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Milky Seas

Seamen have long reported miraculous sightings of luminous, glowing seawater.

milky_sea

Photo: Len Gatey

In the past, these sightings of so-called "milky seas" were chalked up as tall tales.

Alongside the Loch Ness monster and the infamous drop-off at the end of the world, seamen have long reported miraculous sightings of luminous, glowing seawater.

Consider Captain Kingman’s report, made in the dead of night in June, 1854, in the ocean south of Java, Indonesia. “The whole appearance of the ocean was like a plain covered with snow,” Kingman wrote.

In the past, these sightings of so-called “milky seas” were chalked up as tall tales. At most, scientists believed that the glow was due to bioluminescent bacteria, which do produce a soft white glow. Is that soft glow enough to turn the ocean into “a plain covered with snow,” as Kingman saw? That would take an impossibly large population of bacteria, the scientists hypothesized.

As it turns out, they were right.

Scientists now believe the “milky sea” effect of constant light over a wide area comes from the luminous bacteria Vibrio harveyi, living alongside microalgal blooms. In order to create the effect of a milky sea, the populations of these bacteria are, as predicted, phenomenally large. Each contains an estimated 200 times more than the number of background, free-living bacteria spread over the continental shelf waters of all the oceans put together.

Scientists gained the first ever pictures of the milky sea effect in the fall of 2005. The photos, gleaned from images taken by the U.S. Defense Meteorological Satellite Program, show a glowing portion of the ocean that’s about the size of Connecticut. In other words, this milky sea of bright bacteria was visible to the naked eye from space.

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