Water mass exchange, pathways and the mesoscale eddy field in the Lofoten Basin of the Norwegian Sea

• Published in: Ocean Science
• Main Author: Dugstad, Johannes Sandanger
• Other Authors: orcid:0000-0002-9169-5842
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: The University of Bergen 2020
• Subjects: Lofoten; Lofoten Basin; Norwegian Sea; Nordic Seas
• Online Access: https://hdl.handle.net/1956/24440

The Lofoten Basin situated in the Norwegian Sea, plays a central role in redistributing and modifying the warm Atlantic Water carried poleward with the Norwegian Atlantic Current. Increased residence time of the warm Atlantic Water in this region, leads to a large cooling and the largest surface heat losses in the Nordic Seas. This thesis studies the exchange of Atlantic Water with the Lofoten Basin using observations and numerical models, and Lagrangian and Eulerian approaches. A key focus is the study of the mass and heat exchange with the basin outlined by the 3000-m isobath. Surface drifters are analyzed to study the surface circulation in the Nordic Seas and to estimate the water mass exchange with the Lofoten Basin. Fields from Eulerian models and trajectories from Lagrangian simulations at multiple levels are further used to study the processes leading to the exchange, by delineating the mean and eddy component of the flows. Analyses aimed to quantify the mesoscale eddy properties, their interaction with the ambient, heat and vorticity budgets, and to assess the importance of eddies relative to the ambient flow and other submesoscale processes in the mass and heat exchange with the Lofoten Basin. The geographical origins of the water masses having largest interaction with the basin are identified, and these sites are studied in detail to investigate the processes behind the exchange. The thesis also investigates the fate of water masses in the basin to study how their properties evolve with time, and compare this with other regions. The first main finding, obtained from surface drifter observations, indicates an increased exchange of Atlantic Water across the southern sector of the Lofoten Basin. The drifters show a meandering motion between the eastern and western branches of the Norwegian Atlantic Current towards the basin, and Eulerian simulations suggest that the inflow is primarily related to a mean component of the flow. The warm waters experience long residence times and large temperature losses in ...