Eastern North Atlantic deep-sea corals: tracing upper intermediate water v14C during the Holocene

Paired 230Th/U and 14C dating were performed on deep-sea corals (Lophelia pertusa and Madrepora oculata) from the northeastern North Atlantic at V730 m bsl to investigate past changes of the thermohaline circulation. These were estimated using the v14C value of the upper intermediate waters, based on the 14C ages of the top and base of each coral, where possible, and the 230Th/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 230Th/U age of 1995< 4 AD after correction for non-radiogenic 230Th. Another coral, the top of which dated to 1969< 6 AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 1960s. The calculated v14C values from these two corals agree with those measured at GEOSECS Station 23 in 1972^1973 [Oº stlund 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 N234U and 230Th/232Th 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 v14C value of the North Atlantic intermediate waters was estimated at 369< 4x. The reservoir age varies from V400 years to V600 years, and this variation is due to atmospheric 14C/12C changes. A reservoir age of 610< 80 years, close to the pre-anthropogenic value, was determine