How are the processes of freezing and evaporation similar in the way they make seawater more dense?

Answer 1

They are actually not similar.

Water, unlike most substances, becomes less dense when it freezes. This is why ice floats and (in a way) one of the properties of water that allows life as we know it to exist.

Evaporation of sea water leaves behind solutes (salt, minerals, etc) that become more concentrated over time, increasing overall density of the water left behind (if it's not replenished with fresh water). This is why you see people float so easily on dead-sea type bodies of water (the Aral Sea, Great Salt Lake, the Dead Sea).