Mapping iron abundances on the surface of Mercury: Predicted spatial resolution of the MESSENGER Gamma-Ray Spectrometer     

Patrick N. Peplowski  David T. Blewett  Brett W. Denevi  Larry G. Evans  David J. Lawrence  Larry R. Nittler  Edgar A. Rhodes  Christina M. Selby  Sean C. Solomon 《Planetary and Space Science》2011,59(13):1654-1658

To illustrate the spatial resolution of measurements of Mercury's surface elemental composition by the Gamma-Ray Spectrometer on the MESSENGER spacecraft after one year of orbital observations, we have simulated a global coverage map of the 846-keV iron gamma-ray count rate. The simulated map suggests that distinct geologic units larger than 800 km in horizontal dimension will be discernable when the difference in Fe abundance between adjacent geologic units exceeds 4 wt%. These results imply that the MESSENGER Gamma-Ray Spectrometer dataset will provide useful information for regional geological studies of the surface of Mercury.  相似文献   

The effect of the Jessica grounding on Galápagos reef fish communities adjacent to the wreck site     

Edgar GJ  Marshall PA  Mooney P 《Marine pollution bulletin》2003,47(7-8):296-302

The grounding of the oil tanker Jessica off San Cristóbal Island, Galápagos, resulted in generally elevated rather than depressed densities of fishes adjacent to the wreck site 15 weeks post spill. Species richness of fishes declined along transects out from the wreck; however, patterns were inconsistent for different depth strata, with the most clearly defined decline evident for the intermediate 5-7 m depth stratum. Fish species attracted to the immediate wreck site, most notably the surgeonfish Prionurus laticlavius, the damselfish Microspathodon dorsalis and the angelfish Holacanthus passer, were considered to be responding either to the heterogeneity provided by the wreck structure or elevated densities of macroalgae. The fish community at the wreck site lay outside the range of variation for other sites investigated in the region; however, contrary to predictions of grounding impacts, the fish assemblage immediately adjacent to the wreckage showed greater faunal similarity to reference sites than did fish assemblage at 60-90 m distance from the grounding.  相似文献   

Pitfalls in geothermobarometry of eclogites: Fe<Superscript>3+</Superscript> and changes in the mineral chemistry of omphacite at ultrahigh pressures   总被引：1，自引：0，他引：1  

Alexander?ProyerEmail author  Edgar?Dachs  Catherine?McCammon 《Contributions to Mineralogy and Petrology》2004,147(3):305-318

The relatively low-variance mineral assemblage of a talc-kyanite eclogite from Dabie Shan enabled application of both conventional geothermobarometers (garnet-clinopyroxene geothermometer and the garnet-omphacite-phengite geobarometer) and a multi-equilibrium method to determine peak P-T conditions (THERMOCALC, average PT). The results were highly discrepant: 840 °C / 31.1 kbar vs. 590 °C / 29.8 kbar. Mössbauer spectroscopy showed that Fe³⁺/Fe_total in omphacite was significantly higher than the value obtained from standard formula recalculation. When the activities were corrected for Fe endmembers, geothermobarometry gave consistent results (606 °C / 31.3 kbar vs. 585 °C / 30.8 kbar). These are close to those obtained earlier by average PT, confirming the robustness of the multi-equilibrium approach. The high Fe³⁺ concentration in omphacite is best explained using a Ca-eskola endmember Ca_0.5[]_0.5AlSi₂O₆ and allowing corresponding vacancies in the omphacite structure.Editorial responsibility: W. Schreyer  相似文献   

The Signature of Sea Spray in the Hexos Turbulent Heat Flux Data   总被引：7，自引：0，他引：7  

Edgar L Andreas  Janice Decosmo 《Boundary-Layer Meteorology》2002,103(2):303-333

The role of sea spray intransferring heat and moisture across the air-sea interface has remained elusive. Some studies have reported that sea spray does not affect the turbulent air-sea heat fluxes for 10-m wind speeds up to at least 25 m s^-1, while others have reported important spray contributions for wind speeds as low as 12 m s^-1. One goal of the HEXOS (Humidity Exchange over the Sea) program was to quantify spray's contribution to the turbulent air-sea heat fluxes, but original analyses of the HEXOS flux data found the spray signal to be too small to be reliably identified amid the scatter in the data. We look at the HEXOS data again in the context of the TOGA-COARE bulk flux algorithm and a sophisticated microphysical spray model. This combination of quality data andstate-of-the-art modelling reveals a distinct spray signature in virtually all HEXOS turbulent heat flux data collected in winds of 15 m s^-1 and higher. Spray effects are most evident in the latent heat flux data, where spray contributes roughly 10% of the total turbulent flux in winds of 10 m s^-1 and between 10 and 40% in winds of 15–18 m s^-1. The spray contribution to the total sensible heat flux is also at least 10% in winds above 15 m s^-1. These results lead to a new, unified parameterization for the turbulent air-sea heat fluxes that should be especially useful in high winds because it acknowledges both the interfacial and spray routes by which the sea exchanges heat and moisture with the atmosphere.  相似文献   

Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela     

Andrew G. Warne  Robert H. Meade  William A. White  Edgar H. Guevara  James Gibeaut  Rebecca C. Smyth  Andres Aslan  Thomas Tremblay 《Geomorphology》2002,44(3-4)

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km² Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta.The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast.Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Río Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.  相似文献   

Compositional dependence of REE partitioning between diopside and melt at 1 atmosphere   总被引：1，自引：1，他引：0  

Michael Schosnig  Edgar Hoffer 《Contributions to Mineralogy and Petrology》1998,133(3):205-216

The effects of composition on pyroxene-melt partitioning of several REE (rare earth elements), Y, and Sr were experimentally evaluated. Using the synthetic model systems anorthite–diopside, diopside–titanite and anorthite–diopside–titanite different diopsides were grown at atmospheric conditions in a double-ellipsoid mirror furnace. The single samples were melted and crystallised in a Pt/Au crucible with compositions corresponding to the invariant points of these systems. Rotational motion with approximately 25 rpm around the longitudinal axis of the crucible increases the prevailing convection flows. By this means, the exclusively diffusional transport of assembly groups onto the growing crystals is avoided. Quenching is achieved by dropping the crucible into water. Crystals up to 2 mm were obtained and analysed by electron microprobe. No inhomogeneities or compositional zonation, either in the diopsides or in the coexisting melts, were observed within the analytical uncertainty of the electron microprobe. The crystallised diopsides occur as both euhedral single crystals and large symplectitic lamellar intergrowths with anorthite or titanite. The chemical homogeneity and the texture indicate near-equilibrium conditions. The analyses show strong positive correlations between D_REE and tetrahedrally coordinated Al in diopside but are not affected by octahedral Al or Ti-concentration. By means of correlations and mass balances the incorporation of REE can be described by 2 different coupled substitutions: The Al-coupled incorporation of REE³⁺ (1) dominates the D-values. The Na-coupled substitution (2) is of minor importance. Depending on the compositions investigated the D-values vary by up to a factor of 10. This range overlaps most of the published pyroxene-melt partition coefficients. Because we conducted isothermal and isobaric experiments, this overlap indicates that a wide range of D-values is a function of composition. For the coupled substitutions (1) and (2) this indicates that the D_REE strongly depends on the amount of tetrahedrally coordinated Al³⁺ in clinopyroxenes. Received: 5 January 1998 / Accepted: 11 June 1998  相似文献   

Juvenile capelin (Mallotus villosus) off Newfoundland and Labrador in the 1990s     

Anderson  John T.; Dalley  Edgar L.; O'Driscoll  Richard L. 《ICES Journal of Marine Science》2002,59(5):917-928

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The geology of the lower valley of the Gade,and its bearing upon problems connected with the erosion of the chalk and the deposition of superficial gravels,etc.     

Edgar A. Merrett 《Proceedings of the Geologists' Association. Geologists' Association》1927,38(2):217-236

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Using scintillation at two wavelengths to measure path-averaged heat fluxes in free convection     

Edgar L Andreas 《Boundary-Layer Meteorology》1991,54(1-2):167-182

Local free convection scaling is one of the obvious triumphs of boundary-layer similarity theory. In free convection, there is no dynamic velocity scale; the sensible and latent heat fluxes, therefore, scale directly with the temperature and humidity structure parameters C _t ² and C _q ². By using scintillation to measure the refractive index structure parameter C _n ² at two electromagnetic (EM) wavelengths, we can obtain C _t ² and C _q ² and, thus, in effect, measure path-averaged values of the sensible and latent heat fluxes. Here I describe this so-called two-wavelength method for free convection, derive quantitative guidelines for optimizing the method, and evaluate its potential accuracy. I show that the two-wavelength method works best when one EM wavelength is in the visible or infrared region and the other is in the millimeter or radio region. When the Bowen ratio is between -5 and -0.1 or between 0.1 and 5, the expected accuracy of the measured fluxes is ±10–20% — typical of what is possible with eddy-correlation measurements. With the two-wavelength method, however, the fluxes represent spatial averages.  相似文献   

The application of a segmented tidal mixing model to the Great Bay Estuary,N.H.     

Wendell S. Brown  Edgar Arellano 《Estuaries and Coasts》1980,3(4):248-257

Measurements show that in general salt is vertically well-mixed everywhere in the Great Bay Estuary, New Hampshire except near the river entrances at the head of the estuary. Dyer and Taylor’s (1973) modified version of Ketchum’s segmented tidal prism model has been applied to the Great Bay Estuarine System in order to predict high and low water salinity distribution for a specified river flow. The theory has been modified here to account for the mixing which occurs at the junction of two branches of an estuary. The mixing parameter, which in this model is related to the tidal excursion of water in the estuary, has been determined for different segments in the estuary on the basis of a comparison between predictions and a comprehensive data set obtained for a low river flow period. Using a mixing parameter distribution based on the low river flow calibration procedure the salinity distribution has been predicted for high river flow. The resulting salinity distribution compares favorably with observations for most of the estuary. The corresponding flushing times for water parcels entering at the head of the estuary during periods of low and high river flow is 54.5 and 45.9 tidal cycles respectively.  相似文献