On the trail of the milky ocean: How does the mysterious sea glow come about?

Very rarely, parts of the ocean turn into a milky glowing surface at night.

On the trail of the milky ocean: How does the mysterious sea glow come about?

Very rarely, parts of the ocean turn into a milky glowing surface at night. When and where the mysterious sea glow occurs cannot be predicted - so far. A researcher hopes for better research options.

With the help of satellite data, a mysterious sea glow could in future be localized at an early stage and thus possibly better investigated scientifically. As Steven Miller from the University of California reports, observations of a yacht crew that passed through a so-called "Milky Sea" in the East Indian Ocean in early August 2019 correspond to images from space. The crew's on-site reports dispelled any doubt that the phenomenon could be measured by satellite, Miller writes in the Proceedings of the US National Academy of Sciences.

For centuries there have been reports from seafarers of an unusual and rare nocturnal glow in the sea that gives the surface the appearance of a brightly lit sheet of snow. Such observations have been made in the Northwest Indian Ocean and in a marine region of Southeast Asia between the Indian and Pacific Oceans. The continuous glow is probably produced by bacteria that are capable of bioluminescence, i.e. the emission of visible light, possibly in interaction with microalgae.

Because it is so rare and unpredictable, many questions about the phenomenon remain unanswered to this day. According to Miller, measurements from satellites could now make progress possible: The US Meteorological and Oceanographic Administration (NOAA) operates satellites with an instrument that can also detect very weak light. When evaluating measurement data from the past ten years, a team led by Miller recently found, among other things, indications of a sea glow between July and September 2019 south of the Indonesian island of Java. It covered an area of ​​more than 100,000 square kilometers - about the size of Iceland.

At that time, a private yacht with a crew of seven passed through the sea area - and noticed the nocturnal glow. "When I woke up at 2200, the sea was white. There is no moon, the sea seems to be full of plankton, but the bow wave is black! It looks like sailing on snow!" Aug 2019

After hearing media reports about the satellite measurements of the Milky Sea, the crew shared their own experiences with the researchers. Accordingly, she had pulled a bucket of water on board during the night and identified several points with an even glow in it. Taking the water did not interrupt the glow in the sea, stirring the water darkened.

According to the captain's impression, the glow came from deeper water layers, not from the surface. This speaks against the hypothesis that the phenomenon arises in connection with an organic layer on the water surface, Miller writes in his essay. "Many questions related to the structure, composition and importance of the Milky Sea and its importance can only be fully answered by sampling on site. (...) With newly gained confidence in our space-based observation posts, a targeted expedition to a Milky Sea is moving forward realm of possibility."

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