Milky seas, also called mareel, is a luminous phenomenon in the ocean in which large areas of seawater (up to ) appear to glow

translucently In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimension ...

(in varying shades of blue). Such occurrences glow brightly enough at night to be

visible Visibility, in meteorology, is a measure of the distance at which an object or light can be seen. Visibility may also refer to: * A measure of turbidity in water quality control * Interferometric visibility, which quantifies interference contrast ...

from

satellites A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...

orbiting Earth. 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. It is most likely caused by

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...

Effect

Between 1915 and 1993, 235 sightings of milky seas were documented, most of which are concentrated in the northwestern Indian Ocean and near Indonesia. 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''. Mareel is typically caused by '' Noctiluca scintillans'' (popularly known as "sea sparkle"), a

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

that glows when disturbed and is found in oceans throughout much of the world. In July 2015, at Alleppey, Kerala, India, the phenomenon occurred and the National Institute of Oceanography and Kerala Fisheries Department researched it, finding that the glittering waves were the result of ''Noctiluca scintillans''. In 2005, Steven Miller of the Naval Research Laboratory in

Monterey, California Monterey (; es, Monterrey; Ohlone: ) is a city located in Monterey County on the southern edge of Monterey Bay on the U.S. state of California's Central Coast. Founded on June 3, 1770, it functioned as the capital of Alta California under bo ...

, 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 (roughly the size of Connecticut). The luminescent field was observed to glow over three consecutive nights. While monochromatic photos make this effect appear white, Monterey Bay Aquarium Research Institute scientist

Steven Haddock Steven H. D. Haddock is a marine biologist known for his work on bioluminescence of the jellylike animals of the open ocean and the deep sea, and the photoproteins and fluorescent proteins of these animals. Life Haddock was educated at Harvey Mudd ...

(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." In

Shetland Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...

(where generally caused by ''Noctiluca scintillans''), mareel has sometimes been described as being green, rather than the traditional blue or white milky seas effect seen by the rest of the world. It is not known whether this difference depends on the area, or simply a perception of a

cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK color ...

ic colour as being green.

Etymology

The phenomenon is known as '' mareel'' in Shetland. This term is derived from the Norn word ''*mareld'', which is itself derived from the Old Norse word ''mǫrueldr'', which is a compound of ''marr'' (mere, sea) and ''eldr'' (fire).

Effect

Etymology

Notes

References

Further reading