Precipitation δ18O Values Research Articles

Isotope evidence for latitudinal migrations of the dragonfly Sympetrum fonscolombii (Odonata: Libellulidae) in Middle Asia

Sympetrum fonscolombii dragonflies are believed to migrate seasonally. In the spring and early summer, the already‐mature dragonflies arrive in Middle Asia for reproduction. In the late summer and autumn, summer‐generation dragonflies migrate to the south. Their wintering places remain unknown. Stable hydrogen (δ2H) and oxygen (δ18O) isotope analyses were conducted to confirm the migration of S. fonscolombii and determine the wintering area. Stable isotope composition of carbon (δ13C) and nitrogen (δ15N) in wings and legs was used to clarify the habitats in which dragonfly development took place. Three cohorts of dragonflies collected in different regions of Middle Asia were used for analysis: (i) immigrants that arrived in the spring, (ii) residents that developed in Middle Asia, and (iii) transit dragonflies migrating to the south during autumn. The average δ2H values in the wings were significantly higher in immigrants (−96‰) than in residents (−134‰) and transit individuals (−124‰). High δ18O and δ15N values in the tissue of immigrants confirmed their southerly origin. Based on the species range and the global distribution of annual averages of δ2H and δ18O values in precipitation, the latitudinal migrations of S. fonscolombii were inferred to cover the area from the proposed natal regions of immigrants in South‐West Asia (below ∼36°N) to Southern Ural and the south of Western Siberia in the north (54–55°N) with a maximum migration distance of more than 4000 km.

High‐Resolution Proxy Records From Two Simultaneously Grown Stalagmites From Zoolithencave (Southeastern Germany) and their Potential for Palaeoclimate Reconstruction

AbstractTwo small annually laminated stalagmites from Zoolithencave (southeastern Germany) grew between CE 1821 and 1970 (Zoo‐rez‐1) and CE 1835 and 1970 (Zoo‐rez‐2), respectively. Trace element concentrations were determined by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICP‐MS). Samples for δ13C and δ18O analyses were micromilled on annual and subannual resolution. Soil and host rock samples were analyzed by X‐Ray Diffraction (XRD) and their elemental concentrations determined via inductively coupled plasma optical emission spectrometer (ICP‐OES). Trace element concentrations in the stalagmites show two groups in the principal component analyses: one with Mg, Ba, and Sr and another with Y, P, and Al, respectively. The second group reflects the content of detrital material. Increased weathering of soil minerals seems to have a strong influence on the silicate/carbonate weathering ratio controlling the variability of Mg, Ba, and Sr. Meteorological and Global Network of Isotopes in Precipitation (GNIP) station data were used to calculate the δ18O values of the drip water (infiltration‐weighted, mean annual, and the mean of the winter precipitation δ18O values) as well as the corresponding speleothem calcite. The δ18O values calculated by the infiltration‐weighted model show similar patterns and amplitudes as the measured δ18O values of the two stalagmites. This suggests that the δ18O values of speleothem calcite reflect the δ18O values of infiltration‐weighted annual precipitation, which zis related to mean annual temperature, resulting in a significant correlation between mean annual temperature and the measured δ18O values of stalagmite Zoo‐rez‐2. This relationship could potentially be used for quantitative climate reconstruction in the future by extending the time series back in time with further stalagmites from Zoolithencave.

Using water isotopes and hydrogeochemical evidences to characterize groundwater age and recharge rate in the Zhangjiakou area, North China

Despite the increasing depletion of the groundwater at the Zhangjiakou aquifer system in the northwest of Beijing-Tianjin-Hebei region, little information is available on the hydrological process of groundwater in this region. In this study, we utilized water isotopes composition (δ18O, δD and 3H) of groundwater, river and precipitation to identify the characteristics of hydrochemistry, groundwater age and recharge rates in different watersheds of the Zhangjiakou area. Results showed that the river water and groundwater could be characterized as HCO3-Mg·Na, HCO3·Cl-Na and HCO3-Mg·Na, HCO3·Cl-Na, HCO3·Cl-Na·Mg types, respectively. The δD and δ18O values in precipitation were linearly correlated, which is similar to the Global Meteorological Water Line (GMWL). Furthermore, the decreasing values of the δD and δ18O from precipitation to surface water and groundwater indicate that groundwater is mainly recharged by atmospheric precipitation. In addition, the variation of 3H concentration with depth suggests that groundwater shallower than around 100 m is generally modern water. In contrast, groundwater deeper around 100 m is a mixture of modern and old waters, which has longer residence times. Groundwater showed a relatively low tritium concentration in the confined aquifers, indicating the groundwater recharged might be relatively old groundwater of over 60 years. The flow velocity of the groundwater in the study area varied from 1.10 to 2.26 m/a, and the recharge rates ranged from 0.034 to 0.203 m/a. The obtained findings provide important insights into understanding the groundwater recharge sources and hydro-chemistry in the Zhangjiakou area, in turn developing a sustainable groundwater management plan.

Stable isotopes of precipitation and groundwater provide new insight into groundwater recharge and flow in a structurally complex hydrogeologic system: West Hawai‘i, USA

Local meteoric water lines (LMWL) and corresponding relationships between δ2H and δ18O values in precipitation and elevation are useful tools for assessing groundwater recharge areas and flow paths. The LMWL and relationship between δ18O values in precipitation and elevation for the West Hawai‘i region of Hawai‘i (USA) were determined utilizing a network of eight cumulative precipitation collectors sampled at 6-month intervals over a 2-year period. Additionally, δ2H and δ18O values for groundwater samples across the study area were determined. These data were then utilized to develop new conceptual models of groundwater flow and characterize groundwater flow paths in this complex and poorly understood hydrogeologic setting. The West Hawai‘i LMWL indicates a primary source of oceanic moisture from the lee of the island, while the δ18O–elevation relationship resembles that determined for the trade-wind portion of the Hawai‘i Volcano region. Conceptual models incorporating the effects of subsurface geological features on groundwater occurrence and flow in the West Hawai‘i region were developed and subsequently utilized in conjunction with δ18O values for groundwater samples to determine that groundwater flow paths in the West Hawai‘i region generally originate at high elevations located far within the island’s interior. This study demonstrates the utility of considering subsurface structural characteristics in conjunction with H and O isotopic content of precipitation and groundwater to better understand groundwater flow in regions with poorly characterized hydrogeology and has important implications for future development and scientific investigation of water resources in West Hawai‘i.

Resolving combined influences of inflow and evaporation on western Greenland lake water isotopes to inform paleoclimate inferences

Stable isotopes of oxygen (δ18O) and hydrogen (δ2H) in precipitation are widely employed tracers of the global hydrologic cycle, and are frequently inferred from lake-water-derived proxies in sediments of high-latitude lakes. Lake-water isotope proxies archive precipitation δ18O and δ2H values, modulated by lake hydrological processes, which may be functionally classified into processes that affect source water isotope values (i.e. inflow δ18O and δ2H) and catchment-integrated evaporation. Respectively, these controls form the basis of interpretations of precipitation isotope and effective precipitation signals from lake-water isotope proxy records. Conventionally, a single control on lake water isotope variability is assumed for a given record. Yet sensitivity to these controls depends on regional hydroclimate and local hydrology, which may change through time. We quantified the relative impacts of variations in inflow δ18O and evaporative 18O enrichment on lake water δ18O in response to spatially variable aridity, using measurements of lake water δ2H and δ18O from 140 western Greenland lakes located between the Labrador Sea and western Greenland Ice Sheet margin. We calculated source water δ18O of lake waters (δI) using a recently developed Bayesian method and quantified evaporation-to-inflow ratios (E/I) using a modified Craig-Gordon model. δI varied by 11.1‰ across the study region, superimposed by evaporative 18O enrichment of up to 20.0‰ and E/I ranging from nearly no evaporative loss (E/I 1). Lakes can be broadly classified as predominantly sensitive to inflow or evaporation, corresponding to their location along the aridity gradient, and there are significant trends in both δI and E/I across the study area. Substantial local variability in δI and E/I suggests catchment hydrology determines the sensitivity of δI and E/I to changes in aridity, and implies that hydrological end-member lakes within a small region may provide complementary records of seasonal precipitation isotope values and ice-free-season evaporation. Deconvolving modern controls on lake water isotope values provides essential support for quantitative and seasonal paleoclimate inferences from paleolimnological isotope data, which will improve constraints on the long-term variability of the Arctic hydrologic cycle.

Effect of precipitation seasonality on annual oxygen isotopic composition in the area of spring persistent rain in southeastern China and its paleoclimatic implication

Abstract. This study examines the seasonality of precipitation amount and δ18O over the monsoon region of China (MRC). We found that the precipitation amount associated with the East Asian summer monsoon (EASM) in the spring persistent rain (SPR) region is equivalent to that of the nonsummer monsoon (NSM). The latter contributes ∼50 % to amount-weighted annual δ18O values, in contrast with other areas in the MRC, where the δ18O of annual precipitation is dominated by EASM precipitation. Interannual relationships between the El Niño–Southern Oscillation (ENSO) index, simulated δ18O data from IsoGSM, and seasonal precipitation amount in the SPR region were also examined. We found that on interannual timescales, the seasonality of precipitation amount (EASM ∕ NSM ratio) was modulated by ENSO and primarily influences the variability of amount-weighted annual precipitation δ18O values in the SPR region, although integrated regional convection and moisture source and transport distance may also play subordinate roles. During El Niño (La Niña) phases, less (more) EASM and more (less) NSM precipitation leading to lower (higher) EASM ∕ NSM precipitation amount ratios results in higher (lower) amount-weighted annual precipitation δ18O values and, consequently, in higher (lower) speleothem δ18O values. Characterizing spatial differences in seasonal precipitation is, therefore, key to correctly interpreting speleothem δ18O records from the MRC.

Precipitation chemistry and stable isotopic characteristics at Wengguo in the northern slopes of the Himalayas

The major ions in precipitation can reflect the conditions of the atmosphere, while stable isotopic characteristics provide information on the moisture source. In order to understand the local hydro-chemical features and regional geochemical cycle, it is essential to assess the chemical composition of precipitation and the associated sources. Therefore, a total of 57 precipitation samples (2016 to 2017) for major ions and 178 samples (2013 to 2017) for stable isotopes were collected from the Wengguo station and analyzed to explore the major ionic deposition and stable isotopic characteristics in the northern slopes of the Himalayas. The average pH and electrical conductivity were 6.82 ± 0.45 and 15.36 ± 11.67 μS cm−1, respectively. Ca2+ followed by K+ and Mg2+ played a crucial role in neutralizing the precipitation acidity. The major ionic sources in the region were terrigenous (Ca2+, HCO3−, and Mg2+) and sea salt (Na+, Cl−, and Mg2+), as well as anthropogenic emissions (SO42− and NO3−) and biomass burning (K+). The total deposition flux of the major ions was higher in 2016 than in 2017 and was influenced by the higher precipitation. The average values of δ18O and δD in precipitation were − 15.22 ± 5.17 ‰ and − 116.01 ± 41.31 ‰, respectively. The precipitation stable isotopes were not significantly correlated to the local air temperature but the precipitation amount. Moreover, the variation in stable isotopes, local meteoric water line, and d-excess indicated the existence of continental and monsoon moisture transport systems. The transport of chemicals over the high elevation region from polluted cities in South Asia via moisture originating in the Bay of Bengal and the Arabian Sea was determined based on the source identification, clusters of air mass backward trajectory analysis, and the National Center for Environmental Prediction Final dataset. Thus, the ionic concentrations and stable isotopic characteristics of the precipitation from this study provided a valuable dataset to assess the atmospheric environment in the northern slopes of the Himalayas at Southern Tibetan Plateau.

Spatial and temporal variation in the isotopic composition of Ethiopian precipitation

Stable isotopes of oxygen (δ18O) and deuterium (δ2H) in precipitation are used as tracers of the hydrologic cycle in studies of both past and present climate. In Ethiopia, a drought sensitive region where direct observations of climate are limited, understanding the stable isotopic composition of precipitation can provide an integrated view of the hydroclimate today and help interpret records of climate variability in the past. To date, the isotopic composition of precipitation in Ethiopia is known primarily from monthly precipitation collections from one long-term monitoring station in Addis Ababa. Here we report δ18O and δ2H values of precipitation from a 16-month long sampling campaign at four stations in Ethiopia that represent different climate regimes. Precipitation samples collected at daily, weekly and monthly intervals between August 2012 and November 2013 at these stations exhibit a large range of δ18O (−12.6 to +10.3‰), δ2H (−91.8‰ to +80.8‰), and d-excess values (−9.9‰ to +29.9‰). The four stations have similar amount-weighted mean δ18O values, but exhibit different seasonal patterns in δ18O values as clearly shown in daily and weekly data. The most striking feature of this dataset is the synchronous decrease in δ18O values in daily and weekly precipitation samples from the three stations in the northwestern highlands (Gondar, Debre Markos, Jimma) during the first three weeks of August 2013. This decrease in δ18O values does not correlate strongly to precipitation amount but it is likely due to a combination of increased storm intensity and deep convection at the time of lower δ18O values of precipitation. Our high-resolution dataset provides new insights into the controls on the isotopic composition of rainfall in Ethiopia and how we might use it to understand hydroclimate variability today and in the past.

Hydrogen and oxygen stable isotope composition of water in metaschoepite mineralization on U3O8

When exposed to humidity in an oxidizing atmosphere hydrated uranium oxide grows as a secondary mineral on aged U3O8 and may incorporate the oxygen stable isotope signature of the water vapor into the secondary uranium oxide, as well as hydrogen and oxygen stable isotopes into any mineral hydration water. Because geospatial variation in δ2H and δ18O values of atmospheric humidity and precipitation is well understood, the H and O stable isotope composition of mineral hydration waters can give information on the environment of mineral formation. We exposed powdered U3O8 to humidity with known H and O stable isotope composition at constant 30%, 61% and 91% relative humidity. We sampled and analyzed the U3O8 powders along with any secondary hydrated minerals that had formed on the particle surfaces at various intervals from 1 to 10 days throughout the 180-day humidity exposures. We present stable H and O isotope results of mineral hydration waters in uranium oxide materials analyzed by thermogravimetry-enabled isotope ratio infrared spectroscopy (TGA-IRIS), which uses precise heating by thermogravimetric analyzer to liberate water vapor for subsequent online isotope analysis via a laser-based isotope ratio infrared spectroscopy instrument (Picarro L-2130i). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray diffraction (XRD) analysis of humidity-exposed U3O8 heated to 350 °C indicates that the U3O8 had a measurable metaschoepite ((UO3)•2H2O) phase along with α-U3O8. After heating to 350 °C, the metaschoepite is eliminated but the α-U3O8 is retained, meaning that the heating successfully extracted the water in the metaschoepite but did not disturb the crystalline structure of the U3O8. Analysis of the bulk oxygen isotope composition by fluorination of these samples before and after heating, indicates that the oxygen isotope value of the U3O8 is also not affected by heating to 350 °C. Precision for δ2H and δ18O values of metaschoepite mineral hydration water stable isotope values yielded by the TGA-IRIS method on metaschoepite are 5.86‰ for δ2H, and 0.34‰ for δ18O. Hydrogen in the various water reservoirs is highly exchangeable and thus the δ2H values of these waters is not easily interpreted. However, oxygen in the separate water reservoirs is much less exchangeable, and thus δ18O values of the metaschoepite mineral hydration water is likely to reflect that of the water vapor the sample was exposed to. Once metaschoepite is formed on the surface of U3O8 particles, the oxygen isotope signature of the mineral hydration water in metaschoepite does not respond to changes in exposure vapor isotopic composition, and thus appears to be fairly durable in this regard. These results suggest that it may be possible to discern information about the provenance and history of an oxidized U3O8 sample from oxygen stable isotope measurements of metaschoepite mineral hydration water.

Indian monsoon precipitation isotopes linked with high level cloud cover at local and regional scales

Precipitation stable isotopes preserve historic changes of evaporation in the source regions and precipitation processes, therefore, they can be used to reveal regional hydrological cycle dynamics and paleoclimate reconstructions. In monsoon regions, strong inverse impacts of convection on precipitation isotope ratios, have created a debate regarding the interpretation of isotope records as local climate proxies. The proportions of stratiform to convective precipitation on water isotopes, together with the influence mechanisms on seasonal and interannual scales remain highly uncertain. To further address the influence of precipitation patterns on water isotopes, we used 10 yrs of precipitation isotope data from the southern Tibetan Plateau (TP) to explore the effects of large-scale cloud cover and local climate on precipitation isotopes. Correlation analysis performed between local precipitation δ18O values and different level cloud data, indicated significant negative correlations between precipitation isotopes and high level cloud cover on both seasonal and interannual time scales. This result suggests that high-level convection in the upper moisture transport stream is a main control on precipitation isotopes in the southern TP. The clear and coherent variations of precipitation isotopes with the Southern Oscillation Index and outgoing longwave radiation confirmed that strong convection activity in the moisture source region and during transport significantly depleted heavy isotopes in vapor, producing substantially decreased precipitation δ18O in the study region. These results agree with earlier findings of tree ring cellulose isotope records that correlate with cloud cover, but we emphasized the important role of larger-scale regional cloud cover. We also delineated different maximum correlation zones for seasonal and interannual time scales, likely due to different mechanisms. These findings further improve the interpretation of paleoisotope records from the Indian summer monsoon region.

Stable isotopes of atmospheric water vapour and precipitation in the northeast Qinghai‐Tibetan Plateau

AbstractStable water isotopes (δ18O and δ2H) are an important source signature for understanding the hydrological cycle and altered climate regimes. However, the mechanisms underlying atmospheric water vapour isotopes in the northeast Qinghai‐Tibetan Plateau of central Asia remain poorly understood. This study initially investigated water vapour isotopic composition and its controls during the premonsoon and monsoon seasons. Isotopic compositions of water vapour and precipitation exhibited high variability across seasons, with the most negative average δ18O values of precipitation and the most positive δ18O values of water vapour found during the premonsoon periods. Temperature effect was significant during the premonsoon period but not the monsoon period. Both a higher slope and intercept of the local meteoric water line were found during the monsoon period as compared with in the premonsoon period, suggesting that raindrops have been experienced a greater kinetic fractionation process such as reevaporation below the cloud during the premonsoon periods. The δ2H and δ18O signatures in atmospheric water vapour tended to be depleted with the occurrence of precipitation events especially during the monsoon period and probably as a result of rainout processes. The monthly average contribution of evaporation from the lake to local precipitation was 35.2%. High d‐excess values of water vapour were influenced by the high proportion of local moisture mixing, as indicated by the gradually increasing relative humidity along westerly and Asian monsoon trajectories. The daily observation (observed ε) showed deviations from the equilibrium fractionation factors (calculated ε), implying that raindrops experienced substantial evaporative enrichment during their descent. The average fraction of raindrops reevaporation was estimated to be 16.4± 12.9%. These findings provide useful insights for understanding the interaction between water vapour and precipitation, moisture sources, and help in reconstructing the paleoclimate in the alpine regions.

The Seasonal Origins of Streamwater in Switzerland

AbstractQuantifying the relative contributions of winter versus summer precipitation to streamflow may be important for understanding water‐resource sensitivity to precipitation variability. Here we compare volume‐weighted mean δ18O values in precipitation and streamflow for 12 catchments in Switzerland, to determine whether summer or winter precipitation is overrepresented in streamflow, relative to its proportion of total precipitation. Similarities between precipitation and streamflow weighted‐mean δ18O values indicate that roughly equal fractions of summer and winter precipitation supply streams in Switzerland. These results, together with mass conservation, suggest that similar fractions of summer and winter precipitation supply evapotranspiration. These findings contrast with the assumption that because summer precipitation falls when transpiration rates and evaporative demand are high, it should be underrepresented in streamflow and overrepresented in evapotranspiration. This contrast between seasonal water‐balance variations and the partitioning of seasonal precipitation into runoff and evapotranspiration demonstrates substantial interseasonal carryover of precipitation in storages that supply evapotranspiration.

Key Factors of Precipitation Stable Isotope Fractionation in Central-Eastern Africa and Central Mediterranean

The processes of isotope fractionation in the hydrological cycle naturally occur during vapor formation, vapor condensation, and moisture transportation. These processes are therefore dependent on local and regional surface and atmospheric physical features such as temperature, pressure, wind speed, and land morphology, and hence on the climate. Because of the strong influence of climate on the isotope fractionation, latitudinal and altitudinal effects on the δ18O and δ2H values of precipitation at a global scale are observed. In this study, we present and compare the processes governing precipitation isotope fractionation from two contrasting climatic regions: Virunga in Central-Eastern Africa and the Central Mediterranean (Stromboli and Sicily, Italy). While Virunga is a forested rainy tropical region located between Central and Eastern Africa, the Mediterranean region is characterized by a rainy mild winter and a dry hot summer. The reported δ18O and δ2H dataset are from precipitation collected on rain gauges sampled either on a monthly or an approximately bimonthly basis and published in previous papers. Both regions show clearly defined temporal and altitudinal variations of δ18O and δ2H, depending on precipitation amounts. The Central Mediterranean shows a clear contribution of local vapor forming at the sea–air interface, and Virunga shows a contribution from both local and regional vapor. The vapor of Virunga is from two competing sources: the first is the continental recycled moisture from soil/plant evaporation that dominates during the rainy season, and the second is from the East African Great Lakes evaporation that dominates during the dry season.

Influence of Recent Climate Shifts on the Relationship Between ENSO and Asian Monsoon Precipitation Oxygen Isotope Ratios

AbstractRecent studies have revealed robust in‐phase relationships between El Niño–Southern Oscillation (ENSO) and Asian Monsoon precipitation δ18O values (i.e., warm ENSO events with high δ18O values), and this relationship has been used in an attempt to reconstruct past ENSO activity. However, whether this relationship holds in the past is unknown. Here we use precipitation δ18O data from Hong Kong (East Asia) and Bangkok (Southeast Asia) and an ice core δ18O record from Dasuopu glacier (South Asia) to examine the δ18O‐ENSO relationship across two recent climate shifts that occurred during the winters of 1976/1977 and 1988/1989. On an annual scale, the δ18O‐ENSO relationship is weak prior to 1977 and strongest after 1988. We show that the changing δ18O‐ENSO relationship mainly originates from changes in the dry season isotope/climate relationship (which is significant only after 1988), whereas the rainy season relationship is relatively stable. We confirm that, consistent with earlier work on the rainy season, the significant δ18O‐ENSO relationship in the dry season post‐1988 is associated with ENSO's influence on regional convection (Bay of Bengal to South China Sea region). We suggest the insignificant dry season relationship prior to 1989 is due to limited ENSO impacts on convection in the Bay of Bengal to South China Sea region, which is supported by the insignificant relationship between ENSO and vertical velocity at 500 hPa. These findings suggest that without additional constraints, systematic variability in isotope/climate relationships will lead to large uncertainties in ENSO reconstructions based on Asian Monsoon region δ18O data.

Abrupt changes in Indian summer monsoon strength during the last deglaciation and early Holocene based on stable isotope evidence from Lake Chenghai, southwest China

Identifying variability and the mechanisms driving variability in the Indian summer monsoon (ISM) since the last deglaciation is critical for understanding past hydroclimatic change. In this study, we present an accelerator mass spectrometry radiocarbon dated record of δ18O variations in authigenic carbonates derived from Lake Chenghai in southwest China, a region that receives moisture mainly from the Indian Ocean. The δ18O values vary from −11.9 to +0.1‰, providing a detailed record of variations in ISM precipitation δ18O values, and lake hydrological balance. The record shows that the ISM generally strengthened in the post-glacial between 15.6 and 8.8 cal ka BP, but that three centennial to millennial-scale drought events were superimposed on the long-term trend. Drought events, as indicated by substantial positive shifts in δ18O value, occurred from 15.6 ± 0.2 to 14.4 ± 0.2, 12.5 ± 0.2 to 11.7 ± 0.2 and 10.1 ± 0.1 to 10.0 ± 0.1 cal ka BP, corresponding to the Heinrich 1, Younger Dryas, and Bond 7 cold events in the North Atlantic region, respectively. The timings of these droughts are suggested to be related to meltwater discharge into the North Atlantic. The weakened Atlantic Meridional Overturning circulation, which leads in turn to the southward migration of the intertropical convergence zone and cooling in the tropical Indian Ocean.

Expanding the Isotopic Toolbox to Track Monarch Butterfly (Danaus plexippus) Origins and Migration: On the Utility of Stable Oxygen Isotope (δ18O) Measurements

The measurement of naturally occurring stable hydrogen (δ2H) and carbon (δ13C) isotopes in wings of the eastern North American monarch butterflies (Danaus plexippus) have proven useful to infer natal origins of individuals overwintering in Mexico. This approach has provided a breakthrough for monarch conservation because it is the only viable means of inferring origins at continental scales. Recently, routine simultaneous analyses of tissue δ2H and δ18O of organic materials has emerged leading to questions of whether the dual measurement of these isotopes could be used to more accurately infer spatial origins even though the two isotopes are expected to be coupled due to the meteoric relationship. Such refinement would potentially increase the accuracy of isotopic assignment of wintering monarchs to natal origin. We measured a sample of 150 known natal-origin monarchs from throughout their eastern range simultaneously for both δ2H and δ18O wing values. Wing δ2H and δ18O values were correlated (r2=0.42). We found that wing δ2H values were more closely correlated with amount-weighted growing season average precipitation δ2H values predicted for natal sites (r2=0.61) compared to the relationship between wing δ18O values and amount-weighted growing season average precipitation δ18O values (r2=0.30). This suggests that monarch wing δ2H values will be generally more useful in natal assignments than δ18O values. Spatial information related to the use of deuterium excess in environmental waters was similarly found to be not useful when applied to monarch wings likely due to the considerable variance in wing δ18O values. Nonetheless, we recommend further testing of monarch wing δ2H and δ18O values from known natal sites with an emphasis on field data across a strong gradient in precipitation deuterium excess.

Stable isotopes and chemical characteristics of precipitation in Hangzhou and Huzhou, East China.

Atmospheric precipitation is a very important link in the water cycle. The characteristics of major ions (n= 341) and stable isotopes (δ2H, δ18O; n= 157) were analysed in Hangzhou and Huzhou, which are economically prosperous cities in East China. The δ2H and δ18O values of precipitation ranged from - 109.70 to 21.30‰ and from - 14.87 to - 0.95‰, respectively. Compared with the local meteoric water line (LMWL) of China, the slope and intercept of the LMWL were much higher in Hangzhou and Huzhou, which is related to the effects of the humid climate and less secondary evaporation. The δ2H and δ18O values were highest in spring because of the influence of air masses from the northern Asian continent and other nearby sources. In contrast, the air masses from the South China Sea and the western Pacific Ocean in the summer had the lowest δ2H and δ18O. The dominant ions in precipitation indicate that Ca2+, HCO3-, SO42-, NH4+ and NO3- are the main ions of precipitation in Hangzhou and Huzhou, and the dilution of precipitation leads to lower concentrations of ions in spring and summer, similar to the values found in most Chinese cities. The increase in motor vehicle use resulted in a lower [SO42-]/[NO3-] ratio (1.64) of precipitation, indicating mixed acid rain in Hangzhou and Huzhou (HZS). Based on a combination of the correlation analysis, enrichment factors and source contributions, we determined that SO42- and NO3- were introduced mainly from anthropogenic activities such as coal combustion and vehicle exhaust, accounting for 89% and 99%, respectively. The strong correlation between Cl- and Na+, as well as Ca2+, Mg2+ and K+, indicates that these ions commonly have marine and crustal origins, respectively, and 40% of Mg2+ comes from a marine source.

Characteristics of Stable Isotopes in Precipitation and Moisture Sources in the Headwaters of the Yangtze River

Based on the stable isotopes of 73 precipitation samples continuously collected from May to October 2014 and related meteorological statistics in the Dongkemaldi Basin, the characteristics of δD, δ18O, and d-excess of precipitation, as well as the correlations between δ18O and the rainfall amount and air temperature were analyzed. The moisture sources were tracked by the HYSPLIT model to further estimate the contribution of different water vapor sources to the rainfall amount. The results showed that the range of δ18O and δD values varied from -26.5‰ to 1.9‰ and -195.2‰ to 34.0‰, respectively; meanwhile, the δ18O and δD values in precipitation fluctuated greatly with time in response to water vapor transport from different moisture sources of the Qinghai-Tibet Plateau. The slope and intercept of the Local Meteoric Water Line (LMWL) were both higher than those of the Global Meteoric Water Line (GMWL) and close to the LMWL in the northern area of the Qinghai-Tibet Plateau. The relationship between δ18O and δD in different precipitation types showed significant differences, which were mainly related to the source of water vapor and meteorological conditions during the process of precipitation formation. Because of the influence of local evaporation and the transport process of water vapor, the d-excess values of atmospheric precipitation were relatively large; the δ18O in precipitation had a significant amount effect, but had no temperature effect, thus indicating that the rainfall amount was more effective in controlling the stable isotope content of atmospheric precipitation than temperature. The modeled trajectory of vapor sources showed that water vapor of precipitation was mainly derived from the marine vapor carried by the southwest monsoon, local moisture, and the westerly water vapor, and their contributions to the rainfall amount were 43%, 36%, and 21%, respectively. The results of this study can contribute to further understanding of the atmospheric circulation characteristics and water cycle process of the Dongkemadi basin in the headwaters of the Yangtze River.

Characteristics of hydrogen and oxygen isotopes in precipitation and moisture sources in Gaoyou, Jiangsu Province, China

It is necessary to examine the characteristics of hydrological cycle in Gaoyou area of Jiang-su Province in response to climate change and flood disasters. In this study, 121 atmospheric rain samples were collected and environmental factors were recorded from July 2015 to October 2017. We analyzed the hydrogen and oxygen stable isotopic composition of rain and identify moisture sources in this area. Results showed that the hydrogen and oxygen isotopic composition of rain had an seasonal variation, which was positive in the winter but negative in the summer. D-excess value was higher in winter than that in summer. On the annual scale, significantly negative relationships between δD (δ18O) and temperature and between δD (δ18O) and precipitation indicated the "anti-temperature effect" and "precipitation amount effect", respectively. On the seasonal scale, there was no obvious "temperature effect" but "precipitation amount effect" in autumn and winter. Results from the HYSPLIT model showed that the precipitation in this area came mainly from ocean evaporation that was influenced by the Chinese South Sea, Indian Ocean and Pacific Ocean. Precipi-tation in other seasons mainly came from the water vapor mixture from the Eurasian continent, Atlantic Ocean, Arctic Ocean, as well as local evaporation. The seasonal pattern of δD and δ18O values in precipitation was mainly influenced by monsoon activity and El Niño-Southern Oscillation (ENSO). In addition, the precipitation isotopes clearly indicated the shift in climates from El Niño to La Niña.

Influence of the North Atlantic Oscillation on δD and δ18O in meteoric water in the Armenian Highland

The stable hydrogen (δD) and oxygen (δ18O) isotope composition of modern meteoric water are influenced by changes in global temperature, Rayleigh distillation processes, and moisture transport history. However, on a global scale the relative influence of these different meteorological variables is spatially heterogeneous. We collected daily precipitation samples from meteorological stations in the Armenian Highlands for a period of one year in order to determine the constraints on δD and δ18O and relationship to broader climatic conditions. These data are coupled with HYSPLIT back-trajectory analysis to determine how these compositions relate to moisture source and transport path. Multivariate analysis shows the strongest relationship between δD and δ18O and climate variables is temperature at the sampling site. Along with temperature, the intensity of the North Atlantic Oscillation, a pattern of atmospheric circulation which determines the strength and location of Northern Hemisphere midlatitude westerlies, is significant (p < 0.05) for both δ18O and δD values of precipitation. This correlation between NAO and isotopes in precipitation is also observed in four nearby GNIP stations from 2008 to 2015. Negative NAO phases are associated with weakened westerlies, which allows precipitation enriched in heavy isotopes from the Mediterranean and southerly sources to penetrate into the Armenian Highlands, whereas positive NAO phases are associated with stronger westerlies bringing more negative precipitation from the Black Sea. This relationship is most significant (p < 0.001) during the winter and spring months (December to May). These data demonstrate that paleo-archives of δD and δ18O in the Armenian Highlands could serve as a tool to measure changes in the NAO in the past, particularly when coupled with independent measurements of temperature.