Ice Mass Loss in the Central Andes of Argentina Between 2000 and 2018 Derived From a New Glacier Inventory and Satellite Stereo-Imagery

Based on the recently released National Glacier Inventory (NGI), we analyzed the characteristics and the mass balance rates of ice masses in the Argentinean Central Andes (ca. 30°–37° S). The NGI provides unprecedented information on area, number and distribution of different ice masses, including debris-covered glaciers and rock glaciers. In the Central Andes, a number of 8,076 ice masses were identified covering a total area of 1767 km2. For the period 2000–2018, a general lowering of the ice surface was observed with a region-wide mass balance rate of −0.18 ± 0.19 m w.e. yr−1. Clear differences depending on the debris coverage of the different ice masses were identified, with mass balance rates ranging from −0.36 ± 0.19 m w.e. yr−1 for partly debris-covered glaciers to −0.02 ± 0.19 m w.e. yr−1 for rock glaciers. Considering different sub-periods, the region-wide mass balance rate was slightly positive (+0.12 ± 0.23 m w. e. yr−1) from 2000 to 2009 and negative (−0.21 ± 0.30 m w.e. yr−1) from 2009 to 2018. A comparison with the Randolph Glacier Inventory (RGI version 6.0) indicates that the NGI provides more detailed information regarding different type of ice masses whereas region-wide mass balance rates show limited sensitivity to the choice of the inventory. The inclusion of rock glaciers and “debris-covered ice with rock glacier” in the NGI causes mass balance rates to be slightly less negative than when using the RGI. Since the Central Andes are experiencing an unprecedented decade-long drought, our study provides crucial information to estimate current and future hydrological contribution of the different type of ice masses to river discharge in the arid subtropical Andes.

Reversed Surface-Mass-Balance Gradients on Himalayan Debris-Covered Glaciers Inferred from Remote Sensing

Meltwater from the glaciers in High Mountain Asia plays a critical role in water availability and food security in central and southern Asia. However, observations of glacier ablation and accumulation rates are limited in spatial and temporal scale due to the challenges that are associated with fieldwork at the remote, high-altitude settings of these glaciers. Here, using a remote-sensing-based mass-continuity approach, we compute regional-scale surface mass balance of glaciers in five key regions across High Mountain Asia. After accounting for the role of ice flow, we find distinctively different altitudinal surface-mass-balance gradients between heavily debris-covered and relatively debris-free areas. In the region surrounding Mount Everest, where debris coverage is the most extensive, our results show a reversed mean surface-mass-balance gradient of −0.21 ± 0.18 m w.e. a−1 (100 m)−1 on the low-elevation portions of glaciers, switching to a positive mean gradient of 1.21 ± 0.41 m w.e. a−1 (100 m)−1 above an average elevation of 5520 ± 50 m. Meanwhile, in West Nepal, where the debris coverage is minimal, we find a continuously positive mean gradient of 1.18 ± 0.40 m w.e. a−1 (100 m)−1. Equilibrium line altitude estimates, which are derived from our surface-mass-balance gradients, display a strong regional gradient, increasing from northwest (4490 ± 140 m) to southeast (5690 ± 130 m). Overall, our findings emphasise the importance of separating signals of surface mass balance and ice dynamics, in order to constrain better their contribution towards the ice thinning that is being observed across High Mountain Asia.

Estimating ice albedo from fine debris cover quantified by a semi-automatic method: the case study of Forni Glacier, Italian Alps

In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a novel method based on semi-automatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = −0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (Cr) equal to 6 g m−2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).

Tracing glacier changes since the 1960s on the south slope of Mt. Everest (central Southern Himalaya) using optical satellite imagery

This contribution examines glacier changes on the south side of Mt. Everest from 1962 to 2011 considering five intermediate periods using optical satellite imagery. The investigated glaciers cover ~ 400 km2 and present among the largest debris coverage (32%) and the highest elevations (5720 m) of the world. We found an overall surface area loss of 13.0 ± 3.1% (median 0.42 ± 0.06 % a−1), an upward shift of 182 ± 22 m (3.7 ± 0.5 m a−1) in snow-line altitude (SLA), a terminus retreat of 403 ± 9 m (median 6.1 ± 0.2 m a−1), and an increase of 17.6 ± 3.1% (median 0.20 ± 0.06% a−1) in debris coverage between 1962 and 2011. The recession process of glaciers has been relentlessly continuous over the past 50 years. Moreover, we observed that (i) glaciers that have increased the debris coverage have experienced a reduced termini retreat (r = 0.87, p < 0.001). Furthermore, more negative mass balances (i.e., upward shift of SLA) induce increases of debris coverage (r = 0.79, p < 0.001); (ii) since early 1990s, we observed a slight but statistically insignificant acceleration of the surface area loss (0.35 ± 0.13% a−1 in 1962–1992 vs 0.43 ± 0.25% a−1 in 1992–2011), but an significant upward shift of SLA which increased almost three times (2.2 ± 0.8 m a−1 in 1962–1992 vs 6.1 ± 1.4 m a−1 in 1992–2011). However, the accelerated shrinkage in recent decades (both in terms of surface area loss and SLA shift) has only significantly affected glaciers with the largest sizes (> 10 km2), presenting accumulation zones at higher elevations (r = 0.61, p < 0.001) and along the preferable south–north direction of the monsoons. Moreover, the largest glaciers present median upward shifts of the SLA (220 m) that are nearly double than that of the smallest (119 m); this finding leads to a hypothesis that Mt. Everest glaciers are shrinking, not only due to warming temperatures, but also as a result of weakening Asian monsoons registered over the last few decades. We conclude that the shrinkage of the glaciers in south of Mt. Everest is less than that of others in the western and eastern Himalaya and southern and eastern Tibetan Plateau. Their position in higher elevations have likely reduced the impact of warming on these glaciers, but have not been excluded from a relentlessly continuous and slow recession process over the past 50 years.

A novel integrated method to describe dust and fine supraglacial debris and their effects on ice albedo: the case study of Forni Glacier, Italian Alps

We investigated the characteristics of sparse and fine debris coverage at the glacier melting surface and its relation to ice albedo. In spite of the abundant literature dealing with dust and black carbon deposition on glacier accumulation areas (i.e.: on snow and firn), few studies that describe the distribution and properties of fine and discontinuous debris and black carbon at the melting surface of glaciers are available. Furthermore, guidelines are needed to standardize field samplings and lab analyses thus permitting comparisons among different glaciers. We developed a protocol to (i) sample fine and sparse supraglacial debris and dust, (ii) quantify their surface coverage and the covering rate, (iii) describe composition and sedimentological properties, (iv) measure ice albedo and (v) identify the relationship between ice albedo and fine debris coverage. The procedure was tested on the Forni Glacier surface (northern Italy), in summer 2011, 2012 and 2013, when the fine debris and dust presence had marked variability in space and time (along the glacier tongue and from the beginning to the end of summer) thus influencing ice albedo: in particular the natural logarithm of albedo was found to depend on the percentage of glacier surface covered by debris. Debris and dust analyses indicate generally a local origin (from nesting rockwalls) and the organic content was locally high. Nevertheless the finding of some cenospheres suggests an anthropic contribution to the superficial dust as well. Moreover, the effect of liquid precipitation on ice albedo was not negligible, but short lasting (from 1 to 4 day long), thus indicating that also other processes affect ice albedo and ice melt rates and then some attention has to be spent analysing frequency and duration of summer rainfalls for better describing albedo and melt variability.

Tracing glacier changes since the 1960s on the south slope of Mt. Everest (central Southern Himalaya) using optical satellite imagery

We contribute to the debate on glacial shrinkage in the Himalaya by analyzing glaciers in southern slopes of Mt. Everest that are characterized by extensive debris coverage and the highest elevation in the world. In this paper, we make a complete analysis from 1962 to 2011, considering five intermediate periods using optical satellite imagery. We found an overall surface area shrinkage of 13.0 ± 3%, an upward shift of 182 ± 9 m in snow-line altitude (SLA), a terminus retreat of 403 ± 9 m, and an increase of 17.6 ± 3% in debris coverage. The recession process of glaciers has been relentlessly continuous over the past fifty years. Furthermore, since early 1990s, we have observed an acceleration of the surface area shrinkage, which resulted in a median annual rate double that of the previous three decades (an increase from 0.27% a−1 to 0.46% a−1). Comparing the SLA over the same periods, it shifts upward with a velocity almost three times greater (from 2.2 ± 0.5 m a−1 to 6.1 ± 0.9 m a−1), which points to a worsening of the already negative mass balance of these glaciers. However, the increased recession velocity has only significantly affected glaciers with the largest sizes, which are located at higher altitudes and along the preferable south-oriented direction of the monsoons. Moreover, these glaciers present median upward shifts of the SLA that are double others; this finding leads to a hypothesis that Mt. Everest glaciers are shrinking, not only due to warming temperatures, but also as a result of weakening Asian monsoons registered over the last decades. We conclude that the shrinkage of these glaciers is less than that of others in the Himalayan range. Their position in higher elevations have surely reduced the impact of warming on these glaciers, but have not been excluded from a relentlessly continuous and slow recession process over the past fifty years.

Planimetric and volumetric glacier changes in the Khumbu Himal, Nepal, since 1962 using Corona, Landsat TM and ASTER data

Multitemporal space imagery from 1962 (Corona KH-4), 1992 (Landsat TM), 2001 and 2005 (Terra ASTER) was used to investigate the glacier changes in the Khumbu Himal, Nepal. The ice coverage in the investigation area decreased by about 5% between 1962 and 2005, with the highest retreat rates occurring between 1992 and 2001. The debris coverage increased concomitantly with the decrease in total glacier area. The clean-ice area decreased by >10%. Digital terrain model (DTM) generation from the early Corona KH-4 stereo data in this high-relief terrain is time-consuming, and the results still contain some elevation errors. However, these are minor in the snow-free areas with gentle slopes. Thus comparison of the surfaces of the debris-covered glacier tongues based on the Corona DTM and an ASTER DTM is feasible and shows the downwasting of the debris-covered glaciers. The highest downwasting rates, more than 20 m (>0.5 m a−1), can be found near the transition zone between the active and the stagnant glacier parts of the debris-covered glacier tongues. The downwasting is lower, but still evident, in the active ice areas and at the snout with thick debris cover. All investigated debris-covered glaciers in the study area show similar behaviour. The estimated volume loss for the investigated debris-covered glacier tongues is 0.19 km3.