Doing the “tasting sea water” activity again with a different group of students.
A very good introduction to the concept of salinity is the “tasting sea water” activity. Last time I ran that activity, students were very quick to correctly connect the samples with the correct sampling locations without much discussion going on. This time round, though, there was a lot of discussion. Students quickly sorted samples in order of increasing salinity, but there was no agreement to be found on whether the Baltic or the Arctic should be fresher. Since I only pointed to a location and didn’t specify the depth at which the sample had been taken, some students argued that the Arctic was very fresh at the very top, whereas the Baltic was brackish. Others said that the Baltic was a lot fresher than any oceanic location.
In another group, there was a big discussion going on about how in marginal seas, evaporation or precipitation can dominate.
It is always great to see how much you can discuss and learn from an activity as simple as this one!