Pleistocene stratigraphy and paleoenvironment on the Yermak Plateau, Arctic Ocean: New results from a multi-proxy study on ODP Hole 910A

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Matthießen, J. , Knies, J. , Mackensen, A. , Nam, S. , Stein, R. and Vogt, C. (2004): Pleistocene stratigraphy and paleoenvironment on the Yermak Plateau, Arctic Ocean: New results from a multi-proxy study on ODP Hole 910A , Arctic Geology, Hydrocarbon Resources and Environmental Challenges, 23-26 May, Tromsö, Norway. .
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In 1993, the Ocean Drilling Program (ODP) Leg 151 drilled at 7 sites in the Nordic Seas and the adjacent Arctic Ocean to study the Cenozoic paleoceanography and paleoclimate evolution (Myhre et al. 1995). On Yermak Plateau, the northernmost ODP sites to date were drilled and more than 1200 meters of glacial marine sediments of Pleistocene and Pliocene age were obtained in 10 holes (Myhre et al. 1995). Two shallow water drill holes from sites 910 and 911 that are today located in the path of relatively warm North Atlantic waters transported in the Svalbard branch of the Westspitsbergen Current into the Arctic Ocean were selected for a detailed study. Magnetostratigraphic, stable isotope and biostratigraphic age control suggests that Holes 910A and 911A provide an almost complete stratigraphic record of the last 3.5 Ma (Myhre et al. 1996). In particular, Hole 910A is unique compared to other Quaternary marine sequences from the Arctic Ocean because of a relatively well-constrained stable oxygen and carbon isotope stratigraphy for the last 650.000 years (Flower 1997). Therefore, Holes 910A and 911A are important sites to improve the Plio-/Pleistocene chronostratigraphy of the Eastern Arctic Ocean, and to reconstruct the paleoenvironmental history in the past 3.5 Ma. Furthermore, these holes may form stratigraphic reference sections for new holes to be drilled in the Central Arctic Ocean in the frame of the Integrated Ocean Drilling Program (IODP).A multi-proxy study was started in summer 2003 to establish a dinoflagellate cyst stratigraphy for Plio-/Pleistocene sediments of the eastern Arctic Ocean that will be calibrated versus a revised stable oxygen isotope stratigraphy. Furthermore, the variability of sea-surface conditions and its interaction with the discharge of freshwater from Eurasia and the growth and decay of the northern Barents Sea ice sheets since the Pliocene will be reconstructed. Various micropaleontological, sedimentological and organic geochemical methods are applied on the same sample set to reveal the synchroneity/ asynchroneity of changes in the surface water regime and changes in the sediment supply and source areas. In the first year of the project, the studies focussed on the Pleistocene sediments of Hole 910A that has an average sedimentation rate of 2 to 4 cm/k.y. (Flower 1997).A preliminary dinoflagellate cyst biostratigraphy is based on a first set of 80 out of ca. 220 samples from the uppermost 20 meters of Hole 910A, and the results of a low-resolution study on Hole 911A by Matthiessen & Brenner (1996). Most samples of Hole 910A are productive but contain only few specimens of a small number of taxa. The presence of delicate spherical brown cysts indicates that preservation is generally good. Age-diagnostic species were not found in the Pleistocene and the ubiquitous species have long stratigraphic ranges (e.g. Rochon et al. 1999). The freshwater algae Pediastrum is present in a number of samples suggesting some freshwater supply from the Laptev and Kara seas during certain intervals.The coarse sand fraction (250 to 2000µm) and the number of gravel particles (>2mm/10g) that characterise supply by icebergs do not show much variability, except for a pronounced maximum in marine isotope stage 2 that is probably related to the last glacial maximum. Minor fluctuations of the gravel content might be related to glacial/interglacial transitions and the onset of glaciations.Mineralogical and geochemical parameters show some variability in the Pleistocene siliciclastic sediments of Hole 910A. Carbonate contents are principally low and range usually between 0 and 4%. The terrigenous minerals dolomite and siderite clearly dominate in most samples showing that only a rather small portion of bulk carbonate is of biological origin. Small fluctuations are obviously not related to glacial/interglacial cycles. Maximum values of 8 to 10% were measured in samples from MIS 2. Rock eval pyrolysis revealed that total organic carbon contents are predominately of terrestrial origin, and are obviously inversely correlated with carbonate contents.ReferencesFlower, B.P. 1997: Overconsolidated section on the Yermak Plateau, Arctic Ocean: Ice sheet grounding prior to ca. 660 ka? Geology 25, 147-150.Matthiessen, J. & Brenner, W. 1996: Dinoflagellate cyst ecostratigraphy of PliocenePleistocene sediments from the Yermak Plateau (Arctic Ocean, Hole 911A). In: Myhre, A.M., Thiede, J., Firth, J.V. et al. (eds.): Proceedings of the Ocean Drilling Program Scientific Results 151, 243-253. Ocean Drilling Program, College Station.Myhre, A.M., Thiede, J., Firth, J.V. et al. 1995. Proceedings of the Ocean Drilling Program, Initial Reports 151, 915pp. Ocean Drilling Program, College Station.Myhre, A.M., Thiede, J., Firth, J.V. et al. 1996: Proceedings of the Ocean Drilling Program, Scientific Results 151, 685pp. Ocean Drilling Program, College Station.Rochon, A., de Vernal, A., Turon, J.-L., Matthiessen, J. & Head, M.J. 1999: Distribution of dinoflagellate cysts in surface sediments from the North Atlantic Ocean and adjacent basins in relation to sea-surface parameters. American Association of Stratigraphic Palynologists Contribution Series 35, 146pp. American Association of Stratigraphic Palynologists,Dallas.

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