Dynamics of the exchanges between the Sermilik fjord and the North Atlantic

The Greenland Ice Sheet (GrIS) melting is responsible for one-quarter of the present rate of sea level rise. This is partly due to surface melt, but also to the retreat of the marine-terminating outlet glaciers, a highly nonlinear process, resulting from ice-ocean interactions, that's still absent from climate models. The Greenland's marine-terminating glaciers margins are usually located at the head of Greenland's fjords, glacial-origin coastal inlets between the GrIS and the shelf, through which freshwater reaches the ocean. Therefore, the knowledge of fjord dynamics is essential to understand the processes that have led to glaciers retreat and to estimate glaciers melt rate. Sermilik fjord, south-east Greenland, connects the shelf with Helheim glacier, the fifth-largest outlet of the GrIS in terms of total ice discharge. This fjord is characterised by complex dynamics, combining glacier-driven component with shelf-driven one. This thesis aims at describing Sermilik fjord dynamics interactions with shelf dynamics by means of a high resolution nested model, SURF. In the first part the seasonal fjord circulation is analysed. A seasonally reversing two-layer estuarine and anti-estuarine circulation mode is identified for the first time: it is due to seasonal changes in the strength of the East Greenland Coastal Current. The daily fjord circulation is then investigated, confirming the presence of intense two-layer flows reversing every few days (intermediary circulation). This circulation mode is demonstrated to be forced by the shelf circulation synoptic temporal variability and at least mesoscale spatial variability. Moreover, winter intermediary circulation is proven to cause non-negligible fluctuations of temperature and salinity in the waters adjacent to Helheim glacier, thus probably playing a relevant part in determining glaciers submarine melt rate. At the end, summer intermediary circulation is compared to winter one and cross-fjord variability is examined.