You meander down Pensacola Beach and see the emerald green waters that the Gulf of Mexico is so highly noted for.The Scope-colored water looks amazing, even better with polarized glasses on. Scan from horizon to horizon and the beautiful green water may only be interrupted by the white of a breaking wave or the pale green of water over a shallow sandbar. Glance further offshore and see a beautiful blue color. Those who venture miles offshore can attest to the cobalt blue of the open sea. The color of the Gulf is truly beautiful.
However, here is what is amazing… When you take a glass and dip into the Gulf, then raise it to the light to observe its color – you’ll find it’s clear, like a glass of fresh water. The emerald greens and cobalt blues are gone. So, what happened? We say the sea is blue, but what color is it really?
Actually, it is clear - water has no color. So what makes the greens and blues we see? To answer this we need to understand a little about light. Let’s try this without getting too “science-y.” Light is energy moving in the form of a wave – radiating everywhere. If you’re familiar with ocean waves, you know that some have long wavelengths (distance from the crest of one wave to another) and these create the low swells. Others have shorter wavelengths, creating choppy conditions.
Light moves in the exact same way as ocean waves. The longer light wavelengths are the reds, oranges, and yellows. There are light wavelengths longer than red but the human eye cannot see them. The next longest wavelength is what we call infrared, which can only be seen by humans if using night vision goggles. The short wavelengths are the greens, blues, and violets. Even shorter than violet is ultraviolet wavelengths, which some animals can see but humans cannot. White light, or sunlight, combine all wavelengths at once, some of which humans can see and some we cannot. This is why it is sunlight is so bright, it’s carrying a lot of energy at once.
As this white light from the sun meets the ocean, much of it is reflected back as it meets the more dense water. That reflection is what creates the very bright glare we experience over the water and why we need sunglasses at the beach. The light that is not reflected enters the denser world of water. Here the light waves begin to bend – or refract. This causes objects underwater to appear to appear larger and closer than they actually are. Many of us have experienced this change while gigging for flounder or trying to catch crabs with a net.
However, there is another change – absorption. There are particles of salt, sediments, plankton, and others drifting in the water. These particles absorb some wavelengths of light and reflect others. In the ocean, the long waves of light (reds, oranges, and yellows) are absorbed first, reflecting greens and blues. Humans can see red and orange objects up to about 10 feet underwater when they start fading., At around 30 feet the reds and oranges become completely absorbed and the underwater world turns green and blue — the same emerald green and cobalt blue we see at Pensacola Beach. In underwater videos, the colors only return when artificial white light from the camera is used.