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1.
Kenneth H. Dunton Jonathan L. Goodall Susan V. Schonberg Jacqueline M. Grebmeier David R. Maidment 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3462
Using geographic information systems (GIS) software and geostatistical techniques, we utilized three decades of water-column chlorophyll a data to examine the relative importance of autochthonous versus allochthonous sources of reduced carbon to benthic communities that occur from the northern Bering to the eastern Beaufort Sea shelf. Spatial trend analyses revealed areas of high benthic biomass (>300 g m−2) and chlorophyll (>150 mg m−2) on both the southern and northern Chukchi shelf; both areas are known as depositional centers for reduced organic matter that originates on the Bering Sea shelf and is advected northward in Anadyr and Bering shelf water masses. We found a significant correlation between biomass and chlorophyll a in the Chukchi Sea, reflective of the strong benthic–pelagic coupling in a system that is utilized heavily by benthic-feeding marine mammals. In contrast, there was no significant correlation between biomass and chlorophyll in the Beaufort Sea, which by comparison, is considerably less productive (biomass and chlorophyll, <75 g m−2 and <50 mg m−2, respectively). One notable exception is an area of relatively high biomass (50–100 g m−2) and chlorophyll (80 mg m−2) near Barter Island in the eastern Beaufort Sea. Compared to other adjacent areas in the Beaufort Sea, the chlorophyll values in the vicinity of Barter Island were considerably higher and likely reflect a long-hypothesized upwelling in that area and close coupling between the benthos and autochthonous production. In the Bering Sea, a drop in benthic biomass in 1994 compared with previous measurements (1974–1993) may support earlier observations that document a decline in biomass that began between the 1980s and 1990s in the Chirikov Basin and south of St. Lawrence Island. The results of this study indicate that the benthos is an excellent long-term indicator of both local and physical advective processes. In addition, this work provides further evidence that secondary production on arctic shelves can be significantly augmented by reduced carbon advected from highly productive adjacent shelves. 相似文献
2.
Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials
and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms
in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the
insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these
minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion
will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. 相似文献
3.
R Henriques WM Potts CV Santos WHH Sauer PW Shaw 《African Journal of Marine Science》2018,40(1):13-24
The West Coast dusky kob Argyrosomus coronus is a commercially exploited fish with a distribution confined to the Angola–Benguela Frontal Zone (ABFZ) of the southeastern Atlantic Ocean. A previous study revealed that during a recent period of local warming the species extended its distribution into Namibian waters, where it hybridised with the resident and congeneric Argyrosomus inodorus. Environmental changes are a major threat to marine biodiversity and when combined with overfishing have the potential to accelerate the decline of species. However, little is known regarding the evolutionary history and population structure of A. coronus across the ABFZ. We investigated genetic diversity, population structure and historical demographic changes using mtDNA control region sequences and genotypes at six nuclear microsatellite loci, from 180 individuals. A single, genetically homogeneous population was indicated across the distributional range of A. coronus (φST = 0.041, FST = 0.000, D = 0.000; p > 0.05). These findings imply that the oceanographic features within the ABFZ do not appear to significantly influence population connectivity in A. coronus, which simplifies management of the species. However, reconstruction of the demographic history points to a close link between the evolutionary history of A. coronus and the environmental characteristics of the ABFZ. This outcome suggests the species’ vulnerability to the rapid environmental changes being observed across this region, and highlights a pressing need for transboundary management to mitigate the impacts of climate change in this global hotspot of seawater temperature changes. 相似文献
4.
The growth and subsequent dissolution of salts on or within sediment may alter sedimentary structures and textures to such an extent that it is difficult to identify the depositional origin of that sediment and, as a result, the sediment may be misinterpreted. To help to overcome such problems with investigating ancient successions, results are presented from a comprehensive study of the morphology and fabrics of three large areas of modern salt flats in SE Arabia: the Sabkhat Matti inland region and the At Taf coastal region, both in the Emirate of Abu Dhabi, and the Umm as Samim region in Oman. These salt flats are affected by tidal‐marine, alluvial and aeolian depositional processes and include both clastic‐ and carbonate‐dominated surficial sediments. The efflorescent and precipitated salt crusts in these areas can be grouped into two main types: thick crusts, with high relief (>10 cm) and a polygonal or blocky morphology; or thin crusts, with low relief (<10 cm) and a polygonal or blister‐like appearance. The thin crusts may assume the surface morphology of underlying features, such as ripples or biogenic mats. A variety of small‐scale textures were observed: pustular growths, hair‐like spikes and irregular wrinkles. Evolution of these crusts over time results in a variety of distinctive sedimentary fabrics produced by salt‐growth sediment deformation, salt‐solution sediment collapse, sediment aggradation and compound mixtures of these processes. Salt‐crust processes produce features that may be confused with aeolian adhesion structures. An example from the Lower Triassic Ormskirk Sandstone Formation of the Irish Sea Basin demonstrates how this knowledge of modern environments improves the interpretation of the rock record. A distinctive wavy‐laminated facies in this formation had previously been interpreted as the product of fluvial sheetfloods modified by soft‐sediment deformation and bioturbation. Close inspection of laminations seen in core reveals many of the same sedimentary fabrics seen in SE Arabia associated with salt crusts. This facies is the product of salt growth on aeolian sediment and is not of fluvial origin. 相似文献
5.
Jonathan L. Goodall David R. Maidment 《International journal of geographical information science》2013,27(2):233-247
Despite a long history of synergy, current techniques for integrating Geographic Information System (GIS) software with hydrologic simulation models do not fully utilize the potential of GIS for modeling hydrologic systems. Part of the reason for this is a lack of GIS data models appropriate for representing fluid flow in space and time. Here we address this challenge by proposing a spatiotemporal data model designed specifically for large‐scale river basin systems. The data model builds from core concepts in geographic information science and extends these concepts to accommodate mathematical representations of fluid flow at a regional scale. Space–time is abstracted into three basic objects relevant to hydrologic systems: a control volume, a flux and a flux coupler. A control volume is capable of storing mass, energy or momentum through time, a flux represents the movement of these quantities within space–time and a flux coupler insures conservation of the quantities within an overall system. To demonstrate the data model, a simple case study is presented to show how the data model could be applied to digitally represent a river basin system. 相似文献
6.
Fundamentals of gas containment in unlined rock caverns 总被引：3，自引：0，他引：3
Summary The criterion for gas entry into idealized, uniform, water-saturated fractures is examined for one-dimensional, elliptical and cylindrical cavern geometries. This limiting criterion is a necessary condition for gas escape from unlined, pressurized gas storages.Gas-entry phenomena were examined using 450-mm-square glass plates in Hele Shaw configuration with nominal apertures of 50 and 200 microns. The fundamentals of gas entry, as first enunciated by Åberg (1977), are confirmed by the experiments; the critical gas-entry pressure is a function of hydraulic flow regime, fracture-mouth capillarity and fracture-mouth profile. Finite-element simulation based on these fundamentals is substantiated by experimental observations and is therefore used for generalization.The gas-entry criterion is found to be sensitive to details of fracture geometry such as aperture, connection of the fractures to the groundwater regime, geometry of the intersection of the fractures with the gas cavern, disturbance of the rock mass as a consequence of excavation, and cavern shape. In view of the inability to predict or even measure these factors, an alternative criterion which ensures no gas migration away from the gas storage is proposed. This simple criterion insists that gas escape will not occur as long as the water pressure along all possible escape paths increases for some small distance in the direction of potential gas escape. This criterion is a generalization of Åberg's (1977) proposal that the vertical hydraulic gradient should exceed one for no gas escape. 相似文献
7.
This paper presents the results of a recent rocket firing through a quiet, mid-day E-region in which measurements of ionospheric electron densities and electron temperatures were made using improved diagnostic techniques. Excellent agreement was found to exist between the in-situ measurements of electron density and those deduced from ionograms obtained during the flight using ground based equipment. Measurements of the contact potential difference existing between the two graphite coated grids forming the electron temperature probe demonstrated that serious errors can be introduced into the electron temperature measurements if not taken into account and showed further that appreciable changes in the contact potential difference can occur during a short flight. The results of the flight indicate that the modifications made to both experiments represent significant improvements and demonstrate that the data outputs of each experiment are in a convenient form to be electronically stored, read at a subsequent time compatible with the telemetry sampling and telemetred to ground using only a small number of low bandwidth channels. 相似文献
8.
Praharaj Shraddha Chen T. Donna Zahura Faria T. Behl Madhur Goodall Jonathan L. 《Natural Hazards》2021,109(3):2363-2380
Predicting tropical cyclone (TCs) tracks is a primary concern in TC forecasting. Some TCs appear to move in a direction favorable for their development, beyond the influence of the steering flow. Thus, we hypothesize that TCs move toward regions with high water-vapor content in the lower atmosphere. In this study, four numerical experiments, including a control experiment and three sensitivity experiments, were performed using the Weather Research and Forecasting Model, to analyze the relationship between water vapor distribution and the track of Severe Typhoon Hato (2017). Observations validated the features reproduced in the control experiment. The sensitivity experiments were conducted to explore variations in the TC track under different water vapor environments. Results indicate that the horizontal distribution of water-vapor content exerted a greater impact on the TC track than the steering flow when both factors were significant. Further analysis revealed that the TC’s movement vector was between the direction of the steering flow and the direction toward the peak of vorticity increasing area. The peaks of vorticity increasing area were close to the peaks of water vapor increasing area, which also proved the effect of water vapor distribution on the TC track. These results are expected to improve TC track analysis and forecasting.
相似文献9.
Measurements carried out using a cylindrical Langmuir probe operated in the electron accelerating region of the current-voltage characteristics under orbital limited conditions in low density plasmas, show the response of the probe to be in good agreement with Langmuir theory. By making observations in three different plasmas, namely a steady state plasma, an afterglow plasma and the ionospheric plasma it is confirmed that the form of the orbital limited characteristics of the probe is independent of the energy distribution of the electrons in the plasma. Comparative measurements of ionospheric electron densities made between a rocket borne cylindrical probe and a ground based ionosonde show good agreement to exist and thus demonstrate that the probe operated in this mode not only overcomes the significant problems associated with retarding region probe measurements but affords an accurate determination of electron density. This underlines the usefulness of this kind of probe for electron density measurements in plasmas where the energy distribution of the electrons is unknown. 相似文献
10.
J. R. H. Herring D. J. Campbell C. V. Goodall A. M. Cruise I. M. Mason J. P. Osborne 《Astrophysics and Space Science》1983,89(2):325-339
This paper describes the detailed calibration at soft X-ray energies (0.1–2.0 keV; 125 Å-6 Å) of gold coated, paraboloidal X-ray mirrors, four of which were subsequently flow on the Ariel-6 satellite. Uncertainties in the attitude of the satellite together with an apparent reduction in sensitivity of the soft X-ray experiment necessitated observations using the Crab Nebula as a reference. These showed that a dramatic reduction in the reflection efficiencies of all four mirrors had occurred, almost certainly after or during launch. An initial recalibration of the mirrors using the Crab observation is described. 相似文献