Holocene glacial variations in Sarek National Park, northern Sweden   总被引：3，自引：0，他引：3  

WIBJÖRN KARLÉN  GEORGE H. DENTON 《Boreas: An International Journal of Quaternary Research》1976,5(1):25-56

Detailed mapping of well-preserved moraine systems fronting 17 small alpine glaciers in Sarek National Park in Swedish Lapland reveals two Holocene intervals of prolonged glacier expansion, each involving a complex of minor fluctuations. The younger interval, which corresponds to the Little Ice Age, experienced advances that culminated about A.D. 1916–1920, 1880–1890, 1850–1860, 1800–1810, 1780, 1700–1720, 1680, 1650, and 1590–1620. The older expansion interval, which probably centered around 2500 ¹⁴C yr B.P., experienced several minor fluctuations spread through about 600 years.
Lichen data collected on moraine systems in Sarek are internally consistent from glacier to glacier. Lichen measurements on surfaces of known age in Sarek and nearby Kebnekaise match closely, allowing moraine correlations between these areas. Several older expansion intervals are recorded in the Kebnekaise Mountains. Taken together, the two sequences suggest that a series of prolonged expansion intervals, each similar to the Little Ice Age, has characterized the Holocene in Lapland. Fluctuations of the Scandinavian Ice Sheet in Sweden suggest that this series of Little-Ice-Age events extends back into the late Weichsel in the form of the Younger Dryas and Oldest Dryas stadials.  相似文献   

The relation between glacial ages and terrestrial magnetism     

ERIC OLAUSSON  BJÖRN SVENONIUS 《Boreas: An International Journal of Quaternary Research》1973,2(3):109-115

An attempt is made to show that the change of angular momentum of the earth, caused by glaciations, may compensate the slowing down effect from tidal friction forces and even reverse the polarity in the terrestrial magnetic field.  相似文献   

SUMMER TEMPERATURE VARIABILITY IN CENTRAL SCANDINAVIA DURING THE LAST 3600 YEARS     

HANS W. LINDERHOLM  BJÖRN E. GUNNARSON 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):231-241

ABSTRACT. A Scots pine ( Pinus sylvestris L.) tree-ring width chronology from Jämtland, in the central Scandinavian Mountains, built from living and sub-fossil wood, covering the period 1632 BC to AD 2002, with a minor gap during AD 887–907, is presented. This is the first multi-millennial tree-ring chronology from the central parts of Fennoscandia. Pine growth in this tree line environment is mainly limited by summer temperatures, and hence the record can be viewed as a temperature proxy. Using the regional curve standardization (RCS) technique, pine-growth variability on short and long time scales was retained and subsequently summer (June–August) temperatures were reconstructed yielding information on temperature variability during the last 3600 years. Several periods with anomalously warm or cold summers were found: 450–550 BC (warm), AD 300–400 (cold), AD 900–1000 (the Medieval Warm Period, warm) and AD 1550–1900 (Little Ice Age, cold). The coldest period was encountered in the fourth century AD and the warmest period 450 to 550 BC. However, the magnitude of these anomalies is uncertain since the replication of trees in the Jämtland record is low during those periods. The twentieth century warming does not stand out as an anomalous feature in the last 3600 years. Two multi-millennial tree-ring chronologies from Swedish and Finnish Lapland, which have previously been used as summer temperature proxies, agree well with the Jämtland record, indicating that the latter is a good proxy of local, but also regional, summer temperature variability.  相似文献   

The Baltic Ice Lake in the southwestern Baltic: sequence-, chrono- and biostratigraphy   总被引：3，自引：0，他引：3  

JØRN BO JENSEN  OLE BENNIKE  RZEJ WITKOWSKI  WOLFRAM LEMKE  ANTOON KUIJPERS 《Boreas: An International Journal of Quaternary Research》1997,26(3):217-236

Jensen, J. B., Bennike, O., Witkowski, A., Lemke, W. & Kuijpers, A. 1997 (September): The Baltic Ice Lake in the southwestern Baltic: sequence-, chrono- and biostratigraphy. Boreas , Vol. 26, pp. 217–236. Oslo. ISSN 0300–9483.
This multidisciplinary study focuses on late-glacial deposits in the Mecklenburg Bay -Arkona Basin area. The sequence stratigraphical method has been used on shallow seismic and lithological data, in combination with biostratigraphical work and radiocarbon dating. Glacial-till deposits underlie sediments from two Baltic Ice Lake phases. Varved clay deposits from the initial phase cover the deepest parts of the basins. A prograding delta is observed at the western margin of the Arkona Basin, prograding from the Darss Sill area. The delta system is possibly related to a highstand dated at 12.8 ka. A maximum transgression level around 20 m below present sea level (b.s.l.) is inferred, followed by a drop in water level and formation of lowstand features. The final ice lake phase is characterized by a new transgression. The transgression maximum as observed in the Mecklenburg Bay is represented by transgressive and highstand deltaic deposits. These also indicate a maximum shore level of 20 m b.s.l. The deltaic sediments that contain macroscopic plant remains and diatoms have yielded Younger Dryas ages. Mapping of the late-glacial morphology of the Darss Sill area reveals a threshold at 23 to 24 m b.s.l. This means that the Baltic Ice Lake highstand phases inundated the Darss Sill, which implies that the westernmost extension of the Baltic Ice Lake reached as far as Kiel Bay. Forced regressive coastal deposits at the western margin of the Arkona Basin mark a lowstand level of around 40 m b.s.l. caused by the final drainage of the Baltic Ice Lake. The lowstand deposits predate lacustrine deposits from the Ancylus Lake, which date to approximately 9.6 ka BP.  相似文献   

Optimizing sampling strategy for radiocarbon dating of Holocene fluvial systems in a vertically aggrading setting   总被引：1，自引：0，他引：1  

TORBJÖRN E. TÖRNQVIST  GEO J. VAN DIJK 《Boreas: An International Journal of Quaternary Research》1993,22(2):129-145

In this paper we address the question of how to determine the period of activity (sedimentation) of fossil (Holocene) fluvial systems in vertically aggrading environments. Our data base consists of almost 100 ¹⁴C ages (partly AMS) from the Rhine–Meuse delta in the central Netherlands. Radiocarbon samples from the tops of lithostratigraphically correlative organic beds underneath overbank deposits (sample type 1) yield consistent ages, indicating a synchronous onset of overbank deposition over distances of at least up to 20 km along channel belts. Similarly, ¹⁴C ages from the base of organic residual channel fills (sample type 3) generally indicate a clear termination of within-channel sedimentation. In contrast, ¹⁴C ages from the base of organic beds overlying overbank deposits (sample type 2), commonly assumed to represent the end of fluvial sedimentation, show a large scatter reaching up to 1000 ¹⁴C years. This setting usually produces ¹⁴C ages significantly younger than residual channels of the same fluvial system, indicating the presence of non-depositional unconformities. These usually occur on top of slightly elevated sediment bodies (especially natural levee deposits), which often contain palaeosols. Such hiatuses appear to be much more abundant than hitherto supposed. We conclude that a combination of sample types 1 and 3 generally yields a satisfactory delimitation of the period of activity of a fossil fluvial system. The problems associated with ¹⁴C samples of type 2 may also be present in coastal areas with an alternation of tidal deposits and organic beds.  相似文献   

Quantitative forest-composition sensing characteristics of pollen samples from Swedish lakes   总被引：6，自引：0，他引：6  

I. COLIN PRENTICE  BJÖRN E. BERGLUND  TOMMY OLSSON 《Boreas: An International Journal of Quaternary Research》1987,16(1):43-54

Prentice, I. Colin, Berglund, Björn E. & Olsson, Tommy 1987 03 01: Quantitative forest-composition sensing characteristics of pollen samples from Swedish lakes. Boreas , Vol. 16, pp. 43–54. Oslo. ISSN 0300–9483.
Surface pollen percentages of major tree genera in 53 moderate-sized lakes in south and central Sweden were compared with percentages of mean forest volume derived from survey plots within 5, 10, 20, 50 and 100 km of each lake. A maximum likelihood extended R-value method was used to estimate relative slopes and intercepts of the pollen-tree relationship at each forest sampling radius. Slopes generally went up and intercepts down as sampling radius was increased. Visual goodness-of-fit was optimal at 5–10 km for Picea and at 50–100 km for Pinus , consistent with theoretical pollen source areas. Fagus gave good visual fits at all radii, but Quercus gave indifferent fits and Betula and Alnus poor fits. The taxa differed in relative pollen representation, with relative R-values on the order of 0.11 for Picea , 0.90 for Fagus , 1.0 for Pinus , 1.5 for Quercus , 2.3 for Alnus and 2.5 for Betula . Regional forest patterns can be reconstructed from lake pollen spectra by applying R-values, but the 'region' represented depends on each taxon's pollen dispersal characteristics and spatial pattern. The R-values given here could be used to calibrate European Holocene pollen spectra from moderate-sized lakes for long-term forest dynamic mapping.  相似文献   

RAINFALL CHANGE AND ITS IMPLICATIONS FOR BELG HARVEST IN SOUTH WOLLO, ETHIOPIA   总被引：1，自引：0，他引：1  

STAFFAN ROSELL  BJÖRN HOLMER 《Geografiska Annaler: Series A, Physical Geography》2007,89(4):287-299

Most farmers in the Ethiopian highlands depend on rain‐fed agriculture. Some areas have the favourable situation of having two rainy seasons, Belg (February‐May) and the long rainy season Kiremt (June‐October), which is the case in some parts of South Wollo. Tef (Eragrostis tef) is the staple crop that farmers prefer to grow and the 90‐day variety is suitable for growing during the short rainy season. One out of eight Ethiopians lives in tef potential areas which have Belg rainfall. The aim in this study is to analyse rainfall variation in South Wollo, in particular the area east of the small town of Hayk, and to study its effect on the ability to grow tef during the Belg season. Results from interviews showed that a more difficult farming situation had emerged during the past 40 years, largely due to deterioration of physical resources such as rainfall. Rainfall is analysed by comparing daily rainfall data from four stations in two periods, 1963 to 1982 and 1984 to 2003, for changes in totals, seasonal distribution and variability. Coefficient of variance, rainy days, rainfall intensity and dry spells were analysed. Results from this study show that there have been minor rainfall changes but greater rainfall variability. During fieldwork key informants were asked if they were able to harvest tef during the past nine years, a period that has been used in a model of rainfall influence on tef cultivation during the Belg season. In both 20–year periods, farmers were able to grow tef every second year. In spite of a greater variability in rainfall the farmers proved their knowledge and flexibility and were able to harvest tef in the same number of years during both periods.  相似文献   

Amino acid ratios in Quaternary molluscs and foraminifera from western Norway: correlation, geochronology and paleotemperature estimates     

GIFFORD H. MILLER  HANS PETTER SEJRUP  JAN MANGERUD  BJØRN G. ANDERSEN 《Boreas: An International Journal of Quaternary Research》1983,12(2):107-124

Isoleucine epimerization (alle/Ue) ratios in the pelecypod Mya truncata and benthic foraminifer Cibicides lobalulus from emerged marine units in western Norway allow construction of a regional relative chronostratigraphy for the Ecmian and Weichselian. Two in situ interglacial sections are considered correlative by the similar biostratigraphy and alle/Ile ratios in C. lobalulus. Overlying sediments at the two sites are of both marine and glacial origin. Neither site contains a complete Weichselian record, but allelic ratios, lithostratigraphy and fauna! changes suggest at least four stadial and three interstadial events occurred along the western Norwegian coast during Early and Middle Weichselian time. Kinetic data defining the relationship between the isoleucine epimerization rate constant and temperature for the species studied allow the estimation of paleotemperatures for samples of known age. Accepting published age estimates for the Eemian interglacial beds, the average Weichselian temperature in western Norway is calculated to have been ca. 4°C below the average Holocene temperature, whereas the last interglacial was 1 to 2°C warmer that the Holocene. The limited temperature depression over this region during the Weichselian implies that coastal western Norway was ice-covered only about 30% of this period, and that Atlantic water, although not necessarily in a warm surface current as today, entered the Norwegian Sea during much of marine isotope stage 5 and intermittently during stage 3. Interpolated amino acid ages date interstadial events at ca. 94 ka, 78 ka and 52 ka, B.P., whereas glacial events are dated ca. 103 ka and bracketed by limiting dates between 78 and 89 ka, between 52 and 63 ka and less than 36 ka B.P.  相似文献   

Effect of auroral electrojets and solar wind parameters on variations in the intensity of low-latitude geomagnetic disturbances and Dst during the extremely large magnetic storm of November 20–21, 2003   总被引：1，自引：1，他引：0  

S. I. Solovyev  R. N. Boroyev  A. V. Moiseyev  A. Du  K. Yumoto 《Geomagnetism and Aeronomy》2008,48(3):293-306

The effect of auroral electrojets on the variations in the low-latitude geomagnetic disturbances and Dst during a strong magnetic storm of November 20–21, 2003, with Dst ≈ ?472 nT has been studied based on the global magnetic observations. It has been indicated that the magnetospheric storm expansive phase with Δt ≈ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 1–2 h results in positive low-latitude disturbances (ΔH) of the same duration and with an amplitude of ～ 30–100 nT in the premidnight-dawn sector. A growth of negative low-latitude ΔH values and Dst is mainly caused by regular convection electrojets with Δt ≥ 10 h, the centers of which shift to latitudes of ～ 50°–55° during the storm development. It has been established that the maximal low-latitude values of the field ΔH component at 1800–2400 MLT are observed when the auroral luminosity equatorward boundary shifts maximally southward during an increase in the negative values of the IMF B _z component. It has been assumed that, during this storm, a magnetic field depression at low latitudes was mainly caused by an enhancement of the partially-ring current which closes through field-aligned currents into the ionosphere at the equatorward boundary of the auroral luminosity zone.  相似文献   

Southwesterly flows over southern Norway—mesoscale sensitivity to large-scale wind direction and speed     

IDAR BARSTAD  SIGBJØRN GRØN&#;S 《地球，A辑:动力气象学与海洋学》2005,57(2):136-152

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