It has long been noted that in the northern seas, where the water is cold, algae grow better than in the seas

It has long been noted that in the northern seas, where the water is cold, algae grow better than in the seas of the southern latitudes. Explain this phenomenon.

Algae, like other plants, need oxygen to breathe. Get it dissolved from water. And since more oxygen can be dissolved in cold water than in warm water, then an abundance of vegetation will be in cool water. That is why algae predominate in the northern seas, not the southern ones.