Jan 10, 2022 by John Lockton
So you have come to the Caribbean and seen the water. Or you are thinking of going and have seen the pictures. Yes. It's as beautiful as it looks. The water on beaches like White Beach on Jost Van Dyke Island in the British Virgin Islands, Shoal Bay on Anguilla, Galley Bay in Antigua, the beaches of Barbuda, and many more, have the clearest and bluest water in the world. 

I have a distinct memory of sailing into the lee of Tortola on a spectacular Caribbean morning, escaping the fierce trade-wind that blew that day. Behind Tortola small, tremulous zephyrs were playing on the sail, only tiny ripples on the water. Slowly I rounded the headland into a small, shallowing bay. As I advanced the blue water of the open ocean shaded through entrancing shades of azure, then aquamarine, finally a dancing gold and tourquoise as light bounced from the sandy bottom. My wife called out, “This is perfect.” I didn’t have to be told it was perfect. The bluest and clearest water imaginable. What joy I felt. Caribbean water captures one’s soul.
But what causes the Caribbean to have such brilliant clear blue water? 

The blue of the ocean is caused by the refraction of light. Think the colors of the rainbow glittering in water dropped through your fingers on a bright sunlit day. This rainbow effect occurs when sunlight hits the ocean. The wavelengths of red, orange, yellow, and green light are absorbed by the ocean. Blue wavelength is instead reflected and scattered at different angles resulting in the varying shades of blue. (If you look closely at the water of the open ocean you will note it is not a single shade of blue but an amalgamation of shades). 

The more reflection occurs the bluer the water and the more scattering occurs the less blue the water. Here’s where impurities come in. What scatters light in ocean water is impurities in the water. This can be suspended particles or plankton. The Caribbean is freer of suspended particles and plankton than almost all other parts of the world, hence bluer. 

Many Caribbean islands have limited rainfall, and no rivers or streams flowing into the ocean, meaning little particle detritus from land is being carried into the sea. Regarding plankton, plankton lives on nutrients in the water. Few nutrients means little plankton, and the Caribbean has few nutrients near the surface for plankton to feed on, thus little plankton induced scattering of blue light.

The reasons for few nutrients at the surface of the Caribbean are twofold. First, there are few nutrients to begin with. This again has to do with the semi-desert/no river nature of many Caribbean islands. Nutrients from land are not being deposited in the sea as much as is the case in most parts of the world. (Contrast this to the U.S. where rivers and streams punctuate each coast). But more, the lack of nutrients at the surface in the Caribbean has to do with sunlight. Sunlight heats, and heat has the effect of driving what nutrients there are down, away from the surface. 

The Caribbean is a giant bathtub, encompassed by the Lesser Antilles to the East and the coasts of South America, Central America and the U.S. mainland. Water from the Atlantic pours into the Caribbean through the Antilles and sits there under the blazing sun, getting hotter and hotter, until finally escaping as the superheated Gulf Stream past the tip of Florida. Some of the warmest ocean water in the world is found in the Caribbean, and the amount of nutrients and plankton near the surface is accordingly among the lowest in the world. 

One other factor comes in, not unique to the Caribbean but part of the blue Caribbean story, coral. Coral reefs are plankton eating machines. With coral reefs being destroyed by global warming and human invasion I expect we will find a gradual diminishment of the brilliant Caribbean blue, the startling blue I saw in the small bay on Tortola. I hope I don't live to see this. I may not as I am sort of old. But we are already seeing a diminution in the clarity of the Caribbean on the Windward side of islands as a result of global warming. Pernicious Sargasso weed, a parasite of the sea, has exploded its growth in the warmer water of recent years. Beaches are clogged, particles of the weed pollute the water, and I swear it is already less blue on the Windward side of islands. if we do not change our ways one day a great glory of nature, the bluest of blue, will no longer be with us.  

For those of you who love the Caribbean, or who think you may find yourself in the Caribbean, I hope you will read my new book, Odyssey’s Child, a story which wraps the Caribbean history and natural world in an exciting tale full of compassion and joy. 
Odyssey’s Child
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