Boron isotope ratios of surface waters in Guadeloupe, Lesser Antilles
Résumé
Large variations are reported in the B concentrations and isotopic ratios of river and thermal spring
waters in Guadeloupe, Lesser Antilles. Rivers have d11 B values around 40‰ and B concentrations lower
than 30 lg/L, while thermal springs have d11
B of 8–15‰ and B concentrations of 250–1000 lg/L. River
samples strongly impacted by hydrothermal inputs have intermediate d11
B and B contents. None of these
surface water samples have d11 B comparable to the local unweathered volcanic rocks (around 0‰),
implying that a huge isotopic fractionation of 40‰ takes place during rock weathering, which could be
explained by preferential incorporation of 10 B during secondary mineral formation and adsorption on
clays, during rock weathering or in the soils. The soil-vegetation B cycle could also be a cause for such
a fractionation. Atmospheric B with d11
B of 45‰ represents 25–95% of the river B content. The variety
of the thermal spring chemical composition renders the understanding of B behavior in Guadeloupe
hydrothermal system quite difficult. Complementary geochemical tracers would be helpful.