Mass Loss of Larsen B Tributary Glaciers (Antarctic Peninsula) Unabated Since 2002

Ice mass loss continues at a high rate among the large glacier tributaries of the Larsen B Ice Shelf following its disintegration in 2002. We evaluate recent mass loss by mapping elevation changes between 2006 and 201011 using differencing of digital elevation models (DEMs). The measurement accuracy of these elevation changes is confirmed by a null test, subtracting DEMs acquired within a few weeks. The overall 2006201011 mass loss rate (9.0 2.1 Gt a-1) is similar to the 2001022006 rate (8.8 1.6 Gt a-1), derived using DEM differencing and laser altimetry. This unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins. On Crane Glacier, the thinning pulse, initially greatest near the calving front, is now broadening and migrating upstream. The largest losses are now observed for the HektoriaGreen glacier basin, having increased by 33 since 2006. Our method has enabled us to resolve large residual uncertainties in the Larsen B sector and confirm its state of ongoing rapid mass loss

Monitoring of seasonal glacier mass balance over the European Alps using low-resolution optical satellite images

We explore a new method to retrieve seasonal glacier mass balances (MBs) from low- resolution optical remote sensing. We derive annual winter and summer snow maps of the Alps during 1998–2014 using SPOT/VEGETATION 1 km resolution imagery. We combine these seasonal snow maps with a DEM to calculate a ‘mean regional’ altitude of snow (Z) in a region surrounding a glacier. Then, we compare the interannual variation of Z with the observed winter/summer glacier MB for 55 Alpine glaciers over 1998–2008, our calibration period. We find strong linear relationships in winter (mean R² = 0.84) and small errors for the reconstructed winter MB (mean RMSE = 158 mm (w.e.) a⁻¹). This is lower than errors generally assumed for the glaciological MB measurements (200–400 mm w.e. a⁻¹). Results for summer MB are also satisfying (mean R² and RMSE, respectively, 0.74 and 314 mm w.e. a⁻¹). Comparison with observed seasonal MB available over 2009–2014 (our evaluation period) for 19 glaciers in winter and 13 in summer shows good agreement in winter (RMSE = 405 mm w.e. a⁻¹) and slightly larger errors in summer (RMSE = 561 mm w.e. a⁻¹). These results indicate that our approach might be valuable for remotely determining the seasonal MB of glaciers over large regions

Deriving high spatial-resolution coastal topography from sub-meter satellite stereo imagery

High spatial resolution coastal Digital Elevation Models (DEMs) are crucial to assess coastal vulnerability and hazards such as beach erosion, sedimentation, or inundation due to storm surges and sea level rise. This paper explores the possibility to use high spatial-resolution Pleiades (pixel size = 0.7 m) stereoscopic satellite imagery to retrieve a DEM on sandy coastline. A 40-km coastal stretch in the Southwest of France was selected as a pilot-site to compare topographic measurements obtained from Pleiades satellite imagery, Real Time Kinematic GPS (RTK-GPS) and airborne Light Detection and Ranging System (LiDAR). The derived 2-m Pleiades DEM shows an overall good agreement with concurrent methods (RTK-GPS and LiDAR; correlation coefficient of 0.9), with a vertical Root Mean Squared Error (RMS error) that ranges from 0.35 to 0.48 m, after absolute coregistration to the LiDAR dataset. The largest errors (RMS error > 0.5 m) occurred in the steep dune faces, particularly at shadowed areas. This work shows that DEMs derived from sub-meter satellite imagery capture local morphological features (e.g., berm or dune shape) on a sandy beach, over a large spatial domain.French Space Agency (CNES) CNES through the TOSCA program FCT IF/00661/2014/CP1234 FEDER, within the PT2020 Partnership Agreement FEDER, within the Compete 2020 UID/AMB/50017/2019info:eu-repo/semantics/publishedVersio

An Imbalancing Act: The Delayed Dynamic Response of the Kaskawulsh Glacier to Sustained Mass Loss

The Kaskawulsh Glacier is an iconic outlet draining the icefields of the St. Elias Mountains in Yukon, Canada. We determine and attempt to interpret its catchment-wide mass budget since 2007. Using SPOT5/6/7 data we estimate a 2007–18 geodetic balance of −0.46 ± 0.17 m w.e. a−1. We then compute balance fluxes and observed ice fluxes at nine flux gates to examine the discrepancy between the climatic mass balance and internal mass redistribution by glacier flow. Balance fluxes are computed using a fully distributed mass-balance model driven by downscaled and bias-corrected climate-reanalysis data. Observed fluxes are calculated using NASA ITS_LIVE surface velocities and glacier cross-sectional areas derived from ice-penetrating radar data. We find the glacier is still in the early stages of dynamic adjustment to its mass imbalance. We estimate a committed terminus retreat of ~23 km under the 2007–18 climate and a lower bound of 46 km3 of committed ice loss, equivalent to ~15% of the total glacier volume

Elevation Changes Inferred From TanDEM-X Data Over the Mont-Blanc Area: Impact of the X-Band Interferometric Bias

International audienceThe TanDEM-X mission allows generation of Digital Elevation Models (DEM) with high potential for glacier monitoring, but the radar penetration into snow and ice remains a main source of uncertainty. In this study, we generate 5 new DEMs of the Mont-Blanc area from [...

Variabilité des enregistrements polliniques en montagne et reconstitutions paléoécologiques

L’étude pollinique de 5 sites autour d’Annecy (Lac d’Annecy 450 m, Poisy 490 m, Les Rondets 940 m, Bouttecul 1200 m, Plateau des Glières 1500 m) montre les variations des enregistrements polliniques dans une zone géographique restreinte. Deux types de comparaisons ont été faites: l’une sur deux sites proches (Annecy/Poisy) aux caractéristiques des bassins versants différentes dans un même étage de végétation et l’autre sur quatre sites (Poisy, Rondets, Bouttecul, Glières) aux caractéristiques des bassins versants semblables dans différents étages de végétation.La première comparaison montre le meilleur enregistrement des taxons à forte dispersion pollinique (Pinus, Quercus, Abies, Juglans) dans un site de grande taille avec apports fluviatiles. La représentation forte de taxons tels que Fraxinus et Ulmus, voire Alnus glutinosa/incana après 6000 BP dans un site de plus petite taille, sans apports fluviatiles, indique la localisation de ces taxons en bordure de marais. En revanche la bonne représentation de Tilia dans les deux sites malgré sa faible diffusion pollinique signifie une extension remarquable des tilleuls à l’échelle régionale. Le second pic significatif d’Abies dans le site de grande taille non enregistré dans le site de petite taille marque la différence d’origine des apports polliniques. La comparaison de petits sites étagés montre le diachronisme de la colonisation végétale en fonction de l’altitude. Au début de l’Holocène, les bouleaux et les pins colonisent les niveaux inférieurs à 1500 m. A partir de 9000 BP, Corylus, Quercus, Ulmus, Tilia dominent le paysage jusqu’à cette altitude. La représentation de Corylus décroît avec l’altitude et les pins subsistent au dessus de 1500 m. A partir de 8000 BP, la progression des sapins est enregistrée à tous les étages. Cette progression est stoppée dès 5900 BP dans l’étage collinéen où se développent des formations végétales proches des formations actuelles. Plus haut le sapin se maintient jusqu’à la forte progression de l’épicéa vers 4000BP. Fraxinus et Alnus sont mieux représentés dans l’étage collinéen, Tilia dans l’étage montagnard jusqu’à 1200 m. Au diachronisme lié à l’effet de l’altitude sur l’installation des végétaux se surimpose l’amplitude variable de l’action anthropique dès environ 6000 BP.Pollen study of five sedimentary sequences cored in the vicinity of Annecy (Lac d’Annecy 450 m, Poisy 490 m, Les Rondets 940 m, Bouttecul 1200 m, Plateau des Glières 1500 m) shows the variability of pollen records in a small geographical area. Two comparisons display the multiple parameters affecting pollen records. The comparison Lac d’Annecy/Poisy concerns a great site with tributary and a small endoreic site at the same altitudinal belt, whereas the comparison Poisy, Rondets, Bouttecul, Glières concerns similar endoreic sites at different altitudinal belts.The first comparison illustrates the best record of easily wind dispersed taxa (Pinus, Quercus, Abies, Juglans) in the great site. The best record of Fraxinus, Ulmus, even Alnus glutinosa/incana after 6000 BP in the small site reflects the location of those taxa around the site. In the two sites, high Tilia values, a poorly wind dispersed taxon, indicate the large regional distribution of the trees. The difference in the pollen source area recruitment linked to basin characteristics is confirmed by Abies curve which shows in the great site a second peak not recorded at the small one. This constitutes a first impediment to the climatic translation of pollen record in montanous areas characterized by high local variations.The second comparison of small basin at different elevation illustrates the vegetation cover expansion out of phase at higher altitudes. At the first step of the Holocene, Betula and Pinus colonized belt below 1500 m. Around and after 9000 BP Corylus, Quercus, Ulmus, Tilia extended up to 1500 m. An altitudinal gradient is clearly evidenced by Corylus values decreasing with the altitude. Pinus is then present above 1500 m. On and after 8000 BP Abies is recorded at each site. Abies spread has been stopped at 5900 BP at the lowest site where a vegetation cover similar to the present one has developed. At higher altitude Abies expanded until the large development of Picea around 4000 BP. Fraxinus and Alnus percentages are higher at hill belt and Tilia at montane belt up to 1200 m. From about 6000 BP the effects of the different human uses at different altitudes have been added to those altitudinal gradients