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.

Description: Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014, we discovered multiple submarine landslides over a distance of 〉350 km along Lomonosov Ridge. Removal of younger sediments from steep headwalls has led to exhumation of Miocene to early Quaternary sediments close to the seafloor, allowing the retrieval of such old sediments with gravity cores. Multi-proxy biomarker analyses of these gravity cores reveal for the first time that the late Miocene central Arctic Ocean was relatively warm (4-7°C) and ice-free during summer, whereas sea ice occurred during spring and autumn/winter. A comparison of our proxy data with Miocene climate simulations seems to favour relatively high late Miocene atmospheric CO2 concentrations. These new findings from the Arctic region provide new benchmarks for groundtruthing global climate reconstructions and modeling.