What are milky seas, riddle that science is close to solving


One night in January 1864, somewhere in the southeastern Horn of Africa, something inexplicable happened.

“The whole face of nature seemed changed,” wrote Captain Raphael Semmes of the ship Alabama. “Around the horizon there was a faint glow, as if there was a distant illumination, while above there was a dark and eerie sky.”

Alabama had passed “suddenly from the deep blue water we were sailing in to a smear of water so white it startled me” and traveled “illuminated by the unearthly sick glow of a ghost sea” for several hours until it all ended as suddenly as it had been. started.

Semmes and his crew were some of the few eyewitnesses in history to a peculiar phenomenon: a mysterious glow in the open sea occasionally visible at night, known as the milky sea.

resplendent waters

What shines naturally always surprises us, and when it comes to the sea, the effect can be even more incredible.

The bioluminescent creatures that inhabit it offer spectacles as magical as those in the seas of Ardora, where sea sparks light up to the rhythm of the waves or our steps on the sand.

But the phenomenon of milky seas has eluded explanation.

Although it is mentioned sporadically in maritime literature and fiction, few have seen it. And whoever described it wasn’t talking about a short, limited, reactive bioluminescence or blue-green glows, which are the most common. They speak of “a sea of ​​milky whiteness, as if from the nearby headlands came herds of hairy white bears swimming over it”, as Herman Melville wrote in his 1851 “Moby Dick”.


One night in August 2019, Naomi McKinnon was on the deck of the yacht Ganesha when the Indian Ocean lit up.

“Three of the crew were on lookout sailing the boat through the night, making sure to keep the right path to the Cocos Islands, and suddenly the ocean started to look very strange.”

“We asked ourselves: what is wrong with our eyes? Why do they look so strange? And as we sailed, the glow got more intense. We had no idea what was going on,” he told the BBC.

The crew woke Captain Johan Lemmens. “When I came out, I saw that the sea was lit up as if there were big projectors of light underwater.”

“Visually it looked like the boat was floating higher than usual and that we were sailing through a field of snow that glowed with the moon’s glow.”

“And the waves at the bow were black, which was a chilling experience, because normally the waves at the bow are always white and the sea is black.”

McKinnon said the color of the ocean was “a whitish green, like glow-in-the-dark stickers”. “We know because the toilet on the boat was flushing bright water, and the boat was pulling that water at least a meter below sea level.”

They then dropped a bucket into the water for a closer look. “At first we couldn’t see a glow. But when we let the water settle, the glow got more intense.”

“When you looked at the water in the bucket, it had little spots of light, but from the deck the ocean looked smooth.”

And it wasn’t just a part around the boat. “We saw the glow from horizon to horizon. Every ocean we could see was glowing.”

“We were totally blown away. It was extremely beautiful and peaceful. Plus it was a beautiful night to sail so we were blown away by this amazing experience.”


Naomi searched the internet for explanations as soon as she got back ashore. One day, she came across a report from Steve Miller, an Earth observation expert at Colorado State University, who had seen the same glow event off the coast of Java in the Pacific Ocean, but via a satellite.

“The milky sea is my white whale,” Miller told the BBC, referring to Captain Ahab’s obsession in Melville’s classic novel.

“Last year we worked with a new generation of satellites that we were trying to use to find milky seas. In fact, we claim to have seen some milky seas, although we don’t have confirmation directly on the ground.”

“We did everything possible to make sure that what we were seeing were light emissions from the surface, but as a scientist, you never know if you can say 100% that what you think you saw is in fact what you were seeing,” he explained. Miller.

“We would have liked to have data from the water to back up what we saw from the air, but it was difficult to get in touch with boats or people who might have witnessed something. So we took the calculated risk of publishing the work in the hope of finding someone who had it. visa.”

And that’s exactly what happened. “I was so relieved when Naomi contacted me.”

“The Ganesha yacht report provided the first visual confirmation that our new generation of satellite sensors can detect milky seas autonomously.”

“The really important result here is that with confirmation from the surface, we now have confidence in satellite measurements to not only detect this phenomenon and study it remotely, but also guide research vessels to enter the milky seas and learn much more. about them.”

And there was data that could be identified immediately after that encounter, reported in the article “Boat encounter with the 2019 Java bioluminescent milky sea: Views from on-deck confirm satellite detection” from the deck confirm satellite detection”, in free translation), from the Proceedings of the National Academy of Sciences (PNAS).

Naomi, for example, said the sea glistened as far as the eye could see. With satellite observations it was possible to have a more precise idea of ​​this area.

“It’s a remarkable expanse of glistening water, and indeed, historical accounts of the milky seas going back centuries have given pretty much the same kind of description in terms of their experience around it.”

Glitters as ‘propaganda’

Marine biologist Kenneth Nealson, who has long collaborated with Miller on the study of milky seas, has identified another important detail.

Prior to the event south of Java, there was massive algal blooms in the area.

Nealson, who has researched bioluminescent ocean bacteria that feed on dead algae, told the BBC the glow is to attract fish at night to swallow them.

“Most of these bacteria that are able to glow are the E.coli from the sea, they are the intestinal bacteria of the fish.”

“When we defecate E.coli, what these bacteria want is to get back into the gut.”

“In the ocean, if they can find a protein particle, say a dead plankton, and make it glow, that’s fine because in the ocean the glow is a sign that there’s something good to eat.”

So the glow is like an “advertisement” of light.

Individual glowing patches of dead algae can be quickly swallowed by fish, never seen by a passing sailor. But a massive bloom will overwhelm your appetite, and that could be the reason the sea starts to glow.

“It’s basically like growing these bacteria, but instead of 100 milliliters, like in a lab, it’s 100,000 square kilometers.”

“That’s the miraculous thing about these algal blooms, when you get certain areas of upwelling [quando massas de água muito profundas sobem à superfície] and all the nutrients that appear in the algae start to grow like crazy,” said the biologist.

“It’s hundreds of trillions of particles, all glowing at the same time, mingling with the water and giving it this uniformly glowing appearance. That’s what we believe is the process for our visual interpretation of a milky sea,” added Miller.

Between science and folklore

It is not surprising that something as remarkable as this was recorded in the past by sailors who saw it, but “it was a subject that for a long time moved on the fringes of maritime folklore and scientific knowledge”.

And there are still unknowns to solve.

“There weren’t many observations of a scientific nature of the phenomenon, it was mostly anecdotal stories from sailors over the centuries, on trade routes, mostly from the Indian Ocean.”

“And they’re not very common worldwide. Maybe we see one or two milky seas a year, if we’re lucky. But we’ve seen examples of milky seas that last just a day or two, up to 45 days or more… which Ganesha sailed, for example, lasted about 60 nights!”

“It’s great because now we can continue to study them from the sea and the sky until we understand them.”

This text was originally published here.

You May Also Like

Recommended for you

Immediate Peak