Oxygen Isotopic Composition Of Precipitation Research Articles

Concentration of 18O in precipitation over Moscow in 2014

The series of δ18O values is presented for all precipitation events in Moscow in 2014. Precipitation samples were taken at the observation site of the Meteorological Observatory of Lomonosov Moscow State University (MSU MO), and the isotopic analysis was carried out in the isotopic laboratory of the Department of Geography of MSU. The concentration of stable 18O in precipitation over Moscow in 2014 varied from -0.09 to -26.29‰. The maximum amplitudes of δ18O were registered in March-April and October. The pronounced interrelation was revealed between the oxygen isotopic composition of precipitation and surface air temperature (the correlation coefficient is 0.85). The computation of back trajectories of air masses and the analysis of weather charts demonstrated that the most isotopically light precipitation is typical of relatively cold air masses slowly moving over the continent during the last five days before precipitation. In this case, the ongoing condensation leads to the progressive isotopic depletion of precipitation (more and more isotope-depleted precipitation is registered). On the contrary, fast air transport from the middle and even from high latitudes of the Atlantic Ocean leads to the relatively constant of δ18O values of precipitation.

Analysis of the interdecadal variability of summer precipitation in central Japan using a reconstructed 106 year long oxygen isotope record from tree ring cellulose

AbstractWe present a unique proxy for reconstructing the interannual variability of summer precipitation associated with the quasi‐stationary front (Baiu front) in central Japan. The rainfall from the Baiu front has a relatively lower oxygen isotopic composition than other types of nonfrontal precipitation. The variability in the oxygen isotopes in summer rainfall is closely related to the Baiu frontal activity. In this study we used a mechanistic tree ring isotope model to reconstruct a 106 year long oxygen isotopic composition of precipitation during the early rainy season (June) based on the oxygen isotopic compositions of the annual rings of Chamaecyparis obtusa Endl trees from central Japan. The year‐to‐year variations of the isotopes over the most recent 25 years are associated with several teleconnection patterns that often lead to the Baiu precipitation anomalies in central Japan (such as the Pacific‐Japan (PJ) pattern, Silk Road pattern, and wave train pattern along the polar jet). Yet none of these external forcing mechanisms apply further back in time. From the 1950s to 1980s, the interannual isotopic variability is predominantly related to local factors such as anomalous intensification/weakening of the Bonin High. Before the 1950s, the variability of the oxygen isotopic composition of precipitation is mainly associated with a wave train pattern along the polar jet. The isotopic variability is predominantly linked to the PJ pattern, while the PJ index is correlated with El Niño–Southern Oscillation. These findings suggest that the teleconnection patterns influencing Baiu precipitation variability vary according to interdecadal time scales during the twentieth century.

Holocene climate change in Newfoundland reconstructed using oxygen isotope analysis of lake sediment cores

Carbonate minerals that precipitate from open-basin lakes can provide archives of past variations in the oxygen isotopic composition of precipitation (δ18Oppt). Holocene δ18Oppt records from the circum- North Atlantic region exhibit large fluctuations during times of rapid ice sheet deglaciation, followed by more stable conditions when interglacial boundary conditions were achieved. However, the timing, magnitude, and climatic controls on century to millennial-scale variations in δ18Oppt in northeastern North America are unclear principally because of a dearth of paleo-proxy data. Here we present a lacustrine sediment oxygen isotope (δ18O) record spanning 10,200 to 1200 calendar years before present (calyr BP) from Cheeseman Lake, a small, alkaline, hydrologically open lake basin located in west-central Newfoundland, Canada. Stable isotope data from regional lakes, rivers, and precipitation indicate that Cheeseman Lake water δ18O values are consistent with the isotopic composition of inflowing meteoric water. In light of the open-basin hydrology and relatively short water residence time of the lake, we interpret down-core variations in calcite oxygen isotope (δ18Ocal) values to primarily reflect changes in δ18Oppt and atmospheric temperature, although other factors such as changes in the seasonality of precipitation may be a minor influence. We conducted a series of climate sensitivity simulations with a lake hydrologic and isotope mass balance model to investigate theoretical lake water δ18O responses to climate change. Results from these experiments suggest that Cheeseman Lake δ18O values are primarily controlled by temperature and to a much lesser extent, the seasonality of precipitation. Increasing and more positive δ18Ocal values between 10,200 and 8000calyr BP are interpreted to reflect the waning influence of the Laurentide Ice Sheet on atmospheric circulation, warming temperatures, and rapidly changing surface ocean δ18O from the input of glacial meltwater into the western North Atlantic Ocean. The increasing trend is interrupted by abrupt negative δ18Ocal anomalies at 9700calyr BP, associated with a transition to colder sea surface temperatures (SSTs) in the Labrador Sea and renewed Laurentide Ice Sheet retreat, and at 8500calyr BP that coincides with a well-established cooling event in the circum-North Atlantic region. After 8000calyr BP, δ18Ocal values gradually decrease until 4300calyr BP, which reflects a cooling trend related to declining Boreal summer insolation and lower sea surface temperatures in the western North Atlantic Ocean. δ18Ocal becomes slightly more positive from 4300 to 2500calyr BP and thereafter declines to the most negative values of the late Holocene by 1200calyr BP. The middle to late-Holocene transition at ~4300calyr BP corresponds with a shift to wetter conditions in Newfoundland that is also seen in other paleo-proxy records from the region. The discordance between the Cheeseman Lake δ18Ocal record and declining insolation could in part reflect warmer temperatures or an increase (decrease) in warm (cold) season precipitation. Considering evidence from other paleo-records in Newfoundland, we suggest this transition resulted from a change in synoptic scale atmospheric circulation to a configuration similar to the positive mean state phase of the Pacific-North American pattern. Proxy evidence from Cheeseman Lake therefore supports the idea that a substantial climatic change occurred during the middle to late-Holocene transition (between ~5000 to ~4000calyr BP) in northeastern North America.

Spatial patterns in the oxygen isotope composition of daily rainfall in the British Isles

Understanding the modern day relationship between climate and the oxygen isotopic composition of precipitation (δ18OP) is crucial for obtaining rigorous palaeoclimate reconstructions from a variety of archives. To date, the majority of empirical studies into the meteorological controls over δ18OP rely upon daily, event scale, or monthly time series from individual locations, resulting in uncertainties concerning the representativeness of statistical models and the mechanisms behind those relationships. Here, we take an alternative approach by analysing daily patterns in δ18OP from multiple stations across the British Isles (n = 10–70 stations). We use these data to examine the spatial and seasonal heterogeneity of regression statistics between δ18OP and common predictors (temperature, precipitation amount and the North Atlantic Oscillation index; NAO). Temperature and NAO are poor predictors of daily δ18OP in the British Isles, exhibiting weak and/or inconsistent effects both spatially and between seasons. By contrast δ18OP and rainfall amount consistently correlate at most locations, and for all months analysed, with spatial and temporal variability in the regression coefficients. The maps also allow comparison with daily synoptic weather types, and suggest characteristic δ18OP patterns, particularly associated with Cylonic Lamb Weather Types. Mapping daily δ18OP across the British Isles therefore provides a more coherent picture of the patterns in δ18OP, which will ultimately lead to a better understanding of the climatic controls. These observations are another step forward towards developing a more detailed, mechanistic framework for interpreting stable isotopes in rainfall as a palaeoclimate and hydrological tracer.

Recharge processes on typical karst slopes implied by isotopic and hydrochemical indexes in Xiaoyan Cave, Guilin, China

Summary Measurements of the hydrogen and oxygen isotopic composition of precipitation and drip stream water at drip site XY5 in Xiaoyan Cave in Guilin City were conducted to investigate the infiltration and vadose flow processes, and to characterize precipitation–discharge relationship in the overlying karst hillslope area. A marked seasonal variability of oxygen and hydrogen isotopes was observed in precipitation ranging from −18.7‰ to −0.6‰ for δ 18 O and −139‰ to +5‰ for δD, respectively during the study period from November 2013 to October 2014. However, the narrow range observed for cave drip stream water (δD of −43‰ to −22‰, δ 18 O of −7.3‰ to −4.3‰) was attributed to homogenization via mixing of meteoric waters in the unsaturated zone above the cave. Although drip stream waters plot close to or slightly above the local meteoric water line, the weighted average δ 18 O value of precipitation is depleted than in dripwater, which is attributed to evaporation predominantly in the rainy season when cave air circulation is most active. The relationship between surface infiltration or leakage and cave discharge is connected by the distinct models of flow through the epikarst zone. Vadose flow showed high peaking hydraulic responses but buffered rain isotope responses with an attenuate magnitude of 5.0–9.4‰ for δ 18 O. The sudden hydrochemical proxy variability was related closely to increase of discharge and the flushing out of old water with higher dissolved calcite. A threshold of flow generation expressed by precipitation amount must be exceeded to create a peak in discharge, as a function of excessing the field capacity of soil and residual capacity of epikarst zone. The sources of vadose seepage are soil and epikarst reservoir water with the attenuation of the isotopic fluctuations (−4.28‰ to −5.92‰ for δ 18 O) and slight hydrological response, indicating mixed signals of infiltration water in epikarst storage reservoir. The total discharge volume of percolating water is 2084 L derived from piston flow due to the increased hydraulic head in the dry season, which provides a quantitative evidence of the potential adaptive capacity of the system to deal with the extreme droughts.

Variations in the oxygen isotopic composition of precipitation in the Tianshan Mountains region and their significance for the Westerly circulation

Proxy records of the oxygen isotopic composition of meteorological precipitation (δ18Op) preserved in archives such as ice cores, lacustrine carbonates and stalagmite calcite are important for paleoclimatic studies. Therefore, knowledge of the variations and controlling mechanisms of modern δ18Op on different time scales is necessary. Here, we investigate the linear correlations between δ18Op and corresponding temperature and precipitation on monthly and inter-annual timescales, using data from the Urumqi (1986–2003) and Hotan stations of the Global Network of Isotopes in Precipitation (GNIP), and δ18O data from 4 ice cores in the adjacent Tianshan Mountains. Consistent with previous reported results, modern δ18Op variations on a seasonal time scale in the Tianshan region are mainly controlled by a ‘temperature effect’ (indicated by a significant positive correlation between δ18Op and temperature), with more positive δ18Op values occurring in summer. However, on an inter-annual timescale, there is a weak inverse correlation between weighted average annual δ18Op and annual average temperature at Urumqi station. This finding is supported by the inversely varying trends of δ18O data from 4 ice cores in the central and eastern Tianshan Mountains compared to annual average temperatures in the same region during the past 40–50 years. The data from Urumqi station and the 4 ice cores demonstrate that there is inverse correlation between δ18Op and temperature on inter-annual to decadal time scales. Analysis of water vapor sources and pathways for the warm year of 1997 and the cold year of 1988 reveal that relatively more water vapor for the Tianshan region was derived from long-distance transport from high-latitude sources than during the warm year of 1997; and that more water vapor was transported from more proximal sources from mid- to low-latitude areas during the cold year of 1988. In addition, the δ18Op values are more negative in the high latitude areas than those in mid- to low-latitude areas in the Eurasian continent at the upper wind direction of Tianshan Mountains region, according to the weighted averaged warm season (May to September) δ18Op values for 14 GNIP stations in the years 1997 and 1988. Due to the distribution of δ18Op within the Eurasian continent, the relative shift of water vapor sources between warm and cold years convincingly explains the observed variations of δ18Op in the Tianshan Mountains region. Therefore, we conclude that variations in δ18Op in this region are mainly controlled by changes in water vapor sources which are ultimately caused by northward and southward shifts in the Westerly circulation.

Quantification of the impact of moisture source regions on the oxygen isotope composition of precipitation over Eagle Cave, central Spain

The 5-day reconstruction of air mass history for the days with precipitation at Eagle Cave (central Spain), together with the determination of moisture uptake locations along back trajectories, is used to identify the moisture sources of precipitation for this site from 2009 to 2011. During this 3-year period, around 30% of precipitation at Eagle Cave originated from the moisture recycled within the Iberian Peninsula (IP), with the Proximal Atlantic being also a main source region of moisture, whereas the Mediterranean Sea and the Distal Atlantic have large variability during the studied period and other source regions are minor precipitation contributors. The comparison of monthly oxygen isotope composition of precipitation at Eagle Cave with the monthly percentage of precipitation originated in source regions shows a significant negative correlation for the IP region. Thus, the moisture recycling process in the IP region explains 12% of the variability of the monthly oxygen isotope composition of precipitation (p-value<0.1). However, when temperature, amount of precipitation and all source regions are considered, 74% of the variability of the monthly oxygen isotope composition of precipitation is explained (p-value<0.05). Therefore, although for Eagle Cave amount of precipitation and temperature are main contributors of the precipitation oxygen isotope variability (r2=0.54; p-value<0.001), the moisture uptake distribution among source regions is a substantial control and should be considered when interpreting oxygen isotope speleothem records from this cave. This research highlights the importance of moisture sources in controlling the oxygen isotope composition of precipitation in mid-latitudes, and the need of quantification of this effect in order to improve the interpretation of oxygen isotope paleo-records that depend on isotope composition of precipitation.

Oxygen isotope ratios (18O/16O) of hemicellulose-derived sugar biomarkers in plants, soils and sediments as paleoclimate proxy II: Insight from a climate transect study

The oxygen isotopic composition of precipitation (δ18Oprec) is well known to be a valuable (paleo-)climate proxy. Paleosols and sediments and hemicelluloses therein have the potential to serve as archives recording the isotopic composition of paleoprecipitation. In a companion paper (Zech et al., 2014) we investigated δ18Ohemicellulose values of plants grown under different climatic conditions in a climate chamber experiment. Here we present results of compound-specific δ18O analyses of arabinose, fucose and xylose extracted from modern topsoils (n=56) along a large humid-arid climate transect in Argentina in order to answer the question whether hemicellulose biomarkers in soils reflect δ18Oprec.The results from the field replications indicate that the homogeneity of topsoils with regard to δ18Ohemicellulose is very high for most of the 20 sampling sites. Standard deviations for the field replications are 1.5‰, 2.2‰ and 1.7‰, for arabinose, fucose and xylose, respectively. Furthermore, all three hemicellulose biomarkers reveal systematic and similar trends along the climate gradient. However, the δ18Ohemicellulose values (mean of the three sugars) do not correlate positively with δ18Oprec (r=−0.54, p<0.014, n=20). By using a Péclet-modified Craig-Gordon (PMCG) model it can be shown that the δ18Ohemicellulose values correlate highly significantly with modeled δ18Oleaf water values (r=0.81, p<0.001, n=20). This finding suggests that hemicellulose biomarkers in (paleo-)soils do not simply reflect δ18Oprec but rather δ18Oprec altered by evaporative 18O enrichment of leaf water due to evapotranspiration. According to the modeling results, evaporative 18O enrichment of leaf water is relatively low (∼10‰) in the humid northern part of the Argentinian transect and much higher (up to 19‰) in the arid middle and southern part of the transect. Model sensitivity tests corroborate that changes in relative air humidity exert a dominant control on evaporative 18O enrichment of leaf water and thus δ18Ohemicellulose, whereas the effect of temperature changes is of minor importance. While oxygen exchange and degradation effects seem to be negligible, further factors needing consideration when interpreting δ18Ohemicellulose values obtained from (paleo-)soils are evaporative 18O enrichment of soil water, seasonality effects, wind effects and in case of abundant stem/root-derived organic matter input a partial loss of the evaporative 18O enrichment of leaf water.Overall, our results prove that compound-specific δ18O analyses of hemicellulose biomarkers in soils and sediments are a promising tool for paleoclimate research. However, disentangling the two major factors influencing δ18Ohemicellulose, namely δ18Oprec and relative air humidity controlled evaporative 18O enrichment of leaf water, is challenging based on δ18O analyses alone.

Climatologic and hydrologic influences on the oxygen isotope ratio of tree cellulose in coastal southern California during the late 20th century

The oxygen isotope ratio (δ18O) of precipitation in continental, midlatitude regions is a complex measure of atmospheric dynamics and regional climate variability and can be preserved in geologic archives. However, continuous modern observations of precipitation δ18O in many midlatitude regions, particularly in the coastal western United States, are sparse. Here, tree‐ring cellulose δ18O from southern California is used to assess the potential of this proxy as an indicator of long‐term hydroclimate and atmospheric variability. From 1954 to 2004, we observed that cellulose δ18O was well replicated within a single stand of blue oak (Quercus douglasii) on interannual and decadal time scales. By using a forward mechanistic model, we demonstrate that cellulose δ18O is not driven solely by the oxygen isotope composition of precipitation at the site nor any other single hydroclimate variable. Instead, the interannual variability in cellulose δ18O prior to 1979 is positively correlated with growing season soil water δ18O and after 1979 is negatively correlated with relative humidity. In addition, 2 years (1983 and 1998) of anomalously low cellulose δ18O coincided with the wettest years in California and the strongest El Niño events of the late 20th century. For these years, decreased near surface evaporation and/or increased upper‐level condensation could account for the more depleted cellulose δ18O values. While blue oak cellulose δ18O is sensitive to atmospheric and hydroclimate variability, the varying temporal correlation between the cellulose δ18O and different environmental variables complicates any attempt to use the cellulose oxygen isotopes for reconstructions of climate variability beyond the calibration period.

Climate controls on Andean precipitation δ18O interannual variability

The stable oxygen isotopic composition of precipitation (δ18Op) is used as a proxy for modern and past atmospheric, biologic, and surface processes. Although the physical processes that fractionate 18O in vapor are known, regional controls of δ18Op are not well understood. Here we present results from a limited‐domain general circulation model (REMOiso) to quantify regional controls on modern (1976–1999) interannual and spatial variations of δ18Op across four Andean domains spanning 50° latitude. Results are compared to observed δ18Op from meteorological stations. Simulated annual amount‐weighted mean δ18Op ranges between −4 and −7‰ (0–5°S), −8 and −20‰ (14°S–26°S), −4 and −8.5‰ (30°S–35°S), and −7 to −10‰ (45°S–50°S). Relationships between climate and δ18Op on interannual timescale vary along the Andes and are tied to changes in precipitation and large‐scale dynamics. In the northern Andes, interannual variations in δ18Op are mainly associated with precipitation amounts driven by low‐latitude sea surface temperature and Amazon Basin conditions. In the north central Andes, δ18Op correlates with precipitation amount and wind trajectory, which is related to the position of the Bolivian High. In the south central Andes, δ18Op variability is mainly influenced by precipitation amounts that are controlled by the position and strength of the westerlies. In the southern Andes, interannual δ18Op variability is linked to the intensification and weakening of the South Pacific High. The regional climate‐δ18Op relationships are discussed in the context of pre‐Quaternary sedimentary δ18O proxy records.

Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model

Abstract. To understand the validity of δ18O proxy records as indicators of past temperature change, a series of experiments was conducted using an atmospheric general circulation model fitted with water isotope tracers (Community Atmosphere Model version 3.0, IsoCAM). A pre-industrial simulation was performed as the control experiment, as well as a simulation with all the boundary conditions set to Last Glacial Maximum (LGM) values. Results from the pre-industrial and LGM simulations were compared to experiments in which the influence of individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea surface temperature (SST), and orbital parameters) were changed each at a time to assess their individual impact. The experiments were designed in order to analyze the spatial variations of the oxygen isotopic composition of precipitation (δ18Oprecip) in response to individual climate factors. The change in topography (due to the change in land ice cover) played a significant role in reducing the surface temperature and δ18Oprecip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and δ18Oprecip further. A global mean cooling of 4.1 °C was simulated with combined LGM boundary conditions compared to the control simulation, which was in agreement with previous experiments using the fully coupled Community Climate System Model (CCSM3). Large reductions in δ18Oprecip over the LGM ice sheets were strongly linked to the temperature decrease over them. The SST and ice sheet topography changes were responsible for most of the changes in the climate and hence the δ18Oprecip distribution among the simulations.

The cause of the seasonal variation in the oxygen isotopic composition of precipitation along the western U.S. coast

This study seeks to find the primary influence on the seasonal cycle of the oxygen isotopic composition of precipitation (δ18Op) along the western U.S. coast. Observed long‐term mean seasonal variations ofδ18Op from 16 different stations along the west coast are presented. The most robust features in the observations are high values in the summer and a drop in δ18Opduring the winter. The Isotope‐incorporated Global Spectral Model (IsoGSM) also simulates this wintertime drop inδ18Op along the west coast of the U.S. Sensitivity experiments are performed with IsoGSM where individual oxygen isotope fractionation processes are turned off. These simulations reveal that the primary control on the seasonal variations is equilibrium oxygen isotopic fractionation during vapor condensation. There is almost no influence of the temperature dependence of equilibrium fractionation on the seasonal δ18Op cycle for both evaporation and condensation. Additional experiments (including tagging simulations) are performed to better understand why Rayleigh distillation causes the seasonal variation in δ18Op. The tagging simulations and budget calculations reveal that vertical oxygen isotope gradients and variations in condensation height cause the seasonal cycle in δ18Op. This results from seasonal changes in the polar jet, and subsequent changes to divergence and vertical velocities, which affects the uplift of moisture. These findings suggest that δ18Op in the western U.S. is a tracer of condensation height on seasonal timescales. The large influence of condensation height on δ18Op seasonality complicates interpretations of interannual climate proxy records based on isotopes in precipitation as the seasonality is likely not static.

Reconstructing the paleoenvironment of East Central Europe in the Late Pleistocene using the oxygen and carbon isotopic signal of tooth in large mammal remains

Stable carbon and oxygen isotope values (δ13C, δ18O) of structural carbonate were determined in the bioapatite component of fossil teeth from the Czech Republic, Slovakia and Hungary. Oxygen isotope compositions of enamel and dentin samples provide new quantitative records of the Late Pleistocene climate in East Central Europe (ECE). These δ18O data were combined with records of oxygen isotope values of recent and paleogroundwaters to study the spatial patterns and temporal variations in the oxygen isotope composition of precipitation and the thermal climate over ECE. The new isotopic data suggest that surface air temperatures in the study region between 33 and 12 ka were 2–9 °C colder than present. Specimens of woolly mammoth, rhino and horse from the Late Pleistocene were primarily C3 grazers.

The oxygen isotopic composition of phytolith assemblages from tropical rainforest soil tops (Queensland, Australia): validation of a new paleoenvironmental tool

Abstract. Phytoliths are micrometric particles of amorphous silica that form inside or between the cells of higher plant tissues throughout the life of a plant. With plant decay, phytoliths are either incorporated into soils or exported to sediments via regional watersheds. Phytolith morphological assemblages are increasingly used as proxy of grassland diversity and tree cover density in inter-tropical areas. Here, we investigate whether, along altitudinal gradients in northeast Queensland (Australia), changes in the δ18O signature of soil top phytolith assemblages reflect changes in mean annual temperature (MAT) and in the oxygen isotopic composition of precipitation (δ18Oprecipitation), as predicted by equilibrium temperature coefficients previously published for silica. Oxygen isotopic analyses were performed on 16 phytolith samples, after controlled isotopic exchange (CIE), using the IR Laser-Heating Fluorination Technique. Long-term mean annual precipitation (MAP) and MAT values at the sampled sites were calculated by the ANUCLIM software. δ18Oprecipitation estimates were calculated using the Bowen and Wilkinson (2002) model, slightly modified. An empirical temperature-dependant relationship was obtained: δ18Owood phytolith-precipitation (‰ vs. VSMOW) = −0.4 (±0.2) t (°C) + 46 (±3) (R2 = 0.4, p &lt; 0.05; n = 12). Despite the various unknowns introduced when estimating δ18Oprecipitation values and the large uncertainties on δ18Owood phytolith values, the temperature coefficient (−0.4 ± 0.2‰ °C−1) is in the range of values previously obtained for natural quartz, fresh and sedimentary diatoms and harvested grass phytoliths (from −0.2 to −0.5‰ °C−1). The consistency supports the reliability of δ18Owood phytolith signatures for recording relative changes in mean annual δ18Osoil water values (which are assumed to be equivalent to the weighted annual δ18O precipitation values in rainforests environments) and MAT, provided these changes were several ‰ and/or several °C in magnitude.

Climate information imprinted in oxygen-isotopic composition of precipitation in Europe

In this study we analyze the interannual variability of the oxygen-isotopic composition of winter precipitation ( δ 18 O prec ) over Europe and investigate its related climate information. For this purpose we compare winter temperature, precipitation and δ 18O prec modeled by the atmospheric general circulation model ECHAM5-wiso with different observational datasets over Europe. In general the model and data results are very similar for the present-day climate and the modeled δ 18 O prec is matching the Global Network of Isotopes in Precipitation station data. ECHAM5-wiso only slightly underestimates the temperatures over Europe (mean difference ~ 0.4 °C). The mean European precipitation amount is very similar (~ 85 mm/month), however in central western Europe the modeled precipitation is overestimated by up to 30 mm/month. We also evaluate the large-scale circulation associated with the regional δ 18 O prec values. By correlating the North Atlantic Oscillation (NAO) index to modeled δ 18 O prec fields, we show that the NAO pattern is most pronouncedly imprinted in δ 18 O prec over central western Europe, consistent with observations. We demonstrate for an example location near a stalagmite site in central Germany, how local isotope-related climate variables are related to large-scale European climate variability. We find that, in both the model results and the data, present-day winter variability of local δ 18 O prec is strongly related to atmospheric circulation (remote sea-level pressure fields) and much less to the local and remote temperature or precipitation fields. The simulated correlation pattern resembles the NAO pattern, but is tilted to the east due to the combined effect of temperature and precipitation.

An isotopic calibration study of precipitation, cave dripwater, and climate in west‐central Florida

AbstractA calibration study of oxygen and hydrogen isotopic composition from precipitation and cave dripwater was conducted in west‐central Florida at Legend Cave during 2007–2008. This study was performed to better understand how modern precipitation patterns can be discerned through examination of cave dripwater and speleothem calcite for paleoclimate reconstruction. The ‘amount effect’ was shown to be a dominant control on the oxygen isotopic composition of precipitation for the study area. A meteoric water line with a slope of 6·7 suggests evaporative effects occur either during precipitation or subsequent hydrological processes. However, δ18O values of cave dripwater averaged near the mean annual amount‐weighted average of precipitation, suggesting that the isotopic composition of dripwater tracks the long‐term average of rainfall. An observed weak seasonal influence occurred in the d‐excess values, with summer precipitation being more enriched due to increased evaporative effects. Comparison of precipitation δ18O values to synoptic weather data shows the dominant amount effect influence occurs due to strong convective storms producing highly 18O‐depleted rainfall at greater amounts during the year. Constant δ18O values of the dripwater indicate that paleoclimate reconstructions using speleothems from this area would record changes in annual to interannual shifts in precipitation amount above the cave. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Quantification of a greenhouse hydrologic cycle from equatorial to polar latitudes: The mid-Cretaceous water bearer revisited

This study aims to investigate the global hydrologic cycle during the mid-Cretaceous greenhouse by utilizing the oxygen isotopic composition of pedogenic carbonates (calcite and siderite) as proxies for the oxygen isotopic composition of precipitation. The data set builds on the Aptian–Albian sphaerosiderite δ 18O data set presented by Ufnar et al. (2002) by incorporating additional low latitude data including pedogenic and early meteoric diagenetic calcite δ 18O. Ufnar et al. (2002) used the proxy data derived from the North American Cretaceous Western Interior Basin (KWIB) in a mass balance model to estimate precipitation–evaporation fluxes. We have revised this mass balance model to handle sphaerosiderite and calcite proxies, and to account for longitudinal travel by tropical air masses. We use empirical and general circulation model (GCM) temperature gradients for the mid-Cretaceous, and the empirically derived δ 18O composition of groundwater as constraints in our mass balance model. Precipitation flux, evaporation flux, relative humidity, seawater composition, and continental feedback are adjusted to generate model calculated groundwater δ 18O compositions (proxy for precipitation δ 18O) that match the empirically-derived groundwater δ 18O compositions to within ± 0.5‰. The model is calibrated against modern precipitation data sets. Four different Cretaceous temperature estimates were used: the leaf physiognomy estimates of Wolfe and Upchurch (1987) and Spicer and Corfield (1992), the coolest and warmest Cretaceous estimates compiled by Barron (1983) and model outputs from the GENESIS-MOM GCM by Zhou et al. (2008). Precipitation and evaporation fluxes for all the Cretaceous temperature gradients utilized in the model are greater than modern precipitation and evaporation fluxes. Balancing the model also requires relative humidity in the subtropical dry belt to be significantly reduced. As expected calculated precipitation rates are all greater than modern precipitation rates. Calculated global average precipitation rates range from 371 mm/year to 1196 mm/year greater than modern precipitation rates. Model results support the hypothesis that increased rainout produces δ 18O-depleted precipitation. Sensitivity testing of the model indicates that the amount of water vapor in the air mass, and its origin and pathway, significantly affect the oxygen isotopic composition of precipitation. Precipitation δ 18O is also sensitive to seawater δ 18O and enriched tropical seawater was necessary to simulate proxy data (consistent with fossil and geologic evidence for a warmer and evaporatively enriched Tethys). Improved constraints in variables such as seawater δ 18O can help improve boundary conditions for mid-Cretaceous climate simulations.

Estimating the Oxygen Isotopic Composition of Equatorial Precipitation During the Mid-Cretaceous

Abstract Recent studies utilize the oxygen isotopic composition of pedogenic carbonates (siderite and calcite) to evaluate empirically the global hydrologic cycle during the Cretaceous. Pedogenic carbonates are used as a proxy for the isotopic composition of meteoric waters in order to estimate precipitation rates in the Aptian–Albian via a mass-balance model. These modeling studies have previously been limited to mid-latitude to high-latitude data, and thus a more extensive latitudinal data set is needed to produce a more globally constrained model. This study provides an equatorial (~ 2° S paleolatitude) data set from pedogenic sphaerosiderites of the Caballos Formation from the Upper Magdalena Valley, Colombia. In addition, macroscopic and microscopic morphological features of paleosols were used to identify ancient soil conditions. The gleyed appearance and presence of sphaerosiderites suggest that soils were dominated by water-saturated conditions, with occasional incursions of marine-influenced water resulting in pyrite precipitation. This observation constrains the sampling sites to paleoelevations near sea level. Paleosols are interpreted to have been Entisols, Inceptisols, and Ultisols similar to soils in coastal equatorial regions of modern Colombia. Relatively invariant δ18O values and more variable δ13C values produce vertical trends in δ13C vs. δ18O space called meteoric sphaerosiderite lines. The average oxygen isotopic composition for these trends is −4.41 ± 0.37‰ (VPDB). The average oxygen isotopic composition of meteoric waters precipitating the sphaerosiderites is estimated at −4.56 ± 0.38‰ (VSMOW). These are slightly more enriched than modern and modeled Cretaceous estimates of equatorial precipitation δ18O but are generally in agreement with expected oxygen isotopic compositions of precipitation for this paleolatitude.

Oxygen isotope values of precipitation and the thermal climate in Europe during the middle to late Weichselian ice age

The oxygen isotope compositions of 28 mammoth tooth enamel samples from Estonia, Latvia, Lithuania, Poland and Denmark provide new quantitative records of the middle to late Weichselian climate in northern Europe. The new δ 18O data was combined with records of oxygen isotope values from earlier investigations on European mammoth tooth enamel and palaeogroundwaters to study the spatial patterns and temporal variations in the oxygen isotope composition of precipitation and the thermal climate over much of Europe. The reconstructed geographical distribution of δ 18O in precipitation during 52–24 ka reflects the progressive isotopic depletion of air masses moving northeast, consistent with a westerly source of moisture for the entire region, and a circulation pattern similar to that of the present-day. Regional long-term average δ 18O w values were 0.6–4.1‰ lower than at present, the largest changes recorded for the currently maritime influenced southern Sweden and the Baltic region. The application of regionally varied δ/ T-slopes, estimated from palaeogroundwater data and modern correlations, yield reasonable estimates of glacial surface temperatures in Europe and imply 2–9 °C lower long-term mean annual surface temperatures during the glacial period.

Controls on oxygen isotope variability in precipitation and cave drip waters, central Texas, USA

summary This study investigates the factors that control the oxygen isotopic composition of precipitation and cave drip waters in central Texas. Precipitation samples collected in Austin, Texas at monthly to bimonthly intervals between 1999 and 2007 have d 18 O values between 12.6‰ and 1.1‰ VSMOW and a weighted average value of 4.1‰. This weighted average value likely reflects the isotopic composition of precipitation generated predominantly by moisture masses that originate from the Gulf of Mexico. Samples with the lowest d 18 O values (12.6 ± 0.1‰) are associated with precipitation from moisture masses related to Pacific tropical cyclones. Precipitation amount appears to be an important control on the oxygen isotope composition of rainfall during summertime periods with the warmest weather, but does not account for the variability of the precipitation isotopic data for colder months. Drip-water samples collected at monthly to quarterly intervals from multiple drip sites in three regionally distributed central Texas caves between 1998 and 2007 have d 18 O values between 5.5‰ and 0.6‰ with individual drip sites generally