Water Oxygen Isotope Research Articles

Hydrogen and Oxygen Isotopic Characteristics of Different Water and Indicative Significance in Baiyangdian Lake

In order to better understand the water cycle processes in Baiyangdian Lake, samples for precipitation, river water, lake water, and groundwater were collected in 2020 via the analysis of oxygen and hydrogen isotopes and the total dissolved solids. A combined approach including correlation analysis, end-member modeling, and evaporation modeling was used to identify hydrogen and oxygen isotopic characteristics of different water types and their indicative significance to evaporation, hydrodynamics, and lake-groundwater interactions. The results showed that the compositions of hydrogen and oxygen isotopes in surface water and groundwater differed from each other. The average values of δD and δ18O were the highest in samples from lake water in June, secondary for lake water in October, and the lightest in groundwater. The slope of the lake water line was lower than that of the local meteoric water line, which could be attributed to a greater evaporative enrichment in lake water. The water loss ratio was estimated to be 18.8%-42.3% in June and 2.7%-30.3% in October by applying an evaporation model using deuterium excess. Lake water isotopes exhibited highly spatial heterogeneity, which indicated that Baiyangdian Lake was a poor-mixed lake controlled by the complex hydrodynamic conditions. The values of δD and δ18O were lighter around the estuary area and higher in the district far from the estuary. Although the main water isotopes in areas such as channels had a short residence time, the spatial differences in lake water isotopes were not remarkable, which suggested that the well-mixed conditions of the lake water contributed to reducing the heterogeneity of the lake water isotopic compositions on a spatial scale. The contribution ratios of lake leakage to groundwater were 0-91.7% and varied spatially. It had a negative relationship with the buried depth of groundwater and the distance to the lakeshore. No obvious relationship was found between lake leakage magnitude and groundwater level gradient. This study could provide a theoretical basis and technical support for the sustainable development of water resources and ecological environment protection in Baiyangdian Lake.

Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

AbstractThe stable isotopes of hydrogen and oxygen in xylem water are often used to investigate tree water sources. But this traditional approach does not acknowledge the contribution of water stored in the phloem to transpiration and how this may affect xylem water and source water interpretations. Additionally, there is a prevailing assumption that there is no isotope fractionation during tree water transport. Here, we systematically sampled xylem and phloem water at daily and subdaily resolutions in a large lysimeter planted with Salix viminalis. Stem diurnal change in phloem water storage and transpiration rates were also measured. Our results show that phloem water is significantly less enriched in heavy isotopes than xylem water. At subdaily resolution, we observed a larger isotopic difference between xylem and phloem during phloem water refilling and under periods of tree water deficit. These findings contrast with the expectation of heavy‐isotope enriched water in phloem due to downward transport of enriched leaf water isotopic signatures. Because of previous evidence of aquaporin mediated phloem and xylem water transport and higher osmotic permeability of lighter hydrogen isotopologues across aquaporins, we propose that radial water transport across the xylem–phloem boundary may drive the relative depletion of heavy isotopes in phloem and their relative enrichment in xylem.

Physical and Biogeochemical Influences on Nutrients Through the Canadian Arctic Archipelago: Insights From Nitrate Isotope Ratios

AbstractThe Canadian Arctic Archipelago (CAA) provides a gateway for the flow of nutrients from the North Pacific to the North Atlantic. The transport and biogeochemical cycling of nutrients throughout the CAA, however, are sparsely documented. Here, we report water column nitrogen and oxygen isotope ratios of nitrate (δ15NNO3 and δ18ONO3) collected in a throughflow of the CAA into Baffin Bay, providing insights on inherent nutrient dynamics. The nitracline shoaled eastward into the CAA, wherein large subsurface chlorophyll maxima and coincident increases in δ15NNO3 and δ18ONO3 indicated enhanced nitrate assimilation relative to the oligotrophic Canada Basin. High δ15NNO3 values characteristic of Pacific Winter Water (PWW) pervaded the Archipelago and Baffin Bay, decreasing eastward due to mixing with underlying Atlantic water (AW)—from the Canada Basin west of Barrow Strait, and from Baffin Bay east thereof. Nearly 25% of nutrients in the central CAA were of Atlantic origin, a substantially larger fraction than surmised previously. Nutrient properties in the CAA were notably not influenced by benthic denitrification. Those in underlying AW in the western CAA, however, were modified by remineralization of Pacific‐sourced nutrients, manifested from increases in δ15NNO3 relative to the Canada Basin. Properties in the eastern CAA exposed the complex hydrography of Baffin Bay, characterized by lateral intrusions of nutrient‐poor winter waters into PWW and of cold mode waters in underlying AW. High δ15NNO3 values in AW revealed the presence of a substantial fraction of N from remineralization, stemming from the high productivity in Baffin Bay fueled by Pacific nutrients.

A simple CO2 equilibration method for measuring blood oxygen isotope compositions.

Blood water oxygen isotope compositions can provide valuable insights into physiological processes and ecological patterns. While blood samples are commonly drawn for medical or scientific purposes, blood fractions are infrequently measured for oxygen isotopic compositions (δ18 O) because such measurements are time consuming and expensive. We sampled blood from sheep, goats, and iguanas raised in field and animal laboratories into serum, EDTA, heparin, and uncoated plastic vials commonly used in medical and scientific research, then separated red blood cell (RBC) and plasma or serum blood fractions. These were injected into helium-flushed Exetainer tubes where they naturally outgassed endogenous CO2 (goat blood), or into He- and CO2 -flushed tubes (iguana blood). The CO2 gas was sampled on a GasBench II system, and δ18 O was measured by an isotope ratio mass spectrometer (IRMS). Repeated δ18 O measurements were stable over multiple days. The addition of desiccated blood solids to water standards had little impact on their δ18 O measurements, suggesting that organic molecular constituents within blood serum and plasma do not interfere with blood water δ18 O values. We observed slight but statistically significant δ18 O offsets between plasma, serum and RBC fractions. Mass-dependent body water turnover times for iguanas were derived from the data. We demonstrate that a simple blood-CO2 equilibration method using the GasBench can quickly, reliably and accurately characterize water δ18 O in the plasma, RBC, and whole blood fractions of mammalian and reptilian blood samples (precision ≤ 0.1‰). This method will expand the application of blood stable isotope analysis in physiological and medical research.

Water sources of Populus euphratica with different tree ages in the oasis of desert hinterland.

Understanding vegetation water utilization can provide scientific basis for vegetation protection and rational distribution of water resources in arid desert oasis area. In this study, sapling (DBH≤10 cm), mature (10 cm<DBH≤40 cm), and overmature (DBH>40 cm) Populus euphratica were chosen as sample trees in natural oasis of Dariaboui. We measured oxygen isotopes of xylem water and potential water sources (surface water, soil water in 0-3 m soil layer and groundwater) of P. euphratica with different tree ages. The IsoSource model was used to study water sources of P. euphratica. The results showed that soil water content increased with increasing soil depth, while the δ18O value of soil water decreased firstly and then stabilized. When groundwater depth was 2 m, the δ18O value of xylem water increased with increasing tree ages. When the depths of groundwater were 4.2 and 8 m, the δ18O values of xylem water decreased with increasing tree ages. Water sources of P. euphratica varied across tree age. When the depth of underground water was 2 m, the main water source for young trees was surface water, and the contribution proportion was 64.7%. For mature and overmature trees, it was deep soil water and ground-water, with a contribution of about 30%. When the depth of groundwater was 4.2 m, the main water sources of P. euphratica of different tree ages were deep soil water and groundwater, and the contribution proportion was about 30%. The lowest contribution of P. euphratica of different tree ages was shallow soil water, accounting for about 10%.

Integrating Stable Isotopes with Mean Residence Time Estimation to Characterize Groundwater Circulation in a Metamorphic Geothermal Field in Yilan, Taiwan

This paper presents a water circulation model by combing oxygen and hydrogen stable isotopes and mean residence time (MRT) estimation in a high-temperature metamorphic geothermal field, Tuchen, in Yilan, Taiwan. A total of 18 months of oxygen and hydrogen stable isotopes of surface water and thermal water show the same variation pattern, heavier values in summer and lighter values in the rest of the year. A shift of δ18O with a relative constant δD indicates the slow fluid–rock interaction process in the study area. Two adjacent watersheds, the Tianguer River and Duowang River, exhibit different isotopic values and imply different recharge altitudes. The seasonal variation enabled us to use stable isotope to estimate mean residence time of groundwater in the study area. Two wells, 160 m and 2200 m deep, were used to estimate mean residence time of the groundwater. Deep circulation recharges from higher elevations, with lighter isotopic values, 5.9‰ and 64‰ of δ18O and δD, and a longer mean residence time, 1148 days, while the shallow circulation comes from another source with heavier values, 5.7‰ and 54.4‰ of δ18O and δD, and a shorter mean residence time, 150 days. A two-circulation model was established based on temporal and spatial distribution characteristics of stable isotopes and the assistance of MRT. This study demonstrates the usefulness of the combined usage for further understanding water circulation of other various temperatures of metamorphic geothermalfields.

Geochemical Characteristics and Origin of Formation Water From the Upper Triassic Xujiahe Tight Sandstone in the Xiaoquan-Fenggu Structural Belt, Western Sichuan Depression, China

Formation water represents an important driving force and carrier for the migration and accumulation of oil and gas; thus, research on its origin is a hot spot in petroleum geology. The Upper Triassic Xujiahe Formation in the Xiaoquan-Fenggu Structural Belt in the western Sichuan Depression, China, has developed thick tight sandstone gas reservoirs. However, previous studies have provided different conclusions on the origin of the formation water in the Xujiahe tight sandstone reservoir. In this paper, the origin of the formation water in the Xujiahe Formation was determined based on the latest major and minor elemental concentration data, hydrogen and oxygen isotopes data of formation water, and carbon and oxygen isotope data of carbonate cements. The results show that the salinity of the formation water of the Xujiahe Formation in the study area is generally greater than 50 g/L. The water type is mainly the CaCl2 type, although a small proportion of NaHCO3 type water with high salinity is observed, which is related to hydrocarbon expulsion by overpressure. Moreover, the formation water in the sandstone of the Xujiahe Formation is obviously rich in Br, which is related to membrane infiltration, overpressured hydrocarbon expulsion of shale and diagenesis of organic matter. The composition of Cl− and Na+ ions in the formation water in the Xujiahe tight sandstone reservoir is consistent with the seawater evaporation curve, which deviates significantly from the freshwater evaporation curve. The hydrogen and oxygen isotopes of condensate water in the Xujiahe Formation tight sandstone are similar to those of atmospheric precipitation water, while the hydrogen and oxygen isotopes of the formation water in the Xujiahe Formation show that it is of seawater origin. Therefore, to use hydrogen and oxygen isotopes to determine the origin of formation water, condensate water must be accurately differentiated from formation water. Otherwise, if the condensate water is misjudged as formation water, then incorrect conclusions will be drawn, e.g., that the formation water of the Xujiahe Formation originated from fresh water. Affected by organic carbon, the carbon isotope Z value of the carbonate cements in the Xujiahe Formation is low (mainly distributed between 110 and 130). A Z value of less than 120 does not indicate that the ancient water bodies formed by cements were fresh water or mixed water bodies. However, Z values greater than 120 correspond to a formation temperature lower than 80 C, which indicates that carbonate cement was not affected by organic carbon; thus, the Z value can reflect the origin of ancient water bodies. The results of this study indicate that the formation water of the Xujiahe tight sandstone in the study area is of seawater origin. The determination of the origin of the formation water and seawater of the Xujiahe Formation provides strong evidence for the determination of the marine sedimentary environment of the Xujiahe Formation in the study area, and can provide scientific guidance for the search for high-quality reservoirs.

Wine characterisation according to geographical origin using analysis of mineral elements and rainfall correlation of oxygen isotope values

SummaryThe wine industry has developed rapidly; however, wine fraud is a potential risk for consumers. In China, methods for detecting wine authenticity are far from perfect. To reduce the risk of counterfeit wines, Inductively Coupled Plasma‐Mass Spectrometry and Isotope Ratio Mass Spectrometry were used to geographically classify 104 wines from four major production areas. In this paper, the naturally distributed characteristics of thirty‐eight mineral elements contents and the effect of rainfall on the oxygen isotope values in wine were investigated. The result of δ18O ranged from −13‰ to 7‰. The oxygen isotope of wine water in Northwest China is obviously more positive than that in South China. Linear discriminant analysis (LDA) showed 88.5% classification accuracy in training set and 81.7% in the cross‐validation result. An artificial neural network (ANN) model determined origin of the wine with higher accuracy than LDA model. Furthermore, δ18O and Sr/Rb are important recognition elements in ANN, and the accuracy of region recognition can reach 90.9%. Thus, mineral elements and isotope ratios are effective in contributing to wine authenticity control in wine origin.

A stable isotope record of late Quaternary hydrologic change in the northwestern Brooks Range, Alaska (eastern Beringia)

ABSTRACTA submillennial‐resolution record of lake water oxygen isotope composition (δ18O) from chironomid head capsules is presented from Burial Lake, northwest Alaska. The record spans the Last Glacial Maximum (LGM; ~20–16k cal a bp) to the present and shows a series of large lake δ18O shifts (~5‰). Relatively low δ18O values occurred during a period covering the LGM, when the lake was a shallow, closed‐basin pond. Higher values characterize deglaciation (~16–11.5k cal a bp) when the lake was still closed but lake levels were higher. A rapid decline between ~11 and 10.5k cal a bp indicates that lake levels rose to overflowing. Lake δ18O values are interpreted to reflect the combined effects of changes in lake hydrology, growing season temperature and meteoric source water as well as large‐scale environmental changes impacting this site, including opening of the Bering Strait and shifts in atmospheric circulation patterns related to ice‐sheet dynamics. The results indicate significant shifts in precipitation minus evaporation across the late Pleistocene to early Holocene transition, which are consistent with temporal patterns of vegetation change and paludification. This study provides new perspectives on the paleohydrology of eastern Beringia concomitant with human migration and major turnover in megafaunal assemblages.

Seasonal Variation and Sources Identification of Dissolved Sulfate in a Typical Karst Subterranean Stream Basin Using Sulfur and Oxygen Isotopes

Karst water, which provides approximately 25% of the world's drinking water, is especially vulnerable to anthropogenic pollutants. To determine the variations between high and low flow periods and the sources of dissolved sulfate (SO42-) in small karst basins, SO42- concentrations, stable sulfur and oxygen isotopes (δ34S-SO4 and δ18O-SO4), and oxygen isotopes of water (δ18O-H2O) were investigated in surface and groundwaters, during the high and low flow seasons, within the Babu subterranean stream basin. Analysis showed that: ① the water samples that were directly impacted by acid mine drainage exhibited high SO42- concentrations (≥250 mg·L-1) and significant seasonal variation, while the seasonal variation of non-AMD-impacted water with low SO42- concentrations was not significant. ② During the high flow season, the mean δ34S-SO4 and δ18O-SO4 values of surface water were -10.5‰ and 4.7‰, respectively, and -11.5‰ and 1.3‰ during the low flow period; the mean values of δ34S-SO4 and δ18O-SO4 in groundwater samples were -2.9‰ and 7.1‰ during the high flow period, respectively, and -3.2‰ and 6.2‰ during the low flow period. Both surface and groundwater samples exhibited higher δ34S-SO4 and δ18O-SO4 values during the high flow period than during the low flow period. ③ The values of δ34S-SO4 in the surface and groundwater samples were relatively stable, indicating that the sources of SO42- at specific sampling sites were stable.④ The main sources of SO42- in surface and groundwaters were rain, sulfide, and gypsum, accounting for 13%, 40%, and 47%, respectively, of SO42- in samples taken from the basin outlet during the high flow season, and 18%, 39%, and 43%, respectively, in samples obtained during the low flow season.

Tracing magma water evolution by H2O-in-zircon: A case study in the Gangdese batholith in Tibet

The presence of water has significant influence on magma properties such as the chemistry, viscosity, and crystallization temperature. Water content in the magma can be modified by magma replenishment or crystal fractionation, but technique for direct tracing of these processes are lacking. In this study, we analyzed zircon water content, oxygen isotopes, and trace element contents for a co-genetic granitic suite (one primitive biotite granite and two evolved garnet-bearing two-mica granites) from the Gangdese batholith in Tibet. The biotite granite shows a relatively narrow H2O-in-zircon range with a sharp peak in the density plot, while multiple peaks are present for the garnet-bearing two-mica granites. The wide Hf range indicates that the zircon grains have a protracted magmatic history, and the positive H2O vs. Hf correlation indicates that H2O-in-zircon faithfully recorded the water variation of the evolving magma. These results suggest that H2O-in-zircon is a good indicator to trace magma fluid evolution.

Geochemical Study on the Annual Variation of Oxygen Isotope and Chemical Composition of Groundwater in the Sho River Alluvium Fan, Toyama, Japan, as an Investigation of Selected Qualitative Aspects of Efficient Utilization of Groundwater Heat

Seasonal variations of water temperature, electric conductivity, and oxygen isotope and chemical composition of shallow groundwaters and river waters were determined in the Sho River alluvial fan, western Toyama Prefecture, Japan, to examine groundwater heat utilization for indoor climate control. Samples were collected at 31 sites every 2 months for 1 year and at 11 representative sites monthly. In addition, the results of monthly precipitation amount and oxygen isotope composition of precipitation collected within the region during the same period were also taken into account. The sources of the shallow groundwaters are a mixture of river water and precipitation. The contribution of precipitation to groundwater is generally small along the Sho River but reaches as much as 80% along the Oyabe River and in the south and west of the alluvial fan. Though the origin of the groundwater differs regionally, water temperature is fixed at around 15 °C throughout the year in the northern part of the alluvial fan, and open-type ground source heat pump systems can be used for cooling and heating there, if adequate quantitative aquifer properties (exploitable groundwater amounts) are present.

Oxygen and hydrogen isotope analysis of experimentally generated magmatic and metamorphic aqueous fluids using laser spectroscopy (WS-CRDS)

We report a new procedure for the analysis of oxygen and hydrogen isotopes in water that is experimentally produced in high-temperature high-pressure experiments via wavelength-scanned cavity ring down spectroscopy (WS-CRDS). This work builds on a recently developed method by Affolter et al. (2014) for the analysis of fluid inclusions in cave carbonate deposits. We show that a simple modification of the setup allows extraction and analysis of experimentally produced fluids from their noble metal capsules in an online water extraction line, and analyse them without further treatment of the water molecule prior to isotope determination. We tested this method on standard water reference samples and water experimentally generated during thermal decomposition of hydrous minerals in hydrothermally altered rocks. Preliminary results indicate that fluids released from hydrothermally altered rocks at conditions of 640 °C and 100 MPa maintain isotopic compositions close to those of the meteoric water involved in their alteration. Further development and application of this method will offer great insights into the origin and evolution of water in magmatic and metamorphic systems, and be a valuable tool in the determination of experimentally derived fluid-melt and fluid-mineral isotope fractionation.

Stable isotopes of oxygen and hydrogen in the tap water in the Jalovecký Creek valley in hydrological years 2018–2020

Stable isotopes of oxygen and hydrogen in the tap water in the Jalovecký Creek valley in hydrological years 2018–2020

Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate

Seasonal variability in sea surface temperatures plays a fundamental role in climate dynamics and species distribution. Seasonal bias can also severely compromise the accuracy of mean annual temperature reconstructions. It is therefore essential to better understand seasonal variability in climates of the past. Many reconstructions of climate in deep time neglect this issue and rely on controversial assumptions, such as estimates of sea water oxygen isotope composition. Here we present absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. We reconstruct highly precise monthly sea surface temperatures at around 50 °N latitude from individual oyster and rudist shells of the Campanian greenhouse period about 78 million years ago, when the seasonal range at 50 °N comprised 15 to 27 °C. In agreement with fully coupled climate model simulations, we find that greenhouse climates outside the tropics were warmer and more seasonal than previously thought. We conclude that seasonal bias and assumptions about seawater composition can distort temperature reconstructions and our understanding of past greenhouse climates.

Raman spectroscopy-based screening of zircon for reliable water content and oxygen isotope measurements

Abstract Water content and oxygen isotopes in zircon provide crucial constraints on magma source and process, yet they can be significantly modified by zircon metamictization, which causes secondary water absorption into the zircon crystal and the concomitant oxygen isotope changes. Therefore, it is imperative to develop a screening scheme to select the least-metamict zircons for the analyses. We propose a screening scheme based on our study on the Suzhou A-type granite (South China) through integrating Raman spectroscopy, water and trace element measurements, and oxygen isotope analysis. The results show that the primary water content is retained in zircon when the full-width at half maximum (FWHM) is &amp;lt;8 cm−1 or the Raman shift is &amp;gt;1007 cm−1 of ν3(SiO4) vibration band, while the primary δ18O is preserved at &amp;lt;10 cm−1 FWHM or &amp;gt;1005.5 cm−1 Raman shift. Changes in trace element concentrations in Suzhou zircons are different from previous observations in metamict zircons but most likely related to magma evolution, which implies that trace elements are insensitive to metamictization. Primary δ18O in Suzhou zircons (4.5–6.0‰) fall into the mantle range, indicating a dominant mantle contribution to Suzhou granites. Primary water content was estimated at ca. 650–1400 ppm, significantly higher than those of typical I-type granite (400–736 ppm) and upper mantle-derived zircons (81–177 ppm). The high primary zircon water content was not controlled by the sub-solidus process, temperature, pressure, and cation charge balance but considered to reflect the high-water content in melts. This suggests a hydrous origin for the Suzhou A-type granite, which challenges the conventional view of anhydrous petrogenesis for A-type granites.

Theoretical inversion of the fossil hydrothermal systems with oxygen isotopes of constituent minerals partially re-equilibrated with externally infiltrated fluids

ABSTRACTWhile the external infiltration of water has been identified from modern geothermal and/or fossil hydrothermal systems through stable isotopes, the physicochemical boundary conditions like the initial oxygen isotopes of water $( {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } ) $ and rock as well as alteration temperature were implicitly presumed or empirically estimated by the conventional forward modelling. In terms of a novel procedure proposed to deal with partial re-equilibration of oxygen isotopes between constituent minerals and water, the externally infiltrated meteoric and magmatic water are theoretically inverted from the early Cretaceous post-collisional granitoid and intruded Triassic gneissic country rock across the Dabie orogen in central-eastern China. The meteoric water with a $ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $ value of −11.01 ‰ was externally infiltrated with a granitoid and thermodynamically re-equilibrated with rock-forming minerals at 140°C with a minimum water/rock (W/R)o ratio around 1.10 for an open system. The lifetime of this meteoric hydrothermal system is kinetically constrained less than 0.7 million years (Myr) via modelling of surface reaction oxygen exchange. A gneissic country rock, however, was externally infiltrated by a magmatic water with $ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $ value of 4.21 ‰ at 340°C with a (W/R)o ratio of 1.23, and this magmatic hydrothermal system could last no more than 12 thousand years (Kyr) to rapidly re-equilibrate with rock-forming minerals. Nevertheless, the external infiltration of water can be theoretically inverted with oxygen isotopes of re-equilibrated rock-forming minerals, and the ancient hydrothermal systems driven by magmatism or metamorphism within continental orogens worldwide can be reliably quantified.

Warm High‐Elevation Mid‐Latitudes During the Miocene Climatic Optimum: Paleosol Clumped Isotope Temperatures From the Northern Rocky Mountains, USA

AbstractInterrupting a long‐term Cenozoic cooling trend, the Miocene Climatic Optimum (MCO; ca. 17–15 Ma) represents a time interval characterized globally by warmer than present temperatures, lower ice volume, and elevated pCO2 levels. Establishing quantitative Neogene temperature estimates is an important element in the effort to explore the long‐term changes in the carbon cycle and associated climate feedbacks, yet terrestrial temperature records are still sparse. Here, we present a clumped isotope (Δ47) temperature record of the MCO from intermontane basins in the Northern Rocky Mountain (NRM) region. Arikareean (22.7–21.5 Ma) to Barstovian (16.9–14.7 Ma) paleosol carbonates from the Hepburn's Mesa Formation (Montana), supplemented with data from fossil localities in western Idaho. These records yield Δ47‐temperatures ranging from 17°C to 24°C, which are rather warm given the high elevation sites and are further relatively stable (mean of 21 ± 2°C) leading into and during the MCO until ca. 14.7 Ma. At ca. 14.7 Ma, we observe low Δ47‐temperatures (8°C–10°C) concomitantly with elevated Δ47‐temperatures (ca. 22°C). In line with recently suggested climate stability in the NRM region leading into the MCO, our Δ47‐temperature record, combined with carbon isotope (δ13C) and reconstructed soil water oxygen isotope (δ18Osw) values, indicates rather stable climate and environmental conditions throughout the MCO. Combining available records from inland sites in the western United States (NRM, Mojave region) points to prevailing stable continental climates even during the MCO.

Provenancing wood used in the Norse Greenlandic settlements: A biogeochemical study using hydrogen, oxygen, and strontium isotopes

A growing number of studies strive to examine wooden archaeological remains recovered from Norse sites in the North Atlantic, contributing to a better understanding of patterns in both wood exploitation and woodland management. Despite the limited diversity and abundance of trees in the North Atlantic islands, the Medieval Norse kept using wood in most everyday activities including the construction and repair of buildings and boats, the production of artifacts and tools, and as a source of fuel. The proximity of the Greenland settlements with the northeastern American coast, puts them at the forefront in the exploration and exploitation of remote resource regions. While some species may have arrived both as driftwood or imported material, there is currently no method to conclusively identify archaeological wood remains as driftwood. Here, we use biogeochemical analysis of stable hydrogen (δ2H), stable oxygen (δ18O), and radiogenic strontium (87Sr/86Sr) isotopes in soil, water, and modern plant samples from various sites in Greenland and Canada to characterize expected local isotopic baselines. While 87Sr/86Sr isotope ratios do not provide a clear distinction between the regions of interest, δ2H and δ18O ratios appear to help discriminate not only between regions but also specific sites. In addition, we completed a pilot study of archaeological wood samples obtained in Greenland to test the effectiveness of the 87Sr/86Sr biogeochemical baseline. Results demonstrate that at least in some cases, diagenetic processes were not sufficient to mask a non-local 87Sr/86Sr signature.

Spatiotemporal variability in stable isotopes of the Ganga River and factors affecting their distributions

Although the Ganga is an important fluvial system of India, the isotopic investigations of its water are limited and not reported for the whole length of the river. This limits the understanding of the hydrological processes of the river whose flow characteristics have been changed considerably over the years due to changes in the climate and land use/land cover patterns of the region. This study intends to fill this gap of data and knowledge. Hence, a robust isotope datasets were generated for a period of 2–3 years from 11 locations covering the entire length of the river (2250 km). These data were further analysed to study the controls on spatiotemporal patterns of river water isotopes and understand dominance of different hydrological processes affecting flow characteristics of the river in different reaches. The stable isotopes of oxygen and hydrogen in river water exhibited large spatial and temporal variation throughout the study periods. The most negative isotopic values (mean δ18O: −15‰ to −9.7‰) between 0 and 318 km in the mountainous region during pre-monsoon period attributes to the dominant glaciers melt contribution while the altitude effect in rainfall is mainly responsible during monsoon season. However, less negative isotopic values (mean δ18O: −9.7‰ to −4.3‰) between 318 and 1000 km correspond to the mixing of water from major tributaries. Other hydrological factors responsible for the increased isotopic values include evaporative enrichment and contribution of isotopically less negative groundwater. The observed relatively low isotopic values (δ18O: −4.3‰ to −6.9‰) in the downstream of 1000 km of the river are due to joining of tributaries originating from the Nepal Himalayas. Results substantiate that distinct isotopic values found in different reaches of the river are because of the variations in basin characteristics, hydro-meteorological processes, and water mixing. These findings would contribute in developing a better knowledge on hydrological behaviour of the Ganga River and help in taking appropriate measures for maintaining its sustainable flows.