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911.
Acoustic reflection signatures of four hydro-carbon seeps were classified using near-bottom 25-kHz echosounder profiles.
Echo patterns were compared with ground-truth data obtained by submersible observations and shallow coring. Six echo types
were distinguished: strong reflections from (1) exposed or (2) buried hard substrates, such as authigenic carbonate or gas
hydrate; acoustic scattering in (3) unlayered or (4) layered sediments owing to gas, shells, or disseminated carbonates; (5) attenuation
caused by gas; and (6) undisturbed sediments. Echo type distributions suggest that high spatial variability indicates a younger,
vigorous seep, whereas extensive hard substrate implies an older, encrusted seep.
Received: 29 May 1998 / Revision received: 7 October 1998 相似文献
912.
Takashi Setoh Shiro Imawaki Alexander Ostrovskii Shin-Ichiro Umatani 《Journal of Oceanography》1999,55(3):385-394
Interdecadal variations of El Niño/Southern Oscillation (ENSO) signals and annual cycles appearing in the sea surface temperature (SST) and zonal wind in the equatorial Pacific during 1950–1997 are studied by wavelet, empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses. The typical timescale of ENSO is estimated to be about 40 months before the late 1970s and 48–52 months after that; the timescale increased by about 10 months. The spatial pattern of the ENSO signal appearing in SST also changed in the 1970s; before that, the area of strong signal spread over the extratropical regions, while it is confined near the equator after that. The center of the strongest signal shifted from the central and eastern equatorial Pacific to the South American coast at that time. These SST fluctuations near the equator are associated with fluctuations of zonal wiond, whose spatial pattern also shifted considerably eastward at that time. In the eastern equatorial Pacific, amplitudes of annual cycles of SST are weak in El Niño years and strong in La Niña years. This relation is not clear, however, in the 1980s and 1990s. 相似文献
913.
Scanning and transmission electron microscopic analyses of shale samples from offshore Louisiana, USA, Gulf of Mexico, reveal
the relationship between mineralogical and microfabric changes during burial diagenesis. The local geopressured zone begins
at 2200-m depth. Above that depth the shales are smectite-rich, generally lack particle orientation, and contain appreciable
pores. Below the 2200-m depth, the shales become more illite-rich with increasing burial, more crystalline, and less porous.
Microfabric changes are mainly caused by compaction during burial diagenesis; mineralogical changes (smectite-to-illite) and
crystal growth also play an important role in fabric alteration during deep burial diagenesis.
Received: 12 May 1998 / Revision received: 14 July 1998 相似文献
914.
The Cenozoic shelf margin of the Amazon Mouth Basin is characterized by a thick prograding prism of siliciclastic sediments.
This prism, composed mainly of Upper Miocene and younger sediments, overlies a Lower Tertiary carbonate shelf. Two tectonic–sedimentary
models for the area were developed with the aid of new deep-reflection seismic data. Gravitational tectonics dominate the
regional geological framework. Tensional stresses are created near the shelf margin, and compressional features dominate at
the base of the slope. The morphology of this compressional zone is closely associated with the St. Paul Fracture Zone and
the boundary between continental and oceanic crusts.
Received: 20 August 1996 / Revision received: 11 June 1998 相似文献
915.
916.
917.
A. S. Drofa V. G. Eran’kov V. N. Ivanov A. G. Shilin G. F. Iskevich 《Izvestiya Atmospheric and Oceanic Physics》2013,49(3):298-306
The results of experimental investigations into the action of polydispersion salt powders on model cloud media are presented. The results of experiments show a considerable positive effect of the modification of convective clouds by salt powders in order to obtain additional precipitation. The introduction of polydispersion salt powder into a forming cloud medium leads to the appearance of large cloud droplets and to the droplet-spectrum broadening. This result is a positive factor for the stimulation of coagulation processes and further precipitation formation. No “overseeding” phenomenon (when, instead of the enlargement of droplets, their sizes decrease and the concentration of cloud droplets increases) is observed at rather high mass concentrations of the introduced powder. 相似文献
918.
S. J. Edmonds 《新西兰海洋与淡水研究杂志》2013,47(1):217-224
Two new species of Sipuncula arc described from New Zealand; Phascolion temporariae from, the empty tubes of the polychaete Temporaria inexpectata (Mestayeri), and Phascolion tortum from the shells of four species of molluscs. Specimens of Golfingia improvisa (Theel) are also reported from the empty frustules of the foraminiferan Ammodiscoides mestayeri (Cushman) and the sandy tubes of the foraminifera Rhizammina sp. All the species were dredged at depths of 370–660 m from Taiaroa and Papanui Canyons, off the Otago Peninsula, New Zealand. The body cavity of several specimens of G. improvisa contained the larval stage of a nematode. 相似文献
919.
The height of widespread tsunami runup about the Bay of Plenty from various volcanic scenarios involving eruptions at White Island is shown to be insignificant in all cases considered, except for Krakatoa‐type explosions. The problem of localised inundation remains unanswered. Some definitions describing volcanic tsunami risk, introduced recently by J. Latter (Bulletin volcanologique 1982), are briefly mentioned. All numerical calculations assumed cylindrical symmetry and used a flux‐corrected Lax‐Wendroff algorithm to solve the modified shallow water equations of Peregrine. 相似文献
920.
V. V. S. S. Sarma M. S. Krishna R. Viswanadham G. D. Rao V. D. Rao B. Sridevi B. S. K. Kumar V. R. Prasad Ch. V. Subbaiah T. Acharyya D. Bandopadhyay 《Journal of Oceanography》2013,69(1):45-55
A study on biogeochemical cycling in the west coastal Bay of Bengal was undertaken during the peak discharge period to understand the influence of enhanced stratification and primary production on the possible intensification of the oxygen minimum zone (OMZ). Our study reveals that oxygen concentrations were below the detection limits in the northwestern (NW) coastal Bay of Bengal between 100 and 500 m associated with strong stratification and high phytoplankton biomass. Such low oxygen concentrations have never been reported so far from the coastal Bay of Bengal. Despite the existence of an environment conducive to denitrification in the coastal Bay of Bengal, accumulation of neither secondary nitrite nor nitrous oxide (N2O) was observed. The absence of denitrification was reported to be caused by faster scavenging of organic matter and low bacterial respiration rates; in contrast, our results suggest that neither of these factors are potential reasons for the absence of denitrification in the coastal Bay of Bengal. 相似文献