title: Another continental pool in the terrestrial silicon cycle.
abstract: Silicon is the second most abundant element on Earth. It is an important nutrient for phytoplankton and is readily absorbed by terrestrial vegetation; it also assists the removal of carbon dioxide from the atmosphere through the weathering of silicates. But the continental cycle of silicon is not well known, and only a few studies have attempted to use silicon stable isotopes (28Si, 29Si and 30Si) to quantify the continental silicon reservoirs. Dissolved silicon in sea and river waters forms a reservoir of mean isotopic value +1.1 per thousand (refs 7, 10). It is enriched in 30Si with respect to the igneous rocks reservoir, which has a mean isotopic value of -0.3 per thousand (refs 4, 9). This enrichment can only be produced by a major fractionation during weathering, and should result in the formation of a continental 30Si-depleted reservoir. Such a reservoir, however, has not been identified to date. Here we analyse silicon isotopes of in situ quartz from a sandstone series in France, using a new-generation secondary ion mass spectrometry apparatus. We show that quartz that precipitates as siliceous cements forms a strongly 30Si-depleted reservoir with isotopic values down to -5.7 per thousand, a more negative value than any previously published for terrestrial samples. Our findings suggest that quartz re-precipitation plays an important role in the biogeochemical cycle of silicon.
authors.affiliation: IRD-Réunion, UR037, LSTUR, BP 172, 97492 St-Denis Messagerie Cedex, France. basile@cerege.fr
authors.forename: Isabelle
authors.initials: I
authors.lastname: Basile-Doelsch
authors.forename: Jean Dominique
authors.initials: JD
authors.lastname: Meunier
authors.forename: Claude
authors.initials: C
authors.lastname: Parron
mesh_terms: D011232:Chemical Precipitation; D002980:Climate; D003460:Crystallization; D017377:Diatoms / Q000378:metabolism; D005602:France; D019015:Geologic Sediments / Q000737:chemistry*; D007554:Isotopes; D010839:Phytoplankton / Q000378:metabolism; D011791:Quartz / Q000737:chemistry / Q000378:metabolism; D012825:Silicon / Q000737:chemistry* / Q000378:metabolism*; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D007554:Isotopes; D014867:Water; D011791:Quartz; D012825:Silicon