| 11. |
- Charpentier Ljungqvist, Fredrik, 1982-
(författare)
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A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia
- 2010
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - Oxford : Wiley-Blackwell. - 0435-3676 .- 1468-0459. ; 92A:3, s. 339-351
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Tidskriftsartikel (refereegranskat)abstract
- A new temperature reconstruction with decadal resolution, covering the last two millennia, is presented for the extra-tropical Northern Hemisphere (90–30°N), utilizing many palaeotemperature proxy records never previously included in any large-scale temperature reconstruction. The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. AD 1–300, reaching up to the 1961–1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300–800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300–1900, followed by a rapid temperature increase in the twentieth century. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961–1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself. Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.
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| 12. |
- Chen, D., et al.
(författare)
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A high-resolution, gridded dataset for monthly temperature normals (1971 – 2000) in Sweden
- 2007
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 89:4, s. 249-261
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Tidskriftsartikel (refereegranskat)abstract
- A baseline climatology is required in evaluating climate variability and changes on regional and local scales. Gridded climate normals, i.e. averages over a 30-year period, are of special interest since they can be readily used for validation of climate models. This study is aimed at creating an updated gridded dataset for Swedish monthly temperature normals over the period 1971–2000, based on standard 2-m air temperature records at 510 stations in mainland Sweden. Spatial trends of the normal temperatures were modelled as functions of latitude, longitude and elevation by multiple linear regression. The study shows that the temperature normals are strongly correlated with latitude throughout the year and especially in cold months, while elevation was a more important factor in June and July. Longitude played a minor role and was only significant in April and May. Regression equations linking temperature to latitude, longitude and elevation were set up for each month. Monthly temperature normals were detrended by subtracting spatial trends given by the regressions. Ordinary kriging was then applied to both original data (simple method) and de-trended data (composite method) to model the spatial variability and to perform spatial gridding. The multiple regressions showed that between 82% (summer) and 96% (winter) of the variance in monthly temperature normals could be explained by latitude and elevation. Unexplained variances, i.e. the residuals, were modelled with ordinary kriging with exponential semivariograms. The composite grid estimates were calculated by adding the multiple linear trends back to the interpolated residuals at each grid point. Kriged original temperature normals provided a performance benchmark. The cross–validation shows that the interpolation errors of the normals are significantly reduced if the composite method rather than the simple one was used. A gridded monthly dataset with 30-arcsecond spacing was created using the established trends, the kriging model and a digital topographic dataset.
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| 13. |
- Englund, David, et al.
(författare)
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A CASE STUDY OF A FRESHWATER PEARL MUSSEL (MARGARITIFERA MARGARITIFERA) POPULATION IN CENTRAL SWEDEN
- 2008
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 90A:4, s. 251-258
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Tidskriftsartikel (refereegranskat)abstract
- Most of the Margaritifera margaritifera populations in Sweden are not reproducing. Land use such as forestry, eutrophication and water regulation for hydropower are commonly reported causes for the absence of reproduction. A brook with a very dense population of pearl mussels has been investigated with regard to the age distribution of the population and their habitat, in order to discover the reason for the absence of reproduction. The population consisted almost entirely of old mussels with very few young ones. The water flow and chemistry of the water are very stable and well buffered, due to a large glacifluvial deposit in the catchment area. The substrate in the stream is favourable and well aerated to a depth of at least 15 cm. Forestry has been practised with care for at least the last 15 years to avoid siltation of the stream sediments. The most likely reason for the lack of reproduction seems to be the water regulation of the main stream introduced 60 years ago, which has left the main stream dry seasonally. This is likely to have affected the population of brown trout which is the host for the first life-stage of the mussels, the glochidia.
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| 14. |
- Hall, Adrian, et al.
(författare)
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Pre-glacial landform inheritance in a glaciated shield landscape
- 2013
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 95:1, s. 33-49
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Tidskriftsartikel (refereegranskat)abstract
- We seek to quantify glacial erosion in a low relief shield landscape in northern Sweden. We use GIS analyses of digital elevation models and field mapping of glacial erosion indicators to explore the geomorphology of three granite areas with the same sets of landforms and of similar relative relief, but with different degrees of glacial streamlining. Area 1, the Parkajoki district, shows no streamlining and so is a type area for negligible glacial erosion. Parkajoki retains many delicate pre-glacial features, including tors and saprolites with exposure histories of over 1 Myr. Area 2 shows the onset of significant glacial erosion, with the development of glacially streamlined bedrock hills. Area 3 shows extensive glacial streamlining and the development of hill forms such as large crag and tails and roches moutonnées.Preservation of old landforms is almost complete in Area 1, due to repeated covers of cold-based, non-erosive ice. In Area 2, streamlined hills appear but sheet joint patterns indicate that the lateral erosion of granite domes needed to form flanking cliffs and to give a streamlined appearance is only of the order of a few tens of metres. The inheritance of large-scale, pre-glacial landforms, notably structurally controlled bedrock hills and low relief palaeosurfaces, remains evident even in Area 3, the zone of maximum glacial erosion. Glacial erosion here has been concentrated in valleys, leading to the dissection and loss of area of palaeosurfaces. Semi-quantitative estimates of glacial erosion on inselbergs and palaeosurfaces and in valleys provide mean totals for glacial erosion of 8 ± 8 m in Area 1 and 27 ± 11 m in Area 3. These estimates support previous views that glacial erosion depths and rates on shields can be low and that pre-glacial landforms can survive long periods of glaciation, including episodes of wet-based flow.
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| 15. |
- Haussmann, Natalie, et al.
(författare)
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Fine scale variability in soil frost dynamics surrounding cushions of the dominant vascular plant species (Azorella selago) on sub-Antarctic Marion island
- 2009
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 91:4, s. 257-268
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Tidskriftsartikel (refereegranskat)abstract
- Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation-banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub-Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winterthan soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winterthan on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, lee-side snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above −2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia.
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| 16. |
- Hormes, Anne, et al.
(författare)
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A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss Alps
- 2006
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 88 A:4, s. 281-294
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Tidskriftsartikel (refereegranskat)abstract
- We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid-latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon-dated periods defined with less extensive glaciers coincide with periods of reduced radio-production, pointing to a connection between solar activity and glacier melting processes. Measured long-term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long-term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances.
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| 17. |
- Isaksson, Elisabeth, et al.
(författare)
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Climate oscillations as recorded in Svalbard ice core δ 18O records between 1200-1997 AD
- 2005
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 87a:1, s. 203-214
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Tidskriftsartikel (refereegranskat)abstract
- We apply two different time series analytical tools to omega18O records from two Svalbard ice cores. One ice core is from Lomonosovfonna at 1250 ma.s.l. and the other from Austfonna at 750 m a.s.l. These cores are estimated to cover at least the past 800 years and have been dated using a combination of known reference horizons and glacial modelling. Wavelet analysis reveals low frequency oscillations on the 60-120-year scale on the lower elevation site Austfonna while the higher altitude site on Lomonosovfonna does not reveal such variability throughout the record. The second method, Significant Zero Crossing of Derivates (SiZer) does not resolve the low-frequency periodicity seen in the wavelet analysis. The low-frequency variability resolved by the wavelet analysis is similar to what has been found in various climate records including instrumental temperatures and tree-rings, and has been proposed as the most important oscillation for the observed trends in Arctic air temperatures.
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| 18. |
- Johnsen, Timothy F., et al.
(författare)
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New 10Be cosmogenic ages from the Vimmerby moraine confirm the timing of Scandinavian Ice Sheet deglaciation in southern Sweden
- 2009
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Blackwell Publishing / Swedish Society for Anthropology and Geography. - 0435-3676 .- 1468-0459. ; 91A:2, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The overall pattern of deglaciation of the southern part of the Scandinavian Ice Sheet has been considered established, although details of the chronology and ice sheet dynamics are less well known. Even less is known for the south Swedish Upland because the area was deglaciated mostly by stagnation. Within this area lies the conspicuous Vimmerby moraine, for which we have used the terrestrial cosmogenic nuclide (10Be) exposure dating technique to derive the exposure age of six glacially transported boulders. The six 10Be cosmogenic ages are internally consistent, ranging from 14.9 ± 1.5 to 12.4 ± 1.3 ka with a mean of 13.6 ±0.9 ka. Adjusting for the effects of surface erosion, snow burial and glacio-isostatic rebound causes the mean age to increase only by c. 6% to c. 14.4± 0.9 ka. The 10Be derived age for the Vimmerby moraine is in agreement with previous estimates forthe timing of deglaciation based on radiocarbon dating and varve chronology. This result shows promise for further terrestrial cosmogenic nuclide exposure studies in southern Sweden.
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| 19. |
- Khanchoul, Kamel, et al.
(författare)
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Sediment rating curves developed on stage and seasonal means in discharge classes for the Mellah wadi, Algeria
- 2008
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 90A:3, s. 227-236
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Tidskriftsartikel (refereegranskat)abstract
- The focus of the present study was to estimate suspended sediment load from the Mellah catchment (550 km(2)) during storms. Suspended sediment rating curves were developed on data from a 23-year period. The regression technique of this paper involves a division of data into discharge-based classes, the mean concentrations and discharges of which are used to develop power regressions through log-transformation. Sediment rating curves were also developed on means of data grouped into seasons and stages. Sediment loads estimated by rating curves uncorrected for bias involved underestimations of down to 9% compared with loads from measured concentrations. Correction for bias reduced underestimations to a range from 0.79 to 3%. Rating curves divided into rising and falling stages had the lowest underestimation and were used to estimate load during periods without concentration measurements. During the 23-year study period, the mean annual suspended sediment yield was 373 T/km(2). Sediment transport is dominated by winter storms accounting for 61% of the annual load. A high exponent 'b' of the power regression equations during the winter season confirms the intense geomorphic work by winter season storms caused by high intensity rainfall, low vegetation cover, and heavy machine activity in the fields.
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| 20. |
- Klingbjer, Per
(författare)
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Recurring jökulhlaups in Sälka, northern Sweden
- 2004
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : John Wiley & Sons, Inc.. - 0435-3676 .- 1468-0459. ; 86:2, s. 169-179
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Tidskriftsartikel (refereegranskat)abstract
- An ice-dammed lake at the margin of the glacier Slkaglaciren, in the Kebnekaise Mountains in northern Sweden, drained suddenly in July 2003 producing a flood with a measured peak discharge of 9.5±0.25 m3s-1. The total lake volume of 4.55×105 million3 drained within two days. The hydrograph of this event is characteristic of a jökulhlaup controlled by a single basal ice tunnel that enlarges due to melting. The jökulhlaup had an exponential rise to a peak discharge, and following the peak, a very steep fall in discharge as the water supply to the drainage system ceased. A similar jökulhlaup was observed in August 1990 with an estimated release of 8.05×105 m3 water. Jökulhlaups at Slkaglaciren are recurring events and have been indirectly observed since the 1950s.
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