ALBERT

Description: The number of debris-covered glaciers featuring supraglacial trees is increasing worldwide as a response of high mountain environments to climate warming. Generally, their distribution on the glacier surface is not homogeneous, thus suggesting that some glacier parameters influence germination and growth of trees. In this study, we focused our attention on the widest Italian debris-covered glacier, the Miage Glacier (Mont Blanc massif). We analyzed the ablation area in the range from 1730 to 2400 m a.s.l. where continuous debris coverage is present and trees are found. Using data obtained by remote sensing investigations and field surveys, we defined a record of glacier parameters to be analyzed with respect to the presence and abundance of trees. We found that supraglacial trees are present at the Miage Glacier (1) whenever exceeding a debris thickness threshold (〉=19 cm), (2) with a gentle slope (〈=10°), (3) with a low glacier surface velocity (〈=7.0 m/yr), and (4) where the vertical changes due to glacier dynamics are positive (i.e. prevalent increase ranging between +7 and +28 m over 28 years due to both slow debris accumulation and preservation of ice flow inputs). The statistical analysis supports our findings. The analysis of the same parameters might be conducted on other debris-covered glaciers featuring supraglacial trees, in order to evaluate whether such conditions are local ones or whether they are general factors driving germination and growth of trees. By identifying the features supporting the presence and growth of trees in these environments, and their thresholds, a contribution is given for a better understanding of the importance of debris-covered glaciers and, in general, of debris-covered ice, as a refuge for trees during glacial and warm intervals of the Holocene.

Description: Supraglacial debris cover allows vegetation to colonize glacier surface, and whenever it is enough stable and thick, also shrubs and trees can germinate and grow. Supraglacial tree growth and distribution patterns on the glacier are closely connected with the debris-covered glacier dynamics and evolution. The aim of the research reported here was to evaluate the tree age and tree distribution patterns on the glacier tongue and the influence of ice-cliff backwasting, close to glacier terminus, on tree loss. We analysed the fragile and fast-changing environment that is present on the lower ablation sector of the Miage Glacier (Mont Blanc Massif, Italian Alps) where some ice cliffs are present and backwasting and downwasting phenomena occur. Tree features and short-term evolution were analysed with respect to glacier variations (mainly surface displacements and ice ablation) and geometry changes of the two most representative ice cliffs. The supraglacial trees’ life time resulted to be mainly controlled by glacier surface displacements and by the occurrence of backwasting and downwasting processes, whereas tree germination was associated with fine debris presence. These factors, controlling plants’ life and growth on the glacier, are an actual limit when supraglacial trees are analysed to reconstruct past environmental changes occurred on the glacier tongue. Moreover, we found that a large number of trees die under conditions of dominating backwasting inducing the loss of debris substrate (condition met especially on the northern glacier lobe). Instead, in the case of prevalence of downwasting (condition mainly observed on the southern glacier lobe), trees more easily survive and flow downvalley transported by the glacier flux.

Description: The recent rapid mass loss of mountain glaciers in response to climate warming has been reported for high and low latitudes all over the Earth. The paper analyses and discusses the recent evolution of a representative glacierized group within the Italian Alps, the Piazzi—Dosdè, where small glaciers are experiencing considerable retreat and shrinking. We analysed aerial photos to calculate area and geometry changes in the time window 1954—2003, and glaciological and geomorphological surveys were also performed. The estimated area change during 1954—2003 was —3.97 km 2 (—51% of the area coverage in 1954). Area reduction increased more recently: area change during 1991—2003 (12 years) was —1.74 km 2 , against —0.67 km 2 during 1981—1991 (10 years), and —1.57 km 2 during 1954—1981 (27 years). Moreover, analysis of the most recent orthophotos acquired during the summer of 2003 under exceptional conditions (i.e. total absence of snow cover) allowed observation and mapping of changes affecting glacier shape and morphology, including growing rock outcrops, tongue separations, formation of proglacial lakes, increasing supraglacial debris and collapse structures. Such processes cause positive feedbacks that accelerate further glacier disintegration once they appear. From a geodynamical perspective, the Dosdè Piazzi is now experiencing transition from a glacial system to a paraglacial one; areas where in the past the shaping and driving factors were glaciers are now subject to the action of melting water, slope evolution and periglacial processes.

Description: Debris-covered glaciers represent a significant, increasing fraction of glaciers and can host plant life on their surface. The goal of this work was to evaluate the suitability of supraglacial debris as a habitat for plant life and to discuss its ecological and biogeographic role. The research was carried out on the Miage Glacier (Mont Blanc massif, Western Alps, Italy). Vegetation cover was sampled using a regular sampling grid, recording plant species and number of individuals in 71 plots. Detailed glaciological parameters (surface temperature, debris thickness, glacier surface velocity) were recorded or derived from published data. Relationships between vegetation and environmental variables were assessed through Generalized Linear Models, Principal Components Analysis and Canonical Correspondence Analysis. The glacier surface hosted a high biodiversity, with 40 vascular plant species, including trees and shrubs. Plant cover was arranged along an altitude/glacier velocity gradient, whilst debris thickness as low as 10 cm could sustain plant growth on moving ice. Glacier velocity was the main physical factor affecting vegetation cover, probably through its influence on debris stability. The observed species assemblage is comparable with those of subalpine glacier forelands, but with the addition of high-altitude species. Debris-covered glaciers can provide a relatively favourable habitat for plant life wherever the glacier surface is sufficiently stable, acting as a refugium of high-altitude taxa below their altitudinal limits. Glaciers may behave as a dispersal vector for alpine plant species, which could have been important both during glacial periods and during warm stages of the Holocene.

Description: Here three glacier surface area records (years 1975, 1999 and 2005) available for Aosta Valley (western Italian Alps) have been synthesized. The 1975 data have been collected by previous authors who compiled the first Aosta Valley regional glacier database. The 1999 and 2005 surface area data were computed by the authors here combining registered colour orthophotos with differential GPS (DGPS) field measurements. The surface changes of 174 glaciers (those shared within the three records of data) were calculated to describe the recent evolution of a representative subset of Italian glaciers. Aosta Valley glaciers lost 44.3 km 2 during 1975–2005, i.e. c. 27% of the initial area. Small glaciers contributed strongly to total area loss, and during 2005 147 glaciers (c. 84.5% of the studied ones) were smaller than 1 km 2 , covering 20.7 km 2 (c. 17% of the total area), but accounted for 43% of the total loss in area (losing 19 km 2 from 1975 to 2005). The area change rate accelerated recently (1999–2005: mean area loss of c. 2.8 km 2 /year; 1975–1999: mean area loss of c. 1.1 km 2 /year). We then analyse records (1975–2005) of temperature, precipitation and snow cover from three high-altitude (1332 m asl to 3488 m asl) stations within Aosta Valley, to investigate modified climate within the area. We find increasing temperature especially during late spring and summer, and substantially unchanged total precipitation, with marked reduction of snowfall, snow cover, number of snowfall events and duration of continuous snow cover, especially during spring and summer, likely driving shrinking of glacier coverage.

Description: The Karakoram Range is one of the most glacierized mountain regions in the world, and glaciers there are an important water resource for Pakistan. The attention paid to this area is increasing because its glaciers remained rather stable in the early twenty-first century, in contrast to the general glacier retreat observed worldwide on average. This condition is also known as "Karakoram Anomaly". Here we focus on the recent evolution of glaciers within the Central Karakoram National Park (CKNP, area: *13,000 km 2 ) to assess their status in this region with respect to the described anomaly. A glacier inventory was produced for the years 2001 and 2010, using Landsat images. In total, 711 ice-bodies were detected and digitized, covering an area of 4605.9 ± 86.1 km 2 in 2001 and 4606.3 ± 183.7 km 2 in 2010, with abundant supraglacial debris cover. The difference between the area values of 2001 and 2010 is not significant (+0.4 ± 202.9 km 2 ), confirming the anomalous behavior of glaciers in this region. The causes of such an anomaly may be various. The increase of snow cover areas from 2001 to 2011 detected using MODIS snow data; the reduction of mean summer temperatures; and the augmented snowfall events during 1980–2009 observed at meteorological stations and confirmed by the available literature, are climatic factors associated with positive mass balances. Because the response of glacier area change to climate variation is very slow for large glaciers, the presence of some of the largest glaciers of the Karakoram Range in this region might have delayed observed effects of such climate change so far, or alternatively, the change may not be sufficient to drive an actual area increase. In this context, improved understanding the role of debris cover, meltwater ponds, and exposed ice cliffs on debris-covered glaciers, and surging glaciers (which are also found abundant here), are required is still an issue to clarify the mechanisms behind the Karakoram Anomaly.

Description: In this study, the early ecological succession patterns of Forni Glacier (Ortles-Cevedale group, Italian Alps) forefield along an 18-year long chronosequence (with a temporal resolution of 1 year) has been reported. Bacterial and fungal community structures were inferred by high-throughput sequencing of 16S rRNA gene and ITS, respectively. In addition, the occurrence of both herbaceous and arboreous plants was also recorded at each plot. A significant decrease of alpha-diversity in more recently deglaciated areas was observed for both bacteria and plants. Time since deglaciation and pH affected the structure of both fungal and bacterial communities. Pioneer plants could be a major source of colonization for both bacterial and fungal communities. Consistently, some of the most abundant bacterial taxa and some of those significantly varying with pH along the chronosequence (Polaromonas, Granulicella, Thiobacillus, Acidiferrobacter) are known to be actively involved in rock-weathering processes due to their chemolithotrophic metabolism, thus suggesting that the early phase of the chronosequence could be mainly shaped by the biologically controlled bioavailability of metals and inorganic compounds. Fungal communities were dominated by ascomycetous filamentous fungi and basidiomycetous yeasts. Their role as cold-adapted organic matter decomposers, due to their heterotrophic metabolism, was suggested.

Description: Hydrological monitoring and modeling of high altitude Alpine catchments is of paramount importance. This is difficult, however, given the complex logistics of field campaigns and the need for long-term data. Here, we present a method for long term monitoring of high altitude catchments, which we tested within the Alps of Italy. This includes i) extensive gathering of climate data and hydrological fluxes, ii) high altitude field campaigns, and iii) robust physically based glacio-hydrological modeling, providing full account of ice flow, ice and snow ablation, and stream flows. We present an application of this method based on six years (2009–2014) of field monitoring in the Dosdè catchment, in the Italian Alps (17 km2, average altitude 2858 masl, outlet 2133 masl), nesting 1.90 km2 of glaciers. We demonstrate that i) high altitude Alpine catchments can be monitored in spite of geographical complexity, and ii) a data based approach delivers accurate stream flow estimates and improves our knowledge of flow components in the high altitudes. We then provide some estimates of the recent glaciers’ dynamics, and water resources from this high-altitude catchment, paradigmatic of the recent cryospheric evolution in the Alps of Italy. We estimated an average ice mass loss nearby −1.76E8 m3yr−1, i.e. −20% of the ice mass in 2009, possibly pointing to accelerated glaciers’ down wasting. Instream discharges increased (+0.12 m3s−1y−1); however, this requires further monitoring. We then benchmark our findings against recent studies in the Alps, and other glacierized areas worldwide, displaying similarities in present glaciers’ dynamics. We suggest that our robust, yet flexible approach can be used for glacio-hydrological investigation in Alpine (and generally mountain) rivers, and for conjectures of potential future hydrological cycle under climate scenarios.

Description: The glacier melt conditions (i.e.: null surface temperature and positive energy budget) can be assessed by analyzing meteorological and energy data acquired by a supraglacial Automatic Weather Station (AWS). In the case this latter is not present the assessment of actual melting conditions and the evaluation of the melt amount is difficult and simple methods based on T-index (or degree days) models are generally applied. These models require the choice of a correct temperature threshold. In fact, melt does not necessarily occur at daily air temperatures higher than 273.15 K. In this paper, to detect the most indicative threshold witnessing melt conditions in the April–June period, we have analyzed air temperature data recorded from 2006 to 2012 by a supraglacial AWS set up at 2631 m a.s.l. on the ablation tongue of the Forni Glacier (Italian Alps), and by a weather station located outside the studied glacier (at Bormio, a village at 1225 m a.s.l.). Moreover we have evaluated the glacier energy budget and the Snow Water Equivalent (SWE) values during this time-frame. Then the snow ablation amount was estimated both from the surface energy balance (from supraglacial AWS data) and from T-index method (from Bormio data, applying the mean tropospheric lapse rate and varying the air temperature threshold) and the results were compared. We found that the mean tropospheric lapse rate permits a good and reliable reconstruction of glacier air temperatures and the major uncertainty in the computation of snow melt is driven by the choice of an appropriate temperature threshold. From our study using a 5.0 K lower threshold value (with respect to the largely applied 273.15 K) permits the most reliable reconstruction of glacier melt.