Solar abundances of lithium,beryllium and boron

New solar abundances have been derived for Li, Be and B. They are mainly based on high-resolution spectra obtained at the Jungfraujoch Scientific Station (Switzerland). For Li, the abundance results from a discussion of the photospheric and sunspot spectra. Our results, log N _Li = 0.42, log N _Be = 1.17 and log N _B < 2.80 (in the log N _H = 12.00 scale), are lower than the previously admitted abundances for these elements. The far UV spectrum ( < 3000 Å) has also been considered in each case. The meaning of our results is discussed from the point of view of the destruction of these elements during the evolution of the sun.This work has been sponsored in part by the Air Force Cambridge Research Laboratories, OAR, through the European Office of Aerospace Research, U.S.A.F., under Contract AF 61 (052)-955, and by the Comité National Belge de la Coopération Géophysique Internationale (C.N.B.C.G.I.).     

Abundances of heavy elements in the sun

Solar abundances have been derived for Pb, Bi, Th and U. For the three first elements, the abundances are determined from the profiles of their lines obtained with the high resolution solar spectrometer installed at the Jungfraujoch Scientific Station (Switzerland) and from new oscillator strengths based on life-time measurements (Pb and Bi). The possible presence of U in the solar spectrum is also examined.Our results are (in the log N _H = 12.00 scale): logN _Pb = 1.83, logN _Bi 0.80, logN _Th = 0.82, and logN _U 0.60.The meaning of these new solar abundances is discussed from the point of view of the nucleosynthesis theories.This work has been sponsored in part by the Air Force Cambridge Research Laboratories, OAR, through the European Office of Aerospace Research, U.S.A.F., under Contract AF 61 (052)-955 and by the Comité National Belge de la Coopération Géophysique Internationale (C.N.B.C.G.I.).     

The Moho transition zone in the Oman ophiolite-relation with wehrlites in the crust and dunites in the mantle

Field data in the Oman ophiolite show that the Moho transition zone (MTZ), which is on average 300 m thick above mantle diapirs, reduces to 50 m away from diapirs, with a sharp transition at the outskirts of the diapirs. We show here that this reduction is dominantly due to compaction of a dunitic mush present above diapirs in the MTZ, with upward injection of a wehrlitic magma in the crust, and, to a lesser extent, due to tectonic stretching. In order to explain the fraction of wehrlites injected into the crust, which is in the range of 25%, it is necessary that mantle upwelling is active, with a mantle flow velocity away from diapirs several times faster than the spreading velocity. If this velocity exceeds 5 times the ridge spreading-rate, a significant part of the MTZ may be entrained down into the mantle, flowing away from the diapir as tabular dunites.     

Inside the magma chamber of a dying ridge segment in the Oman ophiolite

For the first time, the crystallized remnant of an oceanic ridge magma chamber is documented in the Oman ophiolite. It exists in the centre of a 40 km long monoclinal ridge (Jebel Dihm, Wadi Tayin massif), exposing a full crustal section perpendicular to the spreading direction. New detailed mapping supported by U‐Pb zircon geochronology suggests that the active, fast‐spreading ridge that died just prior to detachment of the ophiolite is preserved and largely intact. Our observations provide insights into the crystallizing mush zone of a magma chamber, before it crosses the external walls and solidifies as deformed gabbros. Our data provide new constraints on the shape and internal dynamics of a magma chamber, including gabbro subsidence from the floor of a perched melt lens and the limited contribution of sills to crustal accretion. By locating precisely the palaeo‐ridge axis, prior full spreading rate estimates can be increased to ~140 km Ma^?1.     

Seasonal variability of primary production in a fjord ecosystem of the Chilean Patagonia: Implications for the transfer of carbon within pelagic food webs

We characterized the seasonal cycle of productivity in Reloncaví Fjord (41°30′S), Chilean Patagonia. Seasonal surveys that included measurements of gross primary production, community respiration, bacterioplankton secondary production, and sedimentation rates along the fjord were combined with continuous records of water-column temperature variability and wind forcing, as well as satellite-derived data on regional patterns of wind stress, sea surface temperatures, and surface chlorophyll concentrations. The hydrography and perhaps fjord productivity respond to the timing and intensity of wind forcing over a larger region. Seasonal changes in the direction and intensity of winds, along with a late-winter improvement in light conditions, may determine the timing of phytoplankton blooms and potentially modulate productivity cycles in the region.Depth-integrated gross primary production estimates were higher (0.4–3.8 g C m^?2 d^?1) in the productive season (October, February, and May), and lower (0.1–0.2 g C m^?2 d^?1) in the non-productive season (August). These seasonal changes were also reflected in community respiration and bacterioplankton production rates, which ranged, respectively, from 0.3 to 4.8 g C m^?2 d^?1 and 0.05 to 0.4 g C m^?2 d^?1 during the productive and non-productive seasons and from 0.05 to 0.6 g C m^?2 d^?1 and 0.05 to 0.2 g C m^?2 d^?1 during the same two periods. We found a strong, significant correlation between gross primary production and community respiration (Spearman, r=0.95; p<0.001; n=12), which suggests a high degree of coupling between the synthesis of organic matter and its usage by the planktonic community. Similarly, strong correlations were found between bacterioplankton secondary production and both gross primary production (Spearman, r=0.7, p<0.05, n=9) and community respiration (Spearman, r=0.8, p<0.05, n=9), indicating that bacterioplankton may be processing an important fraction (8–59%) of the organic matter produced by phytoplankton in Reloncaví Fjord. In winter, bacterial carbon utilization as a percentage of gross primary production was >100%, suggesting the use of allochthonous carbon sources by bacterioplankton when the levels of gross primary production are low. Low primary production rates were associated with a greater contribution of small cells to autotrophic biomass, highlighting the importance of small-sized plankton and bacteria for carbon cycling and fluxes during the less productive winter months. Fecal pellet sedimentation was minimal during this period, also suggesting that most of the locally produced organic carbon is recycled within the microbial loop. During the productive season, on the other hand, the area exhibited a great potential to export organic matter, be it to higher trophic levels or vertically towards the bottom.