Seminar

Deciphering Arctic paleoceanograpy and paleoclimate is hampered by multiple problems with dating Arctic sediment cores due to low productivity and poor preservation of biogenic sedimentary records. More recently, geochemical studies using 230Th and 231Pa as constant proxies of particle fluxes estimated radiometric benchmark ages of respectively ∼ 340 and ∼ 150 ka, based on the final decay of 230Th and 231Pa excesses. Here we will present 230Th and 231Pa data, along with sedimentological records, of core ARC5-MA01 from the Mendeleev Ridge. Total collapse depths of 230Thxs and 231Paxs are observed down to 119 and 59cm, respectively, indicating a mean sedimentation rate of ~3.5 mm/ka, which is similar to those in other Arctic cores. All of them support very low sedimentation rates in the central Arctic Ocean. In such a setting, 230Th and 231Pa provide tools for defining a chronostratigraphy spanning the last few glacial-deglacial-interglacial cycles. However, variations of brownish manganese-rich layers, which host high numbers of foraminifera and have been interpreted as being deposited under interglacial/interstadial conditions, are inconsistent with 230Th and 231Pa, leading to the age model estimated here incompatible with the proposed chronostratigraphic framework. Thus, there is a need for revisiting current interpretations of Arctic chronostratigraphies in terms of glacial-interglacial cycles.