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Isotope-enabled General Circulation Models (GCMs) simulate isotope ratios 18O/16O and D/H (expressed as δ18O and δD) in precipitation. The present study evaluates the skills of seven such GCMs in simulating the monthly average precipitation δ18O and δD values over three Indian regions (west coast India WCI, east coast India ECI, and north India NI) during the summer monsoon season (June–September). Analyses show that models underestimate the mean isotope values over WCI and ECI but have variable responses over NI. The mean bias (Δ = model-observed) in the δ18O values varies from − 0.8‰ (GENESIS) to − 4.1‰ (HadAM3) over WCI and from − 0.2‰ (LMDZ4) to − 6.4‰ (GENESIS) over ECI. Overall, the IsoGSM model simulates isotopes and physical fields better. Observed isotope data show only minor dependence on the rainfall (amount effect) in WCI and ECI, but in contrast, most of the models show a substantial amount effect. The model δ18O value decreases with increasing rainfall at a rate of − 1‰/100 mm/month to − 6‰/100 mm/month. Apart from the local factors (temperature, humidity, and rainfall), isotope biases are also affected by large-scale atmospheric circulation in some models. A decomposition of the isotope biases over WCI resulting from five major processes (vapor formation, uplift, transport, condensation, and raindrop evaporation) is explored. This exercise suggests that the skill of the models depends on how proficiently the models simulate (1) mid-tropospheric vapour isotope values and (2) raindrop evaporation. A strong positive correlation between the biases in isotope values and raindrop evaporation across models shows that an increase of about 7‰ in δD bias of the models occurs for a 10% increase in the evaporation bias. [ABSTRACT FROM AUTHOR]

Patterns of stable isotopes of water (18O and 2H) in precipitation have been used as tracers for analyzing environmental processes which can be changed by factors such as the topography or meteorological variables. In this study, we investigated the isotopic data in precipitation for one year in the low mountain range of North Hesse, Germany, and analyzed mainly for altitude, rainfall amount, and air temperature effects on a regional scale. The results indicate that the isotopic composition expressed an altitude effect with a gradient of −0.14‰/100 m for δ18O, −0.28‰/100 m for δ2H and 0.83‰/100 m for Deuterium excess. Patterns of enrichment during warmer months and depletion during colder months were detected. Seasonal correlations were not consistent because the altitude effect was superimposed by other processes such as amount and temperature effects, vapor origins, orographic rainout processes, moisture recycling, and sub-cloud secondary evaporation. Precipitation was mostly affected by secondary evaporation and mixing processes during the summer while depleted moisture-bearing fronts and condensation were more responsible for isotope depletion during winter. In autumn and spring, the amount effect was more prominent in combination with moisture recycling, and large-scale convective processes. The altitude effect was also detected in surface water. The investigated elevation transect with multiple stations provided unique insights into hydrological and climatic processes of North Hesse on a regional scale. The spatial heterogeneity and mixing of different processes suggest that multiple rainfall stations are required when rainfall isotopes serve as forcing data for hydrological applications such as transit time assessments in complex terrains. [ABSTRACT FROM AUTHOR]

Abstract Rising temperatures and changing dynamics can both moisten the air, making it difficult to disentangle these interrelated drivers of water cycle change. However, work by Camille Risi and colleagues presents a new way to distinguish their effects. Using large‐eddy simulations with water isotopic tracers, they show that while warming the sea surface increases the ratio of isotopically heavy‐to‐light water in the tropical marine subcloud layer, strengthening the moisture flux convergence decreases it. This divergent response provides a new framework for examining the complex mechanisms that regulate the development of convection and, ultimately, cloudiness—a target of the 2020 international field campaign EUREC4A (ElUcidating the RolE of Clouds‐Circulation Coupling in ClimAte). Moreover, their findings provide a clearer picture of why water isotopes recorded in tropical paleoproxies are a valuable lens through which to view changes in moisture transport in the past.

Abstract Modern observations from Bay of Bengal (BOB) head have shown that precipitation δ18O value reaches the lowest stage during late postmonsoon when the summer monsoon has weakened or retreated, complicating the traditional interpretation of low δ18O value as strong monsoon. We show that this postmonsoon 18O depletion phenomenon exists from BOB periphery to the southeast and south Tibetan Plateau. Accumulative precipitation along back‐trajectory still explains daily precipitation δ18O variability during both the monsoon and nonmonsoon, thus indicating that longer‐term weighted‐mean δ18O is biased toward synoptic conditions during precipitation events. Further, we propose that transport of moisture from the east (west) of the India‐Burma Trough leads to depleted (enriched) 18O during the postmonsoon (premonsoon). Our results reconcile the apparent contradiction but beg the consideration of potential bias and influence of different precipitation regimes in paleo archives.

Rising temperatures and changing dynamics can both moisten the air, making it difficult to disentangle these interrelated drivers of water cycle change. However, work by Camille Risi and colleagues presents a new way to distinguish their effects. Using large‐eddy simulations with water isotopic tracers, they show that while warming the sea surface increases the ratio of isotopically heavy‐to‐light water in the tropical marine subcloud layer, strengthening the moisture flux convergence decreases it. This divergent response provides a new framework for examining the complex mechanisms that regulate the development of convection and, ultimately, cloudiness—a target of the 2020 international field campaign EUREC4A (ElUcidating the RolE of Clouds‐Circulation Coupling in ClimAte). Moreover, their findings provide a clearer picture of why water isotopes recorded in tropical paleoproxies are a valuable lens through which to view changes in moisture transport in the past. Plain Language Summary: Rising temperatures and changing atmospheric motions can both moisten the air, making it difficult to disentangle these interrelated drivers of water cycle change. However, work by Camille Risi and colleagues presents a new way to distinguish their effects. Using numerical simulations of the atmosphere over tropical oceans, they show that while warming the sea surface increases the ratio of isotopically heavy‐to‐light water vapor (HDO/H2O) below the tropical cloud deck, strengthening the rate at which moisture is imported by winds decreases it. This opposite response provides a new framework for examining the complex mechanisms that regulate the development of tropical convection and clouds—a target of the 2020 international field campaign EUREC4A (ElUcidating the RolE of Clouds‐Circulation Coupling in ClimAte). Moreover, their findings provide a clearer picture of why water isotopes recorded in natural archives, such as the stalagmites and stalactites that form in caves, can reveal variations in atmospheric motion and moisture transport in the past. Key Points: Water isotopes distinguish the effects of surface temperature and moisture convergence on tropical humidity and convectionThe distinct isotopic response can help evaluate thermodynamic and dynamic drivers of water cycle changeStronger convergence decreases tropical isotope ratios, which explains why the latter often anticorrelates with precipitation amount [ABSTRACT FROM AUTHOR]

Stable isotopes in precipitation and spring water were observed in a low mountain region, because seasonal variability in isotope altitude and amount effects based on their simultaneous observations in low latitude area have not been studied so much. Seasonal variability in spatial averages of monthly δ18O and d-excess in precipitation ranged from −11.96 to −5.16 ‰ and from 8.0 to 24.2 ‰, respectively, while those in spring water ranged from −7.64 to −7.18 ‰ and from 11.0 to 13.6 ‰. The seasonal variability in spatial average of monthly δ18O in precipitation was much wider than in spring water. Monthly isotopic composition in spring water was mostly plotted along the local meteoric water lines for precipitation in warm months, suggesting that precipitation in warm months is the main source of spring water. Annual isotope altitude effects in precipitation (−0.12 ‰/100 m) and spring water (−0.13 ‰/100 m) were almost the same, and monthly isotope amount effects for cold months (−7.9 to −0.9 ‰/100 mm) were relatively higher than those for the warm months (−12.0 to −9.6 ‰/100 mm). The isotope amount effect at each sampling sites appeared using only the data in the warm months without extreme weather. [ABSTRACT FROM AUTHOR]

Modern observations from Bay of Bengal (BOB) head have shown that precipitation δ18O value reaches the lowest stage during late postmonsoon when the summer monsoon has weakened or retreated, complicating the traditional interpretation of low δ18O value as strong monsoon. We show that this postmonsoon 18O depletion phenomenon exists from BOB periphery to the southeast and south Tibetan Plateau. Accumulative precipitation along back‐trajectory still explains daily precipitation δ18O variability during both the monsoon and nonmonsoon, thus indicating that longer‐term weighted‐mean δ18O is biased toward synoptic conditions during precipitation events. Further, we propose that transport of moisture from the east (west) of the India‐Burma Trough leads to depleted (enriched) 18O during the postmonsoon (premonsoon). Our results reconcile the apparent contradiction but beg the consideration of potential bias and influence of different precipitation regimes in paleo archives. Plain Language Summary: Oxygen isotope signal (δ18O) retrieved from various geological archives, for example, speleothems, reflects paleo‐precipitation δ18O variability and has been used as a proxy of monsoon intensity in South Asia based on the generally negative correlation between δ18O and rainfall amount. However, precipitation δ18O over the Bay of Bengal (BOB) head shows the lowest values during September–October where rainfall peaks during June–August, complicating the interpretation of δ18O records from paleo archives. We show that daily precipitation δ18O variability still correlates with accumulative rainfall along moisture transport paths. While averaged toward monthly means, precipitation δ18O shows a more robust relationship with rainfall intensity rather than the classical monthly total rainfall, indicating that longer‐term mean δ18O is biased toward precipitation events. We further propose that moisture transport pathways from the east of the trough embedded in the southern branch westerlies after the summer monsoon lead to stronger isotopic distillation and thus more depleted precipitation 18O, and the opposite before the monsoon. Key Points: Precipitation 18O shows a postmonsoon depletion over Bay of Bengal head, and this phenomenon extends to a large region in South AsiaAccumulative precipitation along back‐trajectory well explains daily and monthly precipitation δ18O variabilitiesTransport of moisture from the front of the India‐Burma Trough leads to the postmonsoon 18O depletion and opposite for the premonsoon [ABSTRACT FROM AUTHOR]

The stable isotopic composition of materials such as glacial ice, tree rings, lake sediments, and speleothems from low-to-mid latitudes contains information about past changes in temperature (T) and precipitation amount (P). However, the transfer functions which link δ18Op to changes in T or P, dδ18Op/d T and dδ18Op/d P , can exhibit significant temporal and spatial variability in these regions. In areas affected by the Southeast Asian monsoon, past variations in δ18O and δD of precipitation have been attributed to variations in monsoon intensity, storm tracks, and/or variations in temperature. Proper interpretation of past δ18Op variations here requires an understanding of these complicated stable isotope systematics. Since temperature and precipitation are positively correlated in China and have opposite effects on δ18Op, it is necessary to determine which of these effects is dominant for a specific region in order to perform even qualitative paleoclimate reconstructions. Here, we evaluate the value of the transfer functions in modern precipitation to more accurately interpret the paleorecord. The strength of these transfer functions in China is investigated using multiple regression analysis of data from 10 sites within the Global Network for Isotopes in Precipitation (GNIP). δ18Op is modeled as a function of both temperature and precipitation. The magnitude and signs of the transfer functions at any given site are closely related to the degree of summer monsoon influence. δ18Op values at sites with intense summer monsoon precipitation are more dependent on the amount of precipitation than on temperature, and therefore exhibit more negative values in the summer. In contrast, δ18Op values at sites that are unaffected by summer monsoon precipitation exhibit strong relationships between δ18Op and temperature. The sites that are near the northern limit of the summer monsoon exhibit dependence on both temperature and amount of precipitation. Comparison with simple linear models (δ18Op as a function of T or P) and a geographic model (δ18Op as a function of latitude and altitude) shows that the multiple regression model is more successful at reproducing δ18Op values at sites that are strongly influenced by the summer monsoon. The fact that the transfer function values are highly spatially variable and closely related to the degree of summer monsoon influence suggests that these values may also vary temporally. Since the Southeast Asian monsoon intensity is known to exhibit large variations on a number of timescales (annual to glacial-interglacial), and the magnitude and sign of the transfer functions is related to monsoon intensity, we suggest that as monsoon intensity changes, the magnitude and possibly even the sign of the transfer functions may vary. Therefore, quantitative paleoclimate reconstructions based on δ18Op variations may not be valid. © 2004 Elsevier B.V. All rights reserved.

precipitation and evaporation are two vital components of water cycle, and Hydrogen and oxygen stable isotopes are important tracers in water, which are very sensitive to changes in the climate and the water cycle. Rayleigh Fractionation equation is usually applied to calculate isotope distributions in order to quantify the precipitation and evaporation processes. It is reasonable to explain the evaporation process using the Rayleigh fractionation equation. However, the composition of hydrogen and oxygen stable isotopes in the precipitation will change due to the effects of dynamic fractionation and dilution during raindrop fall. In this case, it is not feasible to rely entirely on the Rayleigh fractionation equation. In this paper, atmospheric precipitation isotopes data recorded during 1996–2016 in Hong Kong from the Global Network of Isotopes in Precipitation (GNIP) are analyzed, including local meteoric water line (LMWL), deuterium-excess (d), temperature effect and rainfall amount effect. The results indicate that precipitation is affected by secondary evaporation and dilution effects. In addition, the stable isotope composition in precipitation is the result of temperature and precipitation. Due to the effects of these two effects, changes of isotope composition in precipitation are not always consistent. When the rainfall density is very large, the temperature effect is covered up and the temperature is inversely related to the isotope composition of precipitation. In contrast, when the rainfall density is small, the temperature is positively related to the isotope composition of precipitation. Therefore, it is suggested to consider the rainfall density while studying the relationship between the isotope composition of precipitation and the local climate. These finds can provide some enlightenments and references on how to investigate the changing pattern of isotope composition in precipitation. [ABSTRACT FROM AUTHOR]

The dominant factor that controls the rainwater isotope ratios in the tropics is believed to be the local or instantaneous rainfall amount. This notion was challenged in several recent observations indicating that the stable ratios in rainwater are controlled by other factors such as source water composition and intensity of convective activity. Since amount effect is the basis for paleoclimate reconstruction of rainfall it is important to develop comprehensive knowledge about it at different time scales. Here we investigated the relationship of rainwater δ18O with the local or instantaneous rainfall amount at different time scales at two Indian stations, Thiruvananthapuram (TRV) and Bangalore (BLR), for four years covering the dual monsoon systems [Indian Summer Monsoon (ISM) and Northeast Monsoon (NEM)]. It was observed that the seasonal variations are more pronounced over BLR due to its continental location in the central Southern peninsular India, compared to TRV which is a coastal station. Isotopically enriched samples were found during seasonal high temperature and low relative humidity at the respective stations. The intra-event observations indicated that the 'amount effect' at the intra-event scale was significant due to post-condensation evaporation, which was supported by low d-excess values and its inverse correlation with rainfall amount. The correlation between event based δ18O and local rainfall amount for both the stations was weak (r = 0.2 and 0.3) whereas the isotopic signature was sensitive to the convective activity during the monsoon period. Significant negative spatio-temporal correlations of δ18O over the moisture convergence regions were obtained with proxies of convective activity over parts of the Arabian Sea as well as over the regions of moisture pathways associated with synoptic scale disturbances from the Bay of Bengal. We observed that the correlation pattern varies with the seasonal changes of moisture source and transport pathways during the periods of ISM and NEM. [ABSTRACT FROM AUTHOR]

Environmental isotope tracers were applied in the Upper Crocodile River Basin, Johannesburg, South Africa, to understand the groundwater recharge conditions, flow mechanisms and interactions between surface and subsurface water. Stable isotope analysis indicated that recharge into the fractured quartzite aquifer occurs through direct mechanisms. The high variability in the stable isotope signature of temporal samples from Albert Farm spring indicated the importance of multiple samples for groundwater characterization, and that using a single sample may be yielding biased conclusions. The observed inverse relationship between spring discharge and isotope signature indicated the traces of rainfall amount effect during recharge, thereby suggesting piston groundwater flow. It is deduced that a measured discharge value can be used in this relationship to calculate the isotopic signature, which resembles effective rainfall. In the shallow alluvial deposits that overlie the granitic bed-rock, piezometer levels and stable isotopes revealed an interaction between Montgomery stream and interflow, which regulates streamflow throughout the year. This suggests that caution should be taken where hydrograph separation is applied for baseflow estimates, because the stream flow that overlies such geology may include significant interflow. The hydrochemistry evolution was observed in a stream fed by karst springs. As pH rises due to CO2 degassing, CaCO3 precipitates, thereby forming travertine moulds. The values of saturation indices that were greater than zero in all samples indicated supersaturation by calcite and dolomite and hence precipitation. Through 14C analysis, groundwater flow rate in the karst aquifer was estimated as 11 km/year, suggesting deep circulation in karst structures.

Stable isotopes in precipitation, both liquid (rain) and solid (snow), can be suitable tracers for hydrological cycles because their concentrations reflect the cumulative record of physical phase changes. Distribution of stable isotopes in precipitation over High-Asian monsoon regions, including Yunnan Plateau is investigated. It has two noticeable features: firstly, the stable isotopes in precipitation distinctly decrease; and secondly, the stable isotopes in precipitation demonstrate smaller concentrations during rainy seasons and higher values during dry seasons. These features were found by the MUGCM simulation developed in the Melbourne Univertisty. Quantitative effect of the stable isotopes in precipitation takes place at different time scales, i.e. in diurnal, monthly or annual variations. Relative to observations, the simulated δ¹⁸O in precipitation shows stronger dependence on precipitation. In the diurnal course, the simulated regression equations of δ¹⁸O in precipitation versus precipitation amount are in good agreement with the observed values at Tengchong and Simao, except that the simulated δ¹⁸O/P curve slope is slightly smaller than the observed one at Mingzi. In the monthly and annual courses both, the simulated and observed δ¹⁸O/P slopes are smaller than it is in the diurnal course. For individual station, the local meteoric water line (LMWL) is simulated well at Mengzi and Tengchong. However, the simulated result does not reproduce truly the observed relationship between δD and δ¹⁸O in precipitation at Simao and Kunming where the LMWL inclination is larger 8.0, and a shift along the y-axis higher 10.0. In addition, all simulated LMWL slopes are higher the observed ones at four stations, suggesting that the GCM can overestimate the decreasing of Hydrogen Deuterium Oxide and, thus, underestimate the second-order parameter, i.e. the deuterium excess, in a particular region Yunnan.

Abstract: Because water isotope ratios respond to phase changes during evaporation (E) and precipitation (P), they are candidate fingerprints of changing atmospheric hydrology. Moreover, through preservation in ice cores and other paleoproxies, they provide important insight into the past. Still, there is disagreement over what specific attributes of hydroclimate variability isotopes reveal. Here we argue that variations in zonal mean isotope ratios of water vapor and precipitation are largely a response to geographically shifting patterns of E and P. Differences in the relative importance of local versus remote changes in these moisture variables explain the apparent distinct isotopic sensitivities to temperature and precipitation amount in high and low latitudes, respectively. Not only does our work provide a unified framework for interpreting water isotopic measurements globally, but it also presents a novel approach for diagnosing water cycle changes in a warmer world. [ABSTRACT FROM AUTHOR]

Many paleoclimatic records in Southeast Asia rely on rainfall isotope ratios as proxies for past hydroclimatic variability. However, the physical processes controlling modern rainfall isotopic behaviors in the region is poorly constrained. Here, we combined isotopic measurements at six sites across Thailand with an isotope-incorporated atmospheric circulation model (IsoGSM) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to investigate the factors that govern the variability of precipitation isotope ratios in this region. Results show that rainfall isotope ratios are both correlated with local rainfall amount and regional outgoing longwave radiation, suggesting that rainfall isotope ratios in this region are controlled not only by local rain amount (amount effect) but also by large-scale convection. As a transition zone between the Indian monsoon and the western North Pacific monsoon, the spatial difference of observed precipitation isotope among different sites are associated with moisture source. These results highlight the importance of regional processes in determining rainfall isotope ratios in the tropics and provide constraints on the interpretation of paleo-precipitation isotope records in the context of regional climate dynamics. [ABSTRACT FROM AUTHOR]

We measured the hydrogen and oxygen isotope composition (δ2H and δ18O) of precipitation and stream water from the Soft Plume River at multiple spatiotemporal scales on sub-Antarctic Marion Island, Indian sector of the Southern Ocean. Monthly precipitation δ2H and δ18O values ranged from -43.7‰ to -14.7‰ and from -7.0‰ to -3.3‰ (n=13), respectively. Stream water values ranged from -48.0‰ to -25.4‰ for δ2H and from -7.6‰ to -4.0‰ for δ18O (n=92). The monthly precipitation data yielded a local meteoric water line with the equation δ2H=8.4δ18O+11.4. There was no clear seasonality in isotope composition present in precipitation and stream water. Along the stream, no significant difference was observed between sites. However, δ2H and δ18O values were lower and more variable at the highest site. This is probably the result of the ‘amount effect’, where more precipitation fell at a higher elevation compared with a downstream site in the catchment. The findings illustrate spatiotemporal patterns in precipitation and stream water isotopes and provide insight into mechanisms affecting their composition on sub-Antarctic Marion Island. [ABSTRACT FROM AUTHOR]

Indian summer monsoon (ISM) rainfall is contributed by two moisture sources; Arabian Sea (AS) and Bay of Bengal (BoB). While monsoonal rainfall in eastern and central India is dominantly contributed by the vapor derived from BoB, the source of rainfall in western India is mostly from AS vapor. Meteorological conditions in these regions also differ. In contrast to the BoB component of monsoon in central India, temporal variations in the AS sourced rainfall from western India are poorly constrained due to lack of paleohydrological records. Towards this, pedogenic carbonates were collected from two chronologically constrained cliff sections in the Gujarat alluvial plain, western India. Oxygen isotopic ratio of carbonate (δ 18 O carbonate ) was used to reconstruct variation in AS derived rainfall and its influence on vegetation and fluvial systems in western India for the last 75 ka. A negative correlation between the δ 18 O value of modern rainwater and its amount (known as amount-effect) in the study site is used as a framework for interpreting variations in δ 18 O carbonate values. The amount-effect based monsoon reconstruction showed that two distinct dry phases at 75 ka to 60 ka and 30 ka to 10 ka were punctuated by a wet phase from 60 ka to 30 ka. These hydroclimatic variations in western India during the late Quaternary were responsible for the changes in regional fluvial architecture. Comparison with published records showed that fluctuations in the AS sourced rainfall were more pronounced compared to BoB component. Carbon isotopic ratio (δ 13 C) of carbonate and co-existing organic matter were used to reconstruct vegetation composition. Significant and strong positive correlation between δ 18 O carbonate and δ 13 C carbonate values indicated that rainfall amount controlled the relative abundance of C 3 -C 4 plants in western India during the late Quaternary period. Furthermore, C 3 plants were more abundant in western India for the last 75 ka relative to central India. [ABSTRACT FROM AUTHOR]

This paper presents the use of stable isotopes of water for hydrological characterization and flow component partitioning in the Red River Delta (RRD), the downstream section of the Red River. Water samples were collected monthly during 2015 from the mainstream section of the river and its right bank tributaries flowing through the RRD. In general, δ18O and δ2H river signatures were depleted in summer-autumn (May-October) and elevated in winter-spring (November-April), displaying seasonal variation in response to regional monsoon air mass contest. The Pacific equatorial-maritime air mass dominates in summer and the northern Asia continental air mass controls in winter. Results show that water of the RRD tributaries stems solely from local sources and is completely separated from water arriving from upstream subbasins. This separation is due to the extensive management of the RRD (e.g., dykes and dams) for the purposes of irrigation and inundation prevention. Mainstream river section δ18O and δ2H compositions range from −10.58 and −73.74‰ to −6.80 and −43.40‰, respectively, and the corresponding ranges inside the RRD were from −9.35 and −64.27‰ to −2.09 and −15.80‰. A combination of data analysis and hydrological simulation confirms the role of upstream hydropower reservoirs in retaining and mixing upstream water. River water inside the RRD experienced strong evaporation characterized by depleted d-excess values, becoming negative in summer. On the other hand, the main stream of the Red River has d-excess values around 10‰, indicating moderate evaporation. Hydrograph separation shows that in upstream subbasins, the groundwater fraction dominates the river flow composition, especially during low flow regimes. Inside the RRD, the river receives groundwater during the dry season, whereas groundwater replenishment occurs in the rainy season. Annual evaporation obtained from this hydrograph separation computation was about 6.3% of catchment discharge, the same order as deduced from the difference between subbasin precipitation and discharge values. This study shows the necessity to re-evaluate empirical approaches in large river hydrology assessment schemes, especially in the context of climate change. [ABSTRACT FROM AUTHOR]

Hydrogen (D) and oxygen (18O) stable isotopes in precipitation are useful tools in groundwater recharge and climatological investigations. This study investigated the isotopes in rainfall during the 2013 and 2014 hydrological years in the Douala and Yaounde urban cities. The objectives were to generate local meteoric water lines (LMWLs), define the spatialδ-temporal variations of the isotopes in rainwater and their relationship to the regional precipitation cycle, and determine the factors controlling the isotopic variation. The LWMLs in Douala and Yaounde were δD = 7.92δ18O + 12.99 and δD = 8.35δ18- O + 15.29, respectively. The slopes indicate isotopic equilibrium conditions during rain formation and negligible evaporation effect during rainfall. Precipitation showed similar wide ranges in δ18O values from -5.26 to -0.75 % in Douala and -5.8 to +1.81 % in Yaounde suggesting a common moisture source from the Atlantic Ocean. Enriched weighted mean δ18O (wδ18O) values during the low pre- and post-monsoon showers coincided with low convective activity across the entire region. Enriched isotopic signatures also marked the West African monsoon transition phase during each hydrological year. Abrupt wδ18O depletion after the transition coincided with the monsoon onset in the region. Peak periods of monsoonal rainfall, associated with high convective activities, were characterised by the most depleted wδ18O values. Controls on isotopic variations are the amount effect and moisture recycling. The stable isotope data provide a tool for groundwater recharge studies while the isotopic correlation with regional rainfall cycle demonstrate their use as markers of moisture circulation and detecting climatic changes in precipitation. [ABSTRACT FROM AUTHOR]

The few previous studies of precipitation isotopes (δ18O and δD) in Indonesia, based on low spatial resolution observation datasets, have found several types of patterns in their seasonal variabilities. This study conducted high spatial resolution rainfall sampling and investigated the temporal characteristics of precipitation isotope in Indonesia. Rainfall samples were collected weekly from 33 stations in Indonesia. Cluster analysis showed that Indonesia could be divided into four types based on the seasonal variability of the precipitation of δ18O. The majority of stations showed seasonal patterns in the variability of δ18O, characterized by high values in the dry season (July-October) as type 1. Type 2 also showed one peak of high δ18O but in the longer period (June-November) was similar to type 1 stations. A region of Northwest Indonesia, comprising North and Central Sumatra and western Borneo, was identified as type 3, having two peaks of high δ18O values in January-February and May-August. Another pattern of variability was the anti-monsoonal type, indicated by low δ18O in May-July found in east part of Indonesia. Asia-Australia monsoon regime was the main factor that controls seasonal δ18O variability. This research showed that stable isotope in precipitation could correspond to precipitation climatology in Indonesia. [ABSTRACT FROM AUTHOR]

Four GNIP sites, Hong Kong, Kunming, Shijiazhuang and Urumqi with relatively complete tritium records, have been selected to determine the characteristics of tritium in precipitation in different climatic and geographical regions in China. The highest concentration, 559 TU, was measured at Hong Kong in April 1963 and resulted from Soviet thermonuclear testing. During 1985-2004, tritium values decreased substantially due to the radioactive decay and the vapor exchange between the atmosphere and ocean. During this period, tritium concentrations tended to be much higher in inland regions than in coastal regions. This difference may be explained by the continental effect and the inland continental thermonuclear testing. Stratosphere-to-troposphere exchange is the important driver for the timing of tritium seasonal peak at Urumqi and Kunming, but this mechanism is less pronounced at Hong Kong and Shijiazhuang. This offset indicates that the complex stratosphere-troposphere exchange process appears to be neither seasonally nor geographically uniform. The amount effect was only observed at the Hong Kong, indicating different tritium sources than at the other locations. Therefore, air masses influencing tritium in precipitation are more complex in inland region than in coastal region. [ABSTRACT FROM AUTHOR]

In everyday life, many probabilistic situations may be characterized as probabilistic waiting. A gambler, for example, bets repeatedly at the racetrack, the casino, or the card table. The gambler may not win on the first try, but if a gamble is repeated enough times, a win is almost certain to occur eventually. If repeated gambles are structured as strings of losses ending in a win (probabilistic waiting) and the amount won is discounted by the delay caused by the series of losses, then strings with many losses will be discounted more than those with fewer losses, thereby causing subjective value of the series of gambles as a whole to increase. The current study used the opposite effect that amount has on the degree of delay and probability discounting as a marker to determine whether people evaluate situations involving probabilistic waiting as they evaluate situations involving delayed outcomes or as situations involving probabilistic outcomes. We find that the more likely a probabilistic waiting situation is to end in reward (e.g., a gamble is repeated indefinitely until reward is obtained), the more that situation conforms to delay discounting; the less likely a probabilistic waiting situation is to end in reward (e.g., a fixed, small number of gambles), the more that situation conforms to probability discounting. We argue that the former situation is applicable to pathological gambling, and that people with steep delay discount functions would therefore be more likely to have gambling problems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Understanding the main controls on stable isotope variations in precipitation is fundamental for the interpretation of the hydrological cycle. However, spatio-temporal variations in δ 18 O p are poorly known in Morocco. Herein, we explore the relative influence of meteorological variables, spatial and orographic (altitudinal) effects, atmospheric circulation and moisture sources on precipitation stable isotopes in Morocco. Precipitation events and two-years-long monthly records from 17 rain-gauge stations in Morocco are investigated and compared in this study to global gridded records of monthly and annual stable isotopes in precipitation. We highlight that the main spatial controls on precipitation stable isotopes are the topography and the distance from marine source. The most depleted mean annual isotopes are located in the High Atlas Mountains (δ 18 O p = −9.56‰ and δ 2 H p = −59.3‰), while the most enriched isotope ratios exist in southwestern Morocco (δ 18 O p = −2.35‰ and δ 2 H p = −7.47‰). The well-constrained relationship between δ 18 O p and altitude describes a gradient of 0.11–0.18‰ per 100 m. The seasonal variation is expressed by a general enrichment that reaches −4.8‰ during the dry season, related to the recycled vapor contained within the summer precipitation. Notwithstanding the scarcity of temperature and precipitation measurements, the amount effect is observed in multiple stations during several rain events and precipitation seems to have more influence on δ 18 O p than temperature. Backward moisture trajectories indicate a distinct depletion in δ 18 O p in extreme events originating from the Atlantic Ocean. The presence of a rain shadow effect is also revealed on the lee side of High Atlas Mountains, southeastern Morocco. [ABSTRACT FROM AUTHOR]

Understanding the modern day relationship between climate and the oxygen isotopic composition of precipitation (δO) is crucial for obtaining rigorous palaeoclimate reconstructions from a variety of archives. To date, the majority of empirical studies into the meteorological controls over δO rely upon daily, event scale, or monthly time series from individual locations, resulting in uncertainties concerning the representativeness of statistical models and the mechanisms behind those relationships. Here, we take an alternative approach by analysing daily patterns in δO from multiple stations across the British Isles ( n = 10-70 stations). We use these data to examine the spatial and seasonal heterogeneity of regression statistics between δO and common predictors (temperature, precipitation amount and the North Atlantic Oscillation index; NAO). Temperature and NAO are poor predictors of daily δO in the British Isles, exhibiting weak and/or inconsistent effects both spatially and between seasons. By contrast δO and rainfall amount consistently correlate at most locations, and for all months analysed, with spatial and temporal variability in the regression coefficients. The maps also allow comparison with daily synoptic weather types, and suggest characteristic δO patterns, particularly associated with Cylonic Lamb Weather Types. Mapping daily δO across the British Isles therefore provides a more coherent picture of the patterns in δO, which will ultimately lead to a better understanding of the climatic controls. These observations are another step forward towards developing a more detailed, mechanistic framework for interpreting stable isotopes in rainfall as a palaeoclimate and hydrological tracer. [ABSTRACT FROM AUTHOR]

Many studies of Quaternary climate make use of terrestrial stable isotope records which are interpreted based on seasonal patterns of stable isotopes in modern precipitation. Multi-decade records of isotopes in rainfall allow testing of the assumed behavior of isotope signals used for this interpretation on multi-year to decadal scales. A 32-year record of stable O and H isotopes in precipitation in Tucson, Arizona permits a detailed examination of stable isotope amount effects, at time scales ranging from individual events to decades, in a location with summer monsoonal and winter frontal rainy seasons. Amount effects are weak to non-existent in Tucson at seasonal and longer time scales, and are not useful for discriminating either wetter or drier rainy seasons or wetter or drier decades. Amount effects are also weak to non-existent in published data for annual and multi-year amount-weighted averages for monsoonal precipitation in New Delhi and Hong Kong, but an annual amount effect appears to be present on Guam (U.S. Territory). In addition, site-specific amount effects do not correlate with measures of regional monsoon intensity. This data analysis challenges the general validity of paleoclimate reconstructions based on short-term (sub-annual) relationships observed in precipitation isotope data when applied to long-term records such as speleothem studies. [ABSTRACT FROM AUTHOR]

Accurate estimation of precipitation amount recharged to the groundwater is essential to the water balance calculation of a groundwater system in regional scale. In the torrid zones, the proportion of heavier water isotopes in precipitation presents a negative correlation with the precipitation amount. The physical processes explicating this so-called amount effect have not been well understood. This paper focuses on the δD relationships of local precipitation and groundwater to explain the isotopic variability in Ordos Plateau, China. In order to better understand the physical process interpreting the amount effect, a numerical threshold model in the vadose zone to relate the ineffective precipitation amount and isotopic abundance of precipitation and groundwater was supposed. By comparing the modelled δD with that in groundwater, ineffective precipitation, a value of 6.12 mm was obtained in Ordos Plateau. Thus, the potential groundwater recharge from the precipitation in the region can be deduced. The methodology proposed in this study will provide useful insights into the estimation of precipitation contribution to groundwater in other similar areas in the world. [ABSTRACT FROM AUTHOR]

Stable oxygen isotope ratios (δO) of tree cellulose and speleothem carbonate are useful proxies for past monsoon rain in many tropical regions, as a decrease in rain δO is observed with increase in rainfall on a monthly time scale. This amount effect varies spatially; therefore a local calibration, with actual measurements of rain amount and its δO is required. Such observations, however, are quite limited in space and time. To circumvent this difficulty, many isotope enabled general circulation models (GCMs) are used to aid the interpretation of O proxies; nevertheless, all such simulations taken together are yet to be evaluated against observations over the Indian summer monsoon (ISM) region. Here we examine ten such GCM simulations archived by the stable water isotope INtercomparison Group, phase 2. The spatial patterns of simulated ISM rainfall and its δO are in good agreement with the limited observations available. Simulations nudged with observed wind fields show better skill in reproducing the observed spatio-temporal pattern of rainfall and its δO. A large discrepancy is observed in the magnitude of the simulated amount effect over the Indian subcontinent between the models and observation, probably because models simulate the spatial distribution of monsoon precipitation differently. Nudged simulations show that interannual variability of rainfall δO at proxy sites are controlled by either regional (rather than local) rainfall or upstream rain out. Interannual variability of rainfall δO over the East Asian region is well correlated with ENSO, while it is only weakly correlated over the Indian sub-continent. [ABSTRACT FROM AUTHOR]

The amount effect of delay discounting (by which the value of larger reward amounts is discounted by delay at a lower rate than that of smaller amounts) strictly implies that value functions (value as a function of amount) are steeper at greater delays than they are at lesser delays. That is, the amount effect and the difference in value functions at different delays are actually a single empirical finding. Amount effects of delay discounting are typically found with choice experiments. Value functions for immediate rewards have been empirically obtained by direct judgment. (Value functions for delayed rewards have not been previously obtained.) The present experiment obtained value functions for both immediate and delayed rewards by direct judgment and found them to be steeper when the rewards were delayed-hence, finding an amount effect with delay discounting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable isotope ratios of rainwater with space and time over Southwest India. • Evidence of microclimate impact on water sources in tropical rainforest of India. • Isotopic amount effect over the humid tropical coast of India is demonstrated. • Isotopic reversal of continental and elevation effects is evident in small humid basins. • Fingerprinted critical water reserve in humid tropics through isotope systematics. The changes in precipitation pattern provide an understanding on the hydroclimatic response to global warming during the Anthropocene. The present study investigates sources of precipitation moisture for the Indian Monsoon and the local environmental mechanisms controlling its distribution over the southwest coast of India. This is achieved by the characterization of stable isotope ratios of oxygen (δ18O) and hydrogen (δ2H) in rainwater samples collected from a high humid tropical setting (Swarna-Madisal river basin) of the Western Ghats, South India and another station further south (Bakrabail, southern edge of Nethravati river basin). This study contributes to the detailed investigation on rainwater isotopic composition and microclimate characteristics which is lacking in the humid west coast region. The rainwater isotopic composition of coast was close to that of the Arabian Sea water and reflected the first condensate of vapours which were originally formed under fast evaporation at the nearby ocean. In inland location, the higher d-excess values reflect continental moisture recycling. Evapotranspiration has led to higher kinetic fractionation effect in the inland region. The isotopic storm effect during winter monsoon season suggested the rain distribution from saturated air masses formed under deep convective effect in the Bay of Bengal. The overall local meteoric water line (LMWL) in the Swarna-Madisal basin was found to be δ2H = {(7.2 × δ18O) + 7.5}, R2 = 0.98. Further south, the LMWL of Bakrabail was, δ2H = {(8.19 × δ18O) + 16.1}, R2 = 0.98 for annual observation and displayed minimal variability for inter-seasonal slopes (7.73 for summer monsoon, 8.48 for winter monsoon and 8.36 for pre-monsoon) and intercepts (15.6 for summer monsoon, 17.8 for winter monsoon and 15.5 for pre-monsoon). In regions of vegetation dominance and humid climate, the prevailing local air mass masked the rain-out effect of marine air mass as well as the amount effect which support microclimatic settings at the local precipitation sites in southwest India. The time and space variability of regional moisture circulation in controlling atmospheric water balance has been deduced in this study. Thus, the high efficacy of stable isotopes in tracing the manifestation of microclimate in the humid tropics has been demonstrated. [ABSTRACT FROM AUTHOR]

Several studies have examined discounting by pigeons and rats using concurrent-chains procedures, but the results have been inconsistent. None of these studies, however, has established that discounting functions derived from estimates of indifference points can be obtained with a concurrent-chains procedure, so their validity remains in doubt. The present study used a concurrent-chains procedure within sessions combined with an adjusting-amount procedure across sessions to determine the present, subjective values of food reinforcers to be obtained after a delay. Discounting was well described by the hyperbolic discounting function, suggesting that the concurrent-chains procedure and the more typical adjusting-amount procedure are measuring the same process. Consistent with previous studies with rats and pigeons using adjusting-amount procedures, no significant effect of the amount of the delayed reinforcer on the degree of discounting was observed, suggesting that the amount effect may be unique to humans although consistent with the view that animals' choices are controlled by the relative, rather than the absolute, value of reinforcers. [ABSTRACT FROM AUTHOR]

The relationship between climate variability and rainfall oxygen isotopic (δ18O) variability is poorly constrained, especially in the tropics, where many key paleoclimate records rely on past rainfall isotopes as proxies for hydroclimate. Here we present a daily-resolved, 5-yr-long timeseries of rainfall δ18O from Gunung Mulu National Park, located in northern Borneo (4°N, 114°E) in the heart of the West Pacific Warm Pool, and compare it to local and regional climatic variables. Daily rainfall δ18O values range from +0.7‰ to −18.5‰ and exhibit a weak but significant inverse relationship with daily local precipitation amount (R=−0.19, p<0.05), consistent with the tropical amount effect. Day-to-day δ18O variability at Mulu is best correlated to regional precipitation amount averaged over the preceding week (R=−0.64, p<0.01). The inverse relationship between Mulu rainfall δ18O and local (regional) precipitation amount increases with increased temporal averaging, reaching R=−0.56 (R=−0.72) on monthly timescales. Large, negative, multi-day rainfall δ18O anomalies of up to 16‰ occur every 30–90 days and are closely associated with wet phases of the intraseasonal Madden–Julian Oscillation. A weak, semi-annual seasonal cycle in rainfall δ18O of 2–3‰ bears little resemblance to seasonal precipitation variability, pointing to a complex sequence of moisture sources and/or trajectories over the course of the year. Interannual rainfall δ18O variations of 6–8‰ are significantly correlated with indices of the El Niño Southern Oscillation, with increased rainfall δ18O during relatively dry El Niño conditions, and vice versa during La Nina events. We find that Mulu rainfall δ18O outperforms Mulu precipitation amount as a tracer of basin-scale climate variability, highlighting the time- and space-integrative nature of rainfall δ18O. Taken together, our results suggest that rainfall δ18O variability at Mulu is significantly influenced by the strength of regional convective activity. As such, our study provides further empirical support for the interpretation of δ18O-based paleo-reconstructions from northern Borneo stalagmites as robust indicators of regional-scale hydroclimate variability, where higher δ18O reflects regional drying. [ABSTRACT FROM AUTHOR]

Abstract: Using the isotope enabled ECHAM4, GISS E, HadCM3 and MUGCM GCMs, the spatial distribution of mean δ 18O in precipitation, the mean seasonality (JJA-DJF) and the correlations of δ 18O in precipitation with temperature and precipitation amount are analyzed. The simulation results reproduce well the stable isotopic features by the GNIP observations. Over the East Asia, the distribution of δ 18O in precipitation is of marked latitude effect and altitude effect. The largest seasonality of δ 18O in precipitation appears in the eastern Siberia controlled by cold high pressure, and the smallest one in the Western Pacific controlled by the subtropical high. The comparatively weak seasonality appears in middle latitudes where oceanic and continental air masses interact frequently. Temperature effect occurs mainly in mid-high-latitude and inlands. The higher the latitude is, the closer to inland is, and then the stronger the temperature effect is. Amount effect occurs mainly in low-mid latitudes and monsoon areas, with the strongest effect in low-latitude coasts or islands. A significant difference between simulations and observations is that the standard deviation of GCMs statistics is greater than that of GNIP statistics. On the contrary, as comparing parallelly time series at single station, the standard deviations of GCMs simulations is smaller than that of GNIP observations. [Copyright &y& Elsevier]

Abstract: Results of interannual variations in cellulose oxygen isotopic composition (δ18O) of four teak (Tectona grandis L.F.) trees (one from western India, two from central India and one from southern India) are presented. Cellulose δ18O of teak trees from western and central India show a significant positive correlation with the amount of rainfall, which is contrary to expectation. We propose that this correlation is caused by longer duration of the growing season in years of higher rainfall. Teak from southern India shows a significant negative correlation with the amount of rainfall and this relationship is used to reconstruct rainfall back to A.D. 1743, extending the existing regional and local rainfall records by 70 and 128 years, respectively. The reconstructed series reveals higher rainfall for the period 1743–1830 than for the later periods. [Copyright &y& Elsevier]

Abstract: The purpose of the study was to determine the lowest hypothetical amount a participant would keep for himself/herself, preferring it over a reward that he/she would have shared with another individual representing various levels of past reciprocation. Other manipulated aspects were: emotional closeness of the receiver (close vs. distant person), procedure for deciding on how to share the reward (mutual decision vs. decision made by partner) and amount of reward to be shared (PLN 494 vs. PLN 49,400). It was found that preference for the reward to be shared increased as a function of reciprocity, and that it is higher when sharing with an emotionally close person, when the decision does not depend entirely on the partner, and when sharing a small reward. The effect of the level of reciprocity was the smallest when the reward was shared with an emotionally close person and the decision was mutual. [Copyright &y& Elsevier]

Summary: This study investigates the factors that control the oxygen isotopic composition of precipitation and cave drip waters in central Texas. Precipitation samples collected in Austin, Texas at monthly to bimonthly intervals between 1999 and 2007 have δ 18O values between −12.6‰ and −1.1‰ VSMOW and a weighted average value of −4.1‰. This weighted average value likely reflects the isotopic composition of precipitation generated predominantly by moisture masses that originate from the Gulf of Mexico. Samples with the lowest δ 18O values (−12.6±0.1‰) are associated with precipitation from moisture masses related to Pacific tropical cyclones. Precipitation amount appears to be an important control on the oxygen isotope composition of rainfall during summertime periods with the warmest weather, but does not account for the variability of the precipitation isotopic data for colder months. Drip-water samples collected at monthly to quarterly intervals from multiple drip sites in three regionally distributed central Texas caves between 1998 and 2007 have δ 18O values between −5.5‰ and −0.6‰ with individual drip sites generally varying by no more than 1‰ of their average values. This much narrower range of δ 18O values relative to those for rainfall is consistent with mixing of meteoric water in the unsaturated zone. Average drip-water δ 18O values of all caves are lower than the weighted average of Austin precipitation, which may indicate that a threshold of precipitation amount must be exceeded to provide recharge to drip sites. Unlike Austin precipitation, drip waters at most sites lack seasonal variations and therefore must have a residence time in the unsaturated zone of approximately annual scale or greater. Drip waters from six caves from central Texas to eastern New Mexico display a spatial gradient in which their drip-water δ 18O values are lower for caves located further inland from the Gulf of Mexico. This likely reflects a combination of continental and temperature effects on precipitation above the caves. The observed spatial gradient in drip-water δ 18O values emphasizes the utility of comparing speleothem paleoclimate records from regionally distributed caves. Past variations in such a gradient may imply changes in prevailing storm paths or moisture source region. [Copyright &y& Elsevier]

Abstract: General circulation models (GCMs) fitted with stable isotope schemes are widely used to interpret the isotope–climate relationship. However, previous studies have found that the spatiotemporal isotope/precipitation correlation simulated by GCMs is stronger and more widespread than the observed value. To understand the reason for this failure, we investigated the factors influencing the empirically well-known isotope/precipitation relationship, or precipitation amount effect, in the tropics using newly obtained daily precipitation isotope monitoring data over Asia. As in previous studies, we found an apparent correlation between the long-term monthly mean isotopic content and the corresponding precipitation amount (local precipitation) observed at sub-tropical island stations. Furthermore, on a monthly timescale, the isotopic variability of precipitation for these stations was more clearly related to the regional precipitation amount than to local precipitation. This correlation of isotopic content with the regional precipitation amount was observed at the equatorial (Maritime Continent) stations. For these stations, isotope/local precipitation relationships only appeared over longer timescales, with different regression line slopes at each station. However, at the coastal stations, there was a strong linear relationship between the monthly mean isotopic content and corresponding regional precipitation, and regression line slopes were spatially uniform. For the two sub-tropical terrestrial (Indochina Peninsula) stations, the isotopic minimum appeared without any relationship to rainfall amount but usually occurred at the leeward station during the rainy season. These results suggest that the isotopic variations of precipitation did not depend on the ’local’ rain-out history but on the rain-out process in the surrounding region. However, local rainfall events were associated not only with large-scale disturbances but also with regional circulation. Thus, the scale difference of controlling factors between local rainfall amount and isotopic value results in the weakening of the rainfall amount effect at the observation site and in the discrepancy between GCM simulations and observations. This finding suggests that regional precipitation–isotope relationships should be compared with GCM results. Additionally, because the isotope signal reflects the rain-out history at a regional scale, evaluation of the isotopic field using isotopic GCMs will be useful not only to reconstruct paleoclimate conditions but also to examine how GCMs can reproduce real atmospheric circulation over the tropics. [Copyright &y& Elsevier]

Abstract: An understanding of the climatic controls on precipitation δ 18O is required to interpret isotopic records of paleoclimate and paleoaltimetry. However, variations in precipitation δ 18O in time and space are only poorly known in northern Central America. To test the hypothesis that precipitation and surface water δ 18O values are dominated by temporal and spatial amount effects, we analyzed δ 18O in surface waters collected from Guatemala and Belize, and in precipitation from the Global Network for Isotopes in Precipitation database for Veracruz, Mexico, and San Salvador, El Salvador. Herein we show that the dominant controls on δ 18O values of precipitation and surface waters are fairly simple. Temporally, the dominant control on precipitation δ 18O values is the amount effect, whereby there is an inverse correlation between rainfall amount and δ 18O. Precipitation δ 18O values decrease by 1.24‰ per 100 mm increase of monthly rainfall. Spatially, only two variables – distance from the coast and mean catchment altitude – explain 84% of the surface water δ 18O variability. Surface water δ 18O values show an altitude effect of −1.9 to −2.4‰ km−1 and a continental effect of 0.69‰ per 100 km once corrected for altitude effects. A decrease in surface water δ 18O by 3 to 4‰ from the Caribbean Sea to the Pacific Ocean is evident as an isotopic rain shadow on the Pacific slope. Our data also show that river waters in this humid tropical environment are good proxies for δ 18O values of precipitation in northern Central America. The Guatemala/Belize surface water line is defined as δD=8.0× δ 18O+8.7, which is similar to the meteoric water line at San Salvador of δD=8.1× δ 18O+10.9. Spatial variability in δ 18O values is interpreted to reflect 1) progressive rainout of Caribbean-sourced air masses upon traverse of Central America, and 2) the temperature-dependent equilibrium fractionation between vapor and condensate related to the altitude effect. The data show that the northeast trade winds are the dominant moisture source to Central America, mixing with Pacific-derived moisture west of the cordilleran divide. [Copyright &y& Elsevier]

In this study, we simulated and analyzed the monthly variations of stable water isotopes in different reservoirs at Manaus, Brazil, using the Community Land Model (CLM) that incorporates stable isotopic effects as a diagnostic tool for understanding stable water isotopic processes, filling the observational data gaps and predicting hydrometeorological processes. The simulation results show that the δ18O values in precipitation, vapor and surface runoff have distinct seasonality with the marked negative correlations with corresponding water amount. Compared with the survey results by the International Atomic Energy Agency (IAEA) in co-operation with the World Meteorological Organization (WMO), the simulations by CLM reveal the similar temporal distributions of the δ18O in precipitation. Moreover, the simulated amount effect between monthly δ18O and monthly precipitation amount, and MWL (meteoric water line) are all close to the measured values. However, the simulated seasonal difference in the 518∅ in precipitation is distinctly smaller than observed one, and the simulated temporal distribution of the δ18O in precipitation displays the ideal bimodal seasonality rather than the observed single one. These mismatches are possibly related to the simulation capacity and the veracity in forcing data. [ABSTRACT FROM AUTHOR]

The article presents a study that compares the monthly and daily variations of stable water isotopes in reservoirs in Manaus, Brazil by using the Community Land Model (CLM). On the daily scale, the ʕ18O in vapour, precipitation and surface runoff have clear seasonality, with noted negative correlations with the corresponding water amount. On the diurmal time scale, the ʕ18O in precipitation shows an unclear diurmal variation and unnoted correlation with the precipitation amount.

We present stable oxygen isotopic ratios (δ18O) of rainfall collected over three years (July to October 2000-02) at Mangalore. We observe an apparent positive correlation between the monthly, amount-weighted mean oxygen isotopic ratio of the rainwater and monthly total rainfall, contrary to the generally expected negative trend in many island and continental stations. We offer an explanation for this observation and propose that the 'amount effect' in the annual rainfall still remains with a negative slope, and thus can be useful in palaeomonsoon reconstruction using oxygen isotopic variations of annually laminated speleothems. [ABSTRACT FROM AUTHOR]