Oxygen Isotope Signatures Research Articles

Oxygen and carbon isotope signatures in late Neogene horse teeth from Spain and application as temperature and seasonality proxies

Here we describe a data set of 249 stable O and C isotope compositions from fossil horse teeth from the Upper Neogene of Central Spain and discuss their potential as environmental proxies. It has been shown before that horse tooth enamel δ 18O is a good proxy for local meteoric water δ 18O H2O, which, in turn, bears a distinct relation to temperature during precipitation formation at mid to high latitudes. We discuss the reconstructed δ 18O H2O values, and apply modern δ 18O H2O — temperature equations for the Iberian Peninsula to these values. Results for the Early Pliocene suggest mean annual temperatures up to 2–3 °C higher than today, fitting pollen-based estimates fairly well. Temperatures 5 °C higher than today are predicted for the early Late Miocene (11–9 Ma). These estimations are feasible given the local occurrence of crocodilians and the presence of fruit-eating hominids in Iberia at that time. The estimated amount of cooling since then is similar to the estimated decrease in NW Europe based on plants. The stable carbon isotope record indicates the virtual absence of C4 plants, pointing to an environment consisting of C3 plants under slightly water-stressed conditions. The long-term δ 13C trend follows the expected decrease in average global δ 13C CO2 predicted from planktonic foraminifers. Within-tooth variability is supposed to reflect seasonal change, but the amplitude is expected to have been significantly damped by internal time-averaging effects related to the mixing with atmospheric O 2, reservoir dynamics, enamel maturation and sampling procedure. The exact degree of damping is difficult to estimate, but theoretical considerations suggest values between 50 and 75%, depending on temporal resolution and element used (C/O). Reconstructed seasonal temperature ranges for Central Spain are equal or slightly less than the modern range. Within-tooth δ 13C variation is more difficult to explain, as it can be attributed to multiple factors, such as intra-annual changes in δ 13C CO2, micrometeorology, plant response and diet. The occurrence of both positive and negative intra-tooth δ 18O– δ 13C correlations may be related to orbitally-forced variations in seasonality.

Determination of δ18O in soils: measuring conditions and a potential application

The stable oxygen isotope signature (delta(18)O) of soil is expected to be the result of a mixture of components within the soil with varying delta(18)O signatures. Thus, the delta(18)O of soils should provide information about the soil's substrate, especially about the relative contribution of organic matter versus minerals. As there is no standard method available for measuring soil delta(18)O, the method for the measurement of single components using a high-temperature conversion elemental analyser (TC/EA) was adapted. We measured delta(18)O in standard materials (IAEA 601, IAEA 602, Merck cellulose) and soils (organic and mineral soils) in order to determine a suitable pyrolysis temperature for soil analysis. We consider a pyrolysis temperature suitable when the yield of signal intensity (intensity of mass 28 per 100 microg) is at a maximum and the acquired raw delta(18)O signature is constant for the standard materials used and when the quartz signal from the soil is still negligible. After testing several substances within the temperature range of 1075 to 1375 degrees C we decided to use a pyrolysis temperature of 1325 degrees C for further measurements. For the Urseren Valley we have found a sequence of increasing delta(18)O signatures from phyllosilicates to upland soils, wetland soils and vegetation. Our measurements show that the delta(18)O values of upland soil samples differ significantly from wetland soil samples. The latter can be related to the changing mixing ratio of the mineral and organic constituents of the soil. For wetlands affected by soil erosion, we have found intermediate delta(18)O signatures which lie between typical signatures for upland and wetland sites and give evidence for the input of upland soil material through erosion.

Oxygen stable isotope ratios of tree‐ring cellulose: the next phase of understanding

Analysis of the oxygen isotope ratio of tree-ring cellulose is a valuable tool that can be used as a paleoclimate proxy. Our ability to use this tool has gone through different phases. The first began in the 1970s with the demonstration of empirical relationships between the oxygen isotope ratio of tree-ring cellulose and climate. These empirical relationships, however, did not provide us with the confidence that they are robust through time, across taxa and across geographical locations. The second phase began with a rudimentary understanding of the physiological and biochemical mechanisms responsible for the oxygen isotope ratios of cellulose, which is necessary to increase the power of this tool. This phase culminated in a mechanistic tree-ring model integrating concepts of physiology and biochemistry in a whole-plant system. This model made several assumptions about leaf water isotopic enrichment and biochemistry which, in the nascent third phase, are now being challenged, with surprising results. These third-phase results suggest that, contrary to the model assumption, leaf temperature across a large latitudinal gradient is remarkably constant and does not follow ambient temperature. Recent findings also indicate that the biochemistry responsible for the incorporation of the cellulose oxygen isotopic signature is not as simple as has been assumed. Interestingly, the results of these challenges have strengthened the tree-ring model. There are several other assumptions that can be investigated which will improve the utility of the tree-ring model.

The environmental water of the middle Eocene Arctic: Evidence from δD, δ18O and δ13C within specific compounds

The extensive vertical exposure (> 150 m) of terrestrial sediments on Axel Heiberg Island, which contain thick fossiliferous lignites, presents an exceptional opportunity to follow the establishment and re-establishment of Arctic Metasequoia forests during the middle Eocene. We compared δD values in n-alkanes of chain length 23, 25, 27 and 29 with δ 18O values in phenylglucosazone (P-G) derived from α-cellulose; we also analyzed %-abundance of ferns, gymnosperms and angiosperms using pollen and spores isolated from each lignite. Our results showed that forest composition was altered upon uplift, as gymnosperms became more abundant within the relatively well-drained upland sediments. This was also reflected in the small (1‰), but significant, increase in the δ 13C value of TOM from lowland to upland environments. However, neither the δD values of n-alkanes nor the δ 18O in P-G were statistically different in the upland sediments, as compared to the lowland sediments; from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests. The δD value of environmental water implied by both n-alkanes and P-G ranged from − 168 to − 131% and was considerably enriched compared to all environmental water samples available from the modern Arctic region (< − 180%). In addition to indicating a warmer Eocene Arctic, subject to meteoric transport patterns different from today's, these results argue against the presence of an Eocene polar ice cap.

Transmission of oxygen isotope signals of precipitation-soil water-drip water and its implications in Liangfeng Cave of Guizhou, China

According to systemically monitoring results of oxygen (hydrogen) isotope compositions of precipitation, soil waters, soil CO2, cave drip waters and their corresponding speleothems in Liangfeng Cave (LFC) in Guizhou Province, Southwest China, it is found that local precipitation is the main source of soil waters and drip waters, and that the amplitudes of those δ 18O values of three waters (precipitation, soil water and drip water) decrease in turn in the observed year, which are 0% to −10%, −2% to −9% and −6% to −8%, respectively. Moreover, the δ 18O values for three waters show a roughly simultaneous variation, namely, that those values are lighter in the rainy seasons, weightier in the dry seasons, and that the average δ 18O value of drip waters is about 0.3% weightier than that of precipitation, which is modified by surface evaporation processes. We also find that soxygen isotope equilibrium is reached or neared in the formation processes of speleothems in LFC system, and that it is feasible to reconstruct paleotemperature and paleoprecipitation by using δ 18O values of speleothems. However, it should be noted that surface evaporation would affect the oxygen isotope values in the study area.

Stable isotope variations in stalagmites from northwestern Sweden document changes in temperature and vegetation during the early Holocene: a reply to Hammarlund and Edwards

In a comment on the paper by Sundqvist et al. (2007a), Hammarlund and Edwards suggest that the oxygen isotope signal of the speleothem records K1 and L4 from northwestern Sweden as well as for the earlier published stalagmite SG93 from northern Norway should mainly reflect variation in the δ 18O of mean annual precipitation. The main argument used by the authors is that the SG93 δ18O record should show remarkable similarities with the lacustrine carbonate δ18O record from Lake Tibetanus. The similarities between SG93 and Lake Tibetanus are mainly seen for the period between 10 and 9 ka BP, which is a period where both records have higher δ18O values compared with later in the Holocene. If true, this would indicate that temperatures in northern Scandinavia would have reached their Holocene maximum between 10 and 9 ka BP, which is contrary to what has been reported from other archives in the region which place the Holocene climatic optimum somewhere between 8 and 5 ka BP. Several factors affect the δ18O of speleothems and definitely also by annual mean δ18O of the local precipitation. However, for Holocene speleothems from northern Scandinavia as well as from the Alps this signal seems to be overridden by other factors, such as variable mixing of summer and winter precipitation of cave drip water as well as the temperature-dependent fractionation between calcite and water. But the relative importance of the factors can differ between different timescales, caves and even speleothems from the same cave, depending on hydrological pathways. To better understand the factors controlling the stable oxygen isotopes in precipitation and proxy archives back in time there is a need for more highly resolved records as well as for more atmospheric and hydrological modelling.

Origin of the Zálesí U–Ni–Co–As–Ag/Bi deposit, Bohemian Massif, Czech Republic: fluid inclusion and stable isotope constraints

The Zalesi vein-type deposit is hosted by Early Paleozoic high-grade metamorphic rocks on the northern margin of the Bohemian Massif. The mineralization is composed of three main stages: uraninite, arsenide, and sulfide. The mineral assemblages formed at low temperatures (~80 to 130°C, locally even lower) and low pressures (<100 bars). The salinity of the aqueous hydrothermal fluids (0 to 27 wt.% salts) and their chemical composition vary significantly. Early fluids of the oldest uraninite stage contain a small admixture of a clathrate-forming gas, possibly CO2. Salinity correlates with oxygen isotope signature of the fluid and suggests mixing of brines [δ18O around +2‰ relative to standard mean ocean water (SMOW)] with meteoric waters (δ18O around −4‰ SMOW). The fluid is characterized by highly variable halogen ratios (molar Br/Cl = 0.8 × 10−3 to 5.3 × 10−3; molar I/Cl = 5.7 × 10−6 to 891 × 10−6) indicating a dominantly external origin for the brines, i.e., from evaporated seawater, which mixed with iodine-enriched halite dissolution brine. The cationic composition of these fluids indicates extensive interaction of the initial brines with their country rocks, likely associated with leaching of sulfur, carbon, and metals. The brines possibly originated from Permian–Triassic evaporites in the neighboring Polish Basin, infiltrated into the basement during post-Variscan extension and were finally expelled along faults giving rise to the vein-type mineralization. Cenozoic reactivation by low-salinity, low-δ18O (around −10‰ SMOW) fluids of mainly meteoric origin resulted in partial replacement of primary uraninite by coffinite-like mineral aggregates.

Environmental influences on the recruitment process inferred from otolith stable isotopes in Merluccius merluccius off the Balearic Islands

Oxygen (δ 18 O) and carbon (δ 13 C) isotope ratios in sagittal otoliths were analysed in recruits and juveniles of European hake Merluccius merluccius L. caught in the northwest (Soller, SO) and south (Cabrera, CA) of the Island of Mallorca (western Mediterranean) over 2 consecutive years (2003 and 2004). The analytical method used allowed data to be gathered on both environmen- tal and trophic conditions experienced by fish during the pelagic early life stages (registered in the composition of the inner part of the otolith, core area) and the demersal aggregations of recruits (at the otolith edge). Results on the seasonal variation of oxygen isotope signatures at the edge of fish otoliths captured in SO and CA indicated different vertical migration behaviours of hake between the bottom and the thermocline. δ 13 C showed a clear ontogenetic pattern between the core area and the edge, confirming the differences in diet from the early stages to post-recruits. The seasonal analysis of δ 13 C data from the otolith edge indicated that fish from the early stages in June 2003 encountered poorer trophic resources, which resulted in poor fish condition and subsequent poorer recruitment. The estimated temperature from the core area of otoliths showed lower temperature regimes in the 2002 hatching season compared to the 2003 hatching season, which could be a possible explanation for the observed differences in success of subsequent recruitment.

Evaporation and carbonic anhydrase activity recorded in oxygen isotope signatures of net CO2 fluxes from a Mediterranean soil

AbstractThe oxygen stable isotope composition (δ18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The δ18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the δ18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large‐scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the δ18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed δ18O signatures of net soil CO2 fluxes became progressively enriched with a well‐characterized diurnal cycle. Model simulations indicated that the δ18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2.

Geochemistry of high arsenic groundwater in Chia-Nan plain, Southwestern Taiwan: Possible sources and reactive transport of arsenic

Major ion, trace element, and stable isotope analyses were performed on groundwater samples collected during November 2005 and 2006 in Chia-Nan plain of southwestern Taiwan to examine As mobilization in aquifers. The high concentrations of As, Fe and Mn in the groundwater is consistent with low Eh values (under moderately reduced state). Moreover, the observed Na/Cl and SO4/Cl molar ratios in groundwater demonstrate the influence of seawater intrusion. Seawater intrusion could provide required electron acceptors (i.e., SO4) for bacterial sulfate reduction and promote reducing conditions that are favorable for As mobilization. The concurrent increases in the concentrations of Fe and Mn from 2005 to 2006 may be caused by bacterial Fe(III) and Mn(IV) reduction. Geochemical modeling demonstrate that As(III) is the dominant As species and the presence of Fe-bearing carbonates, sulfides, and oxide phases may locally act as potential sinks for As. Mud volcano fluids were also collected and analyzed to assess the possible source of As in the Chia-Nan plain groundwater. The oxygen and hydrogen isotopic signatures indicate that the As-rich mud volcano fluids may have been modified by chemical exchange with 18O-rich crustal rocks and possibly originated from mixing of deep brines with circulating meteoric water. Thus As in the Chia-Nan plain groundwater may have been evolved from deep crustal fluids or rock sources. The hydrogeochemistry and widespread As enrichment in groundwater of Chia-Nan plain result from multiple processes, e.g., de-watering of deep crustal fluids, seawater intrusion, and biogeochemical cycling of Fe, As, and S in alluvial sediments.

Extreme oxygen isotope signature of meteoric water in magmatic zircon from metagranite in the Sulu orogen, China: Implications for Neoproterozoic rift magmatism

Unusual 18O depletion, with δ 18O values as negative as −10‰ to −4‰ relative to VSMOW, was reported in zircons from ultrahigh-pressure eclogite-facies metamorphic rocks in the Dabie-Sulu orogenic belt, China. But it is critical for the negative δ 18O zircons to be distinguished between magmatic and metamorphic origins, because the 18O depletion can be acquired by high-T eclogite-facies metamorphism of meteoric-hydrothermally altered low δ 18O rocks. While zircon O diffusion kinetics has placed a reasonable constraint on this, zircon trace element compositions can provide a straightforward distinction between the magmatic and metamorphic origins. This paper reports our finding of unusual 18O depletion in zircon from granitic gneiss in the northeastern end of the Sulu orogen. Zircon δ 18O values vary from −7.8‰ to −3.1‰ along a profile of 50 m length at Zaobuzhen. They are close to extremely low δ 18O values of −9.0‰ to −5.9‰ for metagranite at Qinglongshan and adjacent areas in the southwestern end of the Sulu orogen. CL imaging suggests that the low δ 18O zircons at Zaobuzhen are primarily of magmatic origin, but underwent different degrees of metamorphic modification. Zircon U–Pb dating yields middle Neoproterozoic ages of 751 ± 27 to 779 ± 25 Ma for protolith crystallization and Triassic ages of 214 ± 10 to 241 ± 33 Ma for metamorphic resetting. However, no metamorphic modification occurs in zircon REE patterns that only indicate magmatic recrystallization and hydrothermal alteration, respectively. Thus, the negative δ 18O zircons are interpreted as crystallizing from negative δ 18O magmas due to melting of meteoric-hydrothermally altered negative δ 18O rocks in an active rift setting at about 780 Ma. The variation in zircon δ 18O values indicates considerable O isotope heterogeneity in its granitic protolith. Zircon Lu–Hf isotope analyses give positive ε Hf( t) values of 1.6–4.1 and Hf model ages of 1.18–1.30 Ga. This suggests that the granitic protolith was derived from the mid-Neoproterozoic reworking of late Mesoproterozoic juvenile crust. The metagranites at Zaobuzhen and Qinglongshan, about 450 km apart, are two known occurrences of the unusually low δ 18O zircons below −6‰ so far reported in the Sulu orogen. They are similar to each other in both protolith and metamorphic ages, so that they share the same nature of both Neoproterozoic protolith and Triassic metamorphism. Therefore, the locally negative δ 18O zircons may register centers of low δ 18O magmatism during the supercontinental rifting.

Stable carbon, nitrogen, and oxygen isotope analysis as a potential tool for verifying geographical origin of beef

Stable isotope analysis of organic elements such as carbon and nitrogen has been employed as a powerful tool for provenance determination of food materials, because isotopic compositions of the materials reflect many factors in natural environment. In this study, we examined carbon, nitrogen, and oxygen isotope signatures of beef from Australia, Japan, and USA, in order to confirm the method as a potential tool for verifying geographical origin of beef commercially distributed in Japan. Defatted dry matter of beef from USA was characterized by higher carbon isotopic composition (−13.6‰ to −11.1‰) than that from Japan (−19.6‰ to −17.0‰) and Australia (−23.6‰ to −18.7‰). That from Australia was characterized by higher oxygen isotopic composition (+15.0‰ to +19.4‰) than that from Japan (+7.3‰ to +13.6‰) and USA (+9.5‰ to +11.7‰). The oxygen isotopic composition in Japanese beef showed a positive correlation with the isotopic composition of cattle drinking water, the difference in which is clearly latitude dependent. These results suggest that a comparison of carbon, nitrogen, and oxygen isotopic compositions is applicable as a potential tool to discriminate the provenance of beef not only between different countries (i.e. Australia, Japan, and USA) but also among different regions within Japan.

A 600-year-long δ18O record from cellulose of Breonadia salicina trees, South Africa

The oxygen isotope composition in cellulose was analysed along the growth axis of two 600-year-old Breonadia salicina trees (Matumi) from subtropical South Africa, with the aim of testing the isotope variations as a regional climate proxy. The visible tree rings in B. salicina are not annual and therefore radiocarbon analysis was applied to produce an age model for the isotope record, covering the time period between 1375 and 1995 AD. Before ∼1600 AD, a co-variation is evident between the variations in δ 18O cellulose and previously published δ 13C cellulose, indicating that a common factor is responsible for both the carbon and the oxygen isotope signals in the tree cellulose. Between ∼1600 and ∼1900 AD, the correlation between the isotope series weakens, concurrently with drastic changes in growth rates and average ring production rates. Possibly, this phase was a result of extreme changes in the growth environment, affecting the cellulose production rate, the source water δ 18O signal and the proportion of different types of oxygen isotope fractionation processes affecting the final isotope composition in the tree cellulose. We suggest that during the lifetime of the two B. salicina trees, different factors have governed the oxygen isotope signal in the cellulose. Both regional climate conditions and site-specific factors associated with the riparian growth environment have had an impact on the oxygen isotope variations in the two trees, clearly complicating the possibilities to utilise a δ 18O cellulose record from this tree species for paleoclimatic reconstruction.

Climatic sensitivity of δ18O in the wood and cellulose of tree rings: Results from a mixed stand of Acer pseudoplatanus L. and Fagus sylvatica L.

The oxygen isotope composition in tree rings is commonly used to assess the impact of climatic factors on tree growth. However, the relationships between environmental variables and δ 18O in whole wood and the wood components (e.g., cellulose, lignin) are still not completely clear — particularly for deciduous species. It is currently common procedure to consider only one wood constituent, a process that saves time. To test whether the δ 18O of cellulose relates better to environmental variables than that of whole wood, we measured the oxygen isotopic composition of tree ring whole wood and cellulose, for the period 1916–1950, for two different broad-leaved species ( Fagus sylvatica L. and Acer pseudoplatanus L.) on Monti Picentini (Southern Italy). Data show that δ 18O in cellulose is enriched (4.7 ± 1.1‰) compared to the corresponding whole wood. The relationship between the δ 18O of the cellulose and of whole wood is generally poor, especially for A. pseudoplatanus suggesting that the sources of variability for δ 18O differ strongly between the whole wood and the cellulose constituents. Furthermore, we find that the cellulose fraction correlates strongly with climatic variables, while the whole wood fraction generally does not. Monthly temperature during the growing season is strongly correlated with δ 18O of cellulose for F. sylvatica ( r = 0.82) and A. pseudoplatanus ( r = 0.63) but not with δ 18O of whole wood. We found a relevant difference in the isotopic signals of the two species that could be related with difference in seasonal timing of growth. In contrast to F. sylvatica, early spring conditions have an influence on A. pseudoplatanus at our study site. This is evidenced by the high correlation between δ 18O of cellulose and April and May precipitation, and the positive relationship between tree ring width and March and April mean annual temperature. The different climatic sensitivities of the two investigated species suggest that physiological properties, i.e. root system and stomatal conductance responses, or a variation in the proportions of wood constituents play an important role for the oxygen isotopic signal. We conclude that, even when partially obscured by site parameters (soil depth and structure, nutrient availability, etc.), δ 18O in the cellulose compartment strongly reflects climate information. Our study suggests that cellulose extraction is a necessary step in studies seeking to investigate the climatic signatures in the δ 18O of broad-leaved species.

Pre-metamorphic carbon, oxygen and strontium isotope signature of high-grade marbles from the Lützow-Holm Complex, East Antarctica: apparent age constraints of carbonate deposition

Abstract C, O and Sr isotope geochemistry of high-grade marbles from the Lützow-Holm Complex, East Antarctica, has given clues on the depositional ages and post-depositional alterations. Dolomitic and calcitic marbles occur as thin layers with varying thickness (up to 100 m) in several outcrops in eastern Dronning Maud Land, most of which underwent post-depositional geochemical alterations. In particular, the Sr and O isotope alterations are extensive, with 87 Sr/ 86 Sr (550 Ma) ratios as high as 0.758 and δ 18 O values as low as −5‰. These data suggest that multiple stages of fluid–rock interaction processes during diagenesis, prograde to peak and retrograde metamorphic events have altered the depositional isotopic signatures. However, some of the marble layers, exceptionally, preserve pre-metamorphic geochemical characteristics, such as low Sr isotope ratios, high δ 18 O and δ 13 C values, and well-equilibrated unaltered trace and rare earth element patterns. Lowest 87 Sr/ 86 Sr isotopic ratios of 0.7066 and 0.7053 with high δ 13 C and δ 18 O values suggest an apparent age of deposition around 730–830 Ma, although total geochemical resetting of carbonates by seawater of this age cannot be ruled out. The apparent depositional ages are consistent with carbonate deposition in the ‘Mozambique Ocean’ that separated East and West Gondwana.

Oxygen Isotopes in Asteroidal Materials

Measurement of the variation of the 17O/16O and 18O/16O ratios of extraterrestrial materials has proven to be a key tool in understanding the formation and evolution of the Solar System. This chapter attempts to collate the huge data set of oxygen isotopic measurements of asteroidal material, as sampled by meteorites, in order to understand some of the processes involved in the formation of these primitive bodies and how such events have affected the oxygen isotopic ratios, ultimately offering a window back to the very origin of Solar System and its primordialoxygen isotopic heterogeneity. Oxygen is generally a major element in the gas, liquid and solid phases that have interacted throughout the evolution of the Solar System, its chemical properties ensuring that there is abundant opportunity for reactions and exchange, the details of which can be recorded in the isotopic ratios of the products. Such processes can be crudely subdivided into the following six categories: • Early solar nebular isotopic heterogeneity • High-temperature modifi cation of nebular components • Metamorphism and melting in asteroids • Aqueous alteration in asteroids • Mixing of components/brecciation • Terrestrial weathering It is clear from the isotopic variation in the earliest-formed nebular components, such as refractory inclusions and chondrules, that there was considerable oxygen isotopic heterogeneity in the early solar nebula, spanning over 50‰, and perhaps much greater, in both δ17O and δ18O. The origin of this variation is discussed elsewhere in this volume. However, isotopic exchange between the 16O-rich solids and 17O- and 18O-rich gas phase(s) resulted in a wide range of isotopic variation in these early-formed components, offering insight into the conditions of these processes and the evolution of the reservoirs with time and/or space. Once accreted onto the early planetisemals, much of the primitive nebular components experienced considerable modification. The metamorphism and melting experienced by some of these bodies, most probably the result of heating from the decay of short-lived radionuclides (e.g., 26Al), resulted in progressive homogenization, within individual bodies, of any original isotopic heterogeneity. Complete homogenization appears to have been achieved in the HED parent body, indicating very high levels of melting and the development of a large magma ocean. The carbonaceous and ordinary chondrite parent bodies experienced more modest heating, sufficient to mobilize water ice that accreted along with the more refractory materials. The subsequent reactions between the liquid and solid phases at low temperature imparted large isotopic fractionations which record some of the conditions of this alteration, such as water:rock ratio, temperature, and isotopic signature, and thus potentially the origin of the water ice. The evolution of the asteroidal bodies has been far from simple, and an important use of oxygen isotope measurements has been in the identifi cation of the components present in some meteorites, the result of breakup, reassembly and mixing of different bodies during impact processing. The final oxygen isotopic signatures imparted into meteorite samples are those associated with terrestrial weathering. The isotopic compositions of the weathering products depend on location (primarily latitude) while the magnitude of the weathering is dependent on many factors, with some meteorites (e.g., highly reduced enstatite chondrites and the matrix-rich CO3s) particularly susceptible to such effects.

A regional perspective on biotic change during the Classic Maya occupation using zooarchaeological isotopic chemistry

This paper uses stable isotopic research on faunal remains from archaeological sites in the Maya area to describe ancient environments through time in the region. Carbon isotope signatures of white-tailed deer remains recovered from the Petexbatún and Motul de San José polities in Guatemala are combined with other published data to provide a regional diachronic perspective on variations in availability of maize, a C4 plant, to herbivores. These data are used as a proxy for the extent of agricultural fields through time across the Maya world and the results indicate considerable temporal and spatial heterogeneity, likely linked to natural environmental heterogeneity and local land-use histories. The local nature of variations underscores the need for greater detail in paleoenvironmental studies at the drainage-basin or site level. Preliminary oxygen isotope research on white-tailed deer from the Motul de San José polity is also presented as the basis for discussion of the role of archaeologically linked oxygen isotope signatures in correlating large scale climate shifts with other site-specific evidence for environmental change over the period of Maya occupation. Together discussions of the two isotopic data sets emphasize the importance of paleoenvironmental and particularly isotopic research on materials from well-dated archaeological contexts.

造礁サンゴ、冷水サンゴ、深海サンゴの骨格の酸素・炭素同位体比の挙動について

造礁サンゴ、冷水サンゴ、深海サンゴの骨格の酸素・炭素同位体比の挙動について

A Review and Synthesis of Glendonites (Pseudomorphs after Ikaite) with New Data: Assessing Applicability as Recorders of Ancient Coldwater Conditions

Abstract Calcite pseudomorphs after ikaite (glendonite) are associated with coldwater depositional systems, including glaciomarine and deepwater settings, as dictated by the limited stability field of ikaite. Ikaite precipitation is favored by elevated alkalinity and dissolved phosphate, conditions encountered commonly in association with organic-rich marine sediments where methane oxidation is occurring. The rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss, producing a highly porous crystal mesh. Preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures. During later burial diagenesis remaining pore space may be filled with deeper burial calcite cement. Glendonites from the Permian of the Sydney Basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna. Stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater; carbon signatures are usually strongly negative relative to normal marine carbonate, consistent with derivation of carbonate from methane oxidation. Review of published data suggests that while Holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation, precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of depositional conditions. Bulk glendonite samples from the Permian Sydney Basin, Australia, have a broad range of δ18 O and δ13C (δ18OPDB = −5 to −15‰; δ13C = −8 to −16‰), in contrast to the narrow range for brachiopod carbonate (δ18OPDB = +1 to −5‰; δ13C = +5 to +7‰) from the same strata. Handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values. The data from Sydney Basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of ikaite replacement calcite at the scale of micosampling done in this study.

Turnover of oxygen and hydrogen isotopes in the body water, CO 2, hair, and enamel of a small mammal

Oxygen and hydrogen isotope signatures of animal tissues are strongly correlated with the isotope signature of local precipitation and as a result, isotope signatures of tissues are commonly used to study resource utilization and migration in animals and to reconstruct climate. To better understand the mechanisms behind these correlations, we manipulated the isotope composition of the drinking water and food supplied to captive woodrats to quantify the relationships between drinking water ( δ dw), body water ( δ bw), and tissue ( δ t). Woodrats were fed an isotopically constant food but were supplied with isotopically depleted or enriched water. Some animals were switched between these waters, allowing simultaneous determination of body water turnover, isotope change recorded in teeth and hair, and fractional contributions of atmospheric O 2, drinking water, and food to the oxygen and hydrogen budgets of the animals. The half-life of the body water turnover was 3–6 days. A mass balance model estimated that drinking water, atmospheric O 2, and food were responsible for 56%, 30%, and 15% of the oxygen in the body water, respectively. Drinking water and food were responsible for 71% and 29% of the hydrogen in the body water, respectively. Published generalized models for lab rats and humans accurately estimated δ bw, as did an updated version of a specific model for woodrats. The change in drinking water was clearly recorded in hair and tooth enamel, and multiple-pool and tooth enamel forward models closely predicted these changes in hair and enamel, respectively. Oxygen and hydrogen atoms in the drinking water strongly influence the composition of the body water and tissues such as hair and tooth enamel; however, food and atmospheric O 2 also contribute oxygen and/or hydrogen atoms to tissue. Controlled experiments allow researchers to validate models that estimate δ t based on δ dw and so will increase the reliability of estimates of resource utilization and climate reconstruction.