排序方式： 共有14条查询结果，搜索用时 390 毫秒
1.
2.
3.
4.
The Ctenophora Mertensia ovum and Beroe cucumis , collected using both conventional sampling gear and scuba divers, were studied in the Barents Sea east of Bjørnøya and North Norway in spring 1987 and summer 1988. Among the gelatinous zooplankton, Mertensia ovum was the most consistently abundant copepod predator.
Feeding experiments were conducted to evaluate the predation rate of M. ovum in various trophic regimes. This ctenophore can take prey varying in size from small copepods to amphipods and krill, but gut-content analyses from field-collected specimens as well as experimental results showed that the main food source for adults was large-sized copepods (e.g. Calanus finmarchicus, C. glacialis, C. hyperboreus, Metridia longa ). The robust tentacle arrray of M. ovum makes this species effective as a predator on large prey. The high potential predation rate of this ctenophore relative to its estimated metabolic cost of only 1.7% of the body energy content d−1 suggests that M. ovum may be able to maintain a positive energy balance even in conditions of low prey abundance. It is suggested that a single exploitation of a zooplankton patch may provide energy for survival for a very long time.
The potential impact of M. ovum on Barents Sea copepod populations is estimated on the basis of the minimal observed average daily ration in experiments and from field data on gut contents. Using abundances of copepods for the area, and the actual predator biomass collected, it was estimated that an average of 0.7% of the copepod fauna per day could fall prey to this predator. 相似文献
Feeding experiments were conducted to evaluate the predation rate of M. ovum in various trophic regimes. This ctenophore can take prey varying in size from small copepods to amphipods and krill, but gut-content analyses from field-collected specimens as well as experimental results showed that the main food source for adults was large-sized copepods (e.g. Calanus finmarchicus, C. glacialis, C. hyperboreus, Metridia longa ). The robust tentacle arrray of M. ovum makes this species effective as a predator on large prey. The high potential predation rate of this ctenophore relative to its estimated metabolic cost of only 1.7% of the body energy content d
The potential impact of M. ovum on Barents Sea copepod populations is estimated on the basis of the minimal observed average daily ration in experiments and from field data on gut contents. Using abundances of copepods for the area, and the actual predator biomass collected, it was estimated that an average of 0.7% of the copepod fauna per day could fall prey to this predator. 相似文献
5.
ULF HAFSTEN PHILIP A. TALLANTIRE 《Boreas: An International Journal of Quaternary Research》1978,7(2):109-122
Pollen analysis, macrosubfossil determinations and radiocarbon datings from a 0.95 m thick peat deposit resting on sand and buried by a 1.3 m thick beach ridge at Haramsøy (an outer-arc island off the coast of Møre og Romsdal province), reveal changes in the local vegetation and in the groundwater level of the landward lagoon-like area. These are considered to reflect the relative shore-level changes between late Preboreal and early Atlantic times: an initial section with a high groundwater level reflecting the early Boreal high shore level, an intervening section with a low groundwater level, from the time of the Boreal regression minimum, and a final section, with a rising groundwater level, reflecting the late Boreal eustatic rise in sea level, which led to complete burial of the peat and the formation of an extensive Tapes beach ridge. Radiocarbon dates reveal that the basal sand (approx. 8 m above sea level) rose above sea level at approx. 9500 B. P. and that the top of the peat (approx. 9 m above sea level) was transgressed by the sea at approx. 7300 B. P. The spread of alder ( Alnus ) within the area may have been delayed by a thousand years compared with other regions in south Norway. 相似文献
6.
Copepod grazing and its potential impact on the phytoplankton development in the Barents Sea 总被引：2，自引：0，他引：2
ULF BÅMSTEDT HANS CHRISTIAN EILERTSEN KURT S. TANDE DAG SLAGSTAD HEIN RUNE SKJOLDAL 《Polar research》1991,10(2):339-354
Compiled data from published and unpublished sources on copepod grazing of the large-sized copepods in the Barents Sea give wide ranges in grazing rates. Approximate average values indicate daily rations of 7–18% for copepodite stages V and VI and considerably higher values for the earliest copepodite stages. It is demonstrated that individual variability in gut fullness of copepods from a given locality is typically very high and not closely related to variable food abundance or depth of occurrence. There is no diel feeding rhythm during the summer, and even when relating copepod grazing to a number of biotic and abiotic factors through stepwise linear regression analysis, much of the variability remains unexplained. It is suggested that feeding behaviour, food quality and feeding history of the copepods all play important roles as factors which regulate copepod grazing. Model simulations on the phytoplankton succession, using literature data on laboratory-determined growth characteristics for solitary cells and colonies of the prymnesiophyte Phaeocystis pouchetii and large diatoms, indicate that the extent of the mixed layer and selective grazing by zooplankton are important factors that may explain the occurrence of dense blooms of P. pouchetii colonies, frequently observed during the spring. 相似文献
7.
8.
ULF ERLINGSSON 《Geografiska Annaler: Series A, Physical Geography》2008,90(2):125-140
Since the rapid rate of global warming at the onset of the Bølling interstadial became evident, its cause has been under debate. It coincides closely in time with a strong global transgression called meltwater pulse 1a. One attempt at solution says that a meltwater pulse of Antarctic origin could cause an increase in North Atlantic Deep Water formation, and thus give rise to the Bølling interstadial. However, others have disputed that Antarctic meltwater would have that effect, and furthermore, the start of the Bølling interstadial is not even associated with an increase in North Atlantic Deep Water. A controversial hypothesis says that some Laurentian meltwater came from a jökulhlaup (sub-glacial outburst flood), but no study has yet shown unequivocally that sufficient amounts of water could be stored under the ice. Furthermore, according to all available data a melt-water pulse from the Laurentian ice would give rise to strong cooling, not warming. Nevertheless, meg-afloods appear instrumental in accumulating the Mississippi Fan, created entirely during the Quaternary period, and dramatic climate changes are characteristic of this period. This paper presents a hypothetical chain of events, building on the published literature and simple calculations, to investigate whether the order of magnitude is reasonable. The hypothesis is that a jökulhlaup from a Laurentian captured ice shelf flowed out through the Mississippi, boosted the Gulf Stream, reinvigorated the North Atlantic circulation, and as a result triggered the Bølling warm phase. 相似文献
9.
Age, origin, and palaeo-ecological evidence of blanket bogs in Nord-Trøndelag, Norway 总被引：2，自引：0，他引：2
Pollen diagrams, 14 C-datings, and peat stratigraphy are presented from 3 sites in the Forradal sub-oceanic area in Nord-Trøndelag, a moorland complex of flat and sloping fens and blanket bogs lying 400–500 m above sea-level, ca. 40 km E of the Trondheimsfjord. The vegetational and climatic history during the last 8500 years is described, together with a survey of present-day conditions. The origin of the blanket-bog areas is shown to agree generally, in both time and mode of genesis, with similar bog types in Scotland and N England. Dates are given for the expansion of both alder and spruce, the latter occurring more than 1000 years later than in SE Norway. The possible role of provenance formation and Roman Iron Age amelioration of the climate is discussed in this connection. The course of the alder pollen curve indicates a drier and probably colder type of climate at ca. 3000–2400 B.C. 相似文献
10.
Evolution of a large Miocene growth structure in the upper plate of the Whipple detachment fault, northeastern Whipple Mountains, California 总被引：1，自引：0，他引：1
Miocene sedimentary and volcanic rocks in the north-eastern Whipple Mountains, California, and the north-western Aubrey Hills, Arizona, accumulated in the upper plate of the Whipple detachment fault during regional extension and slip on the detachment. Miocene rocks in this area can be divided into three sequences: (1) pre-18.5-Ma dominantly volcanic rocks; (2) the 18.5-Ma Peach Springs Tuff; and (3) post-18.5-Ma dominantly sedimentary rocks. Important stratigraphic markers in sequence 3 include a 100- to 14–0-m-thick basalt unit and the voluminous War Eagle landslide, both of which correlate across Lake Havasu from the north-east Whipple Mountains to the Aurbrey Hills. We divide clastic sedimentary rocks of sequence 3 into three informal members: (3a) conglomerate and sandstone stratigraphically beneath the basalt; (3b) conglomerate and sandstone above the basalt and below the War Eagle landslide; and (3c) conglomerate and sandstone that overlie the War Eagle landslide. Detailed stratigraphic analysis and field mapping reveal dramatic south-westward thickening of member 3b strata, from about 50 m in the Aubrey Hills to over 1500 m in the north-east Whipple Mountains. In the north-east Whipple Mountains, this thick dipping section is overlain by the War Eagle landslide along a major angular unconformity; in the Aubrey Hills the base of the War Eagle landslide is roughly parallel to bedding dips of underlying strata. The above stratigraphic relationships can be explained by syndepositional growth of a rollover monocline by progressive tilting of the hangingwall above a master listric normal fault (Whipple detachment fault). This phase of upper-plate deformation began shortly after deposition of the basalt and ended prior to emplacement of the War Eagle landslide. Interbedded breccias low in member 3b, about 100 m above the basalt, record the first appearance of mylonitic detritus in the section. Growth of this upper-plate rollover was thus initiated at about the same time (shortly after deposition of the basalt) that the lower plate of the Whipple detachment fault was first exposed at the earth's surface by tectonic denudation and large-scale crustal uplift. These events are interpreted to record initiation of a secondary breakaway fault on the north-east flank of the growing Whipple detachment dome shortly after deposition of the basalt at about 14.5 (±1.0) Ma. 相似文献