Puzzle 23

John Baez

Q: Why did a patch of the Indian Ocean 15,000 square kilometers in size glow with an eerie white light so bright it could be seen from space for three nights?

A: The light from approximately 1022 bioluminescent bacteria. Glowing oceans have long been reported by sailors, but the reports were hard to confirm until 1995, when a British ship in the Indian Ocean reported that "it appeared as though the ship was sailing over a field of snow or gliding over the clouds" after steaming into a glowing area stretching to the horizon. The blue-white glow was picked up on satellite images and analyzed by scientists including Steve Miller of the United States Naval Research Laboratory and Steve Haddock of the Monterey Bay Research Institute. It was off the coast of Somalia, precisely where the ship reported it, and it was about 15,000 square kilometers in area - about the size of the state of Connecticut. You can see pictures of it online! It lasted for three nights and then stopped.

This steady glow is different than the sparkling caused by dinoflagellates, which are microorganisms than light up momentarily when attacked as a defense against predators. (The light attracts bigger predators that eat the little ones!) In his book Voyage of the Beagle, Charles Darwin described a "wonderful and beautiful spectacle" of the latter sort as his boat rounded the tip of South America:

There was a fresh breeze, and every part of the surface, which during the day is seen as foam, now glowed with a pale light. The vessel drove before her bows two billows of liquid phosphorus, and in her wake she was followed by a milky train. As far as the eye reached, the crest of every wave was bright, and the sky above the horizon, from the reflected glare of these livid flames, was not so utterly obscure as over the vault of the heavens.

According to Haddock, the steady glow in the Indian ocean was probably caused by something else: a short-lived bloom of densely packed bacteria of the species Vibrio harveyi living in association with the microalga Phaeocystis. He estimates that about 1022 bacteria participated in this bloom! It's a bit like the population explosions of algae that create red tides.

Scientists still don't know why these glowing blooms occur, but they're most common in the Indian Ocean, and Haddock wants to launch a research ship to investigate them.


The first two links have links to other references. The second one has a picture of the ship's route through the milky seas.

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