Description: Past ice sheet conditions in the southern Weddell Sea remain poorly known. Previous studies have led to contradicting scenarios of maximum ice extent during the Last Glacial Maximum (LGM). Scenario A is mainly based on terrestrial data indicating limited ice sheet thickening in the hinterland and suggests a LGM grounding-line position on the inner shelf. Scenario B is based on marine geological/-physical data and concludes that the grounding line was located on the outer shelf (~650 km further offshore than in scenario A). In addition, studies suggest a complex history of ice retreat and drainage pattern since the LGM that needs further constraint. We investigated hydroacoustic data acquired during 17 expeditions. A key finding is a previously unknown stacked grounding zone wedge (GZW) located in Filchner Trough on the outer shelf showing that a palaeo-ice stream stabilized at this position at least twice. Radiocarbon dates from sediment cores indicate that (i) the GZW was formed in the early Holocene and (ii) grounded ice did not extend seaward at the LGM. Hence, the grounding line in Filchner Trough experienced dynamic changes in the Holocene and ice sheet retreat after the LGM was not linear. Ice-flow switches in the hinterland possibly explain this behaviour. Further interesting findings are made in Brunt Basin suggesting the existence of cold-based ice or impacts of large icebergs. In addition, new data will be acquired in the area with RV Polarstern in Jan-Mar 2018.

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: 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: Past ice sheet conditions in the southern Weddell Sea remain poorly known. Previous studies have led to contradicting scenarios of maximum ice extent during the Last Glacial Maximum (LGM). Scenario A is mainly based on terrestrial data indicating limited ice sheet thickening in the hinterland and suggests a LGM grounding-line position on the inner shelf. Scenario B is based on marine geological/-physical data and concludes that the grounding line was located on the outer shelf (~650 km further offshore than in scenario A). In addition, studies suggest a complex history of ice retreat and drainage pattern since the LGM that needs further constraint. We investigated hydroacoustic data acquired during 18 expeditions. A key finding is a previously unknown stacked grounding zone wedge (GZW) located in Filchner Trough on the outer shelf showing that a palaeo-ice stream stabilized at this position at least twice. Radiocarbon dates from sediment cores indicate that (i) the GZW was formed in the early Holocene and (ii) grounded ice did not extend seaward at the LGM. Hence, the grounding line in Filchner Trough experienced dynamic changes in the Holocene and ice sheet retreat after the LGM was not linear. Ice-flow switches in the hinterland changing the drainage pattern of the West and East Antarctic Ice Sheets possibly explain this behaviour. In addition, new data were acquired in the southern Weddell Sea during expedition PS111 with RV Polarstern in Jan-Mar 2018. We intend to provide a brief update on the ongoing work and show some preliminary results.

Description: The palaeoceanographic evolution of the SW Svalbard shelf west of Hornsund over the last 14 000 years was reconstructed using benthic foraminiferal assemblages, stable oxygen and carbon isotopes, and grain-size and ice-rafted debris data. The results reveal the complexity of the feedbacks influencing the shelf environment: the inflow of Atlantic and Arctic waters (AWandArW, respectively), and the influence of sea ice and tidewater glaciers. The inflow of subsurface AW onto the shelf gradually increased with the first major intrusion at the end of the Bølling-Allerød. During the Younger Dryas, the shelf was affected by fresh water originating from sea ice and glacier discharge. Glaciomarine conditions prevailed until the earliest Holocene with the intense deliveries of icebergs and meltwater from retreating glaciers and the occasional penetration of AW onto the shelf. Other major intrusions ofAWoccurred before and after the Preboreal oscillation (early Holocene), which resulted in more dynamic and open-water conditions. Between 10.5 and 9.7 cal. ka BP, the shelf environment transformed from glaciomarine to open marine conditions. Between c. 9.7 and 6.1 cal. ka BP the AW advection reached its maximum, resulting in a highly dynamic and productive environment. At c. 6.1 cal. ka BP, the inflow of AWonto the Svalbard shelf decreased due to the intensification of the Greenland Gyre and the subduction of AW under the sea-ice-bearing ArW. Bioproductivity decreased over the next c. 5500 years. During the Little Ice Age, bioproductivity increased due to favourable conditions in the marginal sea-ice zone despite the effects of cooling. The renewed advection ofAWafter AD 1850 started the climate warming trend observed presently. Our findings show that d18O can be used to reconstruct the dominances of different water-masses and, with some caution, as a proxy for the presence of sea ice in frontal areas over the northwestern Eurasian shelves.