Analysis Of Oxygen Isotope Ratios Research Articles

Testing the Sample Preparation Method and Oxygen Isotopic Analysis of Tooth Enamel for the Reconstruction of the Birth Seasonality of Ovicaprines (the Case of Teeth from Istykskaya Cave, Eastern Pamir)

Cyclic variations of δ18O along the growth line of M2 and M3 molars provide information about the seasonality of enamel formation and thereby about reproductive seasonality in animals, taking into account the time of tooth eruption and full enamel maturation. Determination of birth seasonality of small ruminants is relevant to the reconstruction of pastoralist strategies. Two peaks of reproductive activity per year are one of the most reliable indicators of human control of the small ruminants. As part of this work, for the first time in Russia, a method of sample preparation and analysis of oxygen isotope ratios in the tooth enamel of small ruminants is proposed. Traditionally, breeding seasonality was evaluated by the isotopic analysis of carbonates, the content of which in dental enamel is only 4 %. According to a new approach, oxygen from a sample is converted to gaseous CO by the interaction of enamel with carbon in a helium flow under 1300 °С, enabling one to measure δ18O in all components of the dental enamel, including phosphates, which make up 90 % of enamel mass and are resistant to diagenesis. In this study, four sample preparation protocols depending on the degree of preservation of teeth and their age were tested: (A) cleaning and sampling of enamel, (B) treatment by H2O2, (C) treatment by NaOCl and CH3COOH, and (D) extraction of Ag3PO4. Results show that for assessing seasonality breeding, it suffices to evaluate the lowest and the highest δ18O along the tooth growth line. If the preservation of sample is good, minimal chemical treatment is enough to observe these extremes.

An optimized method for extraction and purification of inorganic phosphate from plant material for oxygen isotope ratio analysis

Compound-specific stable isotope ratio analysis of oxygen isotopes in inorganic phosphate can be used to study biological phosphorus cycling and the transformation processes controlling the fate of phosphorus. However, methods for extraction of inorganic phosphate from plant tissue for oxygen isotope ratio analysis are not consistent. Further, the purification into solid silver phosphate can be challenging and laborious. In this work, a detailed and optimized method to provide a more consistent, easily implementable and reproducible extraction using trichloroacetic acid and subsequent purification of inorganic phosphate from plant material for oxygen isotope ratio analysis is presented. Key focus points were: uniform extraction of inorganic phosphate from barley leaves, removal of dissolved organic material, flexibility in regards to the amount of inorganic phosphate extracted for the purification into silver phosphate, reduced use of chemicals and, removal of co-precipitated oxygen-bearing compounds before analysis. Most notable optimizations to the method and associated effects were:•Drying of plant material before inorganic phosphate extraction increases the method applicability to a broader range of plant sample types.•Removal of dissolved organic matter improves inorganic phosphate purification.•Sample volume adjustment according to inorganic phosphate content is vital for effective and quantitative precipitations.

A new method for phosphate purification for oxygen isotope ratio analysis in freshwater and soil extracts using solid-phase extraction with zirconium-loaded resin.

Phosphate (PO4 ) oxygen isotope (δ18 OPO4 ) analysis is increasingly applied to elucidate phosphorus cycling. Due to its usefulness, analytical methods continue to be developed and improved to increase processing efficiency and applicability to various sample types. A new pretreatment procedure to obtain clean Ag3 PO4 using solid-phase extraction (SPE) with zirconium-loaded resin (ZrME), which can selectively adsorb PO4 , is presented and evaluated here. Our method comprises (1) PO4 concentration, (2) PO4 separation by SPE, (3) cation removal, (4) Cl- removal, and (5) formation of Ag3 PO4 . The method was tested by comparing the resulting δ18 OPO4 of KH2 PO4 reagent, soil extracts (NaHCO3 , NaOH, and HCl), freshwater, and seawater with data obtained using a conventional pretreatment method. PO4 recovery of our method ranged from 79.2% to 97.8% for KH2 PO4 , soil extracts, and freshwater. Although the recovery rate indicated incomplete desorption of PO4 from the ZrME columns, our method produced high-purity Ag3 PO4 and accurate δ18 OPO4 values (i.e., consistent with those obtained using conventional pretreatment methods). However, for seawater, the PO4 recovery was low (1.1%), probably due to the high concentrations of F- and SO4 2- which interfere with PO4 adsorption on the columns. Experiments indicate that the ZrME columns could be regenerated and used repeatedly at least three times. We demonstrated the utility of ZrME for purification of PO4 from freshwater and soil extracts for δ18 OPO4 analysis. Multiple samples could be processed in three days using this method, increasing sample throughput and potentially facilitating more widespread use of δ18 OPO4 analysis to deepen our understanding of phosphorus cycling in natural environments.

New Reference Materials and Assessment of Matrix Effects for SIMS Measurements of Oxygen Isotopes in Garnet

Accurate ion microprobe analysis of oxygen isotope ratios in garnet requires appropriate reference materials to correct for instrumental mass fractionation that partly depends on the garnet chemistry (matrix effect). The matrix effect correlated with grossular, spessartine and andradite components was characterised for the Cameca IMS 1280HR at the SwissSIMS laboratory based on sixteen reference garnet samples. The correlations fit a second‐degree polynomial with maximum bias of ca. 4‰, 2‰ and 8‰, respectively. While the grossular composition range 0–25% is adequately covered by available reference materials, there is a paucity of them for intermediate compositions. We characterise three new garnet reference materials GRS2, GRS‐JH2 and CAP02 with a grossular content of 88.3 ± 1.2% (2s), 83.3 ± 0.8% and 32.5 ± 3.0%, respectively. Their micro scale homogeneity in oxygen isotope composition was evaluated by multiple SIMS sessions. The reference δ18O value was determined by CO2 laser fluorination (δ18OLF). GRS2 has δ18OLF = 8.01 ± 0.10‰ (2s) and repeatability within each SIMS session of 0.30–0.60‰ (2s), GRS‐JH2 has δ18OLF = 18.70 ± 0.08‰ and repeatability of 0.24–0.42‰ and CAP02 has δ18OLF = 4.64 ± 0.16‰ and repeatability of 0.40–0.46‰.

Stable oxygen isotopes in water of concentrated liquid foodstuffs: Are the commonly determined values accurate?

Oxygen isotope analysis of water molecules of liquid foodstuffs is commonly performed under isotopic equilibrium between water in the solution and the vapour water, assuming that the liquid water activity is equal to unity and that liquid water is an ideal mixture of H2 O isotopologues. A priori this behaviour is not realistic for all foodstuffs, which frequently are very concentrated solutions. In this paper we mainly consider "balsamic vinegar" with the aim of defining an appropriate procedure of oxygen isotope ratio analysis of water molecules in these concentrated solutions. Isotope ratio mass spectrometry (IRMS) measurements of the oxygen isotope ratios (δ18 O values) were carried out on CO2 equilibrated with water molecules at 22 ± 0.1°C. Three independently calibrated, very low salinity waters were used as standards. For grape must and wine vinegar (density < 1.15 g/cm3 ) the δ18 O values for water determined directly on these solutions are "true" values. On the contrary, for balsamic vinegar with density higher than 1.15-1.20 g/cm3 , the δ18 O values obtained directly on the solutions are systematically different from those obtained on water produced by distillation of the same samples at 70°C under vacuum. In the case of balsamic vinegar with density higher than 1.15-1.20 g/cm3 , to avoid severe systematic errors, the isotopic analyses must be carried out on water obtained by distillation under stirring.

Oxygen Isotope Variability within Nautilus Shell Growth Bands.

Nautilus is often used as an analogue for the ecology and behavior of extinct externally shelled cephalopods. Nautilus shell grows quickly, has internal growth banding, and is widely believed to precipitate aragonite in oxygen isotope equilibrium with seawater. Pieces of shell from a wild-caught Nautilus macromphalus from New Caledonia and from a Nautilus belauensis reared in an aquarium were cast in epoxy, polished, and then imaged. Growth bands were visible in the outer prismatic layer of both shells. The thicknesses of the bands are consistent with previously reported daily growth rates measured in aquarium reared individuals. In situ analysis of oxygen isotope ratios using secondary ion mass spectrometry (SIMS) with 10 μm beam-spot size reveals inter- and intra-band δ18O variation. In the wild-caught sample, a traverse crosscutting 45 growth bands yielded δ18O values ranging 2.5‰, from +0.9 to -1.6 ‰ (VPDB), a range that is larger than that observed in many serial sampling of entire shells by conventional methods. The maximum range within a single band (~32 μm) was 1.5‰, and 27 out of 41 bands had a range larger than instrumental precision (±2 SD = 0.6‰). The results from the wild individual suggest depth migration is recorded by the shell, but are not consistent with a simple sinusoidal, diurnal depth change pattern. To create the observed range of δ18O, however, this Nautilus must have traversed a temperature gradient of at least ~12°C, corresponding to approximately 400 m depth change. Isotopic variation was also measured in the aquarium-reared sample, but the pattern within and between bands likely reflects evaporative enrichment arising from a weekly cycle of refill and replacement of the aquarium water. Overall, this work suggests that depth migration behavior in ancient nektonic mollusks could be elucidated by SIMS analysis across individual growth bands.

Cattle Management for Dairying in Scandinavia's Earliest Neolithic.

New evidence for cattle husbandry practices during the earliest period of the southern Scandinavian Neolithic indicates multiple birth seasons and dairying from its start. Sequential sampling of tooth enamel carbonate carbon and oxygen isotope ratio analyses and strontium isotopic provenancing indicate more than one season of birth in locally reared cattle at the earliest Neolithic Funnel Beaker (EN I TRB, 3950-3500 cal. B.C.) site of Almhov in Scania, Sweden. The main purpose for which cattle are manipulated to give birth in more than one season is to prolong lactation for the production of milk and dairy-based products. As this is a difficult, intensive, and time-consuming strategy, these data demonstrate complex farming practices by early Neolithic farmers. This result offers strong support for immigration-based explanations of agricultural origins in southern Scandinavia on the grounds that such a specialised skill set cannot represent the piecemeal incorporation of agricultural techniques into an existing hunter-gatherer-fisher economy.

Initiation of East Asia monsoon failure at the climate transition from the Medieval Climate Anomaly to the Little Ice Age

We have reconstructed decadally-resolved continuous sea surface temperature and seawater δ18O (hence salinity) records over the last 1300yr from alkenone and planktonic foraminiferal oxygen isotope ratio analyses of the East Sea/Japan Sea marine sediments to investigate East Asia monsoon variability. Comparisons of the records with other paleoclimate records indicate a possible connection between changes in the mid-latitude East Asia monsoon and Pacific Decadal Oscillation (PDO) over this period. The results show that during the Medieval Climate Anomaly (MCA) when the PDO index was negative, East Asia was characterized by surface warming with a strengthened summer monsoon. Summer monsoon-related precipitation increased and pluvials possibly dominated in the region at that time. Onset of Asia monsoon failure and severe drought occurred at the end of the MCA and extended to the Little Ice Age (LIA) when the PDO became positive.

Influence of radiation damage on Late Jurassic zircon from southern China: Evidence from in situ measurements of oxygen isotopes, laser Raman, U–Pb ages, and trace elements

The influence of radiation damage on chemical alteration and in situ elemental and isotopic analyses in zircons is evaluated in three ~155Ma granites that are associated with W–Sn polymetallic deposits in the Nanling area of southern China. A combined approach is described using SEM imaging, laser Raman spectroscopy, and ion microprobe analysis of oxygen isotope ratios, U–Pb ages, and trace elements, including H. Domains within single zircons can be classified into two groups based on cathodoluminescence (CL) intensity and U–Th concentrations. Type-I are single crystals or clearly defined cores with bright CL, having U<1400ppm and Th<800ppm; type-II are rims surrounding type-I cores or single crystals with dark or intermediate CL-intensity and have 2100–30,000ppm U and 900–6500ppm Th. Both types of zircon display oscillatory zonation. Type-I zircons show a narrow range of δ18Ozircon values (8.5–9.2‰), while type-II zircons have much greater variation of apparent δ18Ozircon values (1.4–8.6‰). Relative to type-I, type-II zircons are characterized by elevated trace-element concentrations (including U, Th, rare earth elements, Y, Hf, Fe and Ti, LaN>10), high cumulative α-dose and background-corrected 16OH/16O, decreased Th/U and Hf/Yb ratios, and deviation in 206Pb/238U ages (up to 70Ma) from the mean age (ca. 155Ma) of type-I zircons. Moreover, laser Raman results show that type-II zircons have much broader FWHM (full width half maximum=6.3–37.8cm−1) and decreased amplitudes for the ~1005cm−1 Raman peak, indicating that they are affected by significant radiation damage. The Raman-measured preserved radiation damage (DαP=0.01–0.49×1015α-decay events/mg) is less than the total alpha-dose (DαT=0.1–1.72×1015α-decay events/mg) for each zircon of type-I and type-II with FWHM<10cm−1, indicating that 30–80% of the total radiation damage experienced by most of these zircons has been annealed. We attribute the negative correlation of δ18O versus U, Th, Y, Hf, La and cumulative α-dose for type-II zircons to open-system behavior resulting from radiation damage of the zircon crystal structure. We interpret type-II zircons to originally represent crystallization from a late-stage granite melt that was enriched in magmatic fluids and incompatible elements. The wide range and low δ18O values recorded by most type-II zircon domains are the result of secondary alteration by fluids (perhaps hydrothermal) facilitated by radiation damage and open system chemical and isotopic exchange. This work shows that a combined approach using imaging, laser Raman and trace element analysis is effective for evaluating the influence of radiation damage and alteration of zircon. This protocol is necessary to evaluate the reliability of in situ oxygen isotopic and U–Pb ages. The 16OH/16O ratio is readily measured during SIMS analysis of oxygen isotopes and can be an effective parameter to monitor alteration of radiation-damaged domains in zircon.

Seasonal climate signals (1990–2008) in a modern Soreq Cave stalagmite as revealed by high-resolution geochemical analysis

High-resolution isotopic and geochemical analyses in a modern (1990–2008) Soreq Cave stalagmite are compared to instrumental records of rainfall and dripwater from the cave, with the aim of determining how seasonal-resolution climate information is transmitted to speleothem geochemistry. In situ, micron-scale analysis of oxygen isotope ratios (δ18O) and trace elements by ion microprobe in combination with a continuous, linear traverse of trace element concentrations by laser-ablation ICP-MS (LA-ICP-MS) allow the definition of geochemical pathways within the cave. Fluorescent banding, imaged by confocal laser fluorescent microscopy (CLFM), as well as δ18O and trace element variations is used to define 18 annual growth increments. Reduced intensity of fluorescent banding and a change in trace element variability reflect the decrease in average rainfall from 628mm/yr (1990–1998) to 433mm/yr (1999–2008). During the wetter period before 1998, Pearson (r-value) and Spearman (ρ-value) correlation coefficients are >0.5 for ion microprobe analyses of the element pairings Sr–Y, Y–P, and Mn–Si. After the transition to the drier period in 1999, a different set of geochemical pairings have r- and ρ-values >0.5, including Mg–δ18O, Mg–Sr, and Sr–Ba. Principal component analysis of data from the adjacent LA-ICP-MS traverse identifies two primary underlying modes of trace element variability. Based on the ion microprobe correlations and principal component analyses, we suggest that a greater seasonal influx of particulate material into the cave during the wetter period (1990–1998) brought about greater P, Cu, Sr, Na, and U variability in the stalagmite. The co-variability of δ18O, Mg, Sr, and Ba is characteristic of the trace element pattern from the drier period (1999–2008) of growth when particulate transport is reduced. These findings support a two-reservoir model of Soreq Cave dripwaters. One reservoir displays a well-mixed “baseline” with a decadal residence time that supplies water to the cave year-round, probably from fine pores or grain-boundary films in the vadose zone. The second reservoir is seasonal rainwater enriched in organic acids, colloids, and small particles and is rapidly transmitted to the cave. Finally, the similar patterns of fluorescence intensity, P, and Cu concentrations support the hypothesis that fluorescent bands in Soreq Cave speleothems are caused by the influx of organic colloids.

Stable isotopes in zooarchaeology: an introduction

Zooarchaeology has a long history as a specialisation thatuses qualitative osteological methods, including the collec-tion of taxonomic data, the recording of bone modification,and the ageing and sexing of animal bones to addressbroader archaeological questions. Metrical analyses, includ-ing geometric morphometrics, the use of scanning electronmicroscopy, thin sectioning, and biomolecular analyseshave all added to the types of quantitative data with whichwe can explore (zoo)archaeological questions. Thesezooarchaeological data cannot only be transformed intoknowledge of the cultural and socioeconomic roles of ani-mals in the past, but can also inform onlargerecological andsocioeconomic structures; they can tell us about palaeoe-thology and palaeobiogeography, site formation processesand use of space within sites, consumption patterns, andreligious and ritual practices. The study of animals in ar-chaeology should not be viewed as an obscure specialisationwith little outside relevance; indeed, it is a critical compo-nent to understanding broader patterns in both the environ-mental and social realms.The applications of stable isotope geochemistry are nu-merous, and its use as an analytical technique in archaeolo-gy has progressed substantially over the past few decades.For example, some early stable isotope studies in archaeol-ogy focused on analysis of oxygen isotope ratios (δ

Late Pleistocene monsoon variability in northwest Thailand: an oxygen isotope sequence from the bivalve Margaritanopsis laosensis excavated in Mae Hong Son province

Long, continuous records of Late Quaternary environmental change are rare in Southeast Asia, yet they are crucial for understanding the nature of early human dispersal and occupation in the Australasian region. We present a new record of palaeomonsoon activity extending back to 35,000 BP (years before the present), based on the analysis of oxygen isotope ratios (δ 18O) in the freshwater bivalve Margaritanopsis laosensis excavated from the Tham Lod and Ban Rai rockshelters in Mae Hong Son Province, northwest Thailand. Long-term changes in the M. laosensis δ 18O record reflect changes in the δ 18O of the river water in which these organisms grew, and correlate well with changes in speleothem δ 18O records of east Asian monsoon rainfall from Hulu Cave and Dongge Cave in China. The new northwest Thailand δ 18O sequence indicates wetter and relatively unstable climatic conditions from 35,000 to 20,000 BP, followed by drier conditions from 20,000 to 11,500 BP. A period of peak aridity occurred around 15,600 BP during Heinrich Event 1, suggesting that the intertropical convergence zone shifted southward when the North Atlantic region cooled. However, there is little evidence for the Younger Dryas event at ∼12,800–11,500 BP. After 9,800 BP, precipitation increased substantially and climatic variability declined. Our findings provide an improved baseline against which to gauge interactions between early humans and climate change in Southeast Asia. For example, there was no significant change in the prehistoric flake stone technology used at Tham Lod and Ban Rai despite the bivalve δ 18O evidence for substantial climate change in the region. Also, the climatic impact of the Younger Dryas event appears to have been less intense in northwest Thailand compared to the cooling and drying observed in China, and may explain why agriculture made a relatively late appearance in Thailand, possibly involving migrants from China.

Essential methodological improvements in the oxygen isotope ratio analysis of N‐containing organic compounds

The quantitative conversion of organically bound oxygen into CO, a prerequisite for the (18)O/(16)O analysis of organic compounds, is generally performed by high-temperature conversion in the presence of carbon at ∼1450°C. Since this high-temperature procedure demands complicated and expensive equipment, a lower temperature method that could be utilized on standard elemental analyzers was evaluated. By substituting glassy carbon with carbon black, the conversion temperature could be reduced to 1170°C. However, regardless of the temperature, N-containing compounds yielded incorrect results, despite quantitative conversion of the bound oxygen into CO. We believe that the problems were partially caused by interfering gases produced by a secondary decomposition of N- and C-containing polymers formed during the decomposition of the analyte. In order to overcome the interference, we replaced the gas chromatographic (GC) separation of CO and N(2) by reversible CO adsorption, yielding the possibility of collecting and purifying the CO more efficiently. After CO collection, the interfering gases were vented by means of a specific stream diverter, thus preventing them from entering the trap and the mass spectrometer. Simultaneously, a make-up He flow was used to purge the gas-specific trap before the desorption of the CO and its subsequent mass spectrometric analysis. Furthermore, the formation of interfering gases was reduced by the use of polyethylene as an additive for analytes with a N:O ratio greater than 1. These methodological modifications to the thermal conversion of N-containing analytes, depending on their structure or O:N ratio, led to satisfactory results and showed that it was possible to optimize the conditions for their individual oxygen isotope ratio analysis, even at 1170°C. With these methodological modifications, correct and precise δ(18)O results were obtained on N-containing analytes even at 1170°C. Differences from the expected standard values were below ±1‰ with standard deviations of the analysis <0.2‰.

Crystal orientation effects in δ18O for magnetite and hematite by SIMS

In situ high precision analysis of oxygen isotope ratios ( δ 18O) by secondary ion mass spectrometry (SIMS) reveals that instrumental bias in δ 18O for magnetite varies due to crystal orientation effects. Multiple analyses of δ 18O have an average precision of ± 0.4‰ (2SD) in single grains of magnetite, close to ± 0.3‰, that obtained for multiple grains of UWQ-1, a homogeneous quartz standard. In contrast, the average precision is five to ten times worse, ± 2–3‰ (2SD), from grain-to-grain of magnetite due to variation in instrumental bias with crystal orientation. Electron backscatter diffraction shows that individual grains of magnetite are single crystals and that crystal orientation varies randomly from grain-to-grain. The crystal orientation for each magnetite grain is plotted relative to the incident angle of the SIMS primary Cs + beam. High values of δ 18O are measured when the Cs + beam is parallel to < uv0>, from [110] to [100], preferred channeling and focusing directions for magnetite. Routine δ 18O analysis at WiscSIMS utilizes a Gaussian focused Cs + primary beam (deep-pit mode) at primary and secondary voltages of + 10 kV and−10 kV respectively (total impact energy 20 keV). Four analytical experiments were conducted in attempts to improve the grain-to-grain precision in measured δ 18O for magnetite: (1) applying an energy offset of 50 eV, (2) using a Köhler illuminated beam (shallow-pit mode), (3) reducing the total impact energy, and (4) varying the primary and secondary accelerating voltages. The best results were obtained in experiment (4) at primary/secondary accelerating voltages of + 3 kV/− 10 kV respectively with an incident Cs + beam angle of 14°. The grain-to-grain precision in measured δ 18O for magnetite improves from ± 2.9‰ to ± 0.8‰ (2SD) at + 10 kV/− 10 kV and + 3 kV/− 10 kV analysis respectively, while precision in single grains is ± 0.4‰ for both. Instrumental bias in δ 18O also varies with crystal orientation for hematite at similar levels as is seen for magnetite. The grain-to-grain precision in measured δ 18O for hematite improves from ± 2.1‰ to ± 1.0‰ (2SD) at + 10 kV/− 10 kV and + 3 kV/− 10 kV analysis respectively, while precision in single grains is ± 0.3‰ (2SD) for both. Importantly, crystal orientation effects have not been identified at levels of ± 0.3‰ for δ 18O in silicates or other minerals analyzed by WiscSIMS though many minerals remain to be examined.

Ion microprobe analysis of oxygen isotopes in garnets of complex chemistry

Accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias, a component of which depends on the cation chemistry of the analyzed mineral. In this study, 26 garnet standards (including 14 new standards) that span the compositional range of pyrope, almandine, grossular, spessartine, and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets. All analyses were normalized to a single master garnet standard (UWG-2) before bias from cation composition was considered. Bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets. Bias is correlated with molar volume in garnets of all compositions in this study. Although this correlation is suitable as a correction scheme for bias, a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed. This method reproduces the bias of all but one standard to within a range of 0.4‰, an accuracy that is on the same order as the reproducibility (± 0.3‰, 2 S.D.) of the master garnet standard UWG-2, but that remains an independent source of error. The new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic, zoned skarn garnet from the Adirondack Mountains. While previous analyses were at the mm-scale, the new data resolve a gradient of δ 18O of 2.1‰ over 16 µm. If experimentally derived diffusion coefficients are correct, these new results show that granulite-facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 Myr.

Climate deterioration in the Eastern Mediterranean as revealed by ion microprobe analysis of a speleothem that grew from 2.2 to 0.9 ka in Soreq Cave, Israel

Analysis of oxygen isotope ratios (δ 18O) by ion microprobe resolves a sub-annual climate record for the Eastern Mediterranean from a Soreq Cave stalagmite that grew between 2.2 and 0.9 ka. In contrast to conventional drill-sampling methods that yield a total variation of 1.0‰ in δ 18O calcite values across our sample, the methods described here reveal up to 2.15‰ variation within single annual growth bands. Values of δ 18O measured by ion microprobe vary in a regular saw-tooth pattern that correlates with annual, fluorescent growth banding where calcite grades from light to dark fluorescence. Modern records of precipitation and of cave dripwater indicate that variable δ 18O calcite values record regular seasonal differences in δ 18O rainfall modified by mixing in the vadose zone. Large differences in δ 18O values measured across a single band (i.e., between the dark and light fluorescent calcite, or Δ 18O dark-light) are interpreted to indicate wetter years, while smaller differences represent drier years. Oxygen isotopes record: 1) month-scale growth increments, 2) changes in Δ 18O dark-light that represent seasonality, 3) a systematic, long-term decrease in maximum Δ 18O dark-light values, and 4) an overall increase in average δ 18O calcite values through time. These results suggest a drying of regional climate that coincides with the decline of the Roman and Byzantine Empires in the Levant region.

Collection of Water Samples from an Autonomous Underwater Vehicle for Tracer Analysis

Abstract A compact water sampler rated to full ocean depth has been deployed from an autonomous underwater vehicle (AUV) to enable oceanographic tracer measurements. Techniques developed to allow the instrument to collect up to 49 samples of sufficient purity for tracer measurement without the need for extensive flushing have increased its sampling frequency, allowing a 200-mL seawater sample to be collected in 10 min. This is achieved by flushing the instrument and sample containers before deployment with a fluid of known properties that can be detected after recovery using salinity analysis. A deployment in which water samples were collected for oxygen isotope ratio analysis is presented as an example. Factors limiting the reliability of the instrument when deployed from an AUV are identified and procedures are developed to address critical problems.

A geochemical method for removing the effect of tephra on lake diatom oxygen isotope records

The analysis of oxygen isotope ratios (δ18O) in biogenic silica (e.g. diatoms, sponge spicules, phytoliths) is an increasingly utilised palaeoclimatic proxy for lakes and oceans, providing an alternative to carbonate δ18O. Currently, the problems associated with the cleaning and extraction of pure diatom silica, especially from lake sediments, may compromise the precision associated with δ18Odiatom records. This is because, despite improvements in cleaning techniques, it is still difficult to remove silica-containing contaminants (e.g. tephra, silts and clays) from biogenic silica. Where it has proved difficult to remove all the silica bearing contaminants from a sample, mass balance calculations involving point counting have been used, but these are inherently inaccurate as they only consider the surface area of the contaminant, rather than volume. The new method described here assesses the volume of contamination in each sample of biogenic silica by using major and trace element geochemistry, allowing the δ18O of the contamination to be removed from the biogenic silica δ18O value by linear mass balance. In this case, diatom silica was contaminated with tephra, however the method should also be applicable to other contaminants such as silts and clays.

Hydrogeochemical properties of a salinity‐affected coastal aquifer in western Japan

AbstractCoastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity‐increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15–20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation–reduction potentials observed in deeper groundwater were low, indicating long residence time for the groundwater. These results, together with hydrogen–oxygen isotope ratio analysis, indicated that the deeper groundwater is affected by seawater. Consequently, observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system, and a 14C isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years. The overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater. The deeper groundwater is, therefore, mainly affected by old seawater. In other words, modern saltwater intrusion has not yet occurred even if some wells contain saline water. The study shows that, even though coastal aquifers are heavily pumped, the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion. Further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Glacial/interglacial changes in the East Australian current

The East Australian Current (EAC) is the western boundary current of the south Pacific gyre transporting warm tropical waters to higher southern latitudes. Recent modelling shows that the partial separation of the EAC (~32°S) and the coupled formation of the Tasman Front (~34°S) are caused by a steep gradient in the zonally integrated wind stress curl. Analysis of oxygen isotope ratios (δ18O) in the planktonic foraminifer, Globigerinoides ruber, from sediment cores from the Coral Sea and Tasman Sea indicates that the EAC separation shifted northward to between 23 and 26°S during the last glacial. We suggest these results indicate a significant change in the Pacific wind stress curl during the glacial. Given recent evidence for El Nino-like conditions in the Pacific during the last glacial, with a reduction in the east–west sea surface temperature (SST) gradient, we suggest that weaker trade winds combined with more northerly, stronger westerlies were associated with a change to the wind stress curl, which repositioned the EAC separation and Tasman Front. In contrast, by ~11 ka BP, the EAC separation was forced south of 26°S. This southward shift was synchronous with a rapid warming of tropical SSTs, and the onset of a La Nina-like SST configuration across the tropical Pacific. It appears that the south Pacific trade winds strengthened accordingly, causing the EAC to readjust its flow. This readjustment of the EAC marks the onset of modern surface-ocean circulation in the southwest Pacific, but the present EAC transport was only achieved in the late Holocene, after 5 ka BP.