Current mass balance and meteorological surveys of Mera glacier located about 30 km south of Mount Everest in Nepal show the dominant role of Asian monsoon precipitation on interannual mass balance ...variability while temperature controls the altitude of snow-rain threshold. As these observations on mass balance variability only explore the recent decades, studies on paleo glacial extents are useful to investigate the long-term climate forcing on glacier evolution. To do so, we investigated the long-term evolution of the debris-free Mera glacier and a neighbouring small debris-free South Khare glacier. Fifty-one 10Be CRE ages were obtained from samples collected on moraine boulders and roches moutonnées. 10Be CRE ages of the boulders span from the end of the Lateglacial (19.0–11.7 ka) to the Little Ice Age (∼0.6–0.1 ka). The oldest dated moraine in this study was observed at the base of South Khare glacier with an age of 13.6 ± 0.5 ka. The two glaciers subsequently experienced their largest Holocene extent in the Early Holocene with moraines dated to 11.0 ± 0.3 ka at the base of Mera glacier and 10.8 ± 0.5 ka at the base of South Khare glacier. We did not observe any moraine from the Mid-Holocene. During the Late Holocene several glacier advances were recorded around 2.3 ± 0.2 ka, 1.5 ka and then during the last centuries at Mera glacier and around 2.8 ± 0.6 ka, and during the Little Ice Age at South Khare glacier. To explore the links between long-term Nepalese glacier changes and climate, we used oceanic and terrestrial Indian Summer monsoon reconstructions and temperature and precipitation output from two transient global climate models TraCE and LOVECLIM. These climate data outputs were corrected by a reconstruction of the Atlantic Meridional Overturning Circulation (AMOC) over the Holocene and its associated climatic impacts. We also used sensitivity experiments from the IPSL (Institut Pierre Simon Laplace) model to discuss the possible influence of horizontal resolution, land hydrology, vegetation and runoff on changes in Asian summer monsoon. Importantly, we show this long-term Nepalese glacier pattern does not perfectly conform neither to the Indian monsoon precipitation that is documented from terrestrial and marine records nor to temperature and precipitation changes simulated by the models. While the maximum glacier extent in the Early Holocene corresponds to enhanced precipitation documented by proxies and models, the Late Holocene glacier advance remains puzzling. We claim that new paleo glacier records and improved climate simulations are necessary to get a better understanding of past glacier changes and the associated climate dynamics, which might be crucial to gain confidence in both glacier and climate future evolutions.
•We investigate the evolution of two debris-free glaciers in the Everest region.•Glacier chronologies are based on 51 10Be ages from moraines and roche moutonnees•The two glaciers show their largest Holocene extent in the Early Holocene.•Several minor advances are recorded during the Late Holocene.•This pattern does not perfectly conform current knowledge on Asian monsoon changes.
Debris-covered glaciers in the central Himalaya have now experienced several decades of sustained ice loss, manifested predominantly in glacier surface lowering. In particular, glacier surfaces of ...low longitudinal gradient and low ice surface velocity have developed locally complex surface topographies and undergone profound changes in supraglacial hydrology. In this study we examine the development of complex ice surface topography across six debris-covered glaciers in the Everest region over the last four decades via a new metric of glacier surface relief applied to Digital Elevation Models (DEMs). We focus in on Khumbu Glacier, and use fine spatial and temporal resolution DEMs covering a period of 28 months to quantify the contemporary contribution of ice cliff and supraglacial pond expansion to overall mass loss from stagnant areas of ice. On the broader scale, we find three common long-term changes in glacier surface topography, (1) glacier-wide expansion of high relief topography in response to ice cliff and supraglacial pond network evolution, (2) up-glacier expansion of high local relief zones that may be caused by differential sub-debris melt beneath thin debris, and (3) increase in glacier surface relief proximal to glacier termini caused by supraglacial stream incision where linked proglacial-supraglacial hydrological networks exist. Overall, we contend that these topographic measurements will be important for understanding glacier surface water storage and also the energy balance of a debris-covered glacier surface, both of which could exacerbate future ice loss and downstream meltwater supply.
•Glaciers flowing south of Mt. Everest have thinned by up to 85 m since the 1980s.•Meltwater storage has resulted in extensive supraglacial pond & ice-cliff formation.•Ponds & cliff expansion has driven the formation of a rougher glacier surface.•Rougher glacier surfaces are more susceptible to melt & further water storage.
This study provides a complete mapping (October 2008) of glacial lakes and debris-covered glaciers in the Mount Everest region. These types of analyses are essential in studies of the impact of ...recent climate change, and therefore the uncertainty of measurements is discussed with the aim of creating a reference study for use when glaciers and lakes are delineated using remote sensing imagery. Moreover, attention is focused on conditions related to the formation of lakes, which is the greatest evidence of the impact of climate change at high altitudes characterized by debris-covered glaciers. Regarding the formation process of supraglacial lakes, our findings confirm that the slope of the glacier where lakes are located is primarily responsible for the low flow velocity of this zone. Otherwise, this study is novel in its identification of a further boundary condition. The slope of the glacier upstream is able to influence both the low flow velocity and the high ablation rates at the glacier terminus. In fact, the imbalance between the two glacier zones generates the down-slope passage of debris, snow and ice. We found the slope of the glacier upstream to be inversely correlated with the relevant total surface of the lakes downstream. The multiple regression model developed in this study, considering the slopes of the two glacier areas distinctly, has been able to predict 90% of the supraglacial lake surfaces. Concerning the surfaces of lakes not directly connected with glaciers (unconnected glacial lakes), we found they are correlated with the dimensions of their drainage basin, whereas no correlation was found with the glacier cover in the basin. Considering that the evaporation/precipitation ratio at these altitudes is approximately 0.34, the evolution of these lakes appears to be a helpful sign for detecting the precipitation trend of these high-altitude regions.
►The glacier slopes upstream and downstream are able to predict 90% of the supraglacial lake surfaces. ►The evolution of lakes not directly connected with glaciers can be used as an helpful sign of the precipitation trend. ►The uncertainty of measurement when satellite imagery is used for mapping glacial lakes and glaciers is assessed in this study.
Gram-stain-negative, aerobic, rod-shaped, non-motile bacterium strain ZFBP2030
T
was isolated from a rock on the North slope of Mount Everest. This strain contained a unique ubiquinone-10 (Q-10) as a ...predominant respiratory quinone. Among the tested fatty acids, the strain contained summed feature 8, C
14:0
2OH, and C
16:0
, as major cellular fatty acids. The polar lipid profile contained phosphatidyl glycerol, phosphatidyl ethanolamine, three unidentified phospholipids, two unidentified aminolipids, and six unidentified lipids. The cell-wall peptidoglycan was a meso-diaminopimelic acid, and cell-wall sugars were ribose and galactose. Phylogenetic analyses based on 16S rRNA gene sequence revealed that strain ZFBP2030
T
was a member of the genus
Sphingomonas,
exhibiting high sequence similarity to the 16S rRNA gene sequences of
Sphingomonas aliaeris
DH-S5
T
(97.9%),
Sphingomonas alpina
DSM 22537
T
(97.3%) and
Sphingomonas hylomeconis
CCTCC AB 2013304
T
(97.0%). The 16S rRNA gene sequence similarity between ZFBP2030
T
and other typical strains was less than 97.0%. The average amino acid identity values, average nucleotide identity, and digital DNA–DNA hybridization values between strain ZFBP2030
T
and its highest sequence similarity strains were 56.9–79.9%, 65.1–82.2%, and 19.3–25.8%, respectively. The whole-genome size of the novel strain ZFBP2030
T
was 4.1 Mbp, annotated with 3838 protein-coding genes and 54 RNA genes. Moreover, DNA G + C content was 64.7 mol%. Stress-related functions predicted in the subsystem classification of the strain ZFBP2030
T
genome included osmotic, oxidative, cold/heat shock, detoxification, and periplasmic stress responses. The overall results of this study clearly showed that strain ZFBP2030
T
is a novel species of the genus
Sphingomonas
, for which the name
Sphingomonas endolithica
sp. nov. is proposed. The type of strain is ZFBP2030
T
(= EE 013
T
= GDMCC 1.3123
T
= JCM 35386
T
).
This study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area ~25km2) under the influence of climate change using multitemporal satellite imagery and local ...climate data. Between 1962 and 2013, Imja Lake expanded from 0.03±0.01 to 1.35±0.05 km2 at a rate of 0.026±0.001 km2 a-1. The mean glacier-wide flow velocity was 37±30ma-1 during 1992–93 and 23±15ma-1 during 2013–14, indicating a decreasing velocity. A mean elevation change of –1.29±0.71ma-1 was observed over the lower part of the glacier in the period 2001–14, with a rate of –1.06±0.63ma-1 in 2001–08 and –1.56±0.80ma-1 in 2008–14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions.
An efficient algorithm, tc-cylinder, has been developed to obtain terrain corrections by considering computational efficiency, data storage and use, spherical curvature effects, water bodies, etc. ...High resolution Digital Elevation Models (DEMs) are fundamental data sources for accurate terrain corrections. But a high-resolution DEM like SRTM1 poses some difficulties during processing, such as data storage, handling, efficiency and computation speed over large areas. In order to overcome these issues, a shortened computation area radius (e.g., 50 km) is preferred for practical studies. This kind of limitation may cause an accuracy loss of over 20 mGal in steep topography. Similarly, spectral methods used to speed up the computations have drawbacks in areas with high slopes. The presented algorithm for segmenting cylinder bodies proves more realistic and effective terrain correction results in all physical conditions. An optimization approach that belongs to the Intel’s processor and compiler architecture improved processing efficiency by a factor of 2.5 times with non-temporal stores, which copies large data directly to memory. Synthetic masses based on known geometric bodies were considered to test program efficiency and numerical results. The contribution was examined at gravity stations in the Konya Closed Basin, which has a sophisticated topography. Additionally, an investigation was conducted in extreme conditions, such as Everest Mountain and the Ağrı Mountain in Turkey, with abrupt elevation profile changes. The numerical analyses of the accuracy of terrain correction values is performed on different combinations of DEM resolutions. Consequently, it is verified that 1′′ inner and 15′′ outer grid resolutions lead to sub-mGal accuracy with less processing time, even in rough topography.
•Improving the accuracy of complete Bouguer anomaly in all terrain circumstances.•Considering negative signed terrain correction contribution caused by sphericity.•Supports NetCDF files in geographic grid without coordinate transformation.•Taken advantage of vectorization and streaming stores of Intel’s compiler.•Time efficiency of TC can be increased by optimizing template rings.
Microbial communities in alpine environments >7,500 m.a.s.l. have not been well studied using modern cultivation-independent sequencing approaches due to the challenges and danger associated with ...reaching such high elevations. For this reason, we know little about the microorganisms found in sediments on Earth's tallest mountains, how they reach these surfaces, and how they survive and remain active at such extreme elevations. Here, we explore the microbial diversity recovered from three sediment samples collected from the South Col (~7,900 m.a.s.l.) of Sagarmatha (Mount Everest) using both culturing and next generation sequencing approaches (16S rRNA gene, internal transcribed spacer ITS region, and 18S rRNA gene sequencing). Both approaches detected very low diversity of bacteria, protists, and fungi that included a combination of cosmopolitan taxa and specialized microorganisms often found at high elevations like those of the genera Modestobacter and Naganishia. Though we managed to grow viable cultures of many of these taxa, it remains likely that few, if any, can be active in situ at the South Col. Instead, these high-elevation surfaces may act as deep-freeze collection zones of organisms deposited from the atmosphere or left by climbers scaling the Earth's highest mountain.
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