Hydrothermal convection in carbonaceous chondrite parent bodies     

Bryan J. Travis  Gerald Schubert 《Earth and Planetary Science Letters》2005,240(2):234-250

Numerical simulations of the thermal evolution of carbonaceous chondrite parent bodies indicate a period of several million years during which convective motion of water could occur. The present study considers variations of permeability, radiogenic heating, and body radius. The model accounts for the radial variation of gravity within the body, melting of ice, freezing of liquid water, and variable water properties and incorporates a realistic equation of state for water. Some regions of a parent body experience no pore water flow while other regions experience hundreds of pore volumes of liquid water flow. The spatial heterogeneity in pore water flow reflects the convective pattern in the body. Hydrothermal alteration of minerals inside the parent body will accordingly vary greatly with location in the body, and one parent body could be the source of chemically diverse meteorites.  相似文献   

Redistribution of sea level rise associated with enhanced greenhouse warming: a simple model study   总被引：1，自引：0，他引：1  

Hsieh  William W.  Bryan  Kirk 《Climate Dynamics》1996,12(8):535-544

Future sea level rise from thermal expansion of the World Ocean due to global warming has been explored in several recent studies using coupled ocean-atmosphere models. These coupled models show that the heat input by the model atmosphere to the ocean in such an event could be quite non-uniform in different areas of the ocean. One of the most significant effects predicted by some of the models is a weakening of the thermohaline circulation, which normally transports heat poleward. Since the greatest heat input from enhanced greenhouse warming is in the higher latitudes, a weakening of the poleward heat transport effectively redistributes the heat anomaly and the associated sea level rise to lower latitudes. In this study, the mechanism of ocean circulation spindown and heat redistribution was studied in the context of a much simpler, linearized shallow water model. Although the model is much simpler than the three-dimensional ocean circulation models used in the coupled model experiments, and neglects several important physical effects, it has a nearly 10-fold increase in horizontal resolution and clearer dynamical interpretations. The results indicated that advanced signals of sea level rise propagated rapidly through the action of Kelvin and Rossby waves, but the full adjustment toward a more uniform sea level rise took place much more slowly. Long time scales were required to redistribute mass through narrow currents trapped along coasts and the equatorial wave guide. For realistic greenhouse warming, the model showed why the sea level rise due to ocean heating could be far from uniform over the globe and hence difficult to estimate from coastal tide gauge stations.  相似文献   

The steric component of sea level rise associated with enhanced greenhouse warming: a model study     

Kirk Bryan 《Climate Dynamics》1996,12(8):545-555

Climate change due to enhanced greenhouse warming has been calculated using the coupled GFDL general circulation model of the atmosphere and ocean. The results of the model for a sustained increase of atmospheric carbon dioxide of 1% per year over a century indicate a marked warming of the upper ocean. Results of the model are used to study the rise in sea level caused by increase in ocean temperatures and associated changes in ocean circulation. Neglecting possible contributions due to changes in the volume of polar ice sheets and mountain glaciers, the model predicts an average rise in sea level of approximately 15 ± 5 cm by the time atmospheric carbon dioxide doubles. Heating anomalies are greatest in subpolar latitudes. This effect leads to a weakening of the ocean thermohaline circulation. Changes in thermohaline circulation redistribute heat within the ocean from high latitudes toward the equator, and cause a more uniform sea level rise than would occur otherwise.  相似文献   

Copper,zinc, and organotin as long-term factors governing the distribution of organisms in the fal estuary in Southwest England     

G. W. Bryan  P. E. Gibbs  L. G. Hummerstone  G. R. Burt 《Estuaries and Coasts》1987,10(3):208-219

Evidence of long-term metal pollution in the Fal Estuary is provided by analyses of Cu in oyster (Ostrea edulis) communities extending over more than 120 yr and by analyses of Cu and Zn in sediments dating back to 1921. Indications are that levels of Cu pollution from mining have declined very slowly but that Zn pollution has not. In Restronguet Creek, the most heavily polluted area, metal levels in waters and sediments are elevated by orders of magnitude. The invertebrate fauna of the creek is limited, but far richer than might be predicted from laboratory toxicity data. The cockleCerastoderma edule exemplifies organisms that are excluded from the creek owing to the toxicity of dissolved Cu, whereasOstrea edulis, by virtue of its innate tolerance to Cu and Zn, grown in the Iower reaches. On the other hand, the population of the ragwornNereis diversicolor, which penetrates into the most heavily polluted areas, is demonstrably far more tolerant of Cu and Zn than population from clean areas and appears to be a tolerant strain. To a considerable degree, therefore, the distribution of species is dependent not only on the innate ability of some species to tolerate Cu and Zn, but on the capacities of other populations to develop metal resistance and thereby maintain their original range of distribution. Present-day problems in the Fal Estuary appear to stem not only from mining wastes but also from the increased usage of tributyltins in antifouling paints. In the dogwhelkNucella lapillus, the incidence of imposex (the appearance of a penis and other male characters in females) is virtually 100% at sites along the English Channel coast of southwest England. The degree of imposex is related to the body concentration of hexane-extractable organotin, which includes both tributyltin and dibutyltin fractions. The highest degree of imposex, where the female penis approaches that of the male in size, occurs in the Fal Estuary; also, in some males the penis becomes deformed. Populations of dogwhelks have declined dramatically in this estuary, and are also characterised by the presence of relatively fewer females and by the absence of juveniles and egg capsules. Reproductive failure in females is now known to be caused by blockage of the pallial oviduct during the development of imposex.  相似文献   

Major element evolution of basaltic magmas: a comparison of the information in CMAS and ALFE projections     

John B. Reid Jr.  Eric Steig  Wilfred B. Bryan 《Contributions to Mineralogy and Petrology》1989,101(3):318-325

Basalt petrologists disagree as to whether the commonly used projection, forsterite-diopside-silica, in the system CMAS (CaO-MgO-Al₂O₃-SiO₂), can adequately resolve differences in basaltic glass compositions for purposes of petrogenetic modelling. Here, we suggest than an analogous plot, the aluminium-factor diagram (ALFE) of Nesbitt and Cramer (1981), has greater diagnostic value than Fo-Di-Sil. A plot of molar (Al₂O₂-CaO-Na₂O-K₂O)/(FeO + MgO) vs FeO/(FeO + MgO), it produces more coherent patterns both for experimental basalt glasses, and for natural lavas. It is, like Fo-Di-Sil, a projection through plagioclase, but has the advantage that it monitors changes in Fe/(Fe + Mg) in melts and associated crystalline phases, and is particularly useful in assessing the timing of clinopyroxene crystallization in a suite of lavas. The diagram owes its greater resolving power to the fact that the computation of its coordinates is less sensitive to analytical uncertainty than for Fo-Di-Sil. In the latter diagram, normative quartz is calculated as a residual and thus manifests the uncertainties in all the major elements.  相似文献   

Mineralogic variability of the uppermost mantle along mid-ocean ridges     

Henry J.B. Dick  Robert L. Fisher  Wilfred B. Bryan 《Earth and Planetary Science Letters》1984,69(1):88-106

Modal analyses of 273 different peridotites representing 43 dredge stations in the Atlantic, Caribbean, and Indian Oceans define three separate melting trends. Peridotites dredged in the vicinity of “mantle plumes” or hot spots have the most depleted compositions in terms of basaltic components, while peridotites dredged at locations removed from such regions are systematically less depleted. The modal data correlate well with mineral compositions, with the peridotites most depleted in pyroxene also having the most refractory mineral compositions. This demonstrates that they are the probable residues of variable degrees of mantle melting. Further, there is a good correlation between the modal compositions of the peridotites and the major element composition of spatially associated dredged basalts. This demonstrates for the first time that the two must be directly related, as is frequently postulated. The high degree of depletion of the peridotites in basaltic major element components in the vicinity of some documented mantle plumes provides direct evidence for a thermal anomaly in such regions—justifying their frequent designation as “hot spots”. The high incompatible element concentrations in these “plume” basalts, however, are contrary to what is expected for such high degrees of melting, and thus require either selective contributions from locally more abundant enriched veins and/or contamination by a volatile-rich metasomatic front from depth.  相似文献   

Mars: Subsurface properties from observed longitudinal variation of the 3.5-mm brightness temperature     

Eugene E. Epstein  Bryan H. Andrew  Frank H. Briggs  Bruce M. Jakosky  Frank D. Palluconi 《Icarus》1983,56(3):465-475

Measurements at 3.5 mm of the disk-average brightness temperature of Mars during the 1978 opposition can be represented by (The errors cited are from the internal scatter; the estimated absolute calibration uncertainty is 3%.) This longitudinal variation must be taken into account if Mars is to be used as a calibration source at millimeter wavelengths. The total range of the 3.5-mm variation is three to four times larger than both the 2.8-cm and 20-μm variations. This unexpected result can possibly be explained by subsurface scattering from rocks ?1.5-cm radius.  相似文献   

Al(III) and Fe(III) binding by humic substances in freshwaters, and implications for trace metal speciation   总被引：2，自引：0，他引：2  

Edward Tipping  Carlos Rey-Castro  Stephen E Bryan  John Hamilton-Taylor 《Geochimica et cosmochimica acta》2002,66(18):3211-3224

Published experimental data for Al(III) and Fe(III) binding by fulvic and humic acids can be explained approximately by the Humic Ion-Binding Model VI. The model is based on conventional equilibrium reactions involving protons, metal aquo ions and their first hydrolysis products, and binding sites ranging from abundant ones of low affinity, to rare ones of high affinity, common to all metals. The model can also account for laboratory competition data involving Al(III), Fe(III) and trace elements, supporting the assumption of common binding sites. Field speciation data (116 examples) for Al in acid-to-neutral waters can be accounted for, assuming that 60-70 % (depending upon competition by iron, and the chosen fulvic acid : humic acid ratio) of the dissolved organic carbon (DOC) is due to humic substances, the rest being considered inert with respect to ion binding. After adjustment of the model parameter characterizing binding affinity within acceptable limits, and with the assumption of equilibrium with a relatively soluble form of Fe(OH)₃, the model can simulate the results of studies of two freshwater samples, in which concentrations of organically complexed Fe were estimated by kinetic analysis.The model was used to examine the pH dependence of Al and Fe binding by dissolved organic matter (DOM) in freshwaters, by simulating the titration with Ca(OH)₂ of an initially acid solution, in equilibrium with solid-phase Al(OH)₃ and Fe(OH)₃. For the conditions considered, Al, which is present at higher free concentrations than Fe(III), competes significantly for the binding of Fe(III), whereas Fe(III) has little effect on Al binding. The principal form of Al simulated to be bound at low pH is Al³⁺, AlOH²⁺ being dominant at pH >6; the principal bound form of Fe(III) is FeOH²⁺ at all pH values in the range 4-9. Simulations suggest that, in freshwaters, both Al and Fe(III) compete significantly with trace metals (Cu, Zn) for binding by natural organic matter over a wide pH range (4-9). The competition effects are especially strong for a high-affinity trace metal such as Cu, present at low total concentrations (∼1 nM). As a result of these competition effects, high-affinity sites in humic matter may be less important for trace metal binding in the field than they are in laboratory systems involving humic matter that has been treated to remove associated metals.  相似文献   

Digital Rectification Techniques for Architectural and Archaeological Presentation     

P. G. Bryan  I. Corner  & D. Stevens 《The Photogrammetric Record》1999,16(93):399-415

Some exciting developments have been made recently, in the field of digital image rectification, which are of interest to both the photogrammetric specialist and non-specialist. This paper outlines the technical processes involved in generating digitally rectified images, as well as raising some of the issues that are becoming apparent when applying this modern technology to archaeological and architectural presentation.  相似文献   

Does hillslope trenching enhance groundwater recharge and baseflow in the Peruvian Andes?          下载免费PDF全文

Lauren D. Somers  Jeffrey M. McKenzie  Samuel C. Zipper  Bryan G. Mark  Pablo Lagos  Michel Baraer 《水文研究》2018,32(3):318-331

As Andean glaciers rapidly retreat due to climate change, the balance of groundwater and glacial meltwater contributions to stream discharge in tropical, proglacial watersheds will change, potentially increasing vulnerability of water resources. The Shullcas River Watershed, near Huancayo, Peru, is fed only partly by the rapidly receding Huaytapallana glaciers (<20% of dry season flow). To potentially increase recharge and therefore increase groundwater derived baseflow, the government and not‐for‐profit organizations have installed trenches along large swaths of hillslope in the Shullcas Watershed. Our study focuses on a nonglacierized subcatchment of the Shullcas River Watershed and has 2 objectives: (a) create a model of the Shullcas groundwater system and assess the controls on stream discharge and (b) investigate the impact of the infiltration trenches on recharge and baseflow. We first collected hydrologic data from the field including a year‐long hydrograph (2015–2016), meteorological data (2011–2016), and infiltration measurements. We use a recharge model to evaluate the impact of trenched hillslopes on infiltration and runoff processes. Finally, we use a 3‐dimensional groundwater model, calibrated to the measured dry season baseflow, to determine the impact of trenching on the catchment. Simulations show that trenched hillslopes receive approximately 3.5% more recharge, relative to precipitation, compared with unaltered hillslopes. The groundwater model indicates that because the groundwater flow system is fast and shallow, incorporating trenched hillslopes (~2% of study subcatchment area) only slightly increases baseflow in the dry season. Furthermore, the location of trenching is an important consideration: Trenching higher in the catchment (further from the river) and in flatter terrain provides more baseflow during the dry season. The results of this study may have important implications for Andean landscape management and water resources.  相似文献