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971.
An analysis of published and original data on the meiobenthos abundance in the depth interval from 100 to 9807 m (in total, 665 records, 445 of them obtained for depths exceeding 1000 m) revealed general regularities in its distribution. The influence of the sampling and data processing methods on the quantitative estimates of the meiobenthos abundance is considered to demonstrate changes in the proportions of the main meiobenthic taxa at different depths and to characterize latitudinal changes in the meiobenthos abundance. The dependence of the abundance of free-living nematodes, the most abundant group of metazoan meiobenthos, on trophic conditions is analyzed. No significant differences in the meiobenthos abundance in the samples obtained by box-and multicorers are established. It is shown that the share of nematodes in metazoan meiobenthos communities increases with the depth. In temperate latitudes, a distinct maximum in the population density confined to depths exceeding 1 km is observed. The quantitative distribution of the meiobenthos at the depths gradient is controlled by the bottom macrotopography and trophic conditions. 相似文献
972.
973.
C. K. Paull W. Ussler H. G. Greene R. Keaten P. Mitts J. Barry 《Geo-Marine Letters》2003,22(4):227-232
A sediment gravity flow descended through the axis of Monterey Canyon on 20 December 2001 at 13:35 Pacific standard time.
The timing of this event is documented by a current-meter package which recorded an 11.9-dbar pressure increase in less than
10 min and was found 550 m down-canyon from its deployment site, buried completely within a >70-cm-thick gravity flow deposit.
This event is believed to have started in less than 290 m of water because an instrument at this location was also lost at
the same time. A 178-cm core collected after the event from the axis of the canyon at 1,297-m water depth contained fresh,
greenish, chlorophyll-rich organic material at 32-cm sub-bottom depth, suggesting the event extended to this water depth.
The only trigger identified for this mass movement event appears to be moderate sea and surf conditions. Thus, gravity flow
events of this magnitude do not require an exceptional triggering event. 相似文献
974.
975.
C. K. Paull W. Ussler H. G. Greene R. Keaten P. Mitts J. Barry 《Geo-Marine Letters》2002,22(4):227-232
A sediment gravity flow descended through the axis of Monterey Canyon on 20 December 2001 at 13:35 Pacific standard time. The timing of this event is documented by a current-meter package which recorded an 11.9-dbar pressure increase in less than 10 min and was found 550 m down-canyon from its deployment site, buried completely within a >70-cm-thick gravity flow deposit. This event is believed to have started in less than 290 m of water because an instrument at this location was also lost at the same time. A 178-cm core collected after the event from the axis of the canyon at 1,297-m water depth contained fresh, greenish, chlorophyll-rich organic material at 32-cm sub-bottom depth, suggesting the event extended to this water depth. The only trigger identified for this mass movement event appears to be moderate sea and surf conditions. Thus, gravity flow events of this magnitude do not require an exceptional triggering event. 相似文献
976.
A model for solving the two-dimensional enhanced Boussinesq equations is presented. The model equations are discretised in space using an unstructured finite element technique. The standard Galerkin method with mixed interpolation is applied. The time discretisation is performed using an explicit three-step Taylor–Galerkin method. The model is extended to the surf and swash zone by inclusion of wave breaking and a moving boundary at the shoreline. Breaking is treated by an existing surface roller model, but a new procedure for the detection of the roller thickness is devised. The model is verified using four test cases and the results are compared with experimental data and results from an existing finite difference Boussinesq model. 相似文献
977.
978.
An iterative frequency domain method of analysis is presented for determining the response behaviour of Guyed Offshore Towers to low-frequency, second-order wave drift forces generated in a random sea environment. For the response analysis, the tower is idealized as a shear beam with a rotational spring at the bottom support. The guylines are replaced by a non-linear spring. The second-order drift force is considered to be proportional to the square of the wave elevation and is simulated using a drift force coefficient and the time history of a slowly varying wave envelope in random sea. The responses due to drift forces are obtained in frequency domain by incorporating the non-linearities produced due to non-linear guy lines. An example problem is solved under different random sea states to compare the response behaviour of the tower obtained by the second-order wave force, the first-order wave force and a combination of the two. 相似文献
979.
980.
Data on East Australian Current (EAC) warm-core eddies were obtained over the period 1976–1978 by the Department of Defence and the Commonwealth Scientific and Industrial Research Organization (CSIRO). In that time we have learned that warm eddies form by pinch-off of poleward EAC meanders, can coalesce with the EAC and appear generally similar to Gulf Stream, Kuroshio and other current system eddies. Two eddies were tracked over 1977–1978 with satellite buoys and one (eddy B) was repeatedly studied over eleven months. A deep winter core formed by winter convective cooling and the following summer a new surface mixed layer formed on top of the core. The seasonal changes have been analysed for heat content and changes in dynamic relief. The eddy decayed with a time constant of 650 ± 150 days, due to upwelling below the seasonal thermocline. Surface cooling had little effect on eddy lifetime. The eddy contracted horizontally, possibly after some interaction with the EAC, giving rise to eddy spin-up with increasing age. Surface currents increased after eleven months to 2.0 m s?1. The dynamic relief during summer was also apparently boosted by contact with the EAC. Eddy B was observed to coalesce with a new meander of the EAC rather than drift away to the south. It is proposed that the formation of these eddies is governed by the westward propagation of the baroclinic Rossby wave known as the Tasman Front. Pinch-off of eddies adjacent to the coast and the variable flow of the EAC may be caused by the baroclinic wave ‘breaking’ on the coast. The eddy formation rate is about two per year and most eddies coalesce with the EAC and do not escape to the south. Eddies coalesce and re-separate, creating many subsurface isothermal layers from old cores south of 34°S. 相似文献