Francisco Navarro - Academia.edu (original) (raw)

Papers by Francisco Navarro

Drones

How do the weather conditions typical of the polar maritime glaciers in the western Antarctic Pen... more How do the weather conditions typical of the polar maritime glaciers in the western Antarctic Peninsula region affect flight operations of fixed-wing drones and how should these be adapted for a successful flight? We tried to answer this research question through a case study for Johnsons and Hurd glaciers, Livingston Island, using a fixed-wing RPAS, in particular, a Trimble UX5 UAV with electric pusher propeller by brushless 700 W motor, chosen for its ability to fly long distances and reach inaccessible areas. We also evaluated the accuracy of the point clouds and digital surface models (DSM) generated by aerial photogrammetry in our case study. The results were validated against ground control points taken by differential GNSS techniques, showing an accuracy of 0.16 ± 0.12 m in the vertical coordinate. Various hypotheses were proposed and flight-tested, based on variables affecting the flight operation and the data collection, namely, gusty winds, low temperatures, battery life, ...

Annals of Glaciology

During the second half of the 20th century, the Antarctic Peninsula region has undergone a long a... more During the second half of the 20th century, the Antarctic Peninsula region has undergone a long and sustained warming period, followed by a shorter but also sustained cooling period, and then a very recent return to warming conditions. All of these have profoundly impacted the glaciers peripheral to the Antarctic Peninsula. This paper focuses on the analysis of the surface mass balance monitoring of such glaciers by the glaciological method, complemented by the analysis of mass-balance estimates by geodetic methods, as well as frontal ablation estimates. We aim to summarize the current knowledge and outline the main challenges faced by investigating the mass balance of such peripheral glaciers and their current contribution to sea-level rise.

Ice and Snow, 2020

The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, whi... more The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, while the latter was obtained by differencing two sets of ArcticDEM digital elevation models. From these surface-elevation change rates we obtained the geodetic mass balance, which was nearly identical for both periods, at −1,72±0,67 Gt a −1 , equivalent to −0,31±0,12 m w.e. a −1 over the whole ice cap area. Using an independent estimate of frontal ablation for 2016−2017 of −1,93±0,12 Gt a −1 (−0,31±0,12 m w.e. a −1), we get an estimate of the climatic mass balance not significantly different from zero, at 0,21±0,68 Gt a −1 (0,04±0,13 m w.e. a −1), which agrees with the near-zero average balance at a decadal scale observed during the last four decades. Making an observationally-based assumption on accumulation rate, we estimate the current total ablation from the ice cap, and its partitioning between frontal ablation, dominated by calving (~54%) and climatic mass balance, mostly surface ablation (~46%).

Prediction of the direction of change of a system under specified environmental conditions is one... more Prediction of the direction of change of a system under specified environmental conditions is one reason for the widespread utility of thermodynamic models in geochemistry. However, thermodynamic influences on the chemical compositions of proteins in nature have remained enigmatic despite much work that demonstrates the impact of environmental conditions on amino acid frequencies. Here, we present evidence that the dehydrating effect of salinity is detectable as chemical differences in protein sequences inferred from 1) metagenomes and metatranscriptomes in regional salinity gradients and 5 2) differential gene and protein expression in microbial cells under hyperosmotic stress. The stoichiometric hydration state (nH2O), derived from the number of water molecules in theoretical reactions to form proteins from a particular set of basis species (glutamine, glutamic acid, cysteine, O2, H2O), decreases along salinity gradients including the Baltic Sea and Amazon River and ocean plume an...

The Antarctic Peninsula region has experienced a recent cooling for about 15 years since the begi... more The Antarctic Peninsula region has experienced a recent cooling for about 15 years since the beginning of the 21st century. In Livingston Island, this cooling has been of 0.8°C over the 12-yr period 2004–2016, and of 1.0°C for the summer average temperatures over the same period. In this paper, we analyse whether this observed cooling has implied a significant change in the density of the snowpack covering Hurd and Johnsons glaciers, and whether such a density change has had, by itself, a noticeable impact in the calculated surface mass balance. Our results indicate a decrease in the snow density by 22 kg m-3 over the study period. The density changes are shown to be correlated with the summer temperature changes. We show that this observed decrease in density does not have an appreciable effect on the calculated surface mass balance, as the corresponding changes are below the usual error range of the surface mass balance estimates. This relieves us from the need of detailed and tim...

We have characterized the snow albedo decay over Hurd Peninsula, Livingston Island, Antarctica, f... more We have characterized the snow albedo decay over Hurd Peninsula, Livingston Island, Antarctica, for the period 2000–2016. The snow albedo was obtained from the MOD10A1 product of the spaceborne MODIS sensor. A low-pass filter is applied to the data in order to eliminate short-term variations and retain the seasonal variation of albedo. The seasonal albedo was fitted to an exponential decay function to obtain the decay rate, the duration and the starting date of the decay. On average, albedo decay starts in late September and lasts for 96 ± 20 days. Snow melting lags behind snow albedo decay. This lag is due, on the one hand, to the occurrence of dry-snow metamorphism and sublimation in the early stages of the decay, and on the other hand to persisting subsurface melting after the completion of the metamorphic processes at the surface. The albedo decay is mainly driven by the shortwave incident radiation, with air and near-surface temperatures unexpectedly playing a minor role. Near-...

Quaternary Science Reviews, 2021

The small ice caps distributed across the Antarctic Peninsula region have undergone large ice vol... more The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60 22 0 W, 62 40' S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 10 Be exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at~22 ka but intense glacial shrinking occurred from~18 to~13 ka, when the nunataks became exposed, being particularly intense at the end of this period (~14 e13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).

Journal of Glaciology, 2021

Up to 30% of the current tidewater mass loss in Svalbard corresponds to frontal ablation through ... more Up to 30% of the current tidewater mass loss in Svalbard corresponds to frontal ablation through submarine melting and calving. We developed two-dimensional (2-D) glacier–line–plume and glacier–fjord circulation coupled models, both including subglacial discharge, submarine melting and iceberg calving, to simulate Hansbreen–Hansbukta system, SW Svalbard. We ran both models for 20 weeks, throughout April–August 2010, using different scenarios of subglacial discharge and crevasse water depth. Both models showed large seasonal variations of submarine melting in response to transient fjord temperatures and subglacial discharges. Subglacial discharge intensity and crevasse water depth influenced calving rates. Using the best-fit configuration for both parameters our two coupled models predicted observed front positions reasonably well (±10 m). Although the two models showed different melt-undercutting front shapes, which affected the net-stress fields near the glacier front, no significa...

Mètode Revista de difusió de la investigació, 2020

Sea-level has been rising at an accelerated rate during recent decades and is projected to contin... more Sea-level has been rising at an accelerated rate during recent decades and is projected to continue increasing at an accelerated rate over the twenty-first century and beyond, mostly as a result of anthropogenic warming. A substantially raised sea level can have severe impacts on low-lying coastal areas, including coastal erosion and flooding of inhabited areas. Under continued climate warming, these impacts will be exacerbated by extreme meteorological events and extreme wave heights, posing severe risks to the human communities and coastal ecosystems. In this paper we review the recent advances on the contributions of glaciers and sheets to sea-level rise, in the light of the recently released IPCC Special Report on the Ocean and Cryosphere in a Changing Climate.

Ice and Snow, 2020

We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemly... more We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during the period November 2016-November 2017, using intensity offset-tracking of Sentinel-1 synthetic-aperture radar images. We used the average of 54 pairs of weekly velocities (with both images in each pair separated by a12-day period) to estimate the mean annual ice discharge from the ice cap. We got an average ice discharge for 2016-2017 of 1,93±0,12 Gt a −1 , which is equivalent to −0,35±0,02 m w.e. a −1 over the whole area of the ice cap. The difference from an estimate of ~1,4 Gt a −1 for 2003-2009 can be attributed to the initiation of ice-stream flow in Basin BC sometime between 2002 and 2016. Since the front position changes between both periods have been negligible, ice discharge is equivalent to calving flux. We compare our results for calving flux with those of previous studies and analyse the possible drivers of the changes observed along the last three decades. Since these changes do not appear to have responded to environmental changes, we conclude that the observed changes are likely driven by the intrinsic characteristics of the ice cap governing tidewater glacier dynamics.

Journal of Glaciology, 2019

We determined ice velocities for the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arcti... more We determined ice velocities for the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during November 2016–November 2017, by feature-tracking 54 pairs of Sentinel-1 synthetic-aperture radar images. Seasonal velocity variations with amplitudes up to 10% of the yearly-averaged velocity were observed. Shorter-term (<15 d) intra-annual velocity variations had average and maximum deviations from the annual mean of up to 16 and 32%, respectively. This indicates the errors that could be incurred if ice discharge values determined from a single pair of images were extrapolated to the whole year. Average ice discharge for 2016–2017 was 1.93 ± 0.12 Gt a−1. The difference from an estimate of ~ 1.4 Gt a−1 for 2003–2009 was attributed to the initiation of ice stream flow in Basin BC. The total geodetic mass balance over 2012–2016 was − 1.72 ± 0.67 Gt a−1 (− 0.31 ± 0.12 m w.e. a−1). The climatic mass balance was not significantly different from zero, at 0.21 ± 0.68 Gt a−1 (0.04 ±...

Journal of Glaciology, 2018

ABSTRACTWe analyse the various error sources in the estimation of ice discharge through flux gate... more ABSTRACTWe analyse the various error sources in the estimation of ice discharge through flux gates, distinguishing the cases with ice-thickness data available for glacier cross-sections or only along the centreline. For the latter, we analyse the performance of three U-shaped cross-sectional approaches. We apply this methodology to glaciers of the Canadian High Arctic. The velocity field is the main error source for small and medium-size glaciers (discharge <100 Mt a−1) with low velocities (<100 m a−1), while for large glaciers (discharge >100 Mt a−1) with high velocities…

Remote Sensing, 2017

The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission pr... more The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission provides a wide coverage per acquisition with resolutions of 5 m in range and 20 m in azimuth, which makes this acquisition mode attractive for glacier velocity monitoring. Here, we retrieve surface velocities from the southern Ellesmere Island ice caps (Canadian Arctic) using both offset tracking and Differential Interferometric Synthetic Aperture Radar (D-InSAR) techniques and combining ascending and descending passes. We optimise the offset tracking technique by omitting the azimuth offsets. By doing so, we are able to improve the final resolution of the velocity product, as Sentinel-1 shows a lower resolution in the azimuth direction. Simultaneously, we avoid the undesired ionospheric effect manifested in the data as azimuth streaks. The D-InSAR technique shows its merits when applied to slow-moving areas, while offset tracking is more suitable for fast-moving areas. This research show...

Nature, 2013

IPCC AR4), both new observations of ice-sheet mass balance and improved computer simulations of i... more IPCC AR4), both new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to ongoing climate change have been published. While Greenland is losing mass at an increasing pace, Antarctic loss is likely to be less than some recently-published estimates. It remains unclear whether East Antarctica has been gaining or losing mass over the last twenty years, and uncertainties in mass change for West Antarctica and the Antarctic Peninsula remain large. We highlight the last six years of progress and examine the key problems that remain.

Annals of Glaciology, 2005

Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spit... more Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50–80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936–90 has been estimated: a glacier tongue retreat of 930 m, a decrease in a...

Journal of Glaciology, 2015

Arctic, Antarctic, and Alpine Research, 2014

Journal of Applied Geophysics, 2005

The capabilities of seismic and radar methods for the study of ice sheets have been analysed by o... more The capabilities of seismic and radar methods for the study of ice sheets have been analysed by other authors in the past. The joint use of both techniques has allowed the comparison of information, such as ice thickness, retrieved from both sources. Though these methods, ...

Cuadernos de Investigación Geográfica, 2016

During the period 1999-2014, the Group of Numerical Simulation in Sciences and Engineering of Uni... more During the period 1999-2014, the Group of Numerical Simulation in Sciences and Engineering of Universidad Politécnica de Madrid carried out many ground-penetrating radar campaigns in Svalbard, aimed to the study of glacier ice-thickness and the physical properties of glacier ice. The regions covered were Nordenskiöld Land, Wedel Jarlsberg Land, Sabine Land and Nordaustlandet. We here present a review of these works, focused on the aspects related to the estimate of the volume of individual glaciers and its extrapolation to the entire set of Svalbard glaciers, for which the authors estimate a total volume of 6700±835 km3, o 17±2 mm in sea-level equivalent.

In order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiop... more In order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiophysical investigations were made at Hansbreen, a polythermal glacier in Spitsbergen, in July-August 2003 and April 2004. These investigations included repeated radar profiling (20 and 25 MHz) along a transverse profile, repeated common-midpoint measurements, continuous radar measurements during 8 days at a fixed site, meteorological observations, and continuous ice surface velocity monitoring by differential GPS. Seasonal and inter-seasonal RWV changes in the temperate ice layer are attributed, respectively, to rapid water redistribution within it during the summer, and to variations in water content from 2.1% in summer to 0.4% in spring. The reflection properties of the temperate ice layer correlate well with the air temperature, with a nearly semi-diurnal time lag. The temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon. Repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography. The spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems.

Drones

How do the weather conditions typical of the polar maritime glaciers in the western Antarctic Pen... more How do the weather conditions typical of the polar maritime glaciers in the western Antarctic Peninsula region affect flight operations of fixed-wing drones and how should these be adapted for a successful flight? We tried to answer this research question through a case study for Johnsons and Hurd glaciers, Livingston Island, using a fixed-wing RPAS, in particular, a Trimble UX5 UAV with electric pusher propeller by brushless 700 W motor, chosen for its ability to fly long distances and reach inaccessible areas. We also evaluated the accuracy of the point clouds and digital surface models (DSM) generated by aerial photogrammetry in our case study. The results were validated against ground control points taken by differential GNSS techniques, showing an accuracy of 0.16 ± 0.12 m in the vertical coordinate. Various hypotheses were proposed and flight-tested, based on variables affecting the flight operation and the data collection, namely, gusty winds, low temperatures, battery life, ...

Annals of Glaciology

During the second half of the 20th century, the Antarctic Peninsula region has undergone a long a... more During the second half of the 20th century, the Antarctic Peninsula region has undergone a long and sustained warming period, followed by a shorter but also sustained cooling period, and then a very recent return to warming conditions. All of these have profoundly impacted the glaciers peripheral to the Antarctic Peninsula. This paper focuses on the analysis of the surface mass balance monitoring of such glaciers by the glaciological method, complemented by the analysis of mass-balance estimates by geodetic methods, as well as frontal ablation estimates. We aim to summarize the current knowledge and outline the main challenges faced by investigating the mass balance of such peripheral glaciers and their current contribution to sea-level rise.

Ice and Snow, 2020

The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, whi... more The former was calculated from differencing of ICESat and ArcticDEM digital elevation models, while the latter was obtained by differencing two sets of ArcticDEM digital elevation models. From these surface-elevation change rates we obtained the geodetic mass balance, which was nearly identical for both periods, at −1,72±0,67 Gt a −1 , equivalent to −0,31±0,12 m w.e. a −1 over the whole ice cap area. Using an independent estimate of frontal ablation for 2016−2017 of −1,93±0,12 Gt a −1 (−0,31±0,12 m w.e. a −1), we get an estimate of the climatic mass balance not significantly different from zero, at 0,21±0,68 Gt a −1 (0,04±0,13 m w.e. a −1), which agrees with the near-zero average balance at a decadal scale observed during the last four decades. Making an observationally-based assumption on accumulation rate, we estimate the current total ablation from the ice cap, and its partitioning between frontal ablation, dominated by calving (~54%) and climatic mass balance, mostly surface ablation (~46%).

Prediction of the direction of change of a system under specified environmental conditions is one... more Prediction of the direction of change of a system under specified environmental conditions is one reason for the widespread utility of thermodynamic models in geochemistry. However, thermodynamic influences on the chemical compositions of proteins in nature have remained enigmatic despite much work that demonstrates the impact of environmental conditions on amino acid frequencies. Here, we present evidence that the dehydrating effect of salinity is detectable as chemical differences in protein sequences inferred from 1) metagenomes and metatranscriptomes in regional salinity gradients and 5 2) differential gene and protein expression in microbial cells under hyperosmotic stress. The stoichiometric hydration state (nH2O), derived from the number of water molecules in theoretical reactions to form proteins from a particular set of basis species (glutamine, glutamic acid, cysteine, O2, H2O), decreases along salinity gradients including the Baltic Sea and Amazon River and ocean plume an...

The Antarctic Peninsula region has experienced a recent cooling for about 15 years since the begi... more The Antarctic Peninsula region has experienced a recent cooling for about 15 years since the beginning of the 21st century. In Livingston Island, this cooling has been of 0.8°C over the 12-yr period 2004–2016, and of 1.0°C for the summer average temperatures over the same period. In this paper, we analyse whether this observed cooling has implied a significant change in the density of the snowpack covering Hurd and Johnsons glaciers, and whether such a density change has had, by itself, a noticeable impact in the calculated surface mass balance. Our results indicate a decrease in the snow density by 22 kg m-3 over the study period. The density changes are shown to be correlated with the summer temperature changes. We show that this observed decrease in density does not have an appreciable effect on the calculated surface mass balance, as the corresponding changes are below the usual error range of the surface mass balance estimates. This relieves us from the need of detailed and tim...

We have characterized the snow albedo decay over Hurd Peninsula, Livingston Island, Antarctica, f... more We have characterized the snow albedo decay over Hurd Peninsula, Livingston Island, Antarctica, for the period 2000–2016. The snow albedo was obtained from the MOD10A1 product of the spaceborne MODIS sensor. A low-pass filter is applied to the data in order to eliminate short-term variations and retain the seasonal variation of albedo. The seasonal albedo was fitted to an exponential decay function to obtain the decay rate, the duration and the starting date of the decay. On average, albedo decay starts in late September and lasts for 96 ± 20 days. Snow melting lags behind snow albedo decay. This lag is due, on the one hand, to the occurrence of dry-snow metamorphism and sublimation in the early stages of the decay, and on the other hand to persisting subsurface melting after the completion of the metamorphic processes at the surface. The albedo decay is mainly driven by the shortwave incident radiation, with air and near-surface temperatures unexpectedly playing a minor role. Near-...

Quaternary Science Reviews, 2021

The small ice caps distributed across the Antarctic Peninsula region have undergone large ice vol... more The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60 22 0 W, 62 40' S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 10 Be exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at~22 ka but intense glacial shrinking occurred from~18 to~13 ka, when the nunataks became exposed, being particularly intense at the end of this period (~14 e13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).

Journal of Glaciology, 2021

Up to 30% of the current tidewater mass loss in Svalbard corresponds to frontal ablation through ... more Up to 30% of the current tidewater mass loss in Svalbard corresponds to frontal ablation through submarine melting and calving. We developed two-dimensional (2-D) glacier–line–plume and glacier–fjord circulation coupled models, both including subglacial discharge, submarine melting and iceberg calving, to simulate Hansbreen–Hansbukta system, SW Svalbard. We ran both models for 20 weeks, throughout April–August 2010, using different scenarios of subglacial discharge and crevasse water depth. Both models showed large seasonal variations of submarine melting in response to transient fjord temperatures and subglacial discharges. Subglacial discharge intensity and crevasse water depth influenced calving rates. Using the best-fit configuration for both parameters our two coupled models predicted observed front positions reasonably well (±10 m). Although the two models showed different melt-undercutting front shapes, which affected the net-stress fields near the glacier front, no significa...

Mètode Revista de difusió de la investigació, 2020

Sea-level has been rising at an accelerated rate during recent decades and is projected to contin... more Sea-level has been rising at an accelerated rate during recent decades and is projected to continue increasing at an accelerated rate over the twenty-first century and beyond, mostly as a result of anthropogenic warming. A substantially raised sea level can have severe impacts on low-lying coastal areas, including coastal erosion and flooding of inhabited areas. Under continued climate warming, these impacts will be exacerbated by extreme meteorological events and extreme wave heights, posing severe risks to the human communities and coastal ecosystems. In this paper we review the recent advances on the contributions of glaciers and sheets to sea-level rise, in the light of the recently released IPCC Special Report on the Ocean and Cryosphere in a Changing Climate.

Ice and Snow, 2020

We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemly... more We have determined the ice-surface velocities of the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during the period November 2016-November 2017, using intensity offset-tracking of Sentinel-1 synthetic-aperture radar images. We used the average of 54 pairs of weekly velocities (with both images in each pair separated by a12-day period) to estimate the mean annual ice discharge from the ice cap. We got an average ice discharge for 2016-2017 of 1,93±0,12 Gt a −1 , which is equivalent to −0,35±0,02 m w.e. a −1 over the whole area of the ice cap. The difference from an estimate of ~1,4 Gt a −1 for 2003-2009 can be attributed to the initiation of ice-stream flow in Basin BC sometime between 2002 and 2016. Since the front position changes between both periods have been negligible, ice discharge is equivalent to calving flux. We compare our results for calving flux with those of previous studies and analyse the possible drivers of the changes observed along the last three decades. Since these changes do not appear to have responded to environmental changes, we conclude that the observed changes are likely driven by the intrinsic characteristics of the ice cap governing tidewater glacier dynamics.

Journal of Glaciology, 2019

We determined ice velocities for the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arcti... more We determined ice velocities for the Academy of Sciences Ice Cap, Severnaya Zemlya, Russian Arctic, during November 2016–November 2017, by feature-tracking 54 pairs of Sentinel-1 synthetic-aperture radar images. Seasonal velocity variations with amplitudes up to 10% of the yearly-averaged velocity were observed. Shorter-term (<15 d) intra-annual velocity variations had average and maximum deviations from the annual mean of up to 16 and 32%, respectively. This indicates the errors that could be incurred if ice discharge values determined from a single pair of images were extrapolated to the whole year. Average ice discharge for 2016–2017 was 1.93 ± 0.12 Gt a−1. The difference from an estimate of ~ 1.4 Gt a−1 for 2003–2009 was attributed to the initiation of ice stream flow in Basin BC. The total geodetic mass balance over 2012–2016 was − 1.72 ± 0.67 Gt a−1 (− 0.31 ± 0.12 m w.e. a−1). The climatic mass balance was not significantly different from zero, at 0.21 ± 0.68 Gt a−1 (0.04 ±...

Journal of Glaciology, 2018

ABSTRACTWe analyse the various error sources in the estimation of ice discharge through flux gate... more ABSTRACTWe analyse the various error sources in the estimation of ice discharge through flux gates, distinguishing the cases with ice-thickness data available for glacier cross-sections or only along the centreline. For the latter, we analyse the performance of three U-shaped cross-sectional approaches. We apply this methodology to glaciers of the Canadian High Arctic. The velocity field is the main error source for small and medium-size glaciers (discharge <100 Mt a−1) with low velocities (<100 m a−1), while for large glaciers (discharge >100 Mt a−1) with high velocities…

Remote Sensing, 2017

The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission pr... more The Terrain Observation by Progressive Scans (TOPS) acquisition mode of the Sentinel-1 mission provides a wide coverage per acquisition with resolutions of 5 m in range and 20 m in azimuth, which makes this acquisition mode attractive for glacier velocity monitoring. Here, we retrieve surface velocities from the southern Ellesmere Island ice caps (Canadian Arctic) using both offset tracking and Differential Interferometric Synthetic Aperture Radar (D-InSAR) techniques and combining ascending and descending passes. We optimise the offset tracking technique by omitting the azimuth offsets. By doing so, we are able to improve the final resolution of the velocity product, as Sentinel-1 shows a lower resolution in the azimuth direction. Simultaneously, we avoid the undesired ionospheric effect manifested in the data as azimuth streaks. The D-InSAR technique shows its merits when applied to slow-moving areas, while offset tracking is more suitable for fast-moving areas. This research show...

Nature, 2013

IPCC AR4), both new observations of ice-sheet mass balance and improved computer simulations of i... more IPCC AR4), both new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to ongoing climate change have been published. While Greenland is losing mass at an increasing pace, Antarctic loss is likely to be less than some recently-published estimates. It remains unclear whether East Antarctica has been gaining or losing mass over the last twenty years, and uncertainties in mass change for West Antarctica and the Antarctic Peninsula remain large. We highlight the last six years of progress and examine the key problems that remain.

Annals of Glaciology, 2005

Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spit... more Aldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50–80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936–90 has been estimated: a glacier tongue retreat of 930 m, a decrease in a...

Journal of Glaciology, 2015

Arctic, Antarctic, and Alpine Research, 2014

Journal of Applied Geophysics, 2005

The capabilities of seismic and radar methods for the study of ice sheets have been analysed by o... more The capabilities of seismic and radar methods for the study of ice sheets have been analysed by other authors in the past. The joint use of both techniques has allowed the comparison of information, such as ice thickness, retrieved from both sources. Though these methods, ...

Cuadernos de Investigación Geográfica, 2016

During the period 1999-2014, the Group of Numerical Simulation in Sciences and Engineering of Uni... more During the period 1999-2014, the Group of Numerical Simulation in Sciences and Engineering of Universidad Politécnica de Madrid carried out many ground-penetrating radar campaigns in Svalbard, aimed to the study of glacier ice-thickness and the physical properties of glacier ice. The regions covered were Nordenskiöld Land, Wedel Jarlsberg Land, Sabine Land and Nordaustlandet. We here present a review of these works, focused on the aspects related to the estimate of the volume of individual glaciers and its extrapolation to the entire set of Svalbard glaciers, for which the authors estimate a total volume of 6700±835 km3, o 17±2 mm in sea-level equivalent.

In order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiop... more In order to study the seasonal and inter-seasonal variations in radio-wave velocity (RWV), radiophysical investigations were made at Hansbreen, a polythermal glacier in Spitsbergen, in July-August 2003 and April 2004. These investigations included repeated radar profiling (20 and 25 MHz) along a transverse profile, repeated common-midpoint measurements, continuous radar measurements during 8 days at a fixed site, meteorological observations, and continuous ice surface velocity monitoring by differential GPS. Seasonal and inter-seasonal RWV changes in the temperate ice layer are attributed, respectively, to rapid water redistribution within it during the summer, and to variations in water content from 2.1% in summer to 0.4% in spring. The reflection properties of the temperate ice layer correlate well with the air temperature, with a nearly semi-diurnal time lag. The temporal variability of the reflection properties of the internal horizon suggests enlargement of water inclusions or water drainage from the horizon. Repeated profiling shows a stable spatial pattern in bed reflection power interpreted as changes in water content controlled by bedrock topography. The spatial variations of internal reflection energy along the repeated profile correlate with the thickness of the cold ice layer and the occurrence of drainage and crevasse systems.