A numerical study of water exchange in sill fjords and the effect of coastal climate change

Abstract

The dynamics of basin water exchange in sill fjords are governed by external factors. This thesis addresses how climate change on the coast may affect the water exchange of the basin water. A three-dimensional hydrostatic ocean model, the Bergen Ocean Model (BOM), is applied to simulate inflows from the coast into an idealized fjord topography, resembling Sørfjorden, located outside Bergen, Norway. Consecutive events of inflow of water from the coast are simulated, and two main cases of water exchange are investigated, with and without coastal warming. In the case of coastal warming, 1 °C and 2 °C of warming are investigated. The lower 100 meters of the basin water is marked. With no coastal warming 88 % of this marked bottom water is replaced by ambient water, after two coastal inflows. For the cases with 1 °C and 2 °C of coastal warming, only 15 % and 3 % are replaced. The model results indicate that a coastal warming of 1 °C has a major effect on the water exchange of the lower basin water. A 2 °C warming results in a further decrease of the basin exchange. Less frequent events of basin water exchange may cause deoxygenation in the basin water due to e.g. biological consumption, and hence worse water quality.