Isotopical aproches Sample Clauses

Isotopical aproches. Processes controlling the chemical composition of natural waters are of major interest for geochemists because they are the main pathways for the transport of elements and particles from the earth surface and subsurface to the oceans. Chemical and mechanical alteration of the continental crust leads to the disaggregation of rocks and minerals, the formation of soil systems and also allows the removal of chemical elements as well as of larger and smaller particles from altered rocks and soils by rain, pore, spring and river water. Several geochemical and isotopic studies focused especially on suspended particulate and dissolved river loads in order to provide information about their origin and to examine elemental fractionation between colloidal and solution phases. Strontium-isotope ratios vary in nature because one of the strontium isotopes (87Sr) is formed by the radioactive decay of the naturally occurring element rubidium (87Rb). The 87Sr/86Sr ratios are mainly used as tracers of water–rock interaction (Blum et al., 1994; Xxxxxx et al., 2001). The primary sources of Sr in natural water are atmospheric input, dissolution of Sr-bearing minerals, and anthropogenic input (Négrel and Petelet-Giraud, 2005). Dissolved 87Sr/86Sr ratios have often been used to trace weathering patterns, water flow paths, erosion sources, and biological processes in groundwater, watershed/lake, riverine, and oceanic systems (Xxxxxx and Xxxxxx, 1989, 1992; Xxxxxx et al., 1993; Xxxx et al., 1996; Xxxxxx and Xxxxxxx, 1998; Xxxxxxx et al., 1998; Xxxxx and Xxxx, 2006). The 87Sr/86Sr ratio in sediments and suspended matter has also been used to identify sediment provenance in freshwater, estuarine, and marine systems (Xxxxx, 1986; Xxxxxxx et al., 1995; Xxxxxxx et al., 1997; Xxxxxx et al., 2000; Xxxxxxxxx Xxx, 2002; Xxxxx and Xxxxxx-Xxxxxx, 2002; Xxxxxxx et al., 2003; Xxxxxxx et al., 2004). Little attention, however, has been paid to the reasons for the distinct and often large differences in the strontium isotopic composition (and geochemistry, Xxxxxxx, 1993) between the particulate (> l µm), colloidal (< 1 µm), and dissolved (<0.003 µm) phases. These differences are potentially important to an understanding of the origin and geochemistry of the various suspended particulate and dissolved fraction entering the ocean. Weathering is the most important factor determining the Nd concentration and isotopic composition in river water. Starting with the studies by Balashov et al. (1964) a nu...