple time series of surface motion over a 66-day period at Breiðamerkurjökull, Iceland, to infer changes in bed separation and longitudinal force budget. We observe multiple, distinct periods of increased surface motion and uplift corresponding to periods of rainfall and/or increased temperatures. We find consistent hysteresis and lags between motion and variations in both the bed separation and longitudinal stress gradient that we attribute to the redistribution of normal stresses at the bed during cavity growth. Increases in the longitudinal stress gradient suggest a downglacier stress transfer during increased basal motion that is consistent with increased drainage system efficiency toward the terminus. Our results suggest that the transient evolution of the subglacial drainage system and shifts in the glacier stress field are important controls on basal motion.
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A vertical crustal uplift rate of 39mmyr−1 is measured between 2003 and 2006 using Global Positioning System (GPS) measurements at the northeastern edge of the Southern Patagonia Icefield (SPI). This is the largest present-day glacial isostatic rate ever recorded. The combination of SPI's rapid melting and the unique regional slab-window tectonics that promotes a relatively low viscosity, is central to our interpretation of the observations. The two effects lead to a strong interaction of short relaxation times with ice loads that change on a comparable time scale. The profile of GPS observations link ice loss to the soft viscoelastic isostatic flow response over the time scale of the Little Ice Age (LIA), including ice loss in the period of observation. The agreement of the results with our model predictions strongly suggests the large crustal uplift in Patagonia is due an accelerated glacier wasting since the termination of the LIA and that the effective regional mantle viscosity is near 4.0–8.0×1018Pas. A century-long diminution of the icefields, at rates that are about 1/4 – 1/2 the contemporary loss rates, is consistent with multidecadal-scale temperature trends estimated for the past 50–100years and is, in fact, a key feature in any model capable of explaining the uplift data.
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Mass balance variations of Glaciar San Rafael, the northernmost tidewater glacier in the Southern Hemisphere, are reconstructed over the period 1950-2005 using NCEP-NCAR reanalysis climate data together with sparse, local historical observations of air temperature, precipitation, accumulation, ablation, thinning, calving, and glacier retreat. The combined observations over the past 50 yr indicate that Glaciar San Rafael has thinned and retreated since 1959, with a total mass loss of ~22 km3 of ice eq. Over that period, except for a short period of cooling from 1998-2003, the climate has become progressively warmer and drier, which has resulted primarily in pervasive thinning of the glacier surface and a decrease in calving rates, with only minor acceleration in retreat of the terminus. A comparison of calving fluxes derived from the mass balance variations and from theoretical calving and sliding laws suggests that calving rates are inversely correlated with retreat rates, and that terminus geometry is more important than balance fluxes to the terminus in driving calving dynamics. For Glaciar San Rafael, regional climate warming has not yet resulted in the significant changes in glacier length seen in other calving glaciers in the region, emphasizing the complex dynamics between climate inputs, topographic constraints and glacier response in calving glacier systems.
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The melting of mountain glaciers and ice caps is expected to contribute significantly to sea-level rise in the twenty-first century, although the magnitude of this contribution is not fully constrained. Glaciers in the Patagonian Icefields of South America are thought to have contributed about 10% of the total sea-level rise attributable to mountain glaciers in the past 50 years. However, it is unclear whether recent rates of glacier recession in Patagonia are unusual relative to the past few centuries. Here we reconstruct the recession of these glaciers using remote sensing and field determinations of trimline and terminal moraine location. We estimate that the North Patagonian Icefield has lost 103+/-20.7km3 of ice since its late Holocene peak extent in AD 1870 and that the South Patagonian Icefield has lost 503+/-101.1km3 since its peak in AD 1650. This equates to a sea-level contribution of 0.0018+/-0.0004mmyr-1 since 1870 from the north and 0.0034+/-0.0007mmyr-1 since 1650 from the south. The centennial rates of sea-level contribution we derive are one order of magnitude lower than estimates of melting over the past 50 years, even when we account for possible thinning above the trimline. We conclude that the melt rate and sea-level contribution of the Patagonian Icefields increased markedly in the twentieth century.
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There are an increasing number of digital elevation models (DEMs) available worldwide for deriving elevation differences over time, including vertical changes on glaciers. Most of these DEMs are heavily post-processed or merged, so that physical error modelling becomes difficult and statistical error modelling is required instead. We propose a three-step methodological framework for assessing and correcting DEMs to quantify glacier elevation changes: (i) remove DEM shifts, (ii) check for elevation-dependent biases, and (iii) check for higher-order, sensor-specific biases. A simple, analytic and robust method to co-register elevation data is presented in regions where stable terrain is either plentiful (case study New Zealand) or limited (case study Svalbard). The method is demonstrated using the three global elevation data sets available to date, SRTM, ICESat and the ASTER GDEM, and with automatically generated DEMs from satellite stereo instruments of ASTER and SPOT5-HRS. After 3-D co-registration, significant biases related to elevation were found in some of the stereoscopic DEMs. Biases related to the satellite acquisition geometry (along/cross track) were detected at two frequencies in the automatically generated ASTER DEMs. The higher frequency bias seems to be related to satellite jitter, most apparent in the back-looking pass of the satellite. The origins of the more significant lower frequency bias is uncertain. ICESat-derived elevations are found to be the most consistent globally available elevation data set available so far. Before performing regional-scale glacier elevation change studies or mosaicking DEMs from multiple individual tiles (e.g. ASTER GDEM), we recommend to co-register all elevation data to ICESat as a global vertical reference system.
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Passive-microwave 37 GHz vertically polarized (V) brightness temperature (Tb) measurements from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) are used to monitor the extent and timing of snowmelt on the Southern Patagonia Icefield (SPI) in Chile and Argentina. Twice daily Tb′s for 2002-08 for high-elevation (>1200 ma.s.l.) pixels exhibit a bimodal histogram, typical of snow-covered regions in Yukon, Alaskan icefields and the Greenland ice sheet. The low count between the two populations represents the Tb threshold for melt (252 K). This Tb value with the ±18K diurnal amplitude variation threshold quantifies onset and duration of the spring melt-refreeze period and is used to identify melt regimes and seasonal Tb signals. Tb histograms for pixels west of the Andean divide have a normal distribution above the melt threshold. We interpret the Tb histogram as controlled by surface moisture; the shape and position with respect to Tb are retained with changes in both latitude and elevation, and the region is known to have a moist climate. Tb is not driven by seasonal temperature changes in the northwest sector of the icefield because the Tb threshold is exceeded 75% of the time. For all pixels, the spring melt-refreeze period has shortened by a mean of 10 days a−1 and a mean of 16 days a−1 for pixels with bimodal distributions between 2002 and 2008.
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Knowledge about the spatio-temporal distribution of fast-flowing Arctic glaciers is still limited. Kronebreen, Svalbard, in particular, includes the confluence - and the dynamic interplay - of the fast-flowing Kronebreen and the currently slow-flowing Kongsvegen. In this study, image-matching techniques on the basis of repeated Landsat 7 Enhanced Thematic Mapper Plus (ETM+) pan and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data are applied in order to derive surface velocity fields of the lowermost 10 km of Kronebreen for the annual periods 1999/2000, 2000/01, 2001/02 and a 40 day period around July 2001. This work perfectly complements differential synthetic aperture radar interferometry (DInSAR) studies available for Kronebreen. A complete surface velocity field is now available from combining the DInSAR studies for the upper part of the glacier and the optical image-matching study presented here. The data obtained within this study are also compared to velocity data of 1964, 1986, 1990 and 1996. As also suggested by previous studies, a significant spatio-temporal variability of the spring/summer and annual ice speeds becomes evident.
Article
Glaciological research was carried out in November and December 1996 in the accumulation area of Glaciar Nef, an eastward-facing glacier from Hielo Patagónico Norte (Northern Patagonia Icefield), South America. A 14.5-m-deep firn core (9.7 m water equivalent: w.e.) was obtained at 1500 m a.s.l., and air temperature and melting rate were also measured. Values of δ¹⁸O of 1- or 2-cm-thick samples in the upper 6 m of the firn fluctuated from −16 to −10±, which are explained by variations in δ¹⁸O of precipitation. Below 6 m in the firn, δ¹⁸O was almost constant, due to percolation of large amounts of meltwater. It was considered that the upper 6 m was deposited during the prior winter; thus winter balance in 1996 was derived as +3.5 m w.e. Based on the measurement results and climatic data, winter and summer ablations were estimated at 0.0 and 3.4 m w.e., respectively, and summer accumulation at 2.1 m w.e. Then, net balance in the calendar year 1996 was estimated at about +2.2 m w.e. Comparison with previous studies and candidate drilling sites are also discussed.
Article
Recent fluctuations of the San Rafael Glacier contrast in timing, direction and intensity with regional trends of glacier behaviour. In this paper, a link is identified between the oscillation history, the topographic situation and variations in winter precipitation. The San Rafael Glacier is the lowest latitude tidewater glacier in the world with unusually high annual mean velocities. Since the late nineteenth century, it has retreated and advanced rapidly over a total distance of 14 km and is now 60 km² smaller than it was 100 years ago. Retreat at up to 300 m a⁻¹ during the 1980s halted in 1990. Since then, a slight readvance has occurred at a time of accelerated regional retreat. Calving glaciers are known to respond indirectly to climate change, but whereas some may oscillate in non-climatic, cyclical ways over decadal and century timescales, the San Rafael Glacier seems to respond rapidly to changes in precipitation. The influence of calving dynamics has, at different times, both damped and amplified the response to climate change, but the topographic geometry does not permit large-scale, non-climatic fluctuations. The Holocene record of glacier behaviour is therefore probably free of calving anomalies.
Article
The first topographic and ice-motion maps of the northwestern flank of Hielo Patagónico Norte (HPN, northern Patagonia Icefield), in Chile, were produced using satellite synthetic-aperture interferometric radar data acquired by NASA’s Spaceborne Imaging Radar C instrument in October 1994. The topographic map has a 10 m vertical precision with a 30 m horizontal spacing, which should be sufficient to serve as a reference for monitoring future mass changes of the icefield. The ice-motion map is accurate to within 4 mm d−1 (or 1 m a−1). The radar-derived surface topography and ice velocity are used to estimate the ice discharge from the accumulation area of four outlet glaciers, and the calving flux and mass balance of Glaciar San Rafael. The results demonstrate the use of SAR interferometry for monitoring glaciological parameters on a spatial and temporal scale unattainable by any other means.
Article
The microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.
Article
During the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h. The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model. The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.