The color that you sea

Why is it that some places the color of the ocean is dark blue, and some places it is aquamarine? Why does the color change?

the blue water of California on a sunny day.

Like all visual perception of color, the answer has a lot to do with light and wavelength, and their absorption.

the visible spectrum
the visible spectrum

White light is made up of all the colors of the rainbow, and the perceived color of an object is the wavelength of color that is not absorbed the most.  So for instance, the ocean water Loves to absorb the color red.  The white light of the sun shines down on the ocean, and the wavelengths of color are divided by how quickly the are absorbed. Red goes first, and then orange, and then yellow, and so on.  But the ocean is very weak at absorbing blue color, so most of the water you see appears blue.

So, why is the water in Belize aqua and the water in California navy?

The answer has a lot to do with the fact that we are not looking at pure water, but at water that has particles in it.

California has a LOT of upwelling, which brings sediment and nutrients toward the surface from deep ocean basins. Those sediments in the water help to reflect and scatter the blue color, giving this part of the ocean a darker color.  It also provides the ocean with a lot of nutrients, allowing for algae like kelp to thrive.

But phytoplankton!


You all know, and love phytoplankton. I know I do.  Phytoplankton use chlorophyll for photosynthesis.  This is the basis of LIFE (carbon), which is why I just went ahead and assumed that you and phytoplankton were (K I S S I N G).

But seriously, chlorophyll has a green pigment, which makes phytoplankton especially good at absorbing blue and red wavelengths, and reflecting that green color back out again.  California has a lot of this science K I S S I N G happening (fine, photosynthesis), and this makes the water turbid (cloudy, opaque, not good viz).

Caye Caulker, Belize, aerial view
Caye Caulker, Belize, aerial view

The light aqua blue colors surrounding many shallow and young islands has to do with the nutrient lacking water (nutrients lacking from the water, therefore less color scattering) and the white sand on the bottom being heavier and less likely to remain stirred up.  The light penetrates deeper with less obstacles, the color is not as scattered, and there isn’t as much nutrient action making the water turbid.

any questions?

what’s your favorite color of sea?