COINCIDENT BORON PROFILES OF BIVALVES FROM THE GULF OF CALIFORNIA - IMPLICATIONS FOR THE CALCULATION OF PALEOSALINITIES

The constant relationship between seawater salinity and boron concentr ation suggests that boron can be used as a measure of salinity. Previo us workers have suggested, on the basis of analyses of the boron conte nt of shells belonging to the bivalved mollusc Mytilus edulis, that sa linity could be reconstructed from biomineral records of boron. Mollus can shells grow by incremental accretion and preserve within. them geo chemical records of their environments. Therefore, if boron concentrat ion is being controlled by an external factor, the ontogenetic boron p rofiles of different shells, contemporaneous and sympatric, should be similar. This paper reports on the analysis of three shells belonging to two species of bivalves, Chionopsis gnidia and Chione californiensi s, collected from the Gulf of California. Ontogenetic profiles constru cted using a spectrophotometric method are quantitatively similar amon g the three specimens. The range of boron concentrations in each shell coincide with estimated ambient salinity variation, but also seems to be influenced by aperiodic regional rainfall, and the resulting influ x of boron-poor freshwater. The similarity among the shells demonstrat es that boron concentration. is under external, environmental control, and directly reflects boron concentration in the surrounding water. T his conclusion raises the possibility of reconstructing ambient boron concentrations from molluscan shells, and perhaps also reconstructing local salinity values. Further research is required to determine if bo ron is deposited in equilibrium with ambient concentrations, the natur e of any dependence of incorporation on temperature, and, therefore, i f paleosalinity reconstruction is possible.