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991.
A cross-ecosystem comparison of spatial and temporal patterns of covariation in the recruitment of functionally analogous fish stocks 总被引:1,自引:1,他引:1
Bernard A. Megrey Jonathan A. Hare William T. Stockhausen Are Dommasnes Harald Gjster William Overholtz Sarah Gaichas Georg Skaret Jannike Falk-Petersen Jason S. Link Kevin D. Friedland 《Progress in Oceanography》2009,81(1-4):63
Temporal and spatial patterns of recruitment (R) and spawning stock biomass (S) variability were compared among functionally analogous species and similar feeding guilds from six marine ecosystems. Data were aggregated into four regions including the Gulf of Maine/Georges Bank, the Norwegian/Barents Seas, the eastern Bering Sea, and the Gulf of Alaska. Variability was characterized by calculating coefficients of variation and anomalies for three response variables: ln(R), ln(R/S), and stock–recruit model residuals. Patterns of synchrony and asynchrony in the response variables were examined among and between ecosystems, between- and within-ocean basins and among functionally analogous species groups using pair-wise correlation analysis corrected for within-time series autocorrelation, multivariate cross-correlation analyses and regime shift detectors. Time series trends in response variables showed consistent within basin similarities and consistent and coherent differences between the Atlantic and Pacific basin ecosystems. Regime shift detection algorithms identified two broad-scale regime shift time periods for the pelagic feeding guild (1972–1976 and 1999–2002) and possibly one for the benthic feeding guild (1999–2002). No spatial patterns in response variable coefficients of variation were observed. Results from multivariate cross-correlation analysis showed similar trends. The data suggest common external factors act in synchrony on stocks within ocean basins but temporal stock patterns, often of the same species or functional group, between basins change in opposition to each other. Basin-scale results (similar within but different between) suggest that the two geographically broad areas are connected by unknown mechanisms that, depending on the year, may influence the two basins in opposite ways. This work demonstrates that commonalities and synchronies in recruitment fluctuations can be found across geographically distant ecosystems but biophysical causes of the fluctuations remain difficult to identify. 相似文献
992.
993.
Tidal flushing of animal burrows in mangrove swamps provides an effective and important mechanism for transport of salt and other soluble substances. The burrows have complex morphologies consisting of multiple loops. Using established computational modelling techniques, burrow geometries were simulated from characteristic burrow dimensions and the effect of multiple loops on flushing is studied. The computational models show that flushing is enhanced in multiple-loop burrows as upper loops can be completely evacuated, increasing the volume of burrow water removed. The models indicate that there may be a depth limit to which flushing occurs in complex burrow structures. Periscope loops extend further than one characteristic loop depth and are shown to affect the flushing of burrows if the surface-water plume penetrates to their lower depth. Periscope loops with surface openings on the downstream side of the burrow, relative to the tidal inundation, most frequently experience this condition and thus have a great impact on burrow flushing. Field measurements of salinity agree with the hypothesis that there is a depth limit of flushing for complex burrows that is independent of burrow salinity, and suggest a value of 30–35 cm. The measurements also support the suggestion that significant flushing of burrows occurs within a single tidal event. An experiment considered the movement of animals across the interface created by low-salinity surface water and high-salinity burrow water after a partial flushing event. The motion enhances the effective diffusion coefficient of salt by a factor of at least 102, as compared with free diffusion of salt in water, resulting in a more even distribution of dissolved salt in the burrow water between tidal inundations. This distribution may lead to an increase in the depth to which flushing occurs during subsequent inundations. 相似文献
994.
S. Aranuvachapun 《Ocean Engineering》1987,14(2)
Monte Carlo simulation of wave spectra was carried out to provide an assessment of JONSWAP spectral model and parameters. The simulation method is found to be satisfactory because (a) it excludes the spectral variability due to geophysical factors from the sampling errors in the spectral estimates and the statistical uncertainty in determining the model parameters; and (b) the simulated spectra can represent ideal spectral estimates where the sampling errors have been minimized by increasing the degrees of freedom of the spectra. The latter (b) allows both the magnitude of sampling errors to be evaluated and errors due to statistical uncertainty to be isolated. Thus, the stimulation study provides a useful error analysis to assess the JONSWAP spectral model and parameters. For instance, it is found from the results that the sampling errors could be as high as 20% while errors due to uncertainty in determining the model parameter could be as high as 17%. However, the overall errors may be reduced to the minimum of approx. 15% if the simulated spectra have 80 degrees of freedom and constant values of σa and σb i.e. σa = 0.07 and σb = 0.09. This implies that the maximum accuracy of 85% may be achieved in JONSWAP spectral model even though the α parameter has been underestimated by about 1.5%. The overestimated values of γ might come from the underestimated α and the biased φm estimator caused by the statistical uncertainty in the presence of a sharp spectral peak. Although the scale parameters (α and φm) exhibit smaller errors and variability than the shape parameters (ψ, σa and σb), they are more sensitive to the degrees of freedom of the spectra and their estimators are not better than the estimators of shape parameters. The simulation experiments have also shown that simulated spectra at 20–40 degrees of freedom contain a substantial amount of sampling errors. Therefore, the measured wave spectra at the same degrees of freedom (20–40) are not suitable and should not be used for evaluating the accuracy of any wave spectral model. 相似文献
995.
Regeneration of sand waves after dredging 总被引:2,自引:0,他引:2
Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves. 相似文献
996.
Abstract. Food preferences of six dominant salt marsh invertebrates were studied to identify detritivores and to assess differences in their diets. Animals fed on agar suspensions of dead and live foods in petri dishes with four compartments. Only two foods were included in each dish. Relative palatability was assessed by measuring the amount of suspension removed or by counting the number of feeding marks left on the surface of the suspensions.
Feeding marks reflected differences in mouth parts and feeding mechanisms of the six invertebrates. Melampus bidentatus, Orchestia grillus , and Philoscia vittata preferred dead litter over live tissues of marsh graminoids, blue-green algae, and sulfur bacteria. No preference for detritus from different graminoids was shown by M. bidentatus. Orchestia grillus fed preferentially on Spartina patens detritus. Philoscia vittata preferred detritus from S. alterniflora and S. patens. Blue-green algae and sulfur bacteria were preferred over detritus by Littorina saxatalis , but detritus was preferred over live graminoids. Littorina saxatalis fed preferentially on Juncus gerardi detritus. Blue-green algae, sulfur bacteria, and live graminoids were preferred over detritus by L. littorea. Talorchestia longicornis also preferred blue-green algae.
On the basis of their food preferences, Littorina saxatalis, Melampus bidentatus, Orchestia grillus , and Philoscia vittata were classified as detritivores. Feeding on detritus from different plant species could result in a partitioning of this food resource in the detritus-based food chains of the salt marsh ecosystem. 相似文献
Feeding marks reflected differences in mouth parts and feeding mechanisms of the six invertebrates. Melampus bidentatus, Orchestia grillus , and Philoscia vittata preferred dead litter over live tissues of marsh graminoids, blue-green algae, and sulfur bacteria. No preference for detritus from different graminoids was shown by M. bidentatus. Orchestia grillus fed preferentially on Spartina patens detritus. Philoscia vittata preferred detritus from S. alterniflora and S. patens. Blue-green algae and sulfur bacteria were preferred over detritus by Littorina saxatalis , but detritus was preferred over live graminoids. Littorina saxatalis fed preferentially on Juncus gerardi detritus. Blue-green algae, sulfur bacteria, and live graminoids were preferred over detritus by L. littorea. Talorchestia longicornis also preferred blue-green algae.
On the basis of their food preferences, Littorina saxatalis, Melampus bidentatus, Orchestia grillus , and Philoscia vittata were classified as detritivores. Feeding on detritus from different plant species could result in a partitioning of this food resource in the detritus-based food chains of the salt marsh ecosystem. 相似文献
997.
A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km3, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene. 相似文献
998.
S. F. Dotsenko 《Physical Oceanography》1993,4(1):1-8
The process of generation of two-dimensional (2D) wave motions during small elliptical displacements of the bottom which occur for a finite time interval is considered within the framework of the linear theory of long waves in a basin of constant depth. The spatial structure and the amplitudinal and energy characteristics of the emerging directional surface wave are analysed for bottom deformations of a special form.Translated by Mikhail M. Trufanov. 相似文献
999.
CTD data provided by the MGI-4204 and MARK-III probes are used to study the quasistationary subpolar front structure in the north-western Sea of Japan. In order to provide further insights into the intermittent scalar hydrophysical fields, the method of inhomogeneity identification using temperature pulsations calculated by the moving interval is suggested. The experimentally-derived inhomogeneity distribution is satisfactorily approximated by the exponential law.Translated by V. Puchkin. 相似文献
1000.
A multipole expansion of the velocity potential is described for two- and three-dimensional wave diffraction and radiation problems. The velocity potential is expressed in terms of a series of multipole potentials. The wave terms and the local disturbance terms are represented by separated multipole potentials. Floating bodies and submerged bodies are treated in the same way. This approach differs from that of some other authors, who considered floating bodies and submerged bodies separately and derived entirely different multipoles. Semi-analytical solutions for a circular cylinder in two-dimensional motions are given. It is found that the local disturbance decays rapidly and steadily. The general application of the multipole expansion to arbitrary geometries is also presented, based on a method coupling multipoles to a boundary integral expression. Numerical results for several floating and submerged cylinders are presented. 相似文献