On the fringes of the Gulf Stream, off the east coast of Florida, the sea is very deep and very blue. I hold tight to the railing on the fly deck of the dive boat as it rolls sharply from side to side, and look down into water that’s a thicker, denser color than I’ve ever seen.

For a moment I imagine that if I leaned over the side and dipped my hand in the water, it would come out coated in blue, like paint. Golden fragments of seaweed float by, escapees, perhaps, from the Sargasso Sea’s swirling gyre in the Atlantic Ocean. I would be content to stay on deck, watching the sea’s colors go by, but there are deeper things for me to see. I pull on my dive gear and jump in. Beneath the waterline, as I kick downward, the colors lose their intensity and slowly fade away.

Sitting on the sandy seabed at 100 feet is a shipwreck. It’s a tanker that was seized in 1989 after U.S. customs found it stuffed with marijuana, and was then deliberately scuttled and sunk to create a new underwater habitat. I aim for the deck that’s become fuzzy with a halo of seaweeds, corals and other soft creatures, and hunker down behind the railing at the back of the ship in a quiet spot away from the current.