13C Record of Benthic Foraminifera in the Last Interglacial Ocean: Implications for the Carbon Cycle and the Global Deep Water Circulation

Abstract

The 13C/12C ratios of Upper Holocene benthic foraminiferal tests (genera Cibicides and Uvigerina) of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide (TCO2) measured during the GEOSECS program. The δ13C difference between benthic foraminifera and TCO2 is 0.07 ± 0.04‰ for Cibicides and −0.83 ± 0.07‰ for Uvigerina at the 95% confidence level. δ13C analyses of the benthic foraminifera that lived during the last interglaciation (isotopic substage 5e, about 120,000 yr ago) show that the bulk of the TCO2 in the world ocean had a δ13C value 0.15 ± 0.12‰ lower than the modern one at the 95% confidence level, reflecting a depletion, compared to the present value, of the global organic carbon reservoir. Regional differences in δ13C between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one: the Antarctic Bottom Water production was higher than today during the last interglaciation, but the eastward transport in the Circumpolar Deep Water was lower.