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  • 1
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    Reconstructed ice thickness fields for Kersten Glacier (KG) and the Northern Icefield (NIF) on Mt. Kilimanjaro for the 2011 glacier extent at 2 m model resolution (2021)
    PANGAEA
    Details
    Publication Date: 2024-04-20
    Description: Glaciers on Kilimanjaro are unique indicators for climatic changes in the tropical mid-troposphere of Africa. The history of severe glacier area loss raises concerns about an imminent future disappearance. Yet, the remaining ice volume is not well known. We reconstruct thickness maps for 2000 and 2011 for the Northern Icefield (NIF) and Kersten Glacier (KG) that are informed by ground-truth thickness measurements and multi-temporal satellite information. For 2011, we find mean thickness values of 26.6 and 9.3 m, respectively. The existing consensus estimate for global glacier ice thickness shows unrealistically thick values for KG in areas that are meanwhile ice-free. The ice thickness fields show the ice thickness in meters for the 2011 reconstruction (Experiment 3) outlined in the linked publication.
    Keywords: Binary Object; Event label; GPR; Ground-penetrating radar; ice thickness; Kersten_Glacier; KG; Kilimanjaro Northern Ice Field; KNIF; Mount Kilimanjaro, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 3 data points
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    DATA PANGAEA
  • 2
    Electronic Resource
    Electronic Resource
    Fluorescence-optical measurements of chloride movements in cells using the membrane-permeable dye diH-MEQ (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 486-493 
    Details
    ISSN: 1432-2013
    Keywords: Key words MEQ ; Chloride concentration ; ICln ; DIDS ; NPPB ; Fluorescence ; Fluorescence-optical measurements ; SPQ ; MQAE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Fluorescence-optical measurements of the intracellular chloride concentration facilitate identification of chloride movements across the cell membrane of living cells. The two main dyes used for this purpose are 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ) and 6-methoxy-quinolyl acetoethyl ester (MQAE). The use of both substances is impaired by their poor membrane permeability and therefore limited loading of the cells to be studied. Here we report the use of 6-methoxy-N-ethylquinolinium iodide (MEQ), a chloride-sensitive dye for which a membrane-permeable form is easily prepared. This makes the loading procedure as easy as with the acetoxymethyl (AM) forms of other dyes for sensing intracellular ions. In addition, the original method, which described absolute concentration measurements of chloride in the cytosol, was modified in so far as only relative measurements were made. This avoids the known limitations of single wavelength excitation and emission dyes with respect to exact concentration measurements. Moreover, to enhance the signal-to-noise ratio the driving force for chloride was considerably increased by changing the original direction of the anion flux in the cells under investigation. We verified the method by using fibroblasts and activating I Cln, a putative chloride channel cloned from epithelial cells and of paramount importance in the regulatory volume decrease in these cells. In the presence of SCN− the MEQ quench measured in NIH 3T3 fibroblasts is dramatically enhanced in hypotonically challenged cells compared with cells under isotonic conditions. Antisense oligodeoxynucleotides sensing I Cln considerably impeded the swelling-induced chloride current (I Cl) in NIH 3T3 fibroblasts. Accordingly, the chloride movement measured by the SCN− quench of the MEQ signal was significantly reduced. Similar results can be obtained in the presence of 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) or 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), two known blockers of chloride transport in the plasma membrane of a variety of cells. In conclusion, fluroscence-optical measurements using MEQ as the chloride-sensitive dye provide a reliable and easy-to-use method for measuring changes of the chloride flux across the cell membrane of living cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050160
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Functional reconstitution of ICln in lipid bilayers (2000)
    Springer
    Pflügers Archiv 440 (2000), S. 100-115 
    Details
    ISSN: 1432-2013
    Keywords: ICln RVD Swelling-dependent chloride channels Volume regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. Reconstitution of purified ICln in lipid bilayer leads to functional ion channels showing varying rectification. The reconstituted single channels have a conductance of ≅3 pS and their open probability is sensitive to nucleoside analogues. Mutation of a putative nucleotide binding site identified at the predicted extracellular mouth of the ICln channel protein leads to the reduction of the nucleoside-analogue sensitivity. Reconstituted ICln channels can be permeated both by cations and anions. The relative permeability of cations over anions depends on the presence of calcium. In the presence of calcium reconstituted ICln channels are more permeable to bromide than chloride, and more permeable to potassium than sodium. Similarly in NIH3T3 fibroblasts, the relative permeability of cations over anions of swelling-dependent chloride channels depends on extracellular calcium. Site-directed mutagenesis revealed the calcium-binding site responsible for the shift of the selectivity from cations towards anions of reconstituted ICln channels. Additional indirect structural information has been obtained by mutating a histidine in the predicted pore region of ICln. This histidine seems to have access to the ion-conducting tunnel of the pore. Our experiments show that ICln can act as an ionic channel, which does not exclude additional functions of the protein in regulatory mechanisms of the cell. Since knocking down the ICln protein in fibroblasts and epithelial cells leads to an impaired regulatory volume decrease (RVD) after cytoplasmic swelling and reconstituted ICln channels show several biophysical features of ion channels activated after swelling, ICln is a molecular candidate for these channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240000250
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    Paper (German National Licenses)
    Fulltext
  • 4
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    Modelling the evolution of Vadret da Morteratsch, Switzerland, since the Little Ice Age and into the future (2015)
    Cambridge University Press
    Details
    Publication Date: 2015-03-24
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of The International Glaciological Society (IGS).
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    PAPER CURRENT
  • 5
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    Fun at Antarctic grounding lines: Ice-shelf channels and sediment transport (2017)
    In:  EPIC3EGU General Assembly, Vienna, 2017-04-23-2017-04-28
    Details
    Publication Date: 2019-08-21
    Description: Meltwater beneath the polar ice sheets drains, in part, through subglacial conduits. Landforms created by such drainages are abundant in areas formerly covered by ice sheets during the last glacial maximum. However, observations of subglacial conduit dynamics under a contemporary ice sheet are lacking. We present results from ice-penetrating radar to infer the existence of subglacial conduits upstream of the grounding line of Roi Baudouin Ice Shelf, Antarctica. The conduits are aligned with ice-shelf channels, and underlain by esker ridges formed from sediment deposition due to reduced water outflow speed near the grounding line. In turn, the eskers modify localice flow to initiate the bottom topography of the ice-shelf channels, and create small surface ridges extending onto the shelf. Relict features on the shelf are interpreted to indicate a history of these interactions and variability of past subglacial drainages. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation, and ice-shelf stability. To investigate the role of sediment transport beneath ice sheets further, we model the sheet-shelf system ofthe Ekstömisen catchment, Antarctica. A 3D finite element model (Elmer/ICE) is used to solve the transients full Stokes equation for isotropic, isothermal ice with a dynamic grounding line. We initialize the model with surface topography from the TanDEM-X satellites and by inverting simultaneously for ice viscosity and basaldrag using present-day surface velocities. Results produce a flow field which is consitent with sattelite and on-site observations. Solving the age-depth relationship allows comparison with radar isochrones from airborne data, and gives information about the atmospheric/dynamic history of this sector. The flow field will eventually be used to identify potential sediment sources and sinks which we compare with more than 400 km of seismic profiles collected over the floating ice shelves and the grounded ice sheet.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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    PAPER (OA)
  • 6
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    Dynamic changes on the Wilkins Ice Shelf during the 2006–2009 retreat derived from satellite observations (2017)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Cryosphere, COPERNICUS GESELLSCHAFT MBH, 11, pp. 1199-1211, ISSN: 1994-0416
    Details
    Publication Date: 2017-05-15
    Description: The vast ice shelves around Antarctica provide significant restraint to the outflow from adjacent tributary glaciers. This important buttressing effect became apparent in the last decades, when outlet glaciers accelerated considerably after several ice shelves were lost around the Antarctic Peninsula (AP). The present study aims to assess dynamic changes on the Wilkins Ice Shelf (WIS) during different stages of ice-front retreat and partial collapse between early 2008 and 2009. The total ice-shelf area lost in these events was 2135 ± 75 km2 ( ∼  15 % of the ice-shelf area relative to 2007). Here, we use time series of synthetic aperture radar (SAR) satellite observations (1994–1996, 2006–2010) in order to derive variations in surface-flow speed from intensity-offset tracking. Spatial patterns of horizontal strain-rate, stress and stress-flow angle distributions are determined during different ice-front retreat stages. Prior to the final break up of an ice bridge in 2008, a strong speed up is observed, which is also discernible from other derived quantities. We identify areas that are important for buttressing and areas prone to fracturing using in-flow and first principal strain rates as well as principal stress components. Further propagation of fractures can be explained as the first principal components of strain rates and stresses exceed documented threshold values. Positive second principal stresses are another scale-free indicator for ice-shelf areas, where fractures preferentially open. Second principal strain rates are found to be insensitive to ice-front retreat or fracturing. Changes in stress-flow angles highlight similar areas as the in-flow strain rates but are difficult to interpret. Our study reveals the large potential of modern SAR satellite time series to better understand dynamic and structural changes during ice-shelf retreat but also points to uncertainties introduced by the methods applied.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 7
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    Calibration of a higher-order 3-D ice flow model of the Morteratsch glacier complex, Engadin, Switzerland (2013)
    INT GLACIOL SOC
    In:  EPIC3Annals of Glaciology, INT GLACIOL SOC, 54(63), pp. 343-351, ISSN: 0260-3055
    Details
    Publication Date: 2019-07-17
    Description: We have reconstructed the ice thickness distribution of the Morteratsch glacier complex, Switzerland, and used this to simulate its flow with a higher-order 3-D model. Ice thickness was measured along transects with a ground-penetrating radar and further extended over the entire glacier using the plastic flow assumption and a distance-weighted interpolation technique. We find a maximum ice thickness of 350+-52.5m for the central trunk of Vadret da Morteratsch, resulting from a bedrock overdeepening. The average thickness of the glacier complex is 72.2+-18.0 m, which corresponds to a total ice volume of 1.14+-0.28km3. The flow of the glacier is modelled by tuning the rate factor and the sliding parameters taking into account higher-order terms in the force balance. The observed velocities can be reproduced closely (root-mean-square error of 15.0ma–1, R2 = 0.93) by adopting a sliding factor of 12x10–16m7N–3 a–1 and a rate factor of 1.6x10–16 Pa–3 a–1. In this setting, ice deformation accounts for 70% of the surface velocity and basal sliding for the remaining 30%. The modelled velocity field reaches values up to 125ma–1, but also indicates an almost stagnant front and confluence area, which are crucial for understanding the ongoing glacier retreat.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Acceleration of dynamic ice loss in Antarctica from satellite gravimetry (2021)
    Frontiers
    In:  EPIC3Frontiers in Earth Science, Frontiers, 9, pp. 1266, ISSN: 9
    Details
    Publication Date: 2022-06-20
    Description: The dynamic stability of the Antarctic Ice Sheet is one of the largest uncertainties in projections of future global sea-level rise. Essential for improving projections of the ice sheet evolution is the understanding of the ongoing trends and accelerations of mass loss in the context of ice dynamics. Here, we examine accelerations of mass change of the Antarctic Ice Sheet from 2002 to 2020 using data from the GRACE (Gravity Recovery and Climate Experiment; 2002–2017) and its follow-on GRACE-FO (2018-present) satellite missions. By subtracting estimates of net snow accumulation provided by re-analysis data and regional climate models from GRACE/GRACE-FO mass changes, we isolate variations in ice-dynamic discharge and compare them to direct measurements based on the remote sensing of the surface-ice velocity (2002–2017). We show that variations in the GRACE/GRACE-FO time series are modulated by variations in regional snow accumulation caused by large-scale atmospheric circulation. We show for the first time that, after removal of these surface effects, accelerations of ice-dynamic discharge from GRACE/GRACE-FO agree well with those independently derived from surface-ice velocities. For 2002–2020, we recover a discharge acceleration of -5.3 ± 2.2 Gt yr−2 for the entire ice sheet; these increasing losses originate mainly in the Amundsen and Bellingshausen Sea Embayment regions (68%), with additional significant contributions from Dronning Maud Land (18%) and the Filchner-Ronne Ice Shelf region (13%). Under the assumption that the recovered rates and accelerations of mass loss persisted independent of any external forcing, Antarctica would contribute 7.6 ± 2.9 cm to global mean sea-level rise by the year 2100, more than two times the amount of 2.9 ± 0.6 cm obtained by linear extrapolation of current GRACE/GRACE-FO mass loss trends.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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