1,720,976 research outputs found
Climate change and rapid ice melt: Suggestions from abrupt permafrost degradation and ice melting in an alpine ice cave
No full textAmong the different elements of the mountain cryosphere, ice caves still represent the lesser known part of it. Here we present a seven-year-long record of air and rock temperature in a cave of the southeastern European Alps. We demonstrate how the presence of a permanent ice deposit in the cave is not only related to the net cooling effect of the air circulation, as it is well known, but also to the occurrence of relict permafrost. Through a detailed representation of temperature patterns inside the cave, both air and rock data show how after a period of perennially subzero (cryotic) conditions in the rock, ongoing anthropogenic climate warming is responsible for permafrost degradation despite the cooling effect of the air circulation in the cave. Data support the important role of cryotic conditions in the rock in preserving a permanent ice cave deposit in the present climate, even once the possible relict permafrost inherited from the past disappears. A thickness of 29–44 m of permafrost, possibly formed during the Little Ice Age, has now almost completely disappeared. The present abrupt ice degradation observed in this cave is further exacerbated by positive feedbacks related to warmer air circulation in the cave system
Rock glaciers, protalus ramparts and pronival ramparts in the south-eastern Alps
No full textRock glaciers and protalus ramparts are characteristic landforms of the periglacial domain often used as markers for the occurrence of permafrost in mountain terrains. As such, relict rock glaciers can be used for paleoclimate reconstructions. We present here the first previously unreported rock glacier inventory of the south-eastern Alps (including the north-eastern-most region of Italy and Slovenia), interpreted from high resolution orthophotos and a high resolution digital terrain model interpolated from airborne laser scanning (LiDAR). We mapped 53 rock glaciers covering a total area of 3.45 km2. The majority of rock glaciers are classified as relict and distributed between 1708 and 1846 m a.s.l. with slope ranging between 19° and 27°. In addition to rock glaciers we observed 66 protalus (pronival) ramparts, having median elevation of 1913 m a.s.l. and covering 0.48 km2. More than half of the inventoried protalus ramparts are located in the more maritime area of the Alps with higher precipitation compared to the location of rock glaciers. Using paleoclimate reconstruction based on the 1981–2010 climatological record of the area, we infer that the rock glaciers formed during one of the dry and cold periods of the late Pleistocene and early Holocene. Possible evolution of the active pronival forms observed in the most maritime area of this alpine sector is also discussed
Velocity analysis from common offset GPR data inversion: Theory and application to synthetic and real data
No full textWe implemented a procedure to estimate the electromagnetic (EM) velocity using common offset ground penetrating radar (GPR) data. The technique is based on the inversion of reflection amplitudes to compute the series of reflection coefficients used to estimate the velocity in each interpreted layer. The proposed method recursively calculates the incident angles at any interface, taking into account the offset between antennas, and needs as input, in addition to the picked amplitudes values, a reference amplitude for each analysed GPR trace and a velocity value for the first (shallowest) layer. The latter two parameters can be estimated directly from the available data or can be better constrained by further dedicated GPR acquisitions or by additional direct measurements. We critically evaluated the performances for both synthetic and real data acquired with different antenna frequencies and we demonstrated that the new method can be applied in several real situations. Despite the necessary approximations and simplifying hypotheses, the velocity values calculated for each layer are consistent with direct information and with cross-validations obtained considering profiles acquired using different antennas and various path directions. Tests of the method on synthetic and real data sets show that the errors in the calculated velocity fields are quite low and comparable with more demanding velocity analysis techniques. The obtained EM velocity field is crucial in many processing steps, such as, for example, true amplitude recovery, depth conversion and imaging, and provide essential information to characterize the subsurface materials
Precipitation–temperature changes and evolution of a small glacier in the southeastern European Alps during the last 90 years.
No full textVery small glaciers (area <0.1 km2) have received increased scientific attention during recent years, both for
their rapid responses to the climate forcing and because they are characterized by microclimatic conditions, often marginal to
glacier formation. They are particularly sensitive to climate changes and characterized by a great mass turnover, particularly
evident in maritime areas with high precipitation. Here we consider the evolution from 1920 of the ‘Canin Eastern Glacier’
(Italian Southeastern Alps) in order to correlate its evolution to the precipitation–temperature trends. We reconstructed a
precipitation–temperature record at the altitude of the glacier, filling a lack of knowledge in this alpine sector. We observed
a decrease in the mean annual precipitation of 10% in 90 years and a warming trend of 0.1∘C decade−1 since 1851, and of
0.7∘C decade−1 in the last 20 years. An inverse correlation between precipitation and mean air temperature during summer and
ablation periods was also observed. Glacier dynamics revealed a phase of stability between 1945 and 1985 that seems to be
a peculiar characteristic of this area. Moreover, through a general regression model the glacial terminus variations seem to be
statistically influenced only by winter precipitation. This fact opens interesting perspectives for the possible future evolution
of this small glacier and, more in general, to other small glaciers in maritime areas in regard to climate change scenarios
GPR velocity and amplitude analyses to characterize stratigraphy and estimate the ice density: Easter Glacier of Mt. Canin, Italy
No full textWe propose a methodology to estimate the density of frozen media (snow, firn and ice) using common offset GPR data. The technique is based on reflection amplitude analysis to calculate series’ of reflection coefficients that we used to estimate the dielectric permittivity of each layer. Applying an empirical equation we determine the vertical density variations for all the acquired GPR traces and, therefore, infer the nature of frozen materials, from fresh snow, to granular snow, firn and ice, and to estimate the snow water equivalent (SWE), which is an essential parameter to determine the actual water volume within a certain frozen body. The proposed technique was tested in the Eastern Glacier of Mt. Canin (Eastern Alps) and validated by direct snow density measurements, obtained using samples collected from manually dug snow pits, and with data from the literature. Despite the necessary approximations, the average value of density for different levels is calculated with acceptable accuracy. Moreover, this analysis can help to find and locate debris or moraines embedded within the ice bodies
Response of ice caves to weather extremes in the southeastern Alps, Europe
Full text linkHigh altitude karstic environments often preserve permanent ice deposits within caves, representing the lesser-known portion of the cryosphere. Despite being not so widespread and easily reachable as mountain glaciers and ice caps, ice caves preserve much information about past environmental changes and climatic evolution.We selected 1111 ice caves from the existing cave inventory, predominantly but not exclusively located in the periglacial domain where permafrost is not dominant (i.e., with mean annual air temperature <. 3 °C but not in a permafrost environment). The influence of climate and topography on ice cave distribution is also investigated. In order to assess the thickness and the inner structure of the deposits, we selected two exemplary ice caves in the Canin massif (Julian Alps) performing several multifrequency GPR surveys. A strong influence of global and local climate change in the evolution of the ice deposits has been particularly highlighted in the dynamic ice cave type, especially in regard to the role of weather extremes. The natural response of ice caves to a warming climate could lead to a fast reduction of such ice masses. The increased occurrence of weather extremes, especially warmer and more intense precipitation caused by higher mean 0 °C-isotherms, could in fact be crucial in the future mass balance evolution of such permanent ice deposits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Recent evolution of Marmolada glacier (Dolomites, Italy) by means of ground and airborne GPR surveys
Full text linkA 10-year-long evolution of ice thickness and volume of the Marmolada glacier is presented. Quantitative measurements have been performed by using two different Ground Penetrating Radar (GPR) datasets. A ground-based survey using two different ground-coupled systems equipped with 100 MHz and 35 MHz antennas was performed in 2004. In 2015 the dataset was collected by using a helicopter-borne step frequency GPR equipped with a 100 MHz antenna. Through a critical discussion of the two different methodologies, we show how both approaches are useful to estimate the ice volume within a glacier, as well as its morphological characteristics and changes with time, even if datasets are acquired in different periods of the year. The observed 2004–2014 ice volume reduction of the Marmolada glacier is equal to about 30%, while the area covered by ice decreased by about 22%. The glacier is now splitted in several separated units. It is very likely that the fragmentation of the Marmolada glacier observed in the period 2004–2014 was accelerated due to irregular karst topography. By applying the observed 2004–2014 ice-melting trend for the future although the Marmolada glacier might behave slightly differently compared to glaciers on non-karstic terrains owing to dominant vertical subglacial drainage, it will likely disappear by the year 2050. Only few isolated very small and thin ice patches will eventually survive due to avalanche feeding and shading at the foot of the north-facing cliffs
200 years of equilibrium-line altitude variability across the European Alps (1901−2100)
Full text linkMountain glaciers are key indicators of climate change. Their response is revealed by the environmental equilibrium-line altitude (ELA), i.e. the regional altitude of zero mass balance averaged over a long period of time. We introduce a simple approach for distributed modelling of the environmental ELA over the entire European Alps based on the parameterization of ELA in terms of summer temperature and annual precipitation at a glacier. We use 200 years of climate records and forecasts to model environmental ELA from 1901 to 2100 at 5 arcmin grid cell resolution. Historical environmental ELAs are reconstructed based on precipitation from the Long-term Alpine Precipitation reconstruction (LAPrec) dataset and temperature from the Historical Instrumental climatological Surface Time series of the greater Alpine region (HISTALP). The simulations of future environmental ELAs are forced with high-resolution EURO-CORDEX regional climate model projections for the European domain using three different greenhouse gas emissions scenarios (Representative Concentration Pathways, RCP). Our reconstructions yielded an environmental ELA across the European Alps of 2980 m above sea level for the period 1901−1930, with a rise of 114 m in the period 1971−2000. The environmental ELA is projected to exceed the maximum elevation of 69%, 81% and 92% of the glaciers in the European Alps by 2071−2100 under mitigation (RCP2.6), stabilization (RCP4.5) and high greenhouse gas emission (RCP8.5) scenarios, respectively
- …
