Isotopic Composition Of Rainwater Research Articles

High‐resolution stable isotope profiles from shells of the land snailPlacostylusreveal contrasting patterns between snails originating from New Zealand and New Caledonia

ABSTRACTThe stable oxygen (δ18Oshell) and carbon (δ13Cshell) isotope ratios retrieved from the carbonate shell of terrestrial gastropods can be used as an environmental proxy and are thought to reflect dietary composition and ambient climatic conditions (e.g. precipitation amount, humidity, temperature). Here, we generate high‐resolution isotopic profiles of nine modern land snails of the genusPlacostylus, collected from two locations in New Caledonia and one location in New Zealand. We found that snails from New Zealand had, on average, higher δ18Oshellvalues than their counterparts in New Caledonia, which surprisingly runs counter to the expected relationship based on the isotopic composition of rainwater between these two regions. Specimens from New Caledonia exhibit ephemeral decreases in their δ18Oshellvalues, which could be linked to extreme precipitation events in this region, while snails from New Zealand have less variation in their δ18Oshellvalues. Snails from New Zealand had, on average, slightly higher δ13Cshellthan their counterparts in New Caledonia, but a large difference in carbon isotopes was sometimes observed between snails collected at the same location. Most snails exhibit a temporal trend in their δ13Cshellvalues, indicating potential shifts in diet through to maturity.

The Absolute Age and Origin of the Giant Gypsum Geode of Pulpí (Almería, SE Spain)

Subaqueous gypsum (CaSO4·2H2O) crystals are relatively common in epithermal systems where sulfide ore deposits are present. The Giant Geode of Pulpí (Almería, SE Spain) hosts some of the largest (up to 2 m in length) subaqueous gypsum crystals discovered to date. Here, we present the first U-series ages of its crystals and reconstruct the oxygen and hydrogen isotopic composition (δ18O and δ2H) of the Pulpí paleo-aquifer from which the crystals formed by using stable isotopes of gypsum hydration water. We successfully dated the onset of gypsum precipitation in the Geode at 164 ± 15 ka. However, the extremely low U concentration (11 ppb) and relatively high detrital Th content (230Th/232Th 3.2) hinder accurate dating other gypsum samples. The δ18O and δD values of the paleo-aquifer during the growth of the crystals aligned with the local meteoric water line, suggesting that the sulfate-enriched mother solution consisted of meteoric water that recharged the aquifer during that period. The mean isotopic composition of the Pulpí paleo-aquifer (δ18O = −6.5 ± 0.1‰ and δ2H = −42.3 ± 0.5‰) during the formation of the crystals was similar to the current groundwater in this area (δ18O = −6.1 ± 0.8‰, δ2H = −42 ± 6‰). The isotopic differences observed in samples collected from distinct locations and in individual crystals were probably related to changes in the isotopic composition of the aquifer, as a consequence of varying climate that impacted on the isotopic composition of rainwater during thousands of years in this region. Our results indicated that subaqueous selenite crystals may be useful for paleo-hydrological reconstructions. However, improving the current analytical techniques for dating gypsum with low U concentrations will be essential to obtain accurate and reliable records from Quaternary gypsum cave crystals in the future.

Study on the isotopic compositionof rainwater in Long Khanh city,Southeast of the Mekong Delta region

The 2H/1H and 18O/16O isotope ratios in rainwater bring a lot of information about the fractionation of water molecules in the hydrosphere. The relationship between the isotope ratios of rainwater in an area characterised by the local meteoric water line, which is known as a reliable reference value for studies related to the identification of the recharge source of groundwater and climate change investigations. This study aims to establish a local meteoric water line in Long Khanh city (LK LMWL) in the period of 2020-2021, which is considered as a basis for research on the origin of groundwater in the area of Long Khanh city and subsequent studies on the origin of groundwater in the Southeast of the Mekong Delta region and the Dong Nai river basin. Results show that δ2H in rainwater ranges from -73.64 to 0.36 (‰ VSMOW) with an average value of -49.74‰ (n=19) and that figure of δ18O ranges from -10.91 to -1.59 (‰ VSMOW) with a mean of -7.68‰ (n=19). Due to the amount and specific meteorological conditions of the region, δ2H and δ18O in rainwater are enriched in the dry season but deplete in the rainy season. The LK LMWL follows a model of δ2H=(7.89±0.38)xδ18O + (10.28±2.93) (R2=0.96, n=19), which shows that the isotopic composition of δ18O in rainwater is more enriched than the isotopic composition of δ2H. The deuterium excess (d-excess) of rainwater in the region is found to be 10.28±2.93‰, which is comparable to those for the global scale of 10‰.

A Multiparametric Approach for Evaluating the Current Carbonate Precipitation and External Soil of Nerja Cave (Málaga, Spain)

The soil above on a cave may act as a regulator of the changes occurring in and on the cavity, modifying water infiltration and retention and providing organic matter, clay minerals, and nutrient elements, all of them essential for the growth of microorganisms and precipitates inside the cave. We assessed the mineralogical and geochemical composition of the soil lying upon Nerja Cave (Malaga, S Spain), as well as its textural properties and some biochemical parameters. At the same time, the isotopic composition of rainwater, drip water and current carbonate precipitated in Nerja Cave was monitored to establish relationships among them. In situ precipitation measurement dishes were placed in strategic areas of the cave, and environmental variables—temperature, humidity and CO2 content of the air—were recorded. The soil sample composition, despite some variation with distance to the cave entrance, can be considered quite homogeneous. Carbonate precipitates do not show dissolution traces. Isotopic data obtained from carbonate precipitates and drip water show an isotopic lightening of δ18O throughout the entire process. The most anthropized soils favor higher water infiltration rates, thus affecting the precipitation of carbonates inside the cave. A significant inverse relationship was observed between the δ13C values of the precipitates and the drip water rates.

Isotopic Study of Springs Near Haditha Dam Western Iraq

Stable isotopic technique and hydrochemistry was used in studying the water resources interaction of near Haditha Reservoir area, western Iraq. Throughout the study area, 14 groundwater samples (Bashina, Zwachi springs and Wells), 8 surface water samples from the study area, and 7 spring samples were analyzed for 2H and 18O stable isotopes and hydrochemical analysis. In this study, the temperature, altitude and continental effects on the isotopic composition of rain water in Iraq were studied. The climate of the study area is classified as semi-arid to arid region. The results show a variation in the isotopic values of Haditha reservoir and Euphrates river. This variation is due to the effect of the low surface area and the low velocity of water of Haditha Reservoir on the amount of evaporation, compared with the high velocity and the large surface area of Euphrates river. There was a variation in the isotopic values between Bishina and Zwachi springs, due to two factors that appear to modify the isotopic signatures of the springs, namely the lack of hydraulic connection between the springs of Bishina and Zwachi, meaning that they recharge from different sources. The changes in oxygen isotope composition of the groundwater between a deep reservoir and the springs (Bishina) may be caused by the dilution with near surface waters (Haditha reservoir) with different oxygen isotope compositions. The variation in the isotopic content in the studied area indicated that there are various origins of springs recharge and a different interactions of the multiple sources of springs with the mutli-depths of springs water.

Experimental evaluation of oxygen isotopic exchange between inclusion water and host calcite in speleothems

Abstract. The oxygen and hydrogen isotopic compositions of water in fluid inclusions in speleothems are important hydroclimate proxies because they provide information on the isotopic compositions of rainwater in the past. Moreover, because isotopic differences between fluid inclusion water and the host calcite provide information on the past isotopic fractionation factor, they are also useful for quantitative estimation of past temperature changes. The oxygen isotope ratio of inclusion water (δ18Ofi), however, may be affected by isotopic exchange between the water and the host carbonate. Thus, it is necessary to estimate the bias caused by this postdepositional effect for precise reconstruction of paleotemperatures. Here, we evaluate the isotopic exchange reaction between inclusion water and host calcite based on a laboratory experiment involving a natural stalagmite. Multiple stalagmite samples cut from the same depth interval were heated at 105 ∘C in the laboratory from 0 to 80 h. Then, the isotopic compositions of the inclusion water were measured. In the 105 ∘C heating experiments, the δ18Ofi values increased from the initial value by 0.7 ‰ and then remained stable after ca. 20 h. The hydrogen isotope ratio of water showed no trend in response to the heating experiments, suggesting that the hydrogen isotopic composition of fluid inclusion water effectively reflects the composition of past drip water. We then evaluated the process behind the observed isotopic variations using a partial equilibration model. The experimental results are best explained by the assumption that a thin CaCO3 layer surrounding the inclusion reacted with the water. The amount of CaCO3 that reacted with the water is equivalent to 2 % of the water inclusions in molar terms. These results suggest that the magnitude of the isotopic exchange effect has a minor influence on paleotemperature estimates for Quaternary climate reconstructions.

Controls on the Isotopic Composition of Precipitation in the South‐Central United States

AbstractThe processes that control the isotopic composition of precipitation in the midlatitudes are complicated, but can provide valuable insights into precipitation‐generating processes and are critical for interpreting stable isotope‐based paleoclimate records. In this study, we investigated the controls on changes in the isotopic composition of rainwater in central Texas using a combination of existing monthly stable isotope data from the global network of isotopes in precipitation and 20 months of event‐based rainwater collection from Austin, TX. We find that the strongest control on the isotopic composition of precipitation is the varying proportion of convective and stratiform rainfall, with other factors such as precipitation amount, temperature, and storm track playing a secondary role. Isotopic values are generally lower in the cold season than the warm season precipitation because cold season precipitation is predominantly stratiform often associated with a northerly storm track. However, the majority of the precipitation in the south‐central United States occurs during the warm season in association with mesoscale convective systems (MCSs) that are fed with moisture by the southerly winds. MCSs are characterized by a combination of a leading edge of organized deep convection and trailing stratiform precipitation. Stronger MCSs tend to contain higher proportions of stratiform rainfall and, as a result, have more isotopically depleted values. Therefore, changes in the stable isotopic composition of rainfall may be interpreted as reflecting changes in the intensity of MCS.

Atmospheric controls on the precipitation isotopes over the Andaman Islands, Bay of Bengal.

Isotopic analysis of precipitation over the Andaman Island, Bay of Bengal was carried out for the year 2012 and 2013 in order to study the atmospheric controls on rainwater isotopic variations. The oxygen and hydrogen isotopic compositions are typical of the tropical marine sites but show significant variations depending on the ocean-atmosphere conditions; maximum depletion was observed during the tropical cyclones. The isotopic composition of rainwater seems to be controlled by the dynamical nature of the moisture rather than the individual rain events. Precipitation isotopes undergo systematic depletions in response to the organized convection occurring over a large area and are modulated by the integrated effect of convective activities. Precipitation isotopes appear to be linked with the monsoon intraseasonal variability in addition to synoptic scale fluctuations. During the early to mid monsoon the amount effect arose primarily due to rain re-evaporation but in the later phase it was driven by moisture convergence rather than evaporation. Amount effect had distinct characteristics in these two years, which appeared to be modulated by the intraseasonal variability of monsoon. It is shown that the variable nature of amount effect limits our ability to reconstruct the past-monsoon rainfall variability on annual to sub-annual time scale.

Isotopic study of water resources in a semi-arid region, western Iraq

Hydrochemistry and stable isotopic technique were used in studying the water resources interaction in a semi-arid area, western Iraq. Throughout Iraq, 28 groundwater samples, 7 surface water samples from the study area, and 18 rainwater samples were analyzed for 2H and 18O stable isotopes and hydrochemical analysis. In this study, the temperature, altitude and continental effects on the isotopic composition of rain water in Iraq were studied. The results show that isotopes content in rainwater, in the current study, increases with increasing temperature and a good correlation exists between increasing latitude with decreasing δ 18O values. Rainwater isotopes show evidence of temperature effect and continental effect associated with altitude effect. Generally, due to variation in temperature and altitude throughout Iraq, the values of isotopic composition of rainwater range from (−7.25 ‰) to (−2.79 ‰), and from (−45 ‰) to (−9.7 ‰) for δ18O and δD, respectively. The similarity of isotopic composition of water of the Euphrates River and Haditha reservoir with that of groundwater taken from neighbor wells gives indication that intermixing between them is exist, while the groundwater of the wells far from the surface water resources is mostly affected by rainwater.

An assessment of water resources in Sinai Peninsula, using conventional and isotopic techniques, Egypt

This paper aims to reveal and to assess the groundwater availability of major multi-layered aquifer systems in Sinai. Eight major aquifer systems were identified in Sinai. These major aquifer systems spread under large areas of Sinai (61,000 km2). Isotopic characteristics for each aquifer system were expressed in terms of Oxygen-18(δ18O), deuterium (δ2H) as well as the characteristics of deuterium excess (d-excess). The hydrologic difference is reflected by d-excess instead of δ18O. The low 'd-excess' values (≤ 10) as 6‰ for quaternary aquifer and 8.6‰ for Nubian sandstones aquifer suggest that there is significant evaporation of rainwater leaving the residual groundwater with lower values of 'd-excess'. High d-excess values (> 10‰) are largely from the Jurassic and Eocene aquifers with 12‰ for Jurassic and from 9 to 11‰ for Eocene aquifers respectively. Isotopic data have reflected different slopes and different constants expressing the non-homogeneity in the isotopic composition of rainwater recharging the aquifers of Sinai, due to the presence of different air masses.

Immigration to Tikal, Guatemala: Evidence from stable strontium and oxygen isotopes

This paper presents strontium and oxygen isotopic measurements on archaeological human teeth from the ancient Maya city of Tikal, Guatemala, that illuminate the role that migration played in the history of the state. Stable strontium isotope ratios of human teeth parallel the bedrock geology of the location where foods were grown, while stable oxygen isotope ratios reflect the sources of water imbibed, and track geographic variation in the isotopic composition of rain water. Because tooth enamel forms during childhood and is not remodeled during life, we can identify foreign-born individuals at Tikal by their outlying strontium and oxygen isotope ratios. These data indicate that approximately 11–16% of the sampled Tikal skeletons spent their childhood at distant sites. Most of the migrant burials date from the Early Classic period and are high status contexts. Several royal burials demonstrate long distance movement of both males and females, and shed light on the identification of epigraphically-known individuals. Yet, both Early and Late Classic migrants are found in lower status domestic burials. Interaction with distant peers was important in the rise of the Tikal polity, however, immigration from all social tiers contributed to the city’s rapid population growth.

Deuterium excess reveals diurnal sources of water vapor in forest air

An understanding of atmospheric water vapor content and its isotopic composition is important if we are to be able to model future water vapor dynamics and their potential feedback on future climate change. Here we present diurnal and vertical patterns of water isotope ratios in forest air (δ(2)H(v) and δ(18)O(v)) not observed previously. Water vapor observed at three heights over 3 consecutive days in a coniferous forest in the Pacific Northwest of the United States, shows a stratified nocturnal structure of δ(2)H(v) and δ(18)O(v), with the most positive values consistently observed above the canopy (60 m). Differences between 0.5 m and 60 m range between 2-6‰ for δ(18)O and 20-40‰ for δ(2)H at night. Using a box model, we simulated H(2)O isotope fluxes and showed that the low to high δ(2)H(v) and δ(18)O(v) profiles can be explained by the vapor flux associated with evaporation from the forest floor and canopy transpiration. We used d-excess as a diagnostic tracer to identify processes that contribute to the diurnal variation in atmospheric moisture. Values of d-excess derived from water vapor measurements showed a repeated diel pattern, with the lowest values occurring in the early morning and the highest values occurring at midday. The isotopic composition of rain water, collected during a light rain event in the first morning of our experiment, suggested that considerable below-cloud secondary evaporation occurred during the descent of raindrops. We conclude that atmospheric entrainment appears to drive the isotopic variation of water vapor in the early morning when the convective boundary layer rapidly develops, while evapotranspiration becomes more important in the mid-afternoon as a primary moisture source of water vapor in this forest. Our results demonstrate the interplay between the effects of vegetation and boundary layer mixing under the influence of rain evaporation, which has implications for larger-scale predictions of precipitation across the terrestrial landscape.

Relationship between the origin of precipitation in the Jordan Rift valley and their geochemical composition

Rainwater was sampled during seven winters at eight sites along the Jordan Rift valley in Israel. The study area is divided into two regions: the northern part located between the Sea of Galilee and the Dead Sea and the southern part between the Dead Sea and the Dead Sea–Red Sea water divide line in the Arava valley. The Dead Sea region is considered as a desert, the northern part of the study area is semidesert whereas the southern region is considered as extreme desert. Good agreement was found between the chemical and isotopic composition of rainwater its sources and air mass trajectories. In the arid areas, the contribution of salts was mainly from local sources (of up to 500 Km in diameter). Significant chemical divergence was found between rainwater deriving from marine air masses characterized by NaCl enrichment and rainwater deriving from continental air masses which are mainly characterized by Ca‐carbonate enrichment. Six main marine and continental air mass trajectories were defined, i.e., northern, northwestern, western, southwestern, eastern and local. The northern air mass trajectories contribute more salts than the southwestern air mass trajectories which exhibit the lowest rainwater salinities. The western trajectory is exclusively marine originating from the Mediterranean, while the eastern trajectory is exclusively continental and originates in the Arabian Desert. Rainwater isotopes revealed three chemically differing systems. The western marine trajectories reflect chemical setting associated with East Mediterranean Meteoric Water Line system; the continental air masses are mainly associated with the Mean Meteoric Water Line system; and whenever the eastern component is significant, a Local Meteoric Water Line prevails.

Influence of small‐ and large‐scale variables on the chemical and isotopic compositions of urban rainwater, as illustrated by a case study in Ashdod, Israel

The source of air pollution must be identified to select the appropriate monitoring activities and remedial measures. The present case study illustrates how analyses of (1) regional‐scale synoptics and air mass trajectories, (2) local‐scale atmospheric measurements (wind direction and speed, air temperature, dust load, sulfur and nitrogen oxide concentrations in the air, rain amount, and intensity) and (3) chemical and isotopic compositions of rainwater from 46 rain events, collected in the coastal city of Ashdod, Israel, were used to identify the various sources contributing to rainwater salts and contaminants and their timing. Rainwater affected by the Mediterranean Sea was characterized by a large marine fraction of salts, high chloride concentrations, and low values of δ18O and δD. These rain events were associated with the Cyprus Low system, which typically prevails in midwinter. Rainwater affected by continental sources had a small contribution of marine salts, high bicarbonate and calcium concentrations, and high values of δ18O and δD. These rains were related to continental trajectories from the Red Sea and north African coast prevailing during the fall and spring. Rainwater affected by anthropogenic sources was characterized by low marine fraction, high sulfate concentrations, and low values of δ34S. Whereas remote anthropogenic source was associated with the Red Sea trough system and were characterized by high nitrate concentrations (representing desert dust), the local anthropogenic source was characterized by high air concentrations of sulfur oxides at the local monitoring stations and high potassium and low nitrate concentrations. The identification of local anthropogenic source suggests that measures taken to reduce emissions from local oil refineries and power stations are likely to reduce the overall air pollution in the study area.

Origin of rainwater acidity near the Los Azufres geothermal field, Mexico

The chemical and isotopic compositions of rainwater were monitored at Los Azufres geothermal field (88 MWe) and its surroundings during May – September 1995, which is the rainy season. Samples were collected from eight sites: three within the field, three in its surroundings and two sufficiently far from the field such that they have no geothermal input. The concentrations of Cl −, SO 4 2− and NO 3 − were measured in about 350 samples and found to be generally <5 ppm. Chloride concentrations remained constant with time, but sulfate and nitrate concentrations decreased, which suggests a nearby industrial source for the sulfate and nitrate. A mixing model for Cl −, SO 4 2− and δ 34S also suggests an industrial source for the rainwater sulfur. The determination of pH was found to be necessary, but is not sufficient to characterize rainwater acidity. The Gran titration method was used to determine alkalinity with respect to equivalence point of H 2CO 3 ∗. Values of alkalinity were found to range from 10 −4 to 10 −6 eq/L, and were negative only for some samples from Vivero and Guadalajara. Thus, SO 4 2− and NO 3 − are in general not in acidic form (i.e. balanced by Na +, Ca 2+, etc. rather than H +). Sulfate δ 34S values were about −1.5‰ in Los Azufres and its surroundings, and in Morelia, but differed from the value of −0.2‰ for Guadalajara. The δ 34S values for H 2S from the Los Azufres geothermal wells are in the range −3.4 to 0.0‰. The δ 34S ranges for the natural and anthropogenic sources for environmental sulfur overlap, making it difficult to differentiate between the contribution of different sources. However, a similarity of values of δ 34S at Los Azufres and Morelia (85 km distant) suggest a regional source of sulfate that is not associated with geothermal emissions from Los Azufres.

Evaluation of evaporation rate from forested soil surface using stable isotopic composition of soil water in a headwater basin

The stable isotopic composition of rain water and soil water was analysed and the soil surface evaporation rate was evaluated using the isotope value of soil water taken from a forested headwater basin in central Japan. Rainfall, throughfall, soil water, groundwater and discharge water were sampled at intervals of one month to determine the isotopic compositions of deuterium (D) and oxygen-18 (18O) therein. In addition, tensiometric observation of soil water was performed continuously. The stable isotopic ratio of soil water was homogenized between the soil surface and a depth of 100 cm by means of active soil water movement above 100 cm in depth. The mean δ18O in deep soil water below a depth of 100 cm was 0·24‰ higher than the volume weighted mean δ18O in throughfall. Consequently, the mean evaporation rate from the soil surface was calculated as 5% of the evapotranspiration rate using the difference between the δ18O in throughfall and in deep soil water, based on the Rayleigh equation under equilibrium condition. Copyright © 1998 John Wiley & Sons, Ltd.

Isotope composition of rain water, well water and fumarole steam on the island of Vulcano, and their implications for volcanic surveillance

Abstract Water samples from eight wells in the Vulcano Porto area and fumarole steam from the crater of Vulcano (Southern Italy) were collected at monthly intervals over a two-year period from February 1987 to January 1989. Samples of bulk precipitation were also collected in three points at Vulcano Porto and Vulcano Piano (island of Vulcano) and Castroreale (Tyrrhenian coast of Sicily), again at monthly intervals. The weighted mean isotopic composition of rain water on Vulcano is δ D =−32‰ , and δ D 18 O =−6.4‰ . Results for well waters tend to support the existence of at least two water bodies: one of purely meteoric water and the other of brackish thermal water. An intermediate water body, probably the result of mixing of the other two, was also recognized. The isotope composition of fumarolic steam from the crater suggests the mixed contribution of both sea and rain waters, although mixing is not the only process occurring. The existence of a deep marine-brine body is inferred, characterized by δD and δ18O values more positive than those of Mediterranean sea water. A close relationship, indicating common source effects, is shown by temporal isotopic variations at some wells and the fumarolic steam, wich may be used for volcano survey at distance from the active crater.

雨水の安定同位体組成

雨水の安定同位体組成

The relation between air mass trajectories and the water isotope composition of rain in the Mediterranean Sea area

The isotopic composition of rainwater near Nahariya, Israel, was measured in 12 individual storms during the winter months of 1980/1981. Rains most depleted in the heavy stable isotopes and enriched in tritium are associated with air masses which come from North East Europe and have a short, intense interaction with the East Mediterranean Sea. Storms most enriched in 18O and D and depleted in tritium are associated with air masses which come from the Atlantic Ocean and enter the Mediterranean Sea on its western part, travelling along the North African Coast, sometimes with a southerly shift. A relatively high correlation coefficient was found between the stable isotopic content of precipitation and the 800 mb temperature.