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41.
Richard T. Jones Jim D. Marshall Stephen F. Crowley Alan Bedford Nigel Richardson Jan Bloemendal Frank Oldfield 《第四纪科学杂志》2002,17(4):329-340
A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
42.
An optoelectronic instrument has been developed to analyze the scales and scale patterns of chum salmon. This device, with specially developed software, has been used to study populations of salmon. Fish from two different rivers approximately 200 km apart from each other were grouped with an accuracy of 82% or more. Machine-measured ages coincided with those derived from visual estimation in approximately 80% of the fish sampled. These results suggest the proposed system could be of practical use for measuring and analyzing the scale patterns that allow one to accurately measure both natural and farmed populations of salmon 相似文献
43.
J. M. Gregory J. A. Church G. J. Boer K. W. Dixon G. M. Flato D. R. Jackett J. A. Lowe S. P. O'Farrell E. Roeckner G. L. Russell R. J. Stouffer M. Winton 《Climate Dynamics》2001,18(3-4):225-240
Sea-level rise is an important aspect of climate change because of its impact on society and ecosystems. Here we present
an intercomparison of results from ten coupled atmosphere-ocean general circulation models (AOGCMs) for sea-level changes
simulated for the twentieth century and projected to occur during the twenty first century in experiments following scenario
IS92a for greenhouse gases and sulphate aerosols. The model results suggest that the rate of sea-level rise due to thermal
expansion of sea water has increased during the twentieth century, but the small set of tide gauges with long records might
not be adequate to detect this acceleration. The rate of sea-level rise due to thermal expansion continues to increase throughout
the twenty first century, and the projected total is consequently larger than in the twentieth century; for 1990–2090 it amounts
to 0.20–0.37 m. This wide range results from systematic uncertainty in modelling of climate change and of heat uptake by the
ocean. The AOGCMs agree that sea-level rise is expected to be geographically non-uniform, with some regions experiencing as
much as twice the global average, and others practically zero, but they do not agree about the geographical pattern. The lack
of agreement indicates that we cannot currently have confidence in projections of local sea-level changes, and reveals a need
for detailed analysis and intercomparison in order to understand and reduce the disagreements.
Received: 1 September 2000 / Accepted: 20 April 2001 相似文献
44.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
45.
The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical 'slab window' which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment. 相似文献
46.
47.
The Middle Jurassic Kirkpatrick flood basalts and comagmatic Ferrar intrusions in the Transantarctic Mountains represent
a major pulse of tholeiitic magmatism related to early stages in the breakup of Gondwana. A record of the volcano-tectonic
events leading to formation of this continental flood-basalt province is provided by strata underlying and only slightly predating
the Kirkpatrick lavas. In the central Transantarctic Mountains, the lavas rest on widespread (≥7500 km2) tholeiitic pyroclastic deposits of the Prebble Formation. The Prebble Formation is dominated by lahar deposits and is an
unusual example of a regionally developed basaltic lahar field. Related, partly fault-controlled pyroclastic intrusions cut
underlying strata, and vents are represented by the preserved flanks of two small tephra cones associated with a volcanic
neck. Lahar and air-fall deposits typically contain 50–60% accidental lithic fragments and sand grains derived from underlying
Triassic – Lower Jurassic strata in the upper part of the Beacon Supergroup. Juvenile basaltic ash and fine lapilli consist
of nonvesicular to scoriaceous tachylite, sideromelane, and palagonite, and have characteristics indicating derivation from
hydrovolcanic eruptions. The abundance of accidental debris from underlying Beacon strata points to explosive phreatomagmatic
interaction of basaltic magma with wet sediment and groundwater, which appears to have occurred in particular where rising
magma intersected upper Beacon sand aquifers. Composite clasts in the lahar deposits exhibit complex peperitic textures formed
during fine-scale intermixing of basaltic magma with wet sand and record steps in subsurface fuel-coolant interactions leading
to explosive eruption.
The widespread, sustained phreatomagmatic activity is inferred to have occurred in a groundwater-rich topographic basin linked
to an evolving Jurassic rift zone in the Transantarctic Mountains. Coeval basaltic phreatomagmatic deposits of the Mawson
and Exposure Hill Formations, which underlie exposures of the Kirkpatrick Basalt up to 1500 km to the north along strike in
Victoria Land, appear to represent other parts of a regional, extension-related Middle Jurassic phreatomagmatic province which
developed immediately prior to rapid outpouring of the flood basalts. This is consistent with models which assign an important
role to lithospheric stretching in the generation of flood-basalt provinces.
Received: 28 August 1995 / Accepted: 18 April 1996 相似文献
48.
This paper compares lead-acid batteries, sodium-sulfur batteries, solid polymer fuel cells and closed-cycle diesel engines for autonomous underwater vehicle (AUV) applications. The service is described in terms of a parametric mission and life cycle. A generic AUV is used as a basis for comparison. Power systems are evaluated by two criteria: (1) submerged endurance capability and (2) life cycle cost. This study determines categories of service for which each power system is preferred. The solid polymer fuel cell can provide greater submerged endurance than other power systems examined. For extremely long duration AUV missions, the fuel cell is the required system, indicating a possible market niche for today's fuel cell technology. Considering cost projections for each power system, the results also show that the SPFC can become cost-competitive with conventional technologies, particularly for services characterized by high levels of utilization 相似文献
49.
D.W. Crawford D.A. Purdie A.P.M. Lockwood P. Weissman 《Estuarine, Coastal and Shelf Science》1997,45(6):799-812
In the Southampton Water estuary (southern England, U.K.), red-tides caused by the planktonic, phototrophic ciliateMesodinium rubrum(=Myrionecta rubra) occur during most summers and sometimes in autumn. These events were investigated in detail between 1985 and 1987 and were characterized by levels of chlorophylla(chl a) of over 100 μg l−1, cell numbers ofM. rubrumof over 1×103 ml−1, oxygen saturations of around 150%, and depleted numbers of macrozooplankton. Initiation of red-water did not appear to be triggered by irradiance or nutrients, but coincided with an increase in temperature and water column stability. This enhanced stability was promoted by increased surface to bottom gradients of both temperature and salinity, and by reduced mixing during neap tides. Development of red-water was accompanied by removal of most of the dissolved NH+4from the water column, whereas some NO−3persisted, presumably maintained by freshwater input. NO−3and NH+4gradually returned to pre-bloom concentrations as the red-water declined in late summer. Maximal biomass ofM. rubrumappeared to be limited by irradiance, and self-shading probably imposed an upper limit of around 300 mg chl a m−2within the water column. At the observed levels of chl a, irradiance values within the population maximum between 1 and 3 m depth were only just of the order (≈15 μmol photons m−2 s−1) required to balance estimated respiratory demands. Oxygen concentration became undersaturated during the late bloom phase, with minimal values of 20–30% saturation recorded in deeper waters; however, despite this and reduced numbers of macrozooplankton, direct deleterious effects on other organisms were not observed. 相似文献
50.