Heterogeneous distributions of CO2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution          下载免费PDF全文

Jason D. Gulley  Jonathon B. Martin  Paul J. Moore  Amy Brown  Patricia D. Spellman  John Ezell 《地球表面变化过程与地形》2015,40(8):1057-1071

Mixing dissolution, a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals, is commonly considered to form cavernous macroporosity (e.g. flank margin caves and banana holes) in eogenetic karst aquifers. On small islands, macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface, suggesting that dissolution processes are decoupled from surface hydrology. Mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pCO₂ was assumed to be homogeneously distributed within the phreatic zone. Here, we report data from two abandoned well fields in an eogenetic karst aquifer on San Salvador Island, Bahamas, that demonstrate pCO₂ in the phreatic zone is distributed heterogeneously. The pCO₂ varied from less than log ?2.0 to more than log ?1.0 atm over distances of less than 30 m, generating dissolution in the subsurface where water flows from regions of low to high pCO₂ and cementation where water flows from regions of high to low pCO_2. Using simple geochemical models, we show dissolution caused by heterogeneously distributed pCO₂ can dissolve 2.5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater. Dissolution resulting from spatial variability in pCO₂ forms isolated, globular chambers lacking initial entrances to the surface, a morphology that is characteristic of flank margin caves and banana holes, both of which have entrances that form by erosion or collapse after cave formation. Our results indicate that heterogeneous pCO₂, rather than mixing dissolution, may be the dominant mechanism for observed spatial distribution of dissolution, cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Complexities in hindcasting models--when should we say enough is enough     

Maslia ML  Aral MM  Faye RE  Grayman WM  Suárez-Soto RJ  Sautner JB  Anderson BA  Bove FJ  Ruckart PZ  Moore SM 《Ground water》2012,50(1):10-6; discussion 16-8

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Single-crystal elasticity of stishovite: New experimental data obtained using high-frequency resonant ultrasound spectroscopy and a Gingham check structure model     

Akira Yoneda  Titus Cooray  Anton Shatskiy 《Physics of the Earth and Planetary Interiors》2012

Single-crystal elasticity of stishovite was examined using a new experimental technique and an empirical macroscopic model. Employing high-frequency resonant ultrasound spectroscopy, single-crystal elastic constants of stishovite were determined: C₁₁ = 443(3), C₃₃ = 781(4), C₁₂ = 193(2), C₂₃ = 199(2), C₄₄ = 256(2), and C₃₃ = 316(2) GPa. The frequency range of the resonant ultrasound spectroscopy techniques was 6–20 MHz, which is much lower than the ～10 GHz range of the Brillouin scattering technique. Of the elastic constants, the shear elastic constants C₄₄ and C₆₆ are consistent with the average value of the previously mentioned Brillouin scattering. Conversely, the four elastic constants, C₁₁, C₃₃, C₁₂, and C₂₃, slightly deviate outside the range of previous Brillouin scattering results. The present results, except those for C₁₂, are consistent with recent lattice dynamic analysis of inelastic X-ray scattering data. The adiabatic bulk modulus was calculated as 298 GPa, which is smaller and more consistent with the result of compression experiments than any other Brillouin scattering results (301–312 GPa). The present result shows greater P-wave velocity anisotropy (24.7%) than any preceding work. To understand the unique elastic properties of stishovite, the Gingham check model was proposed and examined. The result shows that the octahedron of 6-coordinated Si in stishovite crystal has stiffness comparable to that of diamond.  相似文献   

Assessing catch shares' effects evidence from Federal United States and associated British Columbian fisheries     

Dietmar Grimm  Ivan Barkhorn  David Festa  Kate Bonzon  Judd Boomhower  Valerie Hovland  Jason Blau 《Marine Policy》2012,36(3):644-657

What are the effects of transitioning traditionally managed fisheries to incentive-based catch shares fisheries? In a study of all major United States federal catch share fisheries and associated shared stock fisheries in British Columbia, catch shares result in environmental improvements, economic improvements, and a mixture of changes in social performance, relative to the race for fish under traditional management. Environmentally, compliance with total allowable catch increases and discards decrease. Economically, vessel yields rise, total revenues grow, and long-term stock increases are encouraged. Socially, safety increases, some port areas modestly consolidate, needed processing capacity often reduces, and labor markets shift from part time jobs to full time jobs with similar total employment. Newer catch shares address many social concerns through careful design.  相似文献   

Organic carbon inputs,common ions and degassing: rethinking mixing dissolution in coastal eogenetic carbonate aquifers          下载免费PDF全文

Jason D. Gulley  Jonathan B.Martin  Amy Brown 《地球表面变化过程与地形》2016,41(14):2098-2110

Caves deliver freshwater from coastal carbonate landscapes to estuaries but how these caves form and grow remains poorly understood. Models suggest fresh and salt water mixing drives dissolution in eogenetic limestone, but have rarely been validated through sampling of mixing waters. Here we assess controls on carbonate mineral saturation states using new and legacy geochemical data that were collected in vertical profiles through three cenotes and one borehole in the Yucatan Peninsula. Results suggest saturation states are primarily controlled by carbon fluxes rather than mixing. Undersaturation predicted by mixing models that rely on idealized end members is diminished or eliminated when end members are collected from above and below actual mixing zones. Undersaturation due to mixing is limited by CO₂ degassing from fresh water in karst windows, which results in calcite supersaturation. With respect to saline groundwater, controls on capacity for mixing dissolution were more varied. Oxidation of organic carbon increased pCO₂ of saline groundwater in caves (pCO₂ = 10^–2.06 to 10^–0.96 atm) relative to matrix porosity (10^–2.39 atm) and local seawater (10^–3.12 atm). The impact of increased pCO₂ on saturation state, however, depended on the geochemical composition of the saline water and the magnitude of organic carbon oxidation. Carbonate undersaturation due to mixing was limited where gypsum dissolution (Cenote Angelita) or sulfate reduction (Cenote Calica) increased concentrations of common ions (Ca²⁺ or HCO₃^?, respectively). Maximum undersaturation was found to occur in mixtures including saline water that had ion concentrations and ratios similar to seawater, but with moderately elevated pCO₂ (Cenote Eden). Undersaturation, however, was dominated by the initial undersaturation of the saline end member, mixing was irrelevant. Our results add to a growing body of literature that suggests oxidation of organic carbon, and not mixing dissolution, is the dominant control on cave formation and enlargement in coastal eogenetic karst aquifers. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Caldera collapse at near-ridge seamounts: an experimental investigation     

Jason P. Coumans  John Stix 《Bulletin of Volcanology》2016,78(10):70

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Ethnic and Racial Differences in Tornado Hazard Perception,Preparedness, and Shelter Lead Time in Tuscaloosa     

Jason C. Senkbeil  David A. Scott  Pilar Guinazu-Walker  Meganne S. Rockman 《The Professional geographer》2013,65(4):610-620

The 27 April 2011 EF4 Tuscaloosa tornado directly impacted more than 50,000 residents, causing forty-five fatalities within the city and sixty-five in total. It was a rare urban tornado with varying impacts on the three major ethnic and racial groups within the city. A hybrid survey and interview of open-ended and closed questions was conducted with 211 Tuscaloosa area residents in a two-week period after the tornado. Results indicate significant differences in risk perception, preparedness, and shelter lead time among the three ethnic and racial groups. Furthermore, results were still significant for perception after controlling for the effects of age, education, and experience.  相似文献   

Evaluating the impact of data quantity, distribution and algorithm selection on the accuracy of 3D subsurface models using synthetic grid models of varying complexity     

Kelsey E. MacCormack  Jason J. Brodeur  Carolyn H. Eyles 《Journal of Geographical Systems》2013,15(1):71-88

Testing the accuracy of 3D modelling algorithms used for geological applications is extremely difficult as model results cannot be easily validated. This paper presents a new approach to evaluate the effectiveness of common interpolation algorithms used in 3D subsurface modelling, utilizing four synthetic grids to represent subsurface environments of varying geological complexity. The four grids are modelled with Inverse Distance Weighting and Ordinary Kriging, using data extracted from the synthetic grids in different spatial distribution patterns (regular, random, clustered and sparse), and with different numbers of data points (100, 256, 676 and 1,600). Utilizing synthetic grids for this evaluation allows quantitative statistical assessment of the accuracy of both interpolation algorithms in a variety of sampling conditions. Data distribution proved to be an important factor; as in many geological situations, relatively small numbers of randomly distributed data points can generate more accurate 3D models than larger amounts of clustered data. This study provides insight for optimizing the quantity and distribution of data required to accurately and cost-effectively interpolate subsurface units of varying complexity.  相似文献   

拉萨地块和羌塘地块多个二叠纪基性岩及一个古特提斯海山的初步古地磁结果:对模拟东冈瓦纳晚古生代裂解的暗示     

Diane CHUNG  Jason R. ALI  Jonathan C. AITCHISON 《地球学报》2012,33(S1):8-8

Detachment of the sliver-like Cimmerian terrane from eastern Gondwana in the Early Permian triggered mafic volcanism in many parts of the rift zone. To understand this tectonic episode we have carried out paleomagnetic investigations on mafic volcanic for-mations that were erupted on key terranes that now form part of Tibet. Specifically, we will present data from sections near Lhasa City (central Lhasa block) and Tuotuohe (central Qiangtang Block) as well as near Gyanyima (Paleotethyan sea-mount) that was emplaced onto the floor of Palaeotethys during the Late Permian. Paleomagnetic plots from each location will be used for tectonic calculations. Our new data will be used to evaluate regional scale models con-cerned with how the Cimmerian terranes in southern and SE Asia (from Iran-Tibet-SW China-Myanmar- Thailand-Sumatra) formerly abutted eastern Gond-wana.  相似文献   

Ecological Effects of Shoreline Armoring on Intertidal Habitats of a Puget Sound Urban Estuary     

Sarah A. Morley  Jason D. Toft  Karrie M. Hanson 《Estuaries and Coasts》2012,35(3):774-784

Shoreline armoring is extensive in urban areas worldwide, but the ecological consequences are poorly documented. We mapped shoreline armoring along the Duwamish River estuary (Washington State, USA) and evaluated differences in temperature, invertebrates, and juvenile salmon (Oncorhynchus spp.) diet between armored and unarmored intertidal habitats. Mean substrate temperatures were significantly warmer at armored sites, but water temperature similar to unarmored habitats. Epibenthic invertebrate densities were over tenfold greater on unarmored shorelines and taxa richness double that of armored locations. Taxa richness of neuston invertebrates was also higher at unarmored sites, but abundance similar. We did not detect differences in Chinook (O. tshawytscha) diet, but observed a higher proportion of benthic prey for chum (O. keta) from unarmored sites. Given that over 66% of the Duwamish shoreline is armored—similar to much of south and central Puget Sound—our results underscore the need for further ecological study to address the impacts of estuary armoring.  相似文献