Geology/geochemistry ocean water

Lithium isotope geochemistry is characterized by a difference close to 30%c between ocean water (5 Li + 31%c) and bulk silicate earth with a 8 Li-value of 3.2%c (Seitz et al. 2007). In this respect lithium isotope geochemistry is very similar to that of boron (see p. 45). The isotopic difference between the mantle and the ocean can be used as a powerful tracer to constrain water/ rock interactions (Tomaszak 2004). Figure 2.6 gives an overview of Li-isotope variations in major geological reservoirs. 

The lowest observed 5 B-values of around -30%c are for certain tonrma-lines (Chaussidon and Albarede 1992) and some non-marine evaporite seqnences (Swihart et al. 1986), whereas the most enriched HB-reservoir is given by brines from Australia and Israel (Dead Sea) which have 5 B-valnes of np to 60%c (Vengosh et al. 1991a, b). A very characteristic feature of boron geochemistry is the isotopic composition of ocean water with a constant 5 B-valne of 39.5%c (Spivack and Edmond 1987), which is abont 50%c heavier than average continental crnst value of -10 2%o (Chaussidon and Albarede 1992). Isotope variations of boron in some geological reservoirs are shown in Fig. 2.7. 

Another important question concerning the isotopic composition of ocean water is how constant its isotopic composition has been throughout geological history. This remains an area of ongoing controversy in stable isotope geochemistry (see... 

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