Milky seas, also called mareel, is a luminous phenomenon in the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

in which large areas of

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appr ...

(up to ) appear to glow translucently (in varying

shades of blue Varieties of the color blue may differ in hue, chroma (also called saturation, intensity, or colorfulness), or lightness (or value, tone, or brightness), or in two or three of these qualities. Variations in value are also called tints and sha ...

). Such occurrences glow brightly enough at night to be visible from satellites

orbiting In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a ...

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. 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.

Effect

Between 1915 and 1993, 235 sightings of milky seas were documented, most of which are concentrated in the northwestern

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...

and near

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

. The luminescent glow is concentrated on the surface of the ocean and does not mix evenly throughout the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

In 1985, a research vessel in the

Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...

took water samples during milky seas. Their conclusions were that the effect was caused by the

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...

'' Vibrio harveyi''. Mareel is typically caused by ''

Noctiluca scintillans ''Noctiluca scintillans'' is a marine life, marine species of dinoflagellate that can exist in a green or red form, depending on the pigmentation in its vacuoles. It can be found cosmopolitan distribution, worldwide, but its geographical species ...

'' (popularly known as "sea sparkle"), a dinoflagellate 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 The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...

in Monterey, California, was able to match 1995

satellite images Satellite images (also Earth observation imagery, spaceborne photography, or simply satellite photo) are images of Earth collected by imaging satellites operated by governments and businesses around the world. Satellite imaging companies sell ima ...

with a first-hand account of a merchant ship. U.S.

Defense Meteorological Satellite Program The Defense Meteorological Satellite Program (DMSP) monitors meteorological, oceanographic, and solar-terrestrial physics for the United States Department of Defense. The program is managed by the United States Space Force with on-orbit operatio ...

showed the milky area to be approximately (roughly the size of

Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capita ...

). The luminescent field was observed to glow over three consecutive nights. While monochromatic photos make this effect appear white,

Monterey Bay Aquarium Research Institute The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foundation ...

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." In Shetland (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 cyanic colour as being green.

Etymology

The phenomenon is known as ''

mareel Mareel is a multi-purpose entertainment venue located on the waterfront of Lerwick, the capital of Shetland. Opening in 2012, the facility includes a music venue, cinema, conference rooms and educational facilities. Facilities Mareel is de ...

'' in Shetland. This term is derived from the

Norn Norn may refer to: *Norn language, an extinct North Germanic language that was spoken in Northern Isles of Scotland *Norns, beings from Norse mythology *Norn Iron, the local pronunciation of Northern Ireland * Norn iron works, an old industrial c ...

word ''*mareld'', which is itself derived from the

Old Norse Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and their overseas settlemen ...

word ''mǫrueldr'', which is a compound of ''marr'' (mere, sea) and ''eldr'' (fire).

Effect

Etymology

Notes

References

Further reading