Scientists Investigating Patches of Ocean With Otherworldly Glow

We're inching ever closer towards unearthing the secrets behind one of the most enduring marine mysteries: the fabled "milky seas" — glowing stretches of water that cast the ocean in an otherworldly haze of green and white, spanning to the horizon and beyond.

The nocturnal phenomenon has haunted and mystified sailors for centuries. But they're incredibly rare, and scientists have struggled to determine what causes them. The milky seas are believed to be produced by some form of bioluminescence, but by what creature?

To learn more, researchers have created a database of every recorded sighting over the past 400 years, in the hope of predicting when and where the next display will pop up. As detailed in a new paper published in the journal Earth and Space Science, by teasing out an underlying pattern to the phenomenon, the effort could provide scientists a chance to observe the milky seas and collect samples that have so far eluded them.

"It is really hard to study something if you have no data about it," study lead author Justin Hudson, an atmospheric scientist at Colorado State University, said in a statement about the work. "To this point, there is only one known photograph at sea level that came from a chance encounter by a yacht in 2019."

The serendipitous photo was taken off the coast of Indonesia and was published in a 2022 paper led by Steven Miller, Hudson's colleague at CSU. Along with the photo, the other sacred piece of evidence is a water sample collected by a research vessel's chance encounter in 1985 near the Yemeni island of Socotra, which was found to contain the bacteria Vibrio harveyi.

Today, the strain, which is known to be bioluminescent, remains the prime suspect. But it's far from conclusive evidence. Perhaps it doesn't act alone — and regardless, there are other nagging questions. For one, it remains unclear what role milky seas play in the ocean ecosystem, or how they fit into the carbon cycle. Stretching for tens of thousands of square miles and glowing for up to months at a time, their influence could be incalculably vast. 

"It seems possible that milky seas represent an understudied aspect of the large-scale movement of carbon and nutrients through the Earth system," Hudson said.

Based on insights gleaned from modern satellite imagery, combined with mapping hundreds of years of accounts, it appears the milky seas are concentrated around the Arabian Sea and Southeast Asian waters. Intriguingly, the work revealed that the timing of the sightings are statistically related to the Indian Ocean Dipole and the El Niño Southern Oscillation, recurring climate patterns that involve changes to the temperature of the waters. Perhaps the milky seas are the result of a biological response by the bacteria, but it's anyone's guess if it's a healthy sign or a bad one.

"The regions where this happens the most are around the northwest Indian Ocean near Somalia and Socotra, Yemen, with nearly 60 percent of all known events occurring there," Hudson explained. "At the same time, we know the Indian monsoon's phases drive biological activity in the region through changes in wind patterns and currents."

Whatever the cause, Miller, who authored the 2022 paper and contributed to this latest one, is confident they're onto something big.

"Milky seas are incredible expressions of our biosphere whose significance in nature we have not yet fully determined," Miller said in the statement. "Their very existence points to unexplored connections between the surface and the sky, and between microscopic to the global scale roles of bacteria in the Earth system.

More on the ocean: Iceberg Breaks Off Antarctica, Revealing Tentacled Creatures Beneath

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