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1.
Following Roether et al. [1] an upwelling model has been tested to explain the distribution of bomb-produced tritium at the GEOSECS I test station off Baja, California. We have extended their treatment to include the time histories for tritium and for bomb radiocarbon now available for this station. If the CO2 gas exchange rate at this station is similar to the ocean average value of 20 moles/m2 yr, then the upwelling rate must be quite small (<3 m/yr). However, a satisfactory match to the time histories of14C and of3H is achieved only if an upwelling rate of 40 m/yr is used. In this case, however, a CO2 exchange rate of 70 moles/m2 yr would be required to match the observed surface water14C/C ratios and a tritium input 4 times the expected value would be needed. The inconsistency in the bomb14C time history obtained using the accepted CO2 exchange rate is likely the result of horizontal effects which void the validity of one dimensional modeling in this region of the ocean.  相似文献   

2.
A14C balance for the Eastern Caribbean deep water indicates the average inflow of Atlantic water into the basin to be 2.3 × 105 m3/sec (±30%), or about 2–4 times the values estimated previously. The balance uses a model representation of the deep-water turnover, and is based on14C concentrations at a station in the Venezuelan Basin which average Δ14C= 89‰ below 800 m depth with a total range of only 9‰, as well as on a14C concentration of the Atlantic inflow of Δ14C= ?71%. as obtained from measurements outside the Antilles Arch. The turnover time of the basin water below 2500 m depth is 55 years, which corresponds to an average upwelling velocity at this depth of about 35 m/year. With such upwelling, the temperature profile below 1800 m (the depth of the sill determining the inflow of new water) requires a vertical eddy diffusivity of about 5 cm2/sec. The oxygen consumption, and silica and CO2 regeneration, rates below 2500 m depth are obtained as ?0.18, + 0.08, and + 0.2 μmole kg?1 yr?1, respectively. The CO2 regeneration has but a negligible effect on the14C balance.  相似文献   

3.
Radiocarbon data for 11 stations and tritium data for 16 stations in the North Atlantic Ocean from 74°N to 3°N are presented. For radiocarbon, normal errors inΔ14C are± 4‰, and in tritium,± 0.09TU or± 3%, whichever is larger. There is a remarkable, but not simply linear, correlation between oceanic bomb transients in14C and3H. The deep convective mixing in the Greenland Sea is reflected in substantial bomb tracer penetration to all depths, with residence time for the deep, cold core water that seems to be 20 to 30 years. The outflow in the bottom layer southward over the sills of the Denmark Strait and Faroe Passage carries significant tritium concentration, at least to 40°N. Complicated, but coherent, profile structures in the subtropical Atlantic suggest effects of large-scale lateral advection. In particular, a pronounced minimum in both14C and3H might be associated with the Antarctic intermediate water.  相似文献   

4.
A neutron-irradiated bulk sample of the Murray (C-2) carbonaceous chondrite was etched with H2O2 and then divided into colloidal and non-colloidal fractions. The H2O2 treatment removed ～80% of the trapped Xe and greatly increased variations in the129Xe/132Xe ratio measured in stepwise heating. The colloid showed very little excess129Xe, but the anti-colloid gave a fairly good I-Xe correlation corresponding to formation 3.7 ± 2.1 m.y. after Bjurböle.Variations in the trapped Xe component were also observed; most notably the 550°C anti-colloid fraction has large deficiencies relative to AVCC at the heavy isotopes. A tentative decomposition suggests U-Xe, a “primitive” trapped component, as the dominant component with minor contributions from H-Xe, L-Xe, and S-Xe (s-process nucleosynthesis). The identification of U-Xe rests primarily on the agreement of themeasured134Xe/136Xe ratio with U-Xe. This observation lends support to proposals for such a “primitive” trapped Xe component and demonstrates that at least some carbonaceous chondrite phases sampled a xenon reservoir nearly devoid of H-Xe.  相似文献   

5.
We present the main seismological results of our study of the Campania-Lucania earthquake of 23 November 1980. A complete set of far field and local data has been analysed. From long-period body waves data we determine the fault plane solution (φ1 = 140°,δ1 = 60°,φ2 = 75°,δ2 = 54°), a depth of 15 km and calculate a seismic moment of 6 × 1025 dyne cm and a source duration of 6 s. From data of a local network deployed immediately after the event we determine aftershock locations: they are aligned in a direction NW-SE that fit extremely well with the focal solution determined above. We can choose as fault plane the plane striking 140° and dipping at 60° and the event is a normal event with a large component of left-lateral strike slip. The source area evaluated from this aftershock distribution 14 km × 40 km is quite suitable for an earthquake of a seismic moment of 6 × 1025 dyne cm.  相似文献   

6.
Using batch method, the adsorption of thallium(I) ions from aqueous solutions on eucalyptus leaves powder, as a low cost adsorbent, was studied. The effect of various modification of considered adsorbent on the adsorption percentage of Tl(I) is an important feature of this study. The results showed that the unmodified and acidic modified adsorbent are the poor adsorbents for the Tl(I) ions while basic modified adsorbent is a suitable adsorbent. Also, the effect of some experimental conditions such as solution initial pH, agitation speed, contact time, sorbent dosage, temperature, particle size, and thallium initial concentration was studied. The results showed that the adsorption percentage depends on the conditions and the process is strongly pH‐dependent. The satisfactory adsorption percentage of Tl(I) ions, 81.5%, obtained at 25 ± 1°C. The equilibrium data agreed fairly better with Langmuir isotherm than Freundlich and Temkin models. The value of qm that was obtained by extrapolation method is 80.65 mg g?1. Separation factor values, RL, showed that eucalyptus leaves powder is favorable for the sorption of Tl(I). The negative values of ΔH0 and ΔS0 showed that the Tl(I) sorption is an exothermic process and along with decrease of randomness at the solid–solution interface during sorption, respectively.  相似文献   

7.
Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr?1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from ?1.1°C in 1980 to ?0.6°C in 2006 at an average rate of 0.018°C yr?1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×104 to 2.2×104 km2 at an average rate of 74 km2 yr?1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.  相似文献   

8.
A seafloor electrical conductivity profile resulting from a more thorough analysis of magnetotelluric data from station S.F. Revisited than previously presented is compared to an earlier profile at Farewell to Aggy, station III. Both stations are located over the same interfracture zone segment of the Pacific plate, the first roughly 700 km off the coast of California (position 31°18′N, 128°20′W, water depth 4.5 km, plate age 30 m.y. estimated from nearby magnetic reversal number 12), the second approximately 800 km to the NNE of the mainland of Hawaii (position 26°32′N, 151°20′W, depth 5.3 km, age 72 m.y. estimated from adjacent magnetic reversal 30–31).The seafloor impedances at S.F. Revisited are only mildly polarized and their interpretation in terms of an isotropic, horizontally layered structure suggests the occurrence at about 85 km depth of a highly conducting layer with a conductance exceeding by roughly 4 × 103 S, an otherwise monotonically increasing conductivity trend. The implied dependence of conductivity with depth is therefore similar to that found earlier for station III, however with the following differences: the high-conductivity layer at station III occurs at a greater depth (140 km), it appears to have a slightly reduced excess conductance over the background, 3.5 × 103 S although this evidence should be used with caution, and the lithospheric conductivity at station III, surprisingly seems to be somewhat higher, an effect possibly related to the proximity of the Hawaiian chain and to its generic processes.  相似文献   

9.
We evaluated changes in siliceous export production and the source of organic matter preserved in sediment core MD07-3109H recovered from the Gulf of Ancud, Chiloé Inner Sea (42°S, 72°W, water column depth: 328 m), southern Chile. We analyzed the abundance of siliceous microfossils (diatoms, silicoflagellates, sponge spicules, Chrysophyte cysts, phytoliths), geochemical proxies (weight percent silicon %SiOPAL, organic carbon, total nitrogen, C/N molar), and sediment stable isotopes (δ13Corg, δ15N). Chronology based on 210Pb and 14C provided an accumulated age of 144 years at the base of the core.Sediments of core MD07-3109H are predominantly marine in origin, averaging δ13Corg=–20.75‰±0.82, δ15N=8.7±0.35‰, and C/N=8.76±0.36. Marine diatoms compose 94% of the total assemblage of siliceous microfossils. Our record of productivity based on the mass accumulation rates of organic carbon, total nitrogen, SiOPAL, and total diatoms showed high values between 1863 and 1869 AD followed by a declining trend until 1921 AD, a transition period from 1921 to 1959 AD with fluctuating values, and a clear decreasing pattern from 1960 AD to the present. This marked reduction in productivity was associated with decreased precipitation and Puelo River streamflow (41°S), as well as a warmer and more stratified water column, especially since the 1980s.  相似文献   

10.
Tritium is measured as a function of depth in a Surveyor 3 sample. The upper limit for solar-wind-implanted tritium gives a3H/1H limit for the solar wind of 1 × 10?11. The temperature release patterns of14C from lunar soils are measured. The14C release patterns from surface soils differ from a trench bottom soil and gives evidence for the presence of14C in the solar wind with a14C/1H ratio of approximately 4 × 10?11. The implications of these radio nuclide abundances in the solar wind are discussed.  相似文献   

11.
Long-period records of multiple Love waves from the 1957 earthquake in Mongolia (MS = 8.0) at Pasadena are analysed and compared to synthetic seismograms, generated by the method of Kanamori. A fit in the time domain shows that the records are not consistent with the previous solution, achieved through a frequency-domain analysis of directivity by Ben-Menahem and Toksöz. The solution asks for a shorter rupture of 270 km at a velocity of 3.5 km/s. The focal parameters are constrained by updating all the reported first motion and are found to be: strike = 103°, dip = 53°, slip = 32°. A seismic moment of 1.8 · 1028 dyn · cm is obtained. These figures are also consistent with a time-domain analysis of Love waves at Palisades and Strasbourg, and of Rayleigh waves at Pasadena, with a directivity study of Love waves at Pasadena, and with static deformation and isoseismal data. A discussion is given of the relation between moment, magnitude and rupture area, and a comparison is made with other events in the same region: it is concluded that this earthquake does not exhibit an “intra-plate” behavior, but rather compares better with “inter-plate” events, such as the great Assam earthquake.  相似文献   

12.
The palaeomagnetism of Middle Triassic (224 ± 5 m.y.) igneous rocks from the Ischigualasto-Ischichuca Basin (67°40′W, 30°20′S) was investigated through 86 oriented hand samples from 11 sites. At least one reversal of the geomagnetic field has been found in these rocks. Nine sites yield a palaeomagnetic pole at 239°E, 79°S (α95 = 15°, k = 13).The K-Ar age determinations of five igneous units of the Puesto Viejo Formation give a mean age of 232 ± 4 m.y. (Early Triassic). The palaeomagnetism of six igneous units of the Puesto Viejo Formation (68°W, 35°S) was investigated through 60 oriented samples. These units, two reversed relative to the present magnetic field of the Earth and four normal, yield a pole at 236°E, 76°S (α95 = 18°, k = 14).Data from the Puesto Viejo Formation indicate, for the first time on the basis of palaeomagnetic and radiometric data, that the Illawarra Zone, which defines the end of the Kiaman Magnetic Interval, extends at least down to 232 ± 4 m.y. within the Early Triassic. The palaeomagnetic poles for the igneous rocks of the Ischigualasto-Ischichuca Basin and Puesto Viejo Formation form an “age group” with the South American Triassic palaeomagnetic poles (mean pole position: 239°E, 77°S; α95 = 6.6°, k = 190). The Middle and Upper Permian, Triassic and Middle Jurassic palaeomagnetic poles for South America would define a “time group” reflecting a quasi-static interval (mean pole position: 232°E, 81°S; α95 = 4°, k = 131).  相似文献   

13.
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14.
A recently developed approach to carbon isotope methodology (process recognition via isotope diagrams) is applied in a multidisciplinary study of precipitation‐recharged aquifers of the lowlands–plains area of the Manawatu (south‐west North Island). Urban and rural areas rely on groundwater from the upper levels of a deep basin sequence comprising marine and terrestrial sediments of Pleistocene age. Hydrochemical and isotopic (18O, 3H, 13C and 14C) data are merged with known details of geology and hydrogeology to reveal two separate confined aquifers within the depth range to 200 m. The shallower of these, below unconfined, locally recharged groundwater, is recharged on the foothills of the Ruahine Range to the north‐east of the study area; flow direction is NE–SW. The deeper confined aquifer is recharged on the Tararua Range to the immediate east; flow direction essentially is transverse (SE–NW) to that in the shallower aquifer. Two processes are identified as dominant contributors to concentration and isotopic composition of dissolved inorganic carbon (DIC), namely addition of CO2 from decay of organic materials and carbonate dissolution. Limitations of carbon isotope methods in determining residence times are illustrated by the data. Although the confined groundwater is essentially tritium‐free, only a few samples showed conclusive evidence of significant ageing on the time‐scale of 14C. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

15.
Interstitial waters were extracted from cores at three locations in the eastern equatorial Pacific and analyzed for nutrients, dissolved carbonate species, Mn and Fe. From the depth variation in pore water chemistry, we infer that organic matter oxidation reactions occur with depth in the following sequence: O2 reduction, NO3? and MnO2 reduction, and then ferric iron reduction. From NO3? results we infer that O2 is largely or totally consumed within the top few centimeters of sediment. NO3? is completely reduced at a sediment depth of 20 cm at a site near the crest of the East Pacific Rise, but is preserved at levels of 20–30 μmol/kg at 40 cm depth at a Guatemala Basin site.We have calculated the alkalinity for pore water samples assuming ions diffuse according to relative ionic diffusion coefficients, that the stoichiometry of organic matter oxidation reactions is that of “Redfield” organic matter, and that the pore waters are saturated throughout with respect to CaCO3. The measured alkalinity increase is only about half of the predicted value. The difference is probably a result of either enhanced mixing of the pore water in the top few centimeters of sediments by biological or physical processes, or the occurrence of an inorganic reaction which consumes alkalinity.At depths of oxygen and nitrate reduction in the sediments, the ion concentration product of CaCO3 is the same, within the analytical error, as the solubility product of Ingle et al. [34] at 1 atm and 4°C. This result indicates CaCO3 resaturation on pressure change during coring. Where pore water Mn concentrations become measurable, the ion concentration product increases, indicating either supersaturation with respect to calcite or that another phase is controlling the carbonate solubility.  相似文献   

16.
Ten samples were recovered by the submersible “Cyana” submersible from two groups of hydrothermal vents located 2600 m deep along the East Pacific Rise at 13°N. The maximum measured temperature was 317°C and minimum pH 3.8. A systematic determination of major and trace elements has been carried out and mixing lines between a high-temperature component (HTC) and seawater are observed. The water chemistry of the HTC slightly differs for several elements at the two sites. This HTC is deprived of SO4 and Mg and is greatly enriched in most other species. Maximum concentrations are (in units per kg):Cl = 0.72mol; Br = 1.1mmol; Na = 0.55mol; K = 29mmol; Rb = 14 μmol; Ca = 52mmol; Sr = 170 μmol; Mn = 750 μmol; Fe = 1mmol; Al = 15 μmol; Si = 21mmol. For many elements, the magnitude of the anomaly relative to seawater does not compare with the results obtained from the Galapagos or East Pacific Rise 21°N. The enrichment of cations relative to seawater is likely related to the huge Cl excess through charge balance. TheBr/Cl ratio is close to that for seawater. However, it is not clear whether the Cl excess is due to gas release or basalt hydration (formation of amphibole chlorite or epidote).P-T dependence of SiO2 solubility suggests that water-rock interaction last occurred at a depth in excess of 1 km below the sea floor. A mixing line of87Sr/86Sr vs. Mg/Sr demonstrates that the HTCs have a nearly identical87Sr/86Sr ratio of 0.7041 for both sites. A water/rock ratio of about 5 is inferred, which differs from the 1.5 value obtained at 21°N.  相似文献   

17.
 The Mururoa and Fangataufa atoll basement consists of superimposed submarine and subaerial lava flows which have been intruded by late volcanics. The intrusions have developed large hydrothermal alteration haloes throughout the basaltic wall rock. The cuttings of the Natice-1 and Mitre-1 holes, drilled into the submarine volcanic pile at Fangataufa atoll, show a vertical zonation of clay minerals ranging from 270 to 850 m depth. The newly formed clay minerals occurring from top to bottom of the altered pile are: dioctahedral aluminous smectites, saponite, an intimate assemblage of saponite with two random chlorite/saponite mixed layers and an intimate assemblage of one random chlorite/saponite mixed-layer with one ordered chlorite/saponite mixed layer and one chlorite below 816 m depth. These clay mineral assemblages indicate a general increase in the chloritic component with depth. They are associated throughout the pile with secondary carbonates and quartz. The ∂18O and ∂13C of calcite and ∂18O of clay minerals, on the one hand, and the intimate mixtures of trioctahedral species, on the other, suggest a general cooling with the evolution of a paleogeothermal gradient from approximately 300  °C/km during the crystallization of chlorite to 150  °C/km for the late calcite precipitation. Received: 2 October 1995 / Accepted: 14 January 1997  相似文献   

18.
We have developed a closed-system combustion technique and utilized it to progressively oxidize a gas-rich, highly carbonaceous acid residue and a fine-grained (<4 μm) matrix sample from the Allende C3V meteorite and analyze the released gases mass spectrometrically. For the residue complete gas mobilization occurs at temperatures below 600°C. The temperature interval over which most of the gases are released coincides with that for combustion of most of the carbon. Release is primarily due to chemical attack rather than thermal activation of the gases. There are somewhat different oxidation thresholds for the heavy gases (Ar, Kr, and Xe) and the light gases (He, Ne), indicating chemically different sites for the two groups. Relative enhancement of isotopically anomalous components near 600°C is as large as in any open-system oxidation method. Differential combustion of the matrix sample reveals three distinct outgassing peaks, the first matching the release from the carbonaceous residue (“combustibles”), the second attributed to sulfides, and the third tentatively assigned to silicates. They comprise about 53%, 7% and 40% of the total heavy gases respectively. While the “sulfides” exhibit a small fission-like component, the Xe in the “silicates” appears isotopically uniform with roughly AVCC composition. The “combustibles” of the matrix contain relatively less excess129Xe than the residue, perhaps indicating that ～10% of the total129Xe in the residue was acquired from “silicates” by redistribution during acid treatment. We cannot rule out the possibility that planetary gases assigned to “sulfides” or “silicates” actually reside in carbonaceous phases somehow sheltered within soluble mineral assemblages, or in acid-soluble carbonaceous phases resistant to oxidation. Integrated releases below and above 600°C during the matrix combustion exhibit virtually identical heavy gas elemental composition, implying similar fractionation during planetary gas entrapment in various materials or in the same material in various environments.  相似文献   

19.
The sulphur isotope composition of 16 pyrite and chalcopyrite samples from recent sulphide deposits (“Cyana”—project RITA) and active sulphide mineralisation (“Alvin”—project RISE) associated with hydrothermal sources at 380±30°C on the East Pacific Rise at latitude 21°N have been measured. The34S/32S ratios are relatively uniform and essentially identical for both sites: δ34S=+1.4to3.0%. (CDT), mean +2.1‰. The sulphides were analysed after the majority of the very numerous micro-inclusions of anhydrite had been removed.Two independent physico-chemical analyses of the data demonstrate that about 90% of the sulphur was leached from the basaltic host rocks by the circulating seawater-hydrothermal fluids.  相似文献   

20.
Since the 1990s, many meteorological stations in China have passively “entered” cities, which has led to frequent relocation and discontinuity in observational records at many stations. To study the impacts of urbanization on surface air temperature series, 52 meteorological stations in Anhui Province were chosen based firstly on a homogeneity test of the time series, and then their surrounding underlying surfaces during different decades were identified utilizing Landsat Multispectral Scanner images from the 1970s, Landsat Thematic Mapper images from 1980s and 1990s, and Enhanced Thematic Mapper images after 2000, to determine whether or not the station “entered” city, and then these stations were categorized into three groups: urban, suburban, and rural using Landsat-measured land use/land cover (LULC) around the station. Finally, variations in annual mean air temperature (T mean), maximum air temperature (T max), and minimum air temperature (T min) were analyzed in urban-type stations and compared to their surrounding rural-type stations. The results showed that, in Anhui Province over the past two decades, many rural stations experienced urbanization and changed into urban or suburban locations. This process is referred as the “city-entering” phenomena of stations. Consequently, many of the latest stations were relocated and moved to currently rural and suburban areas, which significantly influenced the continuity of observational records and the homogeneity of long-term trends. Based on homogeneous data series, the averaged annual T mean, T max, and T min over Anhui Province increased at a rate of 0.407, 0.383 and 0.432 °C decade?1 from 1970 to 2008. The strongest effect of urbanization on annual T mean, T max, and T min trends occurred at urban stations, with corresponding contributions of 35.824, 14.286, and 45.161 % to total warming, respectively. This work provides convincing evidences that (1) urban expansion has important impacts on the evaluation of regional climate change, (2) high spatial resolution images of Landsat are very useful for selecting reference climate stations for evaluating the potential urban bias in the surface air temperature data in certain regions of the continents, and (3) meteorological observation adjustments of station-relocation-induced inhomogeneities are essential for the study of regional or global climate change.  相似文献   

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