The oxygen isotope composition of human phosphatic tissues (delta18OP) has great potential for reconstructing climate and population migration, but this technique has not been applied to early human evolution. To facilitate this application we analyzed delta18OP values of modern human teeth collected at 12 sites located at latitudes ranging from 4 degrees N to 70 degrees N together with the corresponding oxygen composition of tap waters (delta18OW) from these areas. In addition, the delta18O of some raw and boiled foods were determined and simple mass balance calculations were performed to investigate the impact of solid food consumption on the oxygen isotope composition of the total ingested water (drinking water+solid food water). The results, along with those from three, smaller published data sets, can be considered as random estimates of a unique delta18OW/delta18OP linear relationship: delta18OW=1.54(+/-0.09)xdelta18OP-33.72(+/-1.51)(R2=0.87: p [H0:R2=0]=2x10(-19)). The delta18O of cooked food is higher than that of the drinking water. As a consequence, in a modern diet the delta18O of ingested water is +1.05 to 1.2 per thousand higher than that of drinking water in the area. In meat-dominated and cereal-free diets, which may have been the diets of some of our early ancestors, the shift is a little higher and the application of the regression equation would slightly overestimate delta18OW in these cases.

International audienceThe Early Toarcian Oceanic Anoxic Event (T-OAE), about 183 myr ago, was a global event of environmental and carbon cycle perturbations, which deeply affected both marine biota and carbonate production. Nevertheless, the long-term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood. Here we present a similar to 8 myr-long record of Early Pliensbachian-Middle Toarcian environmental changes from the Lusitanian Basin, Portugal, in order to address the long-term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the T-OAE. Paleotemperature estimates derived from the oxygen isotope compositions of well-reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees C cooling in the Late Pliensbachian (margaritatus-spinatum ammonite Zones boundary). This cooling event is followed by a marked similar to 7-10 degrees C seawater warming in the Early Toarcian that, after a second cooling event in the mid-polymorphum Zone, culminates during the T-OAE. Calcium carbonate (CaCO3) contents, the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer Schizosphaerella, all largely covary with paleotemperatures, indicating a coupling between climatic conditions and both pelagic and neritic CaCO3 production. Furthermore, the cooling and warming episodes coincided with major marine regressions and transgressions, respectively, suggesting that the growth and decay of ice caps may have exerted a strong control on sea-level fluctuations throughout the studied time interval. This revised chronology of environmental changes shows important similarities with Neogene and Paleozoic episodes of deglacial black shale formation, and thus prompts the reevaluation of ice sheet dynamics as a possible agent of Mesozoic events of extinction and organic-rich sedimentation. (C) 2010 Elsevier B.V. All rights reserved

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What the body temperature and thermoregulation processes of extinct vertebrates were are central questions for understanding their ecology and evolution. The thermophysiologic status of the great marine reptiles is still unknown, even though some studies have suggested that thermoregulation may have contributed to their exceptional evolutionary success as apex predators of Mesozoic aquatic ecosystems. We tested the thermal status of ichthyosaurs, plesiosaurs, and mosasaurs by comparing the oxygen isotope compositions of their tooth phosphate to those of coexisting fish. Data distribution reveals that these large marine reptiles were able to maintain a constant and high body temperature in oceanic environments ranging from tropical to cold temperate. Their estimated body temperatures, in the range from 35 degrees +/- 2 degrees C to 39 degrees +/- 2 degrees C, suggest high metabolic rates required for predation and fast swimming over large distances offshore.

The effective stress law for the permeability of a limestone is studied experimentally by performing constant head permeability tests in a triaxial cell with different conditions of confining pressure and pore pressure. Test results have shown that a pore pressure increase and a confining pressure decrease both result in an increase of the permeability, and that the effect of the pore pressure change on the variation of the permeability is more important than the effect of a change of the confining pressure. A power law is proposed for the variation of the permeability with the effective stress. The permeability effective stress coefficient increases linearly with the differential pressure and is greater than one as soon the differential pressure exceeds few bars. The test results are well reproduced using the proposed permeability-effective stress law. A conceptual pore-shell model based on a detailed observation of the microstructure of the studied limestone is proposed. This model is able to explain the experimental observations on the effect of the total stress and of the pore pressure on the permeability of the limestone. Effective stress coefficients for the stress-dependent permeability which are greater than one are obtained. It is shown that the controlling factor is the ratio of the different bulk moduli of the various constituents of the rock. This ratio is studied experimentally by performing microhardness tests.Comment: International Journal of Rock Mechanics and Mining Sciences (2008) In pres

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High precision oxygen isotope analyses were made of phosphate extracted from 17 samples of nektonic and benthic fish debris sampled across the stratigraphic Cretaceous-Tertiary boundary in northern Morocco. A refinement of the silver phosphate method was used to isolate phosphate from biogenic materials. Measured ~180 values of 18.6-20.5%o are interpreted as reflecting high-resolution thermal variations that affected the ocean water column of the western Tethys. The warm (27°C) water masses that characterized Maastrichtian times underwent rapid cooling and stabilized at an average temperature of 19°C during the Dano-Montian and Thanetian. This period of constant and cool temperature was followed by a relatively rapid but more gradual warming to about 25°C achieved in the Middle Ypresian. Significant small shifts in 6180 values between nektonic and benthic fauna recorded only during the stages of rapid warming or cooling may correspond to averaged thermal differences within the water column that developed in response to global climatic changes. The indicated temperature distribution could have been caused by thermal changes in the atmosphere rather than some signal carried by deep ocean currents. The oxygen isotope data coupled with previous measurements of REE and eNd~TI on the same samples support the suggestion that paleo-Pacific westward currents progressed as far as the northwestern part of the African platform at the end of the Cretaceous period.

We have used a high-precision, easy, low-cost and rapid method of oxygen isotope analysis applied to various O-bearing matrices, organic and inorganic (sulfates, nitrates and phosphates), whose (18)O/(16)O ratios had already been measured. It was first successfully applied to (18)O analyses of natural and synthetic phosphate samples. The technique uses high-temperature elemental analysis-pyrolysis (EA-pyrolysis) interfaced in continuous-flow mode to an isotope ratio mass spectrometry (IRMS) system. Using the same pyrolysis method we have been able to generate a single calibration curve for all those samples showing pyrolysis efficiencies independent of the type of matrix pyrolysed. We have also investigated this matrix-dependent pyrolysis issue using a newly developed pyrolysis technique involving 'purge-and-trap' chromatography. As previously stated, silver phosphate being a very stable material, weakly hygroscopic and easily synthesized with predictable (18)O/(16)O values, could be considered as a good candidate to become a reference material for the determination of (18)O/(16)O ratios by EA-pyrolysis-IRMS.