The surreal glowing waters seen by the crew of yacht Ganesha was indeed milky sea

This massive milky sea was spread in more than 100,000 square kilometer area of the Indian ocean.
Rupendra Brahambhatt

When massive sections of ocean water start glowing at night due to the action of luminous bacteria, this phenomenon is called the milky sea. However, milky seas appear very rarely - they are believed to show up only 1-2 times per year and at random locations. Recently, a team of researchers from Colorado State University (CSU) confirmed that the crew of a private yacht Ganesha encountered a milky sea in the south of Java island.

Milky seas produce a strange but steady and widespread marine bioluminescence that occurs in a vast area. While sharing his views about this wonderful phenomenon, lead researcher and professor of atmospheric sciences at CSU, Steven D. Miller told IE, “milky seas are massive bioluminescent displays—the largest known on Earth. I like to call them the unofficial 8th natural wonder of the world!”  

Professor Miller and his team believe that milky seas culminate from a complex coupling (or communication) between the atmosphere, ocean, and marine life. Under suitable conditions, this coupling yields population explosions of luminous bacteria (which are thought to be responsible for the glow). The milky sea phenomenon was first noticed in June 1854 around Java, but interestingly, scientists are still not sure which strains of bacteria cause this unique bioluminescence.  

The strange findings of Ganesha and the science behind them 

The surreal glowing waters seen by the crew of yacht Ganesha was indeed milky sea
Ganesha yacht.  Source: Miller et al. 2022, PNAS

On August 2, 2019, the yacht Ganesha (named after Lord Ganesha, the Hindu god of wisdom and new beginnings) entered a swath of lustrous, glowing water in the Indian Ocean region (between Lombok and Cocos islands) while it was moving on its course to circumnavigate the globe. The crew experienced a milky sea for about eight hours between 9 PM and 5 AM in an area spanning over 100,000 km2.

The CSU study that confirms the bioluminescence is based on the crew member interviews, digital photography, video logs of the yacht, and satellite images of the incident. Moreover, the researchers also analyzed GPS data, log book commentary, and even a dated email from the crew to family the day after their experience, where it was clear they still had no idea about what they had just seen.

 "This is a major expression of our biosphere, and one occurring at the bottom of the marine food chain (i.e., the primary production), so it is very important for us to understand this response way better than we do in only a crude way right now," Professor Miller said about the significance of the milky seas.

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The surreal glowing waters seen by the crew of yacht Ganesha was indeed milky sea
Source: Steven Miller, Leon Schommer (photographer), and Naomi McKinnon, Australian National University, Canberra, Australia

He further added, “this gets at the heart of “earth system science” where we recognize that all the components of the climate system (including life itself) are connected—understanding how these connections change in a changing climate is of utmost importance, especially when it pertains to marine life!” 

The researchers suggest that it is possible there is not just one but many bacteria species that are collectively responsible for the milky sea phenomenon. However, confirming the same is almost impossible because there is no way to sample water with marine bioluminescence. The milky sea phenomenon can appear anywhere and anytime in a water body, and it’s only a matter of chance if you come across one in your lifetime.

Are only luminous bacteria responsible for milky seas?  

Usually, milky seas appear in remote and transient oceanic regions far from the reach of scientists, so most of them are detected using satellite feed. This is why even after 168 years of the first milky sea observation in 1854, scientists don’t know much about the phenomenon. Professor Miller suggests that luminous bacteria are one cause of marine bioluminescence, but maybe it’s not the primary cause; there could be other factors as well.

He believes that by understanding the root cause of milky seas, we can anticipate such future events. So, other than the luminous bacteria, his team is also studying ocean currents, atmospheric circulation, and chemical and biological changes that occur in ocean water due to changes in temperature and climate. 

“We are considering circulations in the atmosphere, which in turn drive ocean currents, on time scales of months to years. How those circulations might translate to changes in oceanic physical, chemical and biological responses, for example, in a changing climate, is a key question in determining whether we will see more or fewer milky seas in the future, and whether they may begin occurring in new areas,” Professor Miller told IE.

Professor Miller has been studying milky seas since 2004 and he thinks that there is still a long journey ahead of him. Along with his team, he will now focus on learning more about atmospheric circulations. He also looks forward to designing advanced satellite sensors that could measure bioluminescence with great efficiency and detail. 

He further added, “Above all, I dream of one day being on a vessel as we cross into a vast milky sea, all of us diving in and basking in its glow! I know, not very scientific, but what inspires us?”

The study is published in the journal PNAS.  


“Milky seas” are massive swaths of uniformly and steadily glowing ocean seen at night. The phenomenon is thought to be caused by luminous bacteria, but details of milky sea composition, structure, cause, and implications in nature remain largely uncertain. Between late July and early September 2019, specialized low-light satellite sensors detected a possible bioluminescent milky sea south of Java, Indonesia, spanning >100,000 km2. Upon learning of these findings, crew members of the yacht Ganesha reached out to confirm and share details of their personal encounter with this same event. Here, we document Ganesha’s experience as recalled by the crew, compare their course to satellite data, and assess their photography of this milky sea.

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