Description: Since about 15 years a growing number of evidence is found in water depth up to more than 1000 m of the Arctic Ocean that grounding of ice has occurred in various places including the "Beringian" continental margin north of the present Chukchi and East-Siberian seas and the Lomonosov Ridge. These landforms include moraines, drumlinized features, glacigenic debris flows, till wedges, mega-scale glacial lineations (MSGL), and iceberg plough marks (Polyak et al. 2001, Niessen et al. 2013, Dove et al. 2014, Jakobsson et al. 2014). They suggest that thick ice has occurred not only on nearly all margins of the Arctic Ocean but also covered pelagic areas. In a recent paper, Jakobsson et al. (2016) present more evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, thereby revitalising an old modelling concept of a kilometre-thick ice shelf extending over the entire central Arctic Ocean (Hughes et al. 1977) now dated to Marine Isotope Stage (MIS) 6. Other (including our) studies, however, suggest that the pattern, and, in particular, the timing of these glaciations is more complex. Most recent discoveries on the Lomonosov Ridge have not only gained different information on Pleistocene glaciations but also allowed for the first time to reconstruct upper Miocene Arctic Ocean sea-ice and SST conditions. This became possible since submarine sliding (likely associated with ice grounding) led to removal of younger sediments from steep headwalls and thus exhumation of Miocene to early Quaternary sediments close to the seafloor, allowing the retrieval and analysis of such old sediments by gravity coring (Stein et al. 2016). Submarine glacial landforms from the western and central Arctic Ocean were discovered and investigated during the cruises of RV "Polarstern" in 2008 and 2014, and RV "Araon" in 2012 and 2015. Orientations of some of these landforms suggest that thick ice has flown north into the deep Arctic Ocean from the continental margin of the East Siberian Sea repeatedly (Niessen et al. 2013), thereby grounded on plateaus and seamounts of the Medeleev Ridge. In addition, hydro-acoustic data is presented from the Lomonosov Ridge (Siberian side to close to the North Pole), which support the hypothesis of widespread grounding of ice in the Arctic Ocean, of which the sources are still difficult to determine. The data suggest that thick ice-shelves could have developed from continental ice sheets on a nearly circum-arctic scale, which disintegrated into large icebergs during glacial terminations. On the slopes of the East Siberian Sea and/or on the Arlis Plateau, three northerly-directed ice advances occurred, which are dated by sediment cores using the chronology of brown layers (B1 to B7) as suggested by Stein et al. (2010). According to our age model, the latest advance is slightly older than B2 (MIS-3/4), which has been interpreted as MIS-6 by Jakobsson et al. (2016). A larger well-constrained glaciation has occurred during MIS-4, of which an ice shelf grounded to 900 m on the Arlis Plateau. In the western Arctic Ocean, the oldest datable ice advance has an intra-MIS-5 age. In our data, the chronology of older ice advances along the East Siberian margin are not well constrained but may extend back as far as MIS-16. In contrast, cores from the southern and central Lomonosov Ridge indicate that the youngest ice grounding there has occurred during MIS-6. This grounding was less intense than previous ice-shelf groundings in the area, of which the chronology remains speculative until longer cores become available. Along the Lomonosov Ridge, detailed bathymetric mapping between 81° and 84°N exhibit numerous amphitheatre-like slide scars, under which large amounts of Cenozoic sediments were remobilized into mass-wasting features on both the Makarov and Amundsen sides of the ridge. In areas shallower than 1000 metres, slide scars appear to be associated with streamlined glacial lineations, whereby some of the bedforms have been removed by sliding. It appears that at least some of the mass-wasting events have been triggered by moving and/or loading of grounded ice. Sub-bottom seismic profiling discovered at least three generations of debris-flow deposits near the ridge, which were generated by the slides. In places, the nearly randomly distributed slide scars and debris-flow deposits make it hard to interpret past ice-flow directions from landforms and re-deposited sediments. The pattern allows interpretation of both directions off East Siberia (e.g. Jakobsson et al. 2016) and off Eurasia (e.g. Polyak et al. 2001) towards the central Arctic Ocean. Underneath the slide scars escarpments of up to 400 m in height were formed. Near the southern end of the Lomonosov Ridge the last exhumation of old sediments has occurred during MIS-6. Some of the old sediments recovered in 2014 were studied in more detail (Stein et al., 2016). We can show for the first time that the mid/late Miocene central Arctic Ocean was relatively warm (4-7°C) and ice-free during summer, but sea ice occurred during spring and autumn/winter. A comparison of our biomarker proxy data with Miocene climate simulations seems to favour relatively high late Miocene atmospheric CO2 concentrations. References Dove, D., Polyak, L. & Coakley, B., 2014. Widespread, multi-source glacial erosion on the Chukchi margin, Arctic Ocean. Quat. Sci. Rev. 92, 112–122 Hughes, T. J., Denton, G. H. & Grosswald, M. G., 1977. Was there a late-Würm Arctic ice sheet? Nature, 266, 596–602 Jakobsson, M. et al., 2014. Arctic Ocean glacial history. Quat. Sci. Rev. 92, 40-67 Jakobsson, M., et al., 2016. Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation. Nat. Comm., 7, 10365, DOI: 10.1038/ncomms10365, 1-10 Niessen, F. et al., 2013. Repeated Pleistocene glaciation of the East Siberian continental margin. Nat. Geosci. 6, 842–846 Polyak, L., Edwards, M. H., Coakley, B. J. & Jakobsson, M., 2001. Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms. Nature 410, 453–459 Stein, R., Matthiessen, J., Niessen, F., Krylov, A., Nam, S., Bazhenova, E., 2010. Towards a better (litho-) stratigraphy and reconstruction of Quaternary paleoenvironment in the Amerasian Basin (Arctic Ocean), Polarforschung, 79 (2), 97-121 Stein, R., K. Fahl, Schreck, M., Knorr, G., Niessen, F., Forwick, M., Gebhardt, C., Jensen, L., Kaminski, M., Kopf, A., Matthiessen, J., Jokat, W., and Lohmann, G., 2016. Evidence for ice-free summers in the late Miocene central Arctic Ocean. Nature Communications 7:11148, doi:10.1038/ncomms11148.

Description: The modern polar cryosphere reflects an extreme climate state with profound temperature gradients towards high-latitudes. It developed in association with stepwise Cenozoic cooling, beginning with ephemeral glaciations and the appearance of sea ice in the late middle Eocene. The polar ocean gateways played a pivotal role in changing the polar and global climate, along with declining greenhouse gas levels. The opening of the Drake Passage finalized the oceanographic isolation of Antarctica, some 40 Ma ago. The Arctic Ocean was an isolated basin until the early Miocene when rifting and subsequent sea-floor spreading started between Greenland and Svalbard, initiating the opening of the Fram Strait / Arctic-Atlantic Gateway (AAG). Although this gateway is known to be important in Earth’s past and modern climate, little is known about its Cenozoic development. However, the opening history and AAG’s consecutive widening and deepening must have had a strong impact on circulation and water mass exchange between the Arctic Ocean and the North Atlantic. To study the AAG’s complete history, ocean drilling at two primary sites and one alternate site located between 73°N and 78°N in the Boreas Basin and along the East Greenland continental margin are proposed. These sites will provide unprecedented sedimentary records that will unveil (1) the history of shallow-water exchange between the Arctic Ocean and the North Atlantic, and (2) the development of the AAG to a deep-water connection and its influence on the global climate system. The specific overarching goals of our proposal are to study: (1) the influence of distinct tectonic events in the development of the AAG and the formation of deep water passage on the North Atlantic and Arctic paleoceanography, and (2) the role of the AAG in the climate transition from the Paleogene greenhouse to the Neogene icehouse for the long-term (~50 Ma) climate history of the northern North Atlantic. Getting a continuous record of the Cenozoic sedimentary succession that recorded the evolution of the Arctic-North Atlantic horizontal and vertical motions, and land and water connections will also help better understanding the post-breakup evolution of the NE Atlantic conjugate margins and associated sedimentary basins.

Description: Lateglacial/early Holocene interval from the sediment core JM09-020GC recovered in Storfjordrenna (western Barents Sea) has been studied for benthic foraminifera assemblages, stable isotopes, IRD, vivianite microconcretions, magnetic susceptibility, and elemental composition in order to identify the causes and mechanisms of abrupt climate change during the Younger Dryas. The core was retrieved with R/V Jan Mayen (University of Tromsø – The Arctic University of Norway, UiT) in November 2009 from the Storfjordrenna (76°31489' N, 19°69957' E) at a bottom depth of 253 m. Prior to sediment core opening, the magnetic susceptibility was measured using a loop sensor installed on a GEOTEK Multi Sensor Core Logger at the Department of Geology, UiT. Core sections were stored in the laboratory for one day prior to measurements, thus allowing the sediments to adjust to room temperature and avoiding measurement errors related to temperature changes (Weber et al., 1997). Qualitative element-geochemical measurements were performed with Avaatech X-ray fluorescence (XRF) core scanner using the following settings: 10 kV, 1000 µA, 10-s measuring time, and no filter. Sediment samples for foraminiferal and vivianite analyses were freeze-dried, weighed, and wet sieved using sieves with mesh sizes of 500 µm and 100 µm. The residues were dried, weighed again, and subsequently split on a dry micro-splitter. Where possible, at least 300 specimens of foraminifera were counted in every 1 cm of sediment. Species identification under a binocular microscope (Nikon SMZ1500) was supported using the classification of Loeblich and Tappan (1987), with few exceptions, and percentages of the eight indicator species were applied. The benthic foraminiferal abundance and ice-rafted debris (IRD; grains 〉500 µm) were counted under a stereo-microscope and expressed as flux values (number of specimens/grains cm-2 ka-1) using the bulk sediment density and sediment accumulation rate.

Description: TOC, IP25, HBI Z-triene (HBI-III), C46-GDGT data and median ages from a marine sediment core, northern Wijdefjorden, Svalbard. The dataset spans from the last deglaciation until present. It has been used to reconstruct the sea-ice history and sea water temperature variations.