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CAMILLA S. ANDRESEN SVANTE BJORCK 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):159-174
ABSTRACT. Two well dated Holocene sediment records bordering the Denmark Strait region have been used to reconstruct past climate variability. The content of biogenic silica, classic and organic material and moss in a lacustrine record from Lake N14 has been used to infer past variability in precipitation and temperature in southern Greenland. Sedimentologic and petrologic composition of sand in a shelf sediment record from the Djúpáll trough is used to infer past variability in the northwestern storm activity on northwestern Iceland, which probably also affected the inflow of polar waters from the East Greenland Current. Our evaluation of these records with a number of previous studies from the region documents Holocene climatic optimum conditions peaking between 8000 and 6500 calendar years before present (cal yr BP). Mid-Holocene climate deterioration set in around 5000 cal yr BP followed by a further marked setback around 3500 cal yr BP. A stacking of climate variability on a centennial timescale from previous studies in the area shows a fairly good correspondence to the timing of marked cold and warm events as evidenced from the Lake N14 and the Djúpáll trough records. Cooler periods are explained as the response to marked incursions of ice-laden polar water from the Arctic Ocean to the Denmark Strait region. Cool northerly and northwesterly winds along the East Greenland coast in relation to frequent strong atmospheric low pressure in the Barents Sea, coupled with strong high pressure over Greenland, would have favoured southward export of polar waters. A comparison with the proxy records of nuclide production (14 C and 10 Be) suggests that solar activity may have had some influence on the atmospheric pressure distribution in the Denmark Strait region. 相似文献
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Two raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by 14 C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions. 相似文献
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Absolute ages of migmatization in the polymetamorphic, parautochthonous basement of the Sveconorwegian Province, Sweden, have been determined using U–Pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses. Migmatite zircon was formed by recrystallization whereas dissolution–reprecipitation and neocrystallization were subordinate. The recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes. It is backscatter electron‐bright, U‐rich (800–4400 ppm) with low Th/U‐ratios (generally 0.01–0.1), unzoned or ‘oscillatory ghost zoned’, and occurs as up to 100 μm‐thick rims with transitional contacts to cores of protolith zircon. Protolith ages of 1686 ± 12 and 1668 ± 11 Ma were obtained from moderately resorbed, igneous zircon crystals (generally Th/U = 0.5–1.5, U < 300 ppm) in mesosomes; protolith zircon is also present as resorbed cores in the leucosomes. Linkage of folding, synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south‐vergent folding at 976 ± 7 Ma. At a second locality, similar recrystallized zircon rims in leucosome date pre‐Sveconorwegian migmatization at 1425 ± 7 Ma; an upper age bracket of 1394 ± 12 Ma for two overprinting phases of deformation (upright folding along gently SSW‐plunging axes and stretching in ESE) was set by zircon in a folded metagranitic dyke. Lower age brackets for these events were set at 952 ± 7 and 946 ± 8 Ma by zircon in two crosscutting and undeformed granite–pegmatite dykes. Together with previously published data the present results demonstrate: (i) Tectonometamorphic reworking during the Hallandian orogenesis at 1.44–1.42 Ga, resulting in migmatization and formation of a coarse gneissic layering. (ii) Sveconorwegian continent–continent collision at 0.98–0.96 Ga, involving (a) emplacement of an eclogite unit, (b) regional high‐pressure granulite facies metamorphism, (c) southvergent folding, subhorizontal, east–west stretching and migmatization, all of which caused overprint or transposition of older Mesoproterozoic and Sveconorwegian structures. The Sveconorwegian migmatization and folding took place during or shortly after the emplacement of Sveconorwegian eclogite and is interpreted as a result of north–south shortening, synchronous with east–west extension and unroofing during late stages of the continent–continent collision. 相似文献
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SUNE ANDERSSON 《International journal of geographical information science》2013,27(3):253-263
Abstract The Swedish Land Data Bank System has been developed in order to rationalize handling of data on real properties and land. The system replaces earlier manual systems for property and land registration. It interacts regularly with other EDP-based information systems and serves as a land information system (LIS) in a broad sense. The system is being steadily extended to cover all parts of the country. The costs for design, implementation and maintenance of the system are covered by reductions of costs for property and land registration. 相似文献
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Rapid Holocene climate changes in the North Atlantic: evidence from lake sediments from the Faroe Islands 总被引：1，自引：1，他引：1
CAMILLA S. ANDRESEN SVANTE BJÖRCK MATS RUNDGREN DANIEL J. CONLEY CATHERINE JESSEN 《Boreas: An International Journal of Quaternary Research》2006,35(1):23-34
Holocene records from two lakes on the Faroe Islands were investigated to determine regional climatic variability: the fairly wind-exposed Lake Starvatn on Streymoy and the more sheltered Lake Lykkjuvötn on Sandoy. Sediment cores were analysed for content of biogenic silica, organic carbon and clastic material, and magnetic susceptibility. In addition, a new qualitative proxy for past lake ice cover and wind activity was developed using the flux of clastic grains that are larger than 255 μm. Both long-term and short-term climatic developments were similar between the two lakes, suggesting a response to a regional climate signal. The long-term climate development is characterized by early Holocene rapid warming followed by Holocene climatic optimum conditions ending around 8300 cal. yr BP. A more open landscape as evidenced from increased sand grain influx in the period 8300–7200 cal. yr BP could reflect the aftermath of the 8200 cal. yr BP event, although the event itself is not recognized in either of the two lake records. From around 7200 cal. yr BP the mid-Holocene climate deterioration is observed and from 4200 cal. yr BP the climate deteriorated further with increased amplitude of centennial cooling episodes. 相似文献
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Abstract Spatial rainfall patterns and seasonal variability were assessed for a mountainous river basin with monsoon climate. Factors were identified that could explain this variability, and a GIS-supported method to determine the areal distribution of precipitation was developed. To find acceptable regression equations, a division had to be made between rainfall stations dominated by the southwest-monsoons and the northeast-monsoons, respectively. Distance to the southwestern border was the main explaining factor for precipitation at southwest-monsoon dominated stations. For northeast-monsoon dominated stations, altitude and slope were the most important factors. The basin was divided into pixels with characteristics typical for northeast- or southwest-monsoon dominated rainfall stations to allow calculation of spatial rainfall. The difference when comparing regression-based estimates with Thiessen-based estimates was small when considering the annual estimates for the whole basin. However, when analysing seasonal rainfall or sub-catchments, the differences between Thiessen-based and regression-based estimates were significant. 相似文献
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Late Quaternary environmental history of central Prins Karls Forland, western Svalbard 总被引：1，自引：0，他引：1
TORBJÖRN ANDERSSON STEVEN L. FORMAN ÓLAFUR INGÓLFSSON WILLIAM F. MANLEY 《Boreas: An International Journal of Quaternary Research》1999,28(2):292-307
This paper presents the results from stratigraphic and geomorphologic investigations in the Poolepynten area, Prins Karls Forland, western Svalbard. Field mapping, soil profile development and 14C dating reveal the existence of at least two generations of raised beach deposits. Well-developed raised beaches rise to the Late Weichselian marine limit at 36 m a.s.l. Discontinuous pre-Late Weichselian beach deposits rise from the Late Weichselian marine limit to approximately 65 m a.s.l. Expansion of local glaciers in the area during the Late Weichselian is indicated by a till that locally overlies pre-Late Weichselian raised beach deposits. Stratigraphic data from coastal sections reveal two shallow marine units deposited during part of oxygen isotope stage 5. The two shallow marine units are separated by a subglacially deposited till that indicates an ice advance from Prins Karls Forland into the Forlandsundet basin some time during the latter part of stage 5. Discontinuous glaciofluvial deposits and a cobble-boulder lag could relate to a Late Weichselian local glacial advance across the coastal site. Late Weichselian/early Holocene beach deposits cap the sedimentary succession. Palaeotemperature estimates derived from amino acid ratios in subfossil marine molluscs indicate that the area has not been submerged or covered by warm based glacier ice for significant periods of time during the time interval ca. 70 ka to 10 ka. 相似文献
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SOFIA ANDERSSON KRISTIAN SCHONING 《Boreas: An International Journal of Quaternary Research》2010,39(4):749-760
Andersson, S. & Schoning, K. 2010: Surface wetness and mire development during the late Holocene in central Sweden. Boreas, Vol. 39, pp. 749–760. 10.1111/j.1502‐3885.2010.00157.x. ISSN 0300‐9483. Late Holocene mire development and surface wetness changes have been studied in a small mixed mire located in central Sweden. Today the mire is characterized by a mainly ombrotrophic centre dominated by Sphagnum mosses, with Carex content increasing towards the more minerotrophic mire margins. Two peat sequences extracted from the central ombrotrophic part were investigated for stratigraphy, humification, testate amoebae analysis, C/N ratio and δ13C and δ15N stable isotopes. Three main stages of mire development are identified, with the first stage, between c. 4200 and 2600 cal. yr BP, characterized by water‐logged conditions, suggesting a minerotrophic fen stage. The second stage, between c. 2600 and 1000 cal. yr BP, is characterized by more ombrotrophic conditions and Sphagnum‐dominated vegetation. The onset of the prominent change at c. 2600 cal. yr BP could have been initiated by climate change coincident with a change in solar activity. The last stage, between c. 1000 and 50 cal. yr BP, is dominated by more ombrotrophic conditions, suggesting increased precipitation. This study shows that the response of hydrological proxies in a mixed mire during its development towards more ombrotrophic conditions might result in conflicting results, a finding that needs to be considered in palaeoenvironmental reconstructions from mires that change between ombrotrophic and minerotrophic settings. 相似文献