Milky seas effect

Milky seas, sometimes confused with mareel, are a luminous phenomenon in the ocean in which large areas of seawater (up to 100,000 km² or 39,000 sq mi) appear to glow diffusely and continuously (in varying shades of blue). Such occurrences glow brightly enough at night to be visible from satellites orbiting Earth. Unlike flashing waves or red-tide luminescence caused by "algae" such as dinoflagellates, milky seas originate from luminous bacteria.

Mariners and other seafarers have reported that the ocean often emits a visible glow which extends for miles at night. In 2005, scientists announced that for the first time, they had obtained photographic evidence of this glow. In a follow-up study, they observed a glow that persisted for over 40 days.

Milky seas are named for the diffuse appearance of the light, since the individual bacteria are too small to make discernible flashes. In the novel Twenty Thousand Leagues Under the Seas, Jules Verne describes the ship as "sailing through a sea of milk."

In the Somali language it is called kaluunka iftiima. The term translates to glowing sea creatures or glowing fish as the word kaluun refers to any bio organism that lives in the sea. It is most commonly used to refer to fish.

Dutch sailors referred to milky seas as the winter sea due to how similar the phenomena looks to a snowy plain at night. Other accounts of milky seas in Dutch refer to the phenomenon as a melkzee which translates to "milky sea."

Between 1915 and 1993, 235 sightings of milky seas were documented, most of which are concentrated in the northwestern Indian Ocean near to Somalia. The luminescent glow is concentrated on the surface of the ocean and does not mix evenly throughout the water column.

In 1985, a research vessel in the Arabian Sea took water samples during milky seas. Their conclusions were that the effect was caused by the bacterium Vibrio harveyi. In 2005, Steven Miller was able to match 1995 satellite images with a first-hand account of a merchant ship. U.S. Defense Meteorological Satellite Program showed the milky area to be approximately 15,400 km² (5,900 sq mi)—roughly the size of Connecticut. The luminescent field was observed to glow over three consecutive nights. In a later study using a newer Day-Night Band sensor, the team was able to observe several additional events, including one from 2019 which covered 100,000 km² (39,000 sq mi) and persisted for over 40 nights.

While monochromatic photos make this effect appear white, Monterey Bay Aquarium Research Institute scientist Steven Haddock (an author of a milky seas effect study) has commented, "the light produced by the bacteria is actually blue, not white. It is white in the graphic because of the monochromatic sensor we used, and it can appear white to the eye because the rods in our eye (used for night vision) don't discriminate color."