We will start to plan the cruise later this week, and I would like you to arrive there with plots on the region, and some general idea about what is going on there.
Some things that you could do:
Plot the sea surface temperature in the Skagerak/Kattegat seas for a given day in the April and May and compare the two. What differences do you observe? How do they relate to the physical properties of the Baltic Sea?
Compute the average temperature, salinity, and current velocity in a given region of the Skagerak/Kattegat seas over a period. How do these variables vary over time? Are there any correlations between them?
Use the salinity data to identify the location of a front in the Skagerak/Kattegat seas between two water masses with different salinity values. How does the location of the front vary over time? What physical processes might be responsible for its movement?
Use the current velocity data to calculate the volume transport of water through a given cross-section between Denmark and Sweden. How does this vary over time? Are there any correlations with other physical properties of the Baltic Sea, such as temperature or salinity?
Some other related ideas are to compare the different datasets, like ERA5 vs GHRSST vs NEMO, and see differences or similarities.