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71.
Sauermilch Isabel Mateo Zenon Richard P. Boaga Jacopo 《Marine Geophysical Researches》2019,40(4):635-641
Marine Geophysical Research - Time–depth relationships (TDR) are required for correlating geological information from drill sites with seismic reflection profiles. Conventional... 相似文献
72.
Richard H. Bennett 《Marine Georesources & Geotechnology》2013,31(1-4):177-189
Abstract A pore‐water pressure probe (piezometer) was implanted in Mississippi delta sediments at a preselected site (Block 28, South Pass area, 29°00´N, 89°15´W) 145 m from an offshore production platform (water depth approx. 19 m) in September 1975. Total pore‐water pressures (uw ) were monitored for extended periods of time at depths of approximately 15 and 8 m below the mudline concurrently with hydrostatic pressures (u8 ) measured at depths of 15 m and approximately 1 m below the mudline. Relatively high excess pore‐water pressures, ue = (uw ‐u8 ), were recorded at the time of probe insertion measuring 99 kPa (14.4 psi) at 15 m and 50 kPa (7.3 psi) at 8 m. Six hours after the probe was implanted, excess pore pressures were still high at 81 kPa (11.8 psi, 15 m) and 37 kPa (5.4 psi, 8 m). Pore pressures appeared to become relatively constant at the 8‐m depth after 7 h had elapsed, and at the 15 m depth after 10–12 h. Excess pore‐water pressures averaged 72 kPa (10.4 psi, 15 m) and 32 kPa (4.6 psi, 8 m) prior to the initial effects of Hurricane Eloise, which passed in close proximity to the probe site. Significant variations in pressures were recorded during storm activity. As the effects of the storm subsided, excess pore‐water pressures began to decline slightly at the 15‐m depth; however, concurrently at the 8‐m depth, pore pressures began to increase gradually. During the period of 21–25 days after the probe was implanted, excess pore pressures appeared to become more constant, averaging 24 kPa (3.5 psi) at 15 m and 43 kPa (6.2 psi) at the 8‐m depth. The presence of methane, a common occurrence in these delta muds, may have influenced, or contributed to, the total pore‐water pressures measured during this experiment. 相似文献
73.
Ralph S. Lewis Mary L. Digiacomo-Cohen Nancy Friedrich Neff Richard Hyde 《Marine Georesources & Geotechnology》2013,31(2-3)
The Connecticut effort in year 9 of the Continental Margins Program concentrated on a 13.6-mi2 area south of the Housatonic River. This area was chosen for a side-scan sonar survey because it lies on and adjacent to the bathymetric expressions of two fairly large, subcropping, potential sources of coarse material. Previous seismic work in the area indicated that outcrops or subcrops of these potential source deposits could be delineated using their bathymetric expression. Owing to the limited resolution of the seismic data, a correlation between bottom type and underlying source deposits could not be made with the seismics alone. Results from the November 1993 side-scan survey show that although the source deposits have discernible bathymetric expressions, they are not cropping out as much as expected. As a result, bottom type is not necessarily determined by subcropping deposits in this particular area. Year 10 work was concentrated in Fishers Island Sound, where three areas of potential interest for near-shore gravel resources had previously been identified. These areas were surveyed, during the spring of 1996, using the RoxAnn Seabed Classification System. A small video camera and a Van Veen grab sampler were used to calibrate and verify the RoxAnn data. Although previous sampling had indicated the presence of gravel or gravelly sediment in all of the survey areas, the RoxAnn results showed less gravel than anticipated. Vibrant eelgrass beds and other habitat indicators were detected in all of the survey areas. Given the variable sediment results, and the high habitat potential of the areas surveyed, the likelihood of developing a sand and gravel supply from the near shore of Fishers Island Sound appears quite low. 相似文献
74.
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
75.
Cheng-Chien Liu Richard L. Miller Kendall L. Carder Zhongping Lee Eurico J. D’Sa James E. Ivey 《Journal of Oceanography》2006,62(3):235-248
We present a new approach that incorporates two models to estimate the underwater light field from remote sensing of ocean
color. The first employs a series of analytical, semi-analytical, and empirical algorithms to retrieve the spectrum of inherent
optical properties (IOPs), including the absorption and the backscatter coefficients, from the spectrum of remote sensing
reflectance. The second model computes the profile of photosynthetically available radiation E
0,PAR
(z) for a vertically homogeneous water column using the information of the retrieved IOPs and the ambient optical environment.
This computation is based on an improved look-up table technology that possesses high accuracy, comparable with the full solution
of the radiative transfer equation, and meets the computational requirement of remote sensing application. This new approach
was validated by in situ measurements and an extensive model-to-model comparison with a wide range of IOPs. We successfully mapped the compensation
depth by applying this new approach to process the SeaWiFS imagery. This research suggests that E
0,PAR
(z) can be obtained routinely from ocean-color data and may have significant implications for the estimation of global heat
and carbon budget. 相似文献
76.
Polychlorinated dibenzo-para-dioxins (PCDDs) and dibenzofurans (PCDFs) were measured in the tissues of the estuarine clamRangia cuneata at four sites in the Neches River that had been subjected to paper mill effluent and at two remote sites. One of the river samplings was taken before dioxin control measures and another 2 yr after the control measures began. Measurable concentrations of PCDD/Fs were present at all sites, but higher concentrations were present at the Neches River sites. Whole tissue concentrations of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) and all PCDD congeners for the two collections were not significantly different (p>0.05), but lipid-normalized concentrations for the two collections were significantly different (p<0.05). Highest concentrations of PCDDs at sites located 8 km and 16 km upriver from the paper mill effluent outfall indicated that the materials were transported upriver by saltwater intrusion and/or that nonpoint sources existed upriver. The presences of PCDD/Fs in clam tissues from the remote sites also indicated that other sources of these materials existed. Even under extreme physiological conditions (spent reproductive phase, low lipid contents, water temperature 10°C; ripe reproductive phase, high lipids, water temperature 32°C)Rangia cuneata was an effective biomonitor to determine the distribution of PCDD/Fs at specific sites. *** DIRECT SUPPORT *** A01BY069 00021 相似文献
77.
Richard B. Wheeler John B. Anderson Rudy R. Schwarzer Claudia L. Hokanson 《Environmental Geology》1980,3(3):163-175
Sediments are the ultimate sink for contaminants in the marine environment, and physical processes of sedimentation influence
the distribution and accumulation of these contaminants. Evaluation of contaminant levels in sediments is one approach to
assessing environmental impact; data interpretation depends on consideration of sediment texture and mineralogy, however,
which profoundly influence chemical composition. In this study, comparison of potentially contaminated sediments from the
production field with control populations was done only within the context of similar (as to texture and organic carbon and
carbonate content) sample groups as determined by cluster analysis. Ba, Cd, and Sr are identified as contaminants. Supported
by the identification of a well-crystallized expandable clay—possibly bentonite—drilling fluids are a potential source of
Ba. Ba and Sr may be unnaturally high because of their abundance in discharged produced formation waters, but may also be
naturally controlled by the unique faunal assemblage associated with the structures. Cd is probably derived from corrosion
of the structures and assorted debris on the seafloor. In general, contamination is limited to an area within 100 m of the
platforms. Furthermore, substantial erosion around platforms has probably effectively removed and dispersed the bulk of the
contaminants introduced into the marine environment by the offshore exploration/production operations. 相似文献
78.
79.
80.
Holocene changes in seasonal precipitation highlighted by fire incidence in eastern Canada 总被引:1,自引:0,他引:1
Postglacial fire history has been reconstructed for eastern Canada from charcoal-influx anomalies from 30 sites taken from
a lacustrine charcoal database. The reconstruction exhibits coherent patterns of fire occurrence in space and time. The early
Holocene is characterised by high fire incidence. There is a major change to much lower occurrence slightly after 8 ka BP.
A return to more fire appears after 3 ka BP. This sequence does not fit with the hydro-climatic reconstruction deduced from
lake level reconstructions for northeastern North America, which indicates a dry early and mid-Holocene, and a wet late-Holocene.
Fire occurrence however closely matches summer relative humidity inferred from δ18O. The differences between fire frequency and lake level history, are due to changes in the seasonality of precipitation and
drought frequency. Lake levels are essentially controlled by winter precipitation while summer precipitation controls fire
occurrence. The early Holocene before 8–7.5 ka BP experienced dry summers due to higher solar radiation and dry adiabatic
winds from the residual Laurentide Ice Sheet. The middle Holocene was dominated by wet summers due to stability of the Atlantic
air mass over eastern Canada. After 2.5 ka BP, summers became drier, albeit not as fire-conducive as during the early Holocene.
Late-Holocene summers conducive to fire are explained by more frequent incursions of dry Cool Pacific or Cold Arctic air masses
over eastern Canada.
Received: 25 January 1999 / Accepted: 14 December 1999 相似文献