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  • 1
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    Ice flux divergence anomalies on 79north Glacier, Greenland (2011)
    Wiley
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    Publication Date: 2011-05-07
    Description: The ice flux divergence of a glacier is an important quantity to examine because it determines the rate of temporal change of its thickness. Here, we combine high-resolution ice surface velocity observations of Nioghalvfjerdsfjorden (79north) Glacier, a major outlet glacier in north Greenland, with a dense grid of ice thickness data collected with an airborne radar sounder in 1998, to examine its ice flux divergence. We detect large variations, up to 100 m/yr, in flux divergence on grounded ice that are incompatible with what we know of the glacier surface mass balance, basal mass balance and thinning rate. We examine the hypothesis that these anomalies are due to the three-dimensional flow of ice around and atop bumps and hollows in basal topography by comparing the flux divergence of three-dimensional numerical models with its surface equivalent. We find that three-dimensional effects have only a small contribution to the observed anomalies. On the other hand, if we degrade the spatial resolution of the data to 10 km the anomalies disappear. Further analysis shows that the source of the anomalies is not the ice velocity data but the interpolation of multiple tracks of ice thickness data onto a regular grid using a scheme (here block kriging) that does not conserve mass or ice flux. This problem is not unique to 79north Glacier but is common to all conventional ice thickness surveys of glaciers and ice sheets; and fundamentally limits the application of ice thickness grids to high-resolution numerical modeling of glacier flow.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Modeling of Store Gletscher's calving dynamics, West Greenland, in response to ocean thermal forcing (2016)
    Wiley
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    Publication Date: 2016-02-26
    Description: Glacier-front dynamics is an important control on Greenland's ice mass balance. Warmer ocean waters trigger ice-front retreats of marine-terminating glaciers, and the corresponding loss in resistive stress leads to glacier acceleration and thinning. Here, we present an approach to quantify the sensitivity and vulnerability of marine-terminating glaciers to ocean-induced melt. We develop a plan-view model of Store Gletscher that includes a level set based moving boundary capability, a parameterized ocean-induced melt and a calving law with complete and precise land and fjord topographies to model the response of the glacier to increased melt. We find that the glacier is stabilized by a sill at its terminus. The glacier is dislodged from the sill when ocean-induced melt quadruples, at which point the glacier retreats irreversibly for 27 km into a reverse bed. The model suggests that ice-ocean interactions are the triggering mechanism of glacier retreat, but the bed controls its magnitude.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Plan for living on a restless planet set NASA's solid earth agenda (2003)
    In:  Eos, Trans., Am. Geophys. Un., Warszawa, Polish Geothermal Association, vol. 84, no. 45, pp. 485, 491, pp. B05406, (ISSN: 1340-4202)
    Details
    Publication Date: 2003
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geodesy ; Global Positioning System ; InSAR ; Strain ; Stress
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, West Greenland. (2016)
    Wiley
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    Publication Date: 2016-03-10
    Description: Marine-terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here, we present a multi-beam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, West Greenland, that extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (〉1,300 m) from glacial erosion, and seafloor depths 100-1,000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (〉2.5 o C) with high melt potential, but we also find numerous glaciers grounded on shallow (〈200 m) sills, standing in cold (〈1 o C) waters in otherwise deep fjords, i.e. with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Submarine moraines in Southeast Greenland fjords reveal contrasting outlet‐glacier behaviour since the Last Glacial Maximum (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Knowledge of the past behaviour of the outlet glaciers of Southeast (SE) Greenland is necessary to understand and model spatial differences in the response of the Greenland Ice Sheet (GIS) to climatic changes. Here, we use bathymetric data to map the distribution of more than 50 major moraines in SE Greenland fjords. Inner‐fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords. We identify, for the first time, 9 mid‐fjord moraines that span the c.150 km long eastern margin of the Julianehåb Ice Cap (JIC). In contrast, mid‐fjord moraines are generally absent from the deeper and wider fjords of the SE GIS. The variable distribution of mid‐fjord moraines along the SE Greenland margin reveals contrasting behaviour of the SE GIS and the eastern JIC during the last deglaciation, which probably reflects differences in fjord geometry and exposure to ocean heat.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Modeling of ocean-induced ice melt rates of five West Greenland glaciers over the past two decades (2016)
    Wiley
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    Publication Date: 2016-05-31
    Description: High-resolution, three-dimensional simulations from the MITgcm ocean model are used to calculate the subaqueous melt rate of the calving faces of Umiamako, Rinks, Kangerdlugssup, Store, and Kangilerngata glaciers, West Greenland, from 1992 to 2015. Model forcing is from monthly reconstructions of ocean state and ice sheet runoff. Results are analyzed in combination with observations of bathymetry, bed elevation, ice-front retreat, and glacier speed. We calculate that subaqueous melt rates are 2-3 times larger in summer compared to winter, and doubled in magnitude since the 1990s due to enhanced subglacial runoff and 1.6±0.3 ∘ C-warmer ocean temperature. Umiamako and Kangilerngata retreated rapidly in the 2000s when subaqueous melt rates exceeded the calving rates and ice front retreated to deeper bed elevation. In contrast, Store, Kangerdlugssup, and Rinks have remained stable because their subaqueous melt rates are 3-4 times lower than their calving rates, i.e. the glaciers are dominated by calving processes.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Grounding line retreat of Pope, Smith, and Kohler Glaciers, West Antarctica, measured with Sentinel-1a radar interferometry data (2016)
    Wiley
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    Publication Date: 2016-08-30
    Description: We employ Sentinel-1a C band satellite radar interferometry data in Terrain Observation with Progressive Scans mode to map the grounding line and ice velocity of Pope, Smith, and Kohler glaciers, in West Antarctica, for the years 2014–2016 and compare the results with those obtained using Earth Remote Sensing Satellites (ERS-1/2) in 1992, 1996, and 2011. We observe an ongoing, rapid grounding line retreat of Smith at 2 km/yr (40 km since 1996), an 11 km retreat of Pope (0.5 km/yr), and a 2 km readvance of Kohler since 2011. The variability in glacier retreat is consistent with the distribution of basal slopes, i.e., fast along retrograde beds and slow along prograde beds. We find that several pinning points holding Dotson and Crosson ice shelves disappeared since 1996 due to ice shelf thinning, which signal the ongoing weakening of these ice shelves. Overall, the results indicate that ice shelf and glacier retreat in this sector remain unabated.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Antarctic grounding line mapping from differential satellite radar interferometry (2011)
    Wiley
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    Publication Date: 2011-05-26
    Description: The delineation of an ice sheet grounding line, i.e., the transition boundary where ice detaches from the bed and becomes afloat in the ocean, is critical to ice sheet mass budget calculations, numerical modeling of ice sheet dynamics, ice-ocean interactions, oceanic tides, and subglacial environments. Here, we present 15 years of comprehensive, high-resolution mapping of grounding lines in Antarctica using differential satellite synthetic-aperture radar interferometry (DInSAR) data from the Earth Remote Sensing Satellites 1–2 (ERS-1/2), RADARSAT-1 and 2, and the Advanced Land Observing System (ALOS) PALSAR for years 1994 to 2009. DInSAR directly measures the vertical motion of floating ice shelves in response to tidal oceanic forcing with millimeter precision, at a sample spacing better than 50 m, simultaneously over areas several 100 km wide; in contrast with earlier methods that detect abrupt changes in surface slope in satellite visible imagery or altimetry data. On stagnant and slow-moving areas, we find that breaks in surface slope are reliable indicators of grounding lines; but on most fast-moving glaciers and ice streams, our DInSAR results reveal that prior mappings have positioning errors ranging from a few km to over 100 km. A better agreement is found with ICESat's data, also based on measurements of vertical motion, but with a detection noise one order of magnitude larger than with DInSAR. Overall, the DInSAR mapping of Antarctic grounding lines completely redefines the coastline of Antarctica.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 9
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    Ice motion of the Patagonian Icefields of South America: 1984-2014 (2015)
    Wiley
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    Publication Date: 2015-02-10
    Description: We present the first comprehensive, high-resolution mosaic of ice velocity of the Northern (NPI) and Southern Patagonian Icefields (SPI), from multiple synthetic-aperture radar and optical data collected between 1984 and 2014. The results reveal that many of the outlet glaciers extend far into the central ice plateaus, which implies that changes in ice dynamics propagate far inside the accumulation area. We report pronounced seasonal to inter-annual variability of ice motion on Pío XI and Jorge Montt, a doubling in speed of Jorge Montt, a major slow down of O'Higgins, significant fluctuations of Upsala and a deceleration of San Rafael, which illustrate the need for sustained, continuous time series of ice motion to understand the long-term evolution of the rapidly thinning icefields. The velocity product also resolves major ambiguities in glacier drainage in areas of relatively flat topography illustrating the need to combine topography and flow direction to map drainage basins.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    Ice flow sensitivity to geothermal heat flux of Pine Island Glacier, Antarctica (2013)
    Wiley
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    Publication Date: 2013-01-03
    Description: [1]  Model projections of ice flow in a changing climate are dependent on model inputs such as surface elevation, bedrock position or surface temperatures, among others. Of all these inputs, geothermal heat flux is the one for which uncertainty is greatest. In the area of Pine Island Glacier, Antarctica, available data sets differ by up to a factor of 2.5. Here, we evaluate the impact of such uncertainty on ice flow, using sampling analyses based on the Latin-Hypercube method. First, we quantify the impact of geothermal heat flux errors on ice hardness, a thermal parameter that critically controls the magnitude of ice flow. Second, we quantify the impact of the same errors on mass balance, specifically on the mass flux advecting through thirteen fluxgates distributed across Pine Island Glacier. We contrast our results with similar uncertainties generated by errors in the specification of ice thickness. Model outputs indicate that geothermal heat flux errors yield uncertainties on ice hardness on the order of 5–7%, with maximum uncertainty reaching 15%. Resulting uncertainties in mass balance remain however below 1%. We discuss the uncertainty distribution and its relationship to the amount of heat available at the base of the ice sheet from friction, viscous and geothermal heating. We also show that comparatively, errors in ice thickness contribute more to model uncertainty than errors in geothermal heat flux, especially for fast-flowing ice streams.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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