Experimental deformation of a synthetic dunite at high temperature and pressure. II. Transmission electron microscopy     

David H. Zeuch  H.W. Green II 《Tectonophysics》1984,110(3-4):263-296

We have performed detailed transmission electron microscope on most of the deformed synthetic dunite specimens prepared in the study by Zeuch and Green (1984). We have identified three basic types of sub-boundaries, simple tilt walls in (100) and (001). composed by b = [100] and b = [001] edge dislocations, respectively, and twist boundaries in (010) composed of b = [100] and b = [001] screws. We have also observed more complex, asymmetric lilt boundaries in (100) and (001). Like the (010) twist boundaries, these asymmetric tilt walls are common only at the highest temperatures and lowest strain rates. Subgrain development is extensive at the higher temperatures and lower strain rates, and subgrains are composed of the above-mentioned three types of sub-boundaries; edge components in (100) and (001) ire “knitted” to screw components in (010) as described by Kirby and Wegner (1978) for naturally deformed olivine. In many areas of the samples which we studied, subgrain development is not observed, but parallel arrays of tilt boundaries of one type or the other are present. At higher temperatures and lower strain rates. “(100) organization” (Durham et al., 1977) is common; this structure consists of parallel arrays of (100) tilt boundaries with b = [100] screws connecting the sub-boundaries. At lower temperatures we have observed an analogous arrangement of (001) sub-boundaries and b = [001] screws, which we refer to as “(001) organization”. Under all experimental conditions, dislocations with b = [100] and b = [001] are present in approximately equal numbers. However, the two types of dislocations also have distinctly different geometries under all test conditions. We suggest that the transition from slip parallel to [001] to slip parallel to [100] with increasing temperature, which has been reported in earlier studies may also depend upon water content. The substructures which we observe are virtually identical to those seen in many naturally deformed peridolites. and we conclude that the mechanisms involved in both natural and laboratory deformation of olivine polycrystals are similar. On the other hand, the substructures reported here are very different from those observed in experimentally deformed olivine single crystals. It seems likely that these substructural differences reflect fundamental differences in the behavior oh single crystals and polycrystals. which are in turn reflected in different measured creep strengths.  相似文献   

Unsteady sedimentation in nonuniform rills     

Thomas E. Croley II  George R. Foster 《Journal of Hydrology》1984,70(1-4):101-122

Runoff and sediment were measured from agricultural land exposed to controlled simulated rainfall. We extended the kinematic unsteady overland sedimentation theory of prismatic channels to the experiments by considering both hydraulics and sediment dynamics of rill flow for changing flow geometries of nonuniform and unsteady rill development. The characteristic unimodal concentration peak observed in the experiments and the changing channel geometry were interpreted in theoretical terms. Overland sedimentation in unsteady nonprismatic rills under uniform rainfall can be described with kinematic models of flow, entrainment and deposition applied to developing flow geometries; this is not possible with sheet-flow models. Other interpretations are considered and experimental needs are identified.  相似文献   

A study of the performance of a land surface process model (LSPM)   总被引：1，自引：0，他引：1  

Claudio Cassardo  Jin Jun II  Arnaldo Longhetto 《Boundary-Layer Meteorology》1995,72(1-2):87-121

In this paper, a reliable Land-Surface Process Model (LSPM), which is a new version of the LPM of Ji and Hu (1989), is described. The LSPM has been validated with experimental data measured at two stations in the Po Valley (Northern Italy).  相似文献   

Assessing the concentration,speciation, and toxicity of dissolved metals during mixing of acid-mine drainage and ambient river water downstream of the Elizabeth Copper Mine,Vermont, USA     

Laurie S. Balistrieri  Robert R. Seal II  Nadine M. Piatak  Barbara Paul 《Applied Geochemistry》2007

The authors determine the composition of a river that is impacted by acid-mine drainage, evaluate dominant physical and geochemical processes controlling the composition, and assess dissolved metal speciation and toxicity using a combination of laboratory, field and modeling studies. Values of pH increase from 3.3 to 7.6 and the sum of dissolved base metal (Cd + Co + Cu + Ni + Pb + Zn) concentrations decreases from 6270 to 100 μg/L in the dynamic mixing and reaction zone that is downstream of the river’s confluence with acid-mine drainage. Mixing diagrams and PHREEQC calculations indicate that mixing and dilution affect the concentrations of all dissolved elements in the reach, and are the dominant processes controlling dissolved Ca, K, Li, Mn and SO₄ concentrations. Additionally, dissolved Al and Fe concentrations decrease due to mineral precipitation (gibbsite, schwertmannite and ferrihydrite), whereas dissolved concentrations of Cd, Co, Cu, Ni, Pb and Zn decrease due to adsorption onto newly formed Fe precipitates.  相似文献   

A method of differential field photometry by video-photographic image subtraction     

R. R. Fisher  R. C. Hill II 《Solar physics》1971,18(2):211-219

A method is presented for subtracting two sequential images by a video technique. This procedure is applied to detect both rotational line-of-sight effects, and velocity fields around an active region (McMath plage No. 10181). The standard deviation of a velocity measurement was found to be ± 0.4 km/sec. This method appears to offer some advantages compared with the photographic subtraction process.  相似文献   

Effect of methane leakage on the greenhouse gas footprint of electricity generation     

Nicolas Sanchez II  David C. Mays 《Climatic change》2015,133(2):169-178

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Recognition of areas effected by petroleum seepage: Northern Gulf of Mexico continental slope     

M. C. Kennicutt II  J. M. Brooks 《Geo-Marine Letters》1990,10(4):221-224

The presence of large amounts of gas and/or liquid hydrocarbon seepage in near surface sediments can produce distinct features including an irregular topography (on several scales, ranging from meters to kilometers); seismically transparent/chaotic sediments; oil staining; gas plumes; sediments containing elevated concentrations of extractable organic matter, organic carbon, and calcium carbonate; associated brine seepage and anoxic conditions; extensive bacterial mats; hydrate formation and decomposition; and dense chemoautotrophic communities. Although no single characteristic is always uniquely associated with seepage, the co-occurrence of several of these features is strongly suggestive of an area being exposed to non-indigenous upward migrating hydrocarbons.  相似文献   

Influence of parasitism in controlling the health, reproduction and PAH body burden of petroleum seep mussels     

Eric N. Powell  Robert D. Barber  Mahlon C. Kennicutt II  Susan E. Ford 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):915

Petroleum seep mussels are often exposed to high hydrocarbon concentrations in their natural habitat and, thus, offer the opportunity to examine the relationship between parasitism, disease and contaminant exposure under natural conditions. This is the first report on the histopathology of cold-seep mussels. Seep mussels were collected by submersible from four primary sites in the Gulf of Mexico, lease blocks Green Canyon (GC) 184, GC-234, GC-233, and Garden Banks 425 in 550–650 m water depth. Five types of parasites were identified in section: (1) gill “rosettes” of unknown affinity associated with the gill bacteriocytes, (2) gill “inclusions” similar to chlamydia/rickettsia inclusions, (3) extracellular gill ciliates, (4) body “inclusions” that also resemble chlamydial/rickettsial inclusions, and (5) Bucephalus-like trematodes. Comparison to shallow-water mytilids demonstrates that: (1) both have similar parasite faunas; (2) seep mytilids are relatively heavily parasitized; and (3) infection intensities are extremely high in comparison to shallow-water mytilids for Bucephalus and chlamydia/rickettsia. In this study, the lowest prevalence for chlamydia/rickettsia was 67%. Prevalences of 100% were recorded from three populations. Bucephalus prevalence was 70% in three of 10 populations. The parasite fauna was highly variable between populations. Some important parasites were not observed in some primary sites. Even within primary sites, some important parasites were not observed in some populations. Bucephalus may exert a significant influence on seep mussel population dynamics. Forty percent of the populations in this study are severely reproductively compromised by Bucephalus infection. Only a fraction of petroleum seep mussel populations are maintaining the entire beta-level population structure of this species. Variation in two parasites, gill ciliates and Bucephalus, explained most of the variation in PAH body burden between mussel populations. PAHs are known to be sequestered preferentially in gametic tissue. Bucephalus would be expected to reduce overall body burden, at high infection intensities, by replacing gametic tissue. PAH concentrations exceeded 1 ppm in 4 of 9 populations, a ratio significantly higher than the 8 of 30 mussel locales in the NOAA Mussel Watch Program. Only five Mussel Watch locales exceeded the highest value for a petroleum seep population. Digestive gland and gill tissue atrophy were not significantly correlated with PAH body burden, even though some populations were characterized by body burdens exceeding 1 ppm, suggesting that seep mussels may not be as sensitive to PAH exposure as are some shallow-water mytilid populations.  相似文献   

Organic geochemistry of sediments from chemosynthetic communities,Gulf of Mexico slope   总被引：5，自引：2，他引：5  

R. Sassen  I. R. MacDonald  A. G. Requejo  N. L. Guinasso Jr.  M. C. Kennicutt II  S. T. Sweet  J. M. Brooks 《Geo-Marine Letters》1994,14(2-3):110-119

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H₂S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C₁–C₅ hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C₁–C₅ hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O₂ in sediments and triggers bacterial sulfate reduction to produce the H₂S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C₁–C₅ hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H₂S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C₁–C₅ concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C₁) is present (8829 ppm).  相似文献   

The biogeography and community structure of kelp forest macroinvertebrates          下载免费PDF全文

Laurel A. Zahn  Jeremy T. Claisse  Jonathan P. Williams  Chelsea M. Williams  Daniel J. Pondella II 《Marine Ecology》2016,37(4):770-785

Understanding species distributions and their community structure is increasingly important when taking an ecosystem‐based approach to conservation and management. However, knowledge of the distribution and community structure of species in mid‐range trophic levels (e.g. macroinvertebrates) is lacking in most marine ecosystems. Our study aimed to examine the spatial distribution and community‐level biogeographic patterns of common kelp forest–rocky reef macroinvertebrates in Southern California and to evaluate the effects of environmental gradients on these communities. Quantitative SCUBA surveys were used to estimate macroinvertebrate densities at 92 sites from 2008–2012. Non‐metric multidimensional scaling was used to evaluate spatial patterns of macroinvertebrate communities among Regions. We found that kelp forest–rocky reef macroinvertebrate communities are distinct among different island and mainland regions, and their community patterns exhibited a strong relationship with an environmental gradient (i.e. sea surface temperature) even after controlling for geographic distance between sites. High abundances of urchin species (Strongylocentrotus purpuratus and Strongylocentrotus franciscanus) were strong drivers of regional differences. Macroinvertebrate community patterns were driven by characteristic species that were typically more prevalent at warmer or colder sites. Our results provide the first quantitative analysis of macroinvertebrate community structure within the California kelp forest ecosystem. We also describe the distribution and abundance of 92 conspicuous kelp forest‐rocky reef macroinvertebrates among nine pre‐defined Regions. This study provides important preliminary information on these macroinvertebrate species that will be directly useful to inform management of invertebrate fisheries and spatial protection of marine resources.  相似文献