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Detailed quantification and interpretation of glacier elevation and mass changes in the Southern Andes and South Georgia
Abstract
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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The surface energy fluxes of glaciers determine surface melt, and their adequate parametrization is one of the keys to a successful prediction of future glacier mass balance and freshwater discharge. Chile hosts glaciers in a large range of latitudes under contrasting climatic settings: from 18∘ S in the Atacama Desert to 55∘ S on Tierra del Fuego. Using three different methods, we computed surface energy fluxes for five glaciers which represent the main glaciological zones of Chile. We found the main energy sources for surface melt change from the Central Andes, where the net shortwave radiation is driving the melt, to Patagonia, where the turbulent fluxes are an important source of energy. We inferred higher surface melt rates for Patagonian glaciers as compared to the glaciers of the Central Andes due to a higher contribution of the turbulent sensible heat flux, less negative net longwave radiation and a positive contribution of the turbulent latent heat flux. The variability in the atmospheric emissivity was high and not able to be explained exclusively by the variability in the inferred cloud cover. The influence of the stability correction and the roughness length on the magnitude of the turbulent fluxes in the different climate settings was examined. We conclude that, when working towards physical melt models, it is not sufficient to use the observed melt as a measure of model performance; the model parametrizations of individual components of the energy balance have to be validated individually against measurements.
As glaciers adjust their size in response to climate variations, long-term changes in meltwater production can be expected, affecting the local availability of water resources. We investigate glacier runoff in the period 1955–2016 in the Maipo River basin (4843 km2, 33.0–34.3∘ S, 69.8–70.5∘ W), in the semiarid Andes of Chile. The basin contains more than 800 glaciers, which cover 378 km2 in total (inventoried in 2000). We model the mass balance and runoff contribution of 26 glaciers with the physically oriented and fully distributed TOPKAPI (Topographic Kinematic Approximation and Integration)-ETH glacio-hydrological model and extrapolate the results to the entire basin. TOPKAPI-ETH is run at a daily time step using several glaciological and meteorological datasets, and its results are evaluated against streamflow records, remotely sensed snow cover, and geodetic mass balances for the periods 1955–2000 and 2000–2013. Results show that in 1955–2016 glacier mass balance had a general decreasing trend as a basin average but also had differences between the main sub-catchments. Glacier volume decreased by one-fifth (from 18.6±4.5 to 14.9±2.9 km3). Runoff from the initially glacierized areas was 177±25 mm yr−1 (16±7 % of the total contributions to the basin), but it shows a decreasing sequence of maxima, which can be linked to the interplay between a decrease in precipitation since the 1980s and the reduction of ice melt. Glaciers in the Maipo River basin will continue retreating because they are not in equilibrium with the current climate. In a hypothetical constant climate scenario, glacier volume would reduce to 81±38 % of the year 2000 volume, and glacier runoff would be 78±30 % of the 1955–2016 average. This would considerably decrease the drought mitigation capacity of the basin.
Glaciers in the central Andes of Chile are fundamental freshwater sources for ecosystems and communities. Overall, glaciers in this region have shown continuous recession and down-wasting, but long-term glacier mass balance studies providing precise estimates of these changes are scarce. Here, we present the first long-term (1955–2013/2015), region-specific glacier elevation and mass change estimates for the Maipo River Basin, from which the densely populated metropolitan region of Chile obtains most of its freshwater supply. We calculated glacier elevation and mass changes using historical topographic maps, Shuttle Radar Topography Mission (SRTM), TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X), and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results indicated a mean regional glacier mass balance of –0.12 ± 0.06 m w.e.a-1, with a total mass loss of 2.43 ± 0.26 Gt for the Maipo River Basin between 1955–2013. The most negative glacier mass balance was the Olivares sub-basin, with a mean value of –0.29 ± 0.07 m w.e.a-1. We observed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, and more negative values between 2000 and 2013, with an acceleration in ice thinning rates starting in 2010, which coincides with the severe drought. Our results provide key information to improve glaciological and hydrological projections in a region where water resources are under pressure.
We use time series of time-variable gravity from the Gravitational Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions to evaluate the mass balance of the world's glaciers and ice caps (GIC) for the time period April 2002 to September 2019, excluding Antarctica and Greenland peripheral glaciers. We demonstrate continuity of the mass balance record across the GRACE/GRACE-FO data gap using independent data from the GMAO Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reanalysis. We report an average mass loss of
281.5 ± 30 Gt/yr, an acceleration of 50 ± 20 Gt/yr per decade, and a 13-mm cumulative sea level rise for the analyzed period. Seven regions dominate the mass loss, with the largest share from the Arctic: Alaska (72.5 ± 8 Gt/yr), Canadian Arctic Archipelago (73.0 ± 9 Gt/yr), Southern Andes (30.4 ± 13 Gt/yr), High Mountain Asia (HMA) (28.8 ± 11 Gt/yr), Russian Arctic (20.2 ± 6 Gt/yr), Iceland (15.9 ± 4 Gt/yr), and Svalbard (12.1 ± 4 Gt/yr). At the regional level, the analysis of acceleration is complicated by a strong interannual to decadal variability in mass balance that is well reproduced by the GRACE-calibrated MERRA-2 data.
Patagonia is thought to be one of the wettest regions on Earth, although available regional precipitation estimates vary considerably. This uncertainty complicates understanding and quantifying the observed environmental changes, such as glacier recession, biodiversity decline in fjord ecosystems and enhanced net primary production. The Patagonian Icefields, for example, are one of the largest contributors to sea-level rise outside the polar regions, and robust hydroclimatic projections are needed to understand and quantify current and future mass changes. The reported projections of precipitation from numerical modelling studies tend to overestimate those from in situ determinations, and the plausibility of these numbers has never been carefully scrutinized, despite the significance of this topic to our understanding of observed environmental changes. Here I use simple physical arguments and a linear model to test the plausibility of the current precipitation estimates and its impact on the Patagonian Icefields. The results show that environmental conditions required to sustain a mean precipitation amount exceeding 6.09±0.64 m yr−1 are untenable according to the regional moisture flux. The revised precipitation values imply a significant reduction in the surface mass balance of the Patagonian Icefields compared to previously reported values. This yields a new perspective on the response of Patagonia's glaciers to climate change and their sea-level contribution and might also help reduce uncertainties in the change of other precipitation-driven environmental phenomena.
The Andes is the longest cordillera in the world and extends from northern South America to the southern extreme of the continent (from 11°N to 53°S). The Andes runs through seven countries and is characterized by a wide variety of ecosystems strongly related to the contrasting climate over its eastern and western sides, as well as along its latitudinal extension. This region faces very high potential impacts of climate change, which could affect food and water security for about 90 million people. In addition, climate change represents an important threat on biodiversity, particularly in the tropical Andes, which is the most biodiverse region on Earth. From a scientific and societal view, the Andes exhibits specific challenges because of its unique landscape and the fragile equilibrium between the growing population and its environment. In this manuscript, we provide an updated review of the most relevant scientific literature regarding the hydroclimate of the Andes with an integrated view of the entire Andes range. This review paper is presented in two parts. Part I is dedicated to summarize the scientific knowledge about the main climatic features of the Andes, with emphasis on mean large-scale atmospheric circulation, the Andes-Amazon hydroclimate interconnections and the most distinctive diurnal and annual cycles of precipitation. Part II, which is also included in the research topic “Connecting Mountain Hydroclimate Through the American Cordilleras,” focuses on the hydroclimate variability of the Andes at the sub-continental scale, including the effects of El Niño-Southern Oscillation.
Abstract. The evaluation of potential mass wasting in mountain areas is a very complex process because there is not enough information to quantify the probability and magnitude of these events. Identifying the whole chain of events is not a straightforward task, and the impacts of mass wasting processes depend on the conditions downstream of the origin. Additionally, climate change is playing an essential role in the occurrence and distribution. Mean temperatures are continuously rising to produce long term instabilities, particularly on steep slopes. Extreme precipitations events are more recurrent as well as heat waves that can melt snow and glaciers, increasing the water available to unstabilized slopes.
In this paper, we present an example that portraits the complexities in the evaluation of the chain of events. On the 16 of December of 2017, a rockslide occurred in the Yelcho mountain range. In that event, 7 million m<sup>3</sup> of rocks and soil fell on the Yelcho glacier depositing 2 million m<sup>3</sup> on the glacier terminal, and the rest continued downstream, triggering a mudflow that hit Villa Santa Lucia in the Chilean Patagonia, killing 22 people. The rockslide event or similar was anticipated in the region by the National Geological and Mining Survey (Sernageomin in Spanish). However, the effects of the terrain characteristics along the runout area were more significant than what was anticipated. In this work, we evaluate the conditions that enable the mudflow that hits Villa Santa Lucia. We used the information generated by Sernageomin's professional after the mudflow. We carried out geotechnical tests to characterize the soil. We simulated the mudflow using two hydrodynamics software (r-avaflow and Flo-2D) that can handle the rheology of the water–soil mixture.
Our results indicate that the soil is classified as volcanic pumices. This type of soil can be susceptible to the collapse of the structure when subjected to shearing (molding), flowing like a viscous liquid. From the numerical modeling, we concluded that r-avaflow performs better than Flo2D. We can reproduce the mudflow satisfactorily using water content in the mixture ranging from 30 to 40 %. Finally, in order to achieve the water content, we need a source of water smaller than 3 million m<sup>3</sup> approximately. From the simulations and soil tests, we determined that in the area scoured by the mudflow, there were around 2 789 500 m<sup>3</sup> of water within the soil. Therefore, the conditions of the valley were crucial to enhance the impacts of the landslide. This result is relevant because it highlights the importance of evaluating the complete chain of events to map hazards. We suggest that in future hazard mapping, geotechnical studies in combination with hydrodynamic simulation should be included, in particular, when human lives are at risk.
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.
The Cordillera Blanca in Peru has been the scene of rapid deglaciation for many decades. One of numerous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and thousands of fatalities in the city of Huaráz at a distance of 23 km. We chose an integrated approach to revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the GIS-based open-source mass flow/process chain simulation framework r.avaflow, which builds on an enhanced version of the Pudasaini (2012) two-phase flow model. Thereby we consider four scenarios: (A) and (AX) breach of the moraine dam of Lake Palcacocha due to retrogressive erosion, assuming two different fluid characteristics; (B) failure of the moraine dam caused by the impact of a landslide on the lake; and (C) geomechanical failure and collapse of the moraine dam. The simulations largely yield empirically adequate results with physically plausible parameters, taking the documentation of the 1941 event and previous calculations of future scenarios as reference. Most simulation scenarios indicate travel times between 36 and 70 min to reach Huaráz, accompanied with peak discharges above 10 000 m3 s−1. The results of the scenarios indicate that the most likely initiation mechanism would be retrogressive erosion, possibly triggered by a minor impact wave and/or facilitated by a weak stability condition of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process initiation farther downstream. Predictive simulations of possible future events have to be based on a larger set of back-calculated GLOF process chains, taking into account the expected parameter uncertainties and appropriate strategies to deal with critical threshold effects.
The formation and expansion of Himalayan glacial lakes has implications for glacier dynamics, mass balance and glacial lake outburst floods (GLOFs). Subaerial and subaqueous calving is an important component of glacier mass loss but they have been difficult to track due to spatiotemporal resolution limitations in remote sensing data and few field observations. In this study, we used near-daily 3 m resolution PlanetScope imagery in conjunction with an uncrewed aerial vehicle (UAV) survey to quantify calving events and derive an empirical area–volume relationship to estimate calved glacier volume from planimetric iceberg areas. A calving event at Thulagi Glacier in 2017 was observed by satellite from before and during the event to nearly complete melting of the icebergs, and was observed in situ midway through the melting period, thus giving insights into the melting processes. In situ measurements of Thulagi Lake’s surface and water column indicate that daytime sunlight absorption heats mainly just the top metre of water, but this heat is efficiently mixed downwards through the top tens of metres due to forced convection by wind-blown icebergs; this heat then is retained by the lake and is available to melt the icebergs. Using satellite data, we assess seasonal glacier velocities, lake thermal regime and glacier surface elevation change for Thulagi, Lower Barun and Lhotse Shar glaciers and their associated lakes. The data reveal widely varying trends, likely signifying divergent future evolution. Glacier velocities derived from 1960/70s declassified Corona satellite imagery revealed evidence of glacier deceleration for Thulagi and Lhotse Shar glaciers, but acceleration at Lower Barun Glacier following lake development. We used published modelled ice thickness data to show that upon reaching their maximum extents, Imja, Lower Barun and Thulagi lakes will contain, respectively, about 90 × 106, 62 × 106 and 5 × 106 m3 of additional water compared to their 2018 volumes. Understanding lake–glacier interactions is essential to predict future glacier mass loss, lake formation and associated hazards.
Global warming led to an increase of the global mean surface air temperature of ~ 1.0 °C from pre-industrial times to now. This strongly affects all components of the Earth’s system and the complex interactions between them. Glaciers, ice caps and ice sheets are sensitive indicators of these changes. The reduction of land ice masses, which are the world’s largest storages of freshwater, already has strong influence on human life on Earth today, but the influence is likely to increase in the future. This ranges from changes in seasonal freshwater availability over geomorphological hazards to global sea level rise, whereof the latter has already considerably accelerated during the last decades. Hence, monitoring and gaining a deep understanding of the behavior of glacial systems is of great importance. Space- and airborne remote sensing allows for regular monitoring of glaciological parameters over large and inaccessible areas. Modern satellite sensors like Sentinel-1 provide free and automatic access to global data at short repeat cycles. Using such data together with acquisitions from older missions, allows to generate long time series of glaciological parameters. Combining the resulting products with other measurements (e.g. climate data) reveals deep insights into driving factors, mechanisms and histories of glacier change. The main goal of this thesis is to investigate the potential of remote sensing and time series analysis for the quantification and understanding of glacier change. For this purpose, study areas with different characteristics in Antarctica and the Karakoram were selected. Glaciers in these areas were investigated using combinations of various glaciological products that were derived by using different remote sensing techniques and data. Time series of multi-spectral and radar (radio detecting and ranging) satellite imagery were used for mapping glacier fronts and surface structure. Glacier surface velocities were derived by means of intensity offset tracking techniques applied to dense, long time series of multi-mission SAR (Synthetic Aperture Radar) data. Interferometric SAR, laser altimetry and airborne lidar (light detection and ranging) data were employed to quantify ice surface elevation change. Spectral indices derived from multi-spectral satellite imagery time series allowed to map supraglacial lakes. Finally, grounding line (i.e. the boundary between grounded and floating ice) and pinning point positions (i.e. smaller bathymetric features, where the ice is locally grounded) of polar tidewater glaciers and ice sheets were located by means of differential SAR interferometry, differential range offset tracking, hydrostatic equilibrium from airborne ice thickness, as well as other data and methods. In a comprehensive review, remote sensing methods and data were critically evaluated regarding their suitability to derive grounding line and pinning point positions. Up to now, such a review did not exist in the literature. There is a considerable amount of techniques that substantially differ in the measured proxies, the accuracy achieved, the spatial coverage and the data used. Additionally, an inconsistent use of terminology in the literature may cause further confusion. A current tradeoff between accuracy and both spatial coverage and temporal resolution of the different techniques was identified. Moreover, data of the new Sentinel-1 mission has only been used in a few studies for estimating the grounding line position so far. Hence, the potential of Sentinel-1 for grounding line mapping was investigated. It was shown for the first time that Sentinel-1 data is suitable for a newish differential range offset tracking technique. At the Antarctic Peninsula several ice shelves like Wordie Ice Shelf disintegrated in the past, which led to acceleration and increased mass loss of their former tributary glaciers in response to the reduction in buttressing. However, how long these changes last, as well as how the current state of the tributary glaciers ~ 20 years after complete disappearance of Wordie Ice Shelf is, has been largely unknown. Furthermore, the current grounding line position was uncharted, as grounding line mapping is very challenging in this area. In this study, an unprecedentedly dense time series of multi-mission SAR surface velocities was related to information on ice surface elevation change, modelled bedrock and the hydrostatic equilibrium condition. It emerged that the ice shelf’s main tributary glacier (Fleming Glacier) had substantially accelerated by up to > 1.4 m d−1 between 2008 and 2011 and thinned by up to > 6 m a−1 between 2011 and 2014. This was caused by the loss in basal friction due to sudden ice unpinning and gradual grounding line retreat along the retrograde glacier bed, likely triggered by oceanic forcing. The study led to a new understanding of the recent changes at Wordie Bay. Similar to Fleming Glacier, Pine Island Glacier, one of the major outlet glaciers of the West Antarctic Ice Sheet, showed considerable acceleration and mass loss due to grounding line retreat in response to increased ocean temperatures in the past. In 2013 and 2015 two large calving events occurred, which led to a reorientation of the calving front. However, the exact mechanisms behind these events were not well known. Analyzing a unique combination of new multibeam bathymetry data of an area previously covered by the ice shelf and a dense time series of multi-mission satellite imagery revealed that a newly detected subglacial ridge underneath the floating ice tongue of Pine Island Glacier and the loss of a pinning point played an important role in controlling these and previous calving events. While Antarctic glaciers are mainly of interest due to their contribution to global sea level rise, glaciers in the Karakoram are important freshwater resources that are expected to be strongly affected if climate change proceeds. Although Baltoro Glacier is one of the largest glaciers in the Karakoram, little was known about differences in timing and magnitude of its (intra-)seasonal velocity variations and their causal mechanisms. Combining a dense and long multi-mission SAR velocity time series with remotely sensed time series on temperature, precipitation and supraglacial lake formation revealed complex interdependencies between winter precipitation, summer melt, supraglacial lakes, crevassing and glacier acceleration. Stronger summer accelerations in recent years with melt seasons warmer than average seem to be indirectly related to global warming. Furthermore, the study successfully demonstrated the viability of Sentinel-1 data for the derivation of glacier flow dynamics in high mountain regions. The studies conducted in this thesis demonstrated that combining time series of different multi-mission remote sensing data enables detailed insights into glacier dynamics and mechanisms of glacier change in both the polar ice sheets and high mountain areas. The recent Sentinel-1 mission opens up completely new perspectives for glaciological remote sensing, as it allows fully automatic monitoring of glaciological variables at global scales and at high temporal resolution. However, the studies also showed that accurate and repeat mapping of the grounding line is still problematic in some areas like the Antarctic Peninsula and the West Antarctic Ice Sheet. Hence, new SAR missions with longer wavelengths and very short repeat cycles are required, in order to enable precise and gapless monitoring of grounding lines at continental scales.
Heterogeneous glacier mass loss has occurred across High Mountain Asia on a multi-decadal timescale.
Contrasting climatic settings infuence glacier behaviour at the regional scale, but high intra-regional
variability in mass loss rates points to factors capable of amplifying glacier recession in addition to
climatic change along the Himalaya. Here we examine the infuence of surface debris cover and glacial
lakes on glacier mass loss across the Himalaya since the 1970s. We fnd no substantial diference in
the mass loss of debris-covered and clean-ice glaciers over our study period, but substantially more
negative (−0.13 to −0.29m w.e.a−1) mass balances for lake-terminating glaciers, in comparison to
land-terminating glaciers, with the largest diferences occurring after 2000. Despite representing
a minor portion of the total glacier population (~10%), the recession of lake-terminating glaciers
accounted for up to 32% of mass loss in diferent sub-regions. The continued expansion of established
glacial lakes, and the preconditioning of land-terminating glaciers for new lake development increases
the likelihood of enhanced ice mass loss from the region in coming decades; a scenario not currently
considered in regional ice mass loss projections.
The Andean snowpack is the primary source of water for many communities in South America. We have used Landsat imagery over the period 1986–2018 in order to assess the changes in the snow cover extent across a north-south transect of approximately 2,500 km (18°–40°S). Despite the significant interannual variability, here we show that the dry-season snow cover extent declined across the entire study area at an average rate of about −12% per decade. We also show that this decreasing trend is mainly driven by changes in the El Niño Southern Oscillation (ENSO), especially at latitudes lower than 34°S. At higher latitudes (34°–40°S), where the El Niño signal is weaker, snow cover losses appear to be also influenced by the poleward migration of the westerly winds associated with the positive trend in the Southern Annular Mode (SAM).
Glaciers in tropical regions are very sensitive to climatic variations and thus strongly affected by climate change. The majority of the tropical glaciers worldwide are located in the Peruvian Andes, which have shown significant ice loss in the last century. Here, we present the first multi-temporal, region-wide survey of geodetic mass balances and glacier area fluctuations throughout Peru covering the period 2000–2016. Glacier extents are derived from Landsat imagery by performing automatic glacier delineation based on a combination of the NDSI and band ratio method and final manual inspection and correction. The mapping of debris-covered glacier extents is supported by synthetic aperture radar (SAR) coherence information. A total glacier area loss of -548.5±65.7 km2 (−29 %, −34.3 km2 a−1) is obtained for the study period. Using interferometric satellite SAR acquisitions, bi-temporal geodetic mass balances are derived. An average specific mass balance of -296±41 kg m−2 a−1 is found throughout Peru for the period 2000–2016. However, there are strong regional and temporal differences in the mass budgets ranging from 45±97 to -752±452 kg m−2 a−1. The ice loss increased towards the end of the observation period. Between 2013 and 2016, a retreat of the glacierized area of -203.8±65.7 km2 (−16 %, −101.9 km2 a−1) is mapped and the average mass budget amounts to -660±178 kg m−2 a−1. The glacier changes revealed can be attributed to changes in the climatic settings in the study region, derived from ERA-Interim reanalysis data and the Oceanic Nino Index. The intense El Niño activities in 2015/16 are most likely the trigger for the increased change rates in the time interval 2013–2016. Our observations provide fundamental information on the current dramatic glacier changes for local authorities and for the calibration and validation of glacier change projections.
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.
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.
This study evaluates hindcast simulations performed with a regional climate model (RCM, RegCM4) driven by reanalysis data (ERA-Interim) over the Pacific coast and Andes Cordillera of extratropical South America. A nested domain configuration at 0.44∘ ( ∼ 50 km) and 0.09∘ ( ∼ 10 km) spatial resolutions is used for the simulations. RegCM4 is also driven by a global climate model (GCM, MPI-ESM-MR) on the same domain configuration to asses the added values for temperature and precipitation (historical simulations). Overall, both 10 km hindcast and historical simulation results are promising and exhibit a better representation of near-surface air temperature and precipitation variability compared to the 50 km simulations. High-resolution simulations suppress an overestimation of precipitation over the Andes Cordillera of northern Chile found with the 50 km simulations. The simulated daily temperature and precipitation extreme indices from 10 km hindcast simulation show a closer estimation of the observed fields. A persistent warm bias ( ∼+4∘C ) over the Atacama Desert in 10 km hindcast simulation reveals the complexity in representing land surface and radiative processes over the desert. Difficulties in capturing the temperature trend in northern Chile are notable for both hindcast simulations. Both resolutions exhibit added values for temperature and precipitation over large parts of Chile, in particular, the 10 km resolves the coastal-valley Andes transitions over central Chile. Our results highlight that resolutions coarser than 50 km (e.g., GCMs and reanalysis) miss important climate gradients imposed by complex topography. Given that the highest spatial resolution of the current regional simulations over the South America is about 50 km, higher resolutions are important to improve our understanding of the dynamical processes that determine climate over complex terrain and extreme environments.
The northern Antarctic Peninsula was affected by a significant warming over the second half of the 20th century and the collapse of several ice shelves. Local climate conditions on James Ross Island on the northeastern coast can differ strongly from the main part of the Antarctic Peninsula. This paper reports the spatial and temporal variability of glacier surface velocities and the area of their outlets throughout James Ross Island, and evaluates potential relationships with atmospheric and oceanic conditions. Velocity estimates were retrieved from intensity feature tracking of scenes from satellite synthetic aperture radar sensors TerraSAR-X and TanDEM-X between 2014 and 2018, which were validated against ground observations. Calving front positions back to 1945 were used to calculate outlet area changes for the glaciers by using a common-box approach. The annual recession rates of almost all investigated glacier calving fronts decelerated for the time periods but their velocity patterns differed. Analysis of atmospheric conditions failed to explain the different patterns in velocity and area changes. We suggest a strong influence from local bathymetric conditions. Future investigations of the oceanic conditions would be necessary for a profound understanding of the super-position of different influencing factors.
Central Chile, along the subtropical west coast of South America, has experienced an uninterrupted sequence of dry winters (annual rainfall deficit 20-40%) since 2010. The so called Mega Drought (MD) is the longest event on record and encompasses a broad area, with detrimental effects on water availability, vegetation and forest fires. Local records and reanalysis data reveal that the exceptional length of the MD results from the reiteration of a circulation dipole -disfavoring the passage of extratropical storms over central Chile- characterized by troposheric-deep positive pressure anomalies over the southeast subtropical Pacific and negative pressure anomalies over the Amundsen-Bellinhausen Sea. Historically, ENSO is a major modulator of such dipole, but the ongoing dry period has occurred under ENSO-neutral conditions, except for the winters of 2010 (La Niña) and 2015 (strong El Niño). Nonetheless, atmospheric-only global model simulations forced with observed global SST and present-day radiative forcing replicate the south Pacific dipole and capture part of the rainfall anomalies during the MD. Further numerical experiments suggest that most of the ocean forcing emanates from the subtropical southwest Pacific, a region that has experienced a marked warming over the last decade. Such warming may excite Rossby waves whose propagation intensify the circulation pattern that lead to dry conditions in central Chile. On the other hand, the positive trend of the Southern Annular Mode also contributes to strength of the south Pacific dipole, signaling that anthropogenic forcing (greenhouse gases concentration increase and stratospheric ozone depletion) have played a role on the maintenance of the central Chile MD. Given the concomitance of natural (ocean sourced) and anthropogenic forcing, we anticipate only a partial recovery of central Chile precipitation in the decades to come.
Himalayan glaciers supply meltwater to densely populated catchments in South Asia, and regional observations of glacier change over multiple decades are needed to understand climate drivers and assess resulting impacts on glacier-fed rivers. Here, we quantify changes in ice thickness during the intervals 1975–2000 and 2000–2016 across the Himalayas, using a set of digital elevation models derived from cold war–era spy satellite film and modern stereo satellite imagery. We observe consistent ice loss along the entire 2000-km transect for both intervals and find a doubling of the average loss rate during 2000–2016 [−0.43 ± 0.14 m w.e. year ⁻¹ (meters of water equivalent per year)] compared to 1975–2000 (−0.22 ± 0.13 m w.e. year ⁻¹ ). The similar magnitude and acceleration of ice loss across the Himalayas suggests a regionally coherent climate forcing, consistent with atmospheric warming and associated energy fluxes as the dominant drivers of glacier change.
Glaciers outside of the ice sheets are known to be important contributors to sea level rise. In this work, we provide an overview of changes in the mass of the world's glaciers, excluding those in Greenland and Antarctica, between 2002 and 2016, based on satellite gravimetry observations of the Gravity Recovery and Climate Experiment (GRACE). Glaciers lost mass at a rate of 199 ± 32 Gt yr−1 during this 14-yr period, equivalent to a cumulative sea level contribution of 8 mm. We present annual mass balances for 17 glacier regions, that show a qualitatively good agreement with published estimates from in situ observations. We find that annual mass balance varies considerably from year to year, which can in part be attributed to changes in the large-scale circulation of the atmosphere. These variations, combined with the relatively short observational record, hamper the detection of acceleration of glacier mass loss. Our study highlights the need for continued observations of the Earth's glacierized regions.
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 largest collection so far of glaciological and geodetic observations suggests that glaciers contributed about 27 millimetres to sea-level rise from 1961 to 2016, at rates of ice loss that could see the disappearance of many glaciers this century.
Glacier mass balance has been estimated on individual glacier and regional scales using repeat digital elevation models (DEMs). DEMs often have gaps in coverage (“voids”), the properties of which depend on the nature of the sensor used and the surface being measured. The way that these voids are accounted for has a direct impact on the estimate of geodetic glacier mass balance, though a systematic comparison of different proposed methods has been heretofore lacking. In this study, we determine the impact and sensitivity of void interpolation methods on estimates of volume change. Using two spatially complete, high-resolution DEMs over southeast Alaska, USA, we artificially generate voids in one of the DEMs using correlation values derived from photogrammetric processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes. We then compare 11 different void interpolation methods on a glacier-by-glacier and regional basis. We find that a few methods introduce biases of up to 20 % in the regional results, while other methods give results very close (<1 % difference) to the true, non-voided volume change estimates. By comparing results from a few of the best-performing methods, an estimate of the uncertainty introduced by interpolating voids can be obtained. Finally, by increasing the number of voids, we show that with these best-performing methods, reliable estimates of glacier-wide volume change can be obtained, even with sparse DEM coverage.
Recent evidence shows that most of Patagonian glaciers are receding rapidly. Due to the lack of in-situ long-term meteorological observations, the understanding of how glaciers are responding to changes in climate over this region is extremely limited and high uncertainties exist in the glacier surface mass balance model parameterizations. This precludes a robust assessment of glacier response to current and projected climate change. An issue of central concern is the accurate estimation of precipitation phase. In this work, we have assessed spatial and temporal patterns in snow accumulation in both the North Patagonia Icefield (NPI) and South Patagonia Icefield (SPI). We used a regional climate model, RegCM4.6 and four Phase Partitioning Methods (PPM) and short-term snow accumulation observations using ultrasonic depth gauges (UDG). Snow accumulation shows that rates are higher on the west side relative to the east side for both Icefields. The values depend on the PPM used and reach a mean difference of 1,500 mm w.e. with some areas reaching differences higher than 3,500 mm w.e. These differences could lead to divergent mass balance estimations, depending on the scheme used to define the snow accumulation. Good agreement is found in comparing UDG observations with modeled data on the plateau area of the SPI during a short time period, however, there are important differences between rates of snow accumulation determined in this work and previous estimations using ice core data at annual scale. Significant positive trends are mainly present in the autumn season on the west side of the SPI, while on the east side, significant negative trends in autumn were observed. Overall, for the rest of the area and during other seasons, no significant changes can be determined. In addition, glaciers with positive and stable elevation and frontal changes determined by previous works, are related to areas where snow accumulation has increased during the period 2000-2015. This suggests that increases in snow accumulation are attenuating the response of some Patagonian glaciers to warming in a regional context of overall glacier retreat.
In this study, rapid topographic changes and high creeping rates caused by
the destabilisation of an active rock glacier in a steep mountain flank were
investigated in detail with five unmanned aerial vehicle (UAV) surveys
between June 2016 and September 2017. State-of-the-art photogrammetric
techniques were employed to derived high-density point clouds and
high-resolution orthophoto mosaics from the studied landform. The accuracy of
the co-registration of subsequent point clouds was carefully examined and
adjusted based on comparing stable areas outside the rock glacier, which
minimised 3-D alignment errors to a mean of 0.12 m. Elevation and volumetric
changes in the destabilised rock glacier were quantified over the study
period. Surface kinematics were estimated with a combination of image
correlation algorithms and visual inspection of the orthophoto mosaics.
Between June 2016 and September 2017, the destabilised part of the rock
glacier advanced up to 60–75 m and mobilised a volume of around
27 000 m3 of material which was dumped over the lower talus slope. This
study has demonstrated a robust and customisable monitoring approach that
allows a detailed study of rock glacier geometric changes during a crisis phase.
Knowledge of the ice thickness distribution of the world’s glaciers is a fundamental prerequisite for a range of studies. Projections of future glacier change, estimates of the available freshwater resources or assessments of potential sea-level rise all need glacier ice thickness to be accurately constrained. Previous estimates of global glacier volumes are mostly based on scaling relations between glacier area and volume, and only one study provides global-scale information on the ice thickness distribution of individual glaciers. Here we use an ensemble of up to five models to provide a consensus estimate for the ice thickness distribution of all the about 215,000 glaciers outside the Greenland and Antarctic ice sheets. The models use principles of ice flow dynamics to invert for ice thickness from surface characteristics. We find a total volume of 158 ± 41 × 10 ³ km ³ , which is equivalent to 0.32 ± 0.08 m of sea-level change when the fraction of ice located below present-day sea level (roughly 15%) is subtracted. Our results indicate that High Mountain Asia hosts about 27% less glacier ice than previously suggested, and imply that the timing by which the region is expected to lose half of its present-day glacier area has to be moved forward by about one decade. © 2019, The Author(s), under exclusive licence to Springer Nature Limited.
Glacial Lake Outburst Floods (GLOFs) have become increasingly common over the past century in response to climate change, posing risks for human activities in many mountain regions. In this paper we document and reconstruct the sequence of events and impact of a large GLOF that took place in December 2015 in the Chileno Valley, Patagonia. Hydrograph data suggests that the flood continued for around eight days with an estimated total discharge of 105.6 × 106 m3 of water. The sequence of events was as follows: (1) A large debris flow entered the lake from two steep and largely non-vegetated mountain gullies located northeast of the Chileno Glacier terminus. (2) Water displaced in the lake by the debris flow increased the discharge through the Chileno Lake outflow. (3) Lake and moraine sediments were eroded by the flood. (4) Eroded sediments were redistributed downstream by the GLOF. The post-GLOF channel at the lake outlet widened in some places by >130 m and the surface elevation of the terrain lowered by a maximum of 38.8 ± 1.5 m. Farther downstream, large amounts of entrained sediment were deposited at the head of an alluvial plain and these sediments produced an ~340 m wide fan with an average increase in surface elevation over the pre-GLOF surface of 4.6 ± 1.5 m. We estimate that around 3.5 million m3 of material was eroded from the flood-affected area whilst over 0.5 million m3 of material was deposited in the downstream GLOF fan. The large debris flow that triggered the GLOF was probably a paraglacial response to glacier recession from its Little Ice Age limits. We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes. Detailed studies of GLOF events are currently limited in Patagonia and the information presented here will therefore help to inform future glacial hazard assessments in this region.
Rock glaciers likely play an important hydrological role in the semiarid Andes (SA; 27°–35°S). They supplement streamflow when water is needed most, especially during dry years in the late summer months. Despite their assumed importance, there are no publications that quantify their hydrological contribution to streamflow in the SA of Chile, based on measurements of rock glacier ice loss or discharge. In this study, we assess the available information on the hydrological importance of rock glaciers in the SA and provide suggestions on how future research can address knowledge gaps. We conclude that there is insufficient data available to quantify the hydrological contribution of rock glaciers in the SA. Measurements of glacier discharge are limited to unpublished data sets from which only very limited conclusions can be drawn. There are no ice volume change measurements or proxies available for individual rock glaciers. Approximations of rock glacier ice volume, calculated from areal extent, thickness, and percentage of ice content are available, and these data provide an initial baseline for calculating ice volume change in the future. While these baseline data are very valuable, they represent rough estimates due to a scarcity of studies, especially on glacier thickness and percentage of ice content. With increased temperatures and a decrease in precipitation expected in the future, rock glaciers could become an increasingly critical water resource in this region, especially in the Elqui and Juncal catchments. Improved estimates of rock glacier discharge, water content, processes, and hydrology are required to model their future evolution and evaluate their contribution to water resources.
We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level.
The glaciers of Patagonia are the largest in South America and are shrinking rapidly, raising concerns about their contribution to sea‐level‐rise in the face of ongoing climatic change. However, modelling studies forecasting future glacier recession are limited by the scarcity of measured on‐glacier air temperatures, and thus tend to use spatially and temporally constant lapse rates. This study presents nine months of air‐temperature observations. The network consists of five automatic weather stations (AWS) and three on‐glacier air temperature sensors installed on the South Patagonia Icefield along a transect at 48° 45’ S. Observed lapse rates are, overall, steeper on the east (‐0.0072 °C m‐1) compared to the west (‐0.0055 °C m‐1) and vary between the lower section (tongue, ablation zone) and the upper section (plateau, accumulation zone) of the glaciers. Warmer off‐glacier temperatures are found in the east compared to the west for similar elevations. However, on‐glacier observations suggest that the glacier cooling effect is higher in the east compared to the west. Through application of distributed temperature‐index and point‐scale energy balance models we show that modelled ablation rates vary by up to 60%, depending on the air temperature extrapolation method applied, and that melt is overestimated and sublimation is underestimated if the glacier cooling effect is not included in the distributed air temperature data. These results can improve current and future modelling efforts of the energy and mass balance of the whole South Patagonia Icefield.
The origin of moisture for the Southern Patagonia Icefield and the transport of moisture toward it are not yet fully understood. These quantities have a large impact on the stable isotope composition of the icefield, adjacent lakes, and nearby vegetation, and is hard to quantify from observations. Clearly identified moisture sources help to interpret anomalies in the stable isotope compositions and contribute to paleoclimatological records from the icefield and the close surrounding. This study detects the moisture sources of the icefield with a Lagrangian moisture source method. The kinematic 18-day backward trajectory calculations use reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA-Interim) from January 1979 to January 2017. The dominant moisture sources are found in the South Pacific Ocean from 80 to 160°W and 30 to 60°S. A persistent anticyclone in the subtropics and advection of moist air by the prevailing westerlies are the principal flow patterns. Most of the moisture travels less than 10 days to reach the icefield. The majority of the trajectories originate from above the planetary boundary layer but enter the Pacific boundary layer to reach the maximum moisture uptake 2 days before arrival. During the last day trajectories rise as they encounter topography. The location of the moisture sources are influenced by seasons, Antarctic Oscillation, El-Niño Southern Oscillation, and the amount of monthly precipitation, which can be explained by variations in the location and strength of the westerly wind belt.”
We present a field‐data rich modelling analysis to reconstruct the climatic forcing, glacier response and runoff generation from a high elevation catchment in central Chile over the period 2000‐2015, to provide insights into the differing contributions of debris‐covered and debris‐free glaciers under current and future changing climatic conditions. Model simulations with the physically‐based glacio‐hydrological model TOPKAPI‐ETH reveal a period of neutral or slightly positive mass balance between 2000‐2010, followed by a transition to increasingly large annual mass losses, associated with a recent mega drought. Mass losses commence earlier, and are more severe, for a heavily debris‐covered glacier, most likely due to its strong dependence on snow avalanche accumulation, which has declined in recent years. Catchment runoff shows a marked decreasing trend over the study period, but with high interannual variability directly linked to winter snow accumulation, and high contribution from ice melt in dry periods and drought conditions. The study demonstrates the importance of incorporating local‐scale processes such as snow avalanche accumulation and spatially variable debris thickness, in understanding the responses of different glacier types to climate change. We highlight the increased dependency of runoff from high Andean catchments on the diminishing resource of glacier ice during dry years.
We introduce the first catchment dataset for large sample studies in Chile. This dataset includes 516 catchments; it covers particularly wide latitude (17.8 to 55.0°S) and elevation (0 to 6993ma.s.l.) ranges, and it relies on multiple data sources (including ground data, remote-sensed products and reanalyses) to characterise the hydroclimatic conditions and landscape of a region where in situ measurements are scarce. For each catchment, the dataset provides boundaries, daily streamflow records and basin-averaged daily time series of precipitation (from one national and three global datasets), maximum, minimum and mean temperatures, potential evapotranspiration (PET; from two datasets), and snow water equivalent. We calculated hydro-climatological indices using these time series, and leveraged diverse data sources to extract topographic, geological and land cover features. Relying on publicly available reservoirs and water rights data for the country, we estimated the degree of anthropic intervention within the catchments. To facilitate the use of this dataset and promote common standards in large sample studies, we computed most catchment attributes introduced by Addor et al. (2017) in their Catchment Attributes and MEteorology for Large-sample Studies (CAMELS) dataset, and added several others.
We used the dataset presented here (named CAMELS-CL) to characterise regional variations in hydroclimatic conditions over Chile and to explore how basin behaviour is influenced by catchment attributes and water extractions. Further, CAMELS-CL enabled us to analyse biases and uncertainties in basin-wide precipitation and PET. The characterisation of catchment water balances revealed large discrepancies between precipitation products in arid regions and a systematic precipitation underestimation in headwater mountain catchments (high elevations and steep slopes) over humid regions. We evaluated PET products based on ground data and found a fairly good performance of both products in humid regions (r > 0.91) and lower correlation (r < 0.76) in hyper-arid regions. Further, the satellite-based PET showed a consistent overestimation of observation-based PET. Finally, we explored local anomalies in catchment response by analysing the relationship between hydrological signatures and an attribute characterising the level of anthropic interventions. We showed that larger anthropic interventions are correlated with lower than normal annual flows, runoff ratios, elasticity of runoff with respect to precipitation, and flashiness of runoff, especially in arid catchments.
CAMELS-CL provides unprecedented information on catchments in a region largely underrepresented in large sample studies. This effort is part of an international initiative to create multi-national large sample datasets freely available for the community. CAMELS-CL can be visualised from http://camels.cr2.cl and downloaded from https://doi.pangaea.de/10.1594/PANGAEA.894885.
Ice cliff backwasting on debris-covered glaciers is recognized
as an important mass-loss process that is potentially responsible for the
debris-cover anomaly, i.e. the fact that debris-covered and
debris-free glacier tongues appear to have similar thinning rates in the
Himalaya. In this study, we quantify the total contribution of ice cliff
backwasting to the net ablation of the tongue of Changri Nup Glacier, Nepal,
between 2015 and 2017. Detailed backwasting and surface thinning rates were
obtained from terrestrial photogrammetry collected in November 2015 and 2016,
unmanned air vehicle (UAV) surveys conducted in November 2015, 2016 and 2017,
and Pléiades tri-stereo imagery obtained in November 2015, 2016 and 2017.
UAV- and Pléiades-derived ice cliff volume loss estimates were
3 % and 7 % less than the value calculated from the
reference terrestrial photogrammetry. Ice cliffs cover between 7 % and
8 % of the total map view area of the Changri Nup tongue. Yet from
November 2015 to November 2016 (November 2016 to November 2017), ice cliffs
contributed to 23±5 % (24±5 %) of the total ablation observed
on the tongue. Ice cliffs therefore have a net ablation rate 3.1±0.6
(3.0±0.6) times higher than the average glacier tongue surface.
However, on Changri Nup Glacier, ice cliffs still cannot compensate for the
reduction in ablation due to debris-cover. In addition to cliff enhancement,
a combination of reduced ablation and lower emergence velocities could be
responsible for the debris-cover anomaly on debris-covered tongues.
The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain.
Glacier recession driven by climate change produces glacial lakes, some of which are hazardous. Our study assesses the evolution of three of the most hazardous moraine-dammed proglacial lakes in the Nepal Himalaya—Imja, Lower Barun, and Thulagi. Imja Lake (up to 150 m deep; 78.4 × 106 m3 volume; surveyed in October 2014) and Lower Barun Lake (205 m maximum observed depth; 112.3 × 106 m3 volume; surveyed in October 2015) are much deeper than previously measured, and their readily drainable volumes are slowly growing. Their surface areas have been increasing at an accelerating pace from a few small supraglacial lakes in the 1950s/1960s to 1.33 km2 and 1.79 km2 in 2017, respectively. In contrast, the surface area (0.89 km2) and volume of Thulagi lake (76 m maximum observed depth; 36.1 × 106 m3; surveyed in October 2017) has remained almost stable for about two decades. Analyses of changes in the moraine dams of the three lakes using digital elevation models (DEMs) quantifies the degradation of the dams due to the melting of their ice cores and hence their natural lowering rates as well as the potential for glacial lake outburst floods (GLOFs). We examined the likely future evolution of lake growth and hazard processes associated with lake instability, which suggests faster growth and increased hazard potential at Lower Barun lake.
We present a satellite-derived glacier inventory for the whole Patagonian Andes south of 45.5°S and Tierra del Fuego including recent changes. Landsat TM/ETM+ and OLI satellite scenes were used to detect changes in the glacierized area between 1986, 2005 and 2016 for all of the 11.209 inventoried glaciers using a semi-automated procedure. Additionally we used geomorphological evidence, such as moraines and trimlines to determine the glacierized area during the Little Ice Age for almost 90% of the total glacierized area. Within the last ~150 years the glacierized area was reduced from 28.091±890 km2 to 22.636±905 km2, marking an absolute area loss of 5.455±1.269 km2 (19.4%). For the whole study region, the annual area decrease was moderate until 1986 with 0.10±0.04% a-1. Afterwards the area reduction increased, reaching annual values of 0.33±0.28% a-1and 0.25±0.5% a-1 for the periods of 1986-2005 and 2005-2016, respectively. There is a high variability of change rates throughout the Patagonian Andes. Small glaciers, especially in the north of the Northern Patagonian Icefield (NPI) and between the latter and the Southern Patagonian Icefield (SPI) had over all periods the highest rates of shrinkage, exceeding 0.92±1.22% a-1 during 2005-2016. In the mountain range of the Cordillera Darwin (CD), and also accounting for small ice fields south of 52°S, highest rates of shrinkage occurred during 1986-2005, reaching values up to 5.6±4.2% a-1, but decreased during the 2005-2016 period. Across the Andean main crest, the eastern parts of the NPI, SPI and adjoined glaciers had in absolute values the highest area reduction exceeding 2.145±482 km2 since the LIA. Large calving glaciers show a smaller relative decrease rate compared to land-terminating glaciers but account for the most absolute area loss. In general, glacier shrinkage is dependent on latitude, the initial glacier area, the environment of the glacial tongue (calving or non-calving glaciers) and in parts by glacial aspect.
Since 1992, there has been a revolution in our ability to quantify the land ice contribution to SLR using a variety of satellite missions and technologies. Each mission has provided unique, but sometimes conflicting, insights into the mass trends of land ice. Over the last decade, over fifty estimates of land ice trends have been published, providing a confusing and often inconsistent picture. The IPCC Fifth Assessment Report (AR5) attempted to synthesise estimates published up to early 2013. Since then, considerable advances have been made in understanding the origin of the inconsistencies, reducing uncertainties in estimates and extending time series. We assess and synthesise results published, primarily, since the AR5, to produce a consistent estimate of land ice mass trends during the satellite era (1992 to 2016). We combine observations from multiple missions and approaches including sea level budget analyses. Our resulting synthesis is both consistent and rigorous, drawing on i) the published literature, ii) expert assessment of that literature, and iii) a new analysis of Arctic glacier and ice cap trends combined with statistical modelling.
We present annual and pentad (five-year mean) time series for the East, West Antarctic and Greenland Ice Sheets and glaciers separately and combined. When averaged over pentads, covering the entire period considered, we obtain a monotonic trend in mass contribution to the oceans, increasing from 0.31±0.35 mm of sea level equivalent for 1992-1996 to 1.85±0.13 for 2012-2016. Our integrated land ice trend is lower than many estimates of GRACE-derived ocean mass change for the same periods. This is due, in part, to a smaller estimate for glacier and ice cap mass trends compared to previous assessments. We discuss this, and other likely reasons, for the difference between GRACE ocean mass and land ice trends.
The southward progression of ice shelf collapse in the Antarctic Peninsula is partially attributed to a strengthening of the circumpolar westerlies and the associated increase in föhn conditions over its eastern ice shelves. We used observations from an automatic weather station at Cabinet Inlet on the northern Larsen C ice shelf between 25 November 2014 and 31 December 2016 to describe föhn dynamics. Observed föhn frequency was compared to the latest version of the regional climate model RACMO2.3p2, run over the Antarctic Peninsula at 5.5-km horizontal resolution. A föhn identification scheme based on observed wind conditions was employed to check for model biases in föhn representation. Seasonal variation in total föhn event duration was resolved with sufficient skill. The analysis was extended to the model period (1979-2016) to obtain a multidecadal perspective of föhn occurrence over Larsen C ice shelf. Föhn occurrence at Cabinet Inlet strongly correlates with near-surface air temperature, and both are found to relate strongly to the location and strength of the Amundsen Sea Low. Furthermore, we demonstrated that föhn occurrence over Larsen C ice shelf shows high variability in space and time.
The Antarctic Peninsula is one of the world's regions most affected by
climate change. Several ice shelves have retreated, thinned or completely
disintegrated during recent decades, leading to acceleration and increased
calving of their tributary glaciers. Wordie Ice Shelf, located in Marguerite
Bay at the south-western side of the Antarctic Peninsula, completely
disintegrated in a series of events between the 1960s and the late 1990s. We
investigate the long-term dynamics (1994–2016) of Fleming Glacier after the
disintegration of Wordie Ice Shelf by analysing various multi-sensor remote
sensing data sets. We present a dense time series of synthetic aperture radar
(SAR) surface velocities that reveals a rapid acceleration of Fleming Glacier
in 2008 and a phase of further gradual acceleration and upstream propagation
of high velocities in 2010–2011.The timing in acceleration correlates with
strong upwelling events of warm circumpolar deep water (CDW) into Wordie Bay,
most likely leading to increased submarine melt. This, together with
continuous dynamic thinning and a deep subglacial trough with a retrograde
bed slope close to the terminus probably, has induced unpinning of the glacier
tongue in 2008 and gradual grounding line retreat between 2010 and 2011. Our
data suggest that the glacier's grounding line had retreated by
∼ 6–9 km between 1996 and 2011, which caused ∼ 56 km2 of
the glacier tongue to go afloat. The resulting reduction in buttressing
explains a median speedup of ∼ 1.3 m d−1 ( ∼ 27 %)
between 2008 and 2011, which we observed along a centre line extending between
the grounding line in 1996 and ∼ 16 km upstream. Current median ice
thinning rates (2011–2014) along profiles in areas below 1000 m altitude
range between ∼ 2.6 to 3.2 m a−1 and are ∼ 70 % higher
than between 2004 and 2008. Our study shows that Fleming Glacier is far away
from approaching a new equilibrium and that the glacier dynamics are not
primarily controlled by the loss of the former ice shelf anymore. Currently,
the tongue of Fleming Glacier is grounded in a zone of bedrock elevation
between ∼ −400 and −500 m. However, about 3–4 km upstream
modelled bedrock topography indicates a retrograde bed which transitions into
a deep trough of up to ∼ −1100 m at ∼ 10 km upstream. Hence,
this endangers upstream ice masses, which can significantly increase the
contribution of Fleming Glacier to sea level rise in the future.
We analysed volume change and mass balance of outlet glaciers on the northern Antarctic Peninsula over the periods 2011 to 2013 and 2013 to 2016, using high-resolution topographic data from the bistatic interferometric radar satellite mission TanDEM-X. Complementary to the geodetic method that applies DEM differencing, we computed the net mass balance of the main outlet glaciers using the mass budget method, accounting for the difference between the surface mass balance (SMB) and the discharge of ice into an ocean or ice shelf. The SMB values are based on output of the regional climate model RACMO version 2.3p2. To study glacier flow and retrieve ice discharge we generated time series of ice velocity from data from different satellite radar sensors, with radar images of the satellites TerraSAR-X and TanDEM-X as the main source. The study area comprises tributaries to the Larsen A, Larsen Inlet and Prince Gustav Channel embayments (region A), the glaciers calving into the Larsen B embayment (region B) and the glaciers draining into the remnant part of the Larsen B ice shelf in Scar Inlet (region C). The glaciers of region A, where the buttressing ice shelf disintegrated in 1995, and of region B (ice shelf break-up in 2002) show continuing losses in ice mass, with significant reduction of losses after 2013. The mass balance numbers for the grounded glacier area of region A are −3.98 ± 0.33 Gt a⁻¹ from 2011 to 2013 and −2.38 ± 0.18 Gt a⁻¹ from 2013 to 2016. The corresponding numbers for region B are −5.75 ± 0.45 and −2.32 ± 0.25 Gt a⁻¹. The mass balance in region C during the two periods was slightly negative, at −0.54 ± 0.38 Gt a⁻¹ and −0.58 ± 0.25 Gt a⁻¹. The main share in the overall mass losses of the region was contributed by two glaciers: Drygalski Glacier contributing 61 % to the mass deficit of region A, and Hektoria and Green glaciers accounting for 67 % to the mass deficit of region B. Hektoria and Green glaciers accelerated significantly in 2010–2011, triggering elevation losses up to 19.5 m a⁻¹ on the lower terminus during the period 2011 to 2013 and resulting in a mass balance of −3.88 Gt a⁻¹. Slowdown of calving velocities and reduced calving fluxes in 2013 to 2016 coincided with years in which ice mélange and sea ice cover persisted in proglacial fjords and bays during summer.
Glacier mass loss is a key contributor to sea-level change1,2, slope instability in high-mountain regions3,4 and the changing seasonality and volume of river flow5–7. Understanding the causes, mechanisms and time scales of glacier change is therefore paramount to identifying successful strategies for mitigation and adaptation. Here, we use temperature and precipitation fields from the Coupled Model Intercomparison Project Phase 5 output to force a glacier evolution model, quantifying mass responses to future climatic change. We find that contemporary glacier mass is in disequilibrium with the current climate, and 36 ± 8% mass loss is already committed in response to past greenhouse gas emissions. Consequently, mitigating future emissions will have only very limited influence on glacier mass change in the twenty-first century. No significant differences between 1.5 and 2 K warming scenarios are detectable in the sea-level contribution of glaciers accumulated within the twenty-first century. In the long-term, however, mitigation will exert strong control, suggesting that ambitious measures are necessary for the long-term preservation of glaciers. Glaciers outside Greenland and Antarctica have been rapidly losing mass. Contemporary ice declines are shown to be a response to past greenhouse gas emissions, with present mitigation efforts unlikely to be beneficial in preventing future short-term ice loss.
Proglacial fjords are critical conduits for the exchange of heat and freshwater between the ocean and land ice, and their dynamics heavily modulate the rate of retreat of tidewater glaciers. Here, the magnitude, spatial structure, and seasonal evolution of the ocean forcing on the proglacial fjord off a rapidly retreating glacier (Jorge Montt, Patagonia) are characterized using data from multiple shipboard surveys from 2010 to 2016, a multi‐year mooring array, and a weather station. The melting of the glacier is forced by relatively warm (8 to 11°C) waters entering the fjord over a shallow (45 m deep) sill about 20 km from the terminus. This warm subsurface water is renewed every summer from the surface layer of Gulf of Penas, is transported along the 100 km long Baker Channel, and reaches the proglacial fjord in the late austral summer to early fall, where it remains relatively warm until late austral spring. Analysis of the freshwater fractions in the fjord reveals that the total freshwater content has a strong seasonal signal with maximum fractional values in the summer, mostly explained by variability in subglacial discharge from the glacier. The submarine melting fraction has no strong seasonal signal, but is a first order contributor to the freshwater content of the fjord in winter. This seasonal evolution is consistent with idealized theories of meltwater production, and suggests that the seasonal supply of heat is critical to sustain a high mean temperature for melting, but do not directly impact the variability of meltwater production.
The ongoing glacier shrinkage in the Alps requires frequent updates of glacier outlines to provide an accurate database for monitoring, modelling purposes (e.g. determination of run-off, mass balance, or future glacier extent), and other applications. With the launch of the first Sentinel-2 (S2) satellite in 2015, it became possible to create a consistent, Alpine-wide glacier inventory with an unprecedented spatial resolution of 10 m. The first S2 images from August 2015 already provided excellent mapping conditions for most glacierized regions in the Alps and were used as a base for the compilation of a new Alpine-wide glacier inventory in a collaborative team effort. In all countries, glacier outlines from the latest national inventories have been used as a guide to compile an update consistent with the respective previous interpretation. The automated mapping of clean glacier ice was straightforward using the band ratio method, but the numerous debris-covered glaciers required intense manual editing. Cloud cover over many glaciers in Italy required also including S2 scenes from 2016. The outline uncertainty was determined with digitizing of 14 glaciers several times by all participants. Topographic information for all glaciers was obtained from the ALOS AW3D30 digital elevation model (DEM). Overall, we derived a total glacier area of 1806±60 km2 when considering 4395 glaciers >0.01 km2. This is 14 % (−1.2 % a−1) less than the 2100 km2 derived from Landsat in 2003 and indicates an unabated continuation of glacier shrinkage in the Alps since the mid-1980s. It is a lower-bound estimate, as due to the higher spatial resolution of S2 many small glaciers were additionally mapped or increased in size compared to 2003. Median elevations peak around 3000 m a.s.l., with a high variability that depends on location and aspect. The uncertainty assessment revealed locally strong differences in interpretation of debris-covered glaciers, resulting in limitations for change assessment when using glacier extents digitized by different analysts. The inventory is available at https://doi.org/10.1594/PANGAEA.909133 (Paul et al., 2019).
The mountainous subantarctic island of South Georgia lies within the belt of strong westerly winds that blow around the Southern Ocean. Interaction of the prevailing circumpolar westerly winds with the island's central mountain chain, which rises to nearly 3000 m, generates warm, dry föhn winds on the downwind side of the island, which are a significant feature of the local climate. We make use of ten years of automatic weather station observations from King Edward Point (KEP), on the northeastern (climatologically downwind) coast of South Georgia, to develop a climatology of the occurrence and properties of föhn winds in this region. Using objective criteria to identify the onset and cessation of föhn, we find that KEP experiences föhn conditions for around 30% of the time. Föhn events last for about 30 hours on average and are associated with significant increases in temperature and wind speed, and decreases in relative humidity. On average, a föhn event is observed every four days, with little seasonal variation seen in the frequency of occurrence. However, föhn events observed during the austral summer season are, on average, both longer and more intense (as measured by changes in temperature, relative humidity and wind speed) than those occurring in other seasons. The fraction of the time for which föhn conditions are observed at KEP increases (decreases) during months when the prevailing westerlies are strengthened (weakened). Monthly mean temperatures at KEP are positively correlated with the föhn fraction but variations in the latter only explain 16% of the variance of monthly mean temperature. We conclude that, while föhn plays an important role in shaping the local climate of South Georgia, other processes may be of greater importance in controlling regional climate variability and change. This article is protected by copyright. All rights reserved.
The precise positioning and long-term monitoring of the grounding line, forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers, is critical for assessing ice sheet/glacier stability, ice sheet/glacier mass balance calculations and numerical ice modelling. However, mapping of the grounding line is a challenging task, since it is a subglacial and transient feature. Remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position. The large variety of methods, products and publications, as well as an inconsistent use of terminology additionally complicate the topic. We present the first detailed review of existing remote sensing techniques and data for grounding line mapping. Benefits and limitations of the different techniques and data sources are discussed and illustrated with examples. We identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products. Rather new methods like Sentinel-1-SAR (Synthetic Aperture Radar) Differential Range Offset Tracking (DROT) and Pseudo Crossover Radar Altimetry (PCRA) offer the potential for recent measurements and to fill gaps in some areas. Nevertheless, there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate Differential SAR Interferometry (DInSAR) on a continental scale.
In contrast to the large surge-type glacier clusters widely known for several mountain ranges around the world, the presence of surging glaciers in the Andes has been historically seen as marginal. The improved availability of satellite imagery during the last years facilitates investigating of glaciers in more detail even in remote areas. The purpose of the study was therefore to revisit existing information about surge-type glaciers for the Central Andes of Argentina and Chile (32° 40′–34° 20′ S), to identify and characterize possible further surge-type glaciers, providing new insights into the mass balance and evolution of the velocity of selected glaciers during the surge phase. Based on the analysis of 1962–2015 satellite imagery, historical aerial images, differencing of digital elevation models and a literature survey, we identified 21 surge-type glaciers in the study area. Eleven surge events and six possible surge-type glaciers were identified and described for the first time. The estimation of annual elevation changes of these glaciers for the 2000–2011 period, which encompasses the latest surge events in the region, showed heterogeneous behavior with strongly negative to positive surface elevation change patterns (−1.1 to +1.0 m yr⁻¹). Additionally, we calculated maximum surface velocities of 3±1.9 m d⁻¹ and 3.1±1.1 m d⁻¹ for two of the glaciers during the latest identifiable surge events of 1985–1987 and 2003–2007. Within this glacier cluster, highly variable advance rates (0.01–1 km yr⁻¹) and dissimilar surface velocities at the surge peak (3–35 m d⁻¹) were observed. In comparison with other clusters worldwide, surge-type glaciers in the Central Andes are on average smaller and show minor absolute advances. Generally low velocities and the heterogeneous duration of the surge cycles are common between them and glaciers in the Karakorum, a region with similar climatic characteristics and many known surge-type glaciers. As a definitive assertion concerning the underlying surge mechanism of surges in the Central Andes could not be drawn based on the remote sensing data, this opens more detailed research avenues for surge-type glaciers in the region.
The Northern and Southern Patagonian Ice Fields (NPI and SPI) in South America are the largest bodies of ice in the Southern hemisphere outside of Antarctica and the largest contributors to eustatic sea level rise (SLR) in the world, per unit area. Here we exploit swath processed CryoSat-2 interferometric data to produce maps of surface elevation change at sub-kilometer spatial resolution over the Ice Fields for six glaciological years between April 2011 and March 2017. Mass balance is calculated independently for nine sub-regions, including six individual glaciers larger than 300 km². Overall, between 2011 and 2017 the Patagonian Ice Fields have lost mass at a combined rate of 21.29 ± 1.98 Gt a⁻¹, contributing 0.059 ± 0.005 mm a⁻¹ to SLR. We observe widespread thinning on the Ice Fields, particularly north of 49° S. However the pattern of surface elevation change is highly heterogeneous, partly reflecting the importance of dynamic processes on the Ice Fields. The Jorge Montt glacier (SPI), whose tidewater terminus is approaching floatation, retreated ~2.5 km during our study period and lost mass at the rate of 2.20 ± 0.38 Gt a⁻¹ (4.64 ± 0.80 mwe a⁻¹). In contrast with the general pattern of retreat and mass loss, Pio XI, the largest glacier in South America, is advancing and gaining mass at 0.67 ± 0.29 Gt a⁻¹ rate.