226Ra in barite: Absolute dating of Holocene Southern Ocean sediments and reconstruction of sea-surface reservoir ages

Absolute dating of marine sediments is necessary to achieve reliable correlations of paleoclimate records. The ²²⁶Ra decay in barite separated from a deep-sea core of the Southern Ocean was used to determine absolute ages for the Holocene Epoch. Comparison with ¹⁴C ages measured on planktic foraminifers provides the first past sea-surface reservoir ages in the Antarctic zone of the Southern Ocean. Throughout the middle to late Holocene, our results indicate a reservoir age of ca. 1100 yr, comparable to modern estimates. A significantly higher reservoir age (ca. 1900 yr) is obtained for the early Holocene, which suggests a major change in the Southern Ocean circulation at that time.