TCD - Latest Articles

Glaciochemical investigations on the subterranean ice deposit of Vukušić Ice Cave, Velebit Mountain, Croatia

Thu, 02 Sep 2010 00:00:00 +0200

Glaciochemical investigations on the subterranean ice deposit of Vukušić Ice Cave, Velebit Mountain, Croatia

The Cryosphere Discussions, 4, 1561-1591, 2010

Author(s): Z. Kern, I. Fórizs, N. Horvatinčić, É. Széles, N. Bočić, and B. Nagy

The ³H activity, ¹⁸O/¹⁶O and ²H/¹H ratio and concentration of 33 metals and metalloids have been analysed on ice core samples from the perennial subterranean cave ice deposit of Vukušić Ice Cave, Velebit Mt. The tritium data suggested that the ice deposition at 2–2.4 m depth is build from precipitation fallen ~45 years before sampling and the uppermost ice layer could be estimated between early 1970s and early 1980s or between ~1954 and 1960. Both the fluctuation range of stable water isotopes and the derived isotopic waterline of the ice agree reasonably well with the corresponding data of the local precipitation. This fact predicts that the potential of Vukušić Ice Cave's ice deposit is superior for paleoclimatological studies to the nearby Ledena Pit. Principal component analysis helped to select three groups of elements. The Ca-Mg governed group (PC1) encompasses the bedrock related components; hence the fluctuation of these elements might reflect the past intensities of the dissolution process of the adjacent epikarst. The Zn governed group (PC2) preserves probably an atmospheric deposition signal and related to the emission of regional non-ferrous metallurgy. PC3 is governed by Al and Fe. This probably carries the distal, non-karstic crustal signal hence might be related to the past atmospheric circulation (i.e. wind direction and speed).

First investigations of an ice core from Eisriesenwelt cave (Austria)

Wed, 01 Sep 2010 00:00:00 +0200

First investigations of an ice core from Eisriesenwelt cave (Austria)

The Cryosphere Discussions, 4, 1525-1559, 2010

Author(s): B. May, C. Spötl, D. Wagenbach, Y. Dublyansky, and J. Liebl

Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (δ¹⁸O, δD) and electrolytic conductivity profiles supplemented by specifically selected samples analysed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb derived tritium removing any ice accumulated, since at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses made radiocarbon dating inconclusive, though a crude estimate gave a maximum ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 4 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cyro-calcite layers, a extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (δD versus δ¹⁸O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.

Parameterization for subgrid-scale motion of ice-shelf calving-fronts

Fri, 27 Aug 2010 00:00:00 +0200

Parameterization for subgrid-scale motion of ice-shelf calving-fronts

The Cryosphere Discussions, 4, 1497-1523, 2010

Author(s): T. Albrecht, M. Martin, M. Haseloff, R. Winkelmann, and A. Levermann

A parameterization for the motion of ice-shelf fronts on a Cartesian grid in finite-difference land-ice models is presented. The scheme prevents artificial thinning of the ice shelf at its edge, which occurs due to the finite resolution of the model. The intuitive numerical implementation diminishes numerical dispersion at the ice front and enables the application of physical boundary conditions to improve the calculation of stress and velocity fields throughout the ice-sheet-shelf system. Numerical properties of this subgrid modification are assessed in the Potsdam Parallel Ice Sheet Model (PISM-PIK) for different geometries in one and two horizontal dimensions and are verified against an analytical solution in a flow-line setup.

Some fundamentals of handheld snow surface thermography

Fri, 27 Aug 2010 00:00:00 +0200

Some fundamentals of handheld snow surface thermography

The Cryosphere Discussions, 4, 1467-1496, 2010

Author(s): C. Shea and B. Jamieson

This paper presents the concepts needed to perform snow surface thermography with a modern thermal imager. Snow-specific issues in the 7.5 to 13 μm spectrum such as ice emissivity, photographic angle, operator heating, and others receive detailed review and discussion. To illustrate the usefulness of this measurement technique, various applications are presented. These include detecting spatial temperature variation on snow pit walls and measuring the dependence of heat conduction on grain type.

Isotope hydrological studies on the perennial ice deposit of Saarhalle, Mammuthöhle, Dachstein Mts, Austria

Thu, 26 Aug 2010 00:00:00 +0200

Isotope hydrological studies on the perennial ice deposit of Saarhalle, Mammuthöhle, Dachstein Mts, Austria

The Cryosphere Discussions, 4, 1449-1465, 2010

Author(s): Z. Kern, I. Fórizs, M. Molnár, B. Nagy, and R. Pavuza

A 5.28 m long ice core was extracted from the major cave ice block of the Mammuthöhle cave system. Tritium concentration in eight samples from the upper 1.2 m of the core was measured. Electrical conductivity measurements were achieved on molten water samples and stable oxygen and hydrogen isotopic compositions were also analysed. The upper ~1.2 m of ice has been deposited from precipitation fallen before the 1960s (based on tritium < 8.5 TU). The Saarhalle ice block is build from atmospheric precipitation and the water perfectly preserved the isotopic composition; however the mean ¹⁸O/¹⁶O ratio of the ice is less depleted compared to the long-term (1973–1983) ¹⁸O/¹⁶O ratio of precipitation at Feuerkogel the nearest (~32 km) reference station situated in the same elevation like Mammuthöhle cave. Characteristic fluctuation was observed in the conductivity along the studied cave ice profile. The conductivity oscillations seem to mirror the changing partition of karstic water and surface meltwater in the water supply of the ice accumulation. The ice layers with low conductivity seem to archive past events when more meltwater-like water have been drained and frozen onto the ice block.

Interplay between linear, dissipative and permanently critical mechanical processes in Arctic sea ice

Wed, 25 Aug 2010 00:00:00 +0200

Interplay between linear, dissipative and permanently critical mechanical processes in Arctic sea ice

The Cryosphere Discussions, 4, 1433-1448, 2010

Author(s): A. Chmel, V. Smirnov, and A. Panov

Mechanical processes in the Arctic ice pack result in fragmented sea ice cover, the regular geometry of which could be described in main features in terms of the conventional mechanics. However, the size distribution of sea ice floes does not exhibit the random (poissonian-like) statistics and follows the power law typical for self-similar (fractal) structures. The analysis of ice floe oscillations in the frequency range specific for cracking, shearing and stick-slip motion evidences the self-organized dynamics of sea ice fracturing, which manifests itself in scaling distributions of both the discrete energy discharges in fracture events and the recurrence times between that one. So determined space-time-energy self-similarity characterises the ice pack as the non-equilibrium, nonlinear thermodynamic system where the synergic relations are established through conventional long propagating wave/oscillations. The presented experimental data were collected at the Russian ice-research camp "North Pole 35" drifting on the Arctic ice pack in 2008.

Permafrost and surface energy balance of a polygonal tundra site in Northern Siberia – Part 2: Winter

Wed, 25 Aug 2010 00:00:00 +0200

Permafrost and surface energy balance of a polygonal tundra site in Northern Siberia – Part 2: Winter

The Cryosphere Discussions, 4, 1391-1431, 2010

Author(s): M. Langer, S. Westermann, S. Muster, K. Piel, and J. Boike

Permafrost is largely determined by the surface energy balance. Its vulnerability to degradation due to climate warming depends on complex soil-atmosphere interactions. This article is the second part of a comprehensive surface energy balance study at a polygonal tundra site in Northern Siberia. It comprises two consecutive winter periods from October 2007 to May 2008 and from October 2008 to January 2009. The surface energy balance is obtained by independent measurements of the radiation budget, the sensible heat flux and the ground heat flux, whereas the latent heat flux is inferred from measurements of the atmospheric turbulence characteristics and a model approach. The measurements reveal that the long-wave radiation is the dominant factor in the surface energy balance. The radiative losses are balanced to about 60% by the ground heat flux and almost 40% by the sensible heat fluxes, whereas the contribution of the latent heat flux is found to be relatively small. The main controlling factors of the surface energy budget are the snow cover, the cloudiness and the soil temperature gradient. Significant spatial differences in the surface energy balance are observed between the tundra soils and a small pond. The heat flux released from the subsurface heat storage is by a factor of two increased at the freezing pond during the entire winter period, whereas differences in the radiation budget are only observed at the end of winter. Inter-annual differences in the surface energy balance are related to differences in snow depth, which substantially affect the temperature evolution at the investigated pond. The obtained results demonstrate the importance of the ground heat flux for the soil-atmosphere energy exchange and reveal high spatial and temporal variabilities in the subsurface heat budget during winter.

Application of ground penetrating radar (GPR) in Alpine ice caves

Mon, 23 Aug 2010 00:00:00 +0200

Application of ground penetrating radar (GPR) in Alpine ice caves

The Cryosphere Discussions, 4, 1365-1389, 2010

Author(s): H. Hausmann and M. Behm

Several caves in high elevated alpine regions host up to several meters thick ice fillings. The age of the ice may exceed some hundreds or thousands of years. However, structure, formation and development of the ice are not fully understood and are subject to relatively recent investigation. The application of ground penetrating radar (GPR) enables to determine thickness, volume, basal and internal structure of the ice fillings and provides as such important constraints for related studies. We present results from four caves located in the Northern Calcareous Alps of Austria and show that cave ice is far from being uniform. The transition from ice to the ground has variable reflection signatures, which is related to the deposit and size of debris. The internal structure of the ice fillings is characterized by banded structures which are inclined or parallel to the subsurface topography. These reflection signatures can result from thin layers of calcitic minerals and might help to understand the ice formation by representing isochrones.

Influence of the Tungurahua eruption on the ice core records of Chimborazo, Ecuador

Fri, 20 Aug 2010 00:00:00 +0200

Influence of the Tungurahua eruption on the ice core records of Chimborazo, Ecuador

The Cryosphere Discussions, 4, 1343-1363, 2010

Author(s): P. Ginot, U. Schotterer, W. Stichler, M. A. Godoi, B. Francou, and M. Schwikowski

The comparison of two shallow ice cores recovered in 1999 and 2000 from the same place on Chimborazo summit glacier revealed the influence of the coincident Tungurahua volcanic eruption on their stable isotope and chemical records. The surface snow melting and water percolation induced from the ash deposition caused a preferential elution and re-localization of certain ionic species, while the stable isotope records were not very affected. Additionally, the comparison of the ionic amount and some selected ratios preserved along the ice core column reports under which processes the chemical species are introduced in the snow pack, as snow flake condensation nuclei, by atmospheric scavenging or by dry deposition. This preliminary study is essential for the interpretation of the deep Chimborazo ice core, or for other sites where surrounding volcanic activity may disturb the glaciochemical records.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

Wed, 18 Aug 2010 00:00:00 +0200

The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 2: Dynamic equilibrium simulation of the Antarctic ice sheet

The Cryosphere Discussions, 4, 1307-1341, 2010

Author(s): M. A. Martin, R. Winkelmann, M. Haseloff, T. Albrecht, E. Bueler, C. Khroulev, and A. Levermann

We present a dynamic equilibrium simulation of the ice sheet-shelf system on Antarctica with the Potsdam Parallel Ice Sheet Model (PISM-PIK). The simulation is initialized with present-day conditions for topography and ice thickness and then run to steady state with constant present-day surface mass balance. Surface temperature and basal melt distribution are parameterized. Grounding lines and calving fronts are free to evolve, and their modeled equilibrium state is compared to observational data. A physically-motivated dynamic calving law based on horizontal spreading rates allows for realistic calving fronts for various types of shelves. Steady-state dynamics including surface velocity and ice flux are analyzed for whole Antarctica and the Ronne-Filchner and Ross ice shelf areas in particular. The results show that the different flow regimes in sheet and shelves, and the transition zone between them, are captured reasonably well, supporting the approach of superposition of SIA and SSA for the representation of fast motion of grounded ice. This approach also leads to a natural emergence of streams in this new 3-D marine ice sheet model.

The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 1: Model description

Wed, 18 Aug 2010 00:00:00 +0200

The Potsdam Parallel Ice Sheet Model (PISM-PIK) – Part 1: Model description

The Cryosphere Discussions, 4, 1277-1306, 2010

Author(s): R. Winkelmann, M. A. Martin, M. Haseloff, T. Albrecht, E. Bueler, C. Khroulev, and A. Levermann

We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams naturally emerge through this approach and can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid scale representation of calving front motion (Albrecht et al., 2010) and a physically motivated dynamic calving law based on horizontal spreading rates. The model is validated within the Marine Ice Sheet Model Intercomparison Project (MISMIP) and is used for a dynamic equilibrium simulation of Antarctica under present-day conditions in the second part of this paper (Martin et al., 2010).

An energy-conserving model of freezing variably-saturated soil

Wed, 11 Aug 2010 00:00:00 +0200

An energy-conserving model of freezing variably-saturated soil

The Cryosphere Discussions, 4, 1243-1276, 2010

Author(s): M. Dall'Amico, S. Endrizzi, S. Gruber, and R. Rigon

In this paper we provide a method for solving the energy equation in freezing soil. The solver is linked with the solution of Richards equation, and therefore able to approximate water movement near the liquid-solid phase transition. The equations show non-linear characteristics causing oscillatory behavior in the solution close to the phase transition, when normal methods of iterative integration, as Newton or Picard, are used. Thus, a globally convergent Newton method has been implemented to achieve convergence. The method is tested by comparison with an analytical solution to the Stefan problem and by comparison with experimental data derived from literature.

A comparison of basal reflectivity and ice velocity in East Antarctica

Wed, 11 Aug 2010 00:00:00 +0200

A comparison of basal reflectivity and ice velocity in East Antarctica

The Cryosphere Discussions, 4, 1225-1241, 2010

Author(s): R. W. Jacobel, K. E. Lapo, J. R. Stamp, B. W. Youngblood, B. C. Welch, and J. L. Bamber

Ground-based radio echo sounding data acquired along the 1700 km US-ITASE traverse have been used to determine ice attenuation and relative basal reflectivity across the major catchments funneling ice from East Antarctica to the Ross Ice Shelf. We find that basal reflectivity varies locally by up to 40 dB which we interpret as due to changes in the phase state at the bed. Some, though not all, areas of high local reflectivity are observed to have flat-lying bed reflections indicative of sub-glacial lakes. We compare basal reflectivity to ice balance velocity and find a general association of higher flow speeds with high radar reflection strength. This set of observations from two independent remotely sensed geophysical data sets extends the range of field observations to the interior of East Antarctica and confirms the importance of basal lubrication on modulating the ice dynamics of the largest ice sheet on the planet.

Freshwater flux to Sermilik Fjord, SE Greenland

Fri, 30 Jul 2010 00:00:00 +0200

Freshwater flux to Sermilik Fjord, SE Greenland

The Cryosphere Discussions, 4, 1195-1224, 2010

Author(s): S. H. Mernild, G. E. Liston, I. M. Howat, Y. Ahn, K. Steffen, B. Hasholt, B. H. Jakobsen, B. Fog, and D. van As

Fluctuations in terrestrial surface freshwater flux to Sermilik Fjord, SE Greenland, were simulated and analyzed. SnowModel, a state-of-the-art snow-evolution, snow and ice melt, and runoff modeling system, was used to simulate the temporal and spatial terrestrial runoff distribution to the fjord based on observed meteorological data (1999–2008) from stations located on and around the Greenland Ice Sheet (GrIS). Simulated runoff was compared and verified against independent glacier catchment runoff observations (1999–2005). Modeled runoff to Sermilik Fjord was highly variable, ranging from 2.9×10⁹ m³ y⁻¹ in 1999 to 5.9×10⁹ m³ y⁻¹ in 2005. The uneven spatial runoff distribution produced an areally-averaged annual maximum runoff at the Helheim glacier terminus of more than 3.8 m w.eq. The sub-catchment runoff of the Helheim glacier region accounted for 25% of the total runoff to Sermilik Fjord. The runoff distribution from the different sub-catchments suggested a strong influence from the spatial variation in glacier coverage. To assess the Sermilik Fjord freshwater flux, simulated terrestrial runoff and net precipitation (precipitation minus evaporation and sublimation) for the fjord area were combined with satellite-derived ice discharge and subglacial geothermal and frictional melting due to basal ice motion. A terrestrial freshwater flux of ~40.4×10⁹ m³ y⁻¹ was found for Sermilik Fjord, with an 11% contribution originated from surface runoff. For the Helheim glacier sub-catchment only 4% of the flux originated from terrestrial surface runoff.

Comparison of direct and geodetic mass balances on a multi-annual time scale

Fri, 23 Jul 2010 00:00:00 +0200

Comparison of direct and geodetic mass balances on a multi-annual time scale

The Cryosphere Discussions, 4, 1151-1194, 2010

Author(s): A. Fischer

Glacier mass balance is measured with the direct or the geodetic method. In this study, the geodetic mass balances of six Austrian glaciers in 19 periods between 1953 and 2006 are compared to the direct mass balances in the same periods. The mean annual geodetic mass balance for all periods is −0.5 m w.e./year. The mean difference between the geodetic and the direct data is −0.7 m w.e., the minimum −7.3 m w.e. and the maximum 5.6 m w.e. The accuracy of geodetic mass balance resulting from the accuracy of the DEMs ranges from 2 m w.e. for photogrammetric data to 0.002 m w.e. for LIDAR data. Basal melt, seasonal snow cover and density changes of the surface layer contribute up to 0.7 m w.e. for the period of 10 years to the difference to the direct method. The characteristics of published data of Griesgletscher, Gulkana Glacier, Lemon Creek glacier, South Cascade, Storbreen, Storglaciären, and Zongo Glacier is similar to these Austrian glaciers. For 26 analyzed periods with an average length of 18 years the mean difference between the geodetic and the direct data is −0.4 m w.e., the minimum −7.2 m w.e. and the maximum 3.6 m w.e. Longer periods between the acquisition of the DEMs do not necessarily result in a higher accuracy of the geodetic mass balance. Specific glaciers show specific trends of the difference between the direct and the geodetic data according to their type and state. In conclusion, geodetic and direct mass balance data are complementary, but differ systematically.

Spatial and temporal variability in summer snow pack in the Dronning Maud Land, Antarctica

Thu, 22 Jul 2010 00:00:00 +0200

Spatial and temporal variability in summer snow pack in the Dronning Maud Land, Antarctica

The Cryosphere Discussions, 4, 1107-1150, 2010

Author(s): T. Vihma, O.-P. Mattila, R. Pirazzini, and M. M. Johansson

Snow temperature, density, and layering were measured in four summers in the Dronning Maud Land, Antarctica. Data from a 310-km-long transect showed that the most homogeneous snow pack located in the Riiser-Larsen Ice Shelf, while horizontal gradients in snow density, temperature, and hardness were larger in the escarpment region. In the local scale, day-to-day temporal variability dominated the standard deviation of snow temperature, while the diurnal cycle was next important, and horizontal variability in the scale of 0.4 to 10 m was the smallest component. The day-to-day and total small-scale variability decreased exponentially with depth with an e-folding depth at 0.25 to 0.30 m. Snow temperature depended on the cloud cover in the uppermost 0.30 m and snow density in the uppermost 0.10 m. Both in the intra-pit and transect scales, the ratio of horizontal to temporal variability increased with depth. In the intra-pit scale the temporal variability in snow density exceeded the horizontal variability throughout the uppermost 0.50 m layer, but in the 100-km scale only in the uppermost centimetres. The horizontal standard deviation of snow density increased rapidly between the scales of 0.4 and 2 m, and much more gradually from 10¹ to 10² m.

Parameterising the grounding line in ice sheet models

Mon, 19 Jul 2010 00:00:00 +0200

Parameterising the grounding line in ice sheet models

The Cryosphere Discussions, 4, 1063-1105, 2010

Author(s): R. M. Gladstone, A. J. Payne, and S. L. Cornford

Realistic predictions of the behaviour of marine ice sheets require that models are able to robustly simulate grounding line migration. Fixed grid ice sheet models have been shown to exhibit inconsistent and hence unreliable grounding line migration behaviour, except at very high resolution not achievable in whole ice sheet simulations. In this study we present several different approaches to parameterising the grounding line. These are distinguished by choices regarding the ice thickness profile from the last grounded to the first floating grid point, and how this profile is allowed to impact on the gravitational driving stress and basal drag. We demonstrate that the most obvious choice of thickness parameterisation, linear interpolation from the last grounded to the first floating grid point, is not the most effective. We show that use of a grounding line parameterisation greatly improves performance, and that choice of a better grounding line parameterisation over a simpler one can bring further improvements, in terms of both accuracy and more self consistent behaviour, comparable to halving the grid resolution. The approach presented here to parameterising the grounding line does not in itself completely solve the grounding line problem, however it reduces requirements in terms of grid resolution. The parameterisations are presented in the context of a 1-D "shelfy-stream" flow-line model, but could be extended to cope with more than one dimension and other model formulations.

Rapid changes of the ice mass configuration in the dynamic Diablotins ice cave – Fribourg Prealps, Switzerland

Mon, 19 Jul 2010 00:00:00 +0200

Rapid changes of the ice mass configuration in the dynamic Diablotins ice cave – Fribourg Prealps, Switzerland

The Cryosphere Discussions, 4, 1035-1061, 2010

Author(s): S. Morard, M. Bochud, and R. Delaloye

The Gouffre des Diablotins is a deep cave system located in the Swiss Prealps. In 1991, the entrance zone of the cave was almost free of ice. Nevertheless ice volume sharply increased in 1994, plugging almost totally the gallery from the lower entrance. The ice cave have also experience flooded period between 1996 and 2007, and very heterogeneous ice surface morphology and textures have formed. Continuous cave climate measurements initiated in 2009 showed the predominant role of winter atmospheric air conditions to drive both the efficiency of chimney-effect circulation and seasonal modifications of the ice mass. Main part of the ice loss is currently due to sublimation in wintertime.

Cryogenic and non-cryogenic pool calcites reflect alternating permafrost and interglacial periods (Breitscheid-Erdbach Cave, Germany)

Thu, 15 Jul 2010 00:00:00 +0200

Cryogenic and non-cryogenic pool calcites reflect alternating permafrost and interglacial periods (Breitscheid-Erdbach Cave, Germany)

The Cryosphere Discussions, 4, 1011-1034, 2010

Author(s): D. K. Richter, P. Meissner, A. Immenhauser, U. Schulte, and I. Dorsten

Weichselian cryogenic calcites collected in what is referred to as the "Rätselhalle" of the Breitscheid-Erdbach Cave were structurally classified as rhombohedral crystal and spherulitic crystal sinters. The carbon and oxygen isotopic composition of these precipitates corresponds to those of known cryogenic calcites of slow genesis of Central European caves (δ¹³C=+0.6 and −7.3‰; δ¹⁸O=−6.9 to −18.0‰). The variant carbon and oxygen isotope pattern differing between different caves is attributed to cave specific ventilation. Particularly, Breitscheid cryogenic calcites reflect mean levels of cave ventilation. By petrographic and geochemical comparisons of Weichselian cryogenic calcite with recent to sub-recent precipitates as well as Weichselian non-cryogenic calcites of the same locality, a model for the precipitation of these calcites is proposed. While the recent and sub-recent pool-calcites isotopically match the geochemistry of interglacial speleothems (stalagmites, etc.), isotope ratios of Weichselian non-cryogenic pool-calcites reflect cooler conditions. Weichselian cryogenic calcites show a trend towards ¹⁸O-depleted values with higher carbon isotope ratios reflecting slow freezing of the precipitating solution. In essence, the isotope geochemistry of the Weichselian calcites reflects the climate history changing from overall initial permafrost (glacial) conditions to an interglacial and subsequently to renewed permafrost conditions. The last stage then grades into the present-day warm period. Judging from the data compiled here, the last permafrost stage is followed by only one interglacial. During this interglacial, the cave ice melted and non-cryogenic Weichselian calcite precipitates were deposited on the cave ground or on fallen blocks, respectively.

Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard

Wed, 14 Jul 2010 00:00:00 +0200

Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard

The Cryosphere Discussions, 4, 981-1010, 2010

Author(s): M. A. G. den Ouden, C. H. Reijmer, V. Pohjola, R. S. W. van de Wal, J. Oerlemans, and W. Boot

Precise measurements of ice-flow velocities are necessary for a proper understanding of the dynamical response of glaciers to climate change. We use stand-alone single-frequency GPS receivers for this purpose. They are designed to operate unattended for multiple years, allowing uninterrupted measurements for long periods with a reasonable temporal resolution. We present the system and illustrate its functioning using data from 9 GPS receivers deployed on Nordenskiöldbreen, Svalbard, for the period 2006–2009. The accuracy of the receivers is 1.62 m 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 in the NBRef data is explained by the atmospheric influence on the GPS signal and by the GPS satellite configuration. 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 55 m/yr at stations on the central flow-line. On weekly to monthly time-scales we observe a peak in the flow velocities (60 to 90 m/yr) 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 in combination with the relatively small distance (max. ±13 km) between the stations.