Biological fractionation of oxygen and carbon isotopes by recent benthic foraminifera

Recent deep-sea benthic foraminifera from five East Pacific Rise box core tops have been analyzed for oxygen and carbon isotopic composition. The five equatorial stations, with water depths of between 3200 and 4600 m, yielded fourteen specific and generic taxonomic groups. Of the taxa analyzed, Uvigerina spp. most closely approaches oxygen isotopic equilibrium with ambient sea water. Pyrgo spp. was next closest to isotopic equilibrium, being on the average 0.59 per thousand depleted in 18O relative to Uvigerina spp. Oridorsalis umbonatus also has relatively high delta18O values. Most other taxa were depleted in 18O by large amounts. In no taxa was the carbon in the CaCO3 secreted in carbon isotopic equilibrium with the dissolved HCO3- of ambient sea water. (Auth.)