Simultaneous measurements of the polarization in Hα and D3 prominence emissions

Simultaneous observations of the polarization of radiations H and D₃ have been performed in 1979 at Pic du Midi on 60 solar prominences (300 pairs of measurements). For the essential part of the sample, the degree of polarization p(D₃) does not depend strongly upon the intensity E(D₃); on the contrary p(H) decreases steeply when E(H) goes beyond the brightness which corresponds to (H) = 1 (Figure 4); the deviation of the polarization direction (H) does not show such a strong dependance upon E(H) (Figure 6). A crude estimate of the possible role of multiple scattering in an optically thick prominence is in general agreement with observational data but a detailed comparison will be possible only when a complete theory of the Hanle effect in non optically thin layers will be available.Therefore, H polarization measurements are presently useful mainly when (H) < 1 and, in connexion with D₃ measurements (Figure 8), they should make possible to determine the three components of the prominence magnetic vector. Prospects are given for the observation of other lines (H; 10 830 Å) which do not suffer heavy self-absorption effects and would be well-suited to this type of study.     

Biokinetics of selected heavy metals and radionuclides in two marine macrophytes: the seagrass Posidonia oceanica and the alga Caulerpa taxifolia

Uptake and loss kinetics of Zn, Ag, Cd, ¹³⁴Cs, and ²⁴¹Am by shoots of the seagrass Posidonia oceanica and fronds of the green alga Caulerpa taxifolia were determined in controlled laboratory radiotracer experiments using low contaminant concentrations. The two species accumulated most of the elements efficiently. The only exceptions were ¹³⁴Cs in both P. oceanica and C. taxifolia and Cd in C. Taxifolia (concentration factors 6.4). Steady state in uptake was reached in C. taxifolia for each element except Ag. In P. oceanica, steady state was noted for the uptake of Ag and ¹³⁴Cs whereas Zn, Cd, and ²⁴¹Am were linearly accumulated during the course of the experiment (15 d). With respect to relative metal bioavailability, the different compartments of P. oceanica shoots were generally ranked in the order: leaf epiphytes > adult LEAVES = intermediate leaves > leaf sheaths. The long-lived component of the loss kinetics for each element in P. oceanica was characterized by a relatively short biological half-life (T_b1/2 28 d). However, observations for the individual compartments indicated that adult leaves had a high retention capacity for Ag and ¹³⁴Cs, with virtually 100% retained after 21 d in uncontaminated sea water. In C. taxifolia, the long-lived component of the loss kinetics for each element was characterized by a T_b1/2 value that was not significantly different from infinity, an observation which suggests that a substantial fraction of the metal or radionuclide incorporated during a contamination event would be irreversibly bound by this algal species.     

Residues of C-4n-nonylphenol in mosquitofish (Gambusia holbrooki) oocytes and embryos during dietary exposure of mature females to this xenohormone

In order to assess in fish the maternal transfer of alkylphenolic compounds to the progeny, the identification and quantification of the labelled compounds present in oocytes and embryos was conducted after dietary exposure of mature female mosquitofish to ¹⁴C-4n-nonylphenol during vitellogenesis and embryogenesis respectively. Radioactivity found in bile and liver extracts accounted for 0.9–0.6 and 0.2–0.1% of ingested radioactivity for females exposed during vitellogenesis and embryogenesis respectively. The amount of extractable radioactivity present in oocytes and embryos was 0.19 and 0.07% of the ingested dose respectively. The radio-HPLC profiles obtained from bile, liver, oocyte and embryo extracts were similar. They showed the presence of 4n-NP-glucuronide as the major metabolite and traces of unchanged 4n-NP. The other metabolites corresponded to 8-hydroxynonylphenol, 9-(4-hydroxyphenyl)-nonanoic acid and para-hydroxybenzoic acid which is the final product of the alkyl chain oxidation. Our results indicate that exposure of ovoviviparous female fish to 4-NP during vitellogenesis and embryogenesis leads to the contamination of the progeny by 4-NP and its metabolites.     

Ra/226Ra activity ratio in oceanic settling particles: implications regarding the use of barium as a proxy for paleoproductivity reconstruction

Activities of the natural radionuclides ²²⁶Ra (T1/2 =1602 years) and 22sRa (T1/2 =5.75 years) in particulate matter are reported from sediment traps deployed in the tropical northeast Atlantic. ²²⁸Ra/²²⁶Ra activity ratios in settling particles are compared to those found in the water column in order to specify the origin of radium incorporated in particulate matter, and consequently that of barium, since the two elements are known to display close geochemical behaviours in the oceans. Whereas ²²⁸Ra/²²⁶Ra activity ratios in the water column display very large variations with depth, they remain nearly constant in particles, with values close to those found in the upper 250 m. These results clearly demonstrate that particles acquire their radium and, by inference, their barium, in the upper water column and that there is very little exchange with the dissolved phase as they settle to the bottom.     

Land-sea correlations for the last glaciation inferred from a pollen and dinocyst record from the portuguese margin

Pollen and dinoflagellate cyst assemblages from Core SU 81-18 recovered off Portugal (37°46′N, 10°11′W; 3135-m water depth) have been used to document the short-term environmental changes that occurred in southwest Europe since 25,000 yr B.P. The relationship between the oceanic and continental environments has been further examined by the use of other marine proxies (coarse sedimentary fraction, foraminifera) and by comparison with proximal land pollen records. Heinrich 2 (H2) and Heinrich 1 (H1) events were the most extreme parts of the highly variable last glacial period, with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site. Our study shows that H1 and H2 are divided in two distinct phases: one with Neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris, reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site; the other with dinoflagellate cysts of subpolar affinity, Bitectatodinium tepikiense, reflecting a seasonal control marked by warm summer SST and cold winter SST.     

Late Ordovician glaciation in southern Turkey

ABSTRACT We present a new survey of several Palaeozoic sections in both the Taurus range and the Border Folds that documents typical glacial features including a glacial pavement and striated dropstones (Halevikdere Formation) and demonstrates the former presence of an ice sheet in southern and south-eastern Turkey. Evidence for the late Ashgill (Hirnantian) age of this episode is provided by macro- and microfossils found within the glacial formation. The extension of ice-related deposits into the northernmost part of the Arabian Platform (Mardin region) implies a much wider distribution of the Ordovician ice sheet than was previously believed, and strongly suggests that southern Turkey lay close to Egypt during the Lower Palaeozoic.     

Comportement de l'oscillateur DORIS/Jason au passage de l'anomalie sud-atlantique

We point out an acceleration of the DORIS clock on-board the Jason satellite during passes over the South Atlantic Anomaly (SAA). When this effect is ignored in the current geodetic positioning of the DORIS stations, derived coordinates show almost linear trends in time, corresponding to anomalous horizontal and vertical velocities of the order of 1 m yr^?1. We propose a simple scientific explanation of this physical phenomenon that is corroborated by direct Jason/TOPEX clock comparisons with respect to the DORIS master beacons in Kourou and Toulouse. To cite this article: P. Willis et al., C. R. Geoscience 336 (2004).