Boron isotope variations during fractional evaporation of sea water: new constraints on the marine vs. nonmarine debate

Examination of boron isotopes, elemental B, Br, and Li in brines, and coprecipitated salts during fractional evaporation of sea water shows that Br, Li, and B in the evaporated sea water have lower concentrations than expected, as determined from mass-balance calculations. The deficiency is found beyond a degree of evaporation of ~30 and is associated with a gradual increase in the δ ¹¹ B values of the evaporated sea water, from 39‰ to 54.7‰. The boron isotope composition of sea water (δ ¹¹ B = 39‰) is significantly higher than that of continental water (δ ¹¹ B = -3‰ ± 5‰). Salt deposits may be depleted in ¹¹ B by 20‰ to 30‰ relative to their parent brines. These variations suggest that boron isotopes can be used to determine the origin (marine vs. nonmarine) of brines and ancient evaporitic environments. -from Authors