An Experimental Study of Trace Element Fluxes from Subducted Oceanic Crust

We have determined experimentally the hydrous phase relations and trace element partitioning behaviour of ocean floor basalt protoliths at pressures and temperatures (3 GPa, 750-1000°C) relevant to melting in subduction zones. To avoid potential complexities associated with trace element doping of starting materials we have used natural, pristine mid-ocean ridge basalt (MORB from Kolbeinsey Ridge) and altered oceanic crust (AOC from Deep Sea Drilling Project leg 46, ∼20°N Atlantic). Approximately 15 wt % water was added to starting materials to simulate fluid fluxing from dehydrating serpentinite underlying the oceanic crust. The vapour-saturated solidus is sensitive to basalt K2O content, decreasing from 825 ± 25°C in MORB (∼0·04 wt % K2O) to ≈750°C in AOC (∼0·25 wt % K2O). Textural evidence indicates that near-solidus fluids are sub-critical in nature. The residual solid assemblage in both MORB and AOC experiments is dominated by garnet and clinopyroxene, with accessory kyanite, epidote, Fe-Ti oxide and rutile (plus quartz-coesite, phengite and apatite below the solidus). Trace element analyses of quenched silica-rich melts show a strong temperature dependence of key trace elements. In contrast to the trace element-doped starting materials of previous studies, we do not observe residual allanite. Instead, abundant residual epidote provides the host for thorium and light rare earth elements (LREE), preventing LREE from being released (ΣLREE 1500 and La/SmPUM (where PUM indicates primitive upper mantle) ∼1, most closely matching the geochemical signal of arc lavas worldwide, were generated from AOC at 800-850°

Predominance of exotic and introduced species among sturgeons captured from the Baltic and North Seas and their watersheds, 1981-1999

Sturgeon catches (n = 256) from 1981-1999 reported mainly by commercial fishermen and anglers in German, Polish, and Dutch coastal waters and tributaries were analysed. During the study period, 20 % of catches were reported from coastal waters and 65 % from rivers and estuaries of large river systems, including the Odra, Elbe, Rhine and Weser. The data indicate that, from 1981- 1993, there was a major decline in the Atlantic sturgeon Acipenser sturio L., 1758, and an increase in the total catches of non-indigenous sturgeon species. The Siberian sturgeon Acipenser baerii Brandt, 1869, the Russian sturgeon Acipenser gueldenstaedtii Brandt & Ratzeberg, 1833, and various hybrids dominated. Occasional catches of the white sturgeon Acipenser transmontanus Richardson, 1836 and the sterlet Acipenser ruthenus L., 1758 were also reported. During the study period, significant changes in species composition and distribution of catches were observed. The predominance of non-indigenous sturgeon species is a result of the increasingly intensive sturgeon aquaculture activities in Germany, Poland, and the Netherlands. The most frequently reared species now dominate the catches. In addition to these escapees from fish farms, several intentional releases of sturgeons were reported. The results show that introduced exotic sturgeon species may thrive under certain natural conditions. Therefore, they may interfere with restoration efforts for the native A. sturio, competing for habitat and introducing diseases and hybridization.Se analizaron las capturas de esturiones (n = 256) entre 1981 y 1999 proporcionadas principalmente por pescadores profesionales y deportivos en las costas alemanas, polacas y holandesas, y en los sistemas fluviales que desembocan en ellas. En el periodo de estudio, el 20 % de las capturas correspondió a aguas litorales y el 65 % a ríos y estuarios de los grandes sistemas fluviales, incluidos los ríos Oder, Elba, Rin y Weser. Los datos indican que entre 1981 y 1993 tuvo lugar el mayor declive del esturión atlántico Acipenser sturio L., 1758 y un incremento en las capturas totales de las especies alóctonas de esturiones. Predominaron las capturas de esturión siberiano Acipenser baerii Brandt, 1869, esturión ruso Acipenser gueldenstaedtii Brandt & Ratzeberg, 1833 y varios híbridos. También se registraron capturas ocasionales de esturión blanco Acipenser transmontanus Richardson, 1836 y esterlete Acipenser ruthenus L., 1758. En el periodo de estudio se observaron cambios significativos en la composición de especies y en la distribución de las capturas. El predominio de las especies alóctonas de esturiones es el resultado de las crecientes actividades en la acuicultura intensiva de esturión en Alemania, Polonia y Países Bajos. Las especies cultivadas más frecuentemente dominan ahora las capturas. Además de estas fugas de las piscifactorías, se han registrado varias sueltas intencionadas. Los resultados muestran que las especies de esturiones exóticas introducidas pueden prosperar en ciertas condiciones naturales. Por esta razón, pueden interferir en los esfuerzos de restauración de la especie autóctona A. sturio, compitiendo por el hábitat e introduciendo enfermedades e hibridación.Instituto Español de Oceanografí

Comportamento de cultivares de algodoeiro herbáceo nas condições do Mato Grosso - safra 1999/2000.

bitstream/CNPA/21189/1/COMTEC141.pd

AN EXPERIMENTAL STUDY OF TRACE ELEMENT FLUXES FROM SUBDUCTED OCEANIC CRUST

ISSN:0022-3530ISSN:1460-241

Latin American platform comparative critical analysis. Learning from the KASSA platforms' reports.

1 CD-ROM. Projeto DG-Research - Contract nº GOCE-CT-2004-505582

The Protein Data Bank: Present status and future plans

The Protein Data Bank (PDB) archival database of dimensional structures of biological macromolecules, an international resource facility, contains information on protein, DNA, RNA, virus and carbohydrate structures. While the vast majority of PDB entries represent crystal structures, results from NMR and theoretical modeling strudies also are included. PDB, which in July 1992 contained 957 atomic coordinate entries, currently is experiencing a time of explosive growth. The present deposition rate is ca. 50 structures per month, doubling in less than two years. Responding to the challenge posed by this. rising data flow, over the past 18 months PDB has attracted increased funding to implement important enhancements of the resource. A rapid pre-release of entries pending for input was inaugurated in April 1992, and a substantial fraction of the accumulated backlog of pending entries is now available via FTP and e-mail in prerelease form. Extrapolation of current data rates suggests that by the year 2000 PDB may contain over 25,000 structures. PDB`s plans, to manage this voluminous amount of data, include the development of PDB-AUTHORIN software to allow depositors to do most of the preparation and validation of their own entries, and a comprehensive upgrade of PDB contents to add new data items and convert the current interchange format to the Crystallographic Information File (CIF) standard established by the International Union of Crystallography (IUCr)

Oxygen-sensing neurons reciprocally regulate peripheral lipid metabolism via neuropeptide signaling in <i>Caenorhabditis elegans</i>

<div><p>The mechanisms by which the sensory environment influences metabolic homeostasis remains poorly understood. In this report, we show that oxygen, a potent environmental signal, is an important regulator of whole body lipid metabolism. <i>C</i>. <i>elegans</i> oxygen-sensing neurons reciprocally regulate peripheral lipid metabolism under normoxia in the following way: under high oxygen and food absence, URX sensory neurons are activated, and stimulate fat loss in the intestine, the major metabolic organ for <i>C</i>. <i>elegans</i>. Under lower oxygen conditions or when food is present, the BAG sensory neurons respond by repressing the resting properties of the URX neurons. A genetic screen to identify modulators of this effect led to the identification of a BAG-neuron-specific neuropeptide called FLP-17, whose cognate receptor EGL-6 functions in URX neurons. Thus, BAG sensory neurons counterbalance the metabolic effect of tonically active URX neurons via neuropeptide communication. The combined regulatory actions of these neurons serve to precisely tune the rate and extent of fat loss to the availability of food and oxygen, and provides an interesting example of the myriad mechanisms underlying homeostatic control.</p></div

Dehydration of subducting slow-spread oceanic lithosphere in the Lesser Antilles

Subducting slabs carry water into the mantle and are a major gateway in the global geochemical water cycle. Fluid transport and release can be constrained with seismological data. Here we use joint active-source/local-earthquake seismic tomography to derive unprecedented constraints on multi-stage fluid release from subducting slow-spread oceanic lithosphere. We image the low P-wave velocity crustal layer on the slab top and show that it disappears beneath 60–100 km depth, marking the depth of dehydration metamorphism and eclogitization. Clustering of seismicity at 120–160 km depth suggests that the slab’s mantle dehydrates beneath the volcanic arc, and may be the main source of fluids triggering arc magma generation. Lateral variations in seismic properties on the slab surface suggest that serpentinized peridotite exhumed in tectonized slow-spread crust near fracture zones may increase water transport to sub-arc depths. This results in heterogeneous water release and directly impacts earthquakes generation and mantle wedge dynamics