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: Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

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: Deep-water agglutinated foraminifera on the crest of the Hovgaard Ridge, west of Spitsbergen, consist mostly of large tubular astrorhizids. At a boxcore station collected from the crest of Hovgaard Ridge at a water depth of 1169 m, the sediment surface was covered with patches of large (1 mm diameter) tubular forms, be longing mostly to the species Astrorhiza crassatina Brady, with smaller numbers of Saccorhiza, Hyperammina, and Psammosiphonella. Non-tubular species consisted mainly of opportunistic forms, such as Psammosphaera and Reophax. The presence of large suspension-feeding tubular genera as well as opportunistic forms point to the presence of deep currents at this locality that are strong enough to disturb the benthic fauna. This is confirmed by data obtained from sediment echosounding, which exhibit lateral variation in relative sedimentation rates within the Pleistocene sedimentary drape covering the ridge, in dicative of winnowing in a south-easterly direction.

Description: Organic-walled dinoflagellate cysts and acritarchs are a vital tool for reconstructing past environmental change, in particular in the Neogene of the high northern latitudes where marine deposits are virtually barren of traditionally used calcareous microfossils. Yet only little is known about the paleoenvironmental value of fossil assemblages that do not have modern analogues, so that reconstructions remain qualitative. Thus, extracting their paleoecological signals still poses a major challenge, in particular on pre-Quaternary timescales. Here we unravel the relationship between species relative abundance and sea surface temperature for extinct dinoflagellate cyst and acritarch taxa from the Neogene of the Iceland Sea using palynological assemblages and organic geochemical (alkenone) data generated from the same set of samples. The reconstructed temperatures for the Miocene to Pliocene sequence of Ocean Drilling Program Site 907 range from 3 to 26 °C and our database consists of 68 dinoflagellate cyst and acritarch samples calibrated to alkenone data. The temperature range of five extant species co-occurring in the fossil assemblage agrees well with their present-day distribution providing confidence to inferred temperature ranges for extinct taxa. The 14 extinct dinoflagellate cyst and acritarch species clearly exhibit a temperature dependency in their occurrence throughout the analysed section. The dinoflagellate cyst species Batiacasphaera hirsuta, Labyrinthodinium truncatum, Cerebrocysta irregulare, Cordosphaeridium minimum, Impagidinium elongatum and Operculodinium centrocarpum s.s., and the acritarch Lavradosphaera elongatum, which are confined to the Miocene, have highest relative abundances and restricted temperature ranges at the warm end of the reconstructed temperature spectrum. The latter five species disappear when Iceland Sea surface temperatures permanently drop below 20 °C, thus indicating a distinct threshold on their occurrence. In contrast, species occurring in both the Miocene and Pliocene interval (Batiacasphaera micropapillata, Habibacysta tectata, Reticulatosphaera actinocoronata, Cymatiosphaera? invaginata) show a broader temperature range and a tolerance towards cooler conditions. Operculodinium? eirikianum may have a lower limit on its occurrence at around 10 °C. The calibration of species relative abundance versus reconstructed sea surface temperature provides a quantitative assessment of temperature ranges for extinct Miocene to Pliocene species indicating that temperature is a decisive ecological factor for regional extinctions that may explain the frequently observed asynchronous highest occurrences across different ocean basins. It demonstrates that qualitative assessments of ecological preferences solely based on (paleo) biogeographic distribution should be treated with caution. In addition to enhancing knowledge on marine palynomorph paleoecology, this study ultimately improves the application of palynomorphs for paleoenvironmental reconstructions in the Neogene of the Arctic and subarctic seas, a region essential for understanding past global climate.

Description: The large-scale circulation and dense water formation (DWF) in the Svalbard archipelago influence the thermohaline circulation in the whole Arctic. In particular, DWF depends on the rate of cooling and homogenisation of the Atlantic water along its northward pathway, brine rejection, boundary convection on shelves and slopes, and open-ocean convection. This study focuses on brine rejection, shelf convection and entrainment processes, which occur in the SW Spitsbergen area. Two short (~140m) moorings (named S1 and ID2), deployed at a depth of ~1040 m over the slope, collected multiannual (2014-2017) time-series in an area of interaction between the West Spitsbergen Current and the descending dense shelf plumes. Time-series revealed a large thermohaline and current variability between October and April. Data highlight the presence of Norwegian Sea Deep Water (θ = -0.90°C, S = 34.90, σθ = 28.07 kg m-3) influenced by occasional intrusions of warmer (up to +2°C), saltier (up to ~35), and less dense (down to 27.98 kg m-3) water during fall-winter periods. Interestingly, such intrusions occur simultaneously at both sites, despite their distance (~170 km), suggesting that winter meteorological perturbations play an important role in triggering dense shelf plumes, which collect particulate matter during their descent. Here we discuss the origin, timing, and role of such turbidity plumes in a period characterized by a general warming and ice reduction of the Arctic.

Description: The glacial history of the Antarctic Ice Sheet in the Weddell Sea embayment during the Last Glacial Maximum (LGM; 23-19 ka) is a matter of debate. Existing onshore and offshore data suggest two alternative reconstructions for the LGM ice sheet extent. One scenario shows an ice sheet grounding line that had advanced to (or at least close to) the shelf edge throughout the Weddell Sea, embayment. The other reconstruction concludes that the grounding line in the two main cross shelf troughs was located only slightly farther offshore than today. Here we present new data from multibeam swath bathymetry surveys, acoustic sub-bottom profiles and sediment cores collected during recent and past British and German marine expeditions. These data provide new constraints on the glacial history of the eastern part of the Weddell Sea embayment. A previously unknown, stacked grounding zone wedge discovered in the outer shelf part of Filchner Trough possibly marks the northernmost position of the LGM grounding line within this palaeo-ice stream trough. Crescentic moraines and a predominantly smooth seabed morphology mapped north of the Brunt Ice Shelf reveal a complex glacial history with repeated advances of grounded ice or episodic retreats, controlled by a hard seafloor substrate. We will compare new radiocarbon dates obtained from the sediment cores to existing chronologies and use them to reconstruct the timing of the last maximum ice sheet advance and post-LGM retreat. Finally, we will set our new findings into context with results from ice sheet models and discuss their implications for Antarctica's contribution to global meltwater pulses during the last deglaciation.

Description: Fertilization of the ocean by eolian dust and icebergs is an effective mechanism to enhance primary productivity. In particular, high-nutrient, low-chlorophyll (HNLC) areas where phytoplankton growth is critically iron-limited, such as the subarctic Pacific Ocean and the Southern Ocean, are proposed to respond to increases in bioavailable Fe supply with enhanced phytoplankton productivity and carbon export to the seafloor. While Fe-fertilization from dust is widely acknowledged to explain a higher export production during glacial periods in the Southern Ocean, paleoceanographic records supporting links between productivity and eolian dust and/or icebergs in the North Pacific are scarce. By combining independent proxies indicative of ice-sheet dynamics and ocean productivity from a single marine sedimentary record (Integrated Ocean Drilling Program [IODP] Site U1417), we present a comprehensive data set of phytoplankton response to different fertilization mechanisms in the subarctic northeast Pacific between 1.5 and 0.5 Ma, including the Mid Pleistocene Transition. Importantly, the timing of the fertilization events is more strongly controlled by local ice-sheet extent than by glacial-interglacial climate variability. Our findings indicate that fertilization by glacigenic debris results in productivity events in HNLC areas adjacent to ice sheets, and that this mechanism may represent an important, yet rarely considered, driver of phytoplankton growth.

Description: Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing paleoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, due to the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, thus, suggesting enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.