Written by Danielle Salley, Four Green Steps

As a child, I remember always wondering why the sky is blue, and on a similar note, why the ocean is blue. Are they mirror images of one another? Which comes first: the ocean is the original blue that reflects into the sky, or vice versa?

Well, many of you may already know this, or perhaps you just forgot. Either way here’s an ultra brief refresher.

It goes like this: the visible light spectrum that we are able to see is between 400-700 nanometers (nm). Shorter wavelengths (400nm) are blue, while longer wavelengths (700nm) are red. From the amount of sunlight that penetrates into the water column, red light gets absorbed much faster than blue light as it has a greater light extinction coefficient. Blue light, however, is able to penetrate to deeper water by light scattering—this is what we see. Blue light is scattered through the water column, and no doubt, as we head deeper into the ocean, it gets to be a darker blue because less light is able to reach these depths.

Think about the Caribbean Sea. Those beautiful, turquoise waters… a number of factors play in to the clarity of the ocean, most are only beneficial for tourists, not marine biologists. This is because a clearer setting means less nitrogen production and lower amounts of primary production.  Unfortunately, there’s a toll to pay for such pristine waters…

Image courtesy of Creative Commons.

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