B in Marine Carbonates

Diverse biogenic and inorganic marine carbonates record boron isotopic compositions close to the boron isotopic composition of B(OH) at modern seawater pH. Therefore, Hemming and Hanson (1992) suggested that it is the charged borate species that is preferably incorporated into marine carbonates. This interpretation has been confirmed by a number of empirical calibration studies on inorganic calcium carbonates (Hemming et al. 1995 Sanyal et al. 

corals (Honisch et al. 2004 Reynaud et al. 2004), and planktonic foraminifers (Sanyal et al. 1996 Sanyal et al. 2001) over a wide range of culture water pH. Although biogenic carbonates and even inorganic-precipitated calcite show 5 B offsets of up to 4%o relative to the theoretical borate curve, all empirical calibration curves follow the shape of the theoretical curve and therefore support the validity of the calculated isotope fractionation factor by Kakihana et al. (1977) (cf Fig. 10.13). 

However, the causes for these offsets are yet not completely understood. Culture experiments using living planktoiuc foraminifers (Hoitisch et al. 

This is contribution No 0335 of the Research Center Ocean Margins (RCOM) which is financed by the Deutsche Forschungsgemeinschaft (DFG) at Bremen University, Germany. 

Antarctic and Greenland ice sheets store today about 2 % of the ocean water mass with an average 8 0 value of -45%o. What would be the 8 0 value of an ice-free world  

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