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  • 1
    In: The Cryosphere, Copernicus GmbH, Vol. 10, No. 3 ( 2016-05-25), p. 1089-1104
    Kurzfassung: Abstract. In this study we simulate the climatic mass balance of Svalbard glaciers with a coupled atmosphere–glacier model with 3 km grid spacing, from September 2003 to September 2013. We find a mean specific net mass balance of −257 mm w.e. yr−1, corresponding to a mean annual mass loss of about 8.7 Gt, with large interannual variability. Our results are compared with a comprehensive set of mass balance, meteorological, and satellite measurements. Model temperature biases of 0.19 and −1.9 °C are found at two glacier automatic weather station sites. Simulated climatic mass balance is mostly within about 100 mm w.e. yr−1 of stake measurements, and simulated winter accumulation at the Austfonna ice cap shows mean absolute errors of 47 and 67 mm w.e. yr−1 when compared to radar-derived values for the selected years 2004 and 2006. Comparison of modeled surface height changes from 2003 to 2008, and satellite altimetry reveals good agreement in both mean values and regional differences. The largest deviations from observations are found for winter accumulation at Hansbreen (up to around 1000 mm w.e. yr−1), a site where sub-grid topography and wind redistribution of snow are important factors. Comparison with simulations using 9 km grid spacing reveal considerable differences on regional and local scales. In addition, 3 km grid spacing allows for a much more detailed comparison with observations than what is possible with 9 km grid spacing. Further decreasing the grid spacing to 1 km appears to be less significant, although in general precipitation amounts increase with resolution. Altogether, the model compares well with observations and offers possibilities for studying glacier climatic mass balance on Svalbard both historically as well as based on climate projections.
    Materialart: Online-Ressource
    ISSN: 1994-0424
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2016
    ZDB Id: 2393169-3
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Online-Ressource
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    Copernicus GmbH ; 2022
    In:  Biogeosciences Vol. 19, No. 2 ( 2022-01-18), p. 271-294
    In: Biogeosciences, Copernicus GmbH, Vol. 19, No. 2 ( 2022-01-18), p. 271-294
    Kurzfassung: Abstract. Arctic amplification of global warming has accelerated mass loss of Arctic land ice over the past decades and led to increased freshwater discharge into glacier fjords and adjacent seas. Glacier freshwater discharge is typically associated with high sediment load which limits the euphotic depth but may also aid to provide surface waters with essential nutrients, thus having counteracting effects on marine productivity. In situ observations from a few measured fjords across the Arctic indicate that glacier fjords dominated by marine-terminating glaciers are typically more productive than those with only land-terminating glaciers. Here we combine chlorophyll a from satellite ocean color, an indicator of phytoplankton biomass, with glacier meltwater runoff from climatic mass-balance modeling to establish a statistical model of summertime phytoplankton dynamics in Svalbard (mid-June to September). Statistical analysis reveals significant and positive spatiotemporal associations of chlorophyll a with glacier runoff for 7 out of 14 primary hydrological regions but only within 10 km distance from the shore. These seven regions consist predominantly of the major fjord systems of Svalbard. The adjacent land areas are characterized by a wide range of total glacier coverage (35.5 % to 81.2 %) and fraction of marine-terminating glacier area (40.2 % to 87.4 %). We find that an increase in specific glacier-runoff rate of 10 mm water equivalent per 8 d period raises summertime chlorophyll a concentrations by 5.2 % to 20.0 %, depending on the region. During the annual peak discharge we estimate that glacier runoff increases chlorophyll a by 13.1 % to 50.2 % compared to situations with no runoff. This suggests that glacier runoff is an important factor sustaining summertime phytoplankton production in Svalbard fjords, in line with findings from several fjords in Greenland. In contrast, for regions bordering open coasts, and beyond 10 km distance from the shore, we do not find significant associations of chlorophyll a with runoff. In these regions, physical ocean and sea-ice variables control chlorophyll a, pointing at the importance of a late sea-ice breakup in northern Svalbard, as well as the advection of Atlantic water masses along the West Spitsbergen Current for summertime phytoplankton dynamics. Our method allows for the investigation and monitoring of glacier-runoff effects on primary production throughout the summer season and is applicable on a pan-Arctic scale, thus complementing valuable but scarce in situ measurements in both space and time.
    Materialart: Online-Ressource
    ISSN: 1726-4189
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2022
    ZDB Id: 2158181-2
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
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    International Glaciological Society ; 2011
    In:  Journal of Glaciology Vol. 57, No. 202 ( 2011), p. 247-259
    In: Journal of Glaciology, International Glaciological Society, Vol. 57, No. 202 ( 2011), p. 247-259
    Kurzfassung: A large part of the ice flux within ice caps occurs through spatially limited fast-flowing units. Some of them permanently maintain fast flow, whereas others operate in an oscillatory mode, characterized by short-lived active phases followed by long quiescent phases. This surge-type behaviour results from intrinsic rather than external factors, thus complicating estimates of glacier response to climate change. Here we present numerical model results from Austfonna, an ice cap on Svalbard that comprises several surge-type basins. Previous studies have suggested a thermally controlled soft-bed surge mechanism for Svalbard. We systematically change the parameters that govern the nature of basal motion and thereby control the transition between permanent and oscillatory fast flow. Surge-type behaviour is realized by a relatively abrupt onset of basal sliding when basal temperatures approach the pressure-melting point and enhanced sliding of marine grounded ice. Irrespective of the dynamic regime, the absence of considerable volumes of temperate ice, both in the observed and simulated ice cap, indicates that fast flow is accomplished by basal motion over a temperate bed. Given an idealized present-day climate, the equilibrium ice-cap size varies significantly, depending on the chosen parameters.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2011
    ZDB Id: 2140541-4
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
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    Wiley ; 2014
    In:  International Journal of Climatology Vol. 34, No. 6 ( 2014-05), p. 2047-2058
    In: International Journal of Climatology, Wiley, Vol. 34, No. 6 ( 2014-05), p. 2047-2058
    Kurzfassung: Only few reliable records are available covering more than 5 years of meteorological conditions on Arctic glaciers. Here, we report on the operation of an automatic weather station at the Austfonna ice cap, Svalbard, over an 8‐year period from 2004 to 2012. Time series of measured and derived quantities are analysed to characterize meteorological conditions close to the equilibrium line altitude at ∼400 m.a.s.l. The mean annual temperature is −8.3 °C but exhibits large variability such that excursions above 0 °C occur even during winter. In general, relative air humidity is high and evaluating the wind pattern, we find that moisture is primarily advected from south‐easterly directions. Net radiation is dominated by shortwave radiation and, hence, surface albedo plays an important role in the radiation budget. Frequent summer snowfalls, as observed in 2008, have the ability to maintain a high albedo over much of the ablation season, thereby having large impact on the energy balance as well as on glacier mass balance. Cloudiness is assessed using records of incoming longwave radiation. Analyzing the radiation data, we find evidence for the radiation paradox, i.e. an increase of average net radiation (2004–2012) from −15.7 W m −2 for clear‐sky conditions to 7.3 W m −2 during overcast skies.
    Materialart: Online-Ressource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    RVK:
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2014
    ZDB Id: 1491204-1
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
    In: Journal of Glaciology, Cambridge University Press (CUP)
    Kurzfassung: Empirical glacier mass-balance models are commonly used in assessments of glacier and runoff evolution. Recent satellite-borne geodetic mass-balance observations of global coverage facilitate large-scale model calibration that previously relied on sparse in situ observations of glacier mass change. Geodetic observations constitute temporally aggregated mass-balance signals with significant uncertainty, raising questions about the role of observations with different temporal resolutions and uncertainties in constraining model parameters. We employ a Bayesian approach and demonstrate the sensitivity of parameter values to commonly used mass-balance observations of seasonal, annual and decadal resolution with uncertainties characteristic to in situ and satellite-borne observations. For glaciers along a continentality gradient in Norway, the use of annual mass balances results in around 20% lower magnitude of modelled ablation and accumulation (1960–2020), compared to employing seasonal balances. Decadal mass balance also underestimates magnitudes of ablation and accumulation, but parameter values are strongly influenced by the prior distribution. The datasets yield similar estimates of annual mass balance with different margins of uncertainty. Decadal observations are afflicted with considerable uncertainty in mass-balance sensitivity due to high parameter uncertainty. Our results highlight the importance of seasonal observations when model applications require accurate magnitudes of ablation, e.g. to estimate meltwater runoff.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    Sprache: Englisch
    Verlag: Cambridge University Press (CUP)
    Publikationsdatum: 2023
    ZDB Id: 2140541-4
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 6
    In: The Cryosphere, Copernicus GmbH, Vol. 11, No. 3 ( 2017-05-04), p. 1041-1058
    Kurzfassung: Abstract. We compare geocoded heights derived from the interferometric mode (SARIn) of CryoSat to surface heights from calibration–validation sites on Devon Ice Cap and western Greenland. Comparisons are included for both the heights derived from the first return (the point-of-closest-approach or POCA) and heights derived from delayed waveform returns (swath processing). While swath-processed heights are normally less precise than edited POCA heights, e.g. standard deviations of  ∼  3 and  ∼  1.5 m respectively for the western Greenland site, the increased coverage possible with swath data complements the POCA data and provides useful information for both system calibration and improving digital elevation models (DEMs). We show that the pre-launch interferometric baseline coupled with an additional roll correction ( ∼  0.0075° ± 0.0025°), or equivalent phase correction ( ∼  0.0435 ± 0.0145 radians), provides an improved calibration of the interferometric SARIn mode. We extend the potential use of SARIn data by showing the influence of surface conditions, especially melt, on the return waveforms and that it is possible to detect and measure the height of summer supraglacial lakes in western Greenland. A supraglacial lake can provide a strong radar target in the waveform, stronger than the initial POCA return, if viewed at near-normal incidence. This provides an ideal situation for swath processing and we demonstrate a height precision of  ∼  0.5 m for two lake sites, one in the accumulation zone and one in the ablation zone, which were measured every year from 2010 or 2011 to 2016. Each year the lake in the ablation zone was viewed in June by ascending passes and then 5.5 days later by descending passes, which allows an approximate estimate of the filling rate. The results suggest that CryoSat waveform data and measurements of supraglacial lake height change could complement the use of optical satellite imagery and be helpful as proxy indicators for surface melt around Greenland.
    Materialart: Online-Ressource
    ISSN: 1994-0424
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2017
    ZDB Id: 2393169-3
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
    In: The Cryosphere, Copernicus GmbH, Vol. 13, No. 9 ( 2019-09-03), p. 2259-2280
    Kurzfassung: Abstract. The climate in Svalbard is undergoing amplified change compared to the global mean. This has major implications for runoff from glaciers and seasonal snow on land. We use a coupled energy balance–subsurface model, forced with downscaled regional climate model fields, and apply it to both glacier-covered and land areas in Svalbard. This generates a long-term (1957–2018) distributed dataset of climatic mass balance (CMB) for the glaciers, snow conditions, and runoff with a 1 km×1 km spatial and 3-hourly temporal resolution. Observational data including stake measurements, automatic weather station data, and subsurface data across Svalbard are used for model calibration and validation. We find a weakly positive mean net CMB (+0.09 m w.e. a−1) over the simulation period, which only fractionally compensates for mass loss through calving. Pronounced warming and a small precipitation increase lead to a spatial-mean negative net CMB trend (−0.06 m w.e. a−1 decade−1), and an increase in the equilibrium line altitude (ELA) by 17 m decade−1, with the largest changes in southern and central Svalbard. The retreating ELA in turn causes firn air volume to decrease by 4 % decade−1, which in combination with winter warming induces a substantial reduction of refreezing in both glacier-covered and land areas (average −4 % decade−1). A combination of increased melt and reduced refreezing causes glacier runoff (average 34.3 Gt a−1) to double over the simulation period, while discharge from land (average 10.6 Gt a−1) remains nearly unchanged. As a result, the relative contribution of land runoff to total runoff drops from 30 % to 20 % during 1957–2018. Seasonal snow on land and in glacier ablation zones is found to arrive later in autumn (+1.4 d decade−1), while no significant changes occurred on the date of snow disappearance in spring–summer. Altogether, the output of the simulation provides an extensive dataset that may be of use in a wide range of applications ranging from runoff modelling to ecosystem studies.
    Materialart: Online-Ressource
    ISSN: 1994-0424
    Sprache: Englisch
    Verlag: Copernicus GmbH
    Publikationsdatum: 2019
    ZDB Id: 2393169-3
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 8
    In: Journal of Glaciology, International Glaciological Society, Vol. 59, No. 217 ( 2013), p. 893-899
    Kurzfassung: Winter balance is an important metric for assessing the change on glaciers and ice caps, yet measuring it using ground-based techniques can be challenging. We use the European Space Agency prototype Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) to extract snow depths from the received altimeter waveforms over Austfonna ice cap, Svalbard. Additionally, we attempt to distinguish the long-term firn area from other glacier facies. We validate our results using snow depth and glacier facies characterizations determined from ground-based radar profiles, snow pits and a multi-look satellite synthetic aperture radar image. We show that the depth of the winter snowpack can be extracted from the altimeter data over most of the accumulation zone, comprising wet snow zone and a superimposed ice zone. The method struggles at lower elevations where internal reflections within the winter snowpack are strong and the winter snow depth is less than ∼1 m. We use the abruptness of the reflection from the last summer surface (LSS) to attempt to distinguish glacier facies. While there is a general correlation between LSS abruptness and glacier facies, we do not find a relationship that warrants a distinct classification based on ASIRAS waveforms alone.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2013
    ZDB Id: 2140541-4
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 9
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    International Glaciological Society ; 2009
    In:  Annals of Glaciology Vol. 50, No. 50 ( 2009), p. 155-162
    In: Annals of Glaciology, International Glaciological Society, Vol. 50, No. 50 ( 2009), p. 155-162
    Kurzfassung: In spring during 2004–07 we conducted ground-penetrating radar (GPR) measurements on the Austfonna ice cap, Svalbard, with the original aim of mapping the thickness and distribution of winter snow. Here, we further exploit the information content of the data and derive a multi-year sequence of glacier-facies distribution that provides valuable spatial information about the total surface mass balance (SMB) of the ice cap, beyond the usually evaluated winter balance. We find that following an initial decrease in the extent of the firn area (2003–04), the firn line lowered within two subsequent years by ∼ 40–100m elevation in the north and west and 150–230m in the south and east of the ice cap, corresponding to a lateral expansion of the firn area along the profiles by up to 7.3 and 13.3 km, respectively. The growth of the firn area is in line with stake measurements from Etonbreen that indicate a trend towards less negative SMB over the corresponding period.
    Materialart: Online-Ressource
    ISSN: 0260-3055 , 1727-5644
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2009
    ZDB Id: 2122400-6
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
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    International Glaciological Society ; 2008
    In:  Journal of Glaciology Vol. 54, No. 185 ( 2008), p. 333-342
    In: Journal of Glaciology, International Glaciological Society, Vol. 54, No. 185 ( 2008), p. 333-342
    Kurzfassung: We investigate snowpack properties at a site in west-central Greenland with ground-penetrating radar (GPR), supplemented by stratigraphic records from snow pits and shallow firn cores. GPR data were collected at a validation test site for CryoSat (T05 on the Expéditions Glaciologiques Internationales au Groenland (EGIG) line) over a 100 m × 100 m grid and along 1 km sections at frequencies of 500 and 800 MHz. Several internal reflection horizons (IRHs) down to a depth of 10 m were tracked. IRHs are usually related to ice-layer clusters in vertically bounded sequences that obtain their initial characteristics near the surface during the melt season. Warm conditions in the following melt season can change these characteristics by percolating meltwater. In cold conditions, smaller melt volumes at the surface can lead to faint IRHs. The absence of simple mechanisms for internal layer origin emphasizes the need for independent dating to reliably interpret remotely sensed radar data. Our GPR-derived depth of the 2003 summer surface of 1.48 m (measured in 2004) is confirmed by snow-pit observations. The distribution of IRH depths on a 1 km scale reveals a gradient of increasing accumulation to the northeast of about 5 cm w.e. km −1 . We find that point measurements of accumulation in this area are representative only over several hundred metres, with uncertainties of about 15% of the spatial mean.
    Materialart: Online-Ressource
    ISSN: 0022-1430 , 1727-5652
    Sprache: Englisch
    Verlag: International Glaciological Society
    Publikationsdatum: 2008
    ZDB Id: 2140541-4
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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