Delta 18O Research Articles

Middle Eocene Climatic Optimum (MECO): The first record based on planktonic foraminifera and stable isotopes from SW Anatolia/Turkiye

The Kayikoy Formation (Isparta, SW Turkiye) consisting of sandstone, claystone, and marl units contains abundant, low-moderate preserved, and diverse planktonic foraminifera assemblages. Eight planktonic foraminiferal biozones (E9-E16) were determined encompassing the Lutetian-Priabonian stages (middle-upper Eocene) by using the biostratigraphic distributions of 17 genera and 62 species of planktonic foraminifera. Stable delta 18O and delta 13C isotope values were measured for 53 individuals belonging to Morozovelloides crassatus, Acarinina bullbrooki, A. topilensis, A. echinata, Globigerinatheka curryi, G. index, G. subconglobata, G. mexicana, G. barri, G. euganea, Orbulinoides beckmanni, Turborotalia frontosa, T. pomeroli, Hantkeninamexicana, H. liebusi, H. dumblei, H. alabamensis, and Dentoglobigerina eotripartita. By integrating planktonic foraminiferal biostratigraphy, stable delta 18O and delta 13C isotopes, and paleotemperature analyses, the first detailed study of the Middle Eocene Climatic Optimum (MECO) record was performed in SW Anatolia/Turkiye. The overall signature of the MECO is similar to global observations but also involves some regional differences. The MECO paleotemperatures, determined to vary between approximately 2 degrees C and 5 degrees C, were similar to the global records, but the slight differences in values in the three sections are most likely due to the paleogeographic position of the studied section in Turkiye.

The Ediacaran metamorphosed banded iron formation (BIF) at Gohar Zamin mine (Gol-e-Gohar #3 anomaly), Sirjan (southeastern Iran): Perspective from ore structures, bulk ore-rock geochemistry and O-S-Pb isotopic signatures

Little is known about the occurrence of the Neoproterozoic banded iron formations (BIFs), except few cases of the glaciogenic Cryogenian BIFs. In this investigation, we describe an Ediacaran metamorphosed BIF interbedded with metamorphosed rocks. The Gohar Zamin iron deposit (643 Mt @ 54.3 % Fe, 2.04 % S, 0.12 % P) is hosted by mica schist, quartz schist and meta-basite that formed by metamorphism of the Fe-oxy-hydroxides, terrigenous (pelitic)-chemical (carbonate) sediments, silica gel and repeated phases of MORB-type submarine basic eruptions in shallow marine syn-rift basins. The sediments, basaltic eruptions and iron oxides were lithified to BIFs and then metamorphosed to greenschist facies during Cimmerian orogeny. The presence of macro-meso-microbandings in BIFs, coarse-grained quartz dropstones and magnetite clasts in the ores-host rocks, chemical index of alteration (CIA) (41.83 to 95.42 %) and positive correlation of Al2O3 against TiO2 and SiO2 values suggests a possible syn-glaciogenic BIF deposition. Fe/Ti-Al (Al + Fe + Mn), Fe-P, Co-Ni, V-Ti, V-Ni and Ni/ (Cr + Mn)-Ti + V diagrams suggest similarity to BIFs rather than the I-type granitoid magmatic-hydrothermal-skarn iron ores. REE + Y patterns display LREE depletion to slight enrichment, low-moderate Y/Ho ratios, HREE flat patterns, a nearly-zero to a seawater-like negative Ce anomaly and negative Eu anomaly. Such signatures may reflect low-T (300–200 °C) hydrothermal fluids for the origin of Fe-oxy-hydroxides formed by seawater-basaltic interaction and syn-glaciogenic meltwater influxes. Delta 18O values in magnetite-hematite (+3.3 to + 9.5 ‰) are in equilibrium with seawater and global BIFs. Delta 34S values in pyrite (+21.51 to + 26.59 ‰) reflect similarity to the Ediacaran pyrite composition formed by both thermal sulfate reduction (TSR) and bacterial sulfate reduction (BSR) processes. The radiogenic ratios of 206Pb/204Pb (19.228–25.105), 207Pb/204Pb (15.50–16.158) and 208Pb/204Pb (38.526–39.895) plot on the right side of 0.0 Ga geochron and were probably originated from the highly radiogenic zircon or galena clasts deposited by glaciogenic deposits. Geochemostratigraphy records zigzag elemental halos with the highest values of Fe (59.08 wt%) and Au (49.9 ppb). Exploration guides may be oriented to surficial sampling of the gossanized outcrops and heavy mineral surveys in drainage crosscutting the schistose rocks.

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

The Ediacaran record of glaciogenic dropstones, diamictites and cap carbonates associated with non-metamorphosed banded iron formations (BIFs) in Iran

The Ediacaran period is marked by global icehouse episode, greenhouse period, increasing levels of oxygen-carbon dioxide, syn-glaciogenic structures-BIFs, typical Ediacaran biota and a marked negative carbon isotope excursion. On this global point, field glaciogenic structures, petrographic textures, Ediacaran biota, U-Pb zircon ages, C-O isotopes and geochemical data record an Ediacaran glaciogenic BIFs event in Iran. The Ediacaran (578–547 or 578–541.8 Ma) glaciogenic sequences in Bafq and Hormuz Island mining districts include submarine syn-glaciovolcanic rhyolitic rocks, rhyolitic tuffs, shaly tuffaceous carbonates, dropstone-bearing jaspilitic BIFs, salt minerals, ferruginous diamictites, and cap carbonates. The presence of polygonal, bullet-shape and flatiron forms of gneiss, greenschist, quartz schist, quartzite, marble and magnetite-hematite clasts in a matrix of jaspilitic magnetite-hematite, muddy sandstones and muddy dolomitic rocks records an Ediacaran glaciogenic event. The dropstones occur as lone-stones, dump-stones and deflect their underlying layers. The diamictites contain similar clasts to those of the dropstones, are gradationally covered by buff to dark-grey cap carbonates ± dropstones and resemble the Ghaub, Chuos and Kingston Peak Formation diamictites. C-O isotopes, REE+Y diagrams, high Y/Ho ratios, positive Eu-Y anomalies and subtle Ce anomaly possibly reflect a possible hydrothermal origin for the cap carbonates. Delta 13C values (−0.42 to −6.33‰) in cap carbonates show similar negative signatures to the Ediacaran Shuram glaciogenic event. Average delta 18O (−8.34‰) in the least-altered cap carbonates gives a precipitation temperature of 252.7 °C in the waning stage of the glaciogenic BIFs-hydrothermal system.

Tree rings as a proxy for seasonal precipitation variability and Early Neolithic settlement dynamics in Bavaria, Germany.

Studying the dynamic of Neolithic settlement on a local scale and its connection to climate variability is often difficult due to missing on-site climate reconstructions from natural archives. Here we bring together archaeological settlement data and a regional climate reconstruction from precipitation-sensitive trees. Both archives hold information about regional settlement dynamics and hydroclimate variability spanning the time of the first farming communities, the so called Linearbandkeramik (LBK) in Bavaria, Germany. Precipitation-sensitive tree-ring series from subfossil oak are used to develop a spring-summer precipitation reconstruction (5700–4800 B.C.E.) representative for southern Germany. Early Neolithic settlement data from Bavaria, mainly for the duration of the LBK settlement activities, are critically evaluated and compared to this unique regional hydroclimate reconstruction as well as to reconstructions of Greenland temperature, summer sea surface temperature, delta 18O and global solar irradiance to investigate the potential impact of climate on Neolithic settlers and their settlement dynamic during the LBK. Our hydroclimate reconstruction demonstrates an extraordinarily high frequency of severe dry and wet spring-summer seasons during the entire LBK, with particularly high year-to-year variability from 5400 to 5101 B.C.E. and with lower fluctuations until 4801 B.C.E. A significant influence of regional climate on the dynamic of the LBK is possible (e.g. around 4960 B.C.E.), but should be interpreted very carefully due to asynchronous trends in settlement dynamics. Thus, we conclude that even when a climate proxy such as tree rings that has excellent spatio-temporal resolution is available, it remains difficult to establish potential connections between the settlement dynamic of the LBK and climate variability.

Early Cenozoic evolution of topography, climate, and stable isotopes in precipitation in the North American Cordillera

Paleoelevation reconstructions of the North American Cordillera in- ferred from the oxygen (delta 18O) and hydrogen (delta D) isotope ratios of terrestrial paleoclimate proxy materials (soils, ashes, lake sediments) suggest rapid north-to- south migration of topography in the early Cenozoic (pre-49 Ma to 28 Ma). The validation of this reconstruction relies on an accurate understanding of the delta 18Op and the associated regional climate change in response to the uplift of the western North America. Here we study this response using a global climate model (GCM) with explicit delta 18Op diagnostics (ECHAM5-wiso) focusing on the isotopic effects of different types of precipitation, vapor mixing, recycling and moisture source and compare the response against estimates made using a Rayleigh distillation models of moist adiabatic condensation (RDM). Four experiments are performed with Eocene topography inferred from terrestrial stable isotope paleoaltimetry records to investigate how southward propagation of topography affects regional climate (temperature, precipitation and circulation pattern) and dela 18Op over North America. Our experiments predict delta 18Op patterns that are broadly consistent with maps of temporally binned proxy delta 18O and generally support an early Cenozoic north-to-south propagation of high topogra- phy in the North American Cordillera. They do not support the commonly made assumption that isotopic fractionation occurs primarily through rainout following Rayleigh distillation nor the application of modern empirical delta 18Op lapse rates to past environments. In our GCM simulations, precipitation processes and climate changes that are not captured by RDMs substantially affect delta 18Op. These processes include shifts in local precipitation type between convective and large-scale rain and between rain and snow; intensification of low-level vapor recycling particularly on leeward slopes; develop- ment of air mass mixing and changes in wind direction and moisture source. Each of these processes can have significant (>2‰) influences on delta 18Op that are comparable in magnitude to surface uplift of hundreds or even thousands of meters. In many regions, these processes fortuitously compensate each other, explaining the apparent agreement between ECHAM5-wiso and proxy delta 18O and, more broadly, between RDM estimates and observed delta 18O-elevation relationships. In some regions, compensation is incomplete, and as a result, ECHAM5-wiso delta 18Op does not agree with estimates from the RDM. In these regions, including the interior of the northern cordillera and the eastern flank of the southern Cordillera, moderate adjustments of paleoelevations may be in order.

Analyzing Effects of Shrub Canopy on Throughfall and Phreatic Water Using Water Isotopes, Western China

Alpine shrub Quercus aquifolioides was selected to study the effects of shrub canopy on throughfall and phreatic water by analyzing the isotopic time series of precipitation, canopy throughfall and phreatic water and examining correlations among these series in Wolong Nature Reserve, Western China. Based on analysis of precipitation data in 2003, ;the local meteoric water line during the rainy season was delta D = 8.28 x delta 18O + 8.93, and the primary precipitation moisture in this region originated from the Pacific Ocean in the summer. Stable isotope analysis showed that the main supply of throughfall and phreatic water was from precipitation, and the shrub canopy has an important effect on the processes of rainwater transmuted into throughfall and phreatic water. Moreover, the differences of delta D and delta 18O values between rainwater and throughfall were relevant to rainfall. Due to interception of the shrub canopy, there had a response hysteresis of phreatic water to the various rainfall events, which was mostly 2 days, except that this hysteresis was 15 mm/day.

Nitrate contamination of groundwater and it's implications in the Limpopo Water Management Area

The increasing nitrate level in groundwater within the Limpopo WMA is a problem that requires urgent attention and is not yet fully understood. Nitrate pollution of water has major health effects attached to it, like methaemoglobinaemia and cancer. It is important that the anthropogenic and natural sources of nitrate in this area be identified and it is also important to understand the relationship between these sources. A combination of statistics, GIS, water quality and isotopes was used to identify and to derive a relationship between the natural and anthropogenic sources of nitrate. The dominant source of nitrate in the study area is animal manure and sewage waste which originate from residential areas and cattle kraal. However a mixing relationship was observed between high nitrate originating from manure or sewage waste and low nitrate background water. Nitrate in the study area also originates from natural sources such as the soil and precipitation. The soil is influenced by the geology as shown by the presence of elevated Si concentration in the samples. This natural origin is shown by the presence of high Si (30 mg/L) which is associated with albite weathering. While land covered by natural vegetation such as tropical bushveld and savannah has low nitrate levels, and the lower limit for nitrogen-nitrate isotope is similar to that for residential and dryland agriculture (maize farming). Cluster analysis results showed a relationship between natural and anthropogenic sources (geology, soil, vegetation, mining, dryland agriculture and residential area) which have delta 18O and delta 15N isotopes signature similar to that for manure or sewage waste, soil and precipitation.

Nitrogen and Carbon Isotopic Systematics of the Florida Reef Tract

The nitrogen isotopic composition of a variety of organisms in coral reefs has been used extensively, not only to study nitrogen dynamics, but also as a tracer for the input of anthropogenic nitrogen. However, the interplay between isotopic fractionation associated with the internal nitrogen cycling and variations in the absolute values supplied by external source signatures is poorly understood. Here we report the (delta)15N and(delta)13C of algae, sponges, and fishes, the (delta)15N and (delta)18O of dissolved NO3-, and the (delta)15N of dissolved organic nitrogen in samples collected from the Florida reef tract over a 2.5-yr period (2003-2005). Our data are synthesized with results from previous studies of the (delta)15N of particulate organic material and coral tissue and zooxanthellae from the same area to provide a more detailed understanding of factors controlling coral reef ?15N and variation among biogenic components. These data show that during the study period there were (1) no clear spatial patterns in the (delta)15N of biogenic components related to proximity to the Florida Reef tract, and (2) no temporal patterns related to the wet or dry seasons. The range of (delta)15N and (delta)13C in the particulate organic material could be best explained as a mixture of material derived from seagrass, algae, mangroves, and fishes. The (delta)15N and (delta)18O of NO3- support a model in which variations in nitrogen isotopic composition are derived mainly from the isotopic effects associated with the nitrification of NH4+ to NO3- and subsequent assimilation by primary producers rather than through the input of isotopically distinct NO3- from external sources.

Cellulose (delta)18O is an index of leaf-to-air vapor pressure difference (VPD) in tropical plants.

Cellulose in plants contains oxygen that derives in most cases from precipitation. Because the stable oxygen isotope composition, δ(18)O, of precipitation is associated with environmental conditions, cellulose δ(18)O should be as well. However, plant physiological models using δ(18)O suggest that cellulose δ(18)O is influenced by a complex mix of both climatic and physiological drivers. This influence complicates the interpretation of cellulose δ(18)O values in a paleo-context. Here, we combined empirical data analyses with mechanistic model simulations to i) quantify the impacts that the primary climatic drivers humidity (e(a)) and air temperature (T(air)) have on cellulose δ(18)O values in different tropical ecosystems and ii) determine which environmental signal is dominating cellulose δ(18)O values. Our results revealed that e(a) and T(air) equally influence cellulose δ(18)O values and that distinguishing which of these factors dominates the δ(18)O values of cellulose cannot be accomplished in the absence of additional environmental information. However, the individual impacts of e(a) and T(air) on the δ(18)O values of cellulose can be integrated into a single index of plant-experienced atmospheric vapor demand: the leaf-to-air vapor pressure difference (VPD). We found a robust relationship between VPD and cellulose δ(18)O values in both empirical and modeled data in all ecosystems that we investigated. Our analysis revealed therefore that δ(18)O values in plant cellulose can be used as a proxy for VPD in tropical ecosystems. As VPD is an essential variable that determines the biogeochemical dynamics of ecosystems, our study has applications in ecological-, climate-, or forensic-sciences.

Isotopic evidence for the source and fate of phosphorus in Everglades wetland ecosystems

Phosphorus has historically been a limiting nutrient in the Florida Everglades. Increased P loading to the Everglades over the past several decades has led to significant changes in water quality and plant communities. Stormwater runoff that drains agricultural lands and enters the Water Conservation Areas (WCAs) are known to contain elevated levels of P, but the exact source of this P has not been fully determined. Here the results of an O isotope study of dissolved inorganic phosphate (DIP) in both polluted and relatively pristine (or reference) areas of the Everglades are reported. The data reveal spatial and temporal variations in the delta 18O signature of DIP, reflecting the source and the degree of cycling of P. The delta 18O values of DIP collected from the Everglades National Park were close or equal to the predicted delta 18O values of DIP formed in situ in equilibrium with ambient water, indicating that P is quickly cycled in the water column in oligotrophic ecosystems with very low P concentrations. However, most DIP samples collected from areas impacted by agricultural runoff yielded delta 18O values that deviated from the predicted equilibrium DIP delta 18O values based on the delta 18O of water and water temperature, suggesting that biological cycling of P was not rapid enough to remove the fertilizer ?18O signature in the DIP pool from areas receiving high P loading. The delta 18O signature of DIP in impacted areas reflects a mixing of fertilizer P and biologically cycled P, where the relative proportions of biologically cycled vs. fertilizer DIP are controlled by both biological (microbial activities and plant uptake) and hydrologic factors (loading rate and residence time). Using a two-end-member (i.e., fertilizer P and biologically cycled P) mixing model, fertilizers were estimated to contribute about 15 100% of the DIP pool in the highly impacted areas of the northern Everglades, whereas the DIP pool in the reference (i.e., relatively pristine) wetlands in the Everglades National Park was dominated by biologically cycled P. The study shows that O isotopic measurements of dissolved PO(exp 3-, sub 4) can be a useful tool for tracing the fertilizer P inputs to freshwater ecosystems.

Multi-proxy evidence for early to mid-Holocene environmental and climatic changes in northeastern Poland

We investigated the sedimentary record of Lake Hancza (northeastern Poland) using a multi-proxy approach, focusing on early to mid-Holocene climatic and environmental changes. AMS 14C dating of terrestrial macrofossils and sedimentation rate estimates from occasional varve thickness measurements were used to establish a chronology. The onset of the Holocene at c. 11 600 cal. a BP is marked by the decline of Lateglacial shrub vegetation and a shift from clastic-detrital deposition to an autochthonous sedimentation dominated by biochemical calcite precipitation. Between 10 000 and 9000 cal. a BP, a further environmental and climatic improvement is indicated by the spread of deciduous forests, an increase in lake organic matter and a 1.7 parts per thousand rise in the oxygen isotope ratios of both endogenic calcite and ostracod valves. Rising delta 18O values were probably caused by a combination of hydrological and climatic factors. The persistence of relatively cold and dry climate conditions in northeastern Poland during the first one and a half millennia of the Holocene could be related to a regional eastern European atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high-pressure cell above the retreating Scandinavian Ice Sheet might have blocked the influence of warm and moist Westerlies and attenuated the early Holocene climatic amelioration in the Lake Hancza region until the final decay of the ice sheet.

How yield relates to ash content, Delta 13C and Delta 18O in maize grown under different water regimes.

Stable isotopes have proved a valuable phenotyping tool when breeding for yield potential and drought adaptation; however, the cost and technical skills involved in isotope analysis limit its large-scale application in breeding programmes. This is particularly so for Delta(18)O despite the potential relevance of this trait in C(4) crops. The accumulation of minerals (measured as ash content) has been proposed as an inexpensive way to evaluate drought adaptation and yield in C(3) cereals, but little is known of the usefulness of this measure in C(4) cereals such as maize (Zea mays). The present study investigates how yield relates to ash content, Delta(13)C and Delta(18)O, and evaluates the use of ash content as an alternative or complementary criterion to stable isotopes in assessing yield potential and drought resistance in maize. A set of tropical maize hybrids developed by CIMMYT were subjected to different water availabilities, in order to induce water stress during the reproductive stages under field conditions. Ash content and Delta(13)C were determined in leaves and kernels. In addition, Delta(18)O was measured in kernels. Water regime significantly affected yield, ash content and stable isotopes. The results revealed a close relationship between ash content in leaves and the traits informing about plant water status. Ash content in kernels appeared to reflect differences in sink-source balance. Genotypic variation in grain yield was mainly explained by the combination of ash content and Delta(18)O, whilst Delta(13)C did not explain a significant percentage of such variation. Ash content in leaves and kernels proved a useful alternative or complementary criterion to Delta(18)O in kernels for assessing yield performance in maize grown under drought conditions.

Physiological responses to fertilization recorded in tree rings: isotopic lessons from a long‐term fertilization trial

Nitrogen fertilizer applications are common land use management tools, but details on physiological responses to these applications are often lacking, particularly for long-term responses over decades of forest management. We used tree ring growth patterns and stable isotopes to understand long-term physiological responses to fertilization using a controlled fertilization experiment begun in 1964 in Washington State (USA), in which three levels of nitrogen fertilizer were applied: 157, 314; and 471 kg/ha. Basal area increment (BAI) increased more than fourfold in the highest treatment to twofold in the lowest, and a significant increase in BAI was observed for 20 years. Latewood delta 13C sharply decreased by 1.4 per thousand after fertilization and was significantly lower than controls for four years, but no differences existed between fertilization levels, and the effect disappeared after four years, indicating that intrinsic water use efficiency (A/gs) increased in response to fertilization. Earlywood delta 13C showed similar trends but was more variable. Latewood delta 18O increased significantly above controls by approximately 2 per thousand in all treatments, but the duration differed with treatment level, with the effect being longer for higher levels of fertilization and lasting as long as nine years after fertilization. Because source water and relative humidity were the same between experimental plots, we interpreted the delta 18O increase with treatment as a decrease in leaf-level transpiration. Earlywood delta 18O did not show any treatment effects. Because the Pacific Northwest has a mediterranean climate with dry summers, we speculated that fertilization caused a substantial increase in leaf area, causing the trees to transpire themselves into drought stress during the late summer. We estimate from the delta 18O data that stomatal conductance (gs) was reduced by approximately 30%. Using the delta 13C data to estimate assimilation rates (A), A during the late season was also reduced by 20-30%. If leaf-level A decreased, but BAI increased, we estimated that leaf area on those trees must have increased by fourfold with the highest level of treatment within this stand. This increase in leaf area resulting from fertilization caused a hydraulic imbalance within the trees that lasted as long as nine years after treatment at the highest levels of fertilization.

LINKING MARINE RESOURCES TO ECOTONAL SHIFTS OF WATER UPTAKE BY TERRESTRIAL DUNE VEGETATION

As evidence mounts that sea levels are rising, it becomes increasingly important to understand the role of ocean water within terrestrial ecosystem dynamics. Coastal sand dunes are ecosystems that occur on the interface of land and sea. They are classic ecotones characterized by zonal distribution of vegetation in response to strong gradients of environmental factors from the ocean to the inland. Despite the proximity of the dune ecosystem to the ocean, it is generally assumed that all vegetation utilizes only freshwater and that water sources do not change across the ecotone. Evidence of ocean water uptake by vegetation would redefine the traditional interpretation of plant-water relations in the dune ecosystem and offer new ideas for assessing maritime influences on function and spatial distribution of plants across the dune. The purpose of this study was to identify sources of water (ocean, ground, and rain) taken up by vegetation using isotopic analysis of stem water and to evaluate water uptake patterns at the community level based on the distribution and assemblage of species. Three coastal dune systems located in southern Florida, USA, and the Bahamian bank/platform system were investigated. Plant distributions across the dune were zonal for 61-94% of the 18 most abundant species at each site. Species with their highest frequency on the fore dune (nearest the ocean) indicate ocean water uptake as evidenced by delta 18O values of stem water. In contrast, species most frequent in the back dune show no evidence of ocean water uptake. Analysis of species not grouped by frequency, but instead sampled along a transect from the ocean toward the inland, indicates that individuals from the vegetation assemblage closest to the ocean had a mixed water-harvesting strategy characterized by plants that may utilize ocean, ground-, and/or rainwater. In contrast, the inland vegetation relies mostly on rainwater. Our results show evidence supporting ocean water use by dune vegetation and demonstrate an exciting relationship between seawater and ecotonal shifts in plant function of a terrestrial ecosystem.

Non‐steady state effects in diurnal 18O discrimination by Picea sitchensis branches in the field

We report diurnal variations in 18O discrimination (18 delta) during photosynthesis (18 delta A) and respiration (18 delta R) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18 delta (18 delta pred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the Delta 18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18 delta pred and observed 18 delta (18 delta obs) compared with the assumption of isotopic steady state (ISS) for the Delta 18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18 delta values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of delta 18O of CO2.

Contributions of evaporation, isotopic non‐steady state transpiration and atmospheric mixing on the δ18O of water vapour in Pacific Northwest coniferous forests

Changes in the 2H and 18O of atmospheric water vapour provide information for integrating aspects of gas exchange within forest canopies. In this study, we show that diurnal fluctuations in the oxygen isotope ratio (delta 18O) as high as 4% per hundred were observed for water vapour (delta (18)Ovp) above and within an old-growth coniferous forest in the Pacific Northwest region of the United States. Values of delta 18Ovp decreased in the morning, reached a minimum at midday, and recovered to early-morning values in the late afternoon, creating a nearly symmetrical diurnal pattern for two consecutive summer days. A mass balance budget was derived and assessed for the 18O of canopy water vapour over a 2-d period by considering the 18O-isoflux of canopy transpiration, soil evaporation and the air entering the canopy column. The budget was used to address two questions: (1) do delta 18O values of canopy water vapour reflect the biospheric influence, or are such signals swamped by atmospheric mixing? and (2) what mechanisms drive temporal variations of delta 18Ovp? Model calculations show that the entry of air into the canopy column resulted in an isotopically depleted 18O-isoflux in the morning of day 1, causing values of delta 18Ovp, to decrease. An isotopically enriched 18O-isoflux resulting from transpiration then offset this decreased delta 18Ovp later during the day. Contributions of 18O-isoflux from soil evaporation were relatively small on day 1 but were more significant on day 2, despite the small H2(16)O fluxes. From measurements of leaf water volume and sapflux, we determined the turnover time of leaf water in the needles of Douglas-fir trees as approximately 11 h at midday. Such an extended turnover time suggests that transpiration may not have occurred at the commonly assumed isotopic steady state. We tested a non-steady state model for predicting delta 18O of leaf water. Our model calculations show that assuming isotopic steady state increased isoflux of transpiration. The impact of this increase on the modelled delta 18Ovp was clearly detectable, suggesting the importance of considering isotopic non-steady state of transpiration in studies of forest 18O water balance.

Characterization of a 1:1 Cu−O2Adduct Supported by an Anilido Imine Ligand

Copper(I) complexes of sterically hindered anilido imine ligands o-C6H4{N(C6H3(i)Pr2)}{C(R)=NC6H3(i)Pr2}- (L(1), R = H; L(2), R = CH3) have been prepared and characterized by spectroscopic and X-ray crystallographic methods. These complexes are highly reactive with O2, and in the case of L2 the product of low-temperature oxygenation was fully characterized by spectroscopic, X-ray crystallographic, and computational methods. The resonance Raman spectrum features an isotope-sensitive vibration at 974 cm(-1) (Delta(18O) = 66 cm(-1)), consistent with assignment as an O-O stretch. Despite the asymmetric coordination environment provided by the supporting anilido imine ligand, the X-ray crystal structure confirms rather symmetric side-on binding of the O2 moiety to the copper center, and the O-O bond length of 1.392(2) Angstroms indicates that this intermediate has significant Cu(III)-peroxo character. Theoretical calculations support this interpretation and predict that while a fully optimized end-on singlet geometry can be obtained, it is higher in energy than the side-on isomer by 3.5 kcal mol(-1) at the CASPT2/TZP level.

Tracking Sources of Unsaturated Zone and Groundwater Nitrate Contamination Using Nitrogen and Oxygen Stable Isotopes at the Hanford Site, Washington

The nitrogen and oxygen isotopic compositions of nitrate in pore water extracts from unsaturated zone (UZ) core samples and groundwater samples indicate at least four potential sources of nitrate in groundwaters at the U.S. DOE Hanford Site in south-central Washington. Natural sources of nitrate identified include microbially produced nitrate from the soil column (delta15N of 4 - 8 per thousand, delta18O of -9 to 2 per thousand) and nitrate in buried caliche layers (delta15N of 0-8 per thousand, delta 18O of -6to 42 per thousand). Isotopically distinctindustrial sources of nitrate include nitric acid in low-level disposal waters (delta15N approximately per thousand, delta 18O approximately 23%o) per thousandnd co-contaminant nitrate in high-level radioactive waste from plutonium processing (6'5delta1of 8-33 % o, per thousand18delta oO -9 to 7%0). per thousandThe isotopic compositions of nitrate from 97 groundwater wells with concentrations up to 1290 mg/L NO3- have been analyzed. Stable isotope analyses from this study site, which has natural and industrial nitrate sources, provide a tool to distinguish nitrate sources in an unconfined aquiferwhere concentrations alone do not. These data indicate that the most common sources of high nitrate concentrations in groundwater at Hanford are nitric acid and natural nitrate flushed out of the UZ during disposal of low-level wastewater. Nitrate associated with high-level radioactive UZ contamination does not appear to be a major source of groundwater nitrate at this time.

Late Pleistocene to Holocene composite speleothem 18O and 13C chronologies from South Island, New Zealand—did a global Younger Dryas really exist?

Oxygen and carbon data from eight stalagmites from northwest South Island are combined to produce composite records of δ 18O and δ 13C from 23.4 ka to the present. The chronology is anchored by 43 thermal ionization mass spectrometry (TIMS) uranium series ages. Delta 18O values are interpreted as having a first order positive relationship to temperature, but also to be influenced by precipitation in a complex manner. Delta 13C is interpreted as responding negatively to increases in atmospheric CO 2 concentration, biological activity and precipitation amount. Six climatic phases are recognized. After adjustment of 1.2‰ for the ice volume effect, the δ 18O record between 23 and 18 ka varies around −3.72‰ compared to the Holocene average of −3.17‰. Late-glacial warming commenced between 18.2 and 17.8 ka and accelerated after 16.7 ka, culminating in a positive excursion between 14.70 and 13.53 ka. This was followed by a significant negative excursion between 13.53 and 11.14 ka of up to 0.55‰ depth that overlapped the Antarctic Cold Reversal (ACR) and spanned the Younger Dryas (YD). Positive δ 18O excursions at 11.14 ka and 6.91–6.47 ka represent the warmest parts of the Holocene. The mid-Holocene from 6 to 2 ka was marked by negative excursions that coincide with increased glacial activity in the South Island. A short positive excursion from 0.71 to 0.57 ka was slightly later than the Medieval Warm Period of Europe. Delta 13C values were high until 17.79 ka after which there was an abrupt decrease to 17.19 ka followed by a steady decline to a minimum at 10.97 ka. Then followed a general increase, suggesting a drying trend, to 3.23 ka followed by a further general decline. The abrupt decrease in δ-values after 17.79 ka probably corresponds to an increase in atmospheric CO 2 concentration, biological activity and wetness at the end of the Last Glaciation, but the reversal identified in the δ 18O record from 13.53 to 11.14 ka was not reflected in δ 13C changes. The lowest δ 13C values coincided with the early Holocene climatic suboptimum when conditions were relatively wet as well as mild. Major trends in the δ 18O c record are similar to the Northern Hemisphere, but second order detail is often distinctly different. Consequently, at the millennial scale, a more convincing case can be made for asymmetric climatic response between the two hemispheres rather than synchronicity.