Combined high-resolution magnetostratigraphy and nannofossil biostratigraphy for late Quaternary Arctic Ocean sediments

Abstract

A detailed paleomagnetic and calcareous nannofossil study has been carried out on long sediment cores taken during the 1987 ARK IV/3 expedition of R.V. Polarstern in the eastern Arctic Ocean. The Brunhes-Matuyama boundary was not recovered in any of the cores. The magnetostratigraphies reflect the complex behaviour of the geomagnetic field during the Brunhes Chron of predominent normal polarity. Several short excursions and polarity events of the earth's magnetic field are documented in the cores. Their regional correlation was possible on the basis of the characteristic downcore magnetic susceptibility patterns and other physical properties of the sediments. Using the calcareous nannofossil chronostratigraphic framework, seven geomagnetic events of short duration were identified for the last 200 ky. Sedimentation rates derived from the stratigraphic data are highly variable for the Nansen-Gakkel Ridge area, ranging from a few mm ky -1 to several cm ky -1 . More uniform rates of 2-3 cm ky -1 were obtained for the central Fram Strait, the eastern Yermak Plateau, and the southern Nansen Basin and up to 9 cm ky -1 at the Svalbard continental slope and the northern edge of the Yermak Plateau. The chronostratigraphic scheme of geomagnetic events and coccolith abundance patterns developed for the Fram Strait area was applied to the sites of the ARK IV/3 expedition further north. It was then possible to relate the occurrence of coccoliths in the sediments to time. Towards the north, coccoliths occur later in the interglacial cycle, reflecting the influx of southerly currents carrying coccolith stocks to the Arctic Ocean.