The shorter and darker the days in the Northeast, the greater the lure of warm white sand beaches fringed with palm trees and topped with bright blue skies. Should you heed this call and book passage to the tropics, try to remember that you’re supposed to turn your brain off and not question much beyond the timing of your next fruity frosty cocktail. I’ve never been too good at this, and so when I visited Petit St. Vincent in the Grenadines in January of this past year and obligingly tried to render myself slack jawed in my beach chair, I found myself both hypnotized by the color of the water and unable to stop wondering why, exactly, this water was so damned blue.
If such thoughts also pester you like so many sand flies (which were not a problem on P.S.V, by the way), a book called Color and Light in Nature will be of help. A single drop of water is crystal clear, a bathtub full has a slight blue tinge and the amount of water deep enough for an ocean is very blue indeed. To understand why, you need to remember that a single beam of light is white, but a prism will reveal that that beam contains all the colors of the rainbow. Water is a substance that does a good job of absorbing every color’s light but blue, which it scatters. The more water you’ve got, the bluer it looks.
There are some factors that boost the appearance of blue: surface reflection of the sky, for instance, and the color of the ocean bottom — if it’s white it will also tend to reflect the sky and amplify the blue of the water. And there are other factors that diminish blue: a gray sky, for instance, or the presence of other things in the water which absorb or scatter other colors, like algae, phosphorus, stirred-up sand and so on.
So to have a really blue sea, what you need is depth, reflection and clarity. The same qualities, come to think of it, that you’ll also hope to find in your own mind as you remember how to relax and enjoy the warm ocean breeze.
You don’t mention it here in your post, but what about sand color as a factor? Doesn’t volcanic ash have something to do with it? Also, what about coral reefs? We have a boutique hotel here in The Republic of Panama (http://www.loscuatrotulipanes.com) and there are beaches that range in color from tan to black to perfect white. I’ve been told that the whiter the sand is (and thus, the clearer or more ‘turquoise’ the water seems) is related to the erosion of coral reefs (thus why islands – surrounded by reefs – are whiter). I may be very confused, but just figured I’d throw it out there
Hi there, yup, I mentioned that the color of the bottom affects the color of the water, so that would include the things you mentioned, like the color of the sand on the bottom, presence of ash, coral and so on!
Water’s intrinsically blue color is easy to see when the water is sufficiently deep, such as in the Caribbean and Mediterranean Seas, and in Colorado mountain lakes. Pure water and ice have a pale blue color, which is most noticeable at tropical white-sand beaches or in ice caves in glaciers. (Green colors are usually derived from algae.) The blueness of the water is neither due to light scattering (which gives the sky its blue color) nor dissolved impurities (such as copper). Because the absorption that gives water its color is in the red end of the visible spectrum, one sees blue, the complementary color of orange, when observing light that has passed through several meters of water. Snow and ice has the same intense blue color, scattered back from deep holes in fresh snow.
Blue water is the only known example of a natural color caused by vibrational transitions. In most other cases, color is caused by the interaction of photons of light with electrons. Some of these mechanisms are resonant interactions, such as absorption, emission, and selective reflection. Others are non-resonant, including Rayleigh scattering, interference, diffraction, and refraction. Unlike with water, these mechanisms rely primarily on the interaction of photons with electrons.