Problems of stratigraphic correlation across the Arctic Ocean

Sammanfattning: Published articles on Arctic Ocean sedimentation rates generally falls into two categories; one suggesting mm/ka-scale sedimentation rates in the Amerasian Basin and the other cm/ka-scale rates in the Eurasian Basin. This is due to the interpretation of the first measured paleomagnetic polarity change in sediment cores as either the Brunhes-Matuyama (781 ka) reversal or as the short time magnetic excursion, Biwa II (220 ka) within the Brunhes Chron. The paleoclimatological and paleoceanographical interpretations will be greatly affected depending on which age model is applied.A “standard” lithostratigraphy was developed in 1980 for cores from the Alpha-Mendeleev Ridge in the Amerasian Basin. An age model was established for this lithostratigraphic model, based on the assumption that the Brunhes-Matuyama reversal boundary was correctly identified in the investigated cores. In this thesis I have tested if this “standard” lithostratigraphy is possible to apply to cores retrieved from the Lomonosov Ridge. The purpose has been to evaluate the two age model scenarios and the difference in sediment accumulation rates between the Amerasian and Eurasian Basins. The study is based on core-to-core correlations using averaged sedimentological proxies (paleomagnetism, grain size, lithostratigraphy, sediment color and foraminiferal abundance) from a selected set of Alpha Ridge cores that were used to establish the “standard” lithostratigraphic model, and the same set of published proxies for a selected set of Lomonosov Ridge cores. In addition, the coarse fraction, foraminifera abundance, and magnetic susceptibility have been analyzed for cores taken on the Alpha Ridge and the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition (HOTRAX) in 2005.The results suggest that it is not possible to establish a common lithostratigraphy throughout the entire Arctic Ocean as the Amerasian Basin and the Eurasian Basin have different depositional environments. Consequently, the “standard” lithostratigraphy can only be applied to the central Amerasian Basin. The paleomagnetic polarity record, however, can be correlated between cores from the Amerasian and Eurasian Basin, indicating that the large apparent differences in sedimentation rates mainly is an artifact from different interpretations. Correlations among the HOTRAX cores using magnetic susceptibility suggest that cores from the Alpha-Mendeleev Ridge in the Amerasian Basin are possible to correlate over 550 km. Finally, grain size variations in HOTRAX core HLY0503-18JPC retrieved from a local depression in the Lomonosov Ridge can be linked to previously studied key cores from the Lomonosov Ridge crest.