| 1. |
- Aartsen, M. G., et al.
(författare)
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South Pole glacial climate reconstruction from multi-borehole laser particulate stratigraphy
- 2013
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:218, s. 1117-1128
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Tidskriftsartikel (refereegranskat)abstract
- The IceCube Neutrino Observatory and its prototype, AMANDA, were built in South Pole ice, using powerful hot-water drills to cleanly bore >100 holes to depths up to 2500 m. The construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques. We made high-resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010. The South Pole laser logs are among the most clearly resolved measurements of Antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail. Here we use manual and algorithmic matching to synthesize our South Pole measurements with ice-core and logging data from Dome C, East Antarctica. We derive impurity concentration, precision chronology, annual-layer thickness, local spatial variability, and identify several widespread volcanic ash depositions useful for dating. We also examine the interval around similar to 74 ka recently isolated with radiometric dating to bracket the Toba (Sumatra) supereruption.
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| 2. |
- Aguilar, J. A., et al.
(författare)
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In situ, broadband measurement of the radio frequency attenuation length at Summit Station, Greenland
- 2022
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 68:272, s. 1234-1242
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Tidskriftsartikel (refereegranskat)abstract
- Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 10(17) electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length L-alpha. We find an approximately linear dependence of L-alpha on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: < L-alpha > = ((1154 +/- 121) - (0.81 +/- 0.14) (v/MHz)) m for frequencies v is an element of [145 - 3501 MHz.
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| 3. |
- Ahlström, A. P., et al.
(författare)
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Historically unprecedented global glacier decline in the early 21st century
- 2015
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 61:228, s. 745-
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Tidskriftsartikel (refereegranskat)abstract
- Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (similar to 42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (similar to 5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.
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| 4. |
- Askebjer, P., et al.
(författare)
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On the age vs depth and optical clarity of deep ice at South Pole
- 1995
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 41:139, s. 445-454
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Tidskriftsartikel (refereegranskat)abstract
- The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800 to 1000 m in ice at the South Pole. During the 1995-96 season an additional six strings will be deployed at greater depths. Provided absorption, scattering, and refraction of visible light are sufficiently small, the trajectory of a muon into which a neutrino converts can be determined by using the array of phototubes to measure the arrival times of \v{C}erenkov light emitted by the muon. To help in deciding on the depth for implantation of the six new strings, we discuss models of age vs depth for South Pole ice, we estimate mean free paths for scattering from bubbles and dust as a function of depth, and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hydrate inclusions and normal ice. We conclude that the depth interval 1600 to 1800 m will be suitably transparent for the next six AMANDA strings and, moreover, that the interval 1600 to 2100 m will be suitably transparent for a future 1-km 3 observatory except possibly in a region a few tens of meters thick at a depth corresponding to a peak in the dust concentration at 60 kyr BP.
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| 5. |
- ASKEBJER, P, et al.
(författare)
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ON THE AGE VS DEPTH AND OPTICAL CLARITY OF DEEP ICE AT THE SOUTH-POLE
- 1995
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Ingår i: JOURNAL OF GLACIOLOGY. - : INT GLACIOL SOC. - 0022-1430. ; 41:139, s. 445-454
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The first four strings of phototubes for the AMANDA high-energy neutrino observatory are now frozen in place at a depth of 800-1000 m in ice at the South Pole. During the 1995-96 season, as many as six more strings will be deployed at greater depths. Prov
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| 6. |
- Barnett, Jamie, 1996-, et al.
(författare)
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Modelled dynamic retreat of Kangerlussuaq Glacier, East Greenland, strongly influenced by the consecutive absence of an ice mélange in Kangerlussuaq Fjord
- 2023
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Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 69:275, s. 433-444
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Tidskriftsartikel (refereegranskat)abstract
- Mass loss at the Greenland Ice Sheet is influenced by atmospheric processes controlling its surface mass balance, and by submarine melt and calving where glaciers terminate in fjords. There, an ice mélange - a composite matrix of calved ice bergs and sea ice - may provide a buttressing force on a glacier terminus and control terminus dynamics. Kangerlussuaq Glacier is a major outlet of the Greenland Ice Sheet, for which recent major retreat events in 2004/2005 and 2016-2018 coincided with the absence of an ice mélange in Kangerlussuaq Fjord. To better understand the response of Kangerlussuaq Glacier to climatic and oceanic drivers, a 2D flowline model is employed. Results indicate that an ice mélange buttressing force exerts a major control on calving frequency and rapid retreat. When an ice mélange forms in Kangerlussuaq Fjord, it provides stabilising forces and conditions favourable for winter terminus re-advance. When it fails to form during consecutive years, model results indicate that Kangerlussuaq Glacier is primed to retreat into the large overdeepenings in Kangerlussuaq Fjord, and to terminus positions more than 30 km farther inland, implying that excessive mass loss from Kangerlussuaq Glacier by the year 2065 cannot be excluded.
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| 7. |
- Beaudon, Emelie, et al.
(författare)
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Lomonosovfonna and Holtedahlfonna ice cores reveal east west disparities of the Spitsbergen environment since AD 1700
- 2013
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:218, s. 1069-1083
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Tidskriftsartikel (refereegranskat)abstract
- An ice core extracted from Holtedahlfonna ice cap, western Spitsbergen, record spanning the period 1700–2005, was analyzed for major ions. The leading empirical orthogonal function (EOF) component is correlated with an index of summer melt (log([Na + ]/[Mg 2+ ]) from 1850 and shows that almost 50% of the variance can be attributed to seasonal melting since the beginning of the industrial revolution. The Holtedahlfonna d 18 O value is less negative than in the more easterly Lomonosovfonna ice core, suggesting that moist air masses originate from a closer source, most likely the Greenland Sea. During the Little Ice Age the lower methanesulfonic acid (MSA) concentration and MSA non-sea-salt sulfate fraction are consistent with the Greenland Sea as the main source for biogenic ions in the ice cores. Both the melt index and the MSA fraction suggest that the early decades of the 18th century may have exhibited the coldest summers of the last 300 years in Svalbard. Ammonium concentrations rise from 1880, which may result from the warming of the Greenland Sea or from zonal differences in atmospheric pollution transport over Svalbard. During winter, neutralized aerosols are trapped within the tropospheric inversion layer, which is usually weaker over open seas than over sea ice, placing Holtedahlfonna within the inversion more frequently than Lomonosovfonna.
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| 8. |
- Campbell, Ian, et al.
(författare)
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The evolution of surface flow stripes and stratigraphic folds within Kamb Ice Stream : why don't they match?
- 2008
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:186, s. 421-427
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Tidskriftsartikel (refereegranskat)abstract
- Flow stripes seen in satellite imagery of ice streams and ice shelves are caused by surface undulations with kilometer-scale spacing and meter-scale relief and generally indicate current or recent fast ice flow. On a similar scale, folding of internal ice stratigraphy depicted in cross-flow icepenetrating radar profiles is also a common occurrence in ice streams, suggesting a possible relationship between the two sets of features. We have traced surface flow stripes in RADARSAT and MODIS imagery on Kamb Ice Stream, West Antarctica, from the onset of streaming flow into the near-stagnant trunk. We compare the morphology and evolution of the surface flow stripes to the folds seen in the internal stratigraphy in cross-ice-stream radar profiles. We find essentially no correspondence in the observed locations or spacings between the radar internal layer folds at depths greater than 100 m and the flow stripes on the surface. The gap in the radar data and the surface mappings in the top 100m of firn prevents a precise depiction of how the flow stripes and fold patterns at depth diverge. We explore hypotheses about how flow stripes and internal stratigraphic folds can originate and evolve differently as ice flows downstream. We suggest that flow stripes are subject to surface processes that can modify their morphology independently of the internal stratigraphy, leading to changes in the pattern of flow stripes relative to the internal layers below.
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| 9. |
- Cerrato, Riccardo, et al.
(författare)
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Pinus cembra L. tree-ring data as a proxy for summer mass-balance variability of the Careser Glacier (Italian Rhaetian Alps)
- 2020
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Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 66:259, s. 714-726
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © The Author(s), 2020. Published by Cambridge University Press. Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (Bs) of an Alpine glacier. The MXD-based Bs well correlates with a Bs reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (Bn) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based Bn well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the 'divergence problem' responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.
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| 10. |
- Clason, Caroline C., et al.
(författare)
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Modelling Late Weichselian evolution of the Eurasian ice sheets forced by surface meltwater-enhanced basal sliding
- 2014
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:219, s. 29-40
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Tidskriftsartikel (refereegranskat)abstract
- We simulated the Late Weichselian extent and dynamics of the Eurasian ice sheets using theshallow-ice approximation ice-sheet model SICOPOLIS. Our simulated Last Glacial Maximum ice-sheetextents closely resemble geomorphological reconstructions, and areas of modelled fast flow areconsistent with the known locations of palaeo-ice streams. Motivated by documented velocity responseto increased meltwater inputs on Greenland, we tested the sensitivity of the simulated ice sheet to thesurface meltwater effect (SME) through a simple parameterization relating basal sliding to local surfacemelt rate and ice thickness. Model runs including the SME produce significantly reduced ice volumeduring deglaciation, with maximum ice surface velocities much greater than in similar runs that neglectthe SME. We find that the simple treatment of the SME is not applicable across the whole ice sheet;however, our results highlight the importance of the SME for dynamic response to increased melting.The southwest sector of the Scandinavian ice sheet is most sensitive to the SME, with fast flow in theBaltic ice stream region shutting off by 15 kaBP when the SME is turned on, coincident with a retreat ofthe ice-margin position into the Gulf of Bothnia.
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| 11. |
- Das, Indrani, et al.
(författare)
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21st-century increase in glacier mass loss in the Wrangell Mountains, Alaska, USA, from airborne laser altimetry and satellite stereo imagery
- 2014
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:220, s. 283-293
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Tidskriftsartikel (refereegranskat)abstract
- Alaskan glaciers are among the largest regional contributors to sea-level rise in the latter half of the 20th century. Earlier studies have documented extensive and accelerated ice wastage in most regions of Alaska. Here we study five decades of mass loss on high-elevation, land-terminating glaciers of the Wrangell Mountains (similar to 4900 km(2)) in central Alaska based on airborne center-line laser altimetry data from 2000 and 2007, a digital elevation model (DEM) from ASTER and SPOT5, and US Geological Survey topographic maps from 1957. The regional mass-balance estimates derived from center-line laser altimetry profiles using two regional extrapolation techniques agree well with that from DEM differencing. Repeat altimetry measurements reveal accelerated mass loss over the Wrangell Mountains, with the regional mass-balance rate evolving from -0.07 +/- 0.19 m w.e. a(-1) during 1957-2000 to -0.24 +/- 0.16 m w.e. a(-1) during 2000-07. Nabesna, the largest glacier in this region (similar to 1056 km(2)), lost mass four times faster during 2000-07 than during 1957-2000. Although accelerated, the mass change over this region is slower than in other glacierized regions of Alaska, particularly those with tidewater glaciers. Together, our laser altimetry and satellite DEM analyses demonstrate increased wastage of these glaciers during the last 50 years.
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| 12. |
- De Angelis, Hernán, 1974-
(författare)
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Hypsometry and sensitivity of the mass balance to changes in equilibrium-line altitude : the case of the Southern Patagonia Icefield
- 2014
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:219, s. 14-28
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Tidskriftsartikel (refereegranskat)abstract
- We study the relation between glacier hypsometry and sensitivity of mass-balance rate to changes in equilibrium line altitude (ELA). Our aim is to assess whether hypsometry can be reliably used as an estimator of the sensitivity of unmeasured glaciers to changes in ELA. We express the sensitivity of mass-balance rate to ELA, \(d\dot{B}/dELA\), as a function of accumulation-area ratio (AAR), its derivative against altitude, \(dAAR/dELA\), and mass-balance functions of ELA. We then apply the concept to 139 glaciers in the Southern Patagonia Icefield for which we derive hypsometry and AAR, and analyze the influence of hypsometry on their mass-balance rate sensitivity. We confirm that glaciers where the bulk of area is located above the ELA are the least sensitive, whereas those where the bulk of area is located below the ELA are the most sensitive. Glaciers with unimodal hypsometric curves where the peak of area fraction is around the present ELA, and glaciers with bi- or multimodal area distributions, with the ELA located approximately between the bulges, have intermediate sensitivities. We conclude that hypsometry can be used as a first order estimator of the mass-balance rate sensitivity to ELA change.
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| 13. |
- Deschamps-Berger, Cesar, et al.
(författare)
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Closing the mass budget of a tidewater glacier : the example of Kronebreen, Svalbard
- 2019
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Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 65:249, s. 136-148
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we combine remote sensing, in situ and model-derived datasets from 1966 to 2014 to calculate the mass-balance components of Kronebreen, a fast-flowing tidewater glacier in Svalbard. For the well-surveyed period 2009-2014, we are able to close the glacier mass budget within the prescribed errors. During these 5 years, the glacier geodetic mass balance was -0.69 +/- 0.12 m w.e. a(-1), while the mass budget method led to a total mass balance of -0.92 +/- 0.16 m w.e. a(-1), as a consequence of a strong frontal ablation (-0.78 +/- 0.11 m w.e. a(-1) ), and a slightly negative climatic mass balance (-0.14 +/- 0.11 m w.e. a(-1) ). The trend towards more negative climatic mass balance between 1966-1990 (+0.20 +/- 0.05 m w.e. a(-1) ) and 2009-2014 is not reflected in the geodetic mass balance trend. Therefore, we suspect a reduction in ice-discharge in the most recent period. Yet, these multidecadal changes in ice-discharge cannot be measured from the available observations and thus are only estimated with relatively large errors as a residual of the mass continuity equation. Our study presents the multidecadal evolution of the dynamics and mass balance of a tidewater glacier and illustrates the errors introduced by inferring one unmeasured mass-balance component from the others.
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| 14. |
- Dyurgerov, Mark, et al.
(författare)
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A new index of glacier area change: a tool for glacier monitoring
- 2009
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 55:192, s. 710-716
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Tidskriftsartikel (refereegranskat)abstract
- Since the mid-19th century, most glaciers have been losing area and volume. This loss of area has not been homogeneous in time and space, and direct observations are sparse, making regional and global estimates of glacier change difficult. This paper focuses on developing a single index for monitoring glacier change, one that would be particularly useful for remote-sensing applications. We combine the results of direct glacier mass-balance observations B, total glacier area S and accumulation area S-c derived from maps or remotely sensed images. Using the accumulation-area ratio (AAR = S-c/S), we note the differences between observed AAR, time-averaged < AAR > and the equilibrium state AAR(0), as determined by its value at B = 0 from a regression of B(AAR). We suggest that alpha(d) = (< AAR > - AAR(0))/ AAR(0) quantifies the difference between the currently observed state of glaciers and their equilibrium state and measures the delay in the dynamic response of S relative to the climatic response of S-c. Using all available observations for the period 1961-2004, alpha(d) approximate to -65% for tropical glaciers, which implies their rapid shrinkage as S continues to decrease and 'catch up' with S-c. During the same period, mid-latitude and polar glaciers show less negative values Of alpha(d). Of 86 glaciers from all latitudes and regions, only 11 show positive alpha(d) at any time between 1961 and 2004. Averaged over 1961-2004, alpha(d) is -15.1 +/- 2.2%, and < B > is -360 +/- 42 mm a(-1) w.e. Values for AAR(0) range between about 40% and 80%, but the bulk of the equilibrium values are between 50% and 60%. The average AAR(0) is 57.9 +/- 0.9% and has remained stable over time (the equilibrium AAR has not changed with climate). Overall, the observed negative alpha(d) suggests a committed retreat of glaciers and their continuing contribution to sea level even if global temperature is held constant.
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| 15. |
- Foy, N., et al.
(författare)
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Recent volume and area changes of Kaskawulsh Glacier, Yukon, Canada
- 2011
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57:203, s. 515-525
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Tidskriftsartikel (refereegranskat)abstract
- Recent surface elevation changes of Kaskawulsh Glacier, Yukon, Canada, are quantified by comparing an air-photo derived DEM from 1977 and airborne lidar measurements from 1995, 2000 and 2007. Surface-area changes are assessed using historical aerial photography from 1956 and satellite imagery from 1977 to 2007. Combined, these measurements provide some of the first detailed records of volume change of a large Yukon glacier. Between 1977 and 2007, Kaskawulsh Glacier underwent a decrease in area of 1.53% and a decrease in volume of 3.27–5.94 km3 w.e.). The terminus also retreated by 655 m over the period 1956–2007. There was relatively minor volume change over the period 1977–95 (<+0.01 km3 w.e.a−1), while over the periods 1995–2000 and 2000–07 volume losses occurred at a relatively constant rate of −0.51 and −0.50 km3 a−1 w.e., respectively. Since 1995, thinning has been prominent throughout the ablation zone, while relative stability and even slight thickening has occurred in the accumulation zone. These findings are similar to those recently observed at other nearby Alaskan glaciers.
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| 16. |
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| 17. |
- Gusmeroli, Alessio, et al.
(författare)
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Twenty years of cold surface layer thinning at Storglaciaren, sub-Arctic Sweden, 1989-2009
- 2012
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:207, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the changes in the thermal structure of the polythermal glacier Storglaciaren, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009. Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciaren has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 +/- 0.24 m a(-1). We suggest that the thinning of the cold layer at Storglaciaren is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
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| 18. |
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| 19. |
- Hills, Benjamin H., et al.
(författare)
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Radar attenuation demonstrates advective cooling in the Siple Coast ice streams
- 2022
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 69:275, s. 566-576
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Tidskriftsartikel (refereegranskat)abstract
- Ice streams are warmed by shear strain, both vertical shear near the bed and lateral shear at the margins. Warm ice deforms more easily, establishing a positive feedback loop in an ice stream where fast flow leads to warm ice and then to even faster flow. Here, we use radar attenuation measurements to show that the Siple Coast ice streams are colder than previously thought, which we hypothesize is due to along-flow advection of cold ice from upstream. We interpret the attenuation results within the context of previous ice-temperature measurements from nearby sites where hot-water boreholes were drilled. These in-situ temperatures are notably colder than model predictions, both in the ice streams and in an ice-stream shear margin. We then model ice temperature using a 1.5-dimensional numerical model which includes a parameterization for along-flow advection. Compared to analytical solutions, we find depth-averaged temperatures that are colder by 0.7°C in the Bindschadler Ice Stream, 2.7°C in the Kamb Ice Stream and 6.2–8.2°C in the Dragon Shear Margin of Whillans Ice Stream, closer to the borehole measurements at all locations. Modelled cooling corresponds to shear-margin thermal strengthening by 3–3.5 times compared to the warm-ice case, which must be compensated by some other weakening mechanism such as material damage or ice-crystal fabric anisotropy.
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| 20. |
- Hock, Regine, 1960-, et al.
(författare)
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GlacierMIP - A model intercomparison of global-scale glacier mass-balance models and projections
- 2019
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 65:251, s. 453-467
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Tidskriftsartikel (refereegranskat)abstract
- Global-scale 21st-century glacier mass change projections from six published global glacier models are systematically compared as part of the Glacier Model Intercomparison Project. In total 214 projections of annual glacier mass and area forced by 25 General Circulation Models (GCMs) and four Representative Concentration Pathways (RCP) emission scenarios and aggregated into 19 glacier regions are considered. Global mass loss of all glaciers (outside the Antarctic and Greenland ice sheets) by 2100 relative to 2015 averaged over all model runs varies from 18 +/- 7% (RCP2.6) to 36 +/- 11% (RCP8.5) corresponding to 94 +/- 25 and 200 +/- 44 mm sea-level equivalent (SLE), respectively. Regional relative mass changes by 2100 correlate linearly with relative area changes. For RCP8.5 three models project global rates of mass loss (multi-GCM means) of >3 mm SLE per year towards the end of the century. Projections vary considerably between regions, and also among the glacier models. Global glacier mass changes per degree global air temperature rise tend to increase with more pronounced warming indicating that mass-balance sensitivities to temperature change are not constant. Differences in glacier mass projections among the models are attributed to differences in model physics, calibration and downscaling procedures, initial ice volumes and varying ensembles of forcing GCMs.
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| 21. |
- Holmes, Felicity Alice, 1995-, et al.
(författare)
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Modelled frontal ablation and velocities at Kronebreen, Svalbard, are sensitive to the choice of submarine melt rate scenario
- 2023
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652.
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Tidskriftsartikel (refereegranskat)abstract
- Both submarine melt and calving are important for the overall mass balance of marine-terminating glaciers, but uncertainty is rife with regards to the magnitude of the processes. Modelling allows for these processes to be investigated without the need to visit inaccessible ice marginal zones. This study looks at the impact of different submarine melt and sea-ice back pressure scenarios on modelled calving activity and dynamics at Kronebreen, Svalbard, by running separate summer and winter simulations with various submarine melt parameterisations and sea-ice characteristics. It is found that submarine melt is an important driver of seasonal variation in modelled glacier dynamics and calving activity, with the choice of sliding law also exerting a significant influence on results.
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| 22. |
- Hooke, Roger LeB., et al.
(författare)
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Intra-seasonal changes in deformation profiles revealed by borehole studies, Storglaciären, Sweden.
- 1992
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 38:130, s. 348-358
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Tidskriftsartikel (refereegranskat)abstract
- In 1985, 1987 and 1988, we measured deformation of bore holes in the ablation zone of Storglaciaren. A different hole was used each year. Deformation profiles were determined for four consecutive time periods between mid-July and early September. All three holes were in an area where the glacier lies in an overdeepened part of the bed, up-glacier from a riegel. The first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin. Despite large standard errors, variations in the deformation profiles during the melt season are broadly consistent with other data. We thus believe that they are real, and that they reflect changes in the stress field resulting from changes in drag at the bed. A decrease in drag early in the melt season, coupled with convergence of the bed contours towards the riegel, is believed to be responsible for a previously documented increase in vertical velocity just upglacier from the riegal at this time of year. Also noteworthy, but perhaps problematical, was an abrupt transverse shear of",! m at a depth of ",25 m near the center of the glacier inJuly 1985. The shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier.
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| 23. |
- Huss, Matthias, et al.
(författare)
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Conventional versus reference-surface mass balance
- 2012
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:208, s. 278-286
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Tidskriftsartikel (refereegranskat)abstract
- Glacier surface mass balance evaluated over the actual glacier geometry depends not only on climatic variations, but also on the dynamic adjustment of glacier geometry. Therefore, it has been proposed that reference-surface balances calculated over a constant glacier hypsometry are better suited for climatic interpretation. Here we present a comparison of 82 year modelled time series (1926-2008) of conventional and reference-surface balance for 36 Swiss glaciers. Over this time period the investigated glaciers have lost 22% of their area, and ice surface elevation close to the current glacier terminus has decreased by 78 m on average. Conventional balance in the last decade, at -0.91 m w.e.a(-1), is 0.14 m w.e.a(-1) less negative than the reference-surface balance. About half of the negative (stabilizing) feedback on mass balance due to glacier terminus retreat is compensated by more negative mass balances due to surface lowering. Short-term climatic variability is clearly reflected in the conventional mass-balance series; however, the magnitude of the long-term negative trend is underestimated compared to that found in the reference-surface balance series. Both conventional and reference-surface specific balances show large spatial variability among the 36 glaciers.
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| 24. |
- Huss, Matthias, et al.
(författare)
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Glacier-dammed lake outburst events of Gornersee, Switzerland
- 2007
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 53:181, s. 189-200
-
Tidskriftsartikel (refereegranskat)abstract
- Gornersee is an ice marginal lake, which drains almost every year subglacially within a few days. We present an analysis of the lake outburst events between 1950 and 2005, as well as results of detailed field investigations related to the lake drainage in 2004 and 2005. The latter included measurements of lake geometry, water pressure in nearby boreholes, and glacier surface motion. A distributed temperature-index melt model coupled to a linear-reservoir runoff model is used to calculate hourly discharge from the catchment of Gornergletscher in order to distinguish between the melt-precipitation component and the outburst component of the discharge hydrograph. In this way, drainage volume and timing are determined. There is a clear trend since 1950 for the outburst flood to occur earlier in the melt season, though lacking any relation to lake discharge volumes. Peak discharges from the lake lie significantly below the values obtained with the empirical relation proposed by Clague and Mathews (1973). The shapes of the 2004 and 2005 lake outflow hydrographs differ substantially, thereby suggesting different drainage mechanisms. From water balance onsiderations we infer a leakage of the glacier-dammed lake starting one week prior to the lake outburst in 2005. During the drainage events up to 50% of lake water is temporarily stored in the glacial system causing substantial uplifts of the glacier surface.
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| 25. |
- Ingvander, Susanne, 1979-, et al.
(författare)
-
Method study : Grain size sampling and digital object oriented image analysis for explanation of snow grain size, shape and distribution
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652.
-
Tidskriftsartikel (refereegranskat)abstract
- We have developed a digital image processing method for snow particle size and shape analysis suitable for quick and reliable analysis in the eld. Snow particle size is an important parameter strongly aecting snow cover albedo from seasonally snow covered areas and ice sheets. It is also important in remote sensing analysis because it influences the reflectance and scattering properties of the snow. Alternatively traditional methods based on visual inspection of samples can be used but they do not yield quantitative data. Our method provides an additional alternative to both simpler and more complex methods by providinga tool that limits the subjective eect of the visual analysis and provides a quantitativeparticle size distribution. The method involves image analysis software and field efficient instrumentation in order to develop a complete process-chain easily implemented under field conditions. The results from the analysis are a two dimensional analysis of particle size, shape and distributions for each sample. The developed method improves snow particle analysis being quantitative, reproducible and applicable for dierent types of eld sites.
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| 26. |
- Kassab, Christine M., et al.
(författare)
-
Formation and evolution of an extensive blue ice moraine in central Transantarctic Mountains, Antarctica
- 2020
-
Ingår i: Journal of Glaciology. - : CAMBRIDGE UNIV PRESS. - 0022-1430 .- 1727-5652. ; 66:255, s. 49-60
-
Tidskriftsartikel (refereegranskat)abstract
- Mount Achernar moraine is a terrestrial sediment archive that preserves a record of ice-sheet dynamics and climate over multiple glacial cycles. Similar records exist in other blue ice moraines elsewhere on the continent, but an understanding of how these moraines form is limited. We propose a model to explain the formation of extensive, coherent blue ice moraine sequences based on the integration of ground-penetrating radar (GPR) data with ice velocity and surface exposure ages. GPR transects (100 and 25 MHz) both perpendicular and parallel to moraine ridges at Mount Achernar reveal an internal structure defined by alternating relatively clean ice and steeply dipping debris bands extending to depth, and where visible, to the underlying bedrock surface. Sediment is carried to the surface from depth along these debris bands, and sublimates out of the ice, accumulating over time (>300 ka). The internal pattern of dipping reflectors, combined with increasing surface exposure ages, suggest sequential exposure of the sediment where ice and debris accretes laterally to form the moraine. Subsurface structure varies across the moraine and can be linked to changes in basal entrainment conditions. We speculate that higher concentrations of debris may have been entrained in the ice during colder glacial periods or entrained more proximal to the moraine sequence.
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| 27. |
- Kienholz, Christian, et al.
(författare)
-
A new semi-automatic approach for dividing glacier complexes into individual glaciers
- 2013
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:217, s. 925-937
-
Tidskriftsartikel (refereegranskat)abstract
- Many glaciological and hydrological studies require outlines of individual glaciers rather than total ice cover. Here we develop a new semi-automatic algorithm that uses a digital elevation model (DEM) and outlines of glacier complexes to calculate the extents of individual glaciers. The algorithm first applies hydrological modeling tools to a modified DEM to calculate flowsheds. It then merges flowsheds that belong to individual glaciers using a distance-based approach, whose required empirical parameters are derived from the Juneau Icefield area in Alaska. In this region, 2% of similar to 1300 glaciers were misclassified. The algorithm was validated on >25 000 km(2) of ice in other regions in Alaska and on >40 000 km(2) of ice in Arctic Canada, resulting in similar to 2% and similar to 3% misclassified glaciers, respectively. Results indicate that the algorithm is robust provided the DEM and the outlines are of good quality.
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| 28. |
- Kienholz, Christian, et al.
(författare)
-
Derivation and analysis of a complete modern-date glacier inventory for Alaska and northwest Canada
- 2015
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 61:227, s. 403-420
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed, complete glacier inventory for Alaska and neighboring Canada using multi-sensor satellite data from 2000 to 2011. For each glacier, we derive outlines and 51 variables, including center-line lengths, outline types and debris cover. We find 86 723 km(2) of glacier area (27 109 glaciers >0.025 km(2)), similar to 12% of the global glacierized area outside ice sheets. Of this area 12.0% is drained by 39 marine-terminating glaciers (74 km of tidewater margin), and 19.3% by 148 lake- and river-terminating glaciers (420 km of lake-/river margin). The overall debris cover is 11%, with considerable differences among regions, ranging from 1.4% in the Kenai Mountains to 28% in the Central Alaska Range. Comparison of outlines from different sources on >2500 km(2) of glacierized area yields a total area difference of similar to 10%, emphasizing the difficulties in accurately delineating debris-covered glaciers. Assuming fully correlated (systematic) errors, uncertainties in area reach 6% for all Alaska glaciers, but further analysis is needed to explore adequate error correlation scales. Preliminary analysis of the glacier database yields a new set of well-constrained area/length scaling parameters and shows good agreement between our area altitude distributions and previously established synthetic hypsometries. The new glacier database will be valuable to further explore relations between glacier variables and glacier behavior.
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| 29. |
- Krabbendam, Maarten, et al.
(författare)
-
Drag forces at the ice-sheet bed and resistance of hard-rock obstacles : the physics of glacial ripping
- 2023
-
Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 69:273, s. 103-119
-
Tidskriftsartikel (refereegranskat)abstract
- Glacial ripping involves glaciotectonic disintegration of rock hills and extensive removal of rock at the ice-sheet bed, triggered by hydraulic jacking caused by fluctuating water pressures. Evidence from eastern Sweden shows that glacial ripping caused significant subglacial erosion during the final deglaciation of the Fennoscandian ice sheet, distinct from abrasion and plucking (quarrying). Here we analyse the ice drag forces exerted onto rock obstacles at the base of an ice sheet, and the resisting forces of such rock obstacles: glaciotectonic disintegration requires that ice drag forces exceed the resisting forces of the rock obstacle. We consider rock obstacles of different sizes, shapes and fracture patterns, informed by natural examples from eastern Sweden. Our analysis shows that limited overpressure events, unfavourable fracture patterns, low-transmissivity fractures, slow ice and streamlined rock hamper rock hill disintegration. Conversely, under fast ice flow and fluctuating water pressures, disintegration is possible if the rock hill contains subhorizontal, transmissive fractures. Rock steps on previously smooth, abraded surfaces, caused by hydraulic jacking, also enhance drag forces and can cause disintegration of a rock hill. Glacial ripping is a physically plausible erosion mechanism, under realistic glaciological conditions prevalent near ice margins.
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| 30. |
- Langhamer, Lukas, et al.
(författare)
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Response of lacustrine glacier dynamics to atmospheric forcing in the Cordillera Darwin
- 2024
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; , s. 1-19
-
Tidskriftsartikel (refereegranskat)abstract
- Calving glaciers respond quickly to atmospheric variability through ice dynamic adjustment. Particularly, single weather extremes may cause changes in ice-flow velocity and terminus position. Occasionally, this can lead to substantial event-driven mass loss at the ice front. We examine changes in terminus position, ice-flow velocity, and calving flux at the grounded la-custrine Schiaparelli Glacier in the Cordillera Darwin using geo-referenced time-lapse camera images and remote sensing data (Sentinel-1) from 2015 to 2022. Lake-level records, lake discharge measurements, and a coupled energy and mass balance model provide insight into the subglacial water discharge. We use downscaled reanalysis data (ERA-5) to identify climate extremes and track land-falling atmospheric rivers to investigate the ice-dynamic response on possible atmospheric drivers.
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| 31. |
- Leeson, Amber A., et al.
(författare)
-
A comparison of supraglacial lake observations derived from MODIS imagery at the western margin of the Greenland ice sheet
- 2013
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 59:218, s. 1179-1188
-
Tidskriftsartikel (refereegranskat)abstract
- Supraglacial lakes (SGLs) affect the dynamics of the Greenland ice sheet by storing runoff and draining episodically. We investigate the evolution of SGLs as reported in three datasets, each based on automated classification of satellite imagery. Although the datasets span the period 2001-10, there are differences in temporal sampling, and only the years 2005-07 are common. By subsampling the most populous dataset, we recommend a sampling frequency of one image per 6.5 days in order to minimize uncertainty associated with poor temporal sampling. When compared with manual classification of satellite imagery, all three datasets are found to omit a sizeable (29, 48 and 41%) fraction of lakes and are estimated to document the average size of SGLs to within 0.78, 0.48 and 0.95 km(2). We combine the datasets using a hierarchical scheme, producing a single, optimized, dataset. This combined record reports up to 67% more lakes than a single dataset. During 2005-07, the rate of SGL growth tends to follow the rate at which runoff increases in each year. In 2007, lakes drain earlier than in 2005 and 2006 and remain absent despite continued runoff. This suggests that lakes continue to act as open surface bed conduits following drainage.
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| 32. |
- Liakka, Johan, et al.
(författare)
-
The impact of topographically forced stationary waves on local ice-sheet climate
- 2010
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 56:197, s. 534-544
-
Tidskriftsartikel (refereegranskat)abstract
- A linear two-level atmospheric model is employed to study the influence of ice-sheet topography on atmospheric stationary waves. In particular, the stationary-wave-induced temperature anomaly is considered locally over a single ice-sheet topography, which is computed using the plastic approximation. It is found that stationary waves induce a local cooling which increases linearly with the ice volume for ice sheets of horizontal extents smaller than 1400 km. Beyond this horizontal scale, the dependence of stationary-wave-induced cooling on the ice volume becomes gradually weaker. For a certain ice-sheet size, and for small changes of the surface zonal wind, it is further shown that the strength of the local stationary-wave-induced cooling is proportional to the basic state meridional temperature gradient multiplied by the vertical stratification in the atmosphere. These results are of importance for the nature of the feedback between ice sheets and stationary waves, and may also serve as a basis for parameterizing this feedback in ice-sheet model simulations (e.g. through the Pleistocene glacial/interglacial cycles).
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| 33. |
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| 34. |
- Marchenko, Sergey, et al.
(författare)
-
A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–14
- 2017
-
Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 63:237, s. 67-78
-
Tidskriftsartikel (refereegranskat)abstract
- Spatial heterogeneity of snow and firn properties on glaciers introduces uncertainty in interpretation of point and profile observations and complicates modelling of meltwater percolation and runoff. Here we present a study of the temporal and spatial dynamics of firn density and stratigraphy at the plot-scale (approximate to 10 m x 10 m x 10 m) repeated annually during 2012-14 at the Lomonosovfonna ice-field, Svalbard. Results from cores, video inspections in boreholes and radar grid surveys are compared. Ice layers 0.1-50 cm thick comprised approximate to 8% of the borehole length. Most of them are 1-3 cm thick and could not be traced between boreholes separated by 3 m. Large lateral variability of firn structure affects representativeness of observations in single holes and calls for repeated studies in multiple points to derive a representative stratigraphy signal. Radar reflections are poorly correlated with ice layers in individual boreholes. However, the match between the high amplitude peaks in the grid-averaged radar signal and horizons of preferential ice layer formation revealed by averaging the video surveys over multiple boreholes is higher. These horizons are interpreted as buried firn layers previously exposed to melt-freeze or wind-driven densification and several of them are consistently recovered throughout three field campaigns.
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| 35. |
- Marchenko, Sergey A., et al.
(författare)
-
Water content of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
- 2021
-
Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 67:265, s. 921-932
-
Tidskriftsartikel (refereegranskat)abstract
- The potential of capillary forces to retain water in pores is an important property of snow and firn at glaciers. Meltwater suspended in pores does not contribute to runoff and may refreeze during winter, which can affect the climatic mass balance and the subsurface density and temperature. However, measurement of firn water content is challenging and few values have been reported in the literature. Here, we use subsurface temperature and density measured at the accumulation zone of Lomonosovfonna (1200 m a.s.l.), Svalbard, to derive water content of the firn profiles after the 2014 and 2015 melt seasons. We do this by comparing measured and simulated rates of freezing front propagation. The calculated volumetric water content of firn is ~1.0–2.5 vol.% above the depth of 5 m and <0.5 vol.% below. Results derived using different thermistor strings suggest a prominent lateral variability in firn water content. Reported values are considerably lower than those commonly used in snow/firn models. This is interpreted as a result of preferential water flow in firn leaving dry volumes within wetted firn. This suggests that the implementation of irreducible water content values below 0.5 vol.% within snow/firn models should be considered at the initial phase of water infiltration.
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| 36. |
- McNabb, B, et al.
(författare)
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Using surface velocities to infer ice thickness and bed topography : A case study a Columbia Glacier, Alaska, USA
- 2012
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 58:212, s. 1151-1164
-
Tidskriftsartikel (refereegranskat)abstract
- Information about glacier volume and ice thickness distribution is essential for manyglaciological applications, but direct measurements of ice thickness can be diffcult and costly. Wepresent a new method that calculates ice thickness via an estimate of ice fux. We solve the familiarcontinuity equation between adjacent fowlines, which decreases the computational time requiredcompared to a solution on the whole grid. We test the method on Columbia Glacier, a large tidewaterglacier in Alaska, USA, and compare calculated and measured ice thicknesses, with favorable results.This shows the potential of this method for estimating ice thickness distribution of glaciers for whichonly surface data are available. We fnd that both the mean thickness and volume of Columbia Glacierwere approximately halved over the period 1957–2007, from 281m to 143m, and from 294km3to134km3, respectively. Using bedrock slope and considering how waves of thickness change propagatethrough the glacier, we conduct a brief analysis of the instability of Columbia Glacier, which leads usto conclude that the rapid portion of the retreat may be nearing an end.
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| 37. |
- Moore, Peter L., et al.
(författare)
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Effect of a cold margin on ice flow at the terminus of Storglaciären, Sweden : implications for sediment transport
- 2011
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 57:201, s. 77-87
-
Tidskriftsartikel (refereegranskat)abstract
- The cold-based termini of polythermal glaciers are usually assumed to adhere strongly toan immobile substrate and thereby supply significant resistance to the flow of warm-based ice upglacier.This compressive environment is commonly thought to uplift basal sediment to the surface ofthe glacier by folding and thrust faulting. We present model and field evidence from the terminus ofStorglaci¨aren, Sweden, showing that the cold margin provides limited resistance to flow from up-glacier.Ice temperatures indicate that basal freezing occurs in this zone at 10−1 –10−2 ma−1, but model resultsindicate that basal motion at rates greater than 1ma−1 must, nevertheless, persist there for surface andbasal velocities to be consistent with measurements. Estimated longitudinal compressive stresses of 20–25 kPa within the terminus further indicate that basal resistance offered by the cold-based terminusis small. These results indicate that where polythermal glaciers are underlain by unlithified sediments,ice-flow trajectories and sediment transport pathways may be affected by subglacial topography andhydrology more than by the basal thermal regime
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| 38. |
- Pettersson, Rickard, et al.
(författare)
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Spatial pattern and stability of the cold surface layer of Storglaciären, Sweden
- 2007
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 53:180, s. 99-109
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have, to date, been poorly investigated and are not fully understood. We have investigated the sensitivity of the cold surface layer thickness to different forcing parameters and the causes for an observed thinning of the cold surface layer on Storglaciären, northern Sweden, between 1989 and 2001 using a one-dimensional thermomechanical model and measurements of ice surface temperature, vertical velocity and net mass balance. Similarities between the spatial patterns of the cold surface layer, net mass balance and emergence velocity together with modelled high sensitivity to variations in emergence velocities suggest that the net ablation and vertical ice advection are the dominant forcing parameters. Results from transient model experiments suggest that the cold surface layer reaches a new equilibrium after a perturbation in the forcing within a few decades. No significant change in ice flow or mass balance has been observed at Storglaciären in recent decades. Instead, an increase of 1°C in winter air temperature since the mid-1980s is probably the cause of the observed thinning of the cold surface layer. Increased winter temperatures at the ice surface result in a reduced formation rate of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition surface. Model results indicate that the cold surface layer is more sensitive to changes in ice surface temperature in areas with lower emergence velocity, which explains the observed complex thinning pattern of the cold surface layer.
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| 39. |
- Pfeffer, W. Tad, et al.
(författare)
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The Randolph Glacier Inventory : a globally complete inventory of glaciers
- 2014
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 60:221, s. 537-552
-
Tidskriftsartikel (refereegranskat)abstract
- The Randolph Glacier Inventory (RGI) is a globally complete collection of digital outlines of glaciers, excluding the ice sheets, developed to meet the needs of the Fifth Assessment of the Intergovernmental Panel on Climate Change for estimates of past and future mass balance. The RGI was created with limited resources in a short period. Priority was given to completeness of coverage, but a limited, uniform set of attributes is attached to each of the similar to 198 000 glaciers in its latest version, 3.2. Satellite imagery from 1999-2010 provided most of the outlines. Their total extent is estimated as 726 800 +/- 34 000 km(2). The uncertainty, about +/- 5%, is derived from careful single-glacier and basin-scale uncertainty estimates and comparisons with inventories that were not sources for the RGI. The main contributors to uncertainty are probably misinterpretation of seasonal snow cover and debris cover. These errors appear not to be normally distributed, and quantifying them reliably is an unsolved problem. Combined with digital elevation models, the RGI glacier outlines yield hypsometries that can be combined with atmospheric data or model outputs for analysis of the impacts of climatic change on glaciers. The RGI has already proved its value in the generation of significantly improved aggregate estimates of glacier mass changes and total volume, and thus actual and potential contributions to sea-level rise.
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| 40. |
- Pohjola, V.A.
(författare)
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TV-video observations of bed and basal sliding on Storglaciären, Sweden
- 1993
-
Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 39:131, s. 111-118
-
Tidskriftsartikel (refereegranskat)abstract
- Four boreholes in Storglaciaren, a small valley glacier in northernSweden, were inspected with a video camera. In two of the boreholes, the apparentglacier bed was filmed. In one borehole, the bed was found to be composed of softsediment, but in the other it consisted of bedrock. In the latter, the camera moved5.6 mm relative to the bed during an 80 min period. The recorded camera movementshowed a background motion which is in the expected range of basal sliding.Superimposed on the background motion, a jerky motion of a high-speed spike wasfound. The jerky motion is interpreted as a stress release induced by local topographyat the ice-bed interface.
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| 41. |
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| 42. |
- Pohjola, Veijo, et al.
(författare)
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Controlled experiments on the diffusion rate of stable isotopes of water in artificial firn
- 2007
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 53:183, s. 537-546
-
Tidskriftsartikel (refereegranskat)abstract
- We studied the diffusion rate of stable isotopes of water ice in a controlled laboratory experiment, where isotopically different layers of fabricated firn were stacked. This experiment was done in order to study the diffusion rate between the isotopically different layers and to further compare the measured results with forward calculated diffusion rates of the fabricated firn stack, using three different analytical and numerical methods. The layers varied in thickness within the stack and the studied period includes variations in firn temperatures. We sampled the firn-stack on five different dates along the totally 144-d long experiment. We get a quantitatively good match between the calculated and the measured diffusion rates, with a RMS similarity of 67-80 % in the depth averaged diffusion rates. Despite the good average match, we find some qualitative discrepancy between our calculations and our measurements. The calculated diffusion rates predict more than 5 % faster isotopic decay of thinner layers and 13 % slower decay of thicker layers in the experiment than measurements show. This We speculate that grain size and grain fabric may influence the tortuosity the firn pack, and that the current generalization of tortuosity being a function of firn density as the only free parameter is an oversimplification
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| 43. |
- Pramanik, Ankit, et al.
(författare)
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Simulating climatic mass balance, seasonal snow development and associated freshwater runoff in the Kongsfjord basin, Svalbard (1980–2016)
- 2018
-
Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 64:248, s. 943-956
-
Tidskriftsartikel (refereegranskat)abstract
- The Kongsfjord basin in northwest Svalbard is the site of a number of interdisciplinary studies concerned with the effect of fresh water from seasonal snow and glacier melt on the physical and biological environment. We use an energy-balance model coupled with a subsurface snow model to simulate the long-term climatic mass-balance evolution of the glaciers and the seasonal snow development of nonglacierized parts of the Kongsfjord basin. Runoff from both glacierized and nonglacierized parts of the basin is simulated to quantify the fresh water flux to the fjord. The model is calibrated with long-term mass-balance data measured at four glaciers, and with automatic weather station data. The simulated area-averaged climatic mass balance for the whole basin is positive (+0.23 m w.e. a−1) over the period 1980–2016; however, the trend for net mass balance is not statistically significant over the simulation period, despite the observed ongoing summer warming. Refreezing equals 0.24 m w.e. a−1, which is equivalent to 17% of the total mass gain from precipitation and moisture deposition. Total runoff comprises contributions from seasonal snow in the nonglacierized area (16%) and glacier discharge (84%). Model time series shows a significant increasing trend for annual glacier runoff (6.83 × 106 m3 a−1) over the simulation period.
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| 44. |
- Radic, Valentina, et al.
(författare)
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Analysis of scaling methods in deriving future volume evolutions of valley glaciers
- 2008
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 54:187, s. 601-612
-
Tidskriftsartikel (refereegranskat)abstract
- Volume-area scaling is a common tool for deriving future volume evolutions of valley glaciers and their contribution to sea-level rise. We analyze the performance of scaling relationships for deriving volume projections in comparison to projections from a one-dimensional ice-flow model. The model is calibrated for six glaciers (Nigardsbreen, Rhonegletscher, South Cascade Glacier, Sofiyskiy glacier, midre Lovenbreen and Abramov glacier). Volume evolutions forced by different hypothetical mass-balance perturbations are compared with those obtained from volume-area (V-A), volume-length (V-L) and volume-area-length (V-A-L) scaling. Results show that the scaling methods mostly underestimate the volume losses predicted by the ice-flow model, up to 47% for V-A scaling and up to 18% for V-L scaling by the end of the 100 year simulation period. In general, V-L scaling produces closer simulations of volume evolutions derived from the ice-flow model, suggesting that V-L scaling may be a better approach for deriving volume projections than V-A scaling. Sensitivity experiments show that the initial volumes and volume evolutions are highly sensitive to the choice of the scaling constants, yielding both over- and underestimates. However, when normalized by initial volume, volume evolutions are relatively insensitive to the choice of scaling constants, especially in the V-L scaling. The 100 year volume projections differ within 10% of initial volume when the V-A scaling exponent commonly assumed, gamma = 1.375, is varied by -30% to +45% (gamma = [0.95, 2.00]) and the V-L scaling exponent, q = 2.2, is varied by -30% to +45% (q = [1.52, 3.20]). This is encouraging for the use of scaling methods in glacier volume projections, particularly since scaling exponents may vary between glaciers and the scaling constants are generally unknown.
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| 45. |
- Rasmussen, L. A., et al.
(författare)
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Surface mass balance, thinning and iceberg production, Columbia Glacier, Alaska, 1948-2007
- 2011
-
Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57:203, s. 431-440
-
Tidskriftsartikel (refereegranskat)abstract
- A mass-balance model using upper-air meteorological data for input was calibrated with surface mass balance measured mainly during 1977-78 at 67 sites on Columbia Glacier, Alaska, between 135 and 2645 m a.s.l. Root-mean-square error, model vs measured, is 1.0 m w.e. a(-1), with r(2) = 0.88. A remarkable result of the analysis was that both precipitation and the factor in the positive degree-day model used to estimate surface ablation were constant with altitude. The model was applied to reconstruct glacier-wide components of surface mass balance over 1948-2007. Surface ablation, 4 km(3) ice eq.a(-1) (ice equivalent), has changed little throughout the period. From 1948 until about 1981, when drastic retreat began, the surface mass balance was positive but changes in glacier geometry were small, so the positive balance was offset by calving, similar to 0.9 km(3) ice eq.a(-)1. During retreat, volume loss of the glacier accounted for 92% of the iceberg production. Calving increased to similar to 4.3 km(3) ice eq.a(-)1 from 1982 to 1995, and after that until 2007 to similar to 8.0 km(3) ice eq.a(-1), which was about twice the loss by surface ablation, whereas prior to retreat it was only about a quarter as much. Calving is calculated as the difference between glacier-wide surface mass balance and geodetically determined volume change.
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| 46. |
- Reinardy, Benedict T. I., et al.
(författare)
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Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate
- 2011
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57:204, s. 596-608
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.
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| 47. |
- Samyn, Denis, et al.
(författare)
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A simple and updated pneumatic method for uniaxial ice compression in the laboratory : experimental settings and creep test results on glacier ice
- 2011
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Ingår i: Journal of Glaciology. - 0022-1430 .- 1727-5652. ; 57:202, s. 337-344
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Tidskriftsartikel (refereegranskat)abstract
- Creep tests provide invaluable data to better understand the physical properties of ice under various conditions. We describe here a simple, updated pneumatic apparatus for experimental studies of ice rheological properties. The apparatus is designed to perform two simultaneous compression creep tests either in a cold room or in atmospheric conditions when coupled to an external cooling circulator. We present results from calibration tests of the apparatus and provide new data from creep tests performed on temperate glacier ice samples. These calibration and creep results show that the apparatus is able to provide fast and reliable mechanical ice characterization. The secondary creep rates measured in this study range between 1.59 x 10(-8) s(-1) (at 0.21 MPa) and 4.38 x 10(-7) s(-1) (at 0.71 MPa) at -10 degrees C for quasi-isotropic ice, which is consistent with former standard published data. The corresponding mean parameter, A, is 5.20 x 10(-16) s(-1) kPa(-3), which also compares well with the range of reported other studies.
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| 48. |
- Schaffer, Nicole, et al.
(författare)
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Ice velocity changes on Penny Ice Cap, Baffin Island, since the 1950s
- 2017
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Ingår i: Journal of Glaciology. - : Cambridge University Press (CUP). - 0022-1430 .- 1727-5652. ; 63:240, s. 716-730
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the velocity response of glaciers to increased surface melt is a major topic of ongoing research with significant implications for accurate sea level rise forecasting. In this study we use optical and radar satellite imagery as well as comparisons with historical ground measurements to produce a multi-decadal record of ice velocity variations on Penny Ice Cap, Baffin Island. Over the period 1985 to 2011, the six largest outlet glaciers on the ice cap decelerated at an average rate of 21 m a-1 , or 12% per decade. The change was not monotonous, however, as most glaciers accelerated until the 1990s, then decelerated. A comparison of recent imagery with historical velocity measurements on Highway Glacier, on the southern part of Penny Ice Cap,shows that this glacier decelerated by 71% between 1953 and 2009/11, from 57 to 17 m a-1 . The recent slowdown of outlet glaciers has coincided with increases in mass loss, terminus retreat and an inferred reduction in basal sliding. Measured decelerations are greater than the total short term variability measured from both seasonal and interannual fluctuations, and supports the hypothesis that glacier thinning and/or increased meltwater production promotes a long-term reduction in ice motion.
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| 49. |
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| 50. |
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