摘要:

ABSTRACTMonthly zonal indices (ZI:s) from January 1899 to August 1992 in a North Atlantic area (40°W-5°W) and a north European area (5°E-40°E) are analysed. The ZI:s are calculated as the sea-level pressure difference between latitudes 45°N and 65°N in a 5°by 5°gridded data set.Time series analysis show that the ZI:s for each area does not show the same evolutionary trends and that any distinct periods are hard to identify, except for a phase with low ZI for winters over the North Atlantic area during 1955–70. Overall positive linear trends (p=0.02) are present during summer in the North Atlantic area and during autumn in the European area. Since about 1970 the strength of the westerlies has increased markedly during winter and spring, especially in the North Atlantic area.Correlations between ZI:s for the eastern area and monthly average temperatures from two stations in southern Scandinavia show a distinct annual course with positive (≈0.7) correlation during December-March and negative correlation (≈-0.6) during summer. In May and September, the correlations are close to zero, bringing the overall correlations in spring and autumn to positive values. Thus, an effect of increased zonality in southern Scandinavia is an increase in annual mean temperature. The correlation between ZI and temperature is shown to vary over time (especially for spring and autumn) indicating that the relationship between the strength of the zonal flow and temperature signal is not consistent.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880419

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThis paper utilizes the partial duration series technique to quantify the flooding regime of high-closure lakes, a typical terrestrial portion of the delta plain, and channel levees in the east-central Mackenzie Delta. This analysis demonstrates that the lowest high-closure lakes are flooded annually to depths of up to 4 m, and for durations of up to 30 days. The highest lakes, however, do not flood annually and have much smaller magnitudes and durations.Since the delta plain is at a higher elevation than the lakes, the land is flooded less frequently and for shorter durations. In fact, much of the delta plain near Inuvik does not flood annually, and when it does flood, it is flooded by relatively shallow depths of water and for short duration. Channel levees in the study area vary greatly in elevation, with the lowest levees found on recently developed channels. They are inundated annually for long periods of time, while the highest elevation levees, found on older, established channels, are inundated infrequently and for short periods of time.Future work is required to relate variations in flooding to other factors such as sedimentation rates, nutrient cyding, and vegetation distributions. This would enable better predietians of the effect of environmental change on the Mackenzie Delta ecosystem.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880420

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTA long-term approach based on detailed mapping and lichenometry provides additional information concerning talus-foot rock glaciers overstepping raised beaches in Svalbard. Their regional distribution is primarily controlled by the tectonic pattern and especially by the network of major thrusting faults. Tentative dating suggests that the rock glacier formation startedca.3500 B.P.,i.e.during the initial phase of a Neoglacial cooling period following the Atlantic optimum. Average rates of movement of rock glacier fronts inferred for the whole period of activity have been tentatively estimated at 1–7 cm/yr. Such values are consistent with those obtained from monitoring of similar forms performed in the eighties by Sollid and Sørbel (1992). Nevertheless, the gradual decrease of the debris size from the rock glacier fronts to the adjoining rock walls is still unexplained. On the NW coast, the possible role of stress relaxation during the initial phase of rock glacier development comes up against the early age of the deglaciation.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880421

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTSubfossil pine (Pinus sylvestrisL.) occurs in various deposits and in great frequency well above the current altitudinal pine limit in the Scandes Mountains. These tree remnants constitute a fairly continuous record of range-limit dynamics throughout the Holocene and offer excellent potential for palaeoecological as well as palaeoclimatological research. General aspects of this record are discussed, including the fundamental issue of the circumstances of preservation. It is proposed that throughout the Holocene conditions for preservation have existed at the fluctuating tree-limit. Hypothetically, temporal clusters and gaps in the frequency distribution of radiocarbon dates can fairly consistently reflect climatic variability. Tree-limit recession in particular may be rapid, in response to episodes of severe winter cold. Such events may appear disproportionately protracted backwards in time, due to frost-heaving and rain-induced erosion of deposits with subfossils. Additional aspects of subfossil pine, which are briefly discussed, include relative altitude, ecological setting, population structure, stress and disturbance, dendrochronology and recent processes.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880422

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTSequences of ancient end moraines are evidence that successively smaller ice sheets centred on the Patagonian Andes developed during successive Quaternary glaciations. At Torres del Paine (51°S, 73°W) the volume and variety of landforms which mark the extent of phases of the last ice sheet are remarkably small, in contrast with far larger moraines deposited by older, more extensive ice sheets. This implies that the sediment budget of the last ice sheet was low. Potential debris sources are considered, and it is concluded that supraglacial sources were few, and that reworking of older drift was limited because much of the last ice sheet advanced over drift free terrain, the deposits of earlier ice sheets being confined to areas beyond the extent of the last ice sheet. As in other mid-latitude areas, glacial erosion in the Torres del Paine area appears to have decreased with successive glaciations. The size of a moraine may be unrelated to the glaciological/climatic significance of a particular glacial fluctuation.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880423

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor