Boaz Luz

Fractionation of oxygen isotopes between mammalian bone-phosphate and environmental drinking water

The δ18O of mammalian bone-phosphate varies linearly with δ18O of environmental water, but is not in isotopic equilibrium with that water. This situation is explained by a model of δ18O in body water in which the important fluxes of exchangeable oxygen through the body are taken into account. Fractionation of oxygen isotopes between body and environmental drinking water is dependent on the rates of drinking and respiration. Isotopic fractionation can be estimated from physiological data and the estimates correlate very well with observed fractionation. Species whose water consumption is large relatively to its energy expenditure is sensitive to isotopic ratio changes in environmental water.

Experimental paleotemperature equation for planktonic foraminifera

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups. Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO3 indicate that the foraminifera precipitate their CaCO3 in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craigs (1965) equation yields: t = −0.07 + 1.01t (r= 0.95) where t is the actual growth temperature and t Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer. Second order regression of the culture temperature and the delta difference (δ18Oc − δ18Ow) yield a correlation coefficient of r = 0.95: t = 17.0 − 4.52(δ18Oc − δ18Ow) + 0.03(δ18Oc − δ18Ow)2t, δ18Oc and δ18Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively. A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.

Oxygen isotope variations in phosphate of biogenic apatites, I. Fish bone apatite—rechecking the rules of the game

Abstract The major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone (and teeth) building organisms are alive, and the record is nearly perfectly preserved after death. Fish from seven water bodies of different temperatures (3–23°C) and different δ 18 O (values −16 to +3) of the water were analysed. The δ 18 O values of the analysed PO 4 vary from 6 to 25. The system passed the following tests: (a) the temperatures deduced from isotopic analyses of the sequence of fish from Lake Baikal are in good agreement with the temperatures measured in the thermally stratified lake; (b) the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish, but only by temperature and water composition. Isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates.

Oxygen isotope variations in phosphate of biogenic apatites, IV. Mammal teeth and bones

Groups of rats grown from birth to death in identical conditions, but with different δ18O of drinking water (δw), were studied for variations of δ18O of their body water (δBW) and bone phosphate (δp). There is a high linear correlation (r = 0.99) between δBW and between δp and δw. The regression lines have similar slope coefficients (0.53 and 0.49). Values of δp of different teeth and bones are the same, within the precision of the method (±0.5‰). The isotopic fractionation coefficient between phosphate and body water is 1.0178 and close to the estimated value of 1.0173 derived from the phosphate paleotemperature equation. Deviations from constant fractionation between bone phosphate and environmental drinking water depend primarily on rates of drinking and metabolism. Environment conditions have relatively little effect on oxygen isotope fractionation between water sources and bone phosphate.

Oxygen isotope variations in phosphate of biogenic apatites, II. Phosphorite rocks

Abstract Phosphorites from sedimentary sequences ranging in age from Archaean to Recent were analysed for δ 18 O in both the PO 4 (δ 18 O p ) and CO 3 (δ 18 O c ) in the apatite lattice. The oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts. The use of the Longinelli and Nuti [8] temperature equation yields temperatures for Recent phosphorites that are in good agreement with those measured in the field. The δ 18 O p values of ancient phosphorites decrease with increasing age. These changes with time are not likely to be due to post-depositional exchange. Changes in δ 18 O values of seawater and variations of temperature with time can account for the δ 18 O p time trend, but the latter explanation is preferred. In Ancient phosphorites δ 18 O c in structurally bound carbonate in apatite is not a reliable geochemical indicator.

Triple-isotope composition of atmospheric oxygen as a tracer of biosphere productivity

Oxygen has three naturally occurring isotopes, of mass numbers 16, 17 and 18. Their ratio in atmospheric O2 depends primarily on the isotopic composition of photosynthetically produced O2 from terrestrial and aquatic plants, and on isotopic fractionation due to respiration. These processes fractionate isotopes in a mass-dependent way, such that 17O enrichment would be approximately half of the 18O enrichment relative to 16O. But some photochemical reactions in the stratosphere give rise to a mass-independent isotope fractionation, producing approximately equal 17O and 18O enrichments in stratospheric ozone and carbon dioxide,, and consequently driving an atmospheric O2 isotope anomaly. Here we present an experimentally based estimate of the size of the 17O/16O anomaly in tropospheric O2, and argue that it largely reflects the influences of biospheric cycling and stratospheric photochemical processes. We propose that because the biosphere removes the isotopically anomalous stratosphere-derived O2 by respiration, and replaces it with isotopically ‘normal’ oxygen by photosynthesis, the magnitude of the tropospheric 17O anomaly can be used as a tracer of global biosphere production. We use measurements of the triple-isotope composition of O2 trapped in bubbles in polar ice to estimate global biosphere productivity at various times over the past 82,000 years. In a second application, we use the isotopic signature of oxygen dissolved in aquatic systems to estimate gross primary production on broad time and space scales.

Oxygen isotopic composition of fossil horse tooth phosphate as a record of continental paleoclimate

Abstract Oxygen isotopic, elemental, and X-ray data are presented for a suite of 24 fossil horse teeth from Nebraska ranging in age from 18.2 to 8.5 Ma, to test the use of δ18O of enamel phosphate (δ18OP04) as a quantitative record of continental climate. Modern equid teeth were analyzed to estimate a relationship between δ8OP04 and environment water. Multiple samples of seven different fossil species from Burge Quarry, a ∼ 12 Ma attritional fossil deposit, indicate the diagenetic overprints exist but can be detected by decreased P concentration and increased crystallinity relative to modern enamel. Isotopic variation for the pristine samples from Burge Quarry is ±1.5% (1σ, n=9), which may represent the resolution of the procedure within a stratigraphic horizon. There are no apparent correlations with body size, hypsodonty, or phylogeny. A range of 7%0 in δ18OP04 occurs over the 10 m.y. interval. A trend towards depleted δ18OP04 of about 4% corresponds to a depletion of up to 6%0 in δ18O of precipitation between 18.2 and 8.5 Ma, but the range of variation of Burge is large relative to the climate signal. Our results demonstrate that δ18OP04 should be useful in quantitatively reconstructing Cenozoic continental paleoclimate on 106-year timescales. Isotopic variation due to taphonomic bias and the terrestrial rock record will likely obscure higher-order climate signals.

The reconstruction of sea surface temperatures in the Pacific Ocean of 18,000 B.P.

Abstract All the major microfossil groups were used to reconstruct the summer and winter sea-surface temperatures of an ice-age Pacific Ocean. The use of these four groups was necessary because of the varying degrees of preservation of siliceous and carbonate-rich sediments in the Pacific. Their use also permits comparisons of temperature estimates for samples in which more than one group is preserved. The standard error of estimate for the transfer function equations used in this study average about ± 1.5° C for the summer temperature estimates, and about ± 1.9° C for winter estimates. Laboratory (counting) errors result in an average error of estimate of about 0.6° C. Most of the individual estimates using different equations on the same samples agree within their pooled standard error. The reconstructions of ice-age temperature patterns show cooling in the subarctic region by about 4°C in both August and February. The equatorial region is 2–4° C cooler only in the winter season (August). Seasonality (August minus February temperatures) is stronger in the western Subarctic and Transition Zones at 18,000 B.P. than it is at present. Such changes in seasonality result primarily from increased winter cooling and equatorward shifts in the frontal zones. Temperatures within the centers of the subtropical gyres at 18,000 B.P. are generally as warm as, or warmer than, modern sea-surface temperatures. In particular, the Southern Hemisphere shows little or no cooling in tropical and subtropical latitudes except along the equator and in the eastern boundary current. The distribution of biotic assemblages and the derived temperature patterns indicate an intensified circulation at 18,000 B.P. Temperature gradients are steeper in the boundary currents, and divergence at the equator is increased. The “spin-up” of the subtropical gyres associated with this intensified flow appear to contain the warm tropical waters within the gyre centers, rather than allowing their dispersal to subpolar regions. These relatively warm gyre centers may act as loci for low pressure systems in the atmosphere which draw moisture away from the land masses.

Oxygen isotope variations in phosphate of deer bones

Abstract Variations of δ 18 O of bone phosphate (δ p ) of white tailed deer were studied in samples with wide geographic distribution in North America. Bones from the same locality have similar isotopic values, and the difference between specimens (0.4‰) is not large relative to the measurement error (0.3‰). The total range of δ p values is about 12‰. This indicates that deer use water from a relatively small area, and thus their δ p indicates local environmental conditions. Multiple regression analysis between oxygen isotope composition of deer bone phosphate and of local relative humidity and precipitation (δ w ) yields a high correlation coefficient (0.95). This correlation is significantly better than the linear correlation (0.81) between δ p and δ w of precipitation alone. Thus δ p depends on both isotopic composition of precipitation and on relative humidity. This is because deer obtain most of their water from leaves, the isotopic composition of which is partly controlled by relative humidity through evaporation/transpiration.

Global climate instability reflected by Eastern Mediterranean marine records during the late Holocene

Abstract Extremely high sediment accumulation rates in the southeastern (SE) Mediterranean off Israel make this region ideal for high-resolution paleoceanographic reconstructions. Two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the SE Mediterranean Basin during the late Holocene (3.6 ka). The δ18O values of Globigerinoides ruber suggest that the freshwater balance changed several times during this time interval. Humid phases took place between 3.5–3.0 ka BP and 1.7–1.0 ka BP. The later was accompanied by enhanced preservation of terrestrial organic matter within the sediment (ORS event). Relatively more arid conditions prevailed in this area between 3.0 and 1.7 ka BP. During the last millennia at ca. 0.8 and 0.27 ka two climatic events occurred which are probably correlative to both the Medieval Warm Period and the cooling global event known as the Little Ice Age, respectively. A long-term slight increase in planktonic foraminiferal δ18O values occurs together with a gradual decrease in the δ13C values of both G. ruber and the benthic foraminifera Uvigerina mediterranea. This trend is associated with an increase in sedimentation rates, Ti/Al ratio, magnetic susceptibility, and color index of the sediments. We suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca. 7.0 ka in the mid–low latitude desert belt and the SE Mediterranean region and continuous until the present. The long-term δ13C decrease shown by surface and bottom water foraminifera reflects a gradual change in the δ13C of the dissolved CO2 of the entire SE Mediterranean water column. This follows the global CO2 rise in the late Holocene as a result of the terrestrial biomass destruction during the aridification process. Moreover the gradual reduction of the vegetation cover in East Africa led to an increased erratic flood-related sediment flux via the Nile River up to the present. This is reflected by the general change in the local sediment composition. At 3.6 ka, the Saharan eolian input reached 65% whereas at about 0.3 ka 70% of the SE Mediterranean sediment was composed of Nile particulate matter.