Question: if apart from places like the Caribbean aqua is clear or dark green in the sea,why on the pictures of the globe is the aqua azure?

Sive Finlay answered on 17 Nov 2013:

Hey tinytardis

Great question! I never thought about this before. I guess it’s all to do with perspective and distance. The ocean looks dark green in some places because of the algae that are living in the waters. Sometimes the sea can also appear different colours because of what’s on the sea bed (sandy bottom vs. lots of rocks or seaweed) or depth (deeper water often looks darker). In general though water and the seas are blue because water filters light so that wavelengths of red light are absorbed and blue light is reflected. Blue light also travels further in water than light with longer wavelengths (red, yellow and green). The seas are also blue because the water reflects the sky – which means that the sea’s colour can change on cloudy days.
So the sea is predominantly blue but you’re right that close up it can appear different colours. When we see pictures of the globe taken from space it’s very much a “blue planet”. I think it’s because the pictures are taken from so far away that the greenish colour from algae can’t be seen and you’re also viewing the oceans through the Earth’s atmosphere and sky – which is also blue – so overall the water and what’s above it combine to appear blue.
These are just my best guesses though!
Sive