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  • 1.
    den Ouden, M. A. G.
    et al.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, Utrecht, Netherlands..
    Reijmer, C. H.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, Utrecht, Netherlands..
    Pohjola, V.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    van de Wal, R. S. W.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, Utrecht, Netherlands..
    Oerlemans, J.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, Utrecht, Netherlands..
    Boot, W.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, Utrecht, Netherlands..
    Stand-alone single-frequency GPS ice velocity observations on Nordenskioldbreen, Svalbard2010In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 4, no 4, p. 593-604Article in journal (Refereed)
    Abstract [en]

    Precise measurements of ice-flow velocities are necessary for a proper understanding of the dynamics of glaciers and their response to climate change. We use stand-alone single-frequency GPS receivers for this purpose. They are designed to operate unattended for 1-3 years, allowing uninterrupted measurements for long periods with hourly temporal resolution. We present the system and illustrate its functioning using data from 9 GPS receivers deployed on Nordenskioldbreen, Svalbard, for the period 2006-2009. The accuracy of the receivers is 1.62m based on the standard deviation in the average location of a stationary reference station (NBRef). Both the location of NBRef and the observed flow velocities agree within one standard deviation with DGPS measurements. Periodicity (6, 8, 12, 24 h) in the NBRef data is largely explained by the atmospheric, mainly ionospheric, influence on the GPS signal. A (weighed) running-average on the observed locations significantly reduces the standard deviation and removes high frequency periodicities, but also reduces the temporal resolution. Results show annual average velocities varying between 40 and 55myr(-1) at stations on the central flow-line. On weekly to monthly time-scales we observe a peak in the flow velocities (from 60 to 90myr(-1)) at the beginning of July related to increased melt-rates. No significant lag is observed between the timing of the maximum speed between different stations. This is likely due to the limited temporal resolution after averaging in combination with the relatively small distance (max. +/- 13 km) between the stations.

  • 2.
    Fujita, S.
    et al.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Holmlund, P.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Andersson, I.
    Royal Inst Technol, Div Geodesy & Geoinformat, Stockholm, Sweden..
    Brown, I.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Enomoto, H.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan.;Kitami Inst Technol, Kitami, Hokkaido 090, Japan..
    Fujii, Y.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Fujita, K.
    Nagoya Univ, Grad Sch Environm Studies, Nagoya, Aichi 4648601, Japan..
    Fukui, K.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Furukawa, T.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Hansson, M.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Hara, K.
    Fukuoka Univ, Fac Sci, Dept Earth Syst Sci, Fukuoka 81401, Japan..
    Hoshina, Y.
    Nagoya Univ, Grad Sch Environm Studies, Nagoya, Aichi 4648601, Japan..
    Igarashi, M.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Iizuka, Y.
    Hokkaido Univ, Inst Low Temp Sci, Sapporo, Hokkaido 060, Japan..
    Imura, S.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Ingvander, S.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Karlin, T.
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Motoyama, H.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Nakazawa, F.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Oerter, H.
    Alfred Wegener Inst Polar & Marine Res, D-27515 Bremerhaven, Germany..
    Sjöberg, L. E.
    Royal Inst Technol, Div Geodesy & Geoinformat, Stockholm, Sweden..
    Sugiyama, S.
    Hokkaido Univ, Inst Low Temp Sci, Sapporo, Hokkaido 060, Japan..
    Surdyk, S.
    Res Org Informat & Syst, Natl Inst Polar Res, Tokyo, Japan..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Uemura, R.
    Univ Ryukyus, Fac Sci, Dept Chem Biol & Marine Sci, Okinawa, Japan..
    Wilhelms, F.
    Alfred Wegener Inst Polar & Marine Res, D-27515 Bremerhaven, Germany..
    Spatial and temporal variability of snow accumulation rate on the East Antarctic ice divide between Dome Fuji and EPICA DML2011In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 5, no 4, p. 1057-1081Article in journal (Refereed)
    Abstract [en]

    To better understand the spatio-temporal variability of the glaciological environment in Dronning Maud Land (DML), East Antarctica, a 2800-km-long Japanese-Swedish traverse was carried out. The route includes ice divides between two ice-coring sites at Dome Fuji and EPICA DML. We determined the surface mass balance (SMB) averaged over various time scales in the late Holocene based on studies of snow pits and firn cores, in addition to radar data. We find that the large-scale distribution of the SMB depends on the surface elevation and continentality, and that the SMB differs between the windward and leeward sides of ice divides for strong-wind events. We suggest that the SMB is highly influenced by interactions between the large-scale surface topography of ice divides and the wind field of strong-wind events that are often associated with high-precipitation events. Local variations in the SMB are governed by the local surface topography, which is influenced by the bedrock topography. In the eastern part of DML, the accumulation rate in the second half of the 20th century is found to be higher by similar to 15% than averages over longer periods of 722 a or 7.9 ka before AD 2008. A similar increasing trend has been reported for many inland plateau sites in Antarctica with the exception of several sites on the leeward side of the ice divides.

  • 3.
    Nitsche, F. O.
    et al.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA..
    Gohl, K.
    Alfred Wegener Inst Polar & Marine Res, Bremerhaven, Germany..
    Larter, R. D.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Hillenbrand, C. -D
    Kuhn, G.
    Alfred Wegener Inst Polar & Marine Res, Bremerhaven, Germany..
    Smith, J. A.
    British Antarctic Survey, Cambridge CB3 0ET, England..
    Jacobs, S.
    Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY 10964 USA..
    Anderson, J. B.
    Rice Univ, Dept Earth Sci, Houston, TX USA..
    Jakobsson, M.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 1, p. 249-262Article in journal (Refereed)
    Abstract [en]

    Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.

  • 4.
    Schafer, M.
    et al.
    Univ Lapland, Arctic Ctr, Rovaniemi, Finland.;Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Gillet-Chaulet, F.
    Univ Grenoble Alpes, CNRS, Lab Glaciol & Geophys Environm, F-38041 Grenoble, France..
    Gladstone, R.
    Univ Lapland, Arctic Ctr, Rovaniemi, Finland..
    Pettersson, R.
    Uppsala Univ, Dept Earth Sci Air Water & Landscape Sci, Uppsala, Sweden..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci Air Water & Landscape Sci, Uppsala, Sweden..
    Strozzi, T.
    Gamma Remote Sensing & Consulting AG, Gumlingen, Switzerland..
    Zwinger, T.
    CSC IT Ctr Sci Ltd, Espoo, Finland..
    Assessment of heat sources on the control of fast flow of Vestfonna ice cap, Svalbard2014In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 8, no 5, p. 1951-1973Article in journal (Refereed)
    Abstract [en]

    Understanding the response of fast flowing ice streams or outlet glaciers to changing climate is crucial in order to make reliable projections of sea level change over the coming decades. Motion of fast outlet glaciers occurs largely through basal motion governed by physical processes at the glacier bed, which are not yet fully understood. Various subglacial mechanisms have been suggested for fast flow but common to most of the suggested processes is the requirement of presence of liquid water, and thus temperate conditions. We use a combination of modelling, field, and remote observations in order to study links between different heat sources, the thermal regime and basal sliding in fast flowing areas on Vestfonna ice cap. A special emphasis lies on Franklinbreen, a fast flowing outlet glacier which has been observed to accelerate recently. We use the ice flow model Elmer/Ice including a Weertman type sliding law and a Robin inverse method to infer basal friction parameters from observed surface velocities. Firn heating, i.e. latent heat release through percolation of melt water, is included in our model; its parameterisation is calibrated with the temperature record of a deep borehole. We found that strain heating is negligible, whereas friction heating is identified as one possible trigger for the onset of fast flow. Firn heating is a significant heat source in the central thick and slow flowing area of the ice cap and the essential driver behind the ongoing fast flow in all outlets. Our findings suggest a possible scenario of the onset and maintenance of fast flow on the Vestfonna ice cap based on thermal processes and emphasise the role of latent heat released through refreezing of percolating melt water for fast flow. However, these processes cannot yet be captured in a temporally evolving sliding law. In order to simulate correctly fast flowing outlet glaciers, ice flow models not only need to account fully for all heat sources, but also need to incorporate a sliding law that is not solely based on the basal temperature, but also on hydrology and/or sediment physics.

  • 5.
    Schafer, M.
    et al.
    Univ Lapland, Arctic Ctr, Rovaniemi, Finland..
    Zwinger, T.
    CSC IT Ctr Sci Ltd, Espoo, Finland.;Beijing Normal Univ, Coll Global Change & Earth Syst Sci, Beijing 100875, Peoples R China..
    Christoffersen, P.
    Univ Cambridge, Scott Polar Res Inst, Cambridge CB2 1ER, England..
    Gillet-Chaulet, F.
    UJF Grenoble 1, LGGE, UMR5183, CNRS, Grenoble, France..
    Laakso, K.
    Univ Helsinki, Dept Geosci & Geog, FIN-00014 Helsinki, Finland..
    Pettersson, R.
    Uppsala Univ, Dept Earth Sci Air Water & Landscape Sci, Uppsala, Sweden..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci Air Water & Landscape Sci, Uppsala, Sweden..
    Strozzi, T.
    Gamma Remote Sensing & Consulting AG, Gumlingen, Switzerland..
    Moore, J. C.
    Univ Lapland, Arctic Ctr, Rovaniemi, Finland.;Beijing Normal Univ, Coll Global Change & Earth Syst Sci, Beijing 100875, Peoples R China.;Uppsala Univ, Dept Earth Sci Air Water & Landscape Sci, Uppsala, Sweden..
    Sensitivity of basal conditions in an inverse model: Vestfonna ice cap, Nordaustlandet/Svalbard2012In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 6, no 4, p. 771-783Article in journal (Refereed)
    Abstract [en]

    The dynamics of Vestfonna ice cap (Svalbard) are dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast-flowing outlet glaciers. Hence, it is a challenging target for ice flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice cap. Here we use the full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier -a simple parametrization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small as not to adversely affect the fidelity of the model.

  • 6. Sparkes, Robert B.
    et al.
    Selver, Aya Dogrul
    Gustafsson, Orjan
    Semiletov, Igor P.
    Haghipour, Negar
    Wacker, Lukas
    Eglinton, Timothy I.
    Talbot, Helen M.
    van Dongen, Bart E.
    Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf2016In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 10, no 5, p. 2485-2500Article in journal (Refereed)
    Abstract [en]

    Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis-gas chromatography-mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r(2) = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (C-14(OC)) which, when coupled with previous measurements, allows us to produce the most comprehensive C-14(OC) map of the ESAS to date. Combining the C-14(OC) and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river-ocean transects of surface sediments transition from river-dominated to coastalerosion-dominated to marine-dominated signatures.

  • 7.
    van Pelt, W. J. J.
    et al.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Oerlemans, J.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Reijmer, C. H.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Pettersson, R.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Isaksson, E.
    Norwegian Polar Res Inst, Tromso, Norway..
    Divine, D.
    Norwegian Polar Res Inst, Tromso, Norway..
    An iterative inverse method to estimate basal topography and initialize ice flow models2013In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 7, no 3, p. 987-1006Article in journal (Refereed)
    Abstract [en]

    We evaluate an inverse approach to reconstruct distributed bedrock topography and simultaneously initialize an ice flow model. The inverse method involves an iterative procedure in which an ice dynamical model (PISM) is run multiple times over a prescribed period, while being forced with space-and time-dependent climate input. After every iteration bed heights are adjusted using information of the remaining misfit between observed and modeled surface topography. The inverse method is first applied in synthetic experiments with a constant climate forcing to verify convergence and robustness of the approach in three dimensions. In a next step, the inverse approach is applied to Nordenskioldbreen, Svalbard, forced with height-and time-dependent climate input since 1300 AD. An L-curve stopping criterion is used to prevent overfitting. Validation against radar data reveals a high correlation (up to R = 0.89) between modeled and observed thicknesses. Remaining uncertainties can mainly be ascribed to inaccurate model physics, in particular, uncertainty in the description of sliding. Results demonstrate the applicability of this inverse method to reconstruct the ice thickness distribution of glaciers and ice caps. In addition to reconstructing bedrock topography, the method provides a direct tool to initialize ice flow models for forecasting experiments.

  • 8.
    van Pelt, W. J. J.
    et al.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Oerlemans, J.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Reijmer, C. H.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Pettersson, R.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    van Angelen, J. H.
    Univ Utrecht, Inst Marine & Atmospher Res, Utrecht, Netherlands..
    Simulating melt, runoff and refreezing on Nordenskioldbreen, Svalbard, using a coupled snow and energy balance model2012In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 6, no 3, p. 641-659Article in journal (Refereed)
    Abstract [en]

    A distributed energy balance model is coupled to a multi-layer snow model in order to study the mass balance evolution and the impact of refreezing on the mass budget of Nordenskioldbreen, Svalbard. The model is forced with output from the regional climate model RACMO and meteorological data from Svalbard Airport. Extensive calibration and initialisation are performed to increase the model accuracy. For the period 1989-2010, we find a mean net mass balance of -0.39 m w.e. a(-1). Refreezing contributes on average 0.27 m w.e. a(-1) to the mass budget and is most pronounced in the accumulation zone. The simulated mass balance, radiative fluxes and subsurface profiles are validated against observations and are generally in good agreement. Climate sensitivity experiments reveal a non-linear, seasonally dependent response of the mass balance, refreezing and runoff to changes in temperature and precipitation. It is shown that including seasonality in climate change, with less pronounced summer warming, reduces the sensitivity of the mass balance and equilibrium line altitude (ELA) estimates in a future climate. The amount of refreezing is shown to be rather insensitive to changes in climate.

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