Water exchange and mixing in a semi-enclosed coastal basin (Pohja Bay)

The processes contributing to the deep water renewal and oxygen balance of Pohja Bay are reviewed here, with reference to the extensive experimental material from the years 1990–1993. The observations reveal previously unreported frequent minor inflows of sea water into the bay. A one-dimensional diffusion model is introduced and applied to computation of the diffusion-corrected biological oxygen sink during apparent deep water stagnation periods; the sink is evaluated as 0.06 ± 0.01 mg l–1 d–1. The results are summarized in a conceptual description of the physical processes underlying the estuarine circulation and oxygen balance of the bay.