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Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants. Silica is an amorphous metal oxide formed by complex inorganic polymerization processes. This is opposed to the other major biogenic minerals, comprising carbonate and phosphate, which occur in nature as crystalline iono-covalent solids (e.g. salts) whose precipitation is dictated by solubility equilibria. Chemically, bSi is hydrated silica (SiO2·nH2O), which is essential to many plants and animals. Diatoms in both fresh and salt water extract dissolved silica from the water to use as a component of their cell walls. Likewise, some holoplanktonic protozoa (Radiolaria), some sponges, and some plants (leaf phytoliths) use silicon as a structural material. Silicon is known to be required by chicks and rats for growth and skeletal development. Silicon is in human connective tissues, bones, teeth, skin, eyes, glands and organs. Silicate, or silicic acid (H4SiO4), is an important nutrient in the ocean. Unlike the other major nutrients such as phosphate, nitrate, or ammonium, which are needed by almost all marine plankton, silicate is an essential chemical requirement for very specific biota, including diatoms, radiolaria, silicoflagellates, and siliceous sponges. These organisms extract dissolved silicate from open ocean surface waters for the buildup of their particulate silica (SiO2), or opaline, skeletal structures (i.e. the biota's hard parts). Some of the most common siliceous structures observed at the cell surface of silica-secreting organisms include: spicules, scales, solid plates, granules, frustules, and other elaborate geometric forms, depending on the species considered. Five major sources of dissolved silica to the marine environment can be distinguished: Riverine influx of dissolved silica to the oceans: 4.2 ± 0.8 × 1014 g SiO2 yr−1 Submarine volcanism and associated hydrothermal emanations: 1.

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Concepts associés (19)

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Séances de cours associées (19)

Siliceous ooze

Siliceous ooze is a type of biogenic pelagic sediment located on the deep ocean floor. Siliceous oozes are the least common of the deep sea sediments, and make up approximately 15% of the ocean floor. Oozes are defined as sediments which contain at least 30% skeletal remains of pelagic microorganisms. Siliceous oozes are largely composed of the silica based skeletons of microscopic marine organisms such as diatoms and radiolarians. Other components of siliceous oozes near continental margins may include terrestrially derived silica particles and sponge spicules.

Biogenic silica

Cycle du dioxyde de silicium

Le cycle du dioxyde de silicium est le cycle biogéochimique dans lequel le dioxyde de silicium (ou silice) est transféré entre les différents systèmes terrestres. Le silicium est un élément bioessentiel et c'est aussi l'un des éléments les plus abondants sur Terre. Le cycle du dioxyde de silicium a un chevauchement significatif avec le cycle du carbone (cycle carbonate-silicate) et joue un rôle important dans l'enfermement du carbone par le biais de l'altération continentale, de l'exportation biogénique et de l'enfouissement sous forme de limons à l'échelle des temps géologiques.

MATH-250: Numerical analysis

Construction et analyse de méthodes numériques pour la solution de problèmes d'approximation, d'algèbre linéaire et d'analyse

Phytolith types and type-frequencies in subalpine-alpine plant species of the European Alps

Biogenic silica extracted from 21 species commonly occurring in subalpine and alpine plant communities in the central Swiss Alps were examined using light and SEM microscopes; 19 species being screened here for the first time. An inventory of phytolith types is provided and type-frequencies are assessed. Light microscope photographs and SEM micrographs provided illustrations of the types described. The monocotyledons analysed belonged to the genera Calamagrostis, Festuca, Nardus, Poa and Carex. Monocotyledons yielded mainly types of epidermal origin (short cells, rods, cork cells, silicified stomata and trichomes). Dicotyledons analysed were from five genera of the Ericaceae family (Arctostaphylos, Calluna, Loiseleuria, Rhododendron, Vaccinium) and from one genus of the Betulaceae (Alnus). In dicotyledons, silicified epidermal jigsaw cells, stomata complexes and vessels were recovered. Conifer species of the genera Abies, Juniperus, Picea, Pinus and Larix were studied. Distinctive conifer cells were mainly silicified endodermids and transfusion tissues. Phytolith taxonomic diagnostic potential was tested by cluster analysis and principal component analysis (PCA). It was shown that grass and sedge species could be easily differentiated on the basis of phytolith types. In general, Ericaceae and conifers could also be distinguished on the basis of phytoliths; however, some species yielding mainly redundant types were not unequivocally identifiable. The aim of the present work is to provide a framework for phytolith-based plaeoecological studies at the treeline in the European Alps. (C) 2004 Elsevier B.V All rights reserved.

2004

Biogenic silica production in selected alpine plant species and plant communities

The biogenic silica extracted from samples of 28 alpine plant species belonging to 23 genera and nine families collected in the Swiss Alps (Valais) accounted for between 0.01 and 5.9% of the dry biomass of leaves and wood. Silica content, and plant contribution to the soil biogenic silica pool, varied widely among taxa. Plant net productivity and biogenic silica production From this study and from the literature have been used to predict the input made by different subalpine and alpine plant communities to soil-borne phytolith assemblages, and their contribution to the silicon biocycle. (C) 2001 Annals of Botany Company.

2001

Biominéralisation de la silice: Diatomées, Radiolaires, Éponges

Plonge dans la biominéralisation de la silice chez les diatomées, les radiolaires et les éponges, explorant leur origine, leur distribution et leur impact sur le cycle de la silice de l'océan.

Analyse numérique des équations différentielles MATH-250: Numerical analysis

Couvre l'analyse numérique des équations différentielles, en se concentrant sur les méthodes et les conditions de stabilité.

Biominéralisation de la silice : évolution et impact sur le climat mondial

Explore la biominéralisation de la silice chez les diatomées, les radiolaires et les éponges, discutant de son impact sur le climat mondial et de la dépendance au pH de la biominéralisation du silicium.