Scientists Link Centuries-Old Ocean Glow Mystery To Weather And Climate Patterns

Imagine being a sailor crossing the Indian Ocean 400-years ago and suddenly witnessing a vast area of glowing ocean water as far as the eye can see. This blue-green glow was so bright it could light up the night sky. At times, lasting for months and stretching as far as 40,000 square miles. This rare phenomenon was coined “milky seas” and has haunted sailors for centuries. However, a team of scientists from Colorado State University recently compiled data that dates as far back as the 1700s and discovered there may be a hidden driver behind this mysterious ocean phenomenon: the weather.

“The regions where this happens the most are around the northwest Indian Ocean near Somalia and Socotra, Yemen, with nearly 60% of all known events occurring there,” said Justin Hudson, a Ph.D. student in the Department of Atmospheric Science at CSU and the paper’s first author.

One sailor in 1854 described what he saw:

“The scene was one of awful grandeur – the sea having turned to phosphorus, and the heavens being hung in blackness, and the stars going out seemed to indicate that all nature was preparing for that last grand conflagration, which we are taught to believe is to annihilate this material world.”

While milky seas have been well-documented, their trigger was largely unknown until now. Researchers recently found a relationship between when the incidents occurred and the overlap of the monsoon season, which possibly holds the key to predicting future events.

More questions than answers still remain, but scientists believe that an increase in milky seas events could be associated with deep-water upwelling, which brings nutrient rich water to the surface during the summer monsoon months. Driven by strong winds, this not only occurs during monsoon season, but can also occur during the Indian Ocean Dipole, which is a phenomenon similar to El Niño.

What creates this glow?

Milky seas are caused by a phenomenon called bioluminescence, which is the ability for living things to emit light. The most common example of this is a firefly. While bioluminescence is very rare on land, it’s quite common in the ocean. It’s estimated that 80% of the organisms that live within 650 to 3,000 feet underwater are bioluminescent.

However, milky seas are different because they are a widespread, uniform and continuous glow that spans vast areas of the ocean.

Weather And Climate Could Be The Driver Of Milky Seas

A research vessel happened to encounter milky seas in 1985 and was able to gather a water sample that showed a specific bioluminescent bacteria. Hudson believes the light is produced by a biological process related to the bacteria.

“We know the Indian monsoon’s phases drive biological activity in the region through changes in wind patterns and currents,” Hudson said. “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.”

Though milky seas still remain somewhat a mystery, scientists are one step closer in cracking the code to this mysterious phenomenon that has plagued sailors for centuries.

“Milky seas are incredible expressions of our biosphere whose significance in nature we have not yet fully determined,” said Miller. Adding, “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.”

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world’s biggest weather and climate stories for the last two decades.