scholarly journals High altitude accumulation and preserved climate information in the western Pamir, observations from the Fedchenko Glacier accumulation basin

2019 ◽  
Vol 66 (256) ◽  
pp. 219-230 ◽  
Author(s):  
Astrid Lambrecht ◽  
Christoph Mayer ◽  
Pascal Bohleber ◽  
Vladimir Aizen
Keyword(s):  
Climate Information ◽  
Accumulation Pattern ◽  
Mean Values ◽  
Pamir Mountains ◽  
Elevation Changes ◽  
Age Relation ◽  
Elevation Difference ◽  
Ground Penetrating ◽  
Accumulation Region ◽  
Accumulation History

AbstractThe accumulation region of Fedchenko Glacier represents an extensive snow reservoir in the Pamir Mountains feeding the longest glacier in Central Asia. Observed elevation changes indicate a continuous ice loss in the ablation region of Fedchenko Glacier since 1928, while the mass balance of the accumulation region is largely unknown. In this study, we show that accumulation varies considerably in the main accumulation basin, with accumulation rates up to 2400 mm w.e. a−1 in the West, decreasing to <1000 mm w.e. a−1 in the center, although the elevation difference is <200 m. The combination of snow/firn samples and ground-penetrating radar profiles suggests that this accumulation pattern is persistent during the recent past. The recent accumulation history is reconstructed from internal radar reflectors using a firn densification model and shows strong interannual variations, but near constant mean values since 2002. Modeling of trajectories, based on accumulation and glacier geometry, results in an estimate of the depth/age relation close to the main divide. This region provides one of the most suitable locations for retrieving climate information with temporal high resolution for the last millennium, with a potential to cover most of the Holocene in less detail.

scholarly journals Elevation change of Fedchenko Glacier, Pamir Mountains, from GNSS field measurements and TanDEM-X elevation models, with a focus on the upper glacier

2018 ◽  
Vol 64 (246) ◽  
pp. 637-648 ◽  
Author(s):  
A. LAMBRECHT ◽  
C. MAYER ◽  
A. WENDT ◽  
D. FLORICIOIU ◽  
C. VÖLKSEN
Keyword(s):  
Field Measurements ◽  
Global Navigation Satellite Systems ◽  
High Accumulation ◽  
Glacier Surface ◽  
Mean Values ◽  
Satellite Systems ◽  
Pamir Mountains ◽  
Elevation Changes ◽  
Global Navigation Satellite ◽  
Radar Wave

ABSTRACTFedchenko Glacier experienced a large thickness loss since the first scientific investigations in 1928. As the largest glacier in the Pamir Mountains, this glacier plays an important role for the regional glacier mass budget. We use a series of Global Navigation Satellite Systems observations from 2009 to 2016 and TanDEM-X elevation models from 2011 to 2016 to investigate recent elevation changes. Accounting for radar wave penetration minimizes biases in elevation that can otherwise reach up to 6 m in dry snow on Fedchenko Glacier, with mean values of 3–4 m in the high accumulation regions. The seasonal elevation changes reach up to ±5 m. The glacier surface elevation decreased along its entire length over multi-year periods. Thinning rates increased between 2000 and 2016 by a factor of 1.8 compared with 1928–2000, resulting in peak values of 1.5 m a−1. Even the highest accumulation basins above 5000 m elevation have been affected by glacier thinning with change rates between −0.2 and −0.4 m a−1 from 2009 to 2016. The estimated glacier-wide mass-balance rates are −0.27 ± 0.05 m w.e. a−1 for 2000 to 2011 and −0.51 ± 0.04 m w.e. a−1 between 2011 and 2016.

scholarly journals Diagnostic and prognostic simulations with a full Stokes model accounting for superimposed ice of Midtre Lovénbreen, Svalbard

2009 ◽  
Vol 3 (2) ◽  
pp. 217-229 ◽  
Author(s):  
T. Zwinger ◽  
J. C. Moore
Keyword(s):  
Free Surface ◽  
Steady State ◽  
Thermal State ◽  
Steady State Solution ◽  
Radar Data ◽  
Data Set ◽  
Surface Evolution ◽  
Steady State Model ◽  
Elevation Changes ◽  
Ground Penetrating

Abstract. We present steady state (diagnostic) and transient (prognostic) simulations of Midtre Lovénbreen, Svalbard performed with the thermo-mechanically coupled full-Stokes code Elmer. This glacier has an extensive data set of geophysical measurements available spanning several decades, that allow for constraints on model descriptions. Consistent with this data set, we included a simple model accounting for the formation of superimposed ice. Diagnostic results indicated that a dynamic adaptation of the free surface is necessary, to prevent non-physically high velocities in a region of under determined bedrock depths. Observations from ground penetrating radar of the basal thermal state agree very well with model predictions, while the dip angles of isochrones in radar data also match reasonably well with modelled isochrones, despite the numerical deficiencies of estimating ages with a steady state model. Prognostic runs for 53 years, using a constant accumulation/ablation pattern starting from the steady state solution obtained from the configuration of the 1977 DEM show that: 1 the unrealistic velocities in the under determined parts of the DEM quickly damp out; 2 the free surface evolution matches well measured elevation changes; 3 the retreat of the glacier under this scenario continues with the glacier tongue in a projection to 2030 being situated ≈500 m behind the position in 1977.

scholarly journals A mean net accumulation pattern derived from radioactive layers and radar soundings on Austfonna, Nordaustlandet, Svalbard

2001 ◽  
Vol 47 (159) ◽  
pp. 555-566 ◽  
Author(s):  
Jean Francis Pinglot ◽  
Jon Ove Hagen ◽  
Kjetil Melvold ◽  
Trond Eiken ◽  
Christian Vincent
Keyword(s):  
Mass Balance ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Equilibrium Line ◽  
Accumulation Pattern ◽  
Ice Cap ◽  
The Mean ◽  
Nuclear Tests ◽  
Ground Penetrating ◽  
High Degree

AbstractWe present the snow-accumulation distribution over Austfonna, Nordaustlandet, Svalbard, based on 29 shallow ice cores that were retrieved from this ice cap during 1998 and 1999. Mean annual net accumulation is deduced from radioactive layers resulting from the 1954–74 atmospheric nuclear tests (maximum in 1963) and the Chernobyl accident (1986). The Chernobyl layer was located in 19 ice cores in the accumulation area, and the nuclear test layer was located in two deeper ice cores. In addition, the spatial variation of the depth of winter 1998/99 snowpack was mapped using snow probing, ground-penetrating radar methods and pit studies. The altitudinal gradient of the mean annual net mass balance and the altitude of the mean equilibrium line are determined along five transects ending at the top of the ice cap. The mean annual net mass balance and the equilibrium-line altitudes show a high degree of asymmetry between the western and eastern parts of Austfonna, in accordance with the distribution of winter accumulation. Large interannual variations of the accumulation exist. However, the study of the mean annual net mass balance shows no trend for two different time periods, 1963–86 and 1986 to the date of the drillings (1998/99).

A computational approach to Quaternary lake-level reconstruction applied in the central Rocky Mountains, Wyoming, USA

2014 ◽  
Vol 82 (1) ◽  
pp. 249-259 ◽  
Author(s):  
Paul Pribyl ◽  
Bryan N. Shuman
Keyword(s):  
Direct Evidence ◽  
Late Quaternary ◽  
Water Levels ◽  
Reconstruction Method ◽  
Facies Classification ◽  
Multiple Cores ◽  
Elevation Changes ◽  
Central Rocky Mountains ◽  
Ground Penetrating ◽  
Hydrologic Responses

AbstractSediment-based reconstructions of late-Quaternary lake levels provide direct evidence of hydrologic responses to climate change, but many studies only provide approximate lake-elevation curves. Here, we demonstrate a new method for producing quantitative time series of lake elevation based on the facies and elevations of multiple cores collected from a lake's margin. The approach determines the facies represented in each core using diagnostic data, such as sand content, and then compares the results across cores to determine the elevation of the littoral zone over time. By applying the approach computationally, decisions are made systematically and iteratively using different facies classification schemes to evaluate the associated uncertainty. After evaluating our assumptions using ground-penetrating radar (GPR), we quantify past lake-elevation changes, precipitation minus evapotranspiration (ΔP−ET), and uncertainty in both at Lake of the Woods and Little Windy Hill Pond, Wyoming. The well-correlated (r = 0.802 ± 0.002) reconstructions indicate that water levels at both lakes fell at >11,300, 8000–5500, and 4700–1600 cal yr BP when ΔP − ET decreased to −50 to −250 mm/yr. Differences between the reconstructions are typically small (10 ± 24 mm/yr since 7000 cal yr BP), and the similarity indicates that our reconstruction method can produce statistically comparable paleohydrologic datasets across networks of sites.

scholarly journals Ice thickness, areal and volumetric changes of Davies Dome and Whisky Glacier (James Ross Island, Antarctic Peninsula) in 1979–2006

2012 ◽  
Vol 58 (211) ◽  
pp. 904-914 ◽  
Author(s):  
Zbynĕk Engel ◽  
Daniel Nývlt ◽  
Kamil Láska
Keyword(s):  
Antarctic Peninsula ◽  
Ground Penetrating Radar ◽  
Ice Thickness ◽  
Bed Topography ◽  
Ice Cap ◽  
Valley Glacier ◽  
Elevation Changes ◽  
James Ross Island ◽  
The Mean ◽  
Ground Penetrating

AbstractThis study calculates area, volume and elevation changes of two glaciers on James Ross Island, Antarctica, during the period 1979-2006. Davies Dome is a small ice cap. Whisky Glacier is a valley glacier. Ground-penetrating radar surveys indicate ice thickness, which was used for calculations of the bed topography and volume of both glaciers. Maximum measured ice thicknesses of Davies Dome and Whisky Glacier are 83 ± 2 and 157 ± 2 m, respectively. Between 1979 and 2006, the area of the ice cap decreased from 6.23 ± 0.05 km2 to 4.94 ± 0.01 km2 (-20.7%), while the area of the valley glacier reduced from 2.69 ± 0.02 km2 to 2.40 ± 0.01 km2 (-10.6%). Over the same period the volume of the ice cap and valley glacier reduced from 0.23 ± 0.03 km3 to 0.16 ± 0.02 km3 (-30.4%) and from 0.27 ± 0.02 km3 to 0.24 ± 0.01 km3 (-10.6%), respectively. The mean surface elevation decreased by 8.5±2.8 and 10.1 ±2.8m. The average areal (~0.048-0.011 km2a-1) and volumetric (~0.003−0.001 km3 a-1) changes are higher than the majority of other estimates from Antarctic Peninsula glaciers.

scholarly journals Regional and temporal variation of accumulation around NorthGRIP derived from ground-penetrating radar

2005 ◽  
Vol 42 ◽  
pp. 326-330 ◽  
Author(s):  
Daniel Steinhage ◽  
Olaf Eisen ◽  
Henrik Brink Clausen
Keyword(s):  
Ground Penetrating Radar ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temporal Variations ◽  
Small Scale ◽  
Internal Layers ◽  
Accumulation Pattern ◽  
Ground Penetrating

AbstractDuring the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75˚06’N, 42˚20’W; 2957ma.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kgm–2a–1 to 200 kg m–2 a -1 over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kgm–2a-1 km- 1 , i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of ± 4% of the mean of the last 400 years, i.e. at NorthGRIP ± 7 kg m–2 a-1. If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.

An Approach to Sinkhole Prevention on Post Pipeline Construction at Trenchless Road Crossings

2012 ◽  
Author(s):  
Everett Wong ◽  
Greg Sasaki ◽  
James Harrison
Keyword(s):  
High Risk ◽  
Ground Penetrating Radar ◽  
Control Measures ◽  
Soil Conditions ◽  
Radio Waves ◽  
The Public ◽  
Oil Pipeline ◽  
Subsurface Soil ◽  
Elevation Difference ◽  
Ground Penetrating

Sinkholes manifest unpredictably at road crossings long after the completion of pipeline installation. In recent pipeline projects, Alberta Clipper Expansion and Line 4 Extension, over 1200 km of NPS 36 oil pipeline was constructed across Alberta, Saskatchewan, and Manitoba. Over 600 road crossings were executed across these provinces utilizing standard industry crossing techniques and under a wide variety of soil conditions. Several months after construction, sinkholes appeared on roads at locations along the centerline of the newly constructed pipeline. It is hypothesized that bores which were observed to have been over-reamed, re-reamed, or had pipe pulled back, may have contributed in development of unconsolidated soil or “voids” in comparison to adjacent native subsurface soil, which then manifested into sinkholes. In other cases, the evolution of voids may have been attributed to pre-existing soil conditions. Since sinkholes pose safety concerns to the public as well as the integrity of the pipeline mitigation, control measures were taken to assess and remediate other locations prior to sinkhole manifestation. An approach to prevent sinkhole manifestation is identifying high-risk crossings, scanning for voids, and void remediation. Identification of high-risk sinkhole manifestation at crossings involved desktop evaluation which was based on: observations noted inspectors’ reports, geotechnical conditions, depth of crossings, the elevation difference between the entry and exit holes, and crossing method. Once prioritized, selected road crossings were scanned for voids using a technology called Ground-Penetrating Radar (GPR), which is the focus of this paper. Ground-penetrating radar employs a system of radio waves at various frequencies directed at the subsoil. The changing velocities between consolidated and unconsolidated soil provides different views of the subsurface. Factors such as pipeline depth, soil type, and interference, played a factor in the ability to accurately scan for voids. For remediation, the injection of polyurethane foam was used. This paper describes the approach, process, accuracy factors, and findings of Ground-penetrating radar used on pipeline projects.

scholarly journals Radar-detected englacial stratigraphy in the Pensacola Mountains, Antarctica: implications for recent changes in ice flow and accumulation

2013 ◽  
Vol 54 (63) ◽  
pp. 91-100 ◽  
Author(s):  
Seth Campbell ◽  
Greg Balco ◽  
Claire Todd ◽  
Howard Conway ◽  
Kathleen Huybers ◽  
...  
Keyword(s):  
Mass Balance ◽  
Surface Elevation ◽  
Ice Flow ◽  
Ice Surface ◽  
Valley Glacier ◽  
Glacier Ice ◽  
Elevation Changes ◽  
Ice Sheet Dynamics ◽  
Surface Ice ◽  
Ground Penetrating

AbstractWe used measurements of radar-detected stratigraphy, surface ice-flow velocities and accumulation rates to investigate relationships between local valley-glacier and regional ice-sheet dynamics in and around the Schmidt Hills, Pensacola Mountains, Antarctica. Ground-penetrating radar profiles were collected perpendicular to the long axis of the Schmidt Hills and the margin of Foundation Ice Stream (FIS). Within the valley confines, the glacier consists of blue ice, and profiles show internal stratigraphy dipping steeply toward the nunataks and truncated at the present-day ablation surface. Below the valley confines, the blue ice is overlain by firn. Data show that upward-progressing overlap of actively accumulating firn onto valley-glacier ice is slightly less than ice flow out of the valleys over the past ∼1200 years. The apparent slightly negative mass balance (-0.25 cm a-1) suggests that ice-margin elevations in the Schmidt Hills may have lowered over this time period, even without a change in the surface elevation of FIS. Results suggest that (1) mass-balance gradients between local valley glaciers and regional ice sheets should be considered when using local information to estimate regional ice surface elevation changes; and (2) interpretation of shallow ice structures imaged with radar can provide information about local ice elevation changes and stability.

scholarly journals Elevation and Volume Changes in Greenland Ice Sheet From 2010 to 2019 Derived From Altimetry Data

2021 ◽  
Vol 9 ◽  
Author(s):  
Guodong Chen ◽  
Shengjun Zhang ◽  
Shenghao Liang ◽  
Jiaheng Zhu
Keyword(s):  
Volume Change ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Altimetry Data ◽  
Elevation Change ◽  
Volume Changes ◽  
Change Rate ◽  
Ice Cloud ◽  
Elevation Changes ◽  
Elevation Difference

Long-term altimetry data are one of the major sources to analyze the change in global ice reserves. This study focuses on the elevation and volume changes in the Greenland ice sheet (GrIS) from 2010 to 2019 derived from altimetry observations. In this study, the methods for determining surface elevation change rates are discussed, and specific strategies are designed. A new elevation difference method is proposed for CryoSat-2 synthetic aperture interferometric (SARin) mode observations. Through validation with Airborne Topographic Mapper (ATM) data, this new method is proved to be effective for slope terrains at the margins of the ice sheet. Meanwhile, a surface fit method is applied for the flat interior of the ice sheet where low resolution mode (LRM) observations are provided. The results of elevation change rates in the GrIS from 2010 to 2019 are eventually calculated by combining CryoSat-2 and ATM observations. An elevation change rate of −11.83 ± 1.14 cm·a−1 is revealed, corresponding to a volume change rate of −200.22 ± 18.26 km3·a−1. The results are compared with the elevation changes determined by Ice, Cloud, and Land Elevation Satellite (ICESat) from 2003 to 2009. Our results show that the overall volume change rate in the GrIS slowed down by approximately 10% during the past decade, and that the main contributor of GrIS ice loss has shifted from the southeast coast to the west margin of the ice sheet.

scholarly journals Changes in Anterior and Posterior Corneal Elevation in Patients With Allergic Conjunctivitis

2021 ◽  
Vol 8 ◽  
Author(s):  
Qian Wang ◽  
Fei Yu ◽  
Ziqing Feng ◽  
Weihua Li ◽  
Naiyang Li ◽  
...  
Keyword(s):  
Allergic Conjunctivitis ◽  
Normal Subjects ◽  
Mean Value ◽  
Ocular Allergy ◽  
Corneal Surface ◽  
Clinical Trial Registration ◽  
Central Location ◽  
Increased Risk ◽  
Elevation Changes ◽  
Elevation Difference

Purpose: To evaluate corneal elevation changes in patients with allergic conjunctivitis (AC) and to analyze their correlations with ocular allergy signs and corneal biomechanical alterations.Methods: Thirty patients (30 eyes) with AC and twenty normal subjects (20 eyes) were included in this prospective study. All participants underwent a complete ocular examination, including corneal tomography by Pentacam and corneal biomechanics evaluation by Corvis ST. AC patients were evaluated for their eye rubbing frequency and ocular allergic signs.Results: The elevation at the thinnest location (TE) and the central location (CE), the elevation difference at the thinnest location (TED) and the central location (CED), and the mean value of elevation difference in the central 4 mm zoom (MED) of both the anterior and posterior corneal surface were significantly higher in the AC group than in the normal group (p &lt; 0.05 for all). In AC patients, only anterior corneal elevation parameters were positively correlated with eye rubbing frequency and ocular allergy sign severity (p &lt; 0.05 for all), while the tomography and biomechanical index (TBI) was positively correlated with the elevation parameters of both the anterior and posterior corneal surfaces (p &lt; 0.05 for all).Conclusion: AC patients carry an increased risk of corneal ectasia. Posterior corneal elevation parameters are sensitive and reliable predictors of keratoconus (KC) risk in AC patients.Clinical Trial Registration:https://clinicaltrials.gov/ct2/show/NCT04299399, identifier [NCT04299399].

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