Evolution of Ossoue Glacier (French Pyrenees) since the end of the Little Ice Age

International audienceLittle is known about the fluctuations of the Pyre-nean glaciers. In this study, we reconstructed the evolution of Ossoue Glacier (42 • 46 N, 0.45 km 2), which is located in the central Pyrenees, from the Little Ice Age (LIA) onwards. To do so, length, area, thickness, and mass changes in the glacier were generated from historical data sets, topo-graphical surveys, glaciological measurements (2001–2013), a ground penetrating radar (GPR) survey (2006), and stereo-scopic satellite images (2013). The glacier has receded considerably since the end of the LIA, losing 40 % of its length and 60 % of its area

Review article of the current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change

The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the LIA (mid 17th–early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the computed global average. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from −0.2m w.e. in the period 1964–1975 to −0.76m w.e. in the period 1976–2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that as a percentage, this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia showed that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance variability at the interannual to decadal time scale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10◦Cdecade−1 in the last 70 yr. The higher frequency of El Nin ̃o events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world

Computation of the space and time evolution of equilibrium-line altitudes on Andean glaciers (10 degrees N-55 degrees S)

International audienceA previous study of Fox [Fox, A.N. 1993. Snowline altitude and climate at present and during the Last Pleistocene Glacial Maximum in the Central Andes (5 degrees-28 degrees S). Ph.D. Thesis. Cornell University.] showed that for a fixed 0 degrees C isotherm altitude, the equilibrium-line altitude (ELA) of the Peruvian and Bolivian glaciers from 5 to 20 degrees S can be expressed based on a log-normal expression of local mid-annual rainfall amount (P). In order to extrapolate the function to the whole Andes (10 degrees N to 55 degrees S) a local 0 degrees C isotherm altitude is introduced. Two applications of this generalised function are presented. One concerns the space evolution of mean inter-annual ELA for three decades (1961-1990) over the whole South American continent. A high-resolution data set (grid data: 10' for latitude/longitude) of mean monthly air surface temperature and precipitation is used. Mean annual values over the 1961-1990 period were calculated. On each grid element, the mean annual 0 degrees C isotherm altitude is determined from an altitudinal temperature gradient and mean annual temperature (T) at ground level. The 0 'C isotherm altitude is then associated with the annual precipitation amount to compute the ELA. Using computed ELA and the digital terrain elevation model GTOPO30, we determine the extent of the glacierised area in Andean regions under modern climatic conditions. The other application concerns the ELA time evolution on Zongo Glacier (Bolivia), where inter-annual ELA variations are computed from 1995 to 1999. For both applications, the computed values of ELA are in good agreement with those derived from glacier mass balance measurements

Une influence glaciaire réduite conditionne la composition et la qualité du périphyton dans les cours d'eau alpins

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Systèmes aquatiques soumis à des pressions multiplesInternational audienceGlacier retreat alters both physical and chemical characteristics of glacially influenced streams, with consequences on the biological communities colonizing these headwaters. While reduced glacial influence is known to alter the structure of alpine stream invertebrate communities, effects on other biotic groups such as primary producers remain poorly quantified. In 68 study sites along a gradient of glacial influence, we characterized both periphyton community structure [biomass and the relative abundance of diatoms (+ chrysophytes), green algae, and cyanobacteria] and functioning (photosynthetic and enzymatic activities), and measured algal growth rate. Using comprehensive data sets from glacier-fed streams in the Eastern and the Western Alps we linked these periphyton features to climate-change associated environmental modifications. In addition to known effects of declining glaciers on algal diversity, we here provide quantitative estimations of periphyton quality and the relative coverage of algal and bacterial groups on streambed surfaces in response to environmental changes. We found, for example, that harsh environmental conditions (e.g., cold water temperatures and high turbidity) favor the dominance of diatoms and chrysophytes within the periphyton, which groups are considered to be of higher nutritional quality for grazing invertebrates when compared to cyanobacteria. These results will thus help to anticipate changes in food resources, and thereby food webs in alpine catchments as response to declining glaciers

Towards the demise of French alpine glaciers: Parameterized modelling and perspectives on glacier evolution for the 1984-2100 period

International audienceThe Rhône river basin is a highly populated area in southeastern France, with a high concentration of alpine glaciers which have been rapidly retreating in the last decades as the climate warms. In order to anticipate potential issues and conflicts concerning water resources in the high alpine valleys, there is a strong need for local-to-regional projections of glacier and snow hydrological contributions. In this study, we present ALPGM (ALpine Parameterized Glacier Model), a fully parameterized glacier model, which makes use of the most recent available data and reanalysis to simulate the evolution of all the ~660 glaciers in the French Alps for the 1984-2100 period. It computes glacier-wide yearly surface mass balances (SMB) using machine learning, and it updates the glacier geometry by redistributing the glacier-wide SMB values along the glacier elevations according to a glacier-specific parameterized function

Réponse des métacommunautées aquatiques de montagne à l'altération d'écoulements à plusieurs échelles

International audienceMountain watersheds exhibit particularly complex hydrographic networks characterized by both a high spatial and temporal environmental heterogeneity linked to the dynamic of the different water source contributions (glacier and snow meltwater, groundwater, rain). Mountain freshwater ecosystems shelter a singular biodiversity characterized by rare species, often endemic, and display a high spatial variability in aquatic community composition linked to this high level of habitats availability. However, these ecosystems are threatened by the ongoing climate change and associated flow alterations linked to both the accelerated glacier shrinkage and the modification in snow cover. In addition, although mountain regions were historically assimilated to water towers of the surrounding low lands with unlimited water resources; these regions are on the contrary facing unprecedented anthropogenic pressures on the resource, especially due to the current boom in hydropower projects but also the growing water needs of ski resorts for drinking water and artificial snow particularly during low-water periods. These flow alterations induce changes in the hydrological regime at the local scale; but also affect, at the catchment scale, the environmental heterogeneity in habitats and the connectivity of the stream network. These multi-scale alterations might have considerable effects on both the structure and functioning of mountain aquatic ecosystems. In this study, we examined the spatial distribution of aquatic invertebrate communities in two mountain glacierized catchments, with low (3%) and high (30%) glacial influence located respectively in the Andes and the Alps. We sampled benthic invertebrate communities and characterized geographical, physico-chemical and food resource conditions in 51 and 29 stream sites in the Andean and Alpine catchment, respectively. Using both distance decay relationship and variation partitioning analyses, we evaluated the relative contribution of local environmental conditions and spatial processes in structuring the aquatic metacommunity. This study allowed a better understanding of the mechanisms driving the spatial organization of the aquatic communities. This knowledge would permit to develop multi-scale environmental flows in mountains watersheds and management tools to mitigate the impacts of flow alteration and maintain these mountain freshwater ecosystems and their resulting ecosystems services

Écosystèmes aquatiques de haute montagne: menaces et conséquences ?

International audienceThough high mountain freshwaters are generally referred as pristine ecosystems, they have been and will be affected by multifaceted anthropogenic pressures combined with the effects of the ongoing climate change. While the acceleration of glacier shrinkage and the reduction in snow cover induce a continuous, relatively slow flow reduction at a global scale; anthropogenic activities generate abrupt but local disturbances. However, the current boom in hydropower plant constructions and the growing water needs of ski resorts for drinking water and artificial snow, particularly during low-water periods, end up multiplying these local disturbances, generating thus flow alteration at the watershed scale. However, because high mountain watersheds were historically (and are still) considered as remote unspoiled areas with unlimited water resources, eco-hydrological scientific studies are scarcer in these regions and the development of management tools have been neglected. Based on observational and experimental studies in glacierized catchments in both the Alps and the Andes, we analysed the processes that drive the distribution of aquatic-invertebrate communities. Our results show that the dynamic of the different water source contribution to mountain stream networks (glacier and snow meltwater, groundwater, rain) generate a mosaic of connected habitats that engender a strong taxonomic heterogeneity at the watershed scale, through local (environmental filtering, species interaction) and spatial (dispersal limitation) processes. These studies indicate that multiple flow alterations modify both quality and availability of aquatic habitats as well as the connectivity among them, altering the freshwater community composition, function, and dynamic. Improving our understanding of the underlying processes driving these ecosystems is crucial to provide environmental flow rules for freshwaters and develop appropriate management tools to mitigate the impacts of flow alteration and maintain these ecosystems and their resulting ecosystem services