Why is the sea blue?

Garibaldi Lake: Notice the blue colour

Garibaldi Lake: Notice the blue colour

There are some things which everyone ought to know, but which seem to evade understanding until later life. I know I ought to be grateful about discovering areas of profound ignorance, but somehow I found the latest example of ‘You learn something new every day‘ rather hard to take. And I am still not sure I grasp it fully. The gist of it is this:

the sea is blue because water itself is blue.

Now when I first came across this, I was immediately dismissive. I ‘know’ that water is not blue: I have looked at water quite a lot lately and I would say it was broadly colourless and substantially transparent. However a colleague assured me that he had seen a vial normal water and a vial of heavy water (- deuterium oxide – in which the hydrogen atoms were replaced by their heavier isotope deuterium) and that viewed side by side, normal water was visibly bluer. I was skeptical, and I am still not sure this is the correct explanation. But my alternatives lack any quantitative support.

While I provisionally accept what I have read, my scepticism arises from the fact that I never been aware of the blueness of water in a context which does not involve a source of blue light – namely the sky. I will make some efforts to take a look at some heavy water in a  lab and report back.

As an aside I would just like to note how shocked I am about this! How could I have lived so long and not known about this! Ahhhh….

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