摘要:

ABSTRACT14C datings of driftwood from raised beaches on the island Alexandra Land, Franz Josef Land, Russia, indicate deglaciation by 680014C years BP. The age of a diamicton containing small shell fragments, found beneath a beach ridge formed c. 5000 BP, has been dated to 8265±9014C years BP (age after sea correction 7755 BP), suggesting that Alexandra Land was at least partly deglaciated by that time. The deposit containing shell fragments has been interpreted as a till which, if the interpretation is correct, indicates that a glacial advance occurred sometime between 7800 and 6800 BP.The highest shoreline, 23.5 m a.s.l., was formed either during a rapid deglaciation of the island or during a transgression. A shoreline displacement curve has been constructed for Alexandra Land. The rate of shore displacement since 6800 BP is calculated to 0.3 m/100 years. No pumice was found on Alexandra Land.Lunar Ice Cap on Alexandra Land was smaller than it is at present when the highest shoreline was formed, 6800 BP. The ice cap is believed to now be close to its Mid- to Late Holocene maximum, as almost all fluctuations of the Lunar Ice Cap since the deglaciation seem to have been within the present day glacier margin. A climatic deterioration c. 2000 BP is indicated by the formation of an ice/snow dammed lake.Evidence of former glácier movement directions, such as striae and chattermarks, were not found on Alexandra Land. However, the large scale bedrock topography and the orientation of elongated bedrock basins seem to indicate ice flow in a southeast to northwest direction.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880371

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTTiksi area in eastern Siberia has generally been believed to have remained ice-free throughout the entire Ice Age. However, new glacial geomorphological research in the region has revealed evidence of a former ice sheet centered on the East Siberian shelf and reaching as far as Tiksi Bay. Among indications supporting this concept are fresh-looking U-shaped valleys, giant flutes, rock drumlins and other ice-erosional features, as well as systems of glacio-tectonic ridges coupled with rock basins (“hill-and-hole pairs”)—all attesting to a former ice motion in a northeast-southwest direction.The work carried out in May 1990 by a Swedish-Soviet field party was aimed at resolving the chronology of the latest glacial events in the Tiksi area. To this end, the bottom sediments of two lakes joined by glaciotectonic ridges were cored, analysed and AMS-14C dated. The ages of 6450+/-110 6870+/-80 and 8500+/-160 radiocarbon years BP were minimum dates obtained for the beginning of lacustrine sedimentation in the basins. This suggested that the last icesheet glaciation of the area had been of Late Pleistocene age.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880372

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTThe glacial landscape in northwestern Sweden is a palimpsest of landforms created by several ice sheets. Using crosscutting relationships and other morphological criteria, the glacial and glaciofluvial landforms formed during the Late Weichselian recession were discriminated and mapped separate from landforms from older glacial events. The geographical pattern of the last deglaciation could thus be reconstructed on the basis of“young”landforms only. The Late Weichselian ice sheet was over large areas continuously cold based. Only in limited zones were thawed-bed conditions reached during the deglaciation. The older land-forms all reflect ice flow and meltwater drainage from smaller ice sheets related to the mountain chain. A marginal position, characterized by lateral moraines, of such an ice sheet was discovered along the eastern rim of the mountain chain. This marginal zone is interpreted to represent a temporary halt in the recession of an older west-centered ice sheet, possibly during isotope stage 5b.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880373

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTGlacial and non-glacial (control) lakes are used to reconstruct a continuous record of Holocene glacier variations from14C-dated glacio-lacustrine sediments in four distal glacial lakes from southern Norway. Silt/clay bands (commonly 5–10 cm thick), characterized by low organic content, high X-ray density, high mineral magnetic susceptibility and high natural remanent magnetisation (NRM) intensity, are attributed to enhanced minerogenic sedimentation following glacierization of the catchment. These glacigenic bands are different from thinner (0–2 cm) minerogenic laminations found in both glacial and non-glacial lakes with steep slopes in the catchment. Glaciers disappeared from at least three of the catchments shortly after 9000 BP and remained absent throughout the‘Climatic Optimum’of the early- to mid-Holocene. Relatively large glaciers and higher-altitude glaciers formed earlier, existed longer and/or exhibited more Neoglacial expansion episodes. Glaciers existed in the lake catchments at least during the following intervals: Midtivatnet, 3400–3000, 2200–2100, and after 1000 BP; Gjuwatnet, 6400–5900, 3000–2600, 2500–2300, 1600–1400, and for two intervals after 750 BP; Flatbrevatnet II, continuously since 4900 BP; Storevatnet, one interval after 1000 BP. All glaciers attained their Neoglacial maxima during the last major Neoglacial expansion episode (the‘Little Ice Age’). This pattern implies a response to a fluctuating but generally deteriorating climate during the mid- to late-Holocene.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880374

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTFloating islands of vegetation-covered peat which include palsas are observed in spring-fed fens within a string bog in the MacMillan Pass, Yukon Territory, Canada. The fens are dammed by stable and long-lived banks of moss and contain floating islands of peat. The smaller 80 m2islands consist of sphagnum peat over 1.5 m deep with the surface rising up to 20 cm above the surrounding water level. They contain seasonal frost and have aSphagnum-Betulavegetation. Larger islands (about 280 m2) have a height of up to 70 cm and contain permafrost. The peat is up to 3.3 m thick and consists of sphagnum peat, although the present-day living vegetation cover consists of aCladonia-Ericaceae-Betulaassociation. The embryonic palsas float in the water and in June a layer of water separates the frozen peat of the permafrost base from the underlying unfrozen peat. A distinct layer of volcanic ash of known origin provides a basis for an estimate of the rate of sphagnum accumulation (approximately 1.1-1.2 mm/yr). Electrical conductivity of the ice demonstrates that initially fen water freezes in the peat, but that subsequently more water from precipitation is added from the overlying active layer and snow bank. In the upper layers, the ratio of volumes of precipitation to fen water is 3:2, but can be as high as 13:1 in nearby mature palsas located in similar fens. Critical conditions for formation of permafrost appear to be a thickness of over 2 m of floating peat with its surface rising more than 40 cm above the level of the surrounding fen.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880375

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTMeteorologic and hydrographic observations 8–12 April, 1991 were collected to analyze the hydraulic and hydrographic relationships between Aarhus Bay and the surrounding marine areas in relation to concurrent hydrographic observations in Aarhus Bay. Thermal IR satellite recordings from the entire area of the domestic Danish waters and the Skagerrak support the conclusions.Aarhus Bay has a direct connection with the south-western Kattegat through a deep and narrow entrance and is hydrographically situated at the frontal zone between the low saline water from the Baltic Sea and the high saline water from the North Sea. There is a large variation of the hydrographic conditions in the bay as a consequence of the alternating dominance of water from the Baltic Sea and water from the North Sea.During the study period, there is a reversal of the current field in the domestic Danish waters. A barotropically driven southward current is replaced by a northerly current in the Great Belt on 10 April.This study shows that Aarhus Bay has a short response time to barotropically induced changes in the hydrographic conditions of the surrounding areas, and that local topography regulates the baroclinically induced purging currents driven by the hydrographic conditions in the bay that contrast the conditions outside the Bay.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880376

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

ABSTRACTPaucity of suitable records of streamflow for the numerous drainage basins in West Africa makes recourse to the water balance approach to hydrological regionalization necessary. Principal components analysis reduced to three components a water balance data set of 12 variables computed for 109 stations in West Africa. Scores on these components were grouped by cluster analysis into seven hydrological regions. The locations of the 21 international drainage basins in the area vis-a-vis these regions are examined, and most are seen to lie in hydrologically unfavourable environments. The implications of this for future large scale water projects are pointed out.

ISSN:0435-3676    

DOI:10.1080/04353676.1992.11880377

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor