Carlo D’Agata

The 1975–2005 glacier changes in Aosta Valley (Italy) and the relations with climate evolution

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 km2 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 km2, covering 20.7 km2 (c. 17% of the total area), but accounted for 43% of the total loss in area (losing 19 km2 from 1975 to 2005). The area change rate accelerated recently (1999–2005: mean area loss of c. 2.8 km2/year; 1975–1999: mean area loss of c. 1.1 km2/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.

Alpine debris-covered glaciers as a habitat for plant life:

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.

Culturable yeasts in meltwaters draining from two glaciers in the Italian Alps

Abstract The meltwaters draining from two glaciers in the Italian Alps contain metabolically active yeasts isolable by culture-based laboratory procedures. The average number of culturable yeast cells in the meltwaters was 10–20 colony-forming units (CFU) L–1, whereas supraglacial stream waters originating from overlying glacier ice contained <1 CFUL–1. Yeast cell number increased as the suspended-sediment content of the water samples increased. Basidiomycetous yeasts represent >80% of isolated strains (Cryptococcus spp. and Rhodotorula spp. were 33.3% and 17.8% of total strains, respectively). Culturable yeasts were psychrotolerant, predominantly obligate aerobes and able to degrade organic macromolecules (e.g. starch, esters, lipids, proteins). To the authors’ knowledge, this is the first study to report the presence of culturable yeasts in meltwaters originating from glaciers. On the basis of these results, it is reasonable to suppose that the viable yeasts observed in meltwaters derived predominantly from the subglacial zone and that they originated from the subglacial microbial community. Their metabolic abilities could contribute to the microbial activity occurring in subglacial environments.

Glacier area stability in the Central Karakoram National Park (Pakistan) in 2001–2010 The “Karakoram Anomaly” in the spotlight

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 km2) 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 km2 in 2001 and 4606.3 ± 183.7 km2 in 2010, with abundant supraglacial debris cover. The difference between the area values of 2001 and 2010 is not significant (+0.4 ± 202.9 km2), 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.

Recent structural evolution of Forni Glacier tongue (Ortles-Cevedale Group, Central Italian Alps)

ABSTRACT Structural glaciology yields important details about the evolution of glacier dynamics in response to climate change. The maps provided here document the occurrence and evolution of brittle and ductile structures on the tongue of Forni Glacier, Ortles-Cevedale Group, Central Italian Alps, between 2003 and 2014. Through the remote sensing-based analysis of structures, we found evidence of brittle fractures such as crevasses, faults and ring faults, and ductile structures such as ogives at the base of the icefall in the eastern glacier tongue. Although each of the three glacier tongues have evolved differently, a reduction in flow-related dynamics and an increase in the number of collapse structures occurred over the study period. Analysis of the glacier structural evolution based on the numbers and the locations of different structures, suggest a slowdown of glacier flow on the eastern tongue. The recent evolution of the glacier also suggests that the occurrence of a disintegration scenario is likely to worsen over the next decades.

Assessing glacier features supporting supraglacial trees: A case study of the Miage debris-covered Glacier (Italian Alps)

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.

Evaluating high-resolution remote sensing data for reconstructing the recent evolution of supra glacial debris: A study in the Central Alps (Stelvio Park, Italy)

Over the last decades, the expansion of supraglacial debris on worldwide mountain glaciers has been reported. Nevertheless, works dealing with the detection and mapping of supraglacial debris and detailed analyses aimed at identifying the temporal and spatial trends affecting glacier debris cover are still limited. In this study, we used different remote sensing sources to detect and map the supraglacial debris cover, to analyze its evolution, and to assess the potential of different remote-sensed image data. We performed our analyses on the glaciers of Ortles-Cevedale Group (Stelvio Park, Italy), one of the most representative glacierized sectors of the European Alps. High-resolution airborne orthophotos (pixel size 0.5 m × 0.5 m) acquired during the summer season in the years 2003, 2007, and 2012 permitted to map in detail, with an error lower than ±5%, the supraglacial debris cover through a maximum likelihood classification. Our findings suggest that over the period 2003–2012, supraglacial debris cover increased from 16.7% to 30.1% of the total glacier area. On Forni Glacier we extended these quantification thanks to the availability of UAV (Unmanned Aerial Vehicle) orthophotos from 2014 and 2015 (pixel size 0.15 m × 0.15 m): this detailed analysis permitted to confirm debris is increasing on the glacier melting surface (+20.4%) and confirms the requirement of high-resolution data in debris mapping on Alpine glaciers. Finally, we also checked the suitability of medium-resolution Landsat ETM+ data and Sentinel 2 data to map debris in a typical Alpine glaciation scenario where small ice bodies (<0.5 km2) are the majority. The results we obtained suggest that medium-resolution data are not suitable for a detailed description and evaluation of supraglacial debris cover in the Alpine scenario, nevertheless Sentinel 2 proved to be appropriate for a preliminary mapping of the main debris features.

Inventory of glaciers and glacial lakes of the Central Karakoram National Park (CKNP – Pakistan)

ABSTRACT This study presents a map reporting valuable information on the cryosphere of the Central Karakoram National Park (CKNP, the largest protected area of Pakistan and the highest park in the world). All the information is provided considering the CKNP as a whole, and in detail by dividing it into five basins (i.e. Shigar, Hunza, Shyok, Upper Indus, and Gilgit). The glacier inventory reports 608 ice bodies covering 3680 km2 (∼35% of the CKNP area), with a total glacier volume of ca. 532 km3. In addition, we modeled the meltwater from glacier ice ablation over the period 23 July to 9 August 2011. The total melt amount is ca. 1.5 km3. Finally, we considered glacial lakes (202 water-bodies, covering 4 km2). For these latter glacier features, we also analyzed their potentially dangerous conditions and two lakes were found having such conditions.