Seaglider: a long-range autonomous underwater vehicle foroceanographic research     

Eriksen  C.C. Osse  T.J. Light  R.D. Wen  T. Lehman  T.W. Sabin  P.L. Ballard  J.W. Chiodi  A.M. 《Oceanic Engineering, IEEE Journal of》2001,26(4):424-436

Seagliders are small, reusable autonomous underwater vehicles designed to glide from the ocean surface to a programmed depth and back while measuring temperature, salinity, depth-averaged current, and other quantities along a sawtooth trajectory through the water. Their low hydrodynamic drag and wide pitch control range allow glide slopes in the range 0.2 to 3. They are designed for missions in a range of several thousand kilometers and durations of many months. Seagliders are commanded remotely and report their measurements in near real time via wireless telemetry. The development and operation of Seagliders and the results of field trials in Puget Sound are reported  相似文献   

Hydrology of the coastal sabkhas of Abu Dhabi, United Arab Emirates   总被引：2，自引：0，他引：2  

Ward E. Sanford  Warren W. Wood 《Hydrogeology Journal》2001,9(4):358-366

Water fluxes were estimated and a water budget developed for the land surface and a surficial 10-m-deep section of the coastal sabkhas that extend from the city of Abu Dhabi, United Arab Emirates, west to the border with Saudi Arabia. The fluxes were estimated on the basis of water levels and hydraulic conductivities measured in wells and evaporation rates measured with a humidity chamber. In contrast with conceptual models proposed in earlier studies, groundwater inflow is estimated to be small, whereas the largest components of the water budget are recharge from rainfall and evaporation from the water table. Estimates within a rectilinear volume of sabkha, defined as 1 m wide by 10 km long by 10 m deep, indicate that about 1 m³/year of water enters and exits by lateral groundwater flow; 40–50 m³/year enters by upward leakage; and 640 m³/year enters by recharge from rainfall. Based on the water and solute fluxes estimated for the upward leakage into the sabkha, 7–8 pore volumes of brine have entered the sabkha from below since the time the sabkha became saturated (7,000 years ago) as a result of the last global sea-level rise.

Ward E. SanfordEmail:

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Hydrochemical tracers in the middle Rio Grande Basin,USA: 1. Conceptualization of groundwater flow   总被引：2，自引：1，他引：1  

L.?Niel?PlummerEmail author  Laura?M.?Bexfield  Scott?K.?Anderholm  Ward?E.?Sanford  Eurybiades?Busenberg 《Hydrogeology Journal》2004,12(4):359-388

Chemical and isotopic data for groundwater from throughout the Middle Rio Grande Basin, central New Mexico, USA, were used to identify and map groundwater flow from 12 sources of water to the basin, evaluate radiocarbon ages, and refine the conceptual model of the Santa Fe Group aquifer system.Hydrochemical zones, representing groundwater flow over thousands to tens of thousands of years, can be traced over large distances through the primarily siliciclastic aquifer system. The locations of the hydrochemical zones mostly reflect the modern predevelopment hydraulic-head distribution, but are inconsistent with a trough in predevelopment water levels in the west-central part of the basin, indicating that this trough is a transient rather than a long-term feature of the aquifer system. Radiocarbon ages adjusted for geochemical reactions, mixing, and evapotranspiration/dilution processes in the aquifer system were nearly identical to the unadjusted radiocarbon ages, and ranged from modern to more than 30 ka. Age gradients from piezometer nests ranged from 0.1 to 2 year cm^–1 and indicate a recharge rate of about 3 cm year^–1 for recharge along the eastern mountain front and infiltration from the Rio Grande near Albuquerque. There has been appreciably less recharge along the eastern mountain front north and south of Albuquerque.

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Resumen Se utilizaron datos químicos e isotópicos de agua subterránea a lo largo de la cuenca central del río Grande, Nuevo México, EEUU, para identificar y mapear el flujo de agua subterránea de 12 fuentes de agua a la cuenca para evaluar edades por medio de radio carbon y para refinar el modelo conceptual del sistema acuífero del Grupo Santa Fé. Se puede establecer zonas hidrotérmicas que representan el flujo de agua subterránea a lo largo de miles a miles de decenas de años en grandes distancias a través del sistema acuífero principalmente siliclástico. Las ubicaciones de las zonas hidroquímicas mayormente reflejan la distribucion de la cabeza hidráulica pre-desarollo moderna pero son inconsistentes con una depresión en los niveles de agua pre-desarollo en la zona central oeste de la cuenca. Esto indica que esta depresión es un rasgo transitorio y no un rasgo de largo plazo del sistema acuífero. Las edades de radio carbon ajustadas para los procesos de reaciones geoquímicas, de mezclado y de evapotranspiración-dilución son casi idénticas a los edades de radio carbon no ajustadas oscilan en un rango desde la modernidad a 30 mil años. Las gradientes de edad de nidos de piezometros van de 0.1 a 2 años cm^–1 e indican un sitio de recarga de aproximadamente 3 cm/yr para la recarga a lo largo del frente montañoso oriental e infiltración del río Grande cerca de Albuquerque. Se aprecia una recarga menor a lo largo del frente oriental de montañas al norte y al sur de Albuquerque.

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Résumé Des données sur les éléments chimiques et les isotopes présents dans leau souterraine prélevée à divers endroits dans le bassin moyen du Rio Grande, au centre du Nouveau-Mexique (É-U), ont permis de déterminer lexistence et létendue de douze sources deau régionales dans le bassin, dévaluer les âges radiocarbones et de raffiner le modèle conceptuel du système aquifère du groupe de Santa Fe. Des zones hydro-chimiques qui représentent lécoulement de leau souterraine depuis des dizaines de milliers dannées peuvent être suivies sur de longues distances à travers laquifère principalement siliclastique. La position des zones hydro-chimiques reflète principalement la distribution moderne des charges hydrauliques mais est incohérente avec une dépression dans le niveau deau dans la partie centre-ouest du bassin, ce qui indique que cette dépression est un élément transitoire du système aquifère plutôt quun élément à long terme. Les âges radiocarbones ajustés aux réactions géochimiques et aux processus de mélange et dévapotranspiration/dilution qui ont lieu dans laquifère sont presque identiques aux âges non ajustés et varient de la période moderne jusquà 30 ka. Les gradients dâge établis à partir des nids de piézomètres sétendent de 0.1 à 2 a cm^–1 et suggèrent un taux de recharge denviron 3 cm a^–1 le long du front des montagnes à lest et pour linfiltration provenant du Rio Grande près dAlbuquerque. Il y a eu substantiellement moins de recharge le long du front des montagnes à lest, au nord et au sud dAlbuquerque.

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Systematics of xenocrystic contamination: preservation of discrete feldspar populations at McCullough Pass Caldera revealed by Ar/Ar dating     

Terry L. Spell  Eugene I. Smith  Aaron Sanford  Kathleen A. Zanetti 《Earth and Planetary Science Letters》2001,190(3-4):153-165

Single crystal ⁴⁰Ar/³⁹Ar dating of K-feldspars from silicic volcanic rocks containing xenocrysts often yields a spectrum of ages slightly older than those of juvenile sanidine phenocrysts. In contrast, feldspars from thin, low-volume units of the Tertiary (14 Ma) McCullough Pass Tuff define discrete age populations at 14 Ma, 15 Ma, and 1.3 Ga, reflecting the time of eruption, xenocrysts from an older ignimbrite exposed in the caldera wall, and Proterozoic basement K-feldspars, respectively. Conductive cooling and diffusion modelling suggests preservation of such discrete populations is likely only when xenocrystic material is incorporated into the magma very near or at the surface, or is engulfed in thin, rapidly cooled pyroclastic flows during emplacement. Incorporation of xenocrysts into the subvolcanic magma chamber, into thick rhyolite domes or lava flows, or into large, welded ignimbrite sheets will result in partial or total resetting of the K/Ar isotopic system. Similarly, petrographic evidence such as exsolution lamellae may be homogenized under these conditions but not in thin ignimbrites. Extremely low diffusion rates for disordering of the Al–Si tetrahedral siting of basement feldspars suggests that they will retain their ordered structural state given rhyolitic magma temperatures. Thus, even when petrographic and K/Ar isotopic evidence for xenocrystic contamination is obscured, it may be preserved in the form of Al–Si ordering.  相似文献   

Correcting for Diffusion in Carbon-14 Dating of Ground Water   总被引：5，自引：0，他引：5  

Ward E. Sanford 《Ground water》1997,35(2):357-361

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Assessment Of A Groundwater Flow Model Of The Bangkok Basin,Thailand, Using Carbon-14-Based Ages And Paleohydrology     

Ward E. Sanford  Somkid Buapeng 《Hydrogeology Journal》1996,4(4):26-40

A study was undertaken to understand the groundwater flow conditions in the Bangkok Basin, Thailand, by comparing ¹⁴C-based and simulated groundwater ages. ¹⁴C measurements were made on about 50 water samples taken from wells throughout the basin. Simulated ages were obtained using 1) backward-pathline tracking based on the well locations, and 2) results from a three-dimensional groundwater flow model. Comparisons of ages at these locations reveal a large difference between ¹⁴C-based ages and ages predicted by the steady-state groundwater flow model. Mainly, ¹⁴C and ¹³C analyses indicate that groundwater in the Bangkok area is about 20,000 years old, whereas steady-state flow and transport simulations imply that groundwater in the Bangkok area is 50,000-100,000 years old. One potential reason for the discrepancy between simulated and ¹⁴C-based ages is the assumption in the model of steady-state flow. Groundwater velocities were probably greater in the region before about 10,000 years ago, during the last glacial maximum, because of the lower position of sea level and the absence of the surficial Bangkok Clay. Paleoflow conditions were estimated and then incorporated into a second set of simulations. The new assumption was that current steady-state flow conditions existed for the last 8,000 years but were preceded by steady-state conditions representative of flow during the last glacial maximum. This "transient" paleohydrologic simulation yielded a mean simulated age that more closely agrees with the mean ¹⁴C-based age, especially if the ¹⁴C-based age corrected for diffusion into clay layers. Although the uncertainties in both the simulated and ¹⁴C-based ages are nontrivial, the magnitude of the improved match in the mean age using a paleohydrologic simulation instead of a steady-state simulation suggests that flow conditions in the basin have changed significantly over the last 10,000-20,000 years. Given that the valid age range of ¹⁴C-dating methods and the timing of the last glacial maximum are of similar magnitude, adjustments for paleohydrologic conditions may be required for many such studies. RÉSUMÉ: Les conditions d'écoulement souterrain dans le bassin de Bangkok (Thaïlande) ont été étudieés en comparant les âges ¹⁴C mesurés et ceux simulés. Les âges mesurés ont été obtenus à partir d'environ 50 échantillons d'eau de puits dans tout le bassin. Les âges simulés proviennent 1) de la position des puits sur les lignes de flux, et 2) des résultats d'un modèle 3-D d'écoulement de nappe. La comparaison des âges aux positions des puits fait apparaître une grande différence entre les âges mesurés et les prédictions du modèle d'écoulement en régime permanent. Dans l'ensemble, les teneurs en ¹⁴C et en ¹³C indiquent que les eaux souterrains du bassin de Bangkok sont âgées d'environ 20 000 ans, alors que les simulations d'écoulement en régime permanent et de transport prédisent un âge compris entre 50 000 et 100 000 ans. Une raison probable du désaccord entre les âges simulés et ceux mesurés est due à l'hypothèse d'écoulement en régime permanent du modèle. Les vitesses d'écoulement souterrain ont probablement été plus fortes dans cette région jusqu'il y a 10 000 ans, lors du dernier maximum glaciaire, du fait de la position plus basse du niveau marin et de l'absence de la couverture par la formation argileuse de Bangkok. Les conditions des paléo-écoulements ont été estimées, puis introduites dans une seconde série de simulations. La nouvelle hypothèse supposait que les conditions actuelles d'écoulement en régime permanent ont existé au cours des 8 000 dernières années, et qu'elles ont été précédées par des conditions d'écoulement en régime permanent représentatives de l'écoulement au cours du dernier maximum glaciaire. La simulation paléohydrologique "transitoire" a donné un âge moyen simulé qui s'accorde mieux avec les âges ¹⁴C mesurés, particulièrement lorsque l'âge ¹⁴C est corrigé pour tenir compte de la diffusion au travers des niveaux argileux. Bien que les incertitudes sur les âges aussi bien simulés que mesurés ne soient pas négligeables, l'ordre de grandeur de l'âge moyen fourni par la simulation s'appuyant sur la paléohydrologie, au lieu de l'écoulement permanent, laisse supposer que les conditions d'écoulement dans le bassin ont nettement changé au cours des 10 000 à 20 000 dernières années. Etant donné que la gamme d'âges ¹⁴C et la durée du dernier maximum glaciaire sont du m{me ordre de grandeur, les ajustement pour les conditions paléohydrologiques peuvent être nécessaires pour nombre d'études de ce type. RESUMEN: Se llevó a cabo un estudio con el objetivo de caracterizar las condiciones del flujo de agua subterránea en la Cuenca de Bangkok, Tailandia, mediante la comparación entre las edades del agua basadas en medidas de ¹⁴C y las simuladas mediante un modelo. Las medidas de ¹⁴C se tomaron en cerca de 50 muestras de agua, en pozos repartidos por toda la cuenca. Las edades simuladas se obtuvieron utilizando 1) seguimiento de partículas a contracorriente, basado en la situación de los pozos, y 2) resultados de un modelo de flujo tridimensional. La comparación entre las edades en estos puntos revelan una gran diferencia entre las basadas en ¹⁴C y las predichas por el modelo de flujo estacionario. Fundamentalmente, los análisis de ¹⁴C y ¹³C indican que la edad del agua subterránea en el área de Bangkok es de alrededor de 20000 años, mientras que las simulaciones de flujo y transporte en condiciones estacionarias revelan una edad de 50000-100000 años. Una posible razón para la discrepancia entre estas dos edades es la hipótesis de flujo estacionario realizada en el modelo. Las velocidades del agua subterránea eran probablemente mayores en esta región anteriormente a los últimos 10000 años, durante el último máximo glaciar, que en la actualidad, debido a que el nivel del mar era menor y a la ausencia de la capa superficial de Arcilla de Bangkok. Por esta razón, se estimaron las condiciones de paleoflujo y se incorporaron a un segundo grupo de simulaciones. La nueva hipótesis era que las condiciones actuales de flujo se habían mantenido estacionarias durante los últimos 8000 años, pero que fueron precedidas por otras condiciones estacionarias representativas del flujo durante el último máximo glaciar. Esta simulación paleohidrológica "transitoria" da lugar a una edad media simulada que se ajusta mejor a la edad basada en ¹⁴C, especialmente si esta última edad se corrige por difusión hacia las capas de arcilla. Aunque las incertidumbres tanto en las edades simuladas con el modelo como en las basadas en ¹⁴C no son sencillas de evaluar, la magnitud de la mejora en el ajuste de la edad media que se produce al utilizar una simulación paleohidrológica en lugar de una estacionaria sugiere que las condiciones de flujo en la cuenca han cambiado significativamente en los últimos 10000-20000 años. Dado que el rango válido de los métodos de datación de ¹⁴C y que el tiempo transcurrido desde el último máximo glaciar son de magnitud similar, los ajustes debidos a condiciones paleohidrológicas serán necesarios para muchos de estudios como éste.  相似文献   

Intense hydrothermal activity at the axis of the east pacific rise near 13°N: Sumbersible witnesses the growth of sulfide chimney     

R. Hekinian  J. Francheteau  V. Renard  R. D. Ballard  P. Choukroune  J. L. Cheminee  F. Albarede  J. F. Minster  J. L. Charlou  J. C. Marty  J. Boulegue 《Marine Geophysical Researches》1983,6(1):1-14

A submersible study of a fast spreading (12 cm yr^-1) Mid-Ocean ridge segment (East Pacific Rise near 12°50′ N) led to the discovery of intense hydrothermal activity. Twenty four sites with active vents and sixty inactive hydrothermal deposits were found within a narrow graben averaging about 300 m in width along a 20 km long segment of the ridge crest. The graben is floored with fresh basaltic sheet flows including collapsed pits or lava lake structures. From both deep towed camera stations and manned submersible observations, it is estimated that the average spacing between the ridge axis hydrothermal deposits averaging in size 10–50 m in diameter lies between 100 to 200 m. The hydrothermal deposits found in the central graben are believed to have formed rapidly (on the order of a few decades). Detailed investigations of one active site have enabled us to witness the growth of an active chimney which increased its height by 40 cm in 5 days i.e. 8 cm per day. Extensive hydrothermal deposits were discovered on an off-axis seamount located 6 km East of the ridge axis. The hydrothermal deposits found on both the ridge axis and on the seamount are similar in composition and consist essentially of zinc, copper and iron mineral phases. Chemical studies conducted on the venting fluids (320°C) showed that the concentration of the dissolved major metal ions (Fe, Mn, and Zn) is about 0.10–0.13 gl^-1. If we accept an average flow rate of 10ls^-1 based on visual observations the mass of metallic products spewing out from an active chimney must be about 100 kg per day.  相似文献   

CMIP5 model simulations of Ethiopian Kiremt-season precipitation: current climate and future changes     

Laifang Li  Wenhong Li  Tristan Ballard  Ge Sun  Marc Jeuland 《Climate Dynamics》2016,46(9-10):2883-2895

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Diversion of heat by Archean cratons: a model for southern Africa     

Sanford Ballard  Henry N. Pollack 《Earth and Planetary Science Letters》1987,85(1-3)

The surface heat flow in the interior of Archean cratons is typically about 40 mW m⁻² while that in Proterozoic and younger terrains surrounding them is generally considerably higher. The eighty-four heat flow observations from southern Africa provide an excellent example of this contrast in surface heat flow, showing a difference of some 25 mW m⁻² between the Archean craton and younger peripheral units. We investigate two possible contributions to this contrast: (1) a shallow mechanism, essentially geochemical, comprising a difference in crustal heat production between the two terrains, and (2) a deeper mechanism, essentially geodynamical, arising from the existence of a lithospheric root beneath the Archean craton which diverts heat away from the craton into the thinner surrounding lithosphere. A finite element numerical model which explores the interplay between these two mechanisms suggests that a range of combinations of differences in crustal heat production and lithospheric thickness can lead to the contrast in surface heat flow observed in southern Africa. Additional constraints derived from seismological observations of cratonic roots, the correlation of surface heat flow and surface heat production, petrological estimates of the mean heat production in continental crust and constraints on upper mantle temperatures help narrow the range of acceptable models. Successful models suggest that a cratonic root beneath southern Africa extends to depths of 200–400 km. A root in this thickness range can divert enough heat to account for 50–100% of the observed contrast in surface heat flow, the remainder being due to a difference in crustal heat production between the craton and the surrounding mobile belts in the range of zero to 0.35 μW m⁻³.  相似文献   

Laboratory spectroscopic studies of atmospherically important radicals using fourier transform spectroscopy     

P. T. Wassell  R. P. Wayne  Ballard  W. B. Johnston 《Journal of Atmospheric Chemistry》1989,8(1):63-85

This paper describes laboratory experiments designed to obtain the infrared spectra of some atmospherically important radical species and related compounds. A Fourier transform spectrometer was used that was capable of yielding resolutions as great as 0.0024 cm^-1, and optical paths of up to 512 m were employed. The objective of the experiments was to obtain the spectra for subsequent application to remote sounding measurements in the atmosphere.Radicals were generated by a variety of chemical reactions involving atoms or other highly reactive precursors. Spectra of the ₃ band of NO₃, at ca. 1500 cm^-1, were obtained with up to 0.005 cm^-1 resolution using the reaction between NO₂ and O₃ to produce the radical. The most satisfactory source of ClO was found to be the reaction between Cl and O₃, and the (1-0) vibration-rotation band in the region 829–880 cm^-1 was recorded at a resolution of 0.02 cm^-1. We were unable to observe infrared absorption of HO₂ with any of the radical sources that we tested. High-resolution survey spectra were obtained of compounds used as reactants, or formed as side-products in the radical-generating processes. These compounds included N₂O₅, HNO₃, ClONO₂, FNO₂, Cl₂O, HO₂NO₂, and probably FO₂.The ability to monitor concentrations of the NO₃ radical in the visible region of the spectrum as well as the concentrations of reactants and other products in the infrared region allowed us to undertake a study of the time-dependent interactions occurring when NO₂ reacts with O₃. The results indicate the importance of heterogeneous processes, especially when traces of water are present, and lend credence to suggestions that heterogeneous mechanisms in the NO₃–N₂O₅–H₂O system might be a viable source of HNO₃ in the atmosphere.  相似文献