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1.
Thermal springs of the Boundary Creek hydrothermal system in the southwestern part of Yellowstone Park outside the caldera boundary vary in chemical and isotopic composition, and temperature. The diversity may be accounted for by a combination of processes including boiling of a deep thermal water, mixing of the deep thermal water with cool meteoric water and/or with condensed steam or steam-heated meteoric water, and chemical reactions with surrounding rocks. Dissolved-silica, Na+, K+ and Ca2+ contents of the thermal springs could result from a thermal fluid with a temperature of 200 ± 20°C. Chloride-enthalpy and silica-enthalpy mixing models suggest mixing of 230°C, 220 mg/l Cl− thermal water with cool, low-Cl− components. A 350 to 390°C component with Cl− ≥ 300 mg/l is possibly present in thermal springs inside the caldera but is not required to fit observed spring chemical and isotopic compositions. Irreversible mass transfer models in which a low-temperature water reacts with volcanic glass as it percolates downward and warms, can account for observed pH and dissolved-silica, K+, Na+, Ca2+ and Mg2+ concentrations, but produces insufficient Cl− or F− for measured concentrations in the warm springs. The ratio of aNa/aH, and Cl− are best accounted for in mixing models. The water-rock interaction model fits compositions of acid-sulfate waters observed at Summit Lake and of low-Cl− waters involved in mixing.The cold waters collected from southwestern Yellowstone Park have δD values ranging from −118 to −145 per mil and δ18O values of −15.9 to −19.4 per mil. Two samples from nearby Island Park have δD values of −112 and −114 per mil and δ18O values of −15.1 and −15.3 per mil. All samples of thermal water plot significantly to the right of the meteoric water line. The low Cl− and variable δD values of the thermal waters indicate isotopic compositions are derived by extensive dilution with cold meteoric water and by steam separation on ascent to the surface. Many of the hot springs with higher δD values may contain in addition a significant amount of high-D, low-Cl−, acid-sulfate or steam-heated meteoric water. Mixing models, Cl− content and isotopic compositions of thermal springs suggest that 30% or less of a deep thermal component is present. For example, the highest-temperature springs from Three Rivers, Silver Scarf and Upper Boundary Creek thermal areas contain up to 70% cool meteoric water and 30% hot water components, springs at Summit Lake and Middle Boundary Creek spring 57 are acid-sulfate or steam-heated meteoric water; springs 27 and 48 from Middle Boundary Creek and 49 from Mountain Ash contain in excess of 50% acid-sulfate water; and Three Rivers spring 46 and Phillips could result from mixing hot water with 55% cool meteoric water followed by mixing of acid-sulfate water. Extensive dilution by cool meteoric water increases the uncertainties in quantity and nature of the deep meteoric, thermal component. 相似文献
2.
Fluid inclusion leachates obtained from vug and vein quartz samples from an Archean (3.23 Ga) Fe-oxide hydrothermal deposit in the west-central part of the Barberton greenstone belt, South Africa, were analyzed by ion chromatography for chloride, bromide, and iodide. The deposit, known as the ironstone pods, formed by seafloor hydrothermal activity and fluid discharge. Quartz is dominated by type I liquid-vapor, aqueous inclusions with a bimodal salinity distribution (0–0.25 MCl− and 0.9–1.8 MCl−). Bulk analytical salinities range from 0.45 to 0.99 MCl− represent averages of type I inclusions. Bulk fluid inclusion bromide and iodide concentrations are 1.44–3.32 mM and 0.01–0.12 mM, respectively. For comparison, modern seawater has halogen contents of 590 mM chloride, 0.9 mM bromide, and 0.5 μM total iodine. In the fluids from the ironstone pods, bromide and iodide are enriched relative to chloride, when compared with modern seawater.Approximate Br−Cl− and I−Cl− ratios of 3.2 Ga Barberton seawater are 2.5 × 10−3 and 40 × 10−6, respectively. Dispersion to higher values was caused principally by reaction with organic sediments whose trends are similar to those seen for modern vent fluids at unsedimented and sedimented ridges, relative to modern seawater. These halide ratios are greater than those of modern seawater, suggesting a change in the halide ratios of seawater over geological time. The analytical data are consistent with a model in which marine organic sedimentation has fractionated bromine and iodine out of seawater relative to chloride, thereby causing the halide ratios of seawater to decrease from high early and mid-Archean values towards their present day values. 相似文献
3.
The meteoric input of36Cl due to cosmogenic or nuclear-weapon-produced36Cl cannot contribute significantly to the36Cl present in the saline groundwaters (up to 700 mg l−1 Cl−) from the Stripa granite. The extent of in-situ production of36Cl has been estimated on the basis of the neutron fluxes within the granite and its surrounding leptite. The36Cl present in the groundwaters is attributed to either admixture of labelled Cl− from the leptite with Cl− from the granite or to the total derivation of groundwater chlorinity within the leptite followed by radiochemical ingrowth of36Cl during subsequent groundwater residence within the granite. The chloride derived from the leptite may be either matrix chloride or chloride from an external source which has had a long residence time within the leptite. The implications of36Cl in-situ production for the estimation of groundwater residence times and for the geochemical evolution of groundwater chlorinity are discussed. 相似文献
4.
A 23-m.y.-old, fossil meteoric-hydrothermal system in the Lake City caldera (11 × 14 km) has been mapped out by measuring δ 18O values of 300 rock and mineral samples. δ 18O varies systematically throughout the caldera, reaching values as low as −2. Great topographic relief, regional tilting, and variable degrees of erosion within the caldera all combine to give us a very complete section through the hydrothermal system, from the surface down to a depth of more than 2000 m. The initial δ 18O value of the caldera-fill Sunshine Peak Tuff was very uniform (+7.2 ± 0.1), making it easy to determine the exact amount of 18O depletion experienced by each sample during hydrothermal alteration. Also, we have excellent stratigraphic control on depths beneath the mid-Tertiary surface, quantitative information on mineralogical alteration products, and accurate data on the shape of the central resurgent intrusion, which was the principal ‘heat engine’ that drove the hydrothermal circulation. Major conclusions are: (1) Although pristine mid-Tertiary meteoric waters in this area had δ 18O −14, these fluids were 18O-shifted upward to about δ18O = −8 to −5 prior to entering the shallow convective system associated with the resurgent intrusive rocks. Although there was undoubtedly radial inflow toward the caldera from all directions, the highly fractured Eureka Graben, southwest of the caldera, was probably the principal source of recharge groundwater for the Lake City system. (2) Fluid flow within the caldera was dominated by three major categories of permeable zones: the porous megabreccia units (which dip outward from the resurgent dome), vertical fractures and faults related to resurgence, and the caldera ring fault itself. All of these zones exhibit marked 18O depletions, and they are also typically intensely mineralogically altered. (3) The resurgent intrusive stock and its contact metamorphic aureole of hornfels both experienced water/rock ratios lower than the permeable zones; however, they have similarly low δ 18O values because they were altered at higher temperatures. (4) Throughout the caldera, the δ 18O of Sunshine Peak Tuff decreases with increasing depth (about 6 per mil/km), indicative of a shallow thermal gradient, typical of a convective hydrothermal system. The near-surface portion of this gradient was controlled by the temperature drop associated with boiling in the uprising fluid. (5) Deeply circulating meteoric water rose along permeable ring fractures 3 to 5 km beneath the mid-Tertiary surface. These fluids were drawn into the shallow convective system through the lower, porous, megabreccia units. Near the resurgent intrusions, fluid flow was again directed upward where resurgence-related, near-vertical fractures intersect the megabreccia units. 相似文献
5.
The chemical composition and D/H,
and
ratios have been determined for the acid hot waters and volcanic gases discharging from Zaō volcano in Japan. The thermal springs in Zaō volcano issue acid sulfate-chloride type waters (Zaō) and acid sulfate type waters (Kamoshika). Gases emitted at Kamoshika fumaroles are rich in CO2, SO2 and N2, exclusive of H2O. Chloride concentrations and oxygen isotope data indicate that the Zaō thermal waters issue a fluid mixture from an acid thermal reservoir and meteoric waters from shallow aquifers. The waters in the Zaō volcanic system have slight isotopic shifts from the respective local meteoric values. The isotopic evidence indicates that most of the water in the system is meteoric in origin. Sulfates in Zaō acid sulfate-chloride waters with δ34S values of around +15‰, are enriched in 34S compared to Zaō H2S, while the acid sulfate waters at Kamoshika contain supergene light sulfate (δ34S = + 4‰) derived from volcanic sulfur dioxide from the volcanic exhalations. The sulfur species in Zaō acid waters are lighter in δ34S than those of other volcanic areas, reflecting the difference in total pressure. 相似文献
6.
Stable isotope compositions (δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O–δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100 m3 volcanic water/day) and indicate a water residence time of 1–2 decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur. 相似文献
7.
Graziella Caprarelli Makoto Tsutsumi Bruno Turi 《Journal of Volcanology and Geothermal Research》1997,76(1-2)
The Campi Flegrei (Naples, Campanian Plain, southern Italy) geothermal system is hosted by Quaternary volcanic rocks erupted before, during and after the formation of the caldera that represents one of the major structural features in the Neapolitan area. The volcanic products rest on a Mesozoic carbonate basement, cropping out north, east and south of the area. Chemical (major, minor and trace elements) and stable isotope (C, H, O) analyses were conducted on drill-core samples recovered from geothermal wells MF-1, MF-5, SV-1 and SV-3, at depths of ˜ 1100 to 2900 m. The study was complemented by petrographic and SEM examination of thin sections. The water which feeds the system is both marine and meteoric in origin. Mineral zonation typical of a high-temperature geothermal system exists in all the geothermal wells; measured temperatures in wells are as high as ˜ 400 °C. The chemical composition of the waters suggests the existence of two reservoirs: a shallow reservoir (depth < 2000 m) fed by seawater that boiled at 320 °C and became progressively diluted by steam-heated local meteoric water during its ascent; and a deeper reservoir (depth > 2000 m) of hypersaline water. The drill-cores are mainly hydrothermally altered volcanics of trachy-latitic affinity, but some altered pelites and limestones are also present. Published Na, Mg and K concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks, with respect to K-feldspar, albite, sericite and chlorite. The measured δ18O(SMOW) values of rocks range from +4.3 to + 16.5%. The measured δD(SMOW) values range from − 79 to − 46%. The calculated isotopic composition of the fluids at equilibrium with the samples vary from + 1 to + 8.3%. δ18O and from − 52 to + 1%. δD. The estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system. The shallower has a marine water signature, while the deeper water has a signature consistent both with magmatic and meteoric origins. In the latter case, the recharge of this aquifer likely occurs at the outcrop of the Mesozoic Limestones surrounding the Campanian Plain; after infiltration, the water percolates through evaporitic layers, becoming hypersaline and D-depleted. 相似文献
8.
The228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg−1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the228Ra/226Ra activity ratios, (0.12–1.29) × 10−2, are in the range reported for the hydrosphere.The surface waters of the Dead Sea are enriched in228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s−1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes. 相似文献
9.
The D/H and 18O/16O ratios of water in the active crater lake situated on the Kusatsu-Shirane volcano, Japan are about 20 and 6‰, respectively, higher than local meteoric water. The ratios show seasonal variations superimposed on a gradual change over nine years. The isotopic ratios started to increase in early 1990 and decrease in the spring of 1995. The seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air. The large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer. The accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter-time isotopic enrichment. The enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake. Considering the water balance in the lake, the isotopic ratios of the thermal fluid were found to be close to the lake water itself, suggesting the circulation of the lake water seeping through lake floor. Based on the correlation between Cl−concentration and the isotopic ratios, the contribution by the heavy end member was estimated to be 25–36% relative to the enrichment by evaporation. The heavy end member could be a liquid phase evolved from a parental fluid, which is a mixture of local meteoric water and a magmatic fluid as found in high-temperature volcanic gases. 相似文献
10.
T. Sriwana M. J. van Bergen J. C. Varekamp S. Sumarti B. Takano B. J. H. van Os M. J. Leng 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern. 相似文献
11.
William W. Carothers Robert H. Mariner Terry E.C. Keith 《Journal of Volcanology and Geothermal Research》1987,31(1-2)
Isotopic compositions were determined for hydrothermal quartz, calcite, and siderite from core samples of the Newberry 2 drill hole, Oregon. The δ15O values for these minerals decrease with increasing temperatures. The values indicate that these hydrothermal minerals precipitated in isotopic equilibrium with water currently present in the reservoirs. The δ18O values of quartz and calcite from the andesite and basalt flows (700–932 m) have isotopic values which require that the equilibrated water δ18O values increase slightly (− 11.3 to −9.2‰) with increasing measured temperatures (150–265°C). The lithic tuffs and brecciated lava flows (300–700 m) contain widespread siderite. Calculated oxygen isotopic compositions of waters in equilibrium with siderite generally increase with increasing temperatures (76–100°C). The δ18O values of siderite probably result from precipitation in water produced by mixing various amounts of the deep hydrothermal water (− 10.5 ‰) with meteoric water (− 15.5 ‰) recharged within the caldera. The δ13C values of calcite and siderite decrease with increasing temperatures and show that these minerals precipitated in isotopic equilibrium with CO2 of about −8 ‰.The δ18O values of weakly altered (<5% alteration of plagioclase) whole-rock samples decrease with increasing temperatures above 100°C, indicating that exchange between water and rock is kinetically controlled. The water/rock mass ratios decrease with decreasing temperatures. The δ18O values of rocks from the bottom of Newberry 2 show about 40% isotopic exchange with the reservoir water.The calculated δ18O and δD values of bottom hole water determined from the fluid produced during the 20 hour flow test are −10.2 and −109‰, respectively. The δD value of the hydrothermal water indicates recharge from outside the caldera. 相似文献
12.
Gary L. Rowe Jr. Susan L. Brantley Jose F. Fernandez Andrea Borgia 《Journal of Volcanology and Geothermal Research》1995,64(3-4)
Comparison of the chemical characteristics of spring and river water draining the flanks of Poa´s Volcano, Costa Rica indicates that acid chloride sulfate springs of the northwestern flank of the volcano are derived by leakage and mixing of acid brines formed in the summit hydrothermal system with dilute flank groundwater. Acid chloride sulfate waters of the Rio Agrio drainage basin on the northwestern flank are the only waters on Poa´s that are affected by leakage of acid brines from the summit hydrothermal system. Acid sulfate waters found on the northwestern flank are produced by the interaction of surface and shallow groundwater with dry and wet acid deposition of SO2 and H2SO4 aerosols, respectively. The acid deposition is caused by a plume of acid gases that is released by a shallow magma body located beneath the active crater of Poa´s.No evidence for a deep reservoir of neutral pH sodium chloride brine is found at Poa´s. The lack of discharge of sodium chloride waters at Poa´s is attributed to two factors: (1) the presence of a relatively volatile-rich magma body degassing at shallow depths (< 1 km) into a high level summit groundwater system; and (2) the hydrologic structure of the volcano in which high rates of recharge combine with rapid lateral flow of shallow groundwater to prevent deep-seated sodium chloride fluids from ascending to the surface. The shallow depth of the volatile-rich magma results in the degassing of large quantities of SO2 and HCl. These gases are readily hydrolyzed and quickly mix with meteoric water to form a reservoir of acid chloride-sulfate brine in the summit hydrothermal system. High recharge rates and steep hydraulic gradients associated with elevated topographic features of the summit region promote lateral flow of acid brines generated in the summit hydrothermal system. However, the same high recharge rates and steep hydraulic gradients prevent lateral flow of deep-seated fluids, thereby masking the presence of any sodium chloride brines that may exist in deeper parts of the volcanic edifice.Structural, stratigraphic, and topographic features of Poa´s Volcano are critical in restricting flow of acid brines to the northwestern flank of the volcano. A permeable lava-lahar sequence that outcrops in the Rio Agrio drainage basin forms a hydraulic conduit between the crater lake and acid chloride sulfate springs. Spring water residence times are estimated from tritium data and indicate that flow of acid brines from the active crater to the Rio Agrio source springs is relatively rapid (3 to 17 years). Hydraulic conductivity values of the lava-lahar sequence calculated from residence time estimates range from 10−5 to 10−7 m/s. These values are consistent with hydraulic conductivity values determined by aquifer tests of fractured and porous lava/pyroclastic sequences at the base of the northwestern flank of the volcano.Fluxes of dissolved rock-forming elements in Rio Agrio indicate that approximately 4300 and 1650 m3 of rock are removed annually from the northwest flank aquifer and the active crater hydrothermal system, respectively. Over the lifetime of the hydrothermal system (100's to 1000's of years), significant increases in aquifer porosity and permeability should occur, in marked contrast to the reduction in permeability that often accompanies hydrothermal alteration in less acidic systems. Average fluxes of fluoride, chloride and sulfur calculated from discharge and compositional data collected in the Rio Agrio drainage basin over the period 1988–1990 are approximately 2, 38 and 30 metric tons/day. These fluxes should be representative of minimum volatile release rates at Poa´s in the last 10 to 20 years. 相似文献
13.
Noncondensible gases from hot springs, fumaroles, and deep wells within the Valles caldera geothermal system (210–300°C) consist of roughly 98.5 mol% CO2, 0.5 mol% H2S, and 1 mol% other components. 3He/4He ratios indicate a deep magmatic source (R/Ra up to 6) whereas δ13C–CO2 values (−3 to −5‰) do not discriminate between a mantle/magmatic source and a source from subjacent, hydrothermally altered Paleozoic carbonate rocks. Regional gases from sites within a 50-km radius beyond Valles caldera are relatively enriched in CO2 and He, but depleted in H2S compared to Valles gases. Regional gases have R/Ra values ≤1.2 due to more interaction with the crust and/or less contribution from the mantle. Carbon sources for regional CO2 are varied. During 1982–1998, repeat analyses of gases from intracaldera sites at Sulphur Springs showed relatively constant CH4, H2, and H2S contents. The only exception was gas from Footbath Spring (1987–1993), which experienced increases in these three components during drilling and testing of scientific wells VC-2a and VC-2b. Present-day Valles gases contain substantially less N2 than fluid inclusion gases trapped in deep, early-stage, post-caldera vein minerals. This suggests that the long-lived Valles hydrothermal system (ca. 1 Myr) has depleted subsurface Paleozoic sedimentary rocks of nitrogen. When compared with gases from many other geothermal systems, Valles caldera gases are relatively enriched in He but depleted in CH4, N2 and Ar. In this respect, Valles gases resemble end-member hydrothermal and magmatic gases discharged at hot spots (Galapagos, Kilauea, and Yellowstone). 相似文献
14.
Roger B. Hanson Lawrence R. Pomeroy Jack O. Blanton B.A. Biddanda S. Wainwright S.S. Bishop J.A. Yoder L.P. Atkinson 《Continental Shelf Research》1988,8(12)
Bacterioplankton productivity, numbers, and cell specific activity were studied in nearshore waters of the southeastern U.S. continental shelf during seasons of maximum freshwater discharge. In April 1984, coastal waters were stratified from normal spring discharge and typical northeastward wind stress. In April 1985, shelf waters were vertically homogeneous due to below normal runoff and southwestward wind stress. In 1984, nearshore bacterial productivity ranged from 7.0 to 14.7 × 106 cells l−1 h−1 and midshelf rates were 40–50% less. In 1985, nearshore productivity ranged from 0.9 to 2.4 × 106 cells 1−1 h−1, and productivity was extremely patchy over the entire shelf. The cell-specific activity (thymidine incorporation per cell) suggests that although productivity was high in 1984, only a fraction of the bacterioplankton was actively growing or incorporating thymidine (0.9–2.9 × 10−21 mol cell−1 h−1). In 1985, a higher percentage of cells appeared to be active and incorporating thymidine (5–13 × 10−21mol cell−1h−1) even though productivity was low. Hydrographic conditions along the southeastern coastline may have had a significant impact on the overall community structure and carbon flow through the microbial food web. When coastal waters were stratified in 1984, bacterial biomass was a significant percentage (35–320%) of the phytoplankton biomass. During vertically homogeneous conditions of 1985, bacterial production and biomass were a small percentage (2–13%) of the phytoplankton production and biomass across the shelf. The interannual variation in the microbial food web was attributed to the interannual variability of the southeastern U.S. hydrology due to changes in freshwater discharge and wind direction and intensity. The ecological implications of these results extend to the potential impact of seasonal microbial food webs on nearshore allochothonous and autochothonous organics before removal from the southeastern U.S. coastline. 相似文献
15.
A. Matthews C. Fouillac R. Hill R.K. O'Nions E.R. Oxburgh 《Earth and Planetary Science Letters》1987,85(1-3)
CO2-rich gases and groundwaters from springs and boreholes originating within the basement of the Massif Central have variable3He/4He ratios with correspondingR/Ra values ranging from 0.8 to 5.5 and 0.3 to 2.8 respectively, indicating the presence of a significant component of mantle helium. Molar concentrations of rare gases in the CO2-rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near-surface Henry's Law fractionation has occurred between exsolving CO2 and water.δ13C values of the CO2-rich gases are in the range −4.2 to −6.1‰, i.e. in that range normally attributed to mantle carbon, but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources.C/3He ratios show 4 orders of magnitude variation from 1.4 × 1012 to 5 × 108 and, compared to a mantleC/3He ratio of 109, indicate that either a complex fractionation has occurred between mantle helium and mantle CO2 or more likely that mantle rare gases have been diluted by large quantities of CO2 with an average crustal carbon isotope composition. The regional distribution of3He and C does not show any obvious relationship to age or proximity of volcanic centres or major faults, suggesting that mantle-derived C and He components decoupled from their silicate melt sources at some depth.The results from this area of active fluid circulation suggest that C-isotope data derived from metamorphic terrains should be interpreted with great caution, but that input of some mantle-derived carbon is expected to accompany crustal extension. 相似文献
16.
Gas concentrations and isotopic compositions of water have been measured in hydrothermal waters from 13°N on the East Pacific Rise. In the most Mg-depleted samples ( 5 × 10−3 moles/kg) the gas concentrations are: 3–4.5 × 10−5 cm3 STP/kg helium, 0.62–1.24 cm3 STP/kg CH4, 10.80–16.71 × 10−3 moles/kg CO2. The samples contain large quantities (95–126 cm3/kg) of H2 and some carbon monoxide (0.26–0.36 cm3/kg) which result from reaction with the titanium sampling bottles. δ13C in methane and CO2 (−16.6 to −19.5 and −4.1 to −5.5 respectively) indicate temperatures between 475 and 550°C, whereas δ13CCO is compatible with formation by reduction of CO2 on Ti at 350°C close to the sampling temperature.3He/4He are very homogeneous at (7.5 ± 0.1)RA(3He/4He = 1.0 × 10−5) and very similar to already published data as well as CH4/3He ratios between 1.4 and 2.1 × 106.18O and D in water show enrichments from 0.39 to 0.69‰ and from 0.62 to 1.49‰ respectively. These values correspond to W/R ratios of 0.4–7. The distinct18O enrichments indicate that the isotopic composition of the oceans is not completely buffered by the hydrothermal circulations. The3He-enthalpy relationship is discussed in terms of both hydrothermal heat flux and3He mantle flux. 相似文献
17.
Water samples were collected from Baffin Bay and surrounding areas in order to evaluate this region as a potential source of Nd from old continental material to Atlantic water. The isotopic data ranged from εNd(0) = −9.0 to −26 with most of the data around εNd(0) = −20 compared with values of North Atlantic Deep Water (NADW) with εNd(0) = −13.5. The concentration of Nd in Baffin Bay waters was as high as 6 × 10−12 g/g compared with 2.5 × 10−12 g/g for NADW. The combination of low εNd and high Nd concentration indicates that Baffin Bay may be a significant source of Nd from very old crustal material. A simple box model was used to evaluate the contribution to the Nd budget of NADW and it was concluded that a substantial fraction of the Nd from ancient crustal sources that is required to maintain the isotopic composition of NADW could be supplied by Baffin Bay outflow. 相似文献
18.
C. Panichi L. Bolognesi M.R. Ghiara P. Noto D. Stanzione 《Journal of Volcanology and Geothermal Research》1992,49(3-4)
The Ischia geothermal system is hosted by silicic rocks of the Quaternary Potassic Roman Province, in southern Italy. Exploration drilling down to 1156 m depth in the mid-1950s provided information on boiling profiles (up to 250°C) and on the depth and permeability of the potential reservoirs. Discharge fluid samples were collected and analyzed to define the inflow of surrounding seawater (C1 ranges from 2.5 to 20 g/kg) into the system.Analyses of samples from surface manifestations and shallow wells collected during 1983 and 1988 point to the existence of three distinct mixing regimes, involving three water components. A dishomogeneous body of diluted water (Cl less than 2.5 g/kg), that occurs at depths > 700 m and reequilibrates at 240°C at least, is overlain by an aquifer of groundwater variably mixed with variably seawater (Cl from 4 to 10 g/kg), which tends to reequilibrate at 160°C. Steam-heated waters locally develop and act as dilutants of the rising geothermal fluids.Dilution, mixing, and evaporation of the ascending chloride fluids are supported by oxygen and hydrogen isotopic data the thermal waters being enriched in 18O and D with respect to local meteoric water by up to 7 and 30‰, respectively. The relative composition of the major cations in thermal solutions was used to discriminate the two main groups of thermal waters, the reservoir temperatures of which are estimated from the Na/K-gethermometer. K-Mg geothermometer indicates reequilibration in near-surface conditions.The isotopic composition of the fumarolic steam varies from −7 to −12‰ in ∂8O and from − 35 to − 70‰ in ∂D, in agreement with a deep mixed fluid that boils adiabatically from 240 to 80°C. The deuterium content of the H2O-H2 pair gives enrichment factor of about 830‰, corresponding to equilibrium temperature conditions slightly higher than the surface boiling temperatures. The ∂13C of CO2is almost constant at −4.5‰ (1δ=0.4), suggesting an important magmatic contribution, and the ∂18O values of CO2appears to in equilibrium with accompanying steam at the measured temperatures.The CO2/Ar and H2/Ar chemical ratios have been used to derive aquifer temperatures, the values obtained being consistent with those of solute geothermometers. 相似文献
19.
Results are presented on scubadiving investigations carried out on thermal manifestations in the area of Panarea (Aeolian Islands). The area investigated falls inside a caldera which extends from the main island to the group of islets located to the northeast. The distribution of the gaseous manifestations is regulated by the NE-SW, NW-SE and N-S regional tectonic directrices, through which the more recent basic magma intruded, giving rise to dikes and pillow lavas. fO2-temperature relation of the gases sampled in the investigated area was calculated to be: logfO2 = 11−24,593/T which indicates that a buffering mechanism acted on the gases as they cooled down during their ascent. The high 3He/4He ratio (6 × 10−6) and the δ13C = −3.2%. (PDB), suggest the presence of a magmatic component in the gas feeding the investigated manifestations. The above relations and the almost constant high He/N2 ratio suggest that all the fumaroles are fed by the same deep hot fluids. On the basis of both the chemical characters of the fluids and the geothermo-barometric data, a deep geothermal body, having a temperature of about 240°C, is recognized. Two other shallower thermal aquifers, with a temperature of 170–210°C, are identified. A circulation pattern of the geothermal fluids is also proposed. On the basis of calculations regarding the convective energy released by the geothermal system of Panarea, and the magmatic mass responsible for the positive gravimetric anomaly of the area, it was estimated that the last volcanic activity took place less then 10,000 years ago. 相似文献
20.
M. A. Armienta S. De la Cruz-Reyna O. Morton O. Cruz N. Ceniceros 《Journal of Volcanology and Geothermal Research》2002,113(1-2)
Leachates from ash samples of the Popocatépetl eruptions of April 30, 1996, May 12, 1997, and October 17, 1998 settled at different distances from the crater were analyzed for anions (SO42−, Cl−, F−) and some metals. This study is aimed at determining the causes of the compositional variations of the leachates, to assist the assessment of water, soil and crop contamination due to ash deposits. Different behavior was observed in the ion concentrations with distance for the three eruptions. On April 30, 1996, SO42− and F− concentrations increased with distance, and Cl− remained almost constant. On May 12, 1997, concentrations of the three anions decreased with distance. On October 17, 1998, F−, Cl− and SO42− increased more than three-fold with distance. Tephra size distributions were also different for the three eruptions. The observed trends of the leachates’ anion concentrations may have different causes: the type and intensity of the eruptions, the distribution of the tephra sizes, the degree of interaction of the tephras with volcanic gases, humidity, static charge, the original characteristics of the solid material, the transport time from the crater to the site of settling, and the relative angle between the wind direction and the sampling line. Enrichment factors and concentration trends for metals with distance suggest that Co, Ni, Cu and Pb in the leachates resulted mostly from volcanic gas adsorption. 相似文献