Origins of high pH mineral waters from ultramafic rocks, Central Portugal     

Jos M. Marques  Paula M. Carreira  Maria Rosrio Carvalho  Maria J. Matias  Fraser E. Goff  Maria J. Basto  Rui C. Graa  Luís Aires-Barros  Luís Rocha 《Applied Geochemistry》2008,23(12):3278-3289

This paper reviews the geochemical, isotopic (²H, ¹⁸O, ¹³C, ³H and ¹⁴C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO₃ type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ²H and δ¹⁸O suggest a common meteoric origin and that the Mg–HCO₃ type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO₃ to Mg–HCO₃ waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO₂ (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of ¹⁴C and ¹³C values, which is in agreement with the ³H concentrations being below the detection limit.  相似文献   

Genetic identification of hake and megrim eggs in formaldehyde-fixed plankton samples   总被引：4，自引：0，他引：4  

Perez  Juliana; Alvarez  Paula; Martinez  Jose L.; Garcia-Vazquez  Eva 《ICES Journal of Marine Science》2005,62(5):908-914

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The distributions of particulate atmospheric trace metals and mineral aerosols over the Indian Ocean     

R. Chester  A. S. Berry  K. J. T. Murphy 《Marine Chemistry》1991,34(3-4)

Data are presented for the concentrations of Al, Fe, Mn, Ni, Co, Cr, V, Cu, Zn, Pb and Cd in aerosols collected over two contrasting regions of the Indian Ocean. These are: (1) the northern Arabian Sea (AS), from which samples were collected in the northeast monsoon, during which the region receives an input of crustal material from the surrounding arid land masses; and (2) the Tropical Southern Indian Ocean (TSIO), a remote region from which samples were collected from air masses for which there were no large-scale up-wind continental aerosol sources. The TSIO samples can be divided into two populations: Population I aerosols, collected from air masses which have probably impinged on Madagascar, and Population II aerosols, which have been confined to open-ocean regions to the south of the area.The data indicate that there are strong latitudinal variations in the chemical signatures of aerosols over the Indian Ocean. The input of crustal material to the Arabian Sea gives rise to an average Al concentration of about 1000 ng m⁻³ of air in the northeast monsoon regime. As a result, the concentrations of all trace metals are relatively high, and the values of crustal enrichment factors are less than 10 for most metals, in the AS aerosols. In contrast, TSIO Population II ‘open-ocean southern air’ sampled during the southwest monsoon season, has an average Al concentration of only about 10 ng m⁻³ of air. Trace metal concentrations in the TSIO ‘open-ocean southern air’ during the southwest monsoon season are representative of ‘clean’ remote marine air and are generally similar to those reported over the central North Pacific.Mineral dust concentrations over the Indian Ocean decrease in a north to south direction, from about 15–20 μg m⁻³ of air in the extreme north to about 0.01–0.25 μg m⁻³ of air in the far south. The deposition of mineral dust over the northern Arabian Sea can account for approximately 75% of the non-carbonate material incorporated into the underlying sediments.In the Arabian Sea the dissolved atmospheric inputs of all the trace metals, with the exception of Cu and Co, exceed those from fluvial run-off by factors which range from 9.6 for Pb to 1.6 for Cr.  相似文献   

Estimation of Contamination of ERS-2 and POSEIDON Satellite Radar Altimetry Close to the Coasts of Australia   总被引：4，自引：0，他引：4  

X. Deng  W. E. Featherstone  C. Hwang  P. A. M. Berry 《Marine Geodesy》2002,25(4):249-271

It is broadly acknowledged that the precision of satellite-altimeter-measured instantaneous sea surface heights (SSH) is lower in coastal regions than in open oceans, due partly to contamination of the radar return from the coastal sea-surface state and from land topography. This study investigates the behavior of ERS-2 and POSEIDON altimeter waveform data in coastal regions and estimates a boundary around Australia's coasts in which the altimeter range may be poorly estimated by on-satellite tracking software. Over one million 20 Hz ERS-2 (March to April 1999) and POSEIDON (January 1998 to January 1999) radar altimeter waveform data were used over an area extending 350 km offshore Australia. The DS759.2 (5'resolution) ocean depth model and the GSHHS (0.2 km resolution) shoreline model were used together to define the coastal regions. Using the 50% threshold retracking points as the estimates of expected tracking gate, we determined that the sea surface height is contaminated out to maximum distance of between about 8 km and 22 km from the Australian shoreline for ERS-2, depending partly on coastal topography. Using the standard deviation of the mean waveforms as an indication of the general variability of the altimeter returns in the Australian coastal region shows obvious coastal contamination out to about 4 km for both altimeters, and less obvious contamination out to about 8 km for POSEIDON and 10 km for ERS-2. Therefore, ERS-2 and POSEIDON satellite altimeter data should be treated with some caution for distances less than about 22 km from the Australian coast and probably ignored altogether for distances less than 4 km.  相似文献   

Dispersal, Genetic Differentiation and Speciation in Estuarine Organisms   总被引：1，自引：0，他引：1  

D. T. Bilton  J. Paula  J. D. D. Bishop   《Estuarine, Coastal and Shelf Science》2002,55(6):937

For some of their occupants, estuaries represent spatially discrete habitats, isolated from each other by barriers to dispersal or physiological tolerance. We present contrasting strategies for the retention or export of larvae from their estuary of origin, and consider the implications these have on population structure and divergence. Reported patterns of genetic differentiation and inferred gene flow in estuarine taxa (principally animals) are reviewed, and difficulties in the interpretation of existing genetic data discussed. Species concepts and models of speciation relevant to estuaries are outlined, and patterns of speciation of estuarine taxa reviewed. It is concluded that estuarine environments tend to restrict gene flow and impose distinct selective regimes, generating physiologically adapted populations divergent from their marine counterparts, and the potential for in situ speciation in complete or partial isolation. The resulting taxa may represent sibling or cryptic species groups of truly estuarine origin, rather than simply estuarine populations of marine eurytopes.  相似文献   

Potential for irradiation of methane to form complex organic molecules in impact craters: Implications for Mars, Titan and Europa     

John Parnell  Martin Baron  Paula Lindgren 《Journal of Geochemical Exploration》2006,89(1-3):322

The release of methane from crater sites following meteorite impact is a possible consequence of the thermal alteration of organic matter, or tapping of reservoired gas of biogenic or abiogenic origin. At least the latter is feasible on Mars. Methane and higher hydrocarbons are susceptible to polymerization and precipitation by radioactive minerals. Where such minerals are present in impact target rocks, the craters can be a preferred site for carbon concentration, and the formation of complex organic molecules. On icy bodies, such as Titan and Europa, methane released by impact could be a fuel for prebiotic chemistry involving other forms of irradiation.  相似文献   

Erratum to “Petrographic criteria for fluid mobility of graphitic carbon in terrestrial and extraterrestrial samples” [J. Geochemical Exploration 89 (2006) 235–238]     

Paula Lindgren  John Parnell 《Journal of Geochemical Exploration》2006,91(1-3)

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Steady, annual, and monthly recharge implied by deep unconfined aquifer flow     

David W. Ostendorf  Paula L. S. Rees  Shawn P. Kelley  Alan J. Lutenegger 《Journal of Hydrology》2004,290(3-4):259-274

We consider the response of a deep unconfined horizontal aquifer to steady, annual, and monthly recharge. A groundwater divide and a zero head reservoir constrain the aquifer, so that sinusoidal monthly and aperiodic annual recharge fluctuations create transient specific discharge near the reservoir and an unsteady water table elevation inland. One existing and two new long-term data sets from the Plymouth-Carver Aquifer in southeastern Massachusetts calibrate and confirm hydraulic properties in a set of analytical models. [Geohydrology and simulated groundwater flow, 1992] data and a new power law for tritiugenic helium to tritium ratios calibrate the steady recharge that drives the classical parabolic model of steady hydraulics [Applied Hydrogeology, 2001]. Observed water table and gradient fluctuations calibrate the transient recharge models. In the latter regard, monitoring wells within 1 km of Buttermilk Bay exhibit appreciable specific discharge and reduced water table fluctuations. We apply [Trans Am Geophys Union 32(1951)238] periodic model to the monthly hydraulics and a recharge convolution integral [J Hydrol 126(1991)315] to annual flow. An infiltration fraction of 0.79 and a consumptive use coefficient of 1.08×10⁻⁸ m/s °C relate recharge to precipitation and daylight weighted temperature across all three time scales. Errors associated with this recharge relation decrease with increasing time scale.  相似文献   

The impact of hydrological changes on travertine deposits related to thermal springs in the Pamukkale area (SW Turkey)   总被引：2，自引：0，他引：2  

Dilsiz  Cüneyt  Marques  José Manuel  Carreira  Paula Maria Mimo 《Environmental Geology》2004,45(6):808-817

Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity.  相似文献