In situ Lithium and Boron isotope determinations in mica, pyroxene, and serpentine by LA-MC-ICP-MS

Boron and Li are light, incompatible elements that preferentially partition into the liquid phase, whether melt or aqueous fluid, and thus are useful for tracking fluid-related processes in rocks. Most of the Li isotopic data presently available on subduction-related rocks are from whole-rock analyses; and the B isotopic analyses of subduction material have been carried out either on whole-rocks or in-situ on an accessory phase, such as tourmaline. The new method presented here couples an ESI New Wave UP-193-FX ArF* (193 nm) excimer laser-ablation microscope with a Neptune Plus (Thermo Scientific) MC-ICP-MS aiming to measure both Li and B isotopes in situ with good spatial resolution (metamorphic minerals are commonly chemically zoned, and whole-rock analyses lose this detail). The data thus obtained are compared with SIMS analyses on the same mineral samples for B, and with MC-ICP-MS analyses on whole-rock or mineral separates from the same sample for Li. Additionally, data acquired on tourmaline standards were compared to SIMS values. The results show that for B concentrations above 5 μg/g, the data obtained by LA-MC-ICP-MS and by SIMS are identical within error, for mica (phengitic muscovite), pyroxene (jadeite), serpentine (antigorite), and tourmaline. For Li concentrations above 10 μg/g, the data obtained by LA-MC-ICP-MS and by MC-ICP-MS are also identical, within error, for mica (phengitic muscovite), and pyroxene (jadeite). However, analyses of tourmaline standards have shown significant differences with reference values, so LA-MC-ICP-MS does not yet appear to be an appropriate method to analyze Li isotopes in tourmalines. Thus, LA-MC-ICP-MS is a suitable method to measure Li and B isotopes with good spatial resolution in major rock-forming silicates from subduction-related rocks where concentrations exceed 10 μg/g and 5 μg/g, respectively, with an error on individual measurements equal to or less than previously used methods, but obtainable in a significantly shorter amount of time. The external reproducibility is ± 2.88 to 3.31 ‰ for B and ± 1.50 to 1.75 for Li, which is lower than or equal to the variations encountered within a given chemically zoned sample (up to 10 ‰ of variation within a given natural sample).

Site n°5. The Pertuis Breton (Bay of Biscay) France

1.This report presents the results of a field study conducted in the ECASA test site nOS in the Pertuis Breton, France. The site is located on the Atlantic West coasts. It is open to the bay of Biscay, but is slightly protected against westerly winds. The bay has been exploited by intertidal mussels culture for centuries. 2. Within the bay, mussels (Mytilus edulis) are cultivated either by the traditional pole technique, around the bay or on longlines in the centre of the bay. The area occupied by these longline s represents 250 ha, and the resulting annual production is 1 000 tonnes of mussels. The average depth at mid tide is of 13.8 m. The sediment is sandy, with a small fraction of mud. 3. The site is subject to several regular monitoring through the local implementation of national networks aiming at protecting the environment and marine resources, on pollutants (RNO), microbiological quality of the waters (REMI), phytoplanktonic toxic species (REPHY) and growth and mortality of molluscs (REMORA). Benthic macrofauna was studied in 1976. 4. Five sampling sations were chosen along a line, starting under the longlines, and at distances of 50, 100, 200, and 400 metres from the area cultivated. A reference station was chosen in a different direction at 2300 metres of the cultivated area. Sampling methods are described in the text. _Sediments were sampled for different analyses: grain size, content in organic matter, total organic carbon and nitrogen, and phytic pigments (chlorophyll a and phaeopigments). Redox were measured in cores. The macrofauna living into the sediment was also sampled. The water column was sampled for physical (temperature, transparency) and chemical parametres, including oxygen content, salinity, organic matter, dissolved nitrogen forms, phosphates and silicates. Results from benthic macrofauna surveys indicate that there were no significant differences between the different stations and the reference station, all being classified as slightly disturbed. The bay is submitted to freshwater runoffs from two adjacent rivers. 7. The sediment is slightly modified by the culture of bivalves. Total organic carbon, total nitrogen, Eh values and pheopigments were significantly higher under the trestles than in any other stations. Other stations often did not differ from the reference station. 8. The effects of shellfish culture on the water column were. However, it was observed a small decrease of the food available to the molluscs near the rearing 9. The DEB model was able to describe and predict adequately the growth of oysters, both in the Baie des Veys and in the Loch Creran. The parametres for its use in other environment are given, but a tuning of one parametre should be performed with the help of authors. 10. Among the indicators and models for use in are as of intertidal bivalve culture, it is recommended to use the sediment quality index, TOC (Total Organic Carbon), redox and pheopigments, in surficial sediment, AMBI for the macrofauna, chlorophyll a contents and nitrogen forms in the water column, and models describing the carrying capacity, filtration rate of molluscs, and a DEB model to predict the growth of molluscs.

Etude écologique de projet. Site de Flamanville. 1er cycle. Traitements mathématiques, Rapport général, Annexes

The study of a first annual hydrobiological cycle on the site of Flamanville was carried out through 19 campaigns conducted between July 76 and June 77. Twelve of them are considered as "heavy" and took place on the following dates: July 8th, 76; August 6th, September 4th, October 3rd, November 3rd, December 16th, January 5th, 77; February 2nd, March 3rd, April 14th, May 10th and May 24th. Seven campaigns consist only in one sample July 23rd, 76; August 21st, September 16th, November 19th, January 19th, 77; February 17th and June 16th. However, some variables which had not been measured during these "light" missions have not been taken into account for the analysis. A first global analysis groups together the first ten campaigns (in May, the nutritive salts had not been measured) and presents the annual variations of nine parameters: temperature, salinity, oxygen, nitrates (N0 3), nitrites (N0 2), phosphates (P0 4), silicates (Si0 2), chlorophyll and pheopigments. A second study of the annual hydrobiological cycle includes all campaigns but only five variables: temperature, salinity, oxygen, chlorophyll and pheopigments.