Late‐glacial to Holocene environmental changes and climate variability: evidence from Voldafjorden,western Norway     

H. P. Sejrup  H. Haflidason  T. Flateb  D. Klitgaard Kristensen  K. Grsfjeld  E. Larsen 《第四纪科学杂志》2001,16(2):181-198

Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS ¹⁴C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine‐grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9–7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large‐scale sliding on the continental margin off Norway (the Storegga Tsunami). During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea‐surface summer temperatures, possibly with year‐round sea‐ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea‐surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4–9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4–0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large‐scale oceanic circulation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Marine evidence for climatic instability during the last interglacial in shelf records from northwest Europe     

Marit-Solveig Seidenkrantz  Peter Kristensen  Karen Luise Knudsen 《第四纪科学杂志》1995,10(1):77-82

Data from the Greenland ice sheet and continental records from Europe have indicated climatic fluctuations during the last interglacial (Eemian: Oxygen Isotope Substage 5e). Similar fluctuations have not, however, been documented previously from marine environments. Here, we show the existence of two cold events during substage 5e in two marine, benthic foraminiferal, shelf records from northwest Europe and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation.  相似文献   

Surface-layer gusts for aircraft operation     

G. S. Young  L. Kristensen 《Boundary-Layer Meteorology》1992,59(3):231-242

We use Monin-Obukhov similarity theory to extend the Kristensen et al. (1991) aviation gust estimation technique from the neutral to the diabatic surface layer. Example calculations demonstrate the importance of this correction. Simple stability class methods using only standard aviation surface observations are shown to be useful although less accurate and less precise than methods which make full use of Monin-Obukhov similarity results.  相似文献   

The ‘good farmer’: Studies of farm management practices and landscape change     

Thanasis Kizos  Lone S. Kristensen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):105-106

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Endemic avifaunal biodiversity and tropical forest loss in Makira, a mountainous Pacific island     

Finn Danielsen  Christopher E. Filardi  Knud A. Jønsson  Victor Kohaia  Niels Krabbe  Jan B. Kristensen  Robert G. Moyle  Patrick Pikacha  Michael K. Poulsen  Mikael K. Sørensen  Charles Tatahu  Joseph Waihuru  Jon Fjeldså 《Singapore journal of tropical geography》2010,31(1):100-114

Anthropogenic habitat changes and the introduction of pigs, dogs, cats and rats have caused a catastrophic decline in the terrestrial biodiversity of Pacific archipelagos. At present, economic globalization and an increased demand for timber are promoting industrial logging and plantation expansion. Commercial logging can be sustainable but in practice it more often leads to land degradation, especially on small flat islands. On large and mountainous islands, however, more modest impacts can be expected as the narrowly endemic species tend to inhabit montane forests where logging is difficult. In this study we use ornithological data collected at different elevations to assess the extent to which the avifauna of Makira, a large mountainous island in Melanesia, will be affected by deforestation of the lowlands, most of which are under timber concessions. Our data suggest that a majority of the endemic bird species use lowland forest to some extent and that this may even apply to species hitherto associated with montane forest. If current commercial forestry programmes are continued, the forest habitat may be disturbed or lost over large parts of Makira, potentially undermining the natural resource base for the local subsistence economy, exacerbating climate change and threatening the integrity of one of the most important areas for biodiversity conservation on earth. Our study highlights the importance of understanding the habitat requirements of endemic species and the urgency of establishing and effectively managing community-based protected areas in suitable lowland forests of the Pacific.  相似文献   

Measurements of powder snow avalanche- nature -     

K. Nishimura  F. Sandersen  K. Kristensen  K. Lied 《Surveys in Geophysics》1995,16(5-6):649-660

Snow cloud growth rates of powder snow avalanche were obtained with analysing the pictures recorded in Ryggfonn, Norway. Although results showed wide scattering, as far as the data obtained in runout zone are concerned, they roughly agreed with the water tank experiments by Beghin and Olagne (1991).Air movement in snow avalanche cloud was measured with an ultra-sonic anemometer in Kurobe Canyon, Japan. It showed rising current existed near the front and downward at the trail. Comparing with drifting snow threshold and particle suspension criterion, entrainment, suspension and deposition of snow particles in the snow cloud were discussed.  相似文献   

Comments on ‘effect of finite sampling on atmospheric spectra’     

L. Kristensen  P. Kirkegaard 《Boundary-Layer Meteorology》1989,48(1-2):205-210

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Afforestation of European landscapes: How do different farmer types respond to EU agri-environmental schemes?   总被引：1，自引：0，他引：1  

Søren Præstholm  Anette Reenberg  Søren Pilgaard Kristensen 《GeoJournal》2006,67(1):71-84

This paper investigates how different types of farmers manage the landscape with primary emphasis on farmland afforestation, planned landscape changes, and the extent to which EU agri-environmental schemes take farm type specific characteristics into account in information strategies. The empirical data concern landscape practices of more than 2,000 landowners in 16 European areas in eight countries who were surveyed using quantitative questionnaires. Supplementary in-depth interviews were conducted for two case areas in Denmark to further investigate the role of the policy information environment. The analysis is based on a categorization of the farmers into hobby, part-time, full-time and retired farmers. This study shows that hobby farmers constitute a high proportion of landowners and manage a large part of the rural landscape. At the same time, hobby farmers are relatively more interested in landscape changes and differ from other landowners by considering farmland afforestation more often than full-time landowners, for example. Yet, 40% of the hobby farmers who are considering farmland afforestation are not familiar with the agri-environmental scheme for farmland afforestation. One reason may be their low membership rate in traditional information networks such as farmers’ or foresters’ associations, as revealed by the in-depth analysis of the cases in Denmark. Thus, it is proposed that policy impact may be improved if farmer type specific differences are explicitly taken into account in the scheme logistics for EU agri-environmental schemes.  相似文献   

Hydrothermal alteration of oceanic crust in the West Philippine Sea Basin (Ocean Drilling Program Leg 195, Site 1201): inferences from a mineral chemistry investigation     

M. D’Antonio  M. B. Kristensen 《Mineralogy and Petrology》2005,83(1-2):87-112

Summary Secondary minerals of a 91 meters-thick sequence of pillow basalts cored during ODP Leg 195 (Site 1201, West Philippine Basin) were investigated to reconstruct the hydrothermal alteration history and regime. The basement was first buried by red clays, and then by a thick turbidite sequence, thereby isolating it from seawater. The basalts are primitive to moderately fractionated, texturally variable from hypocrystalline and spherulitic to intersertal, sub-ophitic and intergranular. Relic primary minerals are plagioclase, clinopyroxene and opaques. Hydrothermal alteration pervasively affected the basalts, generating secondary clay minerals (mostly glauconite, minor Al-saponite and Fe-beidellite), iddingsite, Ca–Na-zeolites, minor alkali-feldspar and calcite. The secondary mineral paragenesis and mutual relationships suggest that the hydrothermal alteration occurred under zeolite-facies conditions, at temperatures <100–150°C. The main phase of alteration occurred under oxidizing conditions, with a high seawater/rock ratio, in an open-circulation regime, at temperatures of 30–60°C, with precipitation of abundant glauconite and iddingsite. A later stage of alteration occurred at ca. 70°C, with precipitation of abundant Ca–Na-zeolites and minor calcite, in a more restricted circulation regime as a consequence of basement burial under the sedimentary cover, which supplied an altered, Ca-rich and Mg–K-sulfate-poor water causing precipitation of almost pure calcite.  相似文献   

The production of relaid blue mussels (Mytilus edulis L.) in a Danish fjord     

Kristensen  Per Sand; Lassen  Hans 《ICES Journal of Marine Science》1997,54(5):854-865

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