| Summary: | Paired 230 Th/U and 14 C dating were performed on deep-sea corals ( Lophelia pertusa and Madrepora oculata ) from the northeastern North Atlantic at 730 m bsl to investigate past changes of the thermohaline circulation. These were estimated using the ? 14 C value of the upper intermediate waters, based on the 14 C ages of the top and base of each coral, where possible, and the 230 Th/U dating. The reliability of these estimates was checked by dating two very young corals of the species L. pertusa . One of these corals, collected alive in 1999 AD, gave a 230 Th/U age of 1995±4 AD after correction for non-radiogenic 230 Th. Another coral, the top of which dated to 1969±6 AD, recorded the atmospheric 14 C/ 12 C increase due to the nuclear tests in the early 1960s. The calculated ? 14 C values from these two corals agree with those measured at GEOSECS Station 23 in 1972–1973 [Östlund et al., Earth Planet. Sci. Lett. 23 (1974) 69–86] and 1991–1992 [Nydal and Gisfelos, Radiocarbon 38 (1996) 389–406]. This, together with the 100% aragonite content and the d 234 U and 230 Th/ 232 Th values of all the dated corals, indicates that none of the corals behaved as open systems with respect to their U-series nuclides and that they closely represent the water mass properties in which they lived. The pre-anthropogenic ? 14 C value of the North Atlantic intermediate waters was estimated at -69±4‰. The reservoir age varies from 400 years to 600 years, and this variation is due to atmospheric 14 C/ 12 C changes. A reservoir age of 610±80 years, close to the pre-anthropogenic value, was determined from one coral dated at 10 430±120 cal yr BP, when the global sea level was approximately at -35 m [Bard et al., Nature 382 (1996) 241–244]. This suggests a modern-like pattern of the oceanic circulation prevailed in the Northeast Atlantic Ocean at this time although the deglaciation was not completely achieved.
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