Milky seas (Somali: Kaluunka iftiima; English: Milky seas), sometimes confused with mareel, are a luminous phenomenon in the ocean in which large areas of seawater (up to [1]) 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 are originate from luminous bacteria[2] [3] .
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.[4] [5] 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.
Between 1915 and 1993, 235 sightings of milky seas were documented,[6] most of which are concentrated in the northwestern Indian Ocean near to Somalia.[7] The luminescent glow is concentrated on the surface of the ocean and does not mix evenly throughout the water column.[8] 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.[9] 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 15400km2 (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 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."[10]
Milky seas are a different phenomenon than "mareel" which is a term used for dinoflagellate-produced bioluminescent displays in Scotland. Dinoflagellates produce impressive bioluminescent bays, and they are responsible for the light visible in breaking waves, or glowing footprints on the beach. However, the two types of large-scale displays can be distinguished because the bacteria that produce milky seas glow continuously when they are at high concentrations and have sufficient oxygen whereas dinoflagellates flash when physically stimulated.
Zettler . Erik . Mincer . Tracy . Amaral-Zettler . Linda . Life in the "Plastisphere": Microbial Communities on Plastic Marine Debris . . 47 . 13 . 2013 . 7137–7146 . 10.1021/es401288x . 10002632 . 23745679 . 2013EnST...47.7137Z .
1 . 2 . 2010 . James . Mark . Steven . Case . Moline . Haddock . 443–493 . Bioluminescence in the Sea . . 10.1146/annurev-marine-120308-081028 . 21141672 . 2010ARMS....2..443H.
These reviews cite this research.
1242338 . 2005 . Miller . S. D. . Detection of a bioluminescent milky sea from space . Proceedings of the National Academy of Sciences . 102 . 40 . 14181–14184 . Haddock . S. H. . Steven Haddock . Elvidge . C. D. . Lee . T. F. . 10.1073/pnas.0507253102 . 2005PNAS..10214181M . 16186481 . free.