Multi-technique monitoring of ocean tide loading in northern France

We have organised afield study of ocean tide loading in the northwestern part of France, where tidal amplitudes are known to be among the highest in the world. GPS and gravimetric techniques have already proved their capability to measure such weak and high-frequency signals. In this study, these classical observations are complemented with less usual techniques, such as tiltmeter and Satellite Laser Ranging (SLR) measurements. We present here the preliminary results for a common period of observations spanning from 12–19 May 2004. Additional measurements from the French Transportable Laser Ranging Station (FTLRS) were available during September and October 2004. Observation residuals are computed as the difference between the observed and the predicted time signals. We obtain small RMS residuals for GPS measurements (2.5/3.1/4.5 mm for the eastward, northward and upward components), for absolute and relative gravimetry (9 nm/s² and 13 nm/s²) and for tiltmeters (0.05 μrad for EW component). We also fit the amplitude of the main M2 tidal constituent to FTLRS observations and we find a value of 3.731 cm, which is comparable to the theoretical value.     

Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.     

Ostracods and palaeobotany from the middle Permian of Oman: implications on Pangaea reconstruction

Discovery of a middle Permian ostracod fauna in the marine Khuff Formation (Sultanate of Oman), combined with palaeobotanical data from the immediately underlying continental Gharif Formation, supports new interpretations of the palaeobiogeography of the Tethys during the late Palaeozoic. A mixed ostracod fauna existed on the Arabian platform. This new record of Permian ostracods, combined with recent data obtained in other Tethyan areas, emphasizes the close relationship between the south-western Tethys realm and South China. The macro- and microfloral assemblages of the continental Gharif Formation demonstrate that this palaeoflora represents a true mixed association in which Gondwanan, Cathaysian and Euramerian elements are intermingled. Two main models exist for the reconstruction of Pangaea during the late Palaeozoic. Both ostracods and palaeobotanical evidence favour the reduction of the oceanic area between South China and Arabian plate as in the B Pangaea model favoured by recent palaeomagnetic data.     

Accumulation of organochlorines and brominated flame retardants in estuarine and marine food chains: field measurements and model calculations

Food chain accumulation of organochlorines and brominated flame retardants in estuarine and marine environments is compared to model estimations and fresh water field data. The food chain consists of herbivores, detritivores and primary and secondary carnivores i.e. fish, fish-eating birds and marine mammals. Accumulation of polychlorinated biphenyls is predicted well by OMEGA for herbi-detritivores and primary and secondary carnivorous fish. Ratios are similar to those found for fresh water species. Accumulation ratios for fish-eating birds and mammals are overestimated by the model, which is attributed partly to biotransformation of meta-para unsubstituted congeners. Additionally, birds may feed in other less polluted areas. For brominated diphenylethers (BDE) accumulation patterns are highly species and congener specific. Accumulation depends on both K(ow) and metabolization capacities. BDE47 is the predominant congener in lower trophic levels. For marine birds and mammals accumulation ratios of BDE99 and 100 are similar to or higher than ratios of persistent PCBs.     

Pollution au plomb dans la Savoie antique (II–IIIe s. apr. J.-C.) en relation avec une installation métallurgique de la cité de Vienne

In Lake Anterne (NW French Alps), the Roman period is characterised by a lead contamination more important than that of the 1970s, due to the use of leaded gasoline. The maximum of this contamination period has been varve-dated 220 AD, i.e., during the optimum of Roman civilization in the Alps. Crossing palaeoenvironmental and archaeological evidences points out the economic importance of the town of Passy for the City of Vienne and yields a new example of lead contamination due to local metallurgical activity rather than distant impact of the exploitation of the Spanish Rio Tinto mine. To cite this article: F. Arnaud et al., C. R. Geoscience 338 (2005).     

Monthly trends and the corresponding altitudinal shift in the snowfall/precipitation day ratio

A better understanding of the impact of changing temperatures on snow amounts is very important for the ski industry, but it is difficult to measure, particularly at different times of the snow season and not only on an annual or seasonal basis. Here, we analyze the snow day vs precipitation day ratios on a monthly basis from November to April in Switzerland and at 52 meteorological stations located between 200 and 2,700 m above sea level over a 48-year time span. Our results show that the conditions measured in the 1960s in November and March correspond to the present ones in December, January, and February.     

A geophysical transect of the Adélie Margin,East Antarctica

In 1982, a geophysical survey of the Antarctic margin, including multichannel seismic, gravity, magnetic and bathymetric surveying, was carried out off Adélie Coast-Wilkes Land and in the eastern Ross Sea. Of the 5000 km of lines recorded, 3000 km were in the Adélie Coast area. Lines ATC 101–102, approximately following meridian 138°E, show the first complete transect of the Adélie Coast margin from the Southeast Indian abyssal plain at DSDP Site 269 to the continental shelf. These lines reveal a thick sedimentary series divided into three main acoustic units by two major unconformities considered to be Upper Eocene (42 Ma) and late Oligocene (25 Ma). Oceanic or continental basement can be traced under the whole area, and the ocean-continent boundary clearly lies beneath the lower continental slope. A deep, high-amplitude, low-frequency horizon, extending under the oceanic basement for over 300 km of line, is considered to be the Moho. Our interpretation supports a recent revision be Cande and Mutter proposing an early Upper Cretaceous opening between Australia and East Antarctica.     

New high-pressure and high-temperature metal/silicate partitioning of U and Pb: Implications for the cores of the Earth and Mars

In order to quantify possible fractionation of U and Pb into a metallic core, we have performed piston cylinder and multi-anvil press experiments at high pressure (up to 20 GPa) and high temperature (up to 2400 °C) and obtained the distribution coefficient D_{metal-silicate} and the exchange partition coefficient K_{metal-silicate} for these elements between metal and silicates (mineral or liquid). and depend strongly on the S content of the metallic phase, and also on the oxygen fugacity, in agreement with an effective valence state of 4 for U in silicates and 2 for Pb in silicates. and show no discernable pressure and temperature trend. U remains lithophile even at high pressure and high temperature but its lithophile nature decreases at very low oxygen fugacity. From our experimental data, it was possible to calculate the U and Pb contents of the cores of Mars and Earth under core-mantle equilibrium conditions at high pressure and high temperature. From the D_{metal-silicate} of the present study, we obtained that: 0.008 ppm < Pb_{in the core} <4.4 ppm, and 0.0003 ppb < U_{in the core} < 0.63 ppb, depending on whether the metal is S-free or S-saturated respectively, and if the mantle was molten or solid during the segregation process of the Earth’s core around ΔIW-2. For Mars, based on a core segregation process around ΔIW-1, we obtained that: 0.005 ppm < Pb_{in the core} < 3 ppm, and 0.00002 ppb < U_{in the core} < 0.05 ppb, depending on the metallic composition: S-free or S-saturated respectively.Our results suggest that the low concentration of Pb in the terrestrial mantle could not be explained by an early Pb sequestration in the Earth’s core even if S is the dominant light element of the core. If we assume a magma ocean scenario, U might produced a maximum value of 1.5% of the total heat budget of the core with a segregation occurring below ΔIW-3. The values found in the present study for U in the Martian core suggest that the magnetic field activity of Mars before ∼0.5 b.y. after its formation would be difficult to ascribe to the decay of U alone.