The timing of deglacial circulation changes in the Atlantic

International audience; We present new benthic isotopic data from core MD07-3076 retrieved in the Atlantic sector of the Southern Ocean (44°09’S, 14°13’W, 3770 m water depth), and place them in the context of well-dated published Atlantic benthic foraminifera isotopic records covering the last 30 ky. Dating of core MD07-3076 was achieved by a combination of 14C AMS measurements on planktonic foraminifera and correlation of sea surface temperature signals derived from both planktonic foraminifera Mg/Ca and census counts, with Antarctic ice isotopic records (Skinner et al., submitted). Comparison of benthic isotopic records from various depths in the North and South Atlantic reveals that circulation changes over the last deglaciation did not take place simultaneously in the 1000-2000 m and in the 3000-4500 m depth ranges. Circulation changes first occurred at lower depth, causing large and relatively rapid changes in benthic δ18O and δ13C at the beginning of Heinrich Stadial 1 (HS1) and the Younger Dryas. Below 3000 m depth, North Atlantic deep water hydrology changed only gradually until a large increase in deep water ventilation took place, resulting from the resumption of North Atlantic Deep Water formation at the end of HS1. In contrast, our deep South Atlantic record indicates that Circumpolar Deep Water around 3800 m depth remained quasi-isolated from northern water masses until the end of HS1. Furthermore, our record shows that core MD07-3076 site was then flushed with better ventilated waters for a few hundred years from ~14.5 to 14 calendar ky BP, before benthic δ18O and δ13C values resumed their progression towards Holocene levels. In conclusion, this set of well-dated Atlantic records demonstrates that benthic δ18O records followed different time evolutions across the last deglaciation, depending on the site latitude and water depth, so that benthic δ18O can not be used as a global correlation tool with a precision better than 3 ky.