| 1. |
- Callaghan, Terry, et al.
(författare)
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Multi-Decadal Changes in Tundra Environments and Ecosystems : Synthesis of the International Polar Year-Back to the Future Project (IPY-BTF)
- 2011
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 40:6, s. 705-716
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the responses of tundra systemsto global change has global implications. Most tundraregions lack sustained environmental monitoring and oneof the only ways to document multi-decadal change is toresample historic research sites. The International PolarYear (IPY) provided a unique opportunity for such researchthrough the Back to the Future (BTF) project (IPY project#512). This article synthesizes the results from 13 paperswithin this Ambio Special Issue. Abiotic changes includeglacial recession in the Altai Mountains, Russia; increasedsnow depth and hardness, permafrost warming, andincreased growing season length in sub-arctic Sweden;drying of ponds in Greenland; increased nutrient availabilityin Alaskan tundra ponds, and warming at mostlocations studied. Biotic changes ranged from relativelyminor plant community change at two sites in Greenland tomoderate change in the Yukon, and to dramatic increasesin shrub and tree density on Herschel Island, and in subarcticSweden. The population of geese tripled at one sitein northeast Greenland where biomass in non-grazed plotsdoubled. A model parameterized using results from a BTFstudy forecasts substantial declines in all snowbeds andincreases in shrub tundra on Niwot Ridge, Colorado overthe next century. In general, results support and provideimproved capacities for validating experimental manipulation,remote sensing, and modeling studies.
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| 2. |
- Den Ouden, M. A. G., et al.
(författare)
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Stand-alone single-frequency GPS ice velocity observations on Nordenskiöldbreen, Svalbard
- 2010
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 4:4, s. 593-604
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Tidskriftsartikel (refereegranskat)abstract
- Precise measurements of ice-flow velocities are necessary for a proper understanding of the dynamics of glaciers and their response to climate change. We use stand-alone single-frequency GPS receivers for this purpose. They are designed to operate unattended for 1–3 years, allowing uninterrupted measurements for long periods with hourly temporal resolution. We present the system and illustrate its functioning using data from 9 GPS receivers deployed on Nordenskiöldbreen, Svalbard, for the period 2006–2009. The accuracy of the receivers is 1.62 m based on the standard deviation in the average location of a stationary reference station (NBRef). Both the location of NBRef and the observed flow velocities agree within one standard deviation with DGPS measurements. Periodicity (6, 8, 12, 24 h) in the NBRef data is largely explained by the atmospheric, mainly ionospheric, influence on the GPS signal. A (weighed) running-average on the observed locations significantly reduces the standard deviation and removes high frequency periodicities, but also reduces the temporal resolution. Results show annual average velocities varying between 40 and 55 m yr−1 at stations on the central flow-line. On weekly to monthly time-scales we observe a peak in the flow velocities (from 60 to 90 m yr−1) at the beginning of July related to increased melt-rates. No significant lag is observed between the timing of the maximum speed between different stations. This is likely due to the limited temporal resolution after averaging in combination with the relatively small distance (max. ±13 km) between the stations.
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| 3. |
- Divine, Dmitri, et al.
(författare)
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Thousand years of winter surface air temperature variations in Svalbard and northern Norway reconstructed from ice-core data
- 2011
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 30, s. 7379-
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Tidskriftsartikel (refereegranskat)abstract
- Two isotopic ice core records from western Svalbard are calibrated to reconstruct more than 1000 years of past winter surface air temperature variations in Longyearbyen, Svalbard, and Vardo, northern Norway. Analysis of the derived reconstructions suggests that the climate evolution of the last millennium in these study areas comprises three major sub-periods. The cooling stage in Svalbard (ca. 800-1800) is characterized by a progressive winter cooling of approximately 0.9 degrees C century(-1) (0.38 degrees C century(-1) for Vardo) and a lack of distinct signs of abrupt climate transitions. This makes it difficult to associate the onset of the Little Ice Age in Svalbard with any particular time period. During the 1800s, which according to our results was the coldest century in Svalbard, the winter cooling associated with the Little Ice Age was on the order of 4 degrees C (1.3 degrees C for Vardo) compared to the 1900s. The rapid warming that commenced at the beginning of the 20th century was accompanied by a parallel decline in sea-ice extent in the study area. However, both the reconstructed winter temperatures as well as indirect indicators of summer temperatures suggest the Medieval period before the 1200s was at least as warm as at the end of the 1990s in Svalbard.
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| 4. |
- Divine, D. V., et al.
(författare)
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Modelling the regional climate and isotopic composition of Svalbard precipitation using REMOiso : a comparison with available GNIP and ice core data
- 2011
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Ingår i: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 25:24, s. 3748-3759
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Tidskriftsartikel (refereegranskat)abstract
- Simulations of a regional (approx. 50 km resolution) circulation model REMOiso with embedded stable water isotope module covering the period 1958-2001 are compared with the two instrumental climate and four isotope series (d18O) from western Svalbard. We examine the data from ice cores drilled on Svalbard ice caps in 1997 (Lomonosovfonna, 1250 m asl) and 2005 (Holtedahlfonna, 1150 m asl) and the GNIP series from Ny-angstrom lesund and Isfjord Radio. The surface air temperature (SAT) and precipitation data from Longyearbyen and Ny-angstrom lesund are used to assess the skill of the model in reproducing the local climate. The model successfully captures the climate variations on the daily to multidecadal times scales although it tends to systematically underestimate the winter SAT. Analysis suggests that REMOiso performs better at simulating isotope compositions of precipitation in the winter than summer. The simulated and measured Holtedahlfonna d18O series agree reasonably well, whereas no significant correlation has been observed between the modelled and measured Lomonosovfonna ice core isotopic series. It is shown that sporadic nature as well as variability in the amount inherent in precipitation process potentially limits the accuracy of the past SAT reconstruction from the ice core data. This effect in the study area is, however, diminished by the role of other factors controlling d18O in precipitation, most likely sea ice extent, which is directly related with the SAT anomalies.
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| 5. |
- Marchenko, Sergey A., et al.
(författare)
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Water content of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
- 2021
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Ingår i: Journal of Glaciology. - : Cambridge University Press. - 0022-1430 .- 1727-5652. ; 67:265, s. 921-932
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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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| 6. |
- Pettersson, Rickard, et al.
(författare)
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Ice thickness and basal conditions of Vestfonna ice cap, eastern Svalbard
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93A:4, s. 311-322
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Tidskriftsartikel (refereegranskat)abstract
- We combined ground-based pulsed radar data collected in 20082009 with airborne radio-echo sounding data acquired in 1983 and 1986 over Vestfonna ice cap, Svalbard. The airborne dataset mainly covers the fast-flowing outlet glaciers and the marginal zone, while the ground-based data explicitly cover the interior part of the ice cap. The data presented here are thus the first complete estimate of bed topography and ice thickness. The subglacial landscape undulates with elevations between -160 and +410 m above sea level. The mean ice thickness is 186 m and the total ice area and volume are 2402 km2 and 442 +/- 0.6 km3, respectively. This is a much smaller volume than those derived from empirical volume-area scaling relationships currently used to estimate regional-to-global glacier volumes. This difference may depend on local conditions for Vestfonna and emphasizes the need to include more volume observations in the derivations of volume-area scaling parameters. We also derive basal reflectivity as a proxy for thermal conditions at the bed. Basal reflectivity values suggest that fast-flowing outlet glaciers are underlain by temperate conditions. The geometric boundaries and basal conditions for Vestfonna will be critical additions to the development of numerical models of the ice cap and to the estimation of more accurate area-volume scaling parameters.
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| 7. |
- van der Wel, Gerko, et al.
(författare)
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Using high-resolution tritium profiles to quantify the effects of melt on two Spitsbergen ice cores
- 2011
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Ingår i: Journal of Glaciology. - : International Glaciological Society. - 0022-1430 .- 1727-5652. ; 57:206, s. 1087-1097
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Tidskriftsartikel (refereegranskat)abstract
- Ice cores from small ice caps provide valuable climatic information, additional to that of Greenland and Antarctica. However, their integrity is usually compromised by summer meltwater percolation. To determine to what extent this can affect such ice cores, we performed high-resolution tritium measurements on samples from two ice cores from Spitsbergen covering the period AD1955-75. The very sharp and distinct peaks in the tritium precipitation record are subject to several post-depositional processes. We developed a model that uses the precipitation record as input and incorporates the three most important processes (radioactive decay, isotope diffusion and meltwater percolation). Results are compared with measured tritium and density profiles. Both ice-core records contain sharp bomb peaks in the pre-1963 period. It is shown that these peaks would be much smoother in the absence of melt. In this case the main effect of melt and the refreezing of percolation water is the formation of ice layers that form barriers for firn diffusion; thus melt paradoxically results in better preservation of the annual isotope signals. Conversely, for the period after 1963 the main effect of melt is a stronger smoothing of the tritium profiles.
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| 8. |
- 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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| 9. |
- Beaudon, Emilie, et al.
(författare)
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Spatial and temporal variability of net accumulation from shallow cores from Vestfonna ice cap (Nordaustlandet, Svalbard)
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 287-299
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Tidskriftsartikel (refereegranskat)abstract
- We analyse ice cores from Vestfonna ice cap (Nordaustlandet, Svalbard). Oxygen isotopic measurements were made on three firn cores (6.0, 11.0 and 15.5 m deep) from the two highest summits of the glacier located on the SW–NE and NW–SE central ridges. Sub-annual δ18O cycles were preserved and could be counted visually in the uppermost parts of the cores, but deeper layers were affected by post-depositional smoothing. A pronounced δ18O minimum was found near the bottom of the three cores. We consider candidates for this δ18O signal to be a valuable reference horizon since it is also seen elsewhere in Nordaustlandet. We attribute it to isotopically depleted snow precipitation, which NCEP/NCAR reanalysis shows was unusual for Vestfonna, and came from northerly air during the cold winter of 1994/95. Finding the 1994/95 time marker allows establishment of a precise depth/age scale for the three cores. The derived annual accumulation rates indirectly fill a geographical gap in mass balance measurements and thus provide information on spatial and temporal variability of precipitation over the glacier for the period spanned by the cores (1992–2009). Comparing records at the two locations also reveals that the snow net accumulation at the easternmost part of Vestfonna was only half of that in the western part over the last 17 years.
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| 10. |
- Braun, Matthias, et al.
(författare)
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Changes of glacial front positions of Vestfonna (Nordaustlandet, Svalbard)
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 301-310
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Tidskriftsartikel (refereegranskat)abstract
- Glaciers in Svalbard have shown considerable mass loss in recent years with a reported acceleration in the western and southern parts of the archipelago. However, for the ice cap Vestfonna, in northeastern Svalbard, climatic mass balance modelling has suggested almost balanced conditions over a period of nine years (2000–2009). A slightly positive geodetic mass balance (1990–2005) has been reported from a comparison of laser altimetry to older DEMs. A heterogeneous situation has been depicted for the various catchments, and hence changes in glacier extent can reveal additional information of glacier status, in particular when dealing with surge-type glaciers. We analysed a 34-year data record of multi-spectral satellite imagery in order to study changes in glacier frontal positions of the ice cap Vestfonna. A consistent pattern of almost steady retreat of the southern and north-eastern outlet glaciers of the ice cap is observed while Franklinbreen, the only major outlet glacier draining towards the north-west shows re-advance. This is consistent with an observed speed up and potential upcoming surge of this outlet. The glacier retreat on the southern coast also agrees with ICESat elevation change measurements. However, due to the glacier response time no direct relations between frontal retreat and surface mass balance can be drawn from the short observation period. The heterogeneous pattern of changes with on-going dynamic adjustments in some areas make the ice cap Vestfonna an ideal test site for future monitoring activities including novel techniques like differential interferometry from bi-static SAR systems.
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