A note on the deep-water inflow to the Bothnian Sea

The deepest connection between the Bothnian Sea and the Baltic Proper is the narrow Understen-Märket trench with a threshold depth of around 90 m. The deep-water flow through this passage, which is of great importance for the hydrographic state of the entire Gulf of Bothnia, was surveyed by the R/V Aranda in October 2004. On the basis of these field results as well as climatological data, it has been concluded that the deep-water flow can be described using a hydraulic framework applied to a channel of parabolic cross-section. The Understen-Märket trench is sufficiently narrow to, in principle, permits neglect of the Coriolis force. Since it may prove useful for other systems, the study, however, also includes the analysis and evaluation of a scheme to determine rotational first-order corrections to controlled transports predicted using standard non-rotating hydraulic theory.