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1.
Dr. C. B. Raleigh 《Contributions to Mineralogy and Petrology》1965,11(7):719-741
A study of the structural petrology of a peridotite exposed on Cypress Island in Skagit Co., Washington, U.S.A. has been carried out. The Cypress peridotite is, by virtue of its composition, structure and associations, typical of ultramafics of the alpine type. It contains relict layering and accumulative textures which show it to have originated by crystal settling from a magma of unknown initial composition. Parallelism of lineations and b-axes of folds in the layering with well-developed [100]-maxima in the fabrics of olivine crystals is considered to have arisen through a penetrative deformation of the mass accompanied by plastic flow or recrystallization of the olivine. An indication of the minimum temperature of the deformation is provided by cross-cutting veins of pyroxenite which have not participated in the folding. The most satisfactory interpretation of the overall fabric of the peridotite is that it was deformed, possibly during intrusion, as a crystal mush, and that filter pressing due to compaction of the solid particles by plastic flow or recrystallization removed all but a small percentage of the magmatic fraction which then crystallized following cessation of the movements. 相似文献
2.
J. Blake Clark Wen Long Maria Tzortziou Patrick J. Neale Raleigh R. Hood 《Estuaries and Coasts》2018,41(3):708-723
Controls on organic matter cycling across the tidal wetland-estuary interface have proved elusive, but high-resolution observations coupled with process-based modeling can be a powerful methodology to address shortcomings in either methodology alone. In this study, detailed observations and three-dimensional hydrodynamic modeling are used to examine biogeochemical exchanges in the marsh-estuary system of the Rhode River, MD, USA. Analysis of observations near the marsh in 2015 reveals a strong relationship between marsh creek salinity and dissolved organic matter fluorescence (fDOM), with wind velocity indirectly driving large amplitude variation of both salinity and fDOM at certain times of the year. Three-dimensional model results from the Finite Volume Community Ocean Model implemented for the wetland system with a new marsh grass drag module are consistent with observations, simulating sub-tidal variability of marsh creek salinity. The model results exhibit an interaction between wind-driven variation in surface elevation and flow velocity at the marsh creek, with northerly winds driving increased freshwater signal and discharge out of the modeled wetland during precipitation events. Wind setup of a water surface elevation gradient axially along the estuary drives the modeled local sub-tidal flow and thus salinity variability. On sub-tidal time scales (>36 h, <1 week), wind is important in mediating dissolved organic matter releases from the Kirkpatrick Marsh into the Rhode River. 相似文献
3.
Katharine A. Smith Elizabeth W. North Fengyan Shi Shih-Nan Chen Raleigh R. Hood Evamaria W. Koch Roger I. E. Newell 《Estuaries and Coasts》2009,32(4):748-757
Seagrass beds have declined in Chesapeake Bay, USA as well as worldwide over the past century. Increased seston concentrations,
which decrease light penetration, are likely one of the main causes of the decline in Chesapeake Bay. It has been hypothesized
that dense populations of suspension-feeding bivalves, such as eastern oysters (Crassostrea virginica), may filter sufficient seston from the water to reduce light attenuation and enhance seagrass growth. Furthermore, eastern
oyster populations can form large three-dimensional reef-like structures that may act like breakwaters by attenuating waves,
thus decreasing sediment resuspension. We developed a quasi-three-dimensional Seagrass-Waves-Oysters-Light-Seston (SWOLS)
model to investigate whether oyster reefs and breakwaters could improve seagrass growth by reducing seston concentrations.
Seagrass growth potential (SGP), a parameter controlled by resuspension-induced turbidity, was calculated in simulations in
which wave height, oyster abundance, and reef/breakwater configuration were varied. Wave height was the dominant factor influencing
SGP, with higher waves increasing sediment resuspension and decreasing SGP. Submerged breakwaters parallel with the shoreline
improved SGP in the presence of 0.2 and 0.4 m waves when sediment resuspension was dominated by wave action, while submerged
groins perpendicular to the shoreline improved SGP under lower wave heights (0.05 and 0.1 m) when resuspension was dominated
by along-shore tidal currents. Oyster-feeding activity did not affect SGP, due to the oysters’ distance from the seagrass
bed and reduced oyster filtration rates under either low or high sediment concentrations. Although the current implementation
of the SWOLS model has simplified geometry, the model does demonstrate that the interaction between oyster filtration and
along-shore circulation, and between man-made structures and wave heights, should be considered when managing seagrass habitats,
planning seagrass restoration projects, and choosing the most suitable methods to protect shorelines from erosion. 相似文献
4.
This article discusses how conflict patterns affect the volume, direction and types of migration within the developing world. Conflict impact and poverty are the two primary drivers directly shaping migrations within poor and high-risk environments. Indirect drivers of migration include livelihood fragility, ecological and political instabilities. Conflicts overwhelmingly occur in states where much of the population is dependent upon the environment/natural resources for their livelihoods. There is little reliable evidence to suggest a link between civil conflict and climate change, however, the environmental changes occurring across developing states shape the ways in which civilians can respond to political and economic threats. The crucial point is that the communities who are subject to increasing environmental variation and disruption, through either external or internal processes, are likely to become poorer as a consequence. This poverty lessens their ability to respond to the myriad of threats in their environs, including conflict, ecological disasters, disease, or economic hardship. Hence, there is an endogeneity to conflict, precipitating factors and possible outcomes: the persistence of violence plays a determining role in the sustainability of livelihoods, poverty levels and the propensity of migration within chronically conflicted areas. Those most vulnerable to forced migration live in ‘chronically vulnerable areas’, which are characterized by the deterioration, loss or destruction of primary livelihood systems and productive assets, environmental degradation and deterioration of natural resources, increasing impoverishment of communities and households, geographical isolation and a dependence on relief. 相似文献
5.
Julian P. McCreary Jr Kevin E. Kohler Raleigh R. Hood Donald B. Olson 《Progress in Oceanography》1996,37(3-4)
A coupled, physical-biological model is used to study the processes that determine the annual cycle of biological activity in the Arabian Sea. The physical model is a
system with a surface mixed layer imbedded in the upper layer, and fluid is allowed to move between layers via entrainment, detrainment and mixing processes. The biological model consists of a set of advective-diffusive equations in each layer that determine the nitrogen concentrations in four compartments: nutrients, phytoplankton, zooplankton and detritus. Coupling is provided by the horizontal-velocity, layer-thickness, entrainment and detrainment fields from the physical solution. Surface forcing fields (such as wind stress and photosynthetically active radiation) are derived from monthly climatological data, and the source of nitrogen for the system is upward diffusion of nutrients from the deep ocean into the lower layer. Our main-run solution compares favorably with observed physical and biological fields; in particular, it is able to simulate all the prominent phytoplankton blooms visible in the CZCS data. Three bloom types develop in response to the physical processes of upwelling, detrainment and entrainment. Upwelling blooms are strong, long-lasting events that continue as long as the upwelling persists. They occur during the Southwest Monsoon off Somalia, Oman and India as a result of coastal alongshore winds, and at the mouth of the Gulf of Aden through Ekman pumping. Detrainment blooms are intense, short-lived events that develop when the mixed layer thins abruptly, thereby quickly increasing the depth-averaged light intensity available for phytoplankton growth. They occur during the fall in the central Arabian Sea, and during the spring throughout most of the basin. In contrast to the other bloom types, entrainment blooms are weak because entrainment steadily thickens the mixed layer, which in turn decreases the depth-averaged light intensity. There is an entrainment bloom in the central Arabian Sea during June in the solution, but it is not apparent in the CZCS data. Bloom dynamics are isolated in a suite of diagnostic calculations and test solutions. Some results from these analyses are the following. Entrainment is the primary nutrient source for the offshore bloom in the central Arabian Sea, but advection and recycling also contribute. The ultimate cause for the decay of the solution's spring (and fall) blooms is nutrient deprivation, but their rapid initial decay results from grazing and self shading. Zooplankton grazing is always an essential process, limiting phytoplankton concentrations during both bloom and oligotrophic periods. Detrital remineralization is also important: in a test solution without remineralization, nutrient levels drop markedly in every layer of the model and all blooms are severely weakened. Senescence, however, has little effect: in a test solution without senescence, its lack is almost completely compensated for by increased grazing. Finally, the model's detrainment blooms are too brief and intense in comparison to the CZCS data; this difference cannot be removed by altering biological parameters, which suggests that phytoplankton growth in the model is more sensitive to mixed-layer thickness than it is in the real ocean. 相似文献
6.
The problem of applying laboratory silicate-flow data to the mantle, where conditions can be vastly different, is approached through a critical review of high-temperature flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-temperature creep in pure metals is found to apply to ceramics as well. It is shown that in ceramics of moderate grain size, compared on the basis of self-diffusivity and elastic modulus, normalized creep rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar creep-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation creep. Creep data in fine-grained ceramics, on the other hand, are found to compare poorly with theories involving the stress-directed diffusion of point defects and have not been successfully correlated by self-diffusion rates.We conclude that these fine-grained materials creep primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. Creep predictions for the mantle reveal that under most conditions the empirical dislocation creep behavior predominates over the mechanisms involving the stress-directed diffusion of point defects. The probable role of polymorphic transformations in the transition zone is also discussed. 相似文献
7.
Plastic Deformation of Upper Mantle Silicate Minerals 总被引：1，自引：0，他引：1
C. B. Raleigh 《Geophysical Journal International》1967,14(1-4):45-49
8.
Estuarine turbidity maxima (ETM) play an important role in zooplankton and larval fish productivity in many estuaries. Yet in many of these systems, little is known about the food web that supports this secondary production. To see if phytoplankton have the potential to be a component of the ETM food web in the Chesapeake Bay estuary a series of cruises were carried out to determine the biomass distribution and floral composition of phytoplankton in and around the ETM during the winter and spring using fluorometry, high-performance liquid chromatography (HPLC), and microscopy. Two distinct phytoplankton communities were observed along the salinity gradient. In lower salinity waters, biomass was low and the community was composed mostly of diatoms, while in more saline waters biomass was high and the community was composed mostly of mixotrophic dinoflagellates, which were often concentrated in a thin layer below the pycnocline. Phytoplankton biomass was always low in the ETM, but high concentrations of phytoplankton pigment degradation products and cellular remains were often observed suggesting that this was an area of high phytoplankton mortality and/or an area where phytoplankton derived particulate organic matter was being trapped. These results, along with a box model analysis, suggest that under certain hydrodynamic conditions phytoplankton derived organic matter can be trapped in ETM and potentially play a role in fueling secondary production. 相似文献
9.
Representation of the subsurface light field is a crucial component of pelagic ecosystem and water quality models. Modeling
the light field in estuaries is a particularly complicated problem due to the significant influence of high concentrations
of dissolved and particulate matter that are derived from both terrestrial and estuarine sources. The goal of this study was
to develop a relatively simple but effective way to model light attenuation variability in a turbuid estuary (Chesapeake Bay,
United States) in a coupled physical-biological model. We adopted a simple, nonspectral empirical approach. Surface water
quality data (salinity was used as a proxy of chromophoric dissolved organic matter [CDOM]) and light measurements from the
Chesapeake Bay Program were used to determine the absorption coefficients in a linear attenuation model using regression methods.
This model predicts Kc (specific attenuation due to phytoplankton/chlorophylla [chla]), Kt (specific attenuation due to total suspended solids), and Ks (a function of specific attenuation coefficients of CDOM in relation to salinity). The Bay-wide fitted relation between the
light attenuation coefficient and water quality concentrations gives generally good estimates of total light attenuation,
Kd. The direct inclusion of salinity in the relationship has one disadvantage: it can yield negative values for Kd at high salinities. We developed two separate models for two different salinity regimes. This approach, in addition to solving
the negative Kd problem, also accounts for some changes in specific light absorption by chla, seston (nonphytoplankton particulate matter), and CDOM that apparently occur in different salinity regimes in Chesapeake
Bay. The resulting model predicts the statistical characteristics (i.e., the mean and variance) of Kd quite accurately in most regions of Chesapeake Bay. We also discuss in this paper the feasibility and caveats of using Kd converted from Secchi depth in the empirical method. 相似文献
10.
Raleigh R. Hood Kevin E. Kohler Julian P. McCreary Sharon L. Smith 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):2917
In this paper, we use a coupled biological/physical model to synthesize and understand observations taken during the US JGOFS Arabian Sea Process Study (ASPS). Its physical component is a variable-density,
-layer model; its biological component consists of a set of advective–diffusive equations in each layer that determine nitrogen concentrations in four compartments, namely, nutrients, phytoplankton, zooplankton, and detritus. Solutions are compared to time series and cruise sections from the ASPS data set, including observations of mixed-layer thickness, chlorophyll concentrations, inorganic nitrogen concentrations, particulate nitrogen export flux, zooplankton biomass, and primary production. Through these comparisons, we adjust model parameters to obtain a “best-fit” main-run solution, identify key biological and physical processes, and assess model strengths and weaknesses.Substantial improvements in the model/data comparison are obtained by: (1) adjusting the turbulence-production coefficients in the mixed-layer model to thin the mixed layer; (2) increasing the detrital sinking and remineralization rates to improve the timing and amplitude of the model's export flux; and (3) introducing a parameterization of particle aggregation to lower phytoplankton concentrations in coastal upwelling regions.With these adjustments, the model captures many key aspects of the observed physical and biogeochemical variability in offshore waters, including the near-surface DIN and phytoplankton P concentrations, mesozooplankton biomass, and primary production. Nevertheless, there are still significant model/data discrepancies of P for most of the cruises. Most of them can be attributed to forcing or process errors in the physical model: inaccurate mixed-layer thicknesses, lack of mesoscale eddies and filaments, and differences in the timing and spatial extent of coastal upwelling. Relatively few are clearly related to the simplicity of the biological model, the model's overestimation of coastal P being the most obvious example. Overall, we conclude that future efforts to improve biogeochemical models of the Arabian Sea should focus on improving their physical component, ensuring that it represents the ocean's physical state as closely as possible. We believe that this conclusion applies to coupled biogeochemical modeling efforts in other regions as well. 相似文献