13C Record of Benthic Foraminifera in the Last Interglacial Ocean: Implications for the Carbon Cycle and the Global Deep Water Circulation
The 13 C/ 12 C 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 (TCO 2 ) measured during the GEOSECS program. The δ 13 C difference between benthic foraminifera and TCO 2 is 0.07 ± 0.04‰ for Cibicides and −0.83 ± 0.07‰ for Uvigerina at the 95% confidence level. δ 13 C 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 TCO 2 in the world ocean had a δ 13 C 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 δ 13 C 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.