If you drop something into the ocean, whether a rubber ducky, a dead body, or a message in a bottle, it's likely to chart a path that will tell you something about the object in question, as well as about the water in which it's floating. It would seem that the data you might get from this would be limited, and mostly a minor curiosity (unless you really like rubber duckies, are intent on making sure that dead body doesn't get recovered, or you're bound and determined to make sure your bottled message gets through to someone).
Dr. Curtis Ebbesmeyer's delightful and informative "Flotsametrics and the Floating World" does a very good job of showing that we not only have a lot to learn from floating "stuff," but that unlocking much of the course of history and determining the course of the future is tied to watching how that stuff floats on the water.
It turns out that the ocean is not just a series of various seas defined mostly by their temperature and the land masses they surround. Rather, the oceans are a kind of machine composed of interlocking gyres whose individual courses and interactions are performing a figurative dance, accompanied by a literal song. It turns out their harmonics produce some of the most beautiful music in the universe (which, alas, we lack the ears to hear). Call it the aquatic version of the Musica Universalis/Harmony of the Spheres about which philosophers have hypothesized for centuries, and poets have waxed since they had tongues to speak.
It's popular science aimed at the curious layman, told by a brilliant and enthusiastic man whose sense of joy is infectious and whose presentation is clear. With illustrations, charts, photos, and some cool appendices, especially the one about the various myths of the sea, which takes pains to judge the credibility (or ridiculousness) of the most commonly-cited legends. Alas, no Flying Dutchman is included in this part. Recommended, regardless.