Towards a better (litho-) stratigraphy and reconstruction of Quaternary paleoenvironment in the Amerasian Basin (Arctic Ocean)

摘要

New sediment cores were recovered along two transects from the Canada Basin across the central Mendeleev Ridge towards the Makarov Basin and the Lomonosov Ridge in the Eurasian Arctic (northern transect along 80°30 N, southern transect along 77°30 N). Here, we present first results from Polarstern ARK-XXIII/3 expedition (Aug-Oct 2008). Based on the visual core description, Clarks standard lithological units A to M (CLARK et al. 1980) could also be clearly identified in sediment cores from the northern transect across Mendeleev Ridge. The content of sand-sized material, the prominent pink-white layers, and especially in the upper part of the records the distinct brown/beige colour cycles were considered to be the key sedimentary characteristics used for core correlation and for establishing a tentative age model. Based on this age model, the sediments recovered in cores from the southern transect are younger than Marine Isotope Stage (MIS) 8, whereas the cores from the northern transect also contain sediments probably significantly older than MIS 16. Average sedimentation rates for the time interval MIS 1 to 5 in cores from the northern transect reach values of 0.5-0.9 cm ky-1 (top Mendeleev Ridge and Canadian side), increasing to 1.9-2.4 cm ky-1 at the Makarov Basin side. Along the southern transect, sedimentation rates are significantly higher, reaching 4.2 to >6 cm ky-1. The most distinct pinkish intervals characterized by high numbers of dolomitic ice-rafted debris (IRD) are related to increased IRD supply due to disintegration of an extended Laurentide Ice Sheet during MIS 8 (/7), MIS 5d, and MIS 4/MIS 3. The sand-rich intervals and detrital-carbonate maxima found in the deeper part of the sediment sections from the northern transect may reflect events of IRD input due to disintegration events of the Laurentide Ice Sheet at the end of glacial MIS 8, 10, 12, and 16, a still speculative hypothesis that has to be approved by further studies. A diamicton with erosional structures at its base was identified on southern Mendeleev Ridge in water depths of 800-900 m, suggesting the impact of grounding ice masses during a glaciation older than MIS 5a. Future research of this unique new core material recovered during the Polarstern Expedition may help to answer key questions in Arctic Ocean stratigraphy/chronology to unravel the history of circum-Arctic glaciations.