Spatio-temporal variability in stable water isotopes of Brahmaputra river system and its implications.

River damming and drought affect water cycle dynamics in an ephemeral river based on stable isotopes: The Dagu River of North China

BackgroundSeasonal variations of stable hydrogen and oxygen isotopes in river water can be used to indicate hydrological processes and the water cycle in the river basin. This study presents a high-resolution time series of stable oxygen isotopic record (δ18O) in the lower Changjiang (Yangtze) River mainstream and aims to investigate the regional water cycle concerning natural climate changes and anthropogenic activities.ResultsThe river water δ18O shows apparent seasonal variations, which is overall higher during the dry season and lower during the flood season. This basin-scale seasonal variation of δ18O in precipitation over the Changjiang catchment is calculated based on the long-term meteorological and hydrological data. The seasonal variation of δ18O in the lower Changjiang river water is largely constrained by monsoon-induced precipitation, but is more directly controlled by the mixing of waters from the upper reaches and the tributary lakes in the middle valley.ConclusionsThe relative contributions of waters from the upstream and tributary lakes to the lower Changjiang mainstream have been considerably altered by the construction of Three Gorges Dam via the regulation of river discharges. A comparison of river water isotopic records with water discharges from the lakes suggests that it takes about 2 weeks (~ 17 days) for the Changjiang river water to circumvent the mid-lower reaches of the catchment before traveling to the sea. This study suggests that the stable hydrogen and oxygen isotopes can be harnessed as sensitive indicators for water cycling within a large catchment that is driven primarily by natural forcing though subject to substantial human impacts.

The δ18O and δD in 17 river waters flowing into and out of Lake Biwa, the lake water itself and precipitation at 11 locations in the Lake Biwa basin were observed from October 1996 to September 1997, to evaluate the origin of river waters and the effect of irrigation water from the lake on the river waters flowing into Lake Biwa. The regional difference and altitude effect of the stable isotopes in precipitation and river water were found in the basin. The δ18O in the rivers which are located in the eastern and the southern areas in the basin is heavier than that of the other rivers, due to the effect of irrigation for the nearby paddy fields. Evaporation from Lake Biwa and the inflow rate into the lake estimated from the δ18O balance agree well with the results of previous studies which used water balance methods. The stable isotopes can enable us to evaluate not only water balance but also the origin of the water and the water flow system. Copyright © 2000 John Wiley & Sons, Ltd.

Orbitally driven evolution of Asian monsoon and stable water isotope ratios during the Holocene: Isotope-enabled climate model simulations and proxy data comparisons

Abstract. Long-term, high-frequency time series of passive tracers in precipitation and streamflow are essential for quantifying catchment transport and storage processes, but few such data sets are publicly available. Here we describe, present, and make available to the public two extensive data sets of stable water isotopes in streamflow and precipitation at the Plynlimon experimental catchments in central Wales. Stable isotope data are available at 7-hourly intervals for 17 months, and at weekly intervals for 4.25 years. Precipitation isotope values were highly variable in both data sets, and the high temporal resolution of the 7-hourly streamwater samples revealed rich isotopic dynamics that were not captured by the weekly sampling. We used ensemble hydrograph separation to calculate new water fractions and transit time distributions from both data sets. Transit time distributions estimated by ensemble hydrograph separation were broadly consistent with those estimated by spectral fitting methods, suggesting that they can reliably quantify the contributions of recent precipitation to streamflow. We found that on average, roughly 3 % of streamwater was made up of precipitation that fell within the previous 7 h, and 13 %–15 % of streamwater was made up of precipitation that fell within the previous week. The contributions of recent precipitation to streamflow were highest during large events, as illustrated by comparing new water fractions for different discharges and precipitation rates. This dependence of new water fractions on water fluxes was also reflected in their seasonal variations, with lower new water fractions and more damped catchment transit time distributions in spring and summer compared to fall and winter. We also compared new water fractions obtained from stable water isotopes against those obtained from concentrations of chloride, a solute frequently used as a passive tracer of catchment transport processes. After filtering the chloride data for dry deposition effects, we found broadly similar new water fractions using chloride and stable water isotopes, indicating that these different tracers may yield similar inferences about catchment storage and transport, if potentially confounding factors are eliminated. These stable isotope time series comprise some of the longest and most detailed publicly available catchment isotope data sets. They complement extensive solute data sets that are already publicly available for Plynlimon, enabling a wide range of future analyses of catchment behavior.

Climate records of ratios of stable water isotopes of oxygen (δ18O) are used to reconstruct the past Indian monsoon precipitation. Identifying the sources of water vapor is important in understanding the role of monsoonal circulation in the δ18O values, to aid in monsoon reconstructions. Here, using an isotope-enabled Earth system model, we estimate the contributions of oceanic and terrestrial water vapor sources to two major precipitation seasons in India—the Southwest monsoon and the Northeast monsoon, and their effects on the δ18O in precipitation (δ18Op). We find that the two monsoon seasons have different dominant sources of water vapor because of the reversal in atmospheric circulation. While Indian Ocean regions, Arabian Sea, and recycling are the major sources of the Southwest monsoon precipitation, North Pacific Ocean and recycling are two crucial sources of Northeast monsoon precipitation. The δ18Op of the Southwest monsoon precipitation is determined by contributions from the Indian Ocean sources and recycling. Despite reduced precipitation, more negative δ18Op values are simulated in the Northeast monsoon season due to larger negative δ18Op contributions from the North Pacific. Our results imply that changes in atmospheric circulation and water vapor sources in past climates can influence climate reconstructions using δ18O.

The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132 000 and 116 000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation, and ocean conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conduct high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, with boundary conditions provided by climate model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include elevated δ18O at SkyTrain Ice Rise in West Antarctica and elevated deuterium excess and δ18O at Hercules Dome in East Antarctica. A combination of records from multiple sites would provide constraints on the timing, rate, and magnitude of past WAIS collapse.

Stable isotope composition of δ2H and δ18O was investigated in the water resources of the Shwan sub-Basin northeast of Iraq. The study objects conceived the possible factors that affect the stable isotopes’ composition in precipitation additionally to achieve information concerning recharge processes and estimate the groundwater recharge sources. In this study, four precipitation samples were collected at the study area for the 2020–2021 hydrological year. Thirty-two groundwater samples and one surface water sample from Lesser Zab River (LZR) were collected during the same period for two sampling seasons. The results of observed meteorological data show a very small amount of precipitation for the sampling year. This year is considered a dry hydrological year with total annual precipitation of 100.62 mm compared with the previous 40 hydrological years with total annual precipitation of 325.43 mm. The isotopic composition in precipitation was highly varied as it primarily depends on environmental conditions. The depleted values are recognized with the increasing precipitation amount, whereas the enriched values were the most affected by evaporation. Back trajectory analysis revealed that stable isotopes in precipitation are primarily influenced by air masses and moisture sources. The sources of the trajectory that came from the Mediterranean Sea, Arabian Gulf and the Red Sea would lead to variations in the values of precipitation stable isotope. Stable isotope values in groundwater showed that the samples for both periods are located between the East Mediterranean water line (EMWL) and global meteoric water line (GMWL) close to the local meteoric water line (LMWL) indicating that the groundwater recharge is mainly through precipitation. Groundwater recharges by an indirect recharge mechanism from the LZR, based on stable isotope similarity between depleted stable isotopes in groundwater and river water. The estimated groundwater recharge based on weighted oxygen isotopes is about 9.2% of annual rainfall infers that the recharge during the sampling year was very low. The low recharge value experiences dry weather conditions from low precipitation amounts besides increasing evaporation during the current study.

Radiogenic and stable Sr isotopes constrain weathering processes in rapidly eroding Taiwan catchments

Abstract. The stable isotopic composition of precipitation (δ2HP, δ18OP; “water isotopes”) is a powerful tool for tracking water through the atmosphere, as well as fingerprinting land-surface water masses and identifying water cycle biases in isotope-enabled climate models. Water isotopes also underpin our understanding of multi-decadal to multi-centennial water cycle variability via their retrieval from palaeoclimate archives. Water isotopes thereby increase our understanding of past and present – and hence future – water cycle variability. Understanding the drivers of spatial and temporal water isotope variability is a critical first step in applying these tracers for a better understanding of the water cycle. However, water isotope observations are sparse in both space and time. Here we develop and apply a machine learning (random forest) approach to predict spatially continuous monthly δ2HP and δ18OP across the Australian continent at 0.25° resolution from 1962–2023. We train the random forest models on monthly δ2HP (n=5199) and δ18OP (n=5217) observations from 60 sites across Australia. We also predict the deuterium excess of precipitation (dxsP, defined as δ2HP-8×δ18OP). Out-of-sample δ2HP and δ18OP prediction skill is high both geographically and temporally. Skill is slightly lower for the secondary parameter dxsP, likely reflecting the larger reliance of spatio-temporal dxsP variability on moisture source conditions. The random forest models accurately capture both the seasonal cycle of precipitation isotopic variability and long-term annual-mean precipitation isotopic variability across the continent, and outperform estimates from an isotope-enabled atmosphere general circulation model over an equivalent time period. We show that spatio-temporal variability in precipitation amount, precipitation intensity, and surface temperature are particularly important for monthly δ2HP and δ18OP variations across the continent, with local surface pressure also important for dxsP. Drivers of site-level δ2HP, δ18OP, and dxsP are more varied. Overall, the new random forest modelled dataset reveals clear spatial and temporal variability in δ2HP, δ18OP, and dxsP across the Australian continent over the past decades – providing a robust foundation for hydrology, ecology, and palaeoclimate research, as well as an accessible framework for predicting water isotope values in other locations.

以呼伦湖流域为例研究该区域氢氧稳定同位素在不同水体中的分布特征，并探讨氢氧稳定同位素对在该区域水文过程的指示作用.流域湖水、入湖河水、周边地下水水样的氢氧稳定同位素分析结果表明，夏季8月份湖水中的重氢氧稳定同位素比7月份的更加富集.而河水中氢氧稳定同位素在同一时间内的河流沿程上存在明显的差异，下游水体中的氢氧稳定同位素要比上游更加富集.研究区的河水和湖水的δ¹⁸OδD关系特征显示，河水和湖水的δ¹⁸OδD的关系点全部位于当地降水线的右下方，说明流域河水和湖水水体受到明显的蒸发作用.而井水的δ¹⁸OδD的关系点大都靠近当地大气降水线，说明这一区域的地下水主要是大气降水渗入地下形成.利用氢氧稳定同位素分馏过程中的氢氧稳定同位素的比率与剩余水体的关系，并在考虑湿度因子的动力分馏模拟下，计算出河水的剩余水体比例在0.85~0.96之间，而湖水的剩余水体比例在0.71~0.77之间.最后，利用氢氧稳定同位素质量平衡法对呼伦湖多年平均蒸发量进行了估算，估算的湖泊蒸发量结果与实测值相近，相对误差为5.4%，说明方法可靠.氢氧稳定同位素对于研究区域水文过程有着重要的作用，在今后呼伦湖流域水文研究中有着更加广泛的应用空间.;The aim of this paper is to analyze water stable isotopes(δD and δ¹⁸O)in Lake Hulun Basin, and to explore the indicative function of stable isotopes in hydrological cycle in this region. The analytical results of lake water, river water and well water around Lake Hulun indicate that there are temporal variations of stable isotopes in lake and river water and spatial variations in river water along the flow path. Furthermore, the relationship between δ¹⁸O and δD in lake water, river water and groundwater in Lake Hulun Basin shows the crossing points of lake and river water are located in the lower right of local meteoric water line, suggesting lake water and river water have suffered from evaporation. However, the crossing points of well water are located closely to the local meteoric water line except southwestern area (W1) around the lake, indicating all groundwater except W1 reflects a precipitation origin, and the weird high isotope values in W1 may have connections to the lake water and well water. Using the relationship between stable isotopic ratio in residual water and residual water proportion with consideration of the effect of temperature and humidity, the proportions of modern lake water and river water after evaporation are calculated as 0.85-0.96 for river water, and 0.71-0.77 for lake water. Obviously, the extent of lake water evaporation is greater than that of river water, with 4%-15% water loss for rivers and 23%-29% water loss for the lake. In addition, the annual lake water evaporation was calculated based on isotopic mass balance method, the low relative error (5.4%) compared with measured data indicates this model is appropriate to calculate water evaporation for Lake Hulun. Using stable isotope (δD and δ¹⁸O) is an essential method to study on hydrological cycle in a basin, thus stable isotope still has a wide application space in hydrological cycle in Lake Hulun Basin.

Stable isotopic composition (δ2H, δ18O) of river water, groundwater, and paddy water in the Mun River catchment, northeast Thailand, were determined to investigate the hydrological processes and the impacts of natural and anthropogenic activities on the water cycle. Quantities of δ2H (−93.9 to −25.4‰) and δ18O (−12.24 to −2.22‰) in river water in the wet season follow the trend: upper reaches > middle reaches ≈ lower reaches. Trends for δ2H (−52.3 to −22.0‰) and δ18O (−6.37 to −1.36‰) in the dry season are: upper reaches ≈ middle reaches > lower reaches. In the dry season, groundwater (δ2H: −57.5 to −34.6‰, δ18O: −8.24 to −4.40‰) shows a lighter isotopic composition, and paddy water (δ2H: −18.2‰, δ18O: −0.72‰) shows the highest isotopic composition. Spatial variation of δ18O and deuterium excess suggests that groundwater exchanges with surface water frequently. Rainfall and river water recharge groundwater in the wet season, and groundwater flows back to the river in the dry season, especially in the middle reaches. This process is most likely related to impoundment of the rivers by large dams. On the other hand, the lowest values of stable isotopes of river water are coincident with the extreme flooding that was produced by Tropical Storm Sonca in July 2017. This study contributes to a better understanding of hydrological processes in the Mun River catchment and provides a perspective on the application of stable isotopes to other large tropical monsoon catchments around the world.

The authors present a seven-year observation dataset of isotope ratio in precipitation at Tibetan Plateau and the potential impact of ENSO and NAM on them. It is important to understand what controls the climate in Tibetan Plateau, in the context of both paleoclimate reconstruction and future prediction. Therefor the dataset presented in this study is highly valuable for the validation of GCMs, not to mention its analysis. However, the seven-year is too short to see the impact of ENSO or NAM as the authors admitted in the manuscript. Even if their claim with relatively short data is true, the reasoning to reach the conclusion seems to contain a lot of jumps. Therefor it is difficult to accept this article as it is.

<strong class="journal-contentHeaderColor">Abstract.</strong> The Last Interglacial (LIG) period, approximately 130,000 to 115,000 years ago, represents one of the warmest intervals in the past 800,000 years. Here we simulate water isotopes in precipitation in Antarctica and the Arctic during the LIG, using three isotope-enabled atmosphere-ocean coupled climate models: HadCM3, MPI-ESM-wiso, and GISS-E2.1. These models were run following the Paleoclimate Modelling Intercomparison Project, phase 4 (PMIP4) protocol for the LIG at 127 ka (kilo-years ago), supplemented by a 3000-year Heinrich Stadial 11 (H11) experiment run with HadCM3. The long H11 simulation has meltwater from the Northern Hemisphere applied to the North Atlantic which causes large-scale changes in ocean circulation including cooling in the North Atlantic and Arctic and warming in the Southern and Global Ocean. We find that the standard 127 ka simulations do not capture the observed Antarctic warming and sea ice reduction in the Southern Ocean and Antarctic regions, but they capture around half of the warming in the Arctic. The H11 simulations align better with observations: they capture more than 80 % of the warming, sea ice loss, and &delta;¹⁸O changes for both Greenland and Antarctica. Decomposition of seasonal &delta;¹⁸O drivers highlights the dominant role of sea-ice retreat and associated changes in precipitation seasonality in influencing isotopic values in all simulations, alongside a small common response to orbital forcing. We use the H11 and multi-model 127 k simulations together to infer LIG surface air temperature (SAT) changes based on ice core measurements. The peak inferred LIG Greenland SAT increase is +2.89 &plusmn; 1.32 K at the NEEM ice core site. This is less than half the previously inferred warming. Peak inferred LIG Antarctic SAT increases are +4.39 &plusmn; 1.45 K at EDC, dropping to +1.67 &plusmn; 3.67 K at TALDICE. These calculated warming values are from climate effects alone, and do not take account of any ice flow or site elevation related impacts. Coastal sites in Greenland and Antarctica appear to have experienced less warming compared with higher central regions.

The significant changes of cryosphere on the Tibetan Plateau (TP) are an important cause of concern for the huge population in Asia which depends on the glacier-permafrost feed rivers. Up to now, little is known about the response of runoff to the cryospheric changes under a warming climate. Taking an example of a typical alpine river (hereafter named KLR River) in Kunlun Mountains Pass on the TP to investigate the hydrological processes and quantify the potential recharge sources using stable isotopes and electrical conductivities. The results showed significantly temporal variations in isotopes of precipitation and river water. Deviations in the precipitation isotopes indicated that precipitation in Kunlun Mountains Pass during summer months mainly originated from local recycled moisture and slightly influenced by monsoon. The KLR river was separated into three hydrological components which include precipitation, meltwater of glacier and meltwater of subsurface ground ice. On average, the meltwater of glacier accounted for 56.64 % of total flow, whereas the meltwater of subsurface ground ice contributed 37.44 % and only 5.92 % was supplied by precipitation. Evidently, the contributions of glacier and thawing permafrost are up to as high as 94 %. The cryosphere played a crucial role on the hydrological cycle on the TP which would be important to understand the water resource distribution in permafrost regions on the TP under the global warming.