Origin and age of thermal waters in Cieplice Spa, Sudeten, Poland, inferred from isotope, chemical and noble gas data

Isotope and hydrochemical data of the thermal water system in Cieplice laskie Zdrój (Spa) indicate the existence of two subsystems that greatly differ in volume and which meet at the fault zones of a granitic horst, where they discharge at an altitude of about 340m. One of the subsystems is very small (about 4 × 10³ m³) as indicated by the tritium age of the order of 10 years and a low outflow rate. Its recharge area found from the δ¹⁸O and δD values, is about 200m above the springs, most probably on the slopes of the foothills of the Karkonosze Mountains south-southwest of the spa. The large subsystem contains water which is free of tritium and whose ¹⁴C content is from 1 to 8 pmc with δ¹³C = −8.0 to −9.2‰. The isotopic composition of this water reflects either the climatic effect (low-altitude recharge during a cooler pre-Holocene climate) or the altitude effect (recharge in the early Holocene period at about 1000m at the heights of the Karkonosze assuming that the ¹⁴C concentration is strongly reduced by exchange with calcite in veins). For the former hypothesis, the recharge area of this water is probably either at the foot of the southeastern slopes of the Kaczawa Mountains or/and at the foot of the Rudawy Janowickie Mountains, to the east of Cieplice. The noble gas temperatures are more consistent with the pre-Holocene recharge. Similarly, the ⁴He excess and ⁴⁰Ar/³⁶Ar ratio support the hypothesis of a pre-Holecene age. The constant ³He/⁴He ratio of 26 × 10⁻⁸ for highly different helium contents indicates crustal origin of helium. For the pre-Holocene age of water its volume is calculated at >- 10⁹m³ (stagnant water in micropores and mobile water in fractures) and the hydraulic conductivity of the host granite massif is estimated at about 7 × 10⁻⁸ ms⁻¹. Two outflows from this subsystem have different and variable fractions of a modern water component (bomb age), most probably originating from the bank infiltration of a nearby stream.     

Implanted radiogenic and other noble gases in crustal diamonds from Northern Kazakhstan

Noble gases were extracted in steps from grain size fractions of microdiamonds ( < 100 μm) from the Kokchetav Massif, Northern Kazakhstan, by pyrolysis and combustion. The concentration of ⁴He in the diamonds proper (liberated by combustion) shows a 1/r dependence on grain size. For grain diameters > 15 μm the concentration also decreases with the combustion step. Both results are clear evidence that ⁴He has been implanted into the diamonds from -decaying elements in the surrounding matrix. The saturation concentration of ⁴He(5.6 × 10⁻⁴ cm³ STP/g) is among the very highest observed in any terrestrial diamonds. Fission xenon from the spontaneous fission of ²³⁸U accompanies the radiogenic ⁴He; the ¹³⁶Xe_f/⁴He ratio of (2.5 ± 0.3) × 10⁻⁹ agrees well with the production ratio of 2.3 × 10⁻⁹ expected in a reservoir where Th/U 3.3. Radiogenic ⁴⁰Ar is predominantly ( > 90%) set free upon combustion; it also resides in the diamonds and appears to have been incorporated into the diamonds upon their formation.

³He, on the other hand is mainly released during pyrolysis and hence is apparently carried by ‘contaminants’. The concentration in the diamonds proper is of the order of 4 × 10⁻¹² cm³ STP/g, with a ³He/⁴He ratio of 1 × 10⁻⁸. Excess ²¹Ne, similarly, appears to be present in contaminants as well as in diamonds proper. These two nuclides in the contaminants must have a nucleogenic origin, but it is difficult to explain their high concentrations.     

U,U andTh in seawater

We have developed techniques to determine²³⁸U,²³⁴U and²³²Th concentrations in seawater by isotope dilution mass spectrometry. U measurements are made using a²³³U²³⁶U double spike to correct for instrumental fractionation. Measurements on uranium standards demonstrate that²³⁴U/²³⁸U ratios can be measured accurately and reproducibly.²³⁴U/²³⁸U can be measured routinely to ± 5‰ (2σ) for a sample of 5 × 10⁹ atoms of²³⁴U (3 × 10⁻⁸ g of total U, 10 ml of seawater). Data acquisition time is 1 hour. The small sample size, high precision and short data acquisition time are superior to-counting techniques.²³⁸U is measured to ± 2‰ (2σ) for a sample of 8 × 10¹² atoms of²³⁸U ( 3 × 10⁻⁹ g of U, 1 ml of seawater).²³²Th is measured to ± 20‰ with 3 × 10¹¹²³²Th atoms (10⁻¹⁰ g²³²Th, 1 1 of seawater). This small sample size will greatly facilitate investigation of the²³²Th concentration in the oceans. Using these techniques, we have measured²³⁸U,²³⁴U and²³²Th in vertical profiles of unfiltered, acidified seawater from the Atlantic and²³⁸U and²³⁴U in vertical profiles from the Pacific. Determinations of²³⁴U/²³⁸U at depths ranging from 0 to 4900 m in the Atlantic (7°44′N, 40°43′W) and the Pacific (14°41′N, 160°01′W) Oceans are the same within experimental error (± 5‰,2σ). The average of these²³⁴U/²³⁸U measurements is 144 ± 2‰ (2σ) higher than the equilibrium ratio of 5.472 × 10⁻⁵. U concentrations, normalized to 35‰ salinity, range from 3.162 to 3.281 ng/g, a range of 3.8%. The average concentration of the Pacific samples (31°4′N, 159°1′W) is 1% higher than that of the Atlantic (7°44′N, 40°43′W and 31°49′N, 64°6′W).²³²Th concentrations from an Atlantic profile range from 0.092 to 0.145 pg/g. The observed constancy of the²³⁴U/²³⁸U ratio is consistent with the predicted range of²³⁴U/²³⁸U using a simple two-☐ model and the residence time of deep water in the ocean determined from¹⁴C. The variation in salinity-normalized U concentrations suggests that U may be much more reactive in the marine environment than previously thought.     

Impacts of domestic sewage effluent on phytoplankton from Bedford Basin, eastern Canada

The impact of domestic sewage effluent (SE) on the dynamics of phytoplankton assemblages from Bedford Basin was evaluated in the laboratory. Phytoplankton production and chlorophyll a increased proportionally with SE enrichment. Phytoplankton species composition also changed. The potentially harmful diatoms, Pseudonitzschia spp., present initially in small numbers (600 cells 1⁻¹) in Bedford Basin seawater, and became dominant (3–5×10⁶ cells 1⁻¹) when the seawater was enriched with 0.5–5% untreated SE. With higher proportions of SE, other harmful species such as Fragilaria spp. and Euglena spp. became dominant (7−15×10⁶ and 2.2×10⁴ cells 1⁻¹, respectively). Treatment of SE with UV light or activated charcoal seems to favour growth of benign species, such as Chaetoceros socialis, Skeletonema costatum and Thalassiosira spp., but not harmful species such as Pseudonitzschia spp. Further research on UV treatment of domestic sewage is recommended.     

Groundwater recharge and palaeoclimate in the Sirte and Kufra basins, Libya

Stable and radio-isotope results (C, H, O) for groundwaters from the Sirte and northern Kufra basins are used to determine the recharge history during the Holocene and late Pleistocene. Radiocarbon ages have been corrected on the basis of their stable carbon isotope ratios and on environmental samples from the areas, and two groups may be recognised: (1) low ¹⁴C activity groundwaters (13000–34000 yr. BP) with δ ¹³C-5.6 to −11.7‰; and (2) higher ¹⁴C activity groundwaters (5000–7800 yr. BP) enriched in ¹³C up to δ ¹³C = −3.2‰. There is a general correlation of age with depth.

A well defined freshwater (< 50 mg/l Cl⁻) channel can be traced within the aquifer for some 130 km through the region, which is considered to represent recharge from a former wadi. This water with an age of ± 7800 yr. BP is chemically and isotopically distinct from the regional groundwaters and provides direct evidence of a significant recharge event during the Holocene.

The stable isotope (O and H) composition of groundwater from the Kufra and Sirte basins are all related by an evaporative line with slope δ D = 4.5δ ¹³O − 35 with an intercept on the meteoric line of -11‰. This suggests a recharge source continuing into the Holocene from air masses, analogous to current heavy monsoon rain derived from south of the Sahara. The spatial and temporal distribution of groundwaters in relation to the evaporative line suggests a progressive change in character of the recharge which is controlled by a shift towards strongly convective rainfall during the Holocene.

The direct hydrogeological and geochemical evidence supports climatic models proposed by several workers in which discrete humid episodes during the Holocene are inferred.     

AMS analysis of I in Japanese soil samples collected from background areas far from nuclear facilities

Analytical procedures in the determination of iodine-129 (half-life: 1.6×10⁷ y) have been studied using accelerator mass spectrometry (AMS), with special references to the separation procedures of iodine from soil samples for the AMS measurement. Iodine was successfully volatilized from soil samples by pyrohydrolysis at 1000 °C and collected in a trap solution. Iodine was purified from the matrix by solvent extraction. Finally, it was precipitated as silver iodide to make a target for AMS. In order to obtain information on the ¹²⁹I/¹²⁷I ratio in a chemical blank (or iodine carrier), we have determined the ratios in several iodine reagents and found that the ratios fell in a narrow range around 1.7×10⁻¹³. The detection limit for soil sample (1 g material) by the present method was about 0.01 mBq/kg or 4×10⁻¹¹ as the ratio of stable iodine (¹²⁹I/¹²⁷I ratio), i.e. these values were much better than that by neutron activation analysis (NAA) used in our previous studies. We have applied this method in the analysis of soil samples collected from different places in Japan. We could successfully determine ¹²⁹I in soil samples with low ¹²⁹I concentrations, which could not be detected by NAA. Sample size necessary for the soil analysis by AMS was only about 0.5 g or less, whereas about 100 g of the sample were required for NAA [Muramatsu, Y., Ohmomo, Y., 1986. Iodine-129 and iodine-127 in environmental samples collected from Tokaimura/ Ibaraki, Japan. Sci. Total Environ. 48, 33-43]. Using this method, new data were obtained for the ¹²⁹I levels in 20 soil samples collected from background areas far from nuclear facilities, and the ranges were 1.4×10⁻⁵−4.5×10⁻³ Bq/kg as ¹²⁹I concentrations and 3.9×10⁻¹¹−2.2×10⁻⁸ as ¹²⁹I/¹²⁷I ratios. These values are useful in understanding the ¹²⁹I levels in Japanese environments. Higher ¹²⁹I concentrations were observed in forest soils than those in field and rice paddy soils should be related to the interception effect of atmospheric ¹²⁹I due to tree canopies. Relatively high ¹²⁹I/¹²⁷I ratios found in rice paddy soils could be explained by their low stable iodine concentrations which were caused by the desorption of stable iodine from the rice paddies during the cultivation.     

Isotope geochemistry of Pantelleria volcanic fluids, Sicily Channel rift: a mantle volatile end-member for volcanism in southern Europe

Chemical and isotopic ratio (He, C, H and O) analysis of hydrothermal manifestations on Pantelleria island, the southernmost active volcano in Italy, provides us with the first data upon mantle degassing through the Sicily Channel rift zone, south of the African–European collision plate boundary. We find that Pantelleria fluids contain a CO₂–He-rich gas component of mantle magmatic derivation which, at shallow depth, variably interacts with a main thermal (100°C) aquifer of mixed marine–meteoric water. The measured ³He/⁴He ratios and δ¹³C of both the free gases (4.5–7.3 R_a and −5.8 to −4.2‰, respectively) and dissolved helium and carbon in waters (1.0–6.3 R_a and −7.1 to −0.9‰), together with their covariation with the He/CO₂ ratio, constrain a ³He/⁴He ratio of 7.3±0.1 R_a and a δ¹³C of ca. −4‰ for the magmatic end-member. These latter are best preserved in fluids emanating inside the active caldera of Pantelleria, in agreement with a higher heat flow across this structure and other indications of an underlying crustal magma reservoir. Outside the caldera, the magmatic component is more affected by air dilution and, at a few sites, by mixing with either organic carbon and/or radiogenic ⁴He leached from the U–Th-rich trachytic host rocks of the aquifer. Pantelleria magmatic end-member is richer in ³He and has a lower (closer to MORB) δ¹³C than all fluids yet analyzed in volcanic regions of Italy and southern Europe, including Mt. Etna in Sicily (6.9±0.2 R_a, δ¹³C=−3±1‰). This observation is consistent with a south to north increasing imprint of subducted crustal material in the products of Italian volcanoes, whose He and C (but also O and Sr) isotopic ratios gradually evolve towards crustal values northward of the African–Eurasian plate collision boundary. Our results for Pantelleria extend this regional isotopic pattern further south and suggest the presence of a slightly most pristine or ‘less contaminated’, ³He-richer mantle source beneath the Sicily Channel rift zone. The lower than MORB ³He/⁴He ratio but higher than MORB CO₂/³He ratio of Pantelleria volatile end-member are compatible with petro-geochemical evidence that this mantle source includes an upwelling HIMU–EM1-type asthenospheric plume component whose origin, according to recent seismic data, may be in the lower mantle.     

Production of selected cosmogenic radionuclides by muons: 2. Capture of negative muons

We have determined the production yields for radionuclides in Al₂O₃, SiO₂, S, Ar, K₂SO₄, CaCO₃, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides ¹⁰Be, ¹⁴C and ²⁶Al produced in quartz targets, ²⁶Al in Al₂O₃ and S targets, ³⁶Cl in K₂SO₄ and CaCO₃ targets, and ⁵³Mn in Fe₂O₃ targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ⁻ capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ⁻ capture, by fast muons and by neutron capture.     

REE diffusion in calcite

Chemical diffusion of four rare-earth elements (La, Nd, Dy and Yb) has been measured in natural calcite under anhydrous conditions, using rare-earth carbonate powders as the source of diffusants. Experiments were run in sealed silica capsules along with finely ground calcite to ensure stability of the single-crystal samples during diffusion anneals. Rutherford backscattering spectroscopy (RBS) was used to measure diffusion profiles. The following Arrhenius relations were obtained over the temperature range 600–850°C: D_La =2.6×10⁻¹⁴ exp(−147±14 kJ mol⁻¹/RT) m² s⁻¹, D_Nd =2.4×10⁻¹⁴ exp(−150±13 kJ mol⁻¹/RT) m² s⁻¹, D_Dy =2.9×10⁻¹⁴ exp(−145±25 kJ mol⁻¹/RT) m² s⁻¹, D_Yb =3.9×10⁻¹² exp(−186±23 kJ mol⁻¹/RT) m² s⁻¹. In contrast to previous findings for refractory silicates (e.g. zircon), differences in transport rates among the REE are not pronounced over the range of temperature conditions investigated in this study. Diffusion of the REE is significantly slower than diffusion of the divalent cations Sr and Pb and slower than transport of Ca and C at temperatures above 650°C. Fine-scale zoning and isotopic and REE chemical signatures may be retained in calcites under many conditions if diffusion is the dominant process affecting alteration.     

Carbon isotopes in submarine basalts

High-sensitivity stepped extraction reveals two isotopically distinct forms of carbon in submarine basalt glasses: an isotopically light carbon component released by combustion from 200 to 600°C and an isotopically heavy CO₂ liberated from vesicles (magmatic carbon) from 600 to 1200°C. The δ¹³C_PDB of the low release temperature carbon varies from −24 to −30‰ and is believed to be surficial organic contamination. A survey of various types of oceanic glasses demonstrates that the δ¹³C of magmatic CO₂ varies from −4.2 to −7.5‰ in mid-ocean ridge basalt (MORB), from −2.8 to −6.7‰ in glasses from Hawaii and Explorer Seamount and from −7.7 to −16.3‰ in glasses from the Scotia Sea and Mariana Trough. Magmatic CO₂ in back-arc basin basalts (BABB) is on average 5‰ lighter than equivalent CO₂ in MORB and can be explained by the mixing in the source regions for BABB magmas of juvenile (MORB-like) CO₂ with an organic carbon component from subducted pelagic sediments. It is inferred that significant amounts of pelagic carbonate carbon (δ¹³C 0‰) must be recycled into the mantle.     

Water flow path interactions with soil hydraulic properties in till soil at Gårdsjön, Sweden

In 1989, in a hydrological research programme within a deacidification project in the Gårdsjön area in southwest Sweden, flow paths and residence times of soil water and groundwater in microcatchments were examined to support the interpretation of the hydrochemical changes. Saturated hydraulic conductivity and soil water retention were analysed on more than 100 cylinder samples. The catchments have shallow sandy-silty till soil with a mean depth in the main catchment of 43 cm. Porosity of the mineral soil in the main catchment was high and ranged from 38 to 85%. The samples from the B-horizon had generally higher porosity. Porosity and the content of organic matter were correlated. The soil water retention was relatively high at all tensions, likely owing to the high content of organic matter. Dissolved organic substances were most probably transported from the shallow soil on the steep sides of the catchment down to the valley where it precipitated. The high porosities could be a consequence of long-term weathering, provided that the organic substances present have increased the leaching of the weathering products. Measured values of saturated hydraulic conductivity were close to log-normally distributed with a mean for all samples of 3 × 10⁻⁵ m s⁻¹. There was a significant increase in conductivity toward the ground surface with the mean conductivity of the samples in the uppermost 10 cm of the mineral soil of 4 × 10⁻⁵ m s⁻¹, which was about 13 times higher than the conductivity of 3 × 10⁻⁶ m s⁻¹ at 1 m depth. From the relationship between runoff at the catchment outlet and groundwater levels, the conductivity was estimated to be 15–200 times higher in the upper soil layer than in the deeper ones. In one profile, 44–64% of the yearly lateral flow was estimated to occur above 30 cm depth. The conductivity was correlated with the content of drainable water, which indicated the importance of the largest pores for the saturated hydraulic conductivity.     

Formation of a salt plume in the Coastal Plain aquifer of Israel: the Be''er Toviyya region

The formation and development of a salt plume (salinity up to 800 mg Cl 1⁻¹) in the inner part of the Coastal Plain aquifer of Israel is analyzed. Massive groundwater exploitation during the 1950s caused a large drop in the water level and formation of a hydrologic depression in the Be'er Toviyya-Kefar Warburg area. The depression reached a maximal depth during the late 1960s; thereafter a reduction in the rate of pumpage led to restoration of water levels and shallowing of the depression, until its complete disappearance towards the end of the 1980s. A spot of high salinity first appeared in 1956, following a deep drawdown in the water levels. This saline plume has been continuously expanding with increasing salinity concentrations (200–800 mg Cl 1⁻¹) in its center. The average rate of radial expansion was about 50 m year⁻¹. The expansion and salinization did not cease as the depression disappeared. Rather, equalization of water levels in wells situated within the plume area with those of situated along its margins resulted in the salinization of the latter within a period of 1 year.

Mass balances for water and chloride contents were made for the period 1967–1990. Taking into consideration the storage change, pumpage, natural replenishment and artificial recharge, the lateral inflow to the depression is estimated as 60 × 10⁶ m³. Upon addition of the chloride balance, and taking into consideration the chloride concentrations of the surrounding fresh water and the apparent possible end-member of the saline source (based on geochemical considerations), the saline inflow is estimated as (40–60) × 10⁶ m³. These estimates indicate that a large amount of saline water penetrated into the aquifer, of about half of the natural replenishment of the study area, with an estimated salinity of 1900–2700 mg Cl 1⁻¹.

It is suggested that the salt plume was formed as a result of a drop in water level combined with a flow of underlying saline water bodies from deeper strata. The chemical composition of the groundwater points to the existence of two saline water bodies of Ca-chloride composition and a marine Br/Cl ratio: (1) saline water with low Na/Cl (0.6), So₄/Cl, and B/Cl ratio; (2) saline water with higher Na/Cl (> 0.6), So₄/Cl, and B/Cl ratios. These chemical compositions resemble Ca-chloride saline waters found in other locations in the Coastal Plain aquifer and in underlying formations. The saline water bodies may occur in either pockets at the bottom of the aquifer or lumachelle and sandstone layers of high hydraulic conductivity in underlying sediments.     

Melting rates beneath Hawaii: Evidence from uranium series isotopes in recent lavas

²³⁸U, ²³²Th, ²³⁰Th and ²²⁶Ra abundances have been measured in six samples of recent Hawaiian basalt by high precision mass spectrometry, in an attempt to compare the melting process in plumes and at spreading ridges. The data reveal a very small range in (²³⁰Th/²³⁸U) activity ratio up to a maximum value of 1.02 ± 0.01, and (²²⁶Ra/²³⁰Th) activity ratios which lie between 1.10 ± 0.015 and 1.19 ± 0.02. UTh and RaTh abundances are linearly correlated demonstrating that the disequilibria predate crystallisation and differentiation. Using recently published estimates for the bulk partition coefficients of U and Th, the results are consistent with melting rates > 10⁻³ kg m⁻³ a⁻¹ at porosities < 10⁻³ for dynamic fractional melting in the garnet stability field.     

Can biomass burning produce a globally significant carbon-isotope excursion in the sedimentary record?

Negative carbon-isotope excursions have been comprehensively studied in the stratigraphic record but the discussion of causal mechanisms has largely overlooked the potential role of biomass burning. The carbon-isotopic ratios (δ¹³C) of vegetation, soil organic matter and peat are significantly lower than atmospheric carbon dioxide (CO₂), and thereby provide a source of low ¹³C CO₂ when combusted. In this study, the potential role of biomass burning to generate negative carbon isotope excursions associated with greenhouse climates is modeled. Results indicate that major peat combustion sustained for 1000 yr increases atmospheric CO₂ from 2.5× present atmospheric levels (PAL) to 4.6× PAL, and yields a pronounced negative δ¹³C excursion in the atmosphere ( 2.4‰), vegetation ( 2.4‰) and the surface ocean ( 1.2‰), but not for the deep ocean ( 0.9‰). Release of CO₂ initiates a short-term warming of the atmosphere (up to 14.4 °C, with a duration of 1628 yr), which is consistent with the magnitude and length of an observed Toarcian excursion event. These results indicate that peat combustion is a plausible mechanism for driving negative δ¹³C excursions in the rock record, even during times of elevated pCO₂.     

Brine history indicated by argon, krypton, chlorine, bromine, and iodine analyses of fluid inclusions from the Mississippi Valley type lead-fluorite-barite deposits at Hansonburg, New Mexico

Argon, krypton, chlorine, bromine, and iodine were measured in a homogeneous population of high-salinity hydrothermal fluid inclusions from the Tertiary-age Mississippi Valley-type (MVT) lead-fluorite-barite deposits at Hansonburg, New Mexico to establish new types of evidence for the history of both the fluid and the major dissolved salts. Noble gases and halogens in fluid inclusions containing 10⁻¹⁰–10⁻⁹ L of brine (Cl= 3 molal) were analyzed by laser microprobe noble-gas mass spectrometry (lmngms) on neutron-irradiated samples.

The concentrations of³⁶Ar (4.7 × 10⁻⁸ molal) and⁸⁴Kr1.8 × 10⁻⁹ molal) in the fluid inclusions are equal to those of fresh surface waters in equilibrium with air at approximately20 ± 5°. The mole ratios ofBr/Cl (1.2 × 10⁻⁴) andI/Cl (1–2 × 10⁻⁶) are among the lowest measured in any natural waters, similar to those of modern brines formed by dissolution of Permian NaCl-bearing evaporites in southeast New Mexico.⁴⁰Ar/³⁶Ar ratios (600) are twice that of air, and indicate that the fluid inclusions had excess radiogenic⁴⁰Ar (1.4 × 10⁻⁵ molal) when trapped. The amount of excess⁴⁰Ar appears to be too large to have been acquired with Cl by congruent dissolution of halite-bearing evaporites, and possibly too small to have been acquired with Pb by congruent dissolution of granitic basement rocks with Proterozoic KAr ages.

From thelmngms data, combined with published Pb and S isotope data, we infer the following sequence of events in the history of the Hansonburg MVT hydrothermal brine: (1) the brine originated as relatively dilute meteoric water, and it did not gain or lose atmospheric Ar or Kr after recharge; (2) the originally dilute fluid acquired the bulk of its Cl and sulfate in the subsurface after recharge by dissolving halite-bearing Permian? marine evaporites; (3) the high salinity brine then acquired most of its Pb and excess radiogenic⁴⁰Ar from interactions with aquifer rocks other than evaporites, possibly clastic sedimentary rocks or basement rocks with Phanerozoic KAr “ages”; and (4) the brine deposited fluorite without having boiled or degassed.     

Ages and composition of gas trapped in Allan Hills and Byrd core ice

Gas is extracted from large (6–31 kg) Antarctic ice samples to obtain sufficient CO₂ for¹⁴C measurements with small low-level proportional counters. The¹⁴C ages of Byrd core ice are in accord with glaciological estimates ranging from (2.2_−1.1^+1.4)×10³ yr at 271 m depth to more than 8 × 10³ yr at 1071 m depth. The CO₂ abundances in gas extracted from Byrd core ice range from 0.0216 to 0.051%, with below present-day atmosphere CO₂ abundances for ice from 1068 and 1469 m depths. The CO₂ abundance in gas from Allan Hills surface ice samples ranges between four and six times the atmospheric value and the CO₂ had a specific activity three times that of contemporary carbon. A possible explanation for the anomalously high specific activity is surface melting with the incorporation into CO₂ of¹⁴C produced by cosmic ray spallation of oxygen in ice. The CO₂ abundance in gas extracted from subsurface Allan Hills ice ranged from 0.030 to 0.065%, and the specific activities are below contemporary carbon, indicating ages greater than 5×10³ yr. The¹⁸O/¹⁶O ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the¹⁸O/¹⁶O ratio in the ice. The O₂, N₂, and Ar abundances and isotopic compositions are similar to those in contemporary air, except for positive¹⁵N/¹⁴N ratios in a few samples.     

A study of the Rima Sirsalis lunar magnetic anomaly

The source of the lunar magnetic anomaly associated with the Rima Sirsalis linear rille has been modelled using the vector field intensities due to arbitrary uniform magnetization in a rectangular prism. It is shown that in order to match the Apollo 16 subsatellite data, the lunar surface near the rille must have a vertical magnetization of 6–9 × 10⁻³ G if the anomaly is due to flux leakage from a gap in the crust with the dimensions of the rille. This is more than one order of magnitude larger than the magnetization of any lunar sample, but is comparable with the high magnetization recently deduced for the Reiner γ formation in Oceanus Procellarum. An alternative explanation is that Rima Sirsalis and its surroundings are the site of a vertical magnetization contrast of 10⁻⁵ – 10⁻⁴ G which is at least as wide as the rille and extends to a depth of tens of kilometers in the crust. A wider magnetic source reduces the required magnetization (or depth) proportionately, since to first order the field at high altitude is proportional to the magnetic dipole moment per unit length.     

Influence of artificial groundwater lakes on the abundance and activity of bacteria in adjacent subsurface systems

Bacterial abundances and activity, estimated by 4′,6-diamidino-2-phenylindole staining (DAPI) and the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT), were investigated in two oligotrophic artificial groundwater lakes and the surrounding aquifers. To evaluate the effect of lake water on groundwater downstream, samples were taken from wells at different distances from the lakes, and the total number of bacteria and the number of active bacteria in these samples were compared with samples collected upstream. In addition, sterilized sandy sediments were exposed in groundwater wells to measure the number and activity of bacteria attached to particles. At one of the study sites, where the lake sediments were disturbed by dredging, total bacterial abundance and the number of respiring bacteria in the groundwater aquifer was clearly influenced by the lake water. The average bacterial abundances decreased from 2.6 ± 1.9 × 10⁵ cells ml⁻¹ in the well closest to the lake (S2) to 2.9 ± 3.8 × 10⁴ cells ml⁻¹ in the most distant one (S4), which was equivalent to cell numbers in the upstream well. The number of respiring bacteria showed a similar tendency with 1.3 ± 2.7 × 10⁴ active cells ml⁻¹ in S2 and 1.9 ± 1.5 × 10³ active cells ml⁻¹ in S4. At the second study site, which was not influenced by dredging, bacteria in the downstream wells seemed not to be affected by the lake water. The number and activity of bacteria, which colonized exposed sediments, were not significantly different in the upstream and downstream wells, indicating a minor influence of lake water on this habitat. Our results suggest that gravel-pit lakes may influence the free living bacterial assemblages in nearshore groundwater systems, but do not visibly affect numbers and activity of bacteria attached to the surface of aquifer sediments.     

Iodine-129 concentrations in marginal seas of the north Pacific and Pacific-influenced waters of the Arctic Ocean

Water sampling during the 1993 IV Russian–US Joint Expedition to the Bering and Chukchi Seas (BERPAC) indicates that Pacific Ocean burdens of the long-lived radionuclide ¹²⁹I are relatively low in the Pacific-influenced Arctic, particularly compared to high latitude waters influenced by the North Atlantic. These low concentrations occur despite the presence of potential submerged anthropogenic sources in the East Sea (Sea of Japan), and in the northwest Pacific Ocean, east of the Kamchatka Peninsula. The concentration of ¹²⁹I entering the Arctic Ocean through Bering Strait, 0.7×10⁸ atoms kg⁻¹, is only slightly higher than observed in deep Pacific waters. Similar concentrations (0.44–0.76×10⁸ atoms kg⁻¹) measured in Long Strait indicate no significant transfer of ¹²⁹I eastward into the Chukchi Sea in the Siberian Coastal Current from the Siberian marginal seas to the west. However, the concentrations reported here are more than an order of magnitude higher than the Bering Strait input concentration estimated (1.0×10⁶ atoms kg⁻¹) from bomb fallout mass balances, which supports other existing evidence for a significant atmospheric deposition term for this radionuclide in surface ocean waters. Near-bottom water samples collected in productive waters of the Bering and Chukchi Seas also suggest that sediment regeneration may locally elevate ¹²⁹I concentrations, and impact its utility as a water mass tracer. As part of this study, two deep ¹²⁹I profiles were also measured in the East Sea in 1993–1994. The near-surface concentration of ¹²⁹I ranged from 0.12 to 0.31×10⁸ atoms kg⁻¹. The ¹²⁹I concentration showed a steady decrease with depth, although because of active deep water ventilation, the entire 3000 m water column exceeded natural concentrations of the radionuclide. Atom ratios of ¹²⁹I/¹³⁷Cs in the East Sea also suggest an excess of ¹²⁹I above bomb fallout estimates, also possibly resulting from atmospheric deposition ultimately originating from nuclear facilities.     

The water balance of a small lake using stable isotopes and tritium

A small maar lake, known as the Blue Lake, set in a karstic region of southeastern Australia, provides the municipal water supply for a population of 20,000. The lake has a volume of 3.6·10⁷m³, of which 10–15% is pumped from it each year. The lake is recharged almost entirely from groundwater and the main objective of this study was to estimate the total groundwater inflow and outflow rates. Estimation of groundwater throughflow in a lake is difficult to assess using classical hydrological techniques and an alternative method involving measurement of the concentrations of the environmental isotopes ³H, ¹⁸O, ²H and ¹⁴C in the lake water and in the recharging groundwater was used to establish the lake-water balance. The water-balance calculations indicated a total groundwater inflow to Blue Lake of between 5.0·10⁶ and 6.5·10⁶m³yr.⁻¹, corresponding to a residence time of water in the lake of 6 yr. It was not possible to derive the relative proportions of inflow to the lake from the two possible source aquifers, using these isotopes, because their concentrations did not show a sufficiently large contrast to distinguish the two water sources.