Magnetostratigraphy and palynology demonstrate at least 4 million years of Arctic Ocean sedimentation

Abstract

It has long been recognized^1,2 that the Arctic Ocean has a major role in regulating the timing of Northern Hemisphere glaciations, global heat exchange and ocean circulation. Several recent studies^3–7 have attempted to interpret the palaeoclimatic record in sediment cores from the Arctic Ocean, but conflicting ages have been reported for palaeoclimatic events dated by different methods^3–6. To establish a consistent chronology for cores from the central Arctic Ocean, we performed detailed palaeomagnetic and palynological studies of three cores collected⁷ near the crest of the Alpha Ridge, and obtained radiocarbon dates from planktonic foraminifers isolated from 1-cm-thick intervals. Magnetic inclination values for these cores clearly record normal and reversed-polarity intervals that apparently correspond to the Brunnes and Matuyama magnetochrons; the longest core also includes polarity intervals typical of the Gauss and Gilbert magnetochrons. This chronology is confirmed by the first and last occurrences of pollen and dinoflagellate species that can be correlated with European^8,9 and DSDP^10–12 chronostratigraphies dated by standard biochronological methods. Micromass radiocarbon dates for foraminifers indicate a sedimentation rate of ∼1 mm per 1,000 yr. We believe that these data confirm a long (>4 Myr) chronology for the Alpha Ridge cores, the lithostratigraphy of which can be correlated over extensive areas of the western Arctic Ocean^2–7, and more important, provide dinoflagellate and palynomorph data that indicate the validity of early chronology.