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941.
Richard N. Hey Gary J. Massoth Robert C. Vrijenhoek Peter A. Rona John Lupton David A. Butterfield 《Marine Geophysical Researches》2006,27(2):137-153
Earth’s fastest present seafloor spreading occurs along the East Pacific Rise near 31°–32° S. Two of the major hydrothermal
plume areas discovered during a 1998 multidisciplinary geophysical/hydrothermal investigation of these mid-ocean ridge axes
were explored during a 1999 Alvin expedition. Both occur in recently eruptive areas where shallow collapse structures mark
the neovolcanic axis. The 31° S vent area occurs in a broad linear zone of collapses and fractures coalescing into an axial
summit trough. The 32° S vent area has been volcanically repaved by a more recent eruption, with non-linear collapses that
have not yet coalesced. Both sites occur in highly inflated areas, near local inflation peaks, which is the best segment-scale
predictor of hydrothermal activity at these superfast spreading rates (150 mm/yr). 相似文献
942.
943.
Daniel S. Scheirer Ken C. Macdonald Donald W. Forsyth Stephen P. Miller Dawn J. Wright Marie-Hélène Cormier Charles M. Weiland 《Marine Geophysical Researches》1996,18(1):1-12
Four large-scale bathymetric maps of the Southern East Pacific Rise and its flanks between 15° S and 19° S display many of the unique features of this superfast spreading environment including abundant seamounts (the Rano Rahi Field), axial discontinuities, discontinuity migration, and abyssal hill variation. Along with a summary of the regional geology, these maps will provide a valuable reference for other sea-going programs on-and off-axis in this area, including the Mantle ELectromagnetic and Tomography (MELT) experiment. 相似文献
944.
cDNA's coding for cytochrome P4501A1 (CYP1A1), phenol UDP-glucuronosyltransferase (UDPGT) and glutathione S-transferase (GST-A) were cloned and sequenced from an expression library prepared from the liver of a 3-methylcholanthrene (3-MC) induced plaice. Plaice CYP1A1 and Phenol UDPGT display a high degree of structural conservation with homologous mammalian isoforms and their mRNAs were shown to be highly induced in liver after 3-MC treatment of fish. Expression of plaice GST-A, which displays closer homology to GSTs from plants and invertebrates than those of mammals, is repressed after 3-MC treatment. 相似文献
945.
M. A. Srokosz 《Ocean Engineering》1988,15(4)
In this note the effect of changes in sea-state, as measured by the significant wave heigh Hs, on the joint distribution of individual wave height and period are considered. Wave data, obtained from a Waverider buoy during the growth phase of a storm, are used in the analysis. It is found that, by correctly scaling the individual heights and periods, the form of the joint distribution does not depend on Hs, but is dependent on the bandwidth of the spectrum. The results obtained also give some indication of the period of individual, high zero-upcrossing waves. 相似文献
946.
947.
Instrument calibration of ocean bottom seismographs 总被引:1,自引:0,他引:1
To increase the accuracy of measuring sea floor motion with ocean bottom seismometers, we calibrate the seismometer system on the ocean floor. Data from the sea floor calibration, augmented with electronic and land calibration data, enables us to find the OBS transfer function to an accuracy of 0.5% in the frequency range of 0.1 to 32 Hz. We are able to distinguish between temperature, instrument and OBS ground coupling effects, all of which alter the transfer function. This paper reviews our method of calibration and discusses the effects of temperature and some of the instrument design features on the vertical seismometer transfer function. 相似文献
948.
Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of
sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes
of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We
investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly
represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in
the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux
exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their
maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other.
Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal
changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal
changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its
sinking rate. 相似文献
949.
Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers. 相似文献
950.
With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km2 dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m3 of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m3 of the originally dumped 2.6 million m3 of dredge spoil had already been removed from the dumping site. 相似文献