Oxygen Isotope Composition Of Water Research Articles

Oxygen and hydrogen isotopic water characteristics of the Aral Sea, Central Asia

The Aral Sea, located in a semi-arid environment, undergoes substantial annual (1200 mm/yr) and decadal lake-level fluctuations due to extreme seasonality in evaporation and precipitation along with steadily reduced river discharge. To trace the source of the lake water and understand the internal dynamics of the lake, we used oxygen and deuterium isotope composition of the lake water collected at different depths during spring and autumn from 2004 to 2006. We collected data from both the western (W) and eastern (E) basins of the Large Aral Sea as well as the channel connecting the two basins. The oxygen and hydrogen isotope ratios of the lake water vary widely (+ 4.6 to − 5.3‰ and − 48 to + 11‰, respectively). We further measured isotopic ratios of groundwater leakage near the shoreline of the W basin of the Large Aral Sea and released in an artesian well on the Kulandy Peninsula. These ratios range from − 16 to + 3.4‰ ( δ 18O) and − 120 to + 2.2‰ ( δD). The river water displays ratios of − 12‰ ( δ 18O) and − 81.3‰ ( δD). Precipitation from winter and early spring 2006 exhibit δ 18O values of − 14‰ (snow) and + 0.2‰ (rain) and δD values of − 97‰ (snow) and + 3.6‰ (rain). The oxygen and hydrogen isotope snapshots show that in addition to evaporation, groundwater effluent flows at different depths are major contributors to the lake in spring and autumn. The d-excess, ranging between − 25‰ (lake water) and + 10‰ (groundwater), further demonstrates the impact of both effluent groundwater and evaporation on the isotopic composition of the lake water. Thus, stable isotope ratios can provide a first insight into seasonally triggered hydrologic interactions in the western part of the endorheic Aral Sea region. Remote sensing studies prove that major groundwater leakage occurs along the entire shoreline, except for the western shore where spatial resolution was too low.

Is small beautiful? A review of the advantages and limitations of using small mammal teeth and the direct laser fluorination analysis technique in the isotope reconstruction of past continental climate change

Oxygen isotopes in mammalian tooth enamel have become a widely used proxy for reconstructing past continental climate change. However, owing to sample size constraints in the chemical separation and precipitation of the phosphate prior to oxygen isotope analysis, this technique has been, until recently, limited to relatively large mammal teeth. As the result of recent developments in chemical and analytical techniques, including the development of a novel pre-treatment technique and a direct laser fluorination methodology of analysis, small mammal teeth (rodents), which are relatively more abundant in the fossil record than large mammal teeth, can now be used. Published examples from the recent literature are provided with the aim of examining the advantages and limitations of using small mammal teeth in palaeoclimate reconstruction studies. Issues that are addressed include 1) the rationale behind the calculation of the mean oxygen isotope composition of local water and the problems associated with the intake of 18O enriched water from plant food and from small water bodies fractionated as a result of evaporation; 2) the methodology, justification and limitations in determining mean annual temperatures (MATs) from calculated δ 18O local water values and also combining the δ 18O local water values with δ 18O values from freshwater biota to calculate, using established thermometry equations, multiple palaeotemperatures of differing climatic significance; 3) specific published examples of how the phosphate oxygen isotope composition of small mammal teeth are being used in studies of continental climate change.

Fish without water: Validation and application of δ18O in Totoaba macdonaldi otoliths

The geochemistry of fish otoliths is a valuable tool for reconstructing environmental conditions, migrations and life histories. In this study we validate the relationship between temperature, the water oxygen isotope composition (δ18O) and otolith δ18O for the endangered Totoaba macdonaldi, raised under controlled aquaculture conditions and in the field. This type of validation is instrumental for habitat reconstruction. By comparing δ18O values in the natal portion of totoaba otoliths from modern and pre-dam specimens ~1000–4500 yr BP, we test the hypothesis that the totoaba used the Colorado River estuary as a nursery site before the river was over-allocated. We found that otolith δ18O could be predicted in a laboratory setting as well as in the wild. Totoaba otoliths from before river diversion had drastically lower natal δ18O values than predicted values, indicating that these differences in δ18O values are the result of a change in the water δ18O, a consequence of diverting the isotopically negative Colorado River flow from the totoaba's nursery grounds. We conclude that the Colorado River flow was a major component of the totoaba's nursery habitat before river diversions. These results are pertinent to ongoing research on this endangered fish, using otoliths to piece together important ecological and life history information.

Sulphur Isotopes, Trace Elements and Mineral Stability Diagrams of Waters from the Abandoned Fe–Cu Mines of Libiola and Vigonzano (Northern Apennines, Italy)

The geochemical characteristics of rills draining pyrite-chalcopyrite tailings impoundments and of bordering streams were investigated at the ophiolite-hosted Libiola and Vigonzano abandoned massive sulphide mines, northern Apennines Italy. Water samples were analysed for major and trace chemical composition, hydrogen and oxygen isotope composition, and sulphur isotope composition of aqueous sulphate. Sulphur isotope composition was determined also for some samples of ore sulphides. At Libiola, the newly acquired chemical results on waters corroborate those from previous investigations, thus providing additional support to existing geochemical models in terms of metal distribution, solid phases precipitation, reaction path modelling and mixing reaction paths, and environmental problems. At Vigonzano, the chemical characteristics of waters are similar to those at Libiola. In both localities, solution-secondary phase equilibria estimated using an updated thermodynamic dataset account for mineralogy in the field, including poorly crystalline phases like jurbanite and hydrowoodwardite. The hydrogen and oxygen isotope composition of waters at Libiola and Vigonzano agrees with their meteoric origin. Acid to neutral mine waters do not show any significant isotope shift with respect to the initial water, in spite of the oxidation of even large amounts of pyrite/chalcopyrite ore. The sulphur isotope composition of aqueous sulphate in mine rills at Libiola (δ 34S = 5.6 to 8.5‰; mean 6.5‰) matches that of massive sulphide ore (δ 34S = −0.5 to 6.7‰; mean 5.8‰), in keeping with the supergenic origin of the sulphate and related isotope effects in the sulphide oxidation process. Sulphate in mine waters at Vigonzano displays lower δ 34S values in the range 0.6 to 1.5‰. The δ 34S signature of massive ore specimens is within the range reported for most volcanic-hosted massive sulphide deposits, including Cyprus-type deposits.

Record of Low-Temperature Alteration in Asteroids

Research Article| January 01, 2008 Record of Low-Temperature Alteration in Asteroids Michael E. Zolensky; Michael E. Zolensky Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas 77058, U.S.A., michael.e.zolensky@nasa.gov Search for other works by this author on: GSW Google Scholar Alexander N. Krot; Alexander N. Krot Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A. Search for other works by this author on: GSW Google Scholar Gretchen Benedix Gretchen Benedix Department of Mineralogy, The Natural History Museum, London SW7 5BD, United Kingdom Search for other works by this author on: GSW Google Scholar Author and Article Information Michael E. Zolensky Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas 77058, U.S.A., michael.e.zolensky@nasa.gov Alexander N. Krot Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A. Gretchen Benedix Department of Mineralogy, The Natural History Museum, London SW7 5BD, United Kingdom Publisher: Mineralogical Society of America First Online: 03 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2008) 68 (1): 429–462. https://doi.org/10.2138/rmg.2008.68.15 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael E. Zolensky, Alexander N. Krot, Gretchen Benedix; Record of Low-Temperature Alteration in Asteroids. Reviews in Mineralogy and Geochemistry 2008;; 68 (1): 429–462. doi: https://doi.org/10.2138/rmg.2008.68.15 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Abstract Most chondritic materials experienced diverse styles of secondary alteration resulting in formation of hydrous and anhydrous oxygen-bearing minerals—silicates, oxides, and carbonates (phyllosilicates, magnetite, calcite, dolomite, breunnerite, ferrous olivine, hedenbergite, wollastonite, grossular, monticellite, forsterite, andradite, nepheline, sodalite) (Brearley 2003, 2005 and references therein). Petrographic, mineralogic, oxygen and short-lived isotope systematics (26Al-26Mg, 53Mn-53Cr, 129I-129Xe) suggest that alteration occurred in the presence of aqueous solutions under variable physico-chemical conditions (temperature, water:rock ratio, pH, fO2, and fluid compositions) in an asteroidal setting; it started within 1–2 m.y. after formation of the CV CAIs, was multistage, and lasted up to 15 m.y. (Krot et al. 2006 and references therein). Here we review bulk O-isotopic compositions of chondritic materials, O-isotopic compositions of secondary minerals produced during asteroidal alteration, and possible effects of fluid-assisted thermal metamorphism on O-isotopic exchange in primary, high-temperature minerals (melilite and anorthite) in the CV and CO CAIs. The implications of these data for understanding temperatures of alteration, water:rock ratios, and oxygen isotopic composition of water, that probably accreted into chondrite parent bodies in the form of ice, are discussed. The inferred or measured O-isotopic composition of the meteoritic water is close to the terrestrial fractionation line (Δ17O = ±2‰); it is very different from the inferred O-isotopic compositions of the Sun [Δ17O ~ −25‰] (Clayton 2002; Yurimoto and Kuramoto 2004; Hashizume and Chaussidon 2005; Lyons and Young 2005), suggesting significant evolution of O-isotopic composition of the gaseous reservoir in the inner protoplanetary disk over its short (~3–5 m.y.) life time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estimation of percolating water dynamics through the vadose zone of the Postojna cave on the basis of isotope composition

Within the scope of monitoring water percolation through the 100-m thick vadose zone in the area of Postojnska jama continuous measurements of precipitation were carried out on the surface, and continuous measurements of water flow and physical and chemical parameters of selected water trickles were performed under the surface. Occasional samples of percolating waters were taken for the analysis of water oxygen isotope composition. An exponential model of groundwater flow was elaborated, by means of which the retention time of water in individual trickles was estimated. Modelled retention times of groundwater range from 2.5 months to over one year.

Fluid Evolution and Origins of Iron Oxide Cu-Au Prospects in the Olympic Dam District, Gawler Craton, South Australia

Geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper-gold systems in the Olympic Dam district, eastern Gawler craton. They contain high-, and moderate- to low-temperature Fe oxide-rich hydrothermal alteration. The mineral assemblages include magnetite-calc-silicate-alkali feldspar ± Fe-Cu sulfides and hematite-sericite-chlorite-carbonate ± Fe-Cu sulfides ± U, REE minerals. In all documented prospects, the minerals of the hematitic assemblages replace the minerals of the magnetite-rich assemblages. The bulk of the subeconomic Cu-Au mineralization is associated with the hematitic alteration assemblages. Microanalysis by proton ion probe (PIXE) of hypersaline fluid inclusions in magnetite-rich assemblages, however, demonstrates that significant amounts of copper (>500 ppm) were transported by the early-stage high-temperature (>400°C) fluids responsible for the magnetite-rich alteration. These brine inclusions contain multiple solid phases (liquid + vapor + multiple solids) including chalcopyrite in some cases. In comparison, inclusions of the hematitic stage are relatively simple liquid + vapor types, with homogenization temperatures of 200° to 300°C and containing 1 to 8 wt percent NaCl equiv. The Br/Cl ratios of the magnetite-forming fluids measured by PIXE lie beyond the range of typical magmatic and/or mantle values, allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement. Sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and/or crystalline igneous rocks carried by relatively oxidized fluids (∑SO42− ≈ ∑ H2S, δ34Ssulfides from −5 to +2‰) or from crustal sedimentary rocks (δ34Ssulfides from +5 to +10‰). Oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite-rich assemblage have δ18O values of +7.7 to +12.8 per mil and δD values of −15 to −21 per mil. The only available δ18O and δDfluid values for the hematitic assemblage are +4.7 and −9 per mil, respectively. The isotopic compositions of both fluids, coupled with the available literature data, can be explained in terms of fluid reequilibration with felsic Gawler Range Volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the Wallaroo Group at low water-to-rock ratios prior to their arrival at the mineralization sites. The lack of significant copper mineralization associated with magnetite-forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization. Association of the copper-gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two-stage model in which preexisting hydrothermal magnetite with minor associated copper-gold mineralization was flushed by late-stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks. The reduction of these brines, driven by conversion of magnetite to hematite, resulted in precipitation of copper and gold. The oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic Cu-Au mineralization. When compared to published models for the Olympic Dam deposit, the new data for fluids in subeconomic Fe-oxide Cu-Au prospects of the Olympic Dam district indicate the diversity of origins of iron oxide-copper-gold systems, even within the same geologic region.

Sulfur and oxygen isotopic compositions of the dissolved sulphate in the meteoric water in Chuncheon, Korea

The meteoric water deposited in the Chuncheon area was collected from July 2002 to May 2004 and its chemical and isotopic compositions were analyzed to examine if the isotopic data can help trace the sources of the sulfur pollutant and understand the details of acid formation processes in the air. The chemical compositions of the meteoric water indicate that the sulfate mostly comes from anthropogenic sources. The sulfur isotopic compositions of the dissolved sulfate in the meteoric water (δ34Sso4) vary from 2.6 to 7.5‰ with little seasonal differences, which are significantly different from those of the sulfur in the coal being locally consumed (−4.5 to −0.7‰). This difference indicates that the local coal consumption gives insignificant contribution to the pollutant sulfur in the acid deposition of the area. The relationship between (δ34Sso4) and the concentration of sulfate suggests that the sources of pollutant sulfur are variable and inhomogeneous. The oxygen isotopic compositions of the dissolved sulfate in the meteoric water (δ18O4) range from 9.0 to 17.2‰ which are generally lower in winter than in spring. Comparison between the measured and calculated values of (δ18Oso4) suggests that the oxygen isotopic exchange between sulfite and water occurs before its oxidation to sulfate. The extent of isotopic exchange seems to be not controlled by equilibrium but by kinetic fractionation. The poor correlation between δ34S4) and the oxygen isotopic composition of the meteoric water confinns the disequilibrium nature of the isotopic exchange.

Seasonality and the isotope hydrology of Lochnagar, a Scottish mountain lake: implications for palaeoclimate research

The relationship between isotope ratios in precipitation and lake waters was monitored by bi-weekly measurements taken over a five and a half year period between May 2000 and September 2005 (a period of 1964 days) at Lochnagar, a remote mountain lake in eastern Scotland. Short-term changes in the oxygen isotope composition of lake water (δ18OL) at Lochnagar follow a seasonal pattern similar to isotopes in local precipitation (δ18OP), however changes in catchment residence time, snow accumulation, lake ice cover and lake stratification modify the temporal structure of δ18OL over the seasonal cycle. Of particular importance is precipitation amount, which controls catchment and lake residence times, and determines the degree of phase lag and amplitude change between δ18OL and δ18OP. A simple mass balance model replicates these effects and demonstrates that the degree of phase lag and amplitude reduction is predictable given known input/volume ratio. The implications of these observations for the use of δ18O records in palaeoclimatology are important, since it is rare that authigenic and biogenic minerals or organic compounds (from which δ18O and/or δ2H can be measured) are produced in a lake evenly throughout the year.

Analysis of water movement through an unsaturated soil zone in Jeju Island, Korea using stable oxygen and hydrogen isotopes

Summary In order to analyze water movement through an unsaturated soil zone in Jeju Island, Korea, temporal variations in the oxygen-18 and deuterium isotopes of precipitation and soil waters at three different depths were monitored for about one year. The stable oxygen and hydrogen isotopic compositions of the soil waters are plotted between or near the two local meteoric water lines for summer and winter precipitation indicating that the soil waters were recharged from the year-around precipitation, and evaporation was negligible even during hot summer season in the study area. Mean residence times of the soil waters were then estimated from the δ18O, δD, and deuterium excess or d-values of the precipitation and soil waters using two well-mixed or exponential models (EM) and one exponential piston-flow model (EPM). The regression results show that the combination of the exponential piston-flow model and the d-values of the precipitation and soil waters gives the most reasonable estimation of the mean residence times of the soil waters in the study area. It suggests that the deuterium excess or d-values can be used as a better parameter than the δ18O or δD values alone for estimating mean residence times of subsurface waters not only in Korea but also in other Northeast Asian countries. The estimated low moisture contents and hydraulic diffusivities of the soils at the three different depths also indicate that the boundary between the upper fine-grained soil and the lower coarse-grained soil may act as a capillary barrier, and the soil waters probably flow slowly through micropores rather than rapidly through macropores in the unsaturated soil zone.

Corroborating ecological depth preferences of planktonic foraminifera in the tropical Atlantic with the stable oxygen isotope ratios of core top specimens

Past variability in upper ocean thermocline depth is commonly estimated from the abundance of different species of planktonic organisms or the difference in oxygen isotopic composition between two species of planktonic foraminifera, one that lives in the mixed layer and one that lives in or near the thermocline. To test the latter relationships, we measured the oxygen isotopic composition of eight species of planktonic foraminifera (pink and white varieties of Globigerinoides ruber, Globigerinoides sacculifer without the final chamber, Orbulina universa, Pulleniatina obliquiloculata, Globorotalia menardii, Neogloborotalia dutertrei, and Globorotalia tumida) in surface sediment samples from 31 tropical Atlantic deep‐sea sediment cores. Bayesian analysis was used to compare measured oxygen isotopic compositions with their predictions based on modern data sets of annual temperatures and oxygen isotopic composition of ocean water in the upper 500 m at the core sites. Posterior probability densities for predictive model parameters were computed. Probability distributions of calcification depth for analyzed species corroborated their ecological preferences inferred from net tow and sediment trap data. Robustness of the habitat signals in core top specimens suggests that reconstructions of the entire upper ocean temperature profiles, not just their thermocline depth or temperature, might be possible.

Seasonal water use patterns of Juniperus ashei on the Edwards Plateau, Texas, based on stable isotopes in water

Summary Naturally occurring stable isotopes of oxygen and hydrogen were used to determine the seasonal water sources of Juniperus ashei and its relationship with soil water content on the Edwards Plateau of central Texas, Honey Creek State Natural Area. The patchy nature of juniper stands rooting in the thin soils over karstified carbonate bedrock imparts large spatial heterogeneity in soil water content and isotopic composition largely by differential shading, but also by canopy interception. There is a seasonal decrease in the oxygen isotope composition of juniper xylem water by ∼2‰ during the transition from hot, dry summer conditions to the cool, moist winter. Prior to this shift, the xylem water isotope composition is similar to local springs, presumed to represent local groundwater; after this shift, the xylem water composition is similar to soil water below 10 cm. These results suggest a change in juniper water use from a dominantly deep water source during the summer to a dominantly soil source during the winter over the study period, but the timing of this transition will likely vary from year to year.

The interactive effect of temperature and humidity on the oxygen isotope composition of kangaroos

Summary A strong relationship between the oxygen isotope composition (expressed as δ18O) of body water and relative humidity has been demonstrated for a number of mammalian herbivores with low drinking water requirements, including kangaroos. Consequently, it has been suggested that the oxygen isotope composition of preserved mammal remains may be used to reconstruct past relative humidity. Other physiological, environmental and ecological factors may also influence mammalian δ18O, thereby confounding the climatic signal, yet these factors have been rigorously examined in few taxa. We examined sources of variation in the δ18O of tooth enamel, assumed to reflect δ18O of body water, of kangaroos (Macropus spp.) collected throughout Australia. Relative humidity explained a large proportion of the variation in enamel δ18O, a finding that is consistent with previous studies. However, we also found a previously unreported interaction between mean annual temperature and relative humidity. At lower temperatures, the relationship between enamel δ18O and relative humidity was much steeper than at higher temperatures. This may be a consequence of the Peclét effect in plant leaves, whereby high transpiration rates diminish the 18O enrichment of bulk leaf water. It is likely that this interaction is also present in other herbivores with low drinking water requirements. We found little evidence that δ18O varied consistently between molars, suggesting that a ‘weaning effect’ is either absent or swamped by seasonal variation in precipitation δ18O. We suggest that the oxygen isotope composition of preserved kangaroo remains cannot be used to reconstruct relative humidity unless ambient air temperature can be reliably estimated.

Stable Hydrogen and Oxygen Isotope Composition of Waters from Mine Tailings in Different Climatic Environments

The stable isotope composition of waters (delta2H, delta18O) can be used as a natural tracer of hydrologic processes in systems affected by acid mine drainage. We investigated the delta2H and delta18O values of pore waters from four oxidizing sulfidic mine tailings impoundments in different climatic regions of Chile (Piuquenes at La Andina with Alpine climate, Cauquenes and Carén at El Teniente with Mediterranean climate, and Talabre at the Chuquicamata deposit with hyperarid climate). No clear relationship was found between altitude and isotopic composition. The observed displacement of the tailings pore waters from the local meteoric water line toward higher delta18O values (by approximately +2 per thousand delta18O relative to delta2H) is partly due to water-rock interaction processes, including hydration and O-isotope exchange with sulfates and Fe(III) oxyhydroxides produced by pyrite oxidation. In most tailings, from the saturated zone toward the surface, isotopically different zones can be distinguished. Zone I is characterized by an upward depletion of 2H and 18O in the pore waters from the saturated zone and the lowermost vadose zone, due to ascending diffused isotopically light water triggered by the constant loss of water vapor by evaporation at the surface. In zone II, the capillary flow of a mix of vapor and liquid water causes an evaporative isotopic enrichment in 2H and 18O. At the top of the tailings in dry climate a zone III between the capillary zone and the surface contains isotopically light diffused and atmospheric water vapor. In temperate climates, the upper part of the profile is affected by recent rainfall and zone III may not differ isotopically from zone II.

Terrestrial alteration of carbonate in a suite of Antarctic CM chondrites: Evidence from oxygen and carbon isotopes

The oxygen (δ 18O, δ 17O) and carbon (δ 13C, FMOD 14C-the fraction of modern 14C) isotopic compositions of carbonate were measured for a set of paired Antarctic CM chondrites (EET 96006, EET 96016, EET 96017, and EET 96019). While the oxygen isotopic compositions do not plot on the terrestrial fractionation line and indicate that a component of the carbonate minerals has an extraterrestrial origin, they also do not fall on the array defined for carbonates by CM falls and are thus consistent with the presence of a terrestrial carbonate component. The δ 13C and FMOD 14C measurements of carbonate suggest the presence of at least two carbon sources: carbonate derived from atmospheric CO 2 that is inferred to have been produced as a result of silicate weathering reactions and carbonate derived from another carbon source that is either old or non-atmospheric. The relationships between oxygen and carbon isotope data provide additional constraints on the weathering process, and allow the possibility that rock-dominated weathering of the meteorite caused the oxygen isotopic composition of Antarctic water added to the meteorite to evolve away from the terrestrial mass-fractionation array, leading to formation of low temperature terrestrial alteration products that do not lie on the terrestrial fractionation line.

Holocene climate change in the eastern Mediterranean region: a comparison of stable isotope and pollen data from Lake Gölhisar, southwest Turkey

AbstractStable isotope and pollen data from Gölhisar Gölü, a small intramontane lake located in southwest Turkey, provide complementary records of Holocene climate change. Modern oxygen and hydrogen isotope water data are used as a means of comparing present‐day isotope composition of the lake water to the past oxygen isotope composition of the lake water as calculated from 18O/16O ratios in calcite precipitated in the summer months. Despite the lake system being chemically dilute, the modern isotope data clearly establish that the lake water is evaporated in relation to its spring input, suggesting that the palaeo data can be interpreted primarily in terms of changing precipitation/evaporation ratios. δ18O and δ13C values from authigenic calcite through the Holocene show predominantly negative values indicating climatic conditions wetter than today. Particularly notable are low (depleted) isotope values during the earliest Holocene (ca. 10 600–8800 cal. yr. BP), a period for which pollen data imply drier conditions than at present. This divergence between pollen‐inferred and stable isotope palaeoclimate data is found in other east Mediterranean lake sediment records, and suggests that vegetation may have taken several millennia to reach climatic equilibrium at the start of the Holocene. Isotopic fluctuations during the early‐to‐mid Holocene (8800–5100 cal. yr. BP) suggest oscillations between aridity and humidity. Higher δ18O and δ13C values for the second half of the Holocene indicate generally drier conditions than during the period before ca.5100 cal. yr BP although there is some evidence for increased humidity coinciding with pollen evidence for increasing human impact and intensification of agriculture, notably during the so‐called Beyşehir Occupation Phase (Classical and early Byzantine periods). The modern trend towards aridity started about 1300 yr ago. Copyright © 2006 John Wiley & Sons, Ltd.

Dominant Northern Hemisphere climate control over millennial-scale glacial sea-level variability

Based on a radiocarbon and paleomagnetically dated sediment record from the northern Red Sea and the exceptional sensitivity of the regional changes in the oxygen isotope composition of sea water to the sea-level-dependent water exchange with the Indian Ocean, we provide a new global sea-level reconstruction spanning the last glacial period. The sea-level record has been extracted from the temperature-corrected benthic stable oxygen isotopes using coral-based sea-level data as constraints for the sea-level/oxygen isotope relationship. Although, the general features of this millennial-scale sea-level records have strong similarities to the rather symmetric and gradual Southern Hemisphere climate patterns, we observe, in constrast to previous findings, pronounced sea level rises of up to 25m to generally correspond with Northern Hemisphere warmings as recorded in Greenland ice-core interstadial intervals whereas sea-level lowstands mostly occur during cold phases. Corroborated by CLIMBER-2 model results, the close connection of millennial-scale sea-level changes to Northern Hemisphere temperature variations indicates a primary climatic control on the mass balance of the major Northern Hemisphere ice sheets and does not require a considerable Antarctic contribution.

Oxygen isotope fractionation between crocodilian phosphate and water

Oxygen isotope compositions of phosphate (δ 18O p) were measured in tooth enamel from captive and wild individuals of 8 crocodilian species. A rough linear correlation is observed between the δ 18O p of all the studied species and the oxygen isotope composition of ambient water (δ 18O w). Differences in mean air temperature, diet and physiology could contribute significantly to the large scatter of δ 18O p values. The combination of these parameters results in a fractionation equation for which the slope (0.82) is lower than that expected (≥ 1) from predictive model equations that assume temperature and diet as fixed parameters. Taking into account large uncertainties, the observed oxygen isotope fractionation between phosphate and ambient water does not statistically differ from that formerly established for aquatic turtles. Case studies show that δ 18O p values of fossil crocodile tooth enamel can be used to discriminate between marine and freshwater living environments within a precision of about ± 2‰ only.

Neogloboquadrina pachyderma (dex. and sin.) Mg/Ca and δ18O records from the Norwegian Sea

Magnesium/calcium (Mg/Ca) records based on N. pachyderma (dex.) and N. pachyderma (sin.) from the last 1200 years have been retrieved from high‐resolution cores in the Norwegian Sea. Comparing temperatures inferred from Mg/Ca and the oxygen isotopic composition of calcite (δ18OC) with instrumental temperature records from Ocean Weather Ship Mike suggests that N. pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0.6‰. In this region, summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline; hence the deeper dwelling N. pachyderma (sin.) provides a winter season signal. Down‐core N. pachyderma (dex.) Mg/Ca temperatures display larger variance than observed in δ18OC temperatures record derived from the same morphotype. The smaller variance in the δ18OCN. pachyderma (dex.) temperatures is probably linked to salinity changes in the upper 50 m of the water column. The Mg/Ca temperature and δ18OC records are used to reconstruct changes in the oxygen isotopic composition of water (δ18Ow) during the last 1200 years. The reconstructed δ18OW records show variation within a realistic range, allowing the influence of other water masses than those present at the site today, and suggest that the Mg/Ca signal in morphotypes of N. pachyderma in the Norwegian Sea responds to changes in climatic parameters.

Progress in isotope paleohydrology using lake sediment cellulose

Recent advances in sample preparation techniques and mass spectrometry have fostered more routine oxygen isotope analysis of aquatic cellulose in lake sediment cores, a proxy for lake water oxygen isotope history. These methodological developments have significantly increased the feasibility of incorporating this approach into high-resolution, multi-site, and multi-proxy studies, which are frequently necessary to answer complex hydrological, hydroecological and hydroclimatic questions requiring a paleoenvironmental perspective. Direct translation of lake sediment aquatic cellulose oxygen isotope composition into lake water oxygen isotope composition offers appreciable opportunity for quantitative paleohydrological reconstructions, as evidenced by studies conducted over the past 15 years that span Holocene and pre-historical timescales.