Integrated analysis of glacial sediment input and ocean circulation in NW Barents Sea

The Arctic Ocean is one of the most climatically sensitive areas, being the crossway of global ocean circulation (Charles et al., 1994; Thiede and Myhre, 1996; Knies et al., 1999; Hald et al., 2004). The West Spitsbergen continental margin is characterized by the presence of the West Spitsbergen Current, a warm Atlantic Water that flows northwards along the continental margin. This Atlantic Water is the major heat advection toward the Arctic, mixing with the cold and partially sea-ice covered Polar Water; thanks to the West Spitsbergen Current, the Polar Water is driven into the northern hemisphere circulation system. Studies on the natural variability of the Arctic Ocean circulation are vital for understanding the future of the Arctic climate system and specifically its feedback mechanisms related to global warming (Spielhagen et al., 2011). Moreover, the investigation of past climate variations in the Arctic Ocean is essential to predict future scenarios. During the Last Glacial Maximum (LGM), around 20.000 years ago, the Arctic was mainly covered by a large ice sheet (Hughes et al., 2016) and the glacial sedimentary processes controlled erosion, transport and deposition along the entire margin. The following deglaciation can be considered to a certain extent as an analog to the climatic period we are facing towards the end of the present century. The sedimentary processes were affected by the ocean circulation to an extent that was also varying according to cyclicity at glacial-interglacial and shorter scales. In this Ph.D. project focuses on the interactions between glacial sedimentary input and ocean circulation in the area of NW Barents Sea, during LGM and deglaciations. The available geophysical data were acquired during several research cruises in the study area. From the analysis of this dataset it was possible to identify a number of sedimentary bodies related both to a glacial sediment input and current circulation, responsible for downslope and along-slope sedimentary processes, respectively. The downslope processes related to the presence of ice sheet and ice streams generated structures like the INBIS Channel System situated between the Bear Island and the Storfjorden Trough Mouth Fans (TMFs). This channel system starts at the shelf edge with a series of gullies that merge and grow in dimensions becoming channels and eventually a 2-15 km large and 60 km long channel. The formation of this channel system was possible thanks to its protected location: the glacial debris flows responsible for the formation of the adjacent TMFs could not reach directly the area where the gullies are situated, due to the presence of the Bear Island to the East, acting as a barrier or watershed for the ice. This part of the INBIS Channel System is inferred to be the product of melt-water flows during ice retreat. The structures mainly controlled by along-slope processes include Isfjorden and Bellsund drifts, sedimentary deposits produced by bottom currents driven by thermohaline circulation, geostrophic currents and also by the effect of the local topography and climate (Voelker et al., 2006; Hanebuth et al., 2015). To investigate the mechanism responsible for the formation of these drifts, comparison with present circulation and hence integration with oceanographic data was necessary. The oceanographic investigation proceeded with the analysis of the datasets recorded for few years in two moorings on top of the Isfjord and Bellsund. From this analysis we infer that dense and salty waters formed at the shelf edge, through shelf convection and brine rejection processes, mix during the descent down the slope with the surrounding cold water through entrainment. During the descent also these waters enrich in sediments: the transport of sediments results in an overall high density and in a high kinetic energy. Thanks to these characteristics, these waters may reach deeper portion of the water column than their equilibrium point.