Phosphate Oxygen Isotope Research Articles

Using Oxygen Isotopes of Phosphate To Trace Phosphorus Sources and Cycling in Lake Erie

Water samples collected during three sampling trips to Lake Erie displayed oxygen isotopic values of dissolved phosphate (delta18Op) that were largely out of equilibrium with ambient conditions, indicating that source signatures may be discerned. delta18Op, values in the Lake ranged from +10% per hundred to +17% per hundred, whereas the equilibrium value was expected to be around +14% per hundred. The riverine weighted average delta18Op, value was +11% per hundred and may represent one source of phosphate to the Lake. The lake delta18Op, values indicated that there must be one or more as yet uncharacterized source(s) of phosphate with a high delta18Op value. Potential sources other than rivers are not yet well-characterized with respectto delta18Op of phosphate, but we speculate that a likely source may be the release of phosphate from sediments under reducing conditions created during anoxic events in the hypolimnion of the central basin of Lake Erie. Identifying potential phosphorus sources to the Lake is vital for designing effective management plans for reducing nutrient inputs and associated eutrophication.

Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology-based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics. We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag(3)PO(4) crystals by using a strongly buffered, moderate-temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as delta(18)O, V-SMOW scale) is typically 0.2-0.3 per thousand (1 s.d.) on samples as small as 300 microg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen.

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

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

Phosphate–oxygen isotopes from marine turtle bones: Ecologic and paleoclimatic applications

While certain freshwater turtle taxa possess a strong correlation between the δ 18O phosphate value of their bone mineral and that of their environmental water, it remains unclear whether the same correlation applies to marine turtles. Isotopic analysis of over 50 individuals representing three species ( Chelonia mydas, Caretta caretta, Dermochelys coriacea) from Atlantic and Pacific waters demonstrates that the correlation is robust for the studied specimens, which include a wide range of growth stages for the loggerhead ( C. caretta). In most cases, intra- and inter-bone isotopic variations are low (standard deviation < ± 0.34‰ and 0.44‰, respectively) which confirms that bone growth occurs, on average, over a narrow body temperature range (ca. ≤ ± 2.0°C) and that samples from any spot on any bone can be considered as representative of the entire skeleton. Applying the correlation between δ 18O w and δ 18O bone PO4 to marine turtles may provide a new route for investigating extant marine turtle ecology and for reconstructing paleoceanic δ 18O w values.

Oxygen isotope signature of P i regeneration from organic compounds by phosphomonoesterases and photooxidation

Phosphomonoesters are an important source of dissolved inorganic orthophosphate (PO 4 or P i), the preferred form of P utilized by microbiota and aquatic plants in marine and freshwater ecosystems. Two enzymes involved in phosphomonoester metabolism and commonly detected in natural waters (alkaline phosphatase and 5′-nucleotidase) have been studied to determine the oxygen isotope signature of P i-regeneration from phosphomonoesters by enzymatic degradation. Oxygen (O) isotope ratios of water and P i released from phosphomonoesters during enzyme hydrolysis experiments demonstrate that released P i incorporates one oxygen atom from water. The isotopic fractionation between this incorporated water O and ambient water O is −30 (±8)‰ for alkaline phosphatase and −10 (±1)‰ for 5′-nucleotidase, with very weak dependence on temperature. The result of these enzyme-specific isotopic fractionations at one of the four O sites in PO 4 is that the δ 18O value of P i regenerated by 5′-nucleotidase is 5‰ higher than P i regenerated by alkaline phosphatase from the same phosphomonoester substrate. The δ 18O value of regenerated P i also reflects inheritance of 75% of O from the phosphomonoester substrate, thus making the δ 18O of phosphomonoester-derived P i a potential tracer of organophosphorous compound sources. Phosphomonoesterase-regenerated P i has a distinct phosphate oxygen isotope signature that is different and distinguishable from that of biologically recycled and subsequently equilibrated P i and P i regenerated from photooxidation of organic matter. The δ 18O value of regenerated P i will correlate positively with the δ 18O value of bulk water and the fractionation, α, between regenerated P i and water, α regen Pi-water , should converge toward equilibrium α Pi-water values with increased biological cycling of P i.

Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California

A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme‐mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ18Op) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ18Op in the bay is primarily controlled by mixing of water masses with different δ18Op signatures. The δ18Op values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two‐component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ18Op can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.

Marine phosphate oxygen isotopes and organic matter remineralization in the oceans

We show that the isotopic composition of oxygen (delta18O) in dissolved inorganic phosphate (Pi) reveals the balance between Pi transport and biological turnover rates in marine ecosystems. Our delta18Op of Pi (delta18Op) measurements herein indicate the importance of cell lysis in the regeneration of Pi in the euphotic zone. Depth profiles of the delta18Op in the Atlantic and Pacific Oceans are near a temperature-dependent isotopic equilibrium with water. Small deviations from equilibrium below the thermocline suggest that P remineralization in the deep ocean is a byproduct of microbial carbon and energy requirements. However, isotope effects associated with phosphohydrolase enzymes involved in P remineralization are quite large and could potentially lead to significant disequilibration of Pi oxygen. The observed near equilibration of deep water Pi likely calls for continued slow rates of microbial uptake and release of Pi and/or extracellular pyrophosphatase-mediated oxygen exchange between water and Pi along the deep water flow path.

Biogeochemical cycling of phosphorus: Insights from oxygen isotope effects of phosphoenzymes

Geochemical cycling of phosphorus (P) in aquatic environments is carried out almost exclusively by biota and involves reactions that are catalyzed by enzymes. Oxygen isotope effects accompanying phosphoenzymatic reactions have been determined in controlled laboratory experiments in order to elucidate processes underlying biogeochemical cycling of P, and to identify possible reaction pathways for P-compounds in nature. Phosphate oxygen isotope effects are distinct for specific enzymatic reaction mechanisms measured in microbial culture experiments and in cell-free systems. P¹⁶O₄ is taken up preferentially from inorganic phosphate (P_i) in the growth medium by intact <i>E. coli</i> cells, producing a kinetic fractionation in the extracellular dissolved P_i pool. Inorganic pyrophosphatase is the intracellular enzyme that catalyzes the temperature-dependent equilibrium oxygen isotope fractionations between phosphates and water in biological systems, and imprints an equilibrium isotope signature on P_i that is turned over or cycled by intact cells. Alkaline phosphatase, a key enzyme involved in extracellular P_i regeneration in aquatic systems, catalyzes hydrolysis of phosphomonoesters, reactions that are accompanied by kinetic fractionations and disequilibrium (inheritance) isotope effects in released P_i. Comparison of laboratory determined enzyme-specific isotopic fractionations with those observed in microbial culture experiments and in natural aquatic systems, provide new insights into processes controlling P cycling and the relations between P availability and the cycling of N and C. Isotopic signatures associated with specific cellular processes and phosphoenzyme reaction pathways may be useful in assessing P status and for tracing P turnover.

Using mammal tooth phosphate with freshwater carbonate and phosphate palaeoproxies to obtain mean paleotemperatures

The use of enamel phosphate oxygen from small mammal teeth in Eocene palaeoclimate research is discussed and its future potential application to Quaternary palaeoclimate research is considered. With reference to published work and additional results presented here from the Late Eocene (Priabonian) Headon Hill Formation of the Hampshire Basin, it is shown how a new direct laser fluorination technique can be used to determine the enamel phosphate oxygen δ 18O value from teeth of the rodents Thalerimys and Isoptychus. It is shown how these values can be used to calculate a mean palaeo-δ 18O local freshwater value, which can be used to calculate a mean annual temperature. The local water value can also be combined with other specific freshwater palaeoproxies to calculate mean palaeotemperatures for the growing season and the warmest months of the growing season. Additional results presented specifically in this paper are (1) oxygen isotope results that indicate that Thalerimys teeth with etched enamel, indicative of digestive activity, have not experienced isotopic fractionation; (2) moulding of Thalerimys teeth to produce a solid 3D record prior to sample preparation and analysis does not affect their enamel phosphate oxygen isotope values. Both of these new results enhance the potential application of the method by making more fossil tooth material available for study.

Box-modeling of bone and tooth phosphate oxygen isotope compositions as a function of environmental and physiological parameters*

A time-dependent box model is developed to calculate oxygen isotope compositions of bone phosphate as a function of environmental and physiological parameters. Input and output oxygen fluxes related to body water and bone reservoirs are scaled to the body mass. The oxygen fluxes are evaluated by stoichiometric scaling to the calcium accretion and resorption rates, assuming a pure hydroxylapatite composition for the bone and tooth mineral. The model shows how the diet composition, body mass, ambient relative humidity and temperature may control the oxygen isotope composition of bone phosphate. The model also computes how bones and teeth record short-term variations in relative humidity, air temperature and δ18O of drinking water, depending on body mass. The documented diversity of oxygen isotope fractionation equations for vertebrates is accounted for by our model when for each specimen the physiological and diet parameters are adjusted in the living range of environmental conditions. *The code to perform calculations is available upon request to the first author.

Sedimentary phosphate formation in warm shallow waters: new insights into the palaeoceanography of the Permian Phosphoria Sea from analysis of phosphate oxygen isotopes

Abstract Oxygen isotopic analyses of the structural phosphate ( δ 18 O P ) in sedimentary phosphorites of the Upper Permian Phosphoria Formation reveal that phosphogenesis occurred across a broad range of palaeoenvironments. The δ 18 O P values from well-preserved hand-picked phosphate-grain separates range from 20.2 to 13.7 (±0.5)‰ SMOW, with the lowest values in the most landward shallow-water deposits and the highest values in the most basinward deeper water deposits. The relationship between the maximum burial depth and δ 18 O P is opposite to that predicted if burial diagenesis was responsible for the isotopic signature of these phosphate grains. This suggests that the regional trend in oxygen isotopic data is not due to burial diagenesis. The range in oxygen isotopic values does correspond to the potential range of palaeotemperatures in the shallow and broad epicontinental Phosphoria Sea. The range is 14–42°C (±3.5°C) assuming a seawater δ 18 O of −2.5 ‰ SMOW. Palaeotemperatures along an offshore to onshore transect indicate that upwelling involved temperate (14–26°C; mean of 21°C) but not cold waters, and that warming across the palaeoshelf resulted in mean shallow-water temperatures of 34–37°C. The latter values approximate those predicted by climate and ocean circulation models. These warm palaeotemperatures provide further evidence that phosphogenesis in the epicontinental Phosphoria Sea occurred under palaeoceanographic conditions that were different from modern phosphorite depositional systems. This suggests that a purely actualistic approach to the interpretation of the Phosphoria phosphorites is not valid.

Stable Isotope Ecology of a Late Miocene Population of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma, USA

Abstract The stable carbon and oxygen isotope compositions of serial samples of enamel from tusks of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma (early Hemphillian North American Land Mammal Age, ca. 7.5 Ma), were measured to examine intra-annual and interannual variation. Sample series from each of six tusks spanned approximately one year of tusk growth. Carbon isotope compositions range from −11.3 to −9.2‰ (VPDB) and exhibit no pattern of seasonal variation, indicating the diet of gomphotheres at Port of Entry Pit was dominated by C3 vegetation throughout the year. Phosphate oxygen isotope composition (δ18Op) ranges from 18.9 to 22.2‰ (VSMOW); carbonate oxygen isotope composition (δ18Oc) ranges from 26.1 to 30.1‰ (VSMOW). None of the tusks exhibit seasonal variation in δ18O, and the average within-tusk range in δ18Op is 1.7‰. Neither the fluorine composition of the specimens nor the relationship between δ18Op and δ18Oc values from splits of the same samples suggest s...

Stable Isotope Ecology of a Late Miocene Population of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma, USA

Other| June 01, 2001 Stable Isotope Ecology of a Late Miocene Population of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma, USA DAVID L. FOX; DAVID L. FOX 1Department of Geological Sciences and Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109 *Current address: Department of Earth Sciences, University of California, Santa Cruz, CA 95064 Search for other works by this author on: GSW Google Scholar DANIEL C. FISHER DANIEL C. FISHER 1Department of Geological Sciences and Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109 Search for other works by this author on: GSW Google Scholar Author and Article Information DAVID L. FOX *Current address: Department of Earth Sciences, University of California, Santa Cruz, CA 95064 1Department of Geological Sciences and Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109 DANIEL C. FISHER 1Department of Geological Sciences and Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109 Publisher: SEPM Society for Sedimentary Geology Accepted: 22 Dec 2000 First Online: 03 Mar 2017 Online ISSN: 1938-5323 Print ISSN: 0883-1351 Society for Sedimentary Geology PALAIOS (2001) 16 (3): 279–293. https://doi.org/10.1669/0883-1351(2001)016<0279:SIEOAL>2.0.CO;2 Article history Accepted: 22 Dec 2000 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DAVID L. FOX, DANIEL C. FISHER; Stable Isotope Ecology of a Late Miocene Population of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma, USA. PALAIOS 2001;; 16 (3): 279–293. doi: https://doi.org/10.1669/0883-1351(2001)016<0279:SIEOAL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Abstract The stable carbon and oxygen isotope compositions of serial samples of enamel from tusks of Gomphotherium productus (Mammalia, Proboscidea) from Port of Entry Pit, Oklahoma (early Hemphillian North American Land Mammal Age, ca. 7.5 Ma), were measured to examine intra-annual and interannual variation. Sample series from each of six tusks spanned approximately one year of tusk growth. Carbon isotope compositions range from −11.3 to −9.2‰ (VPDB) and exhibit no pattern of seasonal variation, indicating the diet of gomphotheres at Port of Entry Pit was dominated by C3 vegetation throughout the year. Phosphate oxygen isotope composition (δ18Op) ranges from 18.9 to 22.2‰ (VSMOW); carbonate oxygen isotope composition (δ18Oc) ranges from 26.1 to 30.1‰ (VSMOW). None of the tusks exhibit seasonal variation in δ18O, and the average within-tusk range in δ18Op is 1.7‰. Neither the fluorine composition of the specimens nor the relationship between δ18Op and δ18Oc values from splits of the same samples suggest significant post-depositional alteration. The oxygen isotope data imply that Hemphillian meteoric water had δ18O values that are indistinguishable from modern values in the region today. However, because polar ice sheets were smaller and mean ocean water δ18O lower than present, the estimates of meteoric water composition from gomphothere tusk δ18Op are consistent with warmer mean annual temperatures during the Hemphillian. The within-tusk variations in δ18Op are consistent with similar or much reduced patterns of seasonal temperature variation in comparison to today, depending on air mass flow during the late Miocene. Alternative explanations include seasonal migratory behavior and reliance by the gomphotheres at Port of Entry Pit on sources of drinking water with relatively constant δ18O values. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Statistical power analysis: application to an investigation of dinosaur thermal physiology

It has been postulated that the variation in an animal's body temperature during different phases of bone deposition can be estimated from the variation in the ratio of two oxygen isotopes in phosphate recovered from its fossil. Using data from a fossil Tyrannosaurus rex skeleton, the previous researchers failed to reject the null hypothesis that the variation found in bones from the body core is significantly less than that found in the extremities; they also failed to reject the null hypothesis that the coldest and hottest parts of the body differed by less than 4 °C. This suggests that either both null hypotheses are true, or that they are false but the statistical tests used were not powerful enough to detect this. Here I use calculation of confidence intervals to differentiate between these two alternatives. In the first case, I find that the data are consistent with the variance in both the core and the extremity being up to 2.5 times that of the other. In the second case, I show that observations are consistent with temperature differences ranging from 2.6 °C to 6.4 °C. Hence, neither case provides any real support for the hypothesis that bone deposition in this specimen occurred under essentially thermostable conditions.

Statistical power analysis: application to an investigation of dinosaur thermal physiology

It has been postulated that the variation in an animal's body temperature during different phases of bone deposition can be estimated from the variation in the ratio of two oxygen isotopes in phosphate recovered from its fossil. Using data from a fossil Tyrannosaurus rex skeleton, the previous researchers failed to reject the null hypothesis that the variation found in bones from the body core is significantly less than that found in the extremities; they also failed to reject the null hypothesis that the coldest and hottest parts of the body differed by less than 4 °C. This suggests that either both null hypotheses are true, or that they are false but the statistical tests used were not powerful enough to detect this. Here I use calculation of confidence intervals to differentiate between these two alternatives. In the first case, I find that the data are consistent with the variance in both the core and the extremity being up to 2.5 times that of the other. In the second case, I show that observations are consistent with temperature differences ranging from 2.6 °C to 6.4 °C. Hence, neither case provides any real support for the hypothesis that bone deposition in this specimen occurred under essentially thermostable conditions.

Enzyme-Catalyzed Oxygen Isotope Exchange between Inorganic Phosphate and Water: Reaction Rates and Temperature Dependence at 5.7–30°C

The resistance of phosphate minerals to isotopic exchange with water and diagenetic alteration makes the oxygen isotope composition of phosphates a very attractive palaeoenvironmental indicator as well as a potential conservative tracer of dissolved inorganic PO4 (Pi) as it is cycled through aquatic and sedimentary environments as a nutrient or pollutant. Currently used phosphate oxygen isotope thermometer equations were developed solely on the basis of empirical measurements of biogenic phosphates such as shells and teeth (e.g. Longinelli and Nuti, 1973; Lecuyer et al., 1996), however, these relations have not been verified by laboratory controlled equilibrium isotope exchange experiments due to sluggish reaction rates at low temperature. It is widely accepted that the oxygen in phosphate is readily exchanged and equilibrated with body water of living organisms via multiple enzyme-catalyzed metabolic reactions. Here we report results of experiments conducted using purified cell-free enzymes, to facilitate oxygen isotope exchange between dissolved Pi and water under wellcontrolled conditions of temperature and oxygen isotope composition of water (818Ow) with the aim of obtaining a laboratory calibration of the phosphatewater oxygen isotope thermometer at low temperature. The most elementary system for Pi-water oxygen isotope exchange would consist of: orthophosphate + water + enzyme. The enzyme inorganic pyrophosphatase (Ppiase) is known to catalyze significant amounts of oxygen isotope exchange between Pi and water in this system during the overall reaction: Mg +2 H2P2 O2+ H20 ~ 2HPO]+ 2H + (1) PPi PPiase Pi

Oxygen isotope systematics of biologically mediated reactions of phosphate: I. Microbial degradation of organophosphorus compounds

Microbial activity has been invoked to explain anomalous oxygen isotope compositions of phosphate mineral deposits as well as fossil biogenic apatite. Results of laboratory experiments on enzyme-mediated reactions of phosphate and microbially mediated degradation of organic matter, an important mechanism for the regeneration of dissolved phosphate in modern porewaters, demonstrate that significant exchange of oxygen isotopes between phosphate and water accompanies the hydrolytic cleavage of organically bound phosphate as well as the metabolism of inorganic orthophosphate. Evaluation of the oxygen isotope systematics of microbially mediated reactions of phosphate suggests that oxygen isotope exchange between phosphate and water mediated by bacteria is governed by equilibrium rather than kinetic factors. Under certain conditions, the microbially mediated exchange appears to result in complete re-equilibration of oxygen isotopes between phosphate and water and in other instances equilibrium exchange may be masked by inheritance of phosphate-oxygen from the organic substrate. Analogous microbial processes in natural sediments may be important in the release of dissolved phosphate to pore fluids, precipitation of authigenic apatite, and in the diagenetic alteration of phosphorite deposits and biogenic apatite. These results have important implications for paleoclimatological and paleoenvironmental studies in which oxygen isotope ratios of biogenic phosphate are used as paleotemperature indicators, as well as for studies employing phosphate oxygen isotopes as a tracer of P transport and cycling in the environment.

Oxygen isotopic composition of fossil equid tooth and bone phosphate: an archive of difficult interpretation

Variation in the concentration of the stable isotopes of hydrogen, oxygen and carbon have been tested in continental records as tools for quantitative or semi-quantitative paleoclimatological studies. Among the different methods, the potential use of oxygen isotopes in mammal bone and tooth phosphate has recently been recognized. Measurements carried out on fossil mammal bones of Holocene age and their paleoclimatological interpretation corresponded well with paleontological and paleobotanical records. In the case of considerably older fossils, diagenetic processes may change the primary oxygen isotopic composition of phosphate. Fossil horse bones and teeth (principally of the species Equus stenonis) were studied to ascertain how far back in time fossil mammal remains may be considered reliable material for paleoclimatological studies. The samples come from 13 different locations in southeastern Spain, their age ranging from Maspinian (late Pleistocene) to Middle Villafranchian (Pliocene). Apart from the variations of the δ 18O(PO 4 3−) values which may be related to climatic changes, it is apparent that the isotopic composition of bones and teeth from the same deposit are frequently rather different from one another. The isotopic differences range from a few tenths of one % to several %. This suggests a strong influence of taphonomy over the measured isotopic values of fossils in each deposit. Time can be considered neither the only variable nor the most important one responsible for the change of the primary isotopic composition of fossils. Under these conditions it is rather difficult to establish lower or upper limits for the age of fossils to be studied for reliable paleoclimatological information since the limits are directly related to taphonomic history. This, in turn, is related to local environmental conditions and not only to the age of fossils.

Tracing Phosphorus Sources and P-Cycling by Oxygen Isotopes in Phosphate; Lake Kinneret (Israel)

Tracing Phosphorus Sources and P-Cycling by Oxygen Isotopes in Phosphate; Lake Kinneret (Israel)

The preservation of glacial-interglacial climatic signatures in the oxygen isotopes of elephant skeletal phosphate

Phosphate δ 18O values ( δ 18O p) of modern elephant bone and teeth are found to vary linearly according to the δ 18O of local meteoric water ( δ 18O mw), a parameter with close ties to regional and local climatic conditions. Enamel, dentine, cementum and bone separates from individual fossil elephant specimens, of Late Pleistocene age, have δO p values which vary by up to elephant specimens. The larger spread in the δ 18O p values of the various skeletal phases for the fossil samples is interpreted as evidence for post-depositional alterantion of primary δ 18O p signatures of some, if not all, of these fossil skeletal components. In the fossil samples investigated, enamel and dentine phases have systematically lower δ 18O values than associated bone and cementum phases. Differential re-equilibration with soil waters, either by the wholesale replacement of primary apatite or by processes of isotopic exchange, is suggested as a mechanism to account for the observed spread in the fossil phosphate δ 18O data.