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Euronews
17-04-2025
- Science
- Euronews
What are milky seas? 400 years of sailors' stories are shedding light on ocean bioluminescence
ADVERTISEMENT 'The whole appearance of the ocean was like a plane covered with snow. There was scarce a cloud in the heavens, yet the sky appeared as black as if a storm was raging.' These are the words written by a sailor in 1854, after encountering the rare phenomenon seafarers called 'milky seas'. These glowing ocean events have baffled humans for centuries. The 'awful grandeur' the nineteenth-century sailor described - which made him think the end was nigh - we now know to be a form of bioluminescence : light emitted by living organisms during chemical reactions in their bodies. But this oceanic bioluminescence is still shrouded in mystery. To try and understand this phenomenon, researchers in the US have created a database combining 400 years of sailors' eyewitness accounts with modern satellite data. Related Toxic dust and stressed seals: What the shrinking Caspian Sea could mean for people and nature Millions of people are tuning in to watch a 24-hour livestream of moose migrating in Sweden The team at Colorado State University (CSU) and the Cooperative Institute for Research in the Atmosphere say this will help research vessels anticipate when and where a milky sea will occur, enabling them to collect samples. 'Milky seas are incredible expressions of our biosphere whose significance in nature we have not yet fully determined,' says Professor Steven Miller, co-author of a new study about the database. '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. 'With the help of this new database, forged from sea-faring ships of the 17th century all the way to spaceships of modern times, we begin to build a bridge from folklore to scientific understanding.' What causes milky seas? From snow white to 'a brilliant and bright green', ghostly grey to turquoise, milky seas have been observed in various shades over the years. They cover a wide distance - sometimes over 100,000 square kilometres - and can last for weeks on end. This steady glow differentiates them from other, more common kinds of bioluminescence in water, like the flashing of plankton. They are so vast and bright that they can sometimes be seen from space. Milky seas are believed to be caused by bacterial activity - most likely from a luminous microscopic bacteria called Vibrio harveyi . This specific strain was found living on the surface of algae within a bloom by a research vessel that managed to take a sample in 1985. But as the milky displays occur only rarely, and typically in remote regions of the Indian Ocean , scientists have struggled to get the biological information to confirm this. 'It is really hard to study something if you have no data about it,' says Justin Hudson, a PhD student in CSU's Department of Atmospheric Science and the paper's first author. 'There is only one known photograph at sea level that came from a chance encounter by a yacht in 2019,' he adds, 'so, there is a lot left to learn about how and why this happens and what the impacts are to those areas that experience this.' Related Scientists were in Antarctica when a giant iceberg broke free. Here's what they found in its shadow HMS Erebus: Can archaeologists solve this 'mysterious puzzle' before climate change stops them? How are milky seas connected to climate events? The new database shows that sightings usually happen around the Arabian Sea and Southeast Asian waters. It also reveals that they are statistically related to the Indian Ocean Dipole and the El Niño Southern Oscillation when sea surface temperatures vary. Since both these climate phenomena can impact global weather, the researchers are curious to know exactly how milky seas are linked to these patterns. 'The regions where this happens the most are around the northwest Indian Ocean near Somalia and Socotra, Yemen, with nearly 60 per cent of all known events occurring there. At the same time, we know the Indian monsoon's phases drive biological activity in the region through changes in wind patterns and currents,' says Hudson. ADVERTISEMENT 'It seems possible that milky seas represent an understudied aspect of the large-scale movement of carbon and nutrients through the Earth system. That seems particularly likely as we learn more and more about bacteria playing a key role in the global carbon cycle both on land and in the ocean.' He notes that the regions where milky seas occur feature a lot of biological diversity and are important economically to fishing operations - so there are significant local implications too. 'We have no idea what milky seas mean for the ecosystems they are found in,' adds Miller. 'They could be an indication of a healthy ecosystem or distressed one - the bacteria we suspect are behind it are a known pest that can negatively impact fish and crustaceans,' he says. ADVERTISEMENT 'Having this data ready allows us to begin answering questions about milky seas beyond hoping and praying a ship runs into one accidentally.'
Yahoo
12-04-2025
- Science
- Yahoo
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
National Geographic
09-04-2025
- Science
- National Geographic
These glowing seas have baffled sailors for centuries. Science may finally have answers.
'It looked as if we were sailing over a boundless plain of snow, or a sea of quicksilver,' writes Captain Kempthorne in his ship's log. Sailing a ship called Moozuffer through the Arabian Sea in January 1849, he witnessed something so rare that there are under 400 known records in 400 years and just one photo. This ghostly phenomenon, called milky seas, has puzzled sailors and scientists for centuries. After delving into centuries of ship logs like Kempthorne's, eyewitness accounts, newspapers, and satellite imagery, Justin Hudson, PhD candidate at Colorado State University (CSU) and Steven Miller, an atmospheric scientist also at CSU, have published the world's largest database of milky sea observations in the journal Earth and Space Science. In it, they write that 'throughout history, this topic has teetered on the edge between myth and scientific knowledge.' But now their database could help to illuminate the centuries-long mystery. A sample taken from a milky seas incident showed the presence of bacteria called Vibrio harveyi, which scientists think could be responsible for this glow. Photograph by Dr. Steve Haddock, Monterey Bay Aquarium Research Institute Rare bioluminescence Milky seas are a rare form of bioluminescence: the light they emit is thought to come from bacteria. Witnesses have described them as 'the most fantastical thing they've ever observed,' Hudson says. They recall night-time seas turning to 'thick milk or cream' and glowing 'as though green neon lights were alight just under the surface of the sea.' According to these eyewitness accounts, it can cause the whole surface of the ocean to shine for months at a time, bright enough to be seen from space. In daylight or moonlight, it vanishes. In the novel 20,000 Leagues Under the Sea, Jules Verne suggests this 'lactified' ocean is caused by a 'diminutive glowworm that's colorless and gelatinous in appearance, as thick as a strand of hair, and no longer than one-fifth of a millimeter.' These NOAA satellite images, taken just two weeks apart in 2019 show an outbreak of bioluminescence in the seas just south of Java, Indonesia. A research vessel that happened upon this phenomenon in 1985 collected water samples that contained a bacteria called Vibrio harveyi, which they hypothesized might be the source of the glow. Like other bacterial bioluminescence, milky seas have a steady, even gleam 'like the glow-in-the-dark plastic stars you can buy your kids,' according to a 1980 U.S. Navy sighting. Accounts indicate that this glow is different from the transient sparkles that occur when plankton create bioluminescence, but the two can happen together. Sailors in 1974 noted that 'bright speckles of marine bioluminescence continued to appear in the water' as they sailed through a milky sea. Among those who witness milky seas, they tend to report the ocean as appearing strangely calm. One captain describes how the unbroken waters 'seemed so dense and solid' that his ship looked like 'she was forcing her way through molten lead.' This might be an optical illusion, or there could be some truth in it. The research vessel that sampled a milky sea in 1985 found bioluminescent bacteria and a type of algae that 'emits this mucus that calms the ocean's surface,' Hudson says. This could account for the eerily flat seas. How the database was compiled People without scientific training 'capture the information completely differently,' says Abigail McQuatters-Gollop a plankton ecologist at University of Plymouth in England, who wasn't involved in the study. 'They never thought it would be used for any ecological study.' Some descriptions found in old documents are too matter-of-fact and vague to know if they're useful. Does 'white water' indicate a milky sea or rough currents? 'I think they did the best job they could do with the kind of data they had available…400 samples over 400 years is really not that much,' says McQuatters-Gollop. 'But I was just intrigued by the whole thing.' Hudson spent around nine months combing through records. Although the descriptions were taken by mariners, this qualitative data is valuable for scientists like the team at CSU. They can pinpoint times and locations that allow scientists to know where to look for more clues. Their rarity makes studying these events almost impossible. Scientists can't 'have a boat permanently sit out there and hope and pray and wait,' Hudson says. The only known photograph was taken by a private yacht sailing just south of Indonesia in 2019. The crew only realized what they'd seen after reading Miller's 2021 Scientific Reports paper. 'There's so much luck involved in witnessing this,' McQuatters-Gollop says. New science emerges from old records These events can span enormous distances, scientists have found. 'Milky seas can exceed [over 38,000 square miles],' Hudson says—that's larger than the state of Indiana—'and last for up to months at a time.' The new database suggests they typically cover around 3,800 square miles, although the data might be skewed because larger milky seas are more noticeable for both satellites and humans. 'The bigger the event, the more likely [people] are to sail to it,' he says. This new database shows that milky seas occur primarily in the Northwest Indian Ocean and in the Maritime Continent—a tropical region between the Indian and Pacific Oceans. The study authors also learned that global climate patterns may play a role in their formation. In summer, 'following a La Niña there are more milky sea events than expected,' Hudson says. In winter, more occur at the peak of the positive Indian Ocean Dipole—when the alternating temperatures on either side of the Indian Ocean are warmer in the west. They may be linked to stronger monsoons. These can cause upwellings, which bring nutrient-rich waters up from the deep, resulting in 'an explosion' in the food chain, he says. By revealing patterns among the complex interactions between these phenomena, this database could help researchers predict and even sample milky seas. For now, milky seas remain enigmatic. 'We don't even know enough about them to know how important they are,' Hudson says. Glimpsing the ghostly spectacle more often might even indicate poor ocean health. 'The bacteria we suspect is causing milky seas is a known pest species that can kill off fish,' Hudson says. If this is the case, fisheries and economies around the world could suffer if these events increase. Says Hudson: 'The ocean is giving a very visible warning sign.'
