Late Quaternary coccoliths at the North Pole; evidence of ice-free conditions and rapid sedimentation in the central Arctic Ocean

Calcareous nannofossils from approximately the past 7000 yr of the Holocene and from oxygen isotope stage 5 are present at 39 analyzed sites in the central Arctic Ocean. This indicates partly ice-free conditions during at least some summers. The depth of Holocene sediments in the Nansen basin is about 20 cm, or more where influenced by turbidites. On the Gakkel Ridge, calcite preservation is excellent and Holocene strata are consistently documented to be at least 4 to 20 cm thick. In the Amundsen Basin, preservation of nannofossils is sometimes poor. Holocene specimens are commonly only found at the surface, although at one site they extend down to 26 cm. The Holocene assemblage is consistently recorded in the upper 5 to 20 cm of sediment on the Lomonosov Ridge and down to 15 cm depth in the Makarov Basin. This implies that linear sedimentation rates for the Holocene in all investigated areas are centimetres per thousand years. Sediments from the last glacial period (oxygen isotope stages 2-4) are relatively thin, suggesting significantly reduced sedimentation, millimetres per thousand years, during this time.