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Glacier response patterns at the catchment scale are highly heterogeneous and defined by a complex interplay of various dynamics and surface factors. Previous studies have explained heterogeneous responses in qualitative ways but quantitative assessment is lacking yet where an intrazone homogeneous climate assumption can be valid. Hence, in the current study, the reason for heterogeneous mass balance has been explained in quantitative methods using a multiple linear regression model in the Sikkim Himalayan region. At first, the topographical parameters are selected from previously published studies, then the most significant topographical and geomorphological parameters are selected with backward stepwise subset selection methods. Finally, the contributions of selected parameters are calculated by least square methods. The results show that, the magnitude of mass balance lies between −0.003±0.24 to −1.029±0.24 m.w.e.a−1 between 2000 and 2020 in the Sikkim Himalaya region. Also, the study shows that, out of the terminus type of the glacier, glacier area, debris cover, ice-mixed debris, slope, aspect, mean elevation, and snout elevation of the glaciers, only the terminus type and mean elevation of the glacier are significantly altering the glacier mass balance in the Sikkim Himalayan region. Mathematically, the mass loss is approximately 0.40 m.w.e.a−1 higher in the lake-terminating glaciers compared to the land-terminating glaciers in the same elevation zone. On the other hand, a thousand meters mean elevation drop is associated with 0.179 m.w.e.a−1 of mass loss despite the terminus type of the glaciers. In the current study, the model using the terminus type of the glaciers and the mean elevation of the glaciers explains 76% of fluctuation of mass balance in the Sikkim Himalayan region. [ABSTRACT FROM AUTHOR]

With global warming, the dramatic retreat of glaciers in the Tibetan Plateau (TP) might accelerate release of stored methane (CH4) into the atmosphere; thus, this region might become a new source of CH4. CH4-metabolic microbial communities can produce or consume CH4 in the environment, which is critical for evaluating the CH4 budget of glaciers. However, studies on the influence of CH4-metabolic microbial communities on the CH4 budget during glacier retreat in the TP remain scarce. In this work, ice samples were collected at the terminus of the Guliya Ice Cap in the northwestern TP. The community composition of CH4-metabolic microorganisms, including methanogens and methanotrophs, was determined using genomic analysis, and the metabolic rates of the two microorganisms were further estimated. The abundance of methanotrophs in Guliya was one order of magnitude higher than that of methanogens. The CH4 consumption flux by the combined action of the two microorganisms was ca. 1.42 × 103 pmol·mL−1·d−1, suggesting that CH4 metabolic microbial communities in the glacier might be an important CH4 sink, and can reduce subglacial CH4 emission during glacier retreat. This is important for predicting the CH4 budget in glaciers on the TP and corresponding climate impacts during glacier retreat. [ABSTRACT FROM AUTHOR]

Background: On the front lines of climate change, glacier termini play crucial roles in linking glaciers and downstream ecosystems during glacier retreat. However, we lack a clear understanding of biological processes that occur in surface and basal ice at glacier termini. Methods: Here, we studied the bacterial communities in surface ice and basal ice (the bottom layer) of a glacier terminus in the Yangtze River Source, Qinghai–Tibet Plateau. Results: Surface and basal ice harbored distinct bacterial communities but shared some core taxa. Surface ice communities had a higher α-diversity than those in basal ice and were dominated by Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Cyanobacteria while basal ice was dominated by Firmicutes and Proteobacteria. The bacterial communities were also substantially different in functional potential. Genes associated with functional categories of cellular processes and metabolism were significantly enriched in surface ice, while genes connected to environmental information processing were enriched in basal ice. In terms of biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur, bacterial communities in surface ice were enriched for genes connected to aerobic carbon fixation, aerobic respiration, denitrification, nitrogen assimilation, nitrogen mineralization, sulfur mineralization, alkaline phosphatase, and polyphosphate kinase. In contrast, bacterial communities in basal ice were enriched for genes involved in anaerobic carbon fixation, fermentation, nitrate reduction, 2-aminoethylphosphonic acid pathway, G3P transporter, glycerophosphodiester phosphodiesterase, and exopolyphosphatase. Structural equation modeling showed that total nitrogen and environmental carbon:phosphorus were positively while environmental nitrogen:phosphorus was negatively associated with taxonomic β-diversity which itself was strongly associated with functional β-diversity of bacterial communities. Conclusions: This study furthers our understanding of biogeochemical cycling of the mountain cryosphere by revealing the genetic potential of the bacterial communities in surface and basal ice at the glacier terminus, providing new insights into glacial ecology as well as the influences of glacier retreat on downstream systems. [ABSTRACT FROM AUTHOR]

Calving and submarine melt drive frontal ablation and sculpt the ice face of marine‐terminating glaciers. However, there are sparse observations of submarine termini, which limit estimates of spatially varying submarine melt. Here we present a detailed survey of a west Greenland glacier to reveal heterogeneity in submarine terminus morphology. We find that the majority of the terminus (~77%) is undercut, driven by calving in the upper water column and submarine melting at depth. The remaining ~23% of the terminus is overcut, driven by calving alone. We use observations of six subglacial discharge outlets, combined with a plume model, to estimate spatially varying discharge fluxes. While small discharge fluxes (<43 m3/s) feed numerous, deeply undercut outlets with subsurface plumes, ~70% of the net subglacial flux emerges at the terminus center, producing a vigorous, surface‐reaching plume. This primary outlet drives large, localized seasonal retreat that exceeds calving rates at secondary outlets. Plain Language Summary: Using a sensor to map the shape of a glacier terminus below sea level, we are able to quantify how the terminus shape changes across the glacier. This allows us to identify different classes of terminus shape, which vary from undercut to overcut. Undercut regions are formed through melting focused near the base of the terminus, where freshwater emerges from discrete channels. Using a model, we explain the degree of undercutting found in channels by varying the flux of freshwater emerging from each channel. This allows us to understand the relative role of small channels on total terminus melt compared to much larger, more frequently observed channels. We find that small channels produce significant melting compared to a much larger channel at the glacier center but not as much iceberg calving. Key Points: We present direct observations of submarine terminus morphology at a Greenland tidewater glacierTerminus morphology is highly heterogeneous and varies from overcut to strongly undercutWe combine our observations with a plume model to estimate spatially varying subglacial discharge fluxes [ABSTRACT FROM AUTHOR]

The present study used the potential of Landsat multispectral data and ASTER-DEM data to identify the changes of glacier lakes in part of Chandra basin and surrounding of Himachal Pradesh of India from 1989 to 2013. The Barashigri, Chotashigri, Hamtahand Parvati glacier are the major glaciers within the area. The Landsat data of TM (1989 and 2009), ETM+ (2001) and OLI-TIRS (2013) sensors having different band combinations were analysed to monitor variation in the glacier lakes and area of glaciers and terminus whereas ASTER-DEM data was used for relief information. Glaciers terminus and glacial lakes were identified and mapped using false-colour composites (FCC) with band combinations of red, near-infrared (NIR) and shortwave infrared (SWIR), and a true-colour composite of red, green and NIR, of Landsat TM/ETM+ images and normalized difference water index (NDWI) methods. It is observed that the number of lakes in the study area increased by 18.69% during the past 34 years while it was increased from 68 in 1989 to 89 in 2013. During the analysis, it is also found that the snow and glacier covered area within this period is also reduced from 1,317.39 to 1,125.59 km2. [ABSTRACT FROM AUTHOR]

Historical variations in the extent of mountain glaciers give insight into natural and forced changes of these bellwethers of the climate. Because of the limited number of ground observations relative to the number of glaciers, it is useful to develop techniques that permit for the monitoring of glacier systems using satellite imagery. Here, we propose a new approach for identifying the glacier terminus over time from Landsat images. The proposed method permits for detecting inflection points in multispectral satellite imagery taken along a glacier's flow path in order to identify candidate terminus locations. A gated tracking algorithm is then applied to identify the best candidate for the glacier terminus location through time. Finally, the long-term trend of the terminus position is estimated with uncertainty bounds. This is achieved by applying nonparametric regression to the temporal sequence of estimated terminus locations. The method is shown to give results consistent with ground-based observations for the Franz Josef and Gorner glaciers and is further applied to estimate the retreat of Viedma, a glacier with no available ground measurements. [ABSTRACT FROM PUBLISHER]

Sea level rise contribution from the Antarctic ice sheet is influenced by changes in glacier and ice shelf front position. Still, little is known about seasonal glacier and ice shelf front fluctuations as the manual delineation of calving fronts from remote sensing imagery is very time-consuming. The major challenge of automatic calving front extraction is the low contrast between floating glacier and ice shelf fronts and the surrounding sea ice. Additionally, in previous decades, remote sensing imagery over the often cloud-covered Antarctic coastline was limited. Nowadays, an abundance of Sentinel-1 imagery over the Antarctic coastline exists and could be used for tracking glacier and ice shelf front movement. To exploit the available Sentinel-1 data, we developed a processing chain allowing automatic extraction of the Antarctic coastline from Seninel-1 imagery and the creation of dense time series to assess calving front change. The core of the proposed workflow is a modified version of the deep learning architecture U-Net. This convolutional neural network (CNN) performs a semantic segmentation on dual-pol Sentinel-1 data and the Antarctic TanDEM-X digital elevation model (DEM). The proposed method is tested for four training and test areas along the Antarctic coastline. The automatically extracted fronts deviate on average 78 m in training and 108 m test areas. Spatial and temporal transferability is demonstrated on an automatically extracted 15-month time series along the Getz Ice Shelf. Between May 2017 and July 2018, the fronts along the Getz Ice Shelf show mostly an advancing tendency with the fastest moving front of DeVicq Glacier with 726 ± 20 m/yr. [ABSTRACT FROM AUTHOR]

The contribution of Antarctica's ice sheet to global sea-level rise depends on the very dynamic behavior of glaciers and ice shelves. One important parameter of ice-sheet dynamics is the location of glacier and ice-shelf fronts. Numerous remote sensing studies on Antarctic glacier and ice-shelf front positions exist, but no long-term record on circum-Antarctic front dynamics has been established so far. The article outlines the potential of remote sensing to map, extract, and measure calving front dynamics. Furthermore, this review provides an overview of the spatial and temporal availability of Antarctic calving front observations for the first time. Single measurements are compiled to a circum-Antarctic record of glacier and ice shelf retreat/advance. We find sufficient frontal records for the Antarctic Peninsula and Victoria Land, whereas on the West Antarctic Ice Sheet (WAIS), measurements only concentrate on specific glaciers and ice sheets. Frontal records for the East Antarctic Ice Sheet exist since the 1970s. Studies agree on the general retreat of calving fronts along the Antarctic Peninsula. East Antarctic calving fronts also showed retreating tendencies between 1970s until the early 1990s, but have advanced since the 2000s. Exceptions of this general trend are Victoria Land, Wilkes Land, and the northernmost Dronning Maud Land. For the WAIS, no clear trend in long-term front fluctuations could be identified, as observations of different studies vary in space and time, and fronts highly fluctuate. For further calving front analysis, regular mapping intervals as well as glacier morphology should be included. We propose to exploit current and future developments in Earth observations to create frequent standardized measurements for circum-Antarctic assessments of glacier and ice-shelf front dynamics in regard to ice-sheet mass balance and climate forcing. [ABSTRACT FROM AUTHOR]