system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are oceans off the coast of places like Ireland and Scotland so dark and grey but seas off Australia and France can be so bright and blue?
gpt
The cold waters off the coast of Ireland/Scotland are rich in nutrient and sediment.  Ocean currents cause upwelling and basically stir everything up.  In places with less nutrients/sediment, or locations buffered by barrier reefs, the water is crystal clear.