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1.
We examine how the stable isotope composition of meteoric water is transmitted through soil and epikarst to dripwaters in a cave in western Romania. δ2H and δ18O in precipitation at this site are influenced by temperature and moisture sources (Atlantic and Mediterranean), with lower δ18O in winter and higher in summer. The stable isotope composition of cave dripwaters mimics this seasonal pattern of low and high δ18O, but the onset and end of freezing conditions in the winter season are marked by sharp transitions in the isotopic signature of cave dripwaters of approximately 1 ‰. We interpret these shifts as the result of kinetic isotopic fractionation during the transition phase from water to ice at the onset of freezing conditions and the input of meltwater to the cave at the beginning of the spring season. This process is captured in dripwaters and therefore speleothems from Ur?ilor Cave, which grew under such dripping points, may have the potential to record past changes in the severity of winters. Similar isotopic changes in dripwaters driven by freeze–thaw processes can affect other caves in areas with winter snow cover, and cave monitoring during such changes is essential in linking the isotopic variability in dripwaters and speleothems to surface climate.  相似文献   

2.
Precisely dated high-resolution speleothems may record past typhoon events, however, the state of the art cave monitoring is a prerequisite to identify suitable stalagmites for the reconstruction of such events. With this motivation, we examined the isotopic composition (δ18O and d-excess values) of rainfall, outside river, cave drip water, and an underground river in the Xianyun cave system, located in southeastern China. Monthly to bi-monthly monitoring of environmental and isotopic conditions was conducted for 1 year, from December 2018 to December 2019, including a typhoon event (August 24, 2019 to August 26, 2019), called Bailu. The δ18O of rainfall samples over the cave and outside river water ranged from −9.7‰ to −1.9‰ and −8.2‰ to −6.3‰, respectively, while the δ18O of Typhoon Bailu rainfall and instantaneous outside river water ranged from −19.6‰ to −6.3‰ and −10.4‰ to −7.7‰, respectively. Typhoon Bailu-induced rainfall showed distinctly negative δ18O values as compared to those of the monthly and bi-monthly rainfall, exhibiting a three-stage inverted U-shaped variation characteristic. Four drip water monitoring sites inside the cave revealed low variations during the studied period with average values of −7.8‰, −8.0‰, −8.0‰, and −8.1‰. However, during the typhoon, the drip water δ18O values exhibited similar characteristic as outside rainfall but with just 0.2‰ negative deviation owing to precipitation amount and drip water source reservoir. The integration of rainfall amount with drip water source reservoir determines the degree to which a typhoon isotopic signature gets diluted during epikarst infiltration. This study provides the first instrumental evidence of typhoon signal in karst system in southeastern China. Our results imply that the δ18O of drip water in Xianyun cave can instantaneously respond to typhoon rainfall. However, the 0.2‰ shift in drip water δ18O is difficult to be recorded by speleothems. We suggest multi-year monitoring to ascertain fully if the stalagmites could be used as paleotyphoon proxy.  相似文献   

3.
A calibration study of oxygen and hydrogen isotopic composition from precipitation and cave dripwater was conducted in west‐central Florida at Legend Cave during 2007–2008. This study was performed to better understand how modern precipitation patterns can be discerned through examination of cave dripwater and speleothem calcite for paleoclimate reconstruction. The ‘amount effect’ was shown to be a dominant control on the oxygen isotopic composition of precipitation for the study area. A meteoric water line with a slope of 6·7 suggests evaporative effects occur either during precipitation or subsequent hydrological processes. However, δ18O values of cave dripwater averaged near the mean annual amount‐weighted average of precipitation, suggesting that the isotopic composition of dripwater tracks the long‐term average of rainfall. An observed weak seasonal influence occurred in the d‐excess values, with summer precipitation being more enriched due to increased evaporative effects. Comparison of precipitation δ18O values to synoptic weather data shows the dominant amount effect influence occurs due to strong convective storms producing highly 18O‐depleted rainfall at greater amounts during the year. Constant δ18O values of the dripwater indicate that paleoclimate reconstructions using speleothems from this area would record changes in annual to interannual shifts in precipitation amount above the cave. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
Characterization of stable isotope compositions (δ2H and δ18O) of surface water and groundwater in a catchment is critical for refining moisture sources and establishing modern isotope–elevation relationships for paleoelevation reconstructions. There is no consensus on the moisture sources of precipitation in the Yellow River source region during summer season. This study presents δ2H and δ18O data from 111 water samples collected from tributaries, mainstream, lakes, and groundwater across the Yellow River source region during summertime. Measured δ18O values of the tributaries range from ?13.5‰ to ?5.8‰ with an average of ?11.0‰. Measured δ18O values of the groundwater samples range from ?12.7‰ to ?10.5‰ with an average of ?11.9‰. The δ18O data of tributary waters display a northward increase of 1.66‰ per degree latitude. The δ18O data and d‐excess values imply that moisture sources of the Yellow River source region during summertime are mainly from the mixing of the Indian Summer Monsoon and the Westerlies, local water recycling, and subcloud evaporation. Analysis of tributary δ18O data from the Yellow River source region and streamwater and precipitation δ18O data from its surrounding areas leads to a best‐fit second‐order polynomial relationship between δ18O and elevation over a 4,600 m elevation range. A δ18O elevation gradient of ?1.6‰/km is also established using these data, and the gradient is in consistence with the δ18O elevation gradient of north and eastern plateau. Such relationships can be used for paleoelevation reconstructions in the Yellow River source region.  相似文献   

5.
Stable isotopic composition of precipitation as preserved in continental proxy climate archives (e.g., ice cores, lacustrine sediments, tree rings, groundwater, and organic matter) can sensitively record fluctuations in local meteorological variables. These are important natural climatic tracers to understand the atmospheric circulation patterns and hydrological cycle and to reconstruct past climate from archives. Precipitation was collected at Dokriani Glacier to understand the response of glaciers to climate change in the Garhwal Central Himalaya, Upper Ganga Basin. The local meteoric water line deviates from the global meteoric water line and is useful for the identification of moisture source in the region. The data suggest different clusters of isotopic signals, that is, summer (June–September) and winter (November–April); the mean values of δ18O, δD, and d ‰ during summer are ?13.03‰, ?84.49‰, and 19.78 ‰, respectively, whereas during winter, the mean values of δ18O, δD, and d ‰ are ?7.59‰, ?36.28‰, and 24.46 ‰, respectively. Backward wind trajectory analysis ascertains that the major source of precipitation during summer is from the Indian Summer Monsoon and during winter from the westerlies. Regression analysis has been carried out in order to establish interrelationship between the precipitation isotopic signatures and meteorological variables such as air temperature, relative humidity, and precipitation. Temperature and precipitation have good correlation with the isotopic signatures of precipitation with R2 values >.5, suggesting that both temperature and amount effects prevail in the study region. Multiple regression analysis found strong relationships for both the seasons. The relationship of deuterium excess with δ18O, relative humidity, and precipitation are significant for the winter season. No significant relationships of deuterium excess were found with other meteorological variables such as temperature and radiation. The correlation and regression analysis performed are significant and valuable for interpretation of processes in the hydrological cycle as well as for interpretation of palaeoclimate records from the region.  相似文献   

6.
The recharge location for many springs is unknown because they can be sourced from proximal, shallow, atmospheric sources or long‐traveled, deep, regional aquifers. The stable isotope (18O and 2H) geochemistry of springs water can provide cost‐effective indications of relative flow path distance without the expense of drilling boreholes, conducting geophysical studies, or building groundwater flow models. Locally sourced springs generally have an isotopic signature similar to local precipitation for that region and elevation. Springs with a very different isotopic composition than local meteoric inputs likely have non‐local recharge, representing a regional source. We tested this local vs. regional flow derived hypothesis with data from a new, large springs isotopic database from studies across Western North America in Arizona, Nevada, and Alberta. The combination of location‐specific precipitation data with stable isotopic groundwater data provides an effective method for flow path determination at springs. We found springs in Arizona issue from a mix of regional and local recharge sources. These springs have a weak elevation trend across 1588 m of elevation where higher elevation springs are only slightly more depleted than low elevation springs with a δ18O variation of 5.9‰. Springs sampled in Nevada showed a strong elevation‐isotope relationship with high‐elevation sites discharging depleted waters and lower elevation springs issuing enriched waters; only a 2.6‰ difference exists in 18O values over an elevation range of more than 1500 m. Alberta's springs are mostly sourced from local flow systems and show a moderate elevation trend of 1200 m, but the largest range in δ18O, 7.1‰.  相似文献   

7.
The isotopic features of Lake Trekhtsvetnoe in the White Sea coast area were studied in 2012–2015 in both winter and summer. Lake Trekhtsvetnoe is a water body, separating from the sea, with constant vertical stratification throughout the observation period. Its isotopic, hydrophysical, and biological characteristics have been studied. By the isotopic profile of lake water body, three zones can be identified in the lake: (1) 0–1 m: mixolimnion zone with δ18O varying from–12 to–11.1‰; (2) 1.0–3.0 m: zone with transitional properties with δ18O varying from–11.1 to–5.5‰; (3) 3.0–7.6 m: monimolimnion zone with highest values of δ18O—from–5.5 to–4.7‰.  相似文献   

8.
Recharge areas of the Guarani Aquifer System (GAS) are particularly sensitive and vulnerable to climate variability; therefore, the understanding of infiltration mechanisms for aquifer recharge and surface run‐off generation represent a relevant issue for water resources management in the southeastern portion of the Brazilian territory, particularly in the Jacaré‐Pepira River watershed. The main purpose of this study is to understand the interactions between precipitation, surface water, and groundwater using stable isotopes during the strong 2014–2016 El Niño Southern Oscillation event. The large variation in the isotopic composition of precipitation (from ?9.26‰ to +0.02‰ for δ18O and from ?63.3‰ to +17.6‰ for δ2H), mainly associated with regional climatic features, was not reflected in the isotopic composition of surface water (from ?7.84‰ to ?5.83‰ for δ18O and from ?49.7‰ to +33.6‰ for δ2H), mainly due to the monthly sampling frequency, and groundwater (from ?7.04‰ to ?7.76‰ for δ18O and from ?49.5‰ to ?44.7‰ for δ2H), which exhibited less variation throughout the year. However, variations in deuterium excess (d‐excess) in groundwater and surface water suggest the occurrence of strong secondary evaporation during the infiltration process, corresponding with groundwater level recovery. Similar isotopic composition in groundwater and surface water, as well as the same temporal variations in d‐excess and line‐conditioned excess denote the strong connectivity between these two reservoirs during baseflow recession periods. Isotopic mass balance modelling and hydrograph separation estimate that the groundwater contribution varied between 70% and 80%, however, during peak flows, the isotopic mass balance tends to overestimate the groundwater contribution when compared with the other hydrograph separation methods. Our findings indicate that the application of isotopic mass balance methods for ungauged rivers draining large groundwater reservoirs, such as the GAS outcrop, could provide a powerful tool for hydrological studies in the future, helping in the identification of flow contributions to river discharge draining these areas.  相似文献   

9.
The stable oxygen and hydrogen isotopic features of precipitation in Taiwan, an island located at the western Pacific monsoon area, are presented from nearly 3,500 samples collected during the past decade for 20 stations. Results demonstrate that moisture sources from diverse air masses with different isotopic signals are the main parameter in controlling the precipitation's isotope characteristics. The air mass from polar continental (Pc) region contributes the precipitation with high deuterium excess values (up to 23‰) and relatively enriched isotope compositions (e.g., ? 3.2‰ for δ18O) during the winter with prevailing northeasterly monsoon. By contrast, air masses from equatorial maritime (Em) and tropical maritime (Tm) supply the precipitation with low deuterium excess values (as low as about 7‰) and more depleted isotope values (e.g., ? 8.9‰ and ? 6.0‰ for δ18O of Tm and Em, respectively) during the summer with prevailing southwesterly monsoon. Thus seasonal differences in terms of δ18O, δD, and deuterium excess values are primarily influenced by the interactions among various precipitation sources. While these various air masses travel through Taiwan, secondary evaporation effects further modify the isotope characteristics of the inland precipitation, such as raindrop evaporation (reduces the deuterium excess of winter precipitation) and moisture recycling (increases the deuterium excess of summer precipitation). The semi-quantitative estimations in terms of evaluation for changes in the deuterium excess suggest that the raindrop evaporation fractions for winter precipitation range 7% to 15% and the proportions of recycling moisture in summer precipitation are less than 5%. Additionally, the isotopic altitude gradient in terms of δ18O for summer precipitation is ? 0.22‰/100 m, greater than ? 0.17‰/100 m of winter precipitation. The greater isotopic gradient in summer can be attributed to a higher temperature vs. altitude gradient relative to winter. The observed spatial and seasonal stable isotopic characteristics in Taiwan's precipitation not only contribute valuable information for regional monsoon research crossing the continent–ocean interface of East Asia, but also can serve as very useful database for local water resources management.  相似文献   

10.
The anomalous drip in the Punkva caves (Moravian Karst) shows specific hydrogeochemical properties such as low SIcalcite ~ 0.14 ± 0.11 (standard deviation), low mineralization (4.53 ± 0.42) × 10?3 mol l?1, and enhanced values of δ13C (?7.85 to ?8.35‰ VPDB), Mg/Ca × 1000 ratio (45.7 ± 3.3), and Sr/Ca × 1000 ratio (0.65 ± 0.06). By these properties, the anomalous drip significantly differs from other regular drips in the same cave and other caves in the region. The study suggests that the anomalous drip properties are a consequence of prior calcite precipitation or/and water mixing along the water flow path. As the former processes are spatially controlled, the knowledge of dripwater flow path seems to be necessary for correct paleoclimatic/paleoenvironmental reconstructions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

11.
δ18O values for 87 chert samples from the 3.4-b.y.-old Onverwacht Group, South Africa, range from +9.4 to +22.1‰. δ-values for cherts representing early silicified carbonates and evaporites, and possible primary precipitates range from +16 to +22‰ and are distinctly richer in18O than silicified volcaniclastic debris and cherts of problematical origin. The lower δ-values for the latter two chert types are caused by isotopic impurities such as sericite and feldspar, and/or late silicification at elevated temperature during burial. Cherts with δ-values below +16‰ are thus not likely to yield geochemical data relevant to earth surface conditions.Fine-grained chert is less than 0.7‰ depleted in18O relative to coexisting coarse drusy quartz. Because coarse quartz preserves its isotopic composition with time, the maximum amount of post-depositional lowering of the δ-values of cherts by long-term isotopic exchange with meteoric groundwaters does not exceed 0.7‰ in 3.4 b.y. In response to metamorphism the δ-values of Onverwacht cherts appear to remain unchanged or to have increased by as much as 4‰. Neither metamorphism nor long-term isotopic exchange with groundwaters can explain why Onverwacht cherts are depleted in18O relative to their Phanerozoic counterparts.Meteoric waters with a δ18O range of at least 3‰ appear to have been involved in Onverwacht chert diagenesis. δ-values for possible primary cherts or cherts representing silicified carbonates and evaporites are compatible with the depositional and diagenetic environments deduced from field and petrographic evidence. Onverwacht cherts appear to have formed with δ-values at least 8‰ lower than Phanerozoic cherts.The new Onverwacht data combined with all published oxygen isotope data for cherts suggest a secular trend similar to that initially suggested by Perry (1967) in which younger cherts are progressively enriched in18O. However, Precambrian cherts appear to be richer in18O than Perry's original samples and can be reasonably interpreted in terms of declining climatic temperatures from ～70°C at 3.4 b.y. to present-day values, as initially suggested by Knauth and Epstein (1976). This surface temperature history is compatible with existing geological, geochemical, and paleontological evidence.  相似文献   

12.
Characterization of spatial and temporal variability of stable isotopes (δ18O and δ2H) of surface waters is essential to interpret hydrological processes and establish modern isotope–elevation gradients across mountainous terrains. Here, we present stable isotope data for river waters across Kyrgyzstan. River water isotopes exhibit substantial spatial heterogeneity among different watersheds in Kyrgyzstan. Higher river water isotope values were found mainly in the Issyk‐Kul Lake watershed, whereas waters in the Son‐Kul Lake watershed display lower values. Results show a close δ18O–δ2H relation between river water and the local meteoric water line, implying that river water experiences little evaporative enrichment. River water from the high‐elevation regions (e.g., Naryn and Son‐Kul Lake watershed) had the most negative isotope values, implying that river water is dominated by snowmelt. Higher deuterium excess (average d = 13.9‰) in river water probably represents the isotopic signature of combined contributions from direct precipitation and glacier melt in stream discharge across Kyrgyzstan. A significant relationship between river water δ18O and elevation was observed with a vertical lapse rate of 0.13‰/100 m. These findings provide crucial information about hydrological processes across Kyrgyzstan and contribute to a better understanding of the paleoclimate/elevation reconstruction of this region.  相似文献   

13.
Secondary calcite residing in open cavities in the unsaturated zone of Yucca Mountain has long been interpreted as the result of downward infiltration of meteoric water through open fractures. In order to obtain information on the isotopic composition (δD and δ18O) of the mineral-forming water we studied fluid inclusions from this calcite. Water was extracted from inclusions by heated crushing and the δD values were measured using a continuous-flow isotope-ratio mass spectrometry method. The δ18O values were calculated from the δ18O values of the host calcite assuming isotopic equilibrium at the temperature of formation determined by fluid-inclusion microthermometry.The δD values measured in all samples range between ? 110 and ? 90‰, similar to Holocene meteoric water. Coupled δ18O–δD values plot significantly, 2 to 8‰, to the right of the meteoric water line. Among the various processes operating at the topographic surface and/or in the unsaturated zone only two processes, evaporation and water–rock exchange, could alter the isotope composition of percolating water. Our analysis indicates, however, that none of these processes could produce the observed large positive δ18O-shifts. The latter require isotopic interaction between mineral-forming fluid and host rock at elevated temperature (>100 °C), which is only possible in the deep-seated hydrothermal environment. The stable isotope data are difficult to reconcile with a meteoric origin of the water from which the secondary minerals at Yucca Mountain precipitated; instead they point to the deep-seated provenance of the mineral-forming waters and their introduction into the unsaturated zone from below, i.e. a hypogene origin.  相似文献   

14.
Abstract

The paper discusses aspects of the isotopic composition (tritium and stable isotopes) of precipitation, which was monitored from 2000 to 2003 at 12 stations in Syria. The seasonal variations in δ18O are smaller at the western stations than at the eastern ones due to low seasonal temperature variations. A good correlation between δ2H and δ18O was obtained for each station, and the slopes of the local meteoric water lines are significantly lower than the Global Meteoric Water Line. Values of d-excess decrease from 19‰ at the western stations to 13‰ at the eastern ones, indicating the influence of precipitation generated by air masses coming from the Mediterranean Sea. A reliable altitude effect represented by depletion of heavy stable isotopes (δ18O and δ2H), of about??0.21‰ and??1.47‰ per 100 m elevation, respectively, was observed. Monthly tritium contents in precipitation, and seasonal variations, are less at the western stations than at the eastern ones. The weighted mean tritium values are between 3 and 9 TU, and increase with distance from the Syrian coast by 1 TU/100 km.

Citation Al Charideh, A. R. & Abou Zakhem, B. (2010) Distribution of tritium and stable isotopes in precipitation in Syria. Hydrol. Sci. J. 55(5), 832–843.  相似文献   

15.
M. Z. Iqbal 《水文研究》2008,22(23):4609-4619
Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of δ18O and δ D are ? 6·43‰ and ? 41·35‰ for Ames, ? 7·53‰ and ? 51·33‰ for Cedar Falls, and ? 6·01‰ and ? 38·19‰ for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi‐arid mid‐continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are δ D = 7·68 δ18O + 8·0 for Ames, δ D = 7·62 δ18O + 6·07 for Cedar Falls, and δ D = 7·78 δ18O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub‐humid in the east to semi‐arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub‐humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d‐excess values are 10·06‰ for Ames, 8·92‰ for Cedar Falls and 9·92‰ for Iowa City. Eighty seven percent of the samples are within the global d‐excess range of 0‰ and 20‰. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on δ18O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

16.
Oxygen and hydrogen isotopic compositions were measured on 12 serpentine and 2 actinolite samples from the Troodos ophiolite complex, Cyprus. The single analyzed antigorite(δD= ?60, δ18O= 7.1) is isotopically similar to all previously analyzed antigorites from ultramafic bodies. However, although their D/H ratios are relatively “normal”(δD= ?70to?92), the δ18O values of most of the Troodos lizardite-chrysotile serpentines (+12.6 to +14.1) are much higher than the 2.0–9.3‰ range typically found in such serpentines. Such high δ18O values have previously been found only in the serpentine-like mineraloids termed “deweylites”, which apparently formed at Earth-surface temperatures, and in a single sample from Vourinos, Greece that is in contact with high-18O limestone. The Troodos lizardite-chrysotile samplescannot have formed by reaction with heated ocean waters, but instead must have formed in contact with large amounts of some type of meteoric, metamorphic, or formation water, either (1) at very low temperatures in a near-surface environment, or (2) at about 100°C from waters that were abnormally enriched in18O(δ18O ≈ +4 to +8). The latter possibility seems most plausible inasmuch as extensive evaporites were deposited throughout the Mediterranean Sea during the late Miocene, and this would have been accompanied by strong18O enrichments of the local meteoric waters. Heated ocean waters, however, probably were responsible for the formation of the actinolitic amphiboles(δ18O= 4.6 to 5.5; δD= ?51to?46) from the gabbro and ultramafic zones in the Troodos complex. The amphiboles must have formed at considerably higher temperatures and at an earlier stage than the lizardite-chrysotile serpentinization.  相似文献   

17.
Water resources are the most critical factors to ecology and society in arid basins, such as Kaidu River basin. Isotope technique was convenient to trace this process and reveal the influence from the environment. In this paper, we try to investigate the temporal and spatial characteristics in stable isotope (18O and 2H) of surface water and groundwater in Kaidu River. Through the water stable isotope composition measurement, spatial and temporal characteristics of deuterium (δ2H) and oxygen 18 (δ18O) were analysed. It is revealed that (1) comparing the stream water line with the groundwater line and local meteorological water line of Urumqi City, it is found that the contribution of precipitation to surface water in stream runoff is the main source, whereas the surface water is the main source of groundwater. Groundwater is mainly drainage of surface runoff in the river; (2) in the main stream of Kaidu River, the spatial variability of river water showed a ‘heavier‐lighter‐heavier’ change along with the main stream for δ18O, and temporal variability showed higher in summer and lower in winter; (3) the δ18O and δ2H values of groundwater samples ranged from ?11.36 to ?7.97‰ and ?73.45 to ?60.05‰, respectively. There is an increasing trend of isotopic values along the groundwater flow path. The seasonal fluctuation of δ18O is not clear in most samples. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

18.
The stable isotopic (2H/1H and 18O/16O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ 18O of precipitation was with local surface relative humidity. The reduced major axis precipitation weighted local meteoric water line was δ 2H = 7.20 δ 18O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ 2H ? 8 δ 18O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water. Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were 18O and 2H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean. The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
The coastal confined aquifer in the Gulf of Urabá (Colombia) is an important water source for the banana agro‐industry as well as for urban and rural communities. However, the main processes controlling recharge and mixing in the aquifer are still poorly understood. Hydrochemical analyses and stable isotope monitoring were conducted to (a) determine groundwater recharge origin, mean groundwater age, and the main processes governing groundwater chemistry and the potential mixing of marine water and the influence of diffusive processes from the two surrounding aquitard layers. Hydrochemical data indicate that the main processes affecting the dissolved chemical composition include cation exchange, dissolution of carbonated and CO2, and silicate weathering. δ18O and δ2H compositions combined with 14C data highlight the differences in climatic conditions between the recharge zone and the confined section of the aquifer, which is close to the Atlantic Ocean. Groundwater samples with 14C ages from recent to 28,300 years BP show a depleted isotopic trend ranging from ?6.43‰ to ?9.14‰ in δ18O and from ?43.2‰ to ?65.7‰ in δ2H. The most depleted δ18O and δ2H compositions suggest a cooler recharge climate than the current conditions (corresponding to the last glacial period of the late Pleistocene). Depleted δ13C values in the total dissolved inorganic carbon indicate the existence of organic material oxidation processes within the geologic formation. These results can be used or transferred to enhance groundwater modelling efforts in other confined coastal aquifers of South America where scarcity of long‐term monitoring data limits water resources planification under a changing climate.  相似文献   

20.
Oxygen and carbon isotopic analyses were carried out for some typical submarine volcanic products (a lava flow, a pillow fragment and four hyaloclastite breccias) from the northwestern zone of the Mt. Iblei volcanic complex, eastern Sicily. The δ18O value of the perental basaltic magma (6.0 ± 0.2‰), estimated from the analyses of some fresh unaltered glassy samples of various type, lies in the values range of primary basalts. Appreciably higher δ18O values, probably due to low-temperature exchanges with sea water, have been found for lava samples and the interior of the pillow fragment. The δ18O and δ13C of the calcites of the groundmass of the hyaloclastite samples, ranging from 30.59 to 33.65 and from ?2.99 to 0.46‰ respectively, are typical of low-temperature marine carbonates. Because calcite is one of the last minerals to form. these results suggest that the hyaloclastites studied formed entirely in a submarine environment. The18O/16O ratios recorded in the silicate portions of the matrices of the hyaloclasites (δ18O=13.99 to 16.61) are interpreted as the result of halmyrolytic processes occurring at temperatures somewhat higher than that of the sea floor.  相似文献   

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