What Causes Swaths of the Ocean to Glow a Magnificent Milky Green?
A sailor who witnessed the rare phenomenon in person and a scientist who saw it from the sky team up to learn about the ghostly light
Sam Keck Scott, Hakai
June 27, 2022
The sky was moonless and overcast, leaving no stars to steer by. Alone at the helm in the middle of the Arabian Sea, somewhere between Oman and India, I could see nothing in the ink-black night save for our ship’s dimly lit compass rolling on its gimbal mount as we heaved and swayed through three-meter seas. But half an hour into my shift, the sails above me began to glow, as if the moon had risen. But there was no moon, nor any stars or other ships. The light, it seemed, was coming from below and growing in intensity. Soon the entire ocean was glow-stick green, but muted, as if the light were shining through a sea of milk.
It was August 2010, and I’d been sailing for over two months by then, volunteering with the NGO the Biosphere Foundation to deliver the Mir, a 35-meter ketch they’d recently acquired in Malta, back to their home port in Singapore. During the voyage, I’d grown accustomed to the usual “sea sparkle” caused by dinoflagellates that ignite when the water is agitated, causing ribbons of light to twist off the Mir’s bow. But this was not that. This was the whole of the ocean, as far as I could see, glowing a uniform, opaque green. Despite the compass still wheeling in its mount, the light in the water created an optical illusion, making the sea appear perfectly calm, as if we were gliding through phosphorescent skies rather than roiling seas.
I woke the rest of the crew, and for over four hours we remained engulfed in this sea of green light, wonderstruck, with no idea what it was we were witnessing. Finally, a razor-sharp line appeared ahead of us where the lambent sea ended and blackness began. Crossing it, we left behind that numinous phantom world and re-entered a familiar one, though we could still see the gauzy green glow to our stern for another hour before it disappeared. It wasn’t until we arrived at port 10 days later that we would learn the name for the eerie phenomenon that had surrounded us: a milky sea.
For centuries, sailors have been describing milky seas, rare occurrences where enormous expanses of the ocean light up uniformly at night, at times stretching for tens of thousands of square kilometers, or more. W. E. Kingman, captain of the clipper Shooting Star, had this to say upon witnessing one in 1854: “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.”
More:
https://www.smithsonianmag.com/science-nature/what-causes-swaths-of-the-ocean-to-glow-a-magnificent-milky-green-180980296/