Each blade weighs 30 tons and is made from composite materials, primarily fiberglass (glass fiber reinforced polymer) and carbon fiber, layered with resins like epoxy or polyester.
Imagine that stuff decomposing in the ocean, releasing tens of millions of tons of glass and carbon fibers!
Actually, I can’t imagine what it would do. It may not sink, though.
I have always been amazed that glass bottles are not viewed as the ultimate environmentally friendly container. At the bottom of the ocean, I would imagine that glass returns quickly into the sand from which it came.