The TRR 181 seminar is held by Erika Henell (Leibniz Institute for Baltic Sea Research Warnemünde) on June 8, Bundesstr. 53 20146 Hamburg, room 22/23.

Derivation and application of a local diahaline Water Mass Transformation framework to the Baltic Sea

In this talk I present new insights into the Baltic Sea overturning circulation. An isohaline water mass transformation framework is applied that quantifies and decomposes the diahaline exchange flow. The two main circulation patterns of the exchange flow are investigated. The first consists of the large-scale overturning circulation with inflow occurring where the isohaline surface is near the bottom, and outflow where the isohaline is surfacing. The second is the small-scale overturning circulation located inside the bottom boundary layer over sloping bathymetry, and is driven by boundary mixing. The latter is consistent with recent theories for the circulation in the bottom boundary layer of the world ocean. These two circulatory patterns are visualized across chosen vertical transects in physical and salinity space. One crucial result of this study is that around 50% of the diahaline exchange flow patterns are produced by numerical mixing. This spurious mixing is generated by the truncation error of the advection scheme, in spite of the fact that an anti-diffusive advection scheme and vertically-adaptive coordinates are used. This diahaline framework calls for its extension to the thermohaline overturning circulation of the World Ocean. Quantifying the contribution of the numerically driven global circulation is of great interest for estimating the reliability of climate models.