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Glaciers in the Southern Patagonia Icefield (SPI) have been shrinking in recent decades, but due to a lack of field observations, understanding of the drivers of ablation is limited. We present a distributed surface energy balance model, forced with meteorological observations from a west–east transect located in the north of the SPI. Between October 2015 and June 2016, humid and warm on-glacier conditions prevailed on the western side compared to dry and cold conditions on the eastern side. Controls of ablation differ along the transect, although at glacier-wide scale sensible heat (mean of 72 W m−2 to the west and 51 W m−2 to the east) and net shortwave radiation (mean of 54 W m−2 to the west and 52 W m−2 to the east) provided the main energy sources. Net longwave radiation was an energy sink, while latent heat was the most spatially variable flux, being an energy sink in the east (−4 W m−2) and a source in the west (20 W m−2). Ablation was high, but at comparable elevations, it was greater to the west. These results provide new insights into the spatial variability of energy-balance fluxes and their control over the ablation of Patagonian glaciers.

Glacier ice thickness is crucial to quantifying water resources in mountain regions, and is an essential input for ice-flow models. Using a surface velocity inversion method, we combine ice thickness measurements with detailed surface elevation and velocity data, and derive ice thickness and volume estimates for the Monte Tronador glaciers, North Patagonian Andes. We test the dependence of the inversion model on surface slope by resampling glacier slopes using variable smoothing filter sizes of 16–720 m. While total glacier volumes do not differ considerably, ice thickness estimates show higher variability depending on filter size. Smaller (larger) smoothing scales give thinner (thicker) ice and higher (lower) noise in ice thickness distribution. A filter size of 300 m, equivalent to four times the mean ice thickness, produces a noise-free thickness distribution with an accuracy of 35 m. We estimate the volume of the Monte Tronador glaciers at 4.8 ± 2 km3 with a mean ice thickness of 75 m. Comparison of our results with earlier regional and global assessments shows that the quality of glacier inventories is a significant source of discrepancy. We show that including surface slope as an input parameter increases the accuracy of ice thickness distribution estimates.

The Southern Patagonia Icefield (SPI) withdrawal in recent decades shows contrasting behaviours between adjacent basins. One of the basins with highest volumetric losses is located at northernmost SPI. We refer to Jorge Montt tidewater glacier (48°30′S/73°30′W, 445 km2in 2018), which retreated 2.7 km between 2011 and 2018 and thinned at rates of up to 21 m a−1over this period. Based on the retreat record, remote-sensing imagery, field data, a mass-balance model and a calving parameterisation, we attempted to differentiate climatic-induced changes (i.e. surface mass balance) and dynamic responses (i.e. calving fluxes). The surface mass balance reached −4.15 km3w.e. a−1between 2012 and 2017. When frontal ablation is included, the net mass balance is −17.79 km3w.e. a−1. This represents a change of trend compared with modelling estimations of positive surface mass balance prior to 2010. This shift is attributed to higher ablation rates given that accumulation is known to have increased between 1980 and 2015. The available evidence, therefore, indicates that frontal ablation is the main factor, supported by observed rates at Jorge Montt as high as 3.81 km3w.e. a−1in 2015, with ice velocities peaking at 11 km a−1.

Glaciers on active volcanoes are subject to changes in both climate fluctuations and volcanic activity. Whereas many studies analysed changes on individual volcanoes, this study presents for the first time a comparison of glacier changes on active volcanoes on a continental scale. Glacier areas were mapped for 59 volcanoes across Latin America around 1986, 1999 and 2015 using a semi-automated band ratio method combined with manual editing using satellite images from Landsat 4/5/7/8 and Sentinel-2. Area changes were compared with the Smithsonian volcano database to analyse possible glacier–volcano interactions. Over the full period, the mapped area changed from 1399.3 ± 80 km2to 1016.1 ± 34 km2(−383.2 km2) or −27.4% (−0.92% a−1) in relative terms. Small glaciers, especially in tropical regions lost more of their area compared to large and extra–tropical glaciers. Interestingly, 46 out of 59 analysed glaciers (78%) showed a decelerating shrinkage rate in the second period (−1.20% a−1before 1999 and −0.70% a−1after 1999). We found a slightly higher (but statistically not significant) area loss rate (−1.03% a−1) for glaciers on volcanoes with eruptions than without (−0.86% a−1).

A number of glaciological observations on debris-covered glaciers around the globe have shown a delayed length and mass adjustment in relation to climate variability, a behavior normally attributed to the ice insulation effect of thick debris layers. Dynamic interactions between debris cover, geometry and surface topography of debris-covered glaciers can nevertheless govern glacier velocities and mass changes over time, with many glaciers exhibiting high thinning rates in spite of thick debris cover. Such interactions are progressively being incorporated into glacier evolution research. In this paper we reconstruct changes in debris-covered area, surface velocities and surface features of three glaciers in the Patagonian Andes over the 1958–2020 period, based on satellite and aerial imagery and Digital Elevation Models. Our results show that debris cover has increased from 40 ± 0.6 to 50 ± 6.7% of the total glacier area since 1958, whilst glacier slope has slightly decreased. The gently sloping tongues have allowed surface flow velocities to remain relatively low (−1) for the last two decades, preventing evacuation of surface debris, and contributing to the formation and rise of the ice cliff zone upper boundary. In addition, mapping of end of summer snowline altitudes for the last two decades suggests an increase in the Equilibrium Line Altitudes, which promotes earlier melt out of englacial debris and further increases debris-covered ice area. The strongly negative mass budget of the three investigated glaciers throughout the study period, together with the increases in debris cover extent and ice cliff zones up-glacier, and the low velocities, shows a strong linkage between debris cover, mass balance evolution, surface velocities and topography. Interestingly, the presence of thicker debris layers on the lowermost portions of the glaciers has not lowered thinning rates in these ice areas, indicating that the mass budget is mainly driven by climate variability and calving processes, to which the influence of enhanced thinning at ice cliff location can be added.

The Patagonian Icefields are among the biggest worldwide glaciers contributors to sea level rise. In spite of ongoing deglaciation in Patagonia, climatic models are estimating that the icefields surface mass balances during at least the last 4 decades has been neutral or even positive. The main mass losses are therefore, mainly related to frontal ablation, namely surface ablation, calving and subaquatic melting. These are the predominant factors in almost every single calving glacier in the region, especially among the eastern glaciers of the Southern Patagonia Icefield that are ending into deep lakes. The only and most remarkable exception to this trend on the eastern side of the SPI is the well-known stable and even advancing state of glaciar Perito Moreno. In spite of the relatively benign surface mass balances modelled for the last 4 decades, during the 2010’s several freshwater calving glaciers experienced strong retreats, and in some cases, the collapse of the whole ice fronts with losses mounting several square kilometers of ice in single events or during a series of huge calving events. In order to study the glacier-lake interactions in the area, a collaborative research program was initiated in 2013 by Chilean and Argentinean scientists allowing the installation of a network of Automatic Weather Stations, fixed photographic cameras, water level pressure sensors and GPS stations at both sides of the international border. Since 2013 several field campaigns were conducted to the area including the survey of lake waters nearby several retreating glaciers. In most of the studied cases were detected very deep bathymetries (up to 600 m in places), and in some cases, a vertical structure of the lake water indicating a highly stratified condition that we estimate is responsible for very low subaquatic melting favoring the presence of glacier foots extending tens or even few hundreds of meters beyond the subaerial ice walls. The most remarkable recent collapses took place at glaciares O’Higgins and Viedma, whilst the rest or our studied glaciers (Chico, Upsala and Dickson) also experienced retreats with smaller rates. In this presentation we will show novel data collected in the main freshwater calving glaciers of the SPI and will discuss the local conditions explaining the recent glacier behavior.

The monitoring of seismic activity at active glacier-hosting volcanoes is challenging as volcanic and glacial earthquakes (i.e. icequakes) can have overlapping characteristics (i.e. frequencies, waveform shape and magnitude). Here we present results from the first study to target glacial activity at active ice-covered volcanoes in the Southern Chile. The primary focus so far has been on Llaima volcano, one of the largest and most active volcanoes in the region while hosting >14 km2 of glacial ice on the flanks. We use a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes in seismic data from the permanent volcano monitoring network recorded in early 2019. We identified dozens of low magnitude families of repeating seismic events across two months, the largest of which included over 200 events. These findings are comparable to results from analysis of seismic data recorded at Llaima volcano during the same time period in 2015. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial stick-slip sources around the upper flanks of the volcano. We also deployed a network of seismo-acoustic sensors at Villarrica volcano in early 2020 to record glacial activity in concurrence with the lava lake and strombolian activity at the summit. We conclude that icequakes at Llaima volcano may be more common than previously thought and has implications for how seismic data at ice-covered volcanoes may be used for assessing future volcanic and glacial hazard potential.

The Southern Patagonia Icefield (SPI) is the largest continuous ice mass in Southern Hemisphere outside Antarctica. It has been shrinking since the little Ice Age (LIA) period with increasing rates in recent years. In response to this deglaciation process an uplift crustal deformation has been expected. In order to test this hypothesis, a number of GNSS stations installed at both side of the international border between Chile and Argentina, have been repeatedly measured in recent decades yielding vertical velocities up to 41 mm/a. The obtained horizontal velocities have also shown that GIA is only one of the main components been the tectonic deformations the other factors, including the western interseismic tectonic deformation field related to plate subduction (Richter et al., 2016).We addressed this hypothesis by installing two permanent GNSS stations in nunataks located in the northern half of the SPI. The first one called ECRG was setup up within the accumulation area at 1417 m asl and was measuring with several interruptions due to power supply between 2015/10/24 and 2018/06/18, yielding a total of 371 days with data. The second station called ECGB was installed at 1610 m asl in 2015/10/08 and was continuously measuring also with interruptions until 2019/05/28, with a total of 542 measured days. The stations were equipped with a Trimble NetR9 receiver and a Trimble Zephyr (TRM41249.00) antennae without protective radomes. The collected data was processed with the Bernese v5.0 software and the data were linked to the International GNSS Service 2008 (IGS08) permanent stations.The preliminary results indicate vertical velocities of 33.03 ±2.14 mm/a at ECRG and 36.55±2.58 mm/a at ECGB. The mean horizontal velocities reached 11.7 mm/a with an azimuth of 43º. These results are within the maximum values obtained in previous studies that measured nearby stations for short periods of time in several occasions. The high vertical velocities and their spatial distribution are a clear indication of the GIA response of this part of Southern Patagonia.ReferenceRichter, A., Ivins, E., Lange, H., Mendoza, L., Schröder, L., Hormaechea, J. L., … Dietrich, R. (2016). Crustal deformation across the Southern Patagonian Icefield observed by GNSS. Earth and Planetary Science Letters, 452, 206–215. https://doi.org/10.1016/j.epsl.2016.07.042

The Southern Ocean occupies 14% of the Earth’s surface and plays a fundamental role in the global carbon cycle and climate. It provides a direct connection to the deep ocean carbon reservoir through biogeochemical processes that include surface primary productivity, remineralization at depth and the upwelling of carbon-rich water masses. However, the role of these different processes in modulating past and future air–sea carbon flux remains poorly understood. A key period in this regard is the Antarctic Cold Reversal (ACR, 14.6–12.7 kyr bp), when mid- to high-latitude Southern Hemisphere cooling coincided with a sustained plateau in the global deglacial increase in atmospheric CO2. Here we reconstruct high-latitude Southern Ocean surface productivity from marine-derived aerosols captured in a highly resolved horizontal ice core. Our multiproxy reconstruction reveals a sustained signal of enhanced marine productivity across the ACR. Transient climate modelling indicates this period coincided with maximum seasonal variability in sea-ice extent, implying that sea-ice biological feedbacks enhanced CO2 sequestration and created a substantial regional marine carbon sink, which contributed to the plateau in CO2 during the ACR. Our results highlight the role Antarctic sea ice plays in controlling global CO2, and demonstrate the need to incorporate such feedbacks into climate–carbon models.

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.

Volcanoes and glaciers are both productive sources of seismic activity which may be easily confused for each other, leading to potential missed warnings or false alarms. This presents a challenge for organizations monitoring active volcanoes with glaciers on or near the edifice. Cryogenic earthquakes (i.e. icequakes) have been studied at only a few volcanoes around the world and there is a ready need to develop robust methods for efficiently differentiating them from volcanic events. Here we present results from an ongoing study of icequakes at active ice-covered volcanoes in the Southern Chilean Volcanic Zone. The primary focus of the project so far has been on seismo-acoustic data collected at Llaima volcano, one of the largest and most active volcanoes in the region. The data, recorded in 2015 and 2019, was analysed using a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes. We identified 11 persistent families of repeating events in 2015, and over 50 families in 2019; the largest family containing over 1000 events from January to April 2019. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial sources on the upper flanks of the volcano. Low levels of volcanic activity at Llaima volcano since 2009 have allowed this clear discrimination of icequake events. We are also targeting Villarrica volcano in early 2020 with a network of seismo-acoustic sensors and to record icequake activity in concurrence with the ongoing eruptive activity at the summit. Altogether, the results from this project so far suggest icequakes may be more common than previously thought and has strong implications for how seismic data at ice-covered volcanoes may be interpreted.

Significance Fifty years ago, it was speculated that the marine-based West Antarctic Ice Sheet is vulnerable to warming and may have melted in the past. Testing this hypothesis has proved challenging due to the difficulty of developing in situ records of ice sheet and environmental change spanning warm periods. We present a multiproxy record that implies loss of the West Antarctic Ice Sheet during the Last Interglacial (129,000 to 116,000 y ago), associated with ocean warming and the release of greenhouse gas methane from marine sediments. Our ice sheet modeling predicts that Antarctica may have contributed several meters to global sea level at this time, suggesting that this ice sheet lies close to a “tipping point” under projected warming., The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) (129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m), ocean thermal expansion, and melting mountain glaciers (∼1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.

Glaciation and deglaciation modify the stress of the slopes affected by these processes and can trigger their instability and landslides. This study describes, characterizes and reconstructs a large rotational landslide of soil and moraine material, which occurred on February 10, 2013 on the western slope of Upsala Channel, North Branch of Argentino Lake, in Southern Patagonia. With this aim a qualitative analysis of the slope condition before and after the date of the landslide occurrence, the possible conditioning and triggering factors, and the destructive consequences of the related tsunami that affected the margins of the lake was carried out. To reconstruct the state of the slope before and after the event, techniques of photo-interpretation of optical satellite imagery, digital elevation models, historical photographs, in situ observations, bathymetric data and stories of the park rangers of Los Glaciares National Park were used. The retreat of the Upsala Glacier has caused the relaxation of the slopes of the channel conditioning its stability. Among the conditioning and triggering factors that favored the process of activation and generation of the landslide event, are the presence of unconsolidated moraine material covering the channel slopes, steep slopes exposed to the east, which increases its exposure to the sun and melting of snow accumulated during the winter, and the existence of soil creep processes. Although the specific triggering factor is unknown, sediment saturation by surface runoff and water infiltration, eventually a severe rain event, foot slope erosion by glacial activity, and local and regional seismic activity can be mentioned as potential triggering factors. The slope showed evidences of instability for more than 20 years prior to the generation of the landslide, and there is currently evidence that the slope may undergo.

espanolA traves de este articulo se presenta una propuesta metodologica para desarrollar la formulacion de un plan de gestion ambiental municipal. Para ello se emplean como herramientas de identificacion y diagnostico de los problemas territoriales de escala local, el analisis de unidades del paisaje y la evaluacion de impacto ambiental. Precisamente, con el fin de visibilizar su facil aplicabilidad, se exponen los resultados obtenidos de un ejercicio academico investigativo efectuado en el municipio de Tona, Cataluna-Espana. Por ultimo, se esbozan una serie de programas y acciones de gestion ambiental para esta localidad, orientados a prevenir, controlar, mitigar y corregir los impactos generados por su urbanizacion y los diferentes usos del suelo. EnglishThrough this article a methodological proposal to develop the formulation of a Municipal Environmental Management Plan is presented. To this end, the analysis of landscape units and environmental impact assessment are used as tools for the identification and diagnosis of the territorial conflicts at the local level. Precisely, to visualize its easy applicability, the results of a research academic exercise carried out in the Municipality of Tona, Catalonia-Spain are exposed. Finally, a series of environmental management programs and actions for this location, designed to prevent, control, mitigate and correct the impacts generated by urbanization and the different land uses are outlined.

Glacier melt is an important source of water for high Andean rivers in central Chile, especially in dry years, when it can be an important contributor to flows during late summer and autumn. However, few studies have quantified glacier melt contribution to streamflow in this region. To address this shortcoming, we present an analysis of meteorological conditions and ablation for Universidad Glacier, one of the largest valley glaciers in the central Andes of Chile at the head of the Tinguiririca River, for the 2009–2010 ablation season. We used meteorological measurements from two automatic weather stations installed on the glacier to drive a distributed temperature-index and runoff routing model. The temperature-index model was calibrated at the lower weather station site and showed good agreement with melt estimates from an ablation stake and sonic ranger, and with a physically based energy balance model. Total modelled glacier melt is compared with river flow measurements at three sites located between 0.5 and 50 km downstream. Universidad Glacier shows extremely high melt rates over the ablation season which may exceed 10 m water equivalent in the lower ablation area, representing between 10 and 13 % of the mean monthly streamflow at the outlet of the Tinguiririca River Basin between December 2009 and March 2010. This contribution rises to a monthly maximum of almost 20 % in March 2010, demonstrating the importance of glacier runoff to streamflow, particularly in dry years such as 2009–2010. The temperature-index approach benefits from the availability of on-glacier meteorological data, enabling the calculation of the local hourly variable lapse rate, and is suited to high melt regimes, but would not be easily applicable to glaciers further north in Chile where sublimation is more significant.

Spanish Abstract: Este trabajo realiza una estimacion de la Productividad Total Factorial para 11 departamentos y 20 divisiones industriales en Colombia durante el periodo 2012-2016, utilizando informacion de la Encuesta Anual Manufacturera del DANE y usando el metodo semi-parametrico propuesto por Levinsohn y Petrin (2003) para este fin. Los resultados muestran que los departamentos de Bolivar, Bogota, Cundinamarca y Antioquia presentaron niveles de productividad superiores a la media nacional, mientras Valle del Cauca, Cauca y Tolima, fueron los de mas bajo desempeno. En cuanto a sectores industriales, se destacan los altos niveles de productividad en la produccion de farmaceuticos y sustancias quimicas medicinales; aparatos y equipo electrico y fabricacion de sustancias y productos quimicos. Por el contrario, sectores tradicionales como fabricacion de productos textiles, elaboracion de alimentos, productos metalurgicos basicos y elaboracion de bebidas, presentaron bajos niveles de productividad, comparado con la media nacional. Estos resultados ponen de relieve la importancia de desarrollar politicas publicas focalizadas en aquellos sectores promisorios y regiones mas relegadas, como manera de impulsar el desarrollo industrial y cerrar las brechas de ingresos y calidad de vida entre regiones. English Abstract: In this paper, we estimate the Total Factor Productivity (TFP) for 11 departments and 20 industrial divisions in Colombia during the period 2012-2016. To this end, we employ a semiparametric method proposed by Levinsohn and Petrin (2003), using official information of the Encuesta Anual Manufacturera –EAM (Annual Manufacturing Survey), which considers microdata information of most Colombian manufacturing firms. The departments of Bolivar, Bogota, Cundinamarca and Antioquia exhibits the higher productivity growth during the period, in contrast with Valle del Cauca, Cauca and Tolima, which shows the lowest performance. In terms of industrial divisions, it stands out the Manufacture of pharmaceuticals, medicinal chemical and botanical products; Manufacture of chemicals and chemical products and Manufacture of electrical equipment; while traditional sectors as Manufacture of food products, beverages and textiles reports the lower productivity growth levels. This results remarks the importance to implement policies that helps to improve the industrial performance of some strategic sectors as a way to close the income gap between regions.

A full understanding of glacier changes in the Patagonian Andes over decadal to century time-scales is presently limited by a lack of detailed and appropriate longterm observations. Here, we present geodetic mass and area changes of three valley glaciers from Monte San Lorenzo derived from stereo aerial photos, the Shuttle Radar Topography Mission (SRTM) and satellite imagery (SPOT5 and Pleiades) spanning four periods from 1958 to 2018. Our results indicate that net mass balance was negative throughout the six decades, with a mean mass loss of −1.35 ± 0.08 m w.e. a−1 and a total glacier area loss of 14.2 ± 0.7 km2 (23 ± 1% or 0.40 ± 0.02% a−1 ). The period 1981–2000 had the most negative mass budget, with an area-averaged mass loss of 1.67 ± 0.11 m w.e. a−1 and a maximum loss of −2.23 ± 0.07 m w.e. a−1 at San Lorenzo Sur glacier. Over the periods of 2000–2012 and 2012–2018, the mass budget of these three glaciers remained virtually unchanged at −1.37 ± 0.06 and −1.36 ± 0.17 m w.e. a−1 , respectively. To place these results into a broader geographical context, the mass balance of a further 15 glaciers from around the Monte San Lorenzo massif was determined from 2000 onwards. This wider analysis reveals a period of reduced mass loss of −0.13 ± 0.21 m w.e. a−1 from 2012 to 2018 after a period of enhanced mass loss of −0.31 ± 0.16 m w.e. a−1 between 2000 and 2012. We find that increasing air temperatures coupled with diminishing precipitation across the region explains the observed patterns and are the main drivers of the negative mass budget. Furthermore, increased calving and melting into recently formed proglacial lakes has further enhanced mass loss at some lake-terminating glaciers. Fil: Falaschi, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Departamento de Geografia; Argentina Fil: Lenzano, María Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Bolch, Tobias. University of St. Andrews; Reino Unido Fil: Rivera, Andrés. Centro de Estudios Cientificos; Chile. Universidad de Chile; Chile Fil: Lo Vecchio Repetto, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras. Departamento de Geografia; Argentina

Glacially- and magmatically-derived seismic events have been noted to heavily overlap in characteristics, thus there exists the potential for false-alarms or missed warnings at ice-covered volcanoes. Here we present the first study to specifically target icequakes at an ice-covered volcano in Southern Chile. Two months of broadband seismic data collected at Llaima volcano in 2015 were analyzed in order to quantify, characterize, and locate glacially-derived seismic events at one of the most active ice-covered volcanoes in the region. We find over 1,000 repeating seismic events across 11 families, the largest of which contains 397 events. Approximate locations and characteristics of the largest families lead us to conclude that these events were derived from persistent stick-slip motion along the ice-rock interface at the base of a glacier near the volcano summit. These results have implications for future seismic monitoring at Llaima volcano and other ice-covered active volcanoes in the region.

In contrast to the general trend for glaciers of the Southern Patagonia Icefield, Glaciar Pio XI has experienced a large cumulative frontal advance since 1945. In an effort to better understand this advancing behaviour, this paper presents a synoptic analysis of frontal fluctuations (1998–2014), ice velocities (1986–2014), ice-surface elevations (1975–2007) and supraglacial moraines (1945–2014) derived from geospatial datasets. These analyses reveal changes in the ice flow of Glaciar Pio XI's freshwater calving northern terminus and tidewater calving southern terminus over recent decades. Between 1986 and 2000, ice flow speed generally accelerated reaching peaks of >15 m d−1 at the frontal edge of the southern terminus. Following this period, flow speed decreased, reducing to −1 for the central part of the southern terminus in 2014, despite advancing to a neoglacial maximum. From 2000 to 2014 the reduction in speed was accompanied by a shift in maximum velocity away from the southern terminus, towards the central glacier trunk. As a result, the northern terminus, which accelerated during this period, represented the new primary flow path in 2014. Notably, the moraine maps presented highlight surges occurring around 1981 and again between 1997 and 2000, marked by arcuate moraine features on the southern terminus.

In this work, we assessed the feasibility of using optical flow to obtain the motion estimation of a glacier. In general, former investigations used to detect glacier changes involve solutions that require repeated observations which are many times based on extensive field work. Taking into account glaciers are usually located in geographically complex and hard to access areas, deploying time-lapse imaging sensors, optical flow may provide an efficient solution at good spatial and temporal resolution to describe mass motion. Several studies in computer vision and image processing community have used this method to detect large displacements. Therefore, we carried out a test of the proposed Large Displacement Optical Flow method at the Viedma Glacier, located at South Patagonia Icefield, Argentina. We collected monoscopic terrestrial time-lapse imagery, acquired by a calibrated camera at every 24 hour from April 2014 until April 2015. A filter based on temporal correlation and RGB color discretization between the images was applied to minimize errors related to changes in lighting, shadows, clouds and snow. This selection allowed discarding images that do not follow a sequence of similarity. Our results show a flow field in the direction of the glacier movement with acceleration in the terminus. We analyzed the errors between image pairs, and the matching generally appears to be adequate, although some areas show random gross errors related to the presence of changes in lighting. The proposed technique allowed the determination of glacier motion during one year, providing accurate and reliable motion data for subsequent analysis.

We report the discovery and on-the-ground radar mapping of a subglacial lake in Antarctica, that we have named Lake CECs (Centro de Estudios Cientificos) in honor of the institute we belong to. It is located in the central part of the West Antarctic Ice Sheet, right underneath the Institute Ice Stream and Minnesota Glacier ice divide, and has not experienced surface elevation changes during the last 10 years. The ratio between the area of the subglacial lake and that of its feeding basin is larger than those for either subglacial lakes Ellsworth or Whillans, and it has a depth comparable to that of Ellsworth and greater than that of Whillans. Its ice thickness is ∼600 m less than that over Ellsworth. The lake is very likely a system with long water residence time. The recent finding of microbial life in Lake Whillans emphasizes the potential of Subglacial Lake CECs for biological exploration.

Despite their importance as freshwater reservoirs for downstream river systems, few glaciers in central Chile have been comprehensively surveyed. This study presents ground-penetrating radar (GPR) and field-based observations for characterizing the englacial and basal conditions of Glaciar Olivares Alfa (33°110 S, 70°130 W), central Chilean Andes. Using a 50 MHz radar mounted onto a helicopter platform, data were collected covering large portions of the glacier accumulation and ablation zones. The radar data revealed boundaries of a temperate-ice layer at the base of the eastern body of Glaciar Olivares Alfa which appears to be covered by colder ice that extends throughout large parts of the glacier. The thickness of the temperate ice layer is highly variable across the glacier, being on average 40% of the total ice thickness. Radar data analyses reveal regions of cold ice at the bottom/base of the glacier and also patterns of highly saturated sediments beneath the glacier. Using GPR data, this study represents the most exhaustive analysis of glacier ice structure performed in the central Chilean Andes. The results will enable improved estimations of the glacier’s mass balance and ice dynamics, helping us to understand its further development and its impact on water availability.

Se presentan las variaciones recientes del area glaciar en el Cerro O'Higgins (1976–2017), Campo de Hielo Patagonico Sur (CHS), las que han sido obtenidas a partir de imagenes de satelites pasivas. Con estas imagenes se calcularon tambien las velocidades de dichos cuerpos de hielo, alcanzandose valores maximos de 230 ± 17 m/a. El analisis de las imagenes satelitales muestra una reduccion de ∼20 km2 del area englaciada en las ultimas 4 decadas, lo que equivale aproximadamente a un ∼17%. Esta reduccion de area ha generado ademas la fragmentacion de algunos cuerpos de hielo. El analisis de las imagenes satelitales no solo muestra la reduccion areal de los glaciares, sino que ademas ha permitido el seguimiento del material morrenico existente en la superficie glaciar. De acuerdo a la morfologia de dichos depositos y sus desplazamientos, se estima que algunos de estos glaciares han experimentado movimientos repentinos y de gran magnitud, descritos en literatura inglesa como “surges”.

A wideband ground penetrating radar was developed in order to detect internal layers in firn and shallow ice, with high resolution. Mapping of near-surface layers improves traditional snow accumulation measurements, extending the spatial and temporal coverage. This system is a frequency-modulated continuous wave (FM-CW) radar, with a transmit signal range from 203 MHz to 1019 MHz and with a power of ∼250 mW. During two over-snow field campaigns in West Antarctica plateau (January and December 2014), this radar mapped near-surface internal layers to a depth of ∼170 m, with a resolution of ∼0.15 m in ice. Future improvement includes the addition of an ultra-wideband microwave snow radar, in order to map internal layers in snow column to a depth of 10 m, with a very high resolution.

An airborne low frequency radar system used to survey the ice thickness of the northern part of the Southern Patagonian Ice Field (SPI) is presented. The radar is an impulse system operating at a central frequency of 20 MHz. The system is controlled and operated from a helicopter cabin connected with an optical fibre cable to the antennas that are fixed to an aluminium structure weighting 350 kg that is hanging 40–50 m below the helicopter. At the antenna, there is a high-power transmitter working at a 5 kHz PRF, and a radar receiver. Also, there is a dual frequency GPS for the real-time positioning of the measurements. The survey took place in August 2015 and October 2016 while flying more than 400 kilometres of Glaciares Jorge Montt, OHiggins and the high plateau of the SPI. The system performance was adequate to survey most of the ice thicknesses, including the steep slopes and inaccessible crevassed areas. The maximum ice thickness penetration yielded 581 m of temperate ice. Several bottom reflections were obscure by englacial water and/or surface crevasses.

International audience; We show how a dynamical system given by a t-score function for some class of monotonic data transformations generates consistent extreme value estimators. The variation of their values increases the uncertainty of proper assessment of climate change. Two important examples illustrate the methodology: mass balance measurements on Guanaco glacier, Chile, and extreme snow loads in Slovakia. We experience singular learning of the transitions in ecosystems.

Here we present the results of a comprehensive glaciological investigation of Union Glacier (79°46' S/83°24' W) in the West Antarctic Ice Sheet (WAIS), a major outlet glacier within the Ellsworth Mountains. Union Glacier flows into the Ronne Ice Shelf, where recent models have indicated the potential for significant grounding line zone (GLZ) migrations in response to changing climate and ocean conditions. To elaborate a glaciological base line that can help to evaluate the potential impact of this GLZ change scenario, we installed an array of stakes on Union Glacier in 2007. The stake network has been surveyed repeatedly for elevation, velocity, and net surface mass balance. The region of the stake measurements is in near-equilibrium, and ice speeds are 10 to 33 m a−1. Ground-penetrating radars (GPR) have been used to map the subglacial topography, internal structure, and crevasse frequency and depth along surveyed tracks in the stake site area. The bedrock in this area has a minimum elevation of −858 m a.s.l., significantly deeper than shown by BEDMAP2 data. However, between this deeper area and the local GLZ, there is a threshold where the subglacial topography shows a maximum altitude of 190 m. This subglacial condition implies that an upstream migration of the GLZ will not have strong effects on Union Glacier until it passes beyond this shallow ice pinning point.

Made available in DSpace on 2019-10-06T15:48:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-10-01 Fondo Nacional de Desarrollo Científico y Tecnológico Southern Patagonia Icefield (SPI) glaciers have been retreating and shrinking at high rates in recent decades, significantly contributing to sea level rise. In spite of the importance of the SPI, very little is known about its mass balance apart from models lacking in situ validation, such as snow accumulation/ablation at high altitude. On the ground, snow changes are normally measured with stakes planted on snow frequently visited. Automation is possible by the use of ranging sensors, based on laser, radar or ultrasound, installed as part of automatic weather stations. In this study, we use for the first time in the SPI the technique of Global Positioning System Reflectometry (GPS-R) for measuring snow level changes. GPS-R uses observations from GPS satellites tracked by GNSS (Global Navigation Satellite Systems) ground stations. GNSS stations, typically installed according to geodetic network standards for geodynamics purposes (e.g., glacial isostatic rebound studies), inadvertently also record the signal reflected on the snow surface in the antenna surroundings. The GPS-R snow level variations were compared to an ultrasonic sensor installed nearby, operating simultaneously between October 2015 and February 2016. During this period the two datasets exhibited a correlation of 0.91 and an RMS of 17 cm, confirming that GNSS receivers can be used not only for geodetic purposes but also for snow accumulation/ablation monitoring in SPI. Departamento de Geomática Instituto Argentino de Nivología Glaciología y Ciencias Ambientales (IANIGLA) Centro Científico y Tecnológico (CCT)-CONICET Centro de Estudios Científicos (CECs) Departamento de Geografía Universidad de Chile Department of Geodesy Federal University of Rio Grande do Sul Universidade Estadual Paulista Unesp Universidade Estadual Paulista Unesp Fondo Nacional de Desarrollo Científico y Tecnológico: 1171832

The transition from the late Pleistocene to the Holocene (30 000–5000 years ago) was a period of considerable climate variability, which has been associated with changes in deep water formation and the intensity of the Meridional Overturning Circulation. Although numerous records exist across the North Atlantic region, few Antarctic ice core records have been obtained from the south. Here we exploit the potential of upwelling ancient ice – so-called blue ice areas (BIAs) – from the Patriot Hills in the Ellsworth Mountains to derive the first deuterium isotope record (δD) from continental Antarctica south of the Weddell Sea. Gas analysis and glaciological considerations provide a first relative chronology. Inferred temperature trends from the Patriot Hills BIA and snow pit suggest changing climate influences during the transition between the last glacial period and Holocene. Under modern conditions, the interplay between the Antarctic high-pressure system and the Southern Annular Mode appears to play a significant role in controlling katabatic wind flow over the site while the BIA record suggests that greater sea ice extent during the last glacial period was a major control. Our results demonstrate the considerable potential of the Patriot Hills site for reconstructing past climate change in the south Atlantic region.

We produce the first icefield-wide volume change rate and glacier velocity estimates for the Cordillera Darwin Icefield (CDI), a 2605 km2 temperate icefield in southern Chile (69.6° W, 54.6° S). Velocities are measured from optical and radar imagery between 2001–2011. Thirty-six digital elevation models (DEMs) from ASTER and the SRTM DEM are stacked and a weighted linear regression is applied to elevations on a pixel-by-pixel basis to estimate volume change rates. The CDI lost mass at an average rate of −3.9 ± 1.5 Gt yr−1 between 2000 and 2011, equivalent to a sea level rise (SLR) of 0.01 ± 0.004 mm yr−1 and an area-averaged thinning rate of −1.5 ± 0.6 m w.e.(water equivalent) yr−1. Thinning is widespread, with concentrations near the front of two northern glaciers (Marinelli, Darwin) and one western (CDI-08) glacier. Thickening is apparent in the south, most notably over the advancing Garibaldi Glacier. The northeastern part of the CDI has an average thinning rate of −1.9 ± 0.7 m w.e. yr−1, while the southwestern part has an average thinning rate of −1.0 ± 0.4 m w.e. yr−1. Velocities are obtained over many of the CDI glaciers for the first time. We provide a repeat speed time series at the Marinelli Glacier. There we measure maximum front speeds of 7.5 ± 0.2 m day−1 in 2001, 9.5 ± 0.6 m day−1 in 2003 and 10 ± 0.3 m day−1 in 2011. The maintenance of high front speeds from 2001 to 2011 supports the hypothesis that Marinelli is in the retreat phase of the tidewater cycle, with dynamic thinning governed by the fjord bathymetry.

We present the first glacier inventory of the Monte San Lorenzo region (47º35′S, 72º18′W) in the southern Patagonian Andes of Chile and Argentina. This region contains the largest and easternmost glaciers at these latitudes in South America. The inventory was developed using a combination of ASTER and Landsat ETM + scenes from 2005 and 2008, respectively, and a semi-automatic band ratio approach to map glacier ice. Manual corrections were applied to include debris-covered ice and ice in cast shadows. We inventoried 213 glaciers that cover a 2005/2008 total area of ca. 207 km2 and lie between 520 m and 3700 m in elevation. Landsat TM images acquired in 1985 and 2000 were subsequently used to assess changes in glacierized area over the 1985–2008 interval. Based on all available information, we determined an 18.6% reduction in the total glacier area since 1985. Glaciers smaller than 1 km2 have shown highly variable (0–100%) relative areal reduction, whereas the formation and growth of proglacial lakes promoted rapid recession of the, larger valley glaciers, which concentrate the major ice losses, representing ca. 32% of the total glacier area reduction. Glacier fragmentation has occurred for 50% of the ice bodies larger than 1 km2. These results agree with the generalized pattern of glacier retreat observed throughout the Patagonian Andes, but the lack of detailed meteorological and glaciological data in the area preclude a more refined analysis of the climate-glacier relationships and processes explaining the recent glacier trends. Fil: Falaschi, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Bravo, Claudio. Departamento de Geofísica. Universidad de Chile; Chile Fil: Masiokas, Mariano Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Rivera, Andrés. Centro de Estudios Científicos; Chile

Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000–11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved ‘horizontal ice core’ from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600–12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

Glaciers in the southern province of the Southern Volcanic Zone (SVZ) of Chile (37–46°S) have experienced significant frontal retreats and area losses in recent decades which have been primarily triggered by tropospheric warming and precipitation decrease. The resulting altitudinal increase of the Equilibrium Line Altitude or ELA of glaciers has lead to varied responses to climate, although the predominant volcanic stratocone morphologies prevent drastic changes in their Accumulation Area Ratios or AAR. Superimposed on climate changes however, glacier variations have been influenced by frequent eruptive activity. Explosive eruptions of ice capped volcanoes have the strongest potential to destroy glaciers, with the most intense activity in historical times being recorded at Nevados de Chillan, Villarrica and Hudson. The total glacier area located on top of the 26 active volcanoes in the study area is ca. 500 km2. Glacier areal reductions ranged from a minimum of −0.07 km2 a −1 at Mentolat, a volcano with one of the smallest ice caps, up to a maximum of −1.16 km2 a −1 at Volcan Hudson. Extreme and contrasting glacier–volcano interactions are summarised with the cases ranging from the abnormal ice frontal advances at Michinmahuida, following the Chaiten eruption in 2008, to the rapid melting of the Hudson intracaldera ice following its plinian eruption of 1991. The net effect of climate changes and volcanic activity are negative mass balances, ice thinning and glacier area shrinkage. This paper summarizes the glacier changes on selected volcanoes within the region, and discusses climatic versus volcanic induced changes. This is crucial in a volcanic country like Chile due to the hazards imposed by lahars and other volcanic processes.

Se reporta el descubrimiento del Lago Subglacial CECs (en honor al nombre de la institución, Centro de Estudios Científicos), ubicado en la parte central del casquete de hielo de la Antártica Occidental (WAIS, por sus siglas en inglés), en la divisoria entre el Glaciar Minnesota y la Corriente de Hielo Institute. Este lago, que fue descubierto mediante una travesía terrestre en enero de 2014 usando radio eco sondaje, se encuentra a una profundidad de 2653 m bajo la superficie del hielo. Los análisis preliminares muestran que se trata de un cuerpo de agua dulce que no ha mostrado cambios volumétricos, según lo observado con datos satelitales existentes hasta la fecha, por lo cual se cree que es un lago estable. Se presentan en este trabajo los datos más relevantes de este lago, así como los obtenidos en una segunda travesía llevada a cabo en diciembre de 2014.

Glacier melt is an important source of water for Andean rivers in central Chile, especially in dry years when it can be the main contributor to lowland flows in late summer and autumn. However, few studies have quantified the glacier melt contribution to river runoff. To address some of these shortcomings, we present an analysis of meteorological conditions and melt for Universidad glacier, a large valley glacier in the Mediterranean climate central Andes of Chile at the head of the Tinguiririca river, for the 2009–2010 ablation season. We used meteorological measurements from two automatic weather stations installed on the glacier to drive a distributed temperature-index melt and runoff routing model, and compare total modelled glacier melt to river flow measurements at three sites located between 0.5 and 50 km downstream. The temperature-index model was calibrated at the lower weather station site showing good agreement with melt estimates from an ablation stake and sonic ranger, and with a physically-based energy balance model. Universidad glacier is characterized by extremely high melt rates over the ablation season which exceed 10 m water equivalent on the lower altitude part of the glacier, representing a contribution between 10 % and 13 % of the total runoff observed in the upper Tinguiririca basin during the November 2009 to March 2010 period. This contribution rises to a maximum of 34 % in late summer demonstrating the importance of glacier runoff to river flow, particularly in dry summers such as 2009–2010. The temperature-index approach benefits from the availability of on-glacier meteorological data and is suited to high melt regimes, but would not be easily applicable to glaciers further north in Chile where sublimation is more significant.

Antibiotic resistance genes are biologically transmitted from microorganism to microorganism in particular micro-environments where dense microbial communities are often exposed to an intensive use of antibiotics, such as intestinal microflora, and the soil microflora of agricultural fields. However, recent studies have detected antibiotic-resistant bacteria and/or antibiotic resistance genes in the natural environment geographically isolated from such areas. Here we sought to examine the prevalence of antibiotic resistance genes in 54 snow and ice samples collected from the Arctic, Antarctic, Central Asia, North and South America and Africa, to evaluate the level of these genes in environments supposedly not affected by anthropogenic factors. We observed a widespread distribution of antibiotic resistance genes in samples from various glaciers in Central Asia, North and South America, Greenland and Africa. In contrast, Antarctic glaciers were virtually free from these genes. Antibiotic resistance genes, of both clinical (i.e. aac(3), blaIMP) and agricultural (i.e. strA and tetW) origin, were detected. Our results show regional geographical distribution of antibiotic resistance genes, with the most plausible modes of transmission through airborne bacteria and migrating birds.

Glaciar Jorge Montt (48°20' S/73°30' W), one of the main tidewater glaciers of the Southern Patagonian Icefield (SPI), has experienced the greatest terminal retreat observed in Patagonia during the past century, with a recession of 19.5 km between 1898 and 2011. This retreat has revealed trees laying subglacially until 2003. These trees were dated using radiocarbon, yielding burial ages between 460 and 250 cal yrs BP. The presence of old growth forest during those dates indicates that Glaciar Jorge Montt was upvalley of its present position before the commonly recognized Little Ice Age (LIA) period in Patagonia. The post-LIA retreat was most likely triggered by climatically induced changes during the 20th century; however, Glaciar Jorge Montt has responded more dramatically than its neighbours. The retreat of Jorge Montt opened a 19.5 km long fjord since 1898, which reaches depths in excess of 390 m. The bathymetry is well correlated with glacier retreat rates, suggesting that dynamic responses of the glacier are at least partially connected to near buoyancy conditions at the ice front, resulting in high calving fluxes, accelerating thinning rates and rapid ice velocities.

Tidewater calving glaciers can undergo large fluctuations not necessarily in direct response to climate, but rather owing to complex ice–water interactions at the glacier termini. One example of this process in Chilean Patagonia is Glaciar Jorge Montt, where two cameras were installed in February 2010, collecting up to four glacier photographs per day, until they were recovered on 22 January 2011. Ice velocities were derived from feature tracking of the geo-referenced photos, yielding a mean value of 13 ±4 md–1 for the whole lower part of the glacier. These velocities were compared to satellite-imagery-derived feature tracking obtained in February 2010, resulting in similar values. During the operational period of the cameras, the glacier continued to retreat (1 km), experiencing one of the highest calving fluxes ever recorded in Patagonia (2.4 km3 a–1). Comparison with previous data also revealed ice acceleration in recent years. These very high velocities are clearly a response to enhanced glacier calving activity into a deep water fjord.

Se presenta una sintesis de la investigacion glaciologica reciente realizada por el Centro de Estudios Cientificos, CECS, en Chile y la Peninsula Antartica mediante el uso de una variedad de metodologias modernas, con el fin de detectar las tendencias de cambio experimentadas por los glaciares en las ultimas decadas.

We analyze Holocene ice flow using global positioning system and radio-echo sounding data acquired near the Amundsen-Weddell ice divide, between Pine Island Glacier and the Institute Ice Stream, West Antarctica. The data show that this part of the West Antarctic Ice Sheet (WAIS) has maintained a stable ice flow regime and ice divide position for similar to 7000 yr. Independent glacial geological data, in support of this assertion, suggest that the interior of the WAIS west of the Ellsworth Mountains has thinned by only a few hundred meters since the Last Glacial Maximum (LGM) and that the position of the ice divide may be recurrent over longer (more than 20 k.y., perhaps pre-Quaternary) time scales. We suggest that basal topography constrains ice flow in this sector of the WAIS, making the ice divide relatively insensitive to perturbations around the margins of the ice sheet compared with other ice divides. Large-scale forcing measured elsewhere in the WAIS as major reorganizations of the ice sheet surface and flowline pattern may be manifested only in simple vertical changes of the Amundsen-Weddell interior.

Regional climate warming has caused several ice shelves on the Antarctic Peninsula to retreat and ultimately collapse during recent decades. Glaciers flowing into these retreating ice shelves have responded with accelerating ice flow and thinning. The Wordie Ice Shelf on the west coast of the Antarctic Peninsula was reported to have undergone a major areal reduction before 1989. Since then, this ice shelf has continued to retreat and now very little floating ice remains. Little information is currently available regarding the dynamic response of the glaciers feeding the Wordie Ice Shelf, but we describe a Chilean International Polar Year project, initiated in 2007, targeted at studying the glacier dynamics in this area and their relationship to local meteorological conditions. Various data were collected during field campaigns to Fleming Glacier in the austral summers of 2007/08 and 2008/09. In situ measurements of ice-flow velocity first made in 1974 were repeated and these confirm satellite-based assessments that velocity on the glacier has increased by 40–50% since 1974. Airborne lidar data collected in December 2008 can be compared with similar data collected in 2004 in collaboration with NASA and the Chilean Navy. This comparison indicates continued thinning of the glacier, with increasing rates of thinning downstream, with a mean of 4.1 ± 0.2 m a−1 at the grounding line of the glacier. These comparisons give little indication that the glacier is achieving a new equilibrium.

Bathymetric and sub-bottom acoustic data were collected in Laguna San Rafael, Chile, to determine sediment yields during the Little Ice Age advance and subsequent retreat of San Rafael Glacier. The sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance–retreat cycle. Sediment yields from San Rafael Glacier averaged 2.7 × 10 m/a since the end of the Little Ice Age, circa AD 1898, corresponding to average basin-wide erosion rates of 23 ± 9 mm/a; the highest erosion rates, 68 ± 23 mm/a, occurred at the start of the retreat phase, and have since been steadily decreasing. Erosion rates were much lower during glacial advance, averaging at most 7 mm/a, than during retreat. Such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today. The detailed sub-bottom information of a proglacial lagoon yields important clues as to the timing of erosion, deposition and transfer of glacigenic sediments from orogens to the continental shelves, and the influence of glacier dynamics on this process.

article i nfo This paper presents an updated, extensive review of glacier fluctuations during the past 1000 years in the extratropical Andes of South America between ca. 17° and 55°S. Given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range, regional accounts are given for the Desert Andes (∼17°-31°S), the Andes of central Chile and Argentina (31°-36°S), and the North (36°-45°S) and South (45°-55°S) Patagonian Andes. The techniques, dating limitations, and interpretations of the glacier records along this transect are also discussed. Information on glacier fluctuations in the Desert Andes is limited to the 20th century. Documentation on past glacier variations is more abundant in the Central Chilean-Argentinean Andes, but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited. Most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. The number and extent of glaciers increase significantly in the Patagonian region, where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area. For some Patagonian glaciers, maximum Little Ice Age (LIA) or post-LIA advances have been precisely dated by dendro- geomorphological determinations or in situ measurements. However, for most sites, the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum LIA expansion identified in most areas between the 16th and 19th centuries. Evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium. These events were generally less extensive than the LIA maximum pulses. Despite the occurrence of several post- LIA readvances over the past 100-110 years, most areas in the Andes of extratropical South America have experienced a general pattern of glacier recession and significant ice mass losses. The differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and/or the dating techniques used in each case together with the varying dominance of precipitation, temperature and other climatic and non-climatic factors on glacier mass balance and glacier dynamics. These differences indicate that the late Holocene glacier history of southern South America is more complex than commonly assumed. The evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed, well-dated records of glacier fluctuations.

Horseshoe Valley (80°18′S, 81°22′W) is a 30 km wide glaciated valley at the south-eastern end of Ellsworth Mountains draining into the Hercules inlet, Ronne Ice Shelf. The ice at Horseshoe Valley has been considered stable; now we use Global Positioning System (GPS) measurements obtained between 1996 and 2006 to investigate ice elevation change and mass balance. Comparison of surface heights on a profile across Horseshoe Valley reveals a slight but significant elevation increase of 0.04 m a-1 ± 0.002 m a-1. The blue ice area of Patriot Hills (∼13 km2) at the mount of Horseshoe Valley shows large interannual variability in area, with a maximum extent in 1997, an exceptionally warm summer, but no clear multi-year trend, and an elevation increase of 0.05 m a-1 in eight years, which agrees with the result from Horseshoe Valley.

Snow and ice in the Central Andes of Chile and Argentina (33–36 °S) are the major source of water for the highly populated regions near the cities of Santiago and Mendoza. However, our knowledge of the forces driving the general glacier retreat in the region is limited. In order to obtain a long-term perspective of glacier fluctuations and their relationships with climate in the Central Andes, historical glacier variations were documented and compared with a tree-ring precipitation reconstruction based upon Austrocedrus chilensis trees. A multi-proxy approach (historical documents, old aerial photographs and satellite imagery) was used to map the fluctuations of eight glaciers, including the Cipreses Glacier, which provides the oldest record of glacier variations in the region starting in AD 1842. All the studied glaciers exhibited a negative trend during the 20th century with mean frontal retreats between − 50 and − 9 m y− 1, thinning rates between 0.76 and 0.56 m y− 1 and a mean ice area reduction of 3% since 1955. More than 350 tree-ring cores were combined into three tree-ring chronologies, which strongly correlate with the instrumental precipitation in Santiago de Chile (33°26′ S; 70°41′ W, 520 m asl). Based on these records, a 712-year precipitation reconstruction was developed. This reconstruction is characterised by a centennial oscillation indicating marked dry conditions around the years 1440 and 1600 AD. Wet conditions were prevalent in the years 1500, 1650 and particularly around 1850 AD. Since this precipitation maximum, the reconstruction shows a clear, secular, decreasing trend. The reduction in precipitation indicated by this reconstruction for the last 150 yr, in combination with a significant warming recorded in Central Chile, are the main causes of the observed current glacier retreats.

We describe the development of a low-frequency airborne radar specifically designed for the sounding of temperate ice. The system operates at a central frequency of 1 MHz and consists of an impulse transmitter with an output voltage up to 5000 V and a digital receiver with a maximum gain of 80 dB. The radar was deployed on board a CASA 212 aircraft, which also carries a laser altimeter, an inertial navigation system, a digital camera and a GPS receiver. A description of the radar system is provided, as well as preliminary results obtained at Glaciar Tyndall, Campo de Hielo Sur (Southern Patagonia Icefield), where an ice depth of 670 m was reached.

We use meteorological data from two automatic weather stations (AWS) on Juncal Norte Glacier, central Chile, to investigate the glacier–climate interaction and to test ablation models of different complexity. The semi-arid Central Andes are characterized by dry summers, with precipitation close to zero, low relative humidity and intense solar radiation. We show that katabatic forcing is dominant both on the glacier tongue and in the fore field, and that low humidity and absence of clouds cause strong radiative cooling of the glacier surface. Surface albedo is basically constant for snow and ice, because of the scarcity of solid precipitation. The energy balance of the glacier is simulated for a 2-month period in austral summer using two models of different complexity, which differ in the inclusion of the heat conduction flux into the snowpack and in the parameterization of the incoming longwave radiation. Net shortwave radiation is the dominant component of the energy balance. The sensible heat flux is always positive, while both the net longwave radiation and latent heat flux are negative. Neglecting the subsurface heat flux and corresponding variations in surface temperature leads to an overestimation of ablation of 2% over a total of 3695 mm water equivalent (w.e.) at the end of the season. Correct modelling of incoming longwave radiation is crucial, and we suggest that parameterizations based on vapour pressure and air temperature should be used rather than on computed cloud amount. We also used an enhanced temperature-index model incorporating the shortwave radiation flux, which has two empirical parameters. We apply it both with values of parameters obtained for Alpine glaciers and recalibrated on Juncal Norte. The model recalibrated against the correct energy balance simulations performs very well. The model parameters respond to the meteorological conditions typical of this climatic setting. Copyright © 2008 John Wiley & Sons, Ltd.

Author(s): Gourlet, P; Rignot, E; Rivera, A; Casassa, G | Abstract: We employ high-resolution, high-precision, helicopter-borne gravity observations of the Northern (NPI) and Southern Patagonia Icefields (SPI), South America, to infer ice thickness and bed topography using a three-dimensional model constrained by Fjord and lake bathymetry, and a land-ice mask. The results reveal thicker ice than the reflecting horizon of radar sounders, with 1 km deep ice for Glaciar San Rafael and Colonia (NPI) and 1.5 km deep ice for Glaciar Occidental (SPI). These bedrock troughs channelize fast motion of ice from the plateaus. Combining ice motion and thickness, we calculate balance accumulation levels of 3–6 m/yr water equivalent for the plateaus. Bed elevation remains below sea/lake level 15–20 km inland for Jorge Montt and O’Higgins, which favors retreat, and is at sea level for San Rafael, which halted its retreat. The results demonstrate the utility of airborne gravity surveys for providing critical data on ice volume, bed elevation, and balance accumulation of temperate ice masses.