Difference In δ18O Research Articles

Negative correlation between altitudes and oxygen isotope ratios of seeds: exploring its applicability to assess vertical seed dispersal.

Vertical seed dispersal, which plays a key role in plant escape and/or expansion under climate change, was recently evaluated for the first time using negative correlation between altitudes and oxygen isotope ratio of seeds. Although this method is innovative, its applicability to other plants is unknown. To explore the applicability of the method, we regressed altitudes on δ 18O of seeds of five woody species constituting three families in temperate forests in central Japan. Because climatic factors, including temperature and precipitation that influence δ 18O of plant materials, demonstrate intensive seasonal fluctuation in the temperate zone, we also evaluated the effect of fruiting season of each species on δ 18O of seeds using generalized linear mixed models (GLMM). Negative correlation between altitudes and δ 18O of seeds was found in four of five species tested. The slope of regression lines tended to be lower in late‐fruiting species. The GLMM analysis revealed that altitudes and date of fruiting peak negatively affected δ 18O of seeds. These results indicate that the estimation of vertical seed dispersal using δ 18O of seeds can be applicable for various species, not just confined to specific taxa, by identifying the altitudes of plants that produced seeds. The results also suggest that the regression line between altitudes and δ 18O of seeds is rather species specific and that vertical seed dispersal in late‐fruiting species is estimated at a low resolution due to their small regression slopes. A future study on the identification of environmental factors and plant traits that cause a difference in δ 18O of seeds, combined with an improvement of analysis, will lead to effective evaluation of vertical seed dispersal in various species and thereby promote our understanding about the mechanism and ecological functions of vertical seed dispersal.

Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling

Abstract. The 8.2 ka BP event could provide important information for predicting abrupt climate change in the future. Although published records show that the East Asian monsoon area responded to the 8.2 ka BP event, there is no high-resolution quantitative reconstructed climate record in this area. In this study, a reconstructed 10-year moving average annual rainfall record in southwest China during the 8.2 ka BP event is presented by comparing two high-resolution stalagmite δ18O records from Dongge cave and Heshang cave. This decade-scale rainfall reconstruction is based on a central-scale model and is confirmed by inter-annual monitoring records, which show a significant positive correlation between the regional mean annual rainfall and the drip water annual average δ18O difference from two caves along the same monsoon moisture transport pathway from May 2011 to April 2014. Similar trends between the reconstructed rainfall and the stalagmite Mg ∕ Ca record, another proxy of rainfall, during the 8.2 ka BP period further increase the confidence of the quantification of the rainfall record. The reconstructed record shows that the mean annual rainfall in southwest China during the central 8.2 ka BP event is less than that of present (1950–1990) by ∼ 200 mm and decreased by ∼ 350 mm in ∼ 70 years experiencing an extreme drying period lasting for ∼ 50 years. Comparison of the reconstructed rainfall record in southwest China with Greenland ice core δ18O and δ15N records suggests that the reduced rainfall in southwest China during the 8.2 ka BP period was coupled with Greenland cooling with a possible response rate of 110 ± 30 mm °C−1.

Surface-to-subsurface temperature variations during the last century in a western boundary upwelling system (Southeastern, Brazil)

The upper thermal gradient of a western boundary upwelling system was reconstructed for the last 100 years. The reconstruction was based on oxygen isotopic composition (δ18O) of four planktonic foraminifera species derived from two boxcores (BCCF10-01 and BCCF10-04) located in the southeastern Brazilian shelf. Calcification depths of the four planktonic foraminifera species were estimated in order to understand which layer of the water column was assessed. Changes in the upper thermal gradient were evaluated by using the δ18O difference from the surface-dwelling species Globigerinoides ruber (pink) and the deep-dwelling Neogloboquadrina dutertrei. The relative abundance of cold-water species and the δ13C of G. ruber (pink) were also used to evaluate changes on the surface layer. Our results demonstrate a trend to reduction on the temperature difference (∆T) between the surface and the thermocline layer towards the present for both cores, together with an increase on the relative abundance of cold-water species for the mid-shelf core (BCCF10-04) and a decrease in δ13C values of G. ruber (pink) for both cores. Despite the observable trend on the proxies, only the relative abundance of Turborotalita quinqueloba and the δ13C of G. ruber (pink) for the mid-shelf core presented statistically significant trends. These results were related to an increase in South Atlantic Central Water (SACW) intrusions in the sub-surface layer, especially on the middle shelf region. The SACW intrusions would lower the sea surface temperature and would bring a depleted δ13C of the dissolved inorganic carbon signature to the surface, which would be in agreement with our findings. Moreover, these mid-shelf SACW intrusions in the region were attributed to the Ekman pumping (wind stress curl-driven), which was previously reported to be an important mechanism in this upwelling system. The major outcomes to this western boundary current ecosystem from an intensification of the mid-shelf upwelling were discussed.

Purification of BaSO4 precipitate contaminated with organic matter for oxygen isotope measurements (δ18 O and Δ17 O).

Sulfate precipitates are often contaminated with nitrates and organic materials (OM), which reduce the precision and accuracy of measurements of δ18 O and Δ17 O values in the sulfate. Although nitrates can be effectively removed using diethylenetriaminepentaacetic acid solution, removing OM from the precipitates is often difficult. One effective approach is to heat powdered precipitates to high temperatures. In this study, the effect of this procedure on the δ18 O and Δ17 O values of BaSO4 precipitate was fully examined. OM-contaminated BaSO4 precipitates and 18 O- and 17 O-labeled purified BaSO4 precipitates were loaded into alumina and gold crucibles and heated at 450°C, 600°C and 800°C for 2h. The nitrogen and carbon contents in the initial and the final BaSO4 were measured using an elemental analyzer. The values of δ18 O and Δ17 O were measured using a temperature conversion/elemental analyzer coupled with an isotope ratio mass spectrometer, and a CO2 laser system coupled with an isotopic ratio mass spectrometer. OM was effectively (88±17%) removed from the BaSO4 precipitates by this treatment, and heating at 800°C had the highest removal efficiency (98%). The differences in δ18 O and Δ17 O values between the final and initial BaSO4 precipitates was -0.6‰ to 0.3‰ (average of -0.1‰) and -0.24‰ to 0.10‰ (average of -0.02‰), respectively. Significant positive relationships between the δ18 O and Δ17 O values of the initial BaSO4 precipitate and those of the high-T-treated aliquots were found, with slopes having mean values of 0.96±0.06 and 1.04±0.01, respectively. The result demonstrates high removal efficiency for OM in BaSO4 precipitates and no significant differences in the oxygen isotopic compositions between high-T treated BaSO4 and initial BaSO4 . This study indicates that the modified high-T treatment (800°C, 2h) is an effective method for purifying BaSO4 precipitated from geological and environmental samples with a high OM content for δ18 O and Δ17 O measurements. Copyright © 2016 John Wiley & Sons, Ltd.

Application of hydrochemical and isotopic techniques to understand groundwater recharge and flow systems in the Dawa River basin, southern Ethiopia

The study of groundwater recharge and of flow systems is crucial to understand availability and sustainability of groundwater resources. This study uses hierarchical cluster analysis (HCA) and various graphical plots of hydrochemical and isotopic data to examine groundwater recharge and the dynamics of flow system in the Dawa River basin. HCA has classified the water samples into five distinctive clusters. Clusters I, II, and III represent the volcanic and most parts of the basement terrain. These clusters are distinguished by low EC, high percentages of HCO3− and Ca2+, Mg2+, or Na+, and dominantly (Ca, Mg, Na, K)–HCO3-type water. Cluster IV contains sulfate-type water with high percentage of Ca2+ + Mg2+ and represents sedimentary terrain. Cluster V, characterized by high EC and abundant Na+ and SO42− + Cl−, is sited at few locations along dry riverbeds. In the basement terrain, the chemical composition of groundwater varies greatly over short distances. In most parts of the basin, groundwater contains elevated levels of tritium at amount comparable to local rainfall. These chemical characteristics supported with tritium data indicate the dominance of groundwater of local flow systems, short residence time, and modern recharge in the basin. Stable isotope data indicate that in the semi-arid region, recharge occurs from high-intensity rainfall. Difference in δ18O and δ2H between the northern and the southern and southeastern groundwater supports distinct recharge sources and the absence of regional groundwater flow between the two regions. Converging evidences reveal that the traditional regional groundwater flow model which is common in most large river basins of Ethiopia does not hold true in the Dawa River basin.

Sex-associated variations in coral skeletal oxygen and carbon isotopic composition of <i>Porites panamensis</i> in the southern Gulf of California

Abstract. Coral δ18O variations are used as a proxy for changes in sea surface temperature (SST) and seawater isotope composition. Skeletal δ13C of coral is frequently used as a proxy for solar radiation because most of its variability is controlled by an interrelationship between three processes: photosynthesis, respiration, and feeding. Coral growth rate is known to influence the δ18O and δ13C isotope record to a lesser extent than environmental variables. Recent published data show differences in growth parameters between female and male coral in the gonochoric brooding coral Porites panamensis; thus, skeletal δ18O and δ13C are hypothesized to be different in each sex. To test this, this study describes changes in the skeletal δ18O and δ13C record of four female and six male Porites panamensis coral collected in Bahía de La Paz, Mexico, whose growth bands spanned 12 years. The isotopic data were compared to SST, precipitation, photosynthetically active radiation (PAR), chlorophyll a, and skeletal growth parameters. Porites panamensis is a known gonochoric brooder whose growth parameters are different in females and males. Splitting the data by sexes explained 81 and 93 % of the differences of δ18O, and of δ13C, respectively, in the isotope record between colonies. Both isotope records were different between sexes. δ18O was higher in female colonies than in male colonies, with a 0.31 ‰ difference; δ13C was lower in female colonies, with a 0.28 ‰ difference. A difference in the skeletal δ18O could introduce an error in SST estimates of ≈ 1.0 to ≈ 2.6 °C. The δ18O records showed a seasonal pattern that corresponded to SST, with low correlation coefficients (−0.45, −0.32), and gentle slopes (0.09, 0.10 ‰ °C−1) of the δ18O–SST relation. Seasonal variation in coral δ18O represents only 52.37 and 35.66 % of the SST cycle; 29.72 and 38.53 % can be attributed to δ18O variability in seawater. δ13C data did not correlate with any of the environmental variables; therefore, variations in skeletal δ13C appear to be driven mainly by metabolic effects. Our results support the hypothesis of a sex-associated difference in skeletal δ18O and δ13C signal, and suggest that environmental conditions and coral growth parameters affect skeletal isotopic signals differently in each sex. Although these findings relate to one gonochoric brooding species, they may have some implications for the more commonly used gonochoric spawning species such as Porites lutea and Porites lobata.

Comparison of δ13C and δ18O from cellulose, whole wood, and resin-free whole wood from an old high elevation Pinus uncinata in the Spanish central Pyrenees

ABSTRACTδ13C and δ18O values from sapwood of a single Pinus uncinata tree, from a high elevation site in the Spanish Pyrenees, were determined to evaluate the differences between whole wood and resin-free whole wood. This issue is addressed for the first time with P. uncinata over a 38-year long period. Results are also compared with published isotope values of α-cellulose samples from the same tree. The differences in δ13C and δ18O between whole wood and resin-free whole wood vary within the analytical uncertainty of 0.3 and 0.5 ‰, respectively, indicating that resin extraction is not necessary for sapwood of P. uncinata. Mean differences between cellulose and whole wood are 0.9 ‰ (δ13C) and 5.0 ‰ (δ18O), respectively. However, further analyses of different species and other sites are needed to evaluate whether the findings reported here are coherent more generally.

Recruitment Sources of Channel and Blue Catfishes Inhabiting the Middle Mississippi River

AbstractInsight into environments that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfishes are an important recreational species in the Mississippi River and are commercially harvested. However, contributions of main channel and tributary habitats to catfish recruitment in large rivers are unknown. Stable isotope and trace elemental signatures in otoliths are useful for determining environmental history of fishes in a variety of aquatic systems, including the Mississippi River. The objectives of this study were to identify the principal natal environments of channel catfish Ictalurus punctatus and blue catfish Ictalurus furcatus in the Middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ18O) and strontium : calcium ratios (Sr : Ca). Catfishes were sampled during July–October 2013–2014, and lapilli otoliths were analysed for δ18O and Sr : Ca. Water samples from the MMR and tributaries were collected seasonally from 2006 to 2014 to characterize site‐specific signatures. Persistent differences in water δ18O and Sr : Ca among the MMR and tributaries (including the upper Mississippi, Illinois, and Missouri rivers as well as smaller tributaries) were evident, enabling identification of natal environment for individual fish. Blue and channel catfish stocks in the MMR were primarily recruited from the large rivers (Missouri and Mississippi) in our study area, with minimal contributions from smaller tributaries. Recruitment and year class strength investigations and efforts to enhance spawning and nursery habitats should be focused on in large rivers with less emphasis on smaller tributaries. Copyright © 2016 John Wiley & Sons, Ltd.

On the enigmatic similarity in Greenland δ18O between the Oldest and Younger Dryas

AbstractThe last deglaciation (20.0–10.0 kyr B.P.) was punctuated by two major cooling events affecting the Northern Hemisphere: the Oldest Dryas (OD; 18.0–14.7 kyr B.P.) and the Younger Dryas (YD; 12.8–11.5 kyr B.P.). Greenland ice core δ18O temperature reconstructions suggest that the YD was as cold as the OD, despite a 50 ppmv increase in atmospheric CO2, while modeling studies suggest that the YD was approximately 4–5°C warmer than the OD. This discrepancy has been surmised to result from changes in the origin of the water vapor delivered to Greenland; however, this hypothesis has not been hitherto tested. Here we use an atmospheric circulation model with an embedded moisture‐tracing module to investigate atmospheric processes that may have been responsible for the similar δ18O values during the OD and YD. Our results show that the summer‐to‐winter precipitation ratio over central Greenland in the OD is twice as high as in the YD experiment, which shifts the δ18O signal toward warmer (summer) temperatures (enriched δ18O values and it accounts for ~45% of the expected YD‐OD δ18O difference). A change in the inversion (cloud) temperature relationship between the two climate states further contributes (~20%) to altering the δ18O‐temperature‐relation model. Our experiments also show a 7% decrease of δ18O‐depleted precipitation from distant regions (e.g., the Pacific Ocean) in the OD, hence further contributing (15–20%) in masking the actual temperature difference. All together, these changes provide a physical explanation for the ostensible similarity in the ice core δ18O temperature reconstructions in Greenland during OD and YD.

Stable isotope paleoaltimetry and the evolution of landscapes and life

Reconstructing topography of our planet not only advances our knowledge of the geodynamic processes that shape the Earth's surface; equally important it adds a key element towards understanding long-term continental moisture transport, atmospheric circulation and the distribution of biomes and biodiversity. Stable isotope paleoaltimetry exploits systematic decreases in the oxygen (δ18O) or hydrogen (δD) isotopic composition of precipitation along a mountain front when the interaction of topography and advected moist air masses induces orographic precipitation. These changes in δ18O or δD can be recovered from the geologic record and recent geochemical and modeling advances allow a broad range of proxy materials to be evaluated.Over the last 10 yr stable isotope paleoaltimetry has witnessed rapidly expanding research activities and has produced a broad array of fascinating tectonic and geomorphologic studies many of which have concentrated on determining the elevation history of continental plateau regions. These single-site studies have greatly expanded what used to be very sparse global paleoaltimetric data. The challenge now lies in disentangling the surface uplift component from the impact of climate change on δ18O and δD in precipitation. The robustness of stable isotope paleoaltimetry can be enhanced when high-elevation δ18O or δD data are referenced against low-elevation sites that track climate-modulated sea level δ18O or δD of precipitation through time (‘δ–δ approach’). Analysis of central Andean paleosols documents that differences in δ18O of soil carbonate between the Subandean foreland and the Bolivian Altiplano are small between 11 and 7 Ma but rise rapidly to ca. 2.9‰ after 7 Ma, corroborating the magnitude of late Miocene change in δ18O on the Altiplano. Future advances in stable isotope paleoaltimetry will greatly benefit from addressing four key challenges: (1) Identifying topographically-induced changes in atmospheric circulation and associated teleconnections in the global climate system that affect δ18O or δD of precipitation; (2) Evaluating on a case-by-case basis if temporal and spatial changes in isotope lapse rates influence interpretations of paleoelevation; (3) Interfacing with phylogenetic techniques to evaluate competing hypotheses with respect to the timing of surface uplift and the diversification of lineages; (4) Characterizing feedbacks between changes in surface elevation and atmospheric circulation as these are likely to be equally important to the diversification of lineages than changes in surface elevation alone. Tackling these challenges will benefit from the accelerating pace of improved data-model comparisons and rapidly evolving geochemical techniques for reconstructing precipitation patterns. Most importantly, stable isotope paleoaltimetry has the potential to develop into a truly interdisciplinary field if innovative tectonic/paleoclimatic and evolutionary biology/phylogenetic approaches are integrated into a common research framework. It therefore, opens new avenues to study the long-term evolution of landscapes and life.

Oxygen and hydrogen isotopic variations between adjacent drips in three caves at increasing elevation in a temperate coastal rainforest, Vancouver Island, Canada

The interpretation of speleothem paleoenvironmental records requires understanding of spatial–temporal variations in vadose drip water chemistry and isotopic composition. This study reports on intra- and inter-cave differences in δD, δ18O and electrical conductivity, using 18 monthly water samples from three adjacent drips (<20m apart) in each of three caves at increasing elevation (0, 550, and 740m ASL) on very steep ground at the head of Tahsis Inlet fjord on the Pacific coast of Vancouver Island, British Columbia.All drips showed isotopic seasonal signals, despite varied patterns of drip hydrology. There was overlap in isotopic ranges (at 1 SD) between all three caves, in contrast with the expected δ18O depletion of −0.15 to −0.5‰/100m of ascent observed in standard precipitation. The isotopic seasonality was approximated with sine curves, and compared to a GNIP data set from Victoria ∼300km to the south. The δD and δ18O drip isotopes lagged the Victoria record by 155±26days and 165±50days respectively. The longest lag was at the slowest drip (sea level), while the shortest lag (87days for δ18O, 550m ASL) implies a short residence time, paradoxically from the drip with the highest mean electrical conductivity. Vadose residence time was less than one climatic year, reflecting a combination of negligible matrix porosity in the host rock and super-humid climatic conditions. Beneath the epikarst, drip hydrology was evidently by simple piston flow.Phase-shifted drip isotope records showed excellent agreement with sea level mean monthly air temperatures at the Tahsis meteorological station over the study period. The δD and δ18O drip amplitudes were damped on average 74% and 73% respectively compared to the Victoria data. The drips at 740m ASL are tightly aligned to the global mean meteoric water line (GMWL) and 18O-depleted; the drips at 550m ASL and at sea level plot along the GMWL, or between it and the Victoria LMWL, with the exception of the slowest drip (sea level) which displays some seasonal evaporitic enrichment.The findings quantify substantial intra- and inter-cave variation of δD and δ18O in drips having a wide range of drip type and volume of flow, sufficient to mute the altitudinal isotopic lapse rate in this local coastal rainforest environment.

Local water resource variability and oxygen isotopic reconstructions of mobility: A case study from the Maya area

Stable oxygen isotopic studies of migration and mobility using human tissue are based on the premise that δ18O values of potable water sources are relatively stable over time and vary predictably across the landscape. Local variability of δ18O is generally assumed to be negligible and negated by an averaging effect as oxygen is consumed primarily as imbibed liquid and incorporated into tissue. This study tests the assumption that variability of δ18O ratios of water from within a region are insufficient to impact the reconstruction of ancient mobility using isotopic measures of human tooth and bone. This case study focuses on the Maya area of Guatemala and Mexico, a region where many analyses of oxygen isotopic ratios in ancient human tissue has been conducted. 71 water samples were obtained over the course of five years, from precipitation, streams, rivers, lakes, aguadas (watering holes), civals (perennial wetlands), and caves. Unlike most baseline studies, the objective here was the repeated testing of a diversity of sources from the same location. δ18OVSMOW values from surface and meteoric water range from −16.0 to +3.6‰. The precipitation range is −16.0 to 1.58‰ (n=22) with the highest and lowest values measured at the same location (El Zotz, Guatemala). The surface water range is −9.2 to 3.6 (n=48), the lowest value is the Usumacinta River at Yaxchilan and the highest value is from a lake located 65 kilometers away. The δ18O values of local streams were remarkably stable over time. Major rivers, such as the Usumacinta River, have relatively constant values. Closed water basins (lakes, aguadas, and civals) demonstrated an evaporative effect and δ18O was variable both between basins and in individual basins over time. In the Petén region, mean δ18O of precipitation is statistically different than that of lake and aguada water. Local δ18O differences in consumed water likely explain the variability observed in human tooth enamel at Tikal and other Petén region sites. This case study demonstrates that local isotopic values may be more diverse than is generally assumed in studies of human mobility that rely on little to no baseline data. Future studies of mobility based on oxygen isotopic measures of ancient human tooth and bone should include measures of both meteoric water and a diverse range of surface and groundwater to develop more robust interpretations of oxygen isotopic values in ancient human tissue.

Consistently dated records from the Greenland GRIP, GISP2 and NGRIP ice cores for the past 104 ka reveal regional millennial-scale δ18O gradients with possible Heinrich event imprint

We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104 ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and δ15N of N2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was ∼10% greater at Summit compared to at NGRIP. The δ18O temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The δ18O differences between Summit and NGRIP, however, changed slowly over the Last Glacial–Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal δ18O gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit–NGRIP δ18O difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records.

Inferring movement patterns of a coral reef fish using oxygen and carbon isotopes in otolith carbonate

Ratios of oxygen and carbon isotopes (δ18O and δ13C) in otolith carbonate provide information on stock separation and migration of fish populations inhabiting isotopically different environments. δ18O and δ13C were analysed from Lethrinus miniatus (Forster 1801) otoliths to elucidate the probability of broad-scale movement in the Great Barrier Reef. Otolith core and edge portions were compared between and within individuals from the same cohort (n=120) to determine whether isotopically different environments were inhabited by juveniles and adults from different latitudes. A comparison between individuals revealed that δ18O and δ13C increased with latitude and were generally higher in edge than in core portions. Similarly, within most individual otoliths, δ18O and δ13C were higher in edge than in core portions. For some individuals, however, there was no difference in δ18O between core and edge portions, potentially signifying self-recruitment to the area or occupation of areas of similar chemistry. The majority of individuals from 19 to 22°S and almost half of individuals from 18°S displayed juvenile δ18O signatures characteristic of a warmer environment, suggesting movement to cooler environments or potential southerly migration of early life stages to adult habitat. In contrast, almost half of adult individuals in the most northern latitude (18°S) appeared to originate from cooler environments, suggesting movement to warmer environments or potential northward migration with ontogeny. These results infer that movement of L. miniatus individuals occurred across different isotopic environments with life stage and was related to latitude. Isotope ratios provided insight into movement patterns of L. miniatus at scales that will be important for delineating management units for this commercially important species.

Experimental determinations of isotopic fractionation factors associated with N2O production and reduction during denitrification in soils

Quantifying denitrification in arable soils is crucial in predicting nitrogen fertiliser losses and N2O emissions. Stable isotopologue analyses of emitted N2O (δ15N, δ18O and SP=15N site preference within the linear N2O molecule) may help to distinguish production pathways and to quantify N2O reduction to N2. However, such interpretations are often ambiguous due to insufficient knowledge on isotopic fractionation mechanisms. Here we present a complex experimental approach to determine the net fractionation factors (η) associated with denitrification. This determination is based on three laboratory experiments differing in their experimental set-up and soil properties. Static and dynamic incubation techniques were compared. All available methods for independent determination of N2O reduction contribution were used, namely, N2-free atmosphere incubation, acetylene inhibition technique and 15N gas-flux method.For N2O production: (i) the determined difference in δ18O between soil water and produced N2O vary from +18‰ to +42‰ and show very strict negative correlation with soil water saturation; (ii) the determined η15N of N2O production vary from −55‰ to −38‰ and the fractionation decreases with decreasing substrate availability; (iii) the determined SP of produced N2O vary from −3‰ to +9‰. For N2O reduction: (i) the determined η18O and η15N of N2O reduction vary in very wide ranges from −18‰ to +4‰ and from −11‰ to +12‰, respectively, and depend largely on the differences in experimental setups; whereas (ii) the determined ηSP of N2O reduction shows a very consistent value with all previous studies and varies in a rather narrow range from −2‰ to −8‰. It can be concluded that η values of N2O production determined during laboratory incubations yield only roughly estimates for respective values expectable under field study conditions. η18O and η15N associated with N2O reduction may vary largely, probably depending on spatial and temporal coincidence of N2O production and reduction, and are hence not yet predictable for natural conditions. However, the ηSP of N2O reduction appeared to be relatively robust and a most probable value of about −5‰ can be used to constrain N2O reduction based on SP of soil emitted N2O.

Usefulness of pioneer vegetation for the phytomanagement of metal(loid)s enriched tailings: Grasses vs. shrubs vs. trees

The goal of this work was to assess the selection of the most suitable combination of plant species for the phytomanagement of mine tailings, by comparing among different plant life-forms (grasses, shrubs and trees). A comparison on induced rhizosphere changes generated by four plant species (the grass Piptatherum miliaceum, the shrub Helichrysum decumbens, and the trees, Pinus halepensis and Tetraclinis articulata) and high density vegetation patches (fertility islands) at a mine tailing located at Southeast Spain and the description of their physiological status employing stable isotopes analyses were carried out. The edaphic niches for plant growth were determined by salinity, organic matter and total soil nitrogen while metal(loid)s concentrations played a minor role. Induced changes in plant rhizospheres had a significant impact in soil microbiology. While grasses and shrubs may play an important role in primary ecological succession, trees seem to be the key to the development of fertility islands. The low δ15N values (−8.00‰) in P. halepensis needles may reflect higher ectomycorrhizal dependence. Large differences in leaf δ18O among the plant species indicated contrasting and complementary water acquisition strategies. Leaf δ13C values (−27.6‰) suggested that T. articulata had higher water use efficiency than the rest of species (−29.9‰). The implement of a diverse set of plant species with contrasting life forms for revegetating tailings may result in a more efficient employment of water resources and a higher biodiversity not only in relation to flora but soil microbiology too.

Characteristics of silicon and oxygen isotopic compositions of basalts near East Pacific Rise 13°N

In this study, 13 groups of silicon and oxygen isotopes and major elements of the basalts near the East Pacific Rise 13°N are used to study the fractionation of silicon and oxygen isotopes. Among these data, Δ30Si values of basalts vary from −0.4‰ to 0.2‰ with a mean value of Δ30Si of (−0.18±0.22)‰. The δ18O values range from 4.1‰ to 6.4‰ with a mean Δ18O value of (+5.35±0.73)‰. Since the δ30Si values increase in the series of basalt-basaltic andesite-andesite, and δ18O values display a positive correlation with the SiO2 content, we propose that the fractionation of silicon and oxygen isotopes is influenced by the SiO2 content in igneous rocks. Compared with the igneous rocks from Manus Basin with clinopyroxene as their dominant mineral phase, MORBs in this study containing olivine and plagioclase as primary minerals have lower Δ18O and Δ30Si values, indicating that the fractionation of silicon and oxygen isotopes is also affected by different Si-O bridges in silicate minerals. Furthermore, our samples from the EPR are defined as E-MORB based on K/Ti ratios. Probably, the difference in Δ30Si and Δ18O between our samples and a normal MORB are cause by the enriched components in E-MORBs.

Stable isotope analyses of tooth enamel carbonate of large herbivores from the Tugen Hills deposits: Palaeoenvironmental context of the earliest Kenyan hominids

Understanding shifts in past climatic and environmental conditions are crucial for throwing light on human evolution. Available reconstructions of the palaeoecology of faunal and floral assemblages indicate that the earliest Kenyan hominids, including Orrorin tugenensis, are associated with forest landscapes. In this study, we present stable isotope data of tooth enamel carbonate of large herbivores associated with these hominids in order further to evaluate their environmental context. Fossil teeth were sampled in the Lukeino Formation (6.1–5.7 Ma, Late Miocene) and the Mabaget Formation (5.3–4.5 Ma, Early Pliocene) at the foot of the Tugen Hills (Great Rift Valley). Despite chemical changes in fossil enamel, preservation of the palaeoenvironmental signals is supported by the difference in δ18O between hippos and terrestrial fauna. Moreover, the giraffid specimen from the Mabaget Formation exhibits one of the highest δ18O values, as expected for a drought-tolerant animal. The δ13C of large herbivores indicates that the earliest Kenyan hominids inhabited a mixed C3–C4 environment as did Ardipithecus (Ethiopia) and Sahelanthropus (Chad), two early putative hominids. The Tugen Hills might have been a wooded grassland with patches of woodland. There is no record of closed-canopy forest at the time of deposition. We emphasize differences in food habits among herbivore groups. Deinotheres, nearly all elephantids and the giraffid individual had a C3 diet which reflected browsing behaviour. The intake of C4 plants prevailed for equids and gomphotheres and was consistent with grazing habits. Most hippos and suids were mixed C3–C4 feeders and consequently were generalist herbivores. Bovids and rhinos had a diet ranging from C3 to C4 plants. Variations in δ13C and δ18O among faunal assemblages suggest changes in local climate and vegetation. Moister conditions likely occurred in the Early Pliocene and the latest Miocene (ca. 5.7 Ma) than before. The C3 plant biomass would have increased in the latest Miocene. There were probably denser stands of trees within the depositional environment during the Early Pliocene than in the Late Miocene, which is consistent with palaeontological studies.

A trial of the utilization of stable isotope analysis for the estimation of the geographic origins of unidentified cadavers

The number of unidentified cadavers is increasing worldwide and the effective methods which reveal their geographic origin are not well known. In this study, we analyzed the urine stable isotope ratio of hydrogen and oxygen collected from three locations: Chiba (Japan), Fuzhou (China), and Denpasar (Indonesia) from healthy volunteers. In addition, analysis of the effect of drinking bottled water on stable isotope ratios found in urine, and the comparison of the stable isotope ratios of urine and saliva, were conducted. Statistically significant differences in δ2H and δ18O values from the three locations were found. In this pilot study, urine δ18O values became increasingly similar to those of bottled drinking water during an eight-day period of drinking only bottled water. In a separate pilot study significant differences in δ18O, δ13C, and δ15N values from urine and saliva were found, but not in δ2H values. In all three studies, although the number of samples was limited, the results suggest that with further research, stable isotope analysis from urine samples might be used to identify the origins of unidentified corpses, assist in determining the length of time an individual has been in a given area and distinguish between body fluids.

A record of the last 460 thousand years of upper ocean stratification from the central Walvis Ridge, South Atlantic

The upper branch of the Atlantic Meridional Overturning Circulation predominantly enters the Atlantic Ocean through the southeast, where the subtropical gyre is exposed to the influence of the Agulhas leakage (AL). To understand how the transfer of Indian Ocean waters via the AL affected the upper water column of this region, we have generated new proxy records of planktic foraminifera from a core on the central Walvis Ridge, on the eastern flank of the South Atlantic Gyre (SAG). We analyzed the isotopic composition of subsurface dweller Globigerinoides ruber sensu lato, and thermocline Globorotalia truncatulinoides sinistral, spanning the last five Pleistocene glacial‐interglacial (G‐IG) cycles. The former displays a response to obliquity, suggesting connection with high latitude forcing, and a warming tendency during each glacial termination, in response to the interhemispheric seesaw. The δ18O difference between the two species, interpreted as a proxy for upper ocean stratification, reveals a remarkably regular sawtooth pattern, bound to G‐IG cyclicity. It rises from interglacials until glacial terminations, with fast subsequent decrease, appearing to promptly respond to deglacial peaks of AL. Stratification, however, bears a different structure during the last cycle, being minimal at Last Glacial Maximum, and peaking at Termination I. We suggest this to be the result of the intensified glacial wind field over the SAG and/or of the invasion of the South Atlantic thermocline by Glacial North Atlantic Intermediate Waters. The δ13C time series of the two species have similar G‐IG pattern, whereas their difference is higher during interglacials. We propose that this may be the result of the alternation of intermediate water masses in different circulation modes, and of a regionally more efficient biological pump at times of high pCO2.