Particulate barium fluxes and export production in the northwestern Mediterranean

Biogenic barium, mostly in the barite (BaSO₄) form, has been proposed as a tracer for export production in the ocean. Here we report on biogenic barium (Ba_xs) and particulate organic carbon (POC) fluxes from sediment traps deployed at the DYFAMED site in the Northwestern Mediterranean Sea. Ba_xs fluxes display average values of 37 ± 45 and 50 ± 58 μg/m²/d at 200 and 1000 m respectively, and are linearly correlated to POC fluxes (mean values of 7.9 ± 9.3 and 6.8 ± 6.8 mg C/m²/d at 200 and 1000 m). Export production estimates, calculated using published Ba_xs- or POC-based algorithms, all fall below or close to the lower limit of potential export values proposed in the literature. This work clearly demonstrates the usefulness of Ba_xs as a tracer of oceanic export production in the Northwestern Mediterranean Sea. However, development of a quantitative export production proxy requires a clear understanding of the underlying cause(s) for the observed spatial variations in the relationship between Ba_xs and POC fluxes. The present study confirms that the processes leading to barite formation differ between margin and open-ocean sites and probably account for much of the regional variability in the POC/Ba_xs ratio.     

Evidence from the Northeastern Atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation

A first study from the subtropical western Atlantic, using ²³¹Pa/²³⁰Th ratios as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of Meridional Overturning Circulation (MOC) over the last deglaciation. However, these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary ²³¹Pa/²³⁰Th ratio in terms of circulation vigor can be biased by variations in particle flux and composition. We have measured ²³¹Pa/²³⁰Th in a core from the Iberian margin, in the Northeastern Atlantic basin, and have compared these new results to the data from the western Atlantic basin. We find that the reduction in the circulation during H1 and YD and the subsequent increases first recognized in the sediment deposited on Bermuda Rise are also evident in the eastern basin, in a totally different sedimentary regime, confirming that sedimentary ²³¹Pa/²³⁰Th ratios record basin-wide changes in deep water circulation. However, some differences between the eastern and western records are also recognized, providing preliminary evidence to differentiate between renewal rates in the two North Atlantic basins and between shallower and deeper overturning. Our results suggest the possible existence of two sources of Glacial North Atlantic Intermediate Deep Water (GNAIW), one in the south Labrador Sea and another west of Rockall Plateau. Both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the Laurentide and the Fennoscandian ice sheets during the deglaciation. These results indicate that additional information on the geometry and strength of the ventilation of the deep Atlantic can be obtained by contrasting the evolution of sediment ²³¹Pa/²³⁰Th in different sections of the Atlantic Ocean.     

A Compilation of Silicon,Rare Earth Element and Twenty‐One other Trace Element Concentrations in the Natural River Water Reference Material SLRS‐5 (NRC‐CNRC)

The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given.     

A field comparison of two methods for the determination of copper complexation: Bacterial bioassay and fixed-potential amperometry

Complexation of copper added to seawater was determined by bacterial bioassay and fixedpotential amperometry. Consistent results were obtained by these two fundamentally different methods. The results of this study support the validity of both techniques and the field applicability of fixed-potential amperometry.The intercomparison studies were performed on samples collected at the N.Y.C. sewage sludge dumpsite and in relatively unpolluted coastal waters. In this limited study, the calculated free cupric ion concentrations at ambient total copper concentrations were similar at both sites.     

An experimental study on the shallow-level migmatization of ferrogabbros from the Fuerteventura Basal Complex, Canary Islands

Spectacular shallow-level migmatization of ferrogabbroic rocks occurs in a metamorphic contact aureole of a gabbroic pluton of the Tierra Mala massif (TM) on Fuerteventura (Canary Islands). In order to improve our knowledge of the low pressure melting behavior of gabbroic rocks and to constrain the conditions of migmatization of the TM gabbros, we performed partial melting experiments on a natural ferrogabbro, which is assumed as protolith of the migmatites. The experiments were performed in an internally heated pressure vessel (IHPV) at 200 MPa, 930–1150 °C at relatively oxidizing conditions. Distinct amounts of water were added to the charge.

From 930 to 1000 °C, the observed experimental phases are plagioclase (An_60–70), clinopyroxene, amphibole (titanian magnesiohastingsites), two Fe–Ti oxides, and a basaltic, K-poor melt. Above 1000 °C, amphibole is no longer stable. The first melts are very rich in normative plagioclase (>70 wt.%). This indicates that at the beginning of partial melting plagioclase is the major phase which is consumed to produce melt. In the experiments, plagioclase is stable up to high temperatures (1060 °C) showing increasing An content with temperature. This is not compatible with the natural migmatites, in which An-rich plagioclase is absent in the melanosomes, while amphibole is stable. Our results show that the partial melting of the natural rocks cannot be regarded as an “in-situ” process that occurred in a closed system. Considerable amounts of alkalis probably transported by water-rich fluids, derived from the mafic pluton underplating the TM gabbro, were necessary to drive the melting reaction out of the stability range of plagioclase. A partial melting experiment with a migmatite gabbro showing typical “in-situ” textures as starting material supports this assumption.

Crystallization experiments performed at 1000 °C on a glass of the fused ferrogabbro with different water contents added to the charge show that generally high water activities could be achieved (crystallization of amphibole), independently of the bulk water content, even in a system with very low initial bulk water content (0.3 wt.%). Increasing water contents produce plagioclase richer in An, reduces the modal proportion of plagioclase in the crystallizing assemblage and extends the melt fraction. High melt fractions of >30 wt.% could only be observed in systems with high bulk water contents (>2 wt.%). This indicates that the migmatites were generated under water-rich conditions (probably water-saturated), since those migmatites, which are characterized as “in-situ” formations, show generally high amounts of leucosomes (>30 wt.%).     

小型激光天文动力学空间计划概念

小型激光天文动力学空间计划是 :使用在太阳轨道上无拖曳航天器和地面站以激光干涉和脉冲测距的方法 ,精确地探讨天文动力学 ,检测相对论与时空基本定律 ,改进探测引力波的灵敏度以及更准确地测定太阳、行星和小行星的参数。 1 969年开始的月球激光 (反射 )测距 ,对地球物理、参考坐标的选定、相对论的检验均有重要的贡献。 3 0年来 ,激光技术的长足进步 ,使现在正是适合于开始进行研究空间有源 (主动 )测距和光波空间通讯的时候。激光天文动力学的兴起是必然的趋势 ,其精确度将比现在提高 3到 6个数量级 ,将是天文动力学革命性的发展。小型激光天文动力学空间计划可以起到带头作用。它的关键技术有三 ,即 :弱光锁相、极精确无拖曳航天和高衰减日冕仪。弱光锁相已有长足的进步。对高衰减日冕仪的研究 ,也有了初步的方案。LISA空间计划将于 2 0 0 6年 8月发射SMART -2 ,研究测试极精确无拖曳航天。小型激光天文动力学空间计划的关键技术已日趋成熟。在第一届国际激光天文动力学研讨会 ( 2 0 0 1 ,9.1 3 -2 3 )中介绍了各相关学科背景及前沿研究 ,讨论了激光天文动力学空间计划科学目标及相关技术 ,并召开了两次小型激光天文动力学空间计划预研究筹备会 ,建立了和欧洲的合作关系。会后着手进行此项对基础     

Radiation pressure and dust particle dynamics

The dynamics of small dust grains orbiting a planet are investigated when solar radiation pressure forces are added to the planet's gravitational central field. In the first part a set of differential equations is derived in a reference frame linked to the solar motion. The complete solution of these equations is given for particles lying in the planet's orbital plane, and we show that the orbital eccentricity may undergo considerable variation. At the same time the pericenter longitude librates or circulates according to initial conditions. With this result we establish a criterion for any orbiting particle (because of its highly eccentric orbit) to collide with its planet's atmosphere. The case of inclined orbit is studied through a numerical integration and allows us to draw conclusions related to the stability of the orbital plane. All solutions are periodic, with the period being independent of the initial conditions. This last point permits us to investigate the different time scales involved in that problem. Finally, the Poynting-Robertson drag is included, along with the radial radiation pressure forces, and the secular trend is considered. A coupling effect between the two components is ascertained, yielding a systematic behavior in the eccentricity and thus in the pericenter distance. Our solutions generalize the results of S. J. Peale (1966, J. Geophys. Res.71, 911–933) and J. A. Burns, P. Lamy, and S. Soter (1979, Icarus40, 1–48) by allowing eccentricities to be large (of order 1) and inclinations to be nonzero and by considering Poynting-Robertson drag.     

Annual survey of water vapor behavior from the OMEGA mapping spectrometer onboard Mars Express

We present here the annual behavior of atmospheric water vapor on Mars, as observed by the OMEGA spectrometer on board Mars Express during its first martian year. We consider all the different features of the cycle of water vapor: temporal evolution, both at a seasonal and at a diurnal scale; longitudinal distribution; and the vertical profile, through the variations in the saturation height. We put our results into the context of the current knowledge on the water cycle through a systematic comparison with the already published datasets. The seasonal behavior is in very good agreement with past and simultaneous retrievals both qualitatively and quantitatively, within the uncertainties. The average water vapor abundance during the year is ∼10 pr. μm, with an imbalance between northern and southern hemisphere, in favor of the first. The maximum of activity, up to 60 pr. μm, occurs at high northern latitudes during local summer and shows the dominance of the northern polar cap within the driving processes of the water cycle. A corresponding maximum at southern polar latitudes during the local summer is present, but less structured and intense. It reaches ∼25 pr. μm at its peak. Global circulation has some influence in shaping the water cycle, but it is less prominent than the results from previous instruments suggest. No significant correlation between water vapor column density and local hour is detected. We can constrain the amount of water vapor exchanged between the surface and the atmosphere to few pr. μm. This is consistent with recent results by OMEGA and PFS-LW. The action of the regolith layer on the global water cycle seems to be minor, but it cannot be precisely constrained. The distribution of water vapor on the planet, after removing the topography, shows the already known two-maxima system, over Tharsis and Arabia Terra. However, the Arabia Terra increase is quite fragmented compared with previous observations. A deep zone of minimum separates the two regions. The saturation height of water vapor is mainly governed by the variations of insolation during the year. It is confined within 5-15 km from the surface at aphelion, while in the perihelion season it stretches up to 55 km of altitude.