ALBERT

Description: 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.

Description: Holocene climate variability is investigated in the North Pacific and North Atlantic realms, using alkenone-derived sea-surface temperature (SST) records as well as a millennial scale simulation with a coupled atmosphere-ocean general circulation model (AOGCM). The alkenone SST data indicate a temperature increase over almost the entire North Pacific from 7 cal kyr BP to the present. A dipole pattern with a continuous cooling in the northeastern Atlantic and a warming in the eastern Mediterranean Sea and the northern Red Sea is detected in the North Atlantic realm. Similarly, SST variations are opposite in sign between the northeastern Pacific and the northeastern Atlantic. A 2300 year long AOGCM climate simulation reveals a similar SST seesaw between the northeastern Pacific and the northeastern Atlantic on centennial time scales. Our analysis of the alkenone SST data and the model results suggests fundamental inter-oceanic teleconnections during the Holocene.

Description: Concrete planning continues for launching the IODP Arctic Ocean expedition in summer 2004. The two major objectives are (1) to understand the long-term (50 Ma) and short-term (Neogene) paleoceanographic history and (2) the tectonic evolution of the central Arctic Ocean.So far, the history of Arctic Ocean paleoceanography is so poorly known that scientists can look at the recovery of any material as a true exploration that will, by definition, increase the knowledge and understanding of this critical region for climate change. As an important contribution to the planned drilling in the central part of the Arctic Ocean, we have worked out a refined chronostratigraphy for Marine Isotope Stage (MIS) 16 to MIS 2 on existing ODP site 910 from the marginal Arctic Ocean (Yermak Plateau), which will serve as important correlating tools for establishing a sound stratigraphy in the central Arctic Ocean.Various approaches including sedimentological, physical and micropaleontological methods are needed to establish a chronostratigraphy for the central Arctic Ocean. However, low resolution and discontinuous records of biogenic material as well as equivocal interpretations of paleomagnetic records have limited the stratigraphic resolution so far. An elegant way for tackling these ongoing chronostratigraphic problems integrates various chronostratigraphic approaches to date records from the marginal eastern Arctic Ocean that underlies the submerging Atlantic-water derived intermediate waters. Once these records are exactly dated, they may provide useful stratigraphic reference sections for central Arctic Ocean records underlying the submerging Atlantic-water derived intermediate waters, like for example, the Lomonossov Ridge area.We chose the Yermak Plateau the Atlantic/Arctic Ocean gateway as key area for our study because, (1) here, rather than in central Arctic Ocean, carbonate bearing sequences permit establishment of a relatively continuous stable oxygen isotope stratigraphy, which is still the prerequisite for any subsequent application of chronological approaches, and (2) the dynamic coupling between the northernmost branch of the Gulf Stream and the Arctic Ocean. Up to now, the time resolution in ODP site 910 A is by far too low to address most relevant question in climate changes. Here, we verify the existing but equivocal age model of Hole 910A down to Marine Isotope Stage 16 by compiling new and existing chronostratigraphic age fix points in site 910A to strengthen the reliability of Arctic Ocean chronology and establish a new, fundamental basis for generating high-resolution paleoenvironmental reconstructions in the central Arctic Ocean.

Description: 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.

Description: So far, the history of Arctic Ocean paleoceanography is so poorly known that scientists can look at the recovery of any material as a true exploration that will, by definition, increase the knowledge and understanding of this critical region for climate change. As an important contribution to the planned drilling in the central part of the Arctic Ocean, we have worked out a refined chronostratigraphy for Marine Isotope Stage (MIS) 16 to MIS 2 on existing ODP site 910 from the marginal Arctic Ocean (Yermak Plateau), which will serve as important correlating tools for establishing a sound stratigraphy in the central Arctic Ocean.We chose the Yermak Plateau the Atlantic/Arctic Ocean gateway as key area for our study because, (1) here, rather than in central Arctic Ocean, carbonate bearing sequences permit establishment of a relatively continuous stable oxygen isotope stratigraphy, which is still the prerequisite for any subsequent application of chronological approaches, and (2) the dynamic coupling between the northernmost branch of the Gulf Stream and the Arctic Ocean. Up to now, the time resolution in ODP site 910 A is by far too low to address most relevant question in climate changes. Here, we verify the existing but equivocal age model of Hole 910A down to Marine Isotope Stage 16 by compiling new and existing chronostratigraphic age fix points in site 910A to strengthen the reliability of Arctic Ocean chronology and establish a new, fundamental basis for generating high-resolution paleoenvironmental reconstructions in the central Arctic Ocean.

Description: The Pleistocene paleoceanographic and paleoclimate development in the eastern Arctic Ocean is still widely unexplored due to contradictory stratigraphic models and sparsity of calc-areous or silious microfossils. We have selected ODP Hole 910 for a study because presence of some biogenic carbonate permits establishment of a relatively continuous stable oxygen isotope stratigraphy on planktic foraminifer Neogloboquadrina pachyderma sin. that is the basic stratigraphic tool in the Pleistocene. Furthermore, the Yermak Plateau is located in the path of relatively warm Atlantic waters, and its sediments record the dynamic coupling between the northernmost branch of the Gulf Stream and the Arctic Ocean. A multiproxy strategy is applied on the same sample set to reveal the synchronicity/ asynchronies of changes in the surface water regi-me and in the sediment supply and source areas.The revised chronostratigraphy indicates that the uppermost 20 m of Hole 910A range from Marine Isotope Stages (MIS) 17 to MIS 2. Several stratigraphic age fixpoints support the interpretation of the stable oxygen isotope record that is punctuated by numerous short-term meltwater events, often accompanied by an IRD increase and distinct changes in mineral assemblages. Organic-walled dinoflagellate cysts that have the best microfossil preservation potential establish a biostratigraphy calibrated vs the new chronostratigraphy and help to reconstruct the history of surface waters and sea-ice coverage and its interaction with the northern Barents Sea ice sheet developments. Planktic foraminifer assemblages are almost monospecific and often affectted by selective dissolution overprinting the paleorecord. Most samples analysed are productive suggesting that Atlantic water inflow into the Arctic Ocean was suppressed only for relatively short periods in the past 600,000 years. Presence of freshwater algae combined with a typical clay mineral assemblage rich in smectites in a number of samples suggests some freshwater supply from the Laptev and Kara Seas.The terrigenous minerals dolomite and siderite dominate the max. 4% carbonate content in most samples showing that only a rather small portion of bulk carbonate is of biological origin. Rock eval pyrolysis revealed that total organic carbon contents are predominately of terrestrial origin. Finally, our study will provide reference data sets records which can be compared to the new boreholes that will be drilled on the Lomonosov Ridge (Central Arctic Ocean) in the frame of the Arctic Coring Expedition (ACEX, IODP) in summer 2004.

Description: The Pleistocene paleooceanographic and paleoclimate development in the eastern Arctic Ocean is still widely unexplored: this is mainly due to contradictory stratigraphic models and relatively low contents of micropaleontological proxies such as foraminifers, coccoliths and diatoms that are tradionally used to unravel the history of surface and deep waters as well as sea-ice coverage. We have selected ODP Hole 910 for a paleoenvironmental study because presence of biogenic carbonate permits establishment of a relatively continuous stable oxygen isotope stratigraphy on planktic foraminifer Neogloboquadrina pachyderma sin. that is the basic stratigraphic tool in the Pleistocene. Furthermore, the Yermak Plateau is located in the path of inflowing relatively warm North Atlantic waters, and its sediments record the dynamic coupling between the northernmost branch of the Gulf Stream and the Arctic Ocean. Various micropaleontological, sedimentological and organic-geochemical methods are applied on the same sample set to reveal the synchroneity/ asynchroneity of change in the surface water regime and changes in the sediment supply and source areas.The revised chronostratigraphy indicates that the uppermost 20 m of Hole 910A range from Marine Isotope Stages (MIS) 16 to MIS 2. Several stratigraphic age fixpoints support the interpretation of the stable oxygen isotope record that is punctuated by numerous short-term meltwater events. Organic-walled dinoflagellate cysts that have a preservation potential superior to most calcareous and biosiliceous microfossil groups are used to establish a biostratigraphy calibrated vs. the new chronostratigraphy, and to reconstruct the history of surface waters and sea-ice coverage and its interaction with the discharge of freshwater from Eurasia and the growth and decay of the northern Barents Sea ice sheets. Most dinoflagellate cyst samples analysed so far are productive suggesting that Atlantic water inflow into the Arctic Ocean was suppressed only for relatively short periods in the past 600,000 years. Presence of freshwater algae in a number of samples suggests some freshwater supply from the Laptev and Kara seas during certain intervals. Interpretations of the almost monospecific planktic foraminifer assemblages are biased because selective dissolution may have overprinted the paleorecord.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 MIS marine isotope stage 2 that is probably related to the Last Glacial Maximum (LGM). Minor fluctuations of the gravel content might be related to glacial/interglacial transitions and the onset of glaciations in the adjacent northern Svalbard/Barents Sea.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%. Maximum values of 8 to 10% were measured in samples from MIS 2. 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. Rock Eval pyrolysis and isotopic signatures of the organic matter (?13Corg) revealed that total organic carbon contents are predominately of terrestrial origin, and are obviously inversely correlated with carbonate contents.Finally, our study will provide reference stratigraphic data sets for interpreting the micropaleontological, sedimentological and organic-geochemical records of the new boreholes that will be drilled on the Lomonosov Ridge (Central Arctic Ocean) in the frame of the Arctic Coring Expedition (ACEX, IODP) in summer 2004.