The ocean is in a perpetual motion that is enabled by Water Mass Transformation (WMT) processes, i.e., the mixing of different water masses and the exchange with the atmosphere that generates new water masses with different properties. Therefore, to address the WMT processes and their influence on the ocean dynamics, we study in this project the dynamics of a regional sea, the Skagerrak connecting the North Sea and the Baltic Sea, as a natural laboratory for WMT processes. The circulation in the Skagerrak consists of three inflowing waters masses, the Jutland Current from the German Bight, the Baltic Outflow and the Atlantic Sea water. These water masses are then transformed into the outflowing waters of the Norwegian Coastal Current and the Baltic Inflow. The underlying WMT processes will be quantified by a suite of observational and numerical methods. We hypothesise that frontal dynamics in the surface waters are responsible for a large part of the WMT, but we will also aim to identify deep-water mixing processes. A ship campaign will be organised with two research vessels during spring / summer 2025, concentrating on a synoptic view of frontal dynamics and mixing. During the cruise, drifter experiments, turbulence microstructure observations and fine-scale echo sounding surveys combined with remote sensing will be carried out. Beyond this experimental approach, a 15-year realistic numerical hindcast model simulation for the Skagerrak region will be set up to investigate the dynamics in the region and guide the field observations. An existing Eulerian WMT framework will be further developed to quantify WMT processes in the region. A Lagrangian particle backtracking model will be integrated into the numerical model, to understand pathways of water masses, their residence times and mixing properties. In the end, we expect to have obtained a validated and complete assessment of the WMT processes in the Skagerrak that can be generalised and transferred to other regions. To internationally coordinate and carry out the WMT research in the Skagerrak, we have formed the SkaMix Consortium with a total of 21 members from Norway, Sweden, The Netherlands and Germany by signing a joint Memorandum of Understanding.