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An atoll (), sometimes known as a coral atoll, is a ring-shaped
coral reef A coral reef is an underwater ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient c ...

coral reef
, including a coral rim that encircles a
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' and ''atoll lagoons''. They ...

lagoon
partially or completely. There may be
coral island A coral island is a type of island formed from coral detritus and associated organic material. It occurs in tropical and sub-tropical areas, typically as part of a coral reef which has grown to cover a far larger area under the sea. Ecosystem ...
s or
cay A cay ( or ), also spelled caye or key, is a small, low-elevation, sandy island on the surface of a coral reef A coral reef is an underwater ecosystems, ecosystem characterized by reef-building corals. Reefs are formed of Colony (biolog ...
s on the rim. Two different, well-cited models, the subsidence and antecedent karst models, have been used to explain the development of atolls.Droxler, A.W. and Jorry, S.J., 2021. ''The Origin of Modern Atolls: Challenging Darwin's Deeply Ingrained Theory.'' ''Annual Review of Marine Science'', 13, pp.537-573. According to Charles Darwin's subsidence model, the formation of an atoll is explained by the subsidence of a
volcanic island Geologically, a high island or volcanic island is an island of volcano, volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the Tectonic uplift, uplifting of coral reefs (w ...
around which a coral fringing reef has formed. Over geologic time, the volcanic island became extinct and eroded as it subsides completely beneath the surface of the ocean. As the volcanic island subsides, the coral fringing reef becomes a barrier reef that is detached from the island. Eventually, reef and the small coral islets on top of it are all that is left of the original island, and a lagoon has taken the place of the former volcano. For the atoll to persist, the coral reef must be maintained at the sea surface, with coral growth matching any relative change in sea level (subsidence of the island or rising oceans). An alternative model for the origin of atolls, called the ''antecedent karst'' model, was first proposed by J. E. Hoffmeister,Hoffmeister, J.E., 1930. ''Erosion of elevated fringing coral reefs''. ''Geological Magazine'', 67(12), pp.549-554.Hoffmeister, J.E., and Ladd, H.S., 1935. "The foundations of atolls: a discussion." ''The Journal of Geology'', 43, no. 6, 653-665. later revised by E. G. Prudy,Purdy, E. G., 1974. ''Reef configurations, cause and effect''. In Laporte, L. F. (ed.), ''Reefs in Time and Space''. ''Society of Economic Palaeontologists and Mineralogists Special Publication'' 18, pp. 9–76. and evaluated and modified using a compilation of seismic reflection and drillhole data from various atolls by A. W. Droxler and others. In the antecedent karst model, the first step in the formation of an atoll is the development of a flat top, mound-like coral reef during the subsidence of an oceanic island of either volcanic or nonvolcanic origin below sea level. Then, when relative sea level drops below the level of the flat surface of coral reef, it is exposed to the atmosphere as a flat topped island which is dissolved by rainfall to form limestone karst. Because of hydrologic properties of this karst, the rate of dissolution of the exposed coral is lowest along its rim and the rate of dissolution increases inward to its maximum at the center of the island. As a result, a saucier shaped island with a raised rim forms. When relative sea level submerges the island again, the rim provides a rocky core on which coral grow again to form the islands of an atoll and the flooded bottom of the saucier forms the lagoon within them.


Usage

The word ''atoll'' comes from the Dhivehi word ''atholhu'' ( Dhivehi: , ), meaning the palm of the hand.'' OED'' Dhivehi is an
Indo-Aryan language The Indo-Aryan or Indic languages form a major language family A language is a structured system of communication used by humans, including speech ( spoken language), gestures (Signed language, sign language) and writing. Most languages h ...
spoken in
Maldives Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje IPA: ), officially the Republic of Maldives, is an archipelagic country in the Indian subcontinent of Asia, situated in the Indian Ocean. It lies southwest of Sri Lanka and ...

Maldives
. The word's first recorded English use was in 1625 as ''atollon''.
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
coined the term in his monograph, ''
The Structure and Distribution of Coral Reefs ''The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836'', was published in 1842 as Charles Darwin Charles ...
''. He recognized the word's indigenous origin and defined it as a "circular group of coral islets", synonymously with "lagoon-island". More modern definitions of ''atoll'' describe them as "annular reefs enclosing a lagoon in which there are no other than reefs and
islet An islet is a very small island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll ( ...

islet
s composed of reef
detritus In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...

detritus
" or "in an exclusively morphological sense, a ring-shaped ribbon reef enclosing a lagoon".


Distribution and size

There are approximately 440 atolls in the world. Most of the world's atolls are in the Pacific Ocean (with concentrations in the
Caroline Islands The Caroline Islands (or the Carolines) are a widely scattered archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island An island (or isle) is an isolat ...
, the
Coral Sea Islands The Coral Sea Islands Territory is an external territory of Australia which comprises a group of small and mostly uninhabited tropical islands and reefs in the Coral Sea The Coral Sea () is a marginal sea of the Pacific Ocean, South Pac ...

Coral Sea Islands
, the
Marshall Islands The Marshall Islands, officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ), is an independent near the in the , slightly west of the . Geographically, the country is part of the larger island group of . The countr ...
, the
Tuamotu Islands The Tuamotus, also referred to in English as the Tuamotu Archipelago or the Tuamotu Islands (french: Îles Tuamotu, officially ), are a French Polynesia )Territorial motto: ( en, "Great Tahiti of the Golden Haze") , anthem = "La Marseillaise" , ...
, and the island groups of
Kiribati Kiribati (), officially the Republic of Kiribati (Gilbertese language, Gilbertese: '' ibaberikiKiribati''),
,
Tokelau Tokelau (; "north-northeast"; known previously as the Union Islands, and, until 1976, known officially as the Tokelau Islands) is a dependent territory of New Zealand in the southern Pacific Ocean. It consists of three tropical coral atolls: A ...

Tokelau
, and
Tuvalu Tuvalu ( or ; formerly known as the Ellice Islands Tuvalu ( ; formerly known as the Ellice Islands) is an island country An island country or an island nation is a country A country is a distinct territory, territorial ...

Tuvalu
) and the
Indian Ocean The Indian Ocean is the third-largest of the world's five ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large ...

Indian Ocean
(the
Chagos Archipelago The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) are a group of seven atolls comprising more than 60 individual tropical island upright=1.15, Great_Britain.html"_;"title="Ireland_(lef ...
,
Lakshadweep Lakshadweep (), also known as Laccadives (), is a union territory #REDIRECT Union territory#REDIRECT Union territory A union territory ( hi, script=latn, kendraśāsit pradeś, , centrally administered province) is a type of administrative d ...

Lakshadweep
, the
atolls of the Maldives The Maldives Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje IPA: ), officially the Republic of Maldives, is an archipelagic country in the Indian subcontinent of Asia Asia () is 's largest and most popul ...

atolls of the Maldives
, and the Outer Islands of
Seychelles Seychelles (; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic island country An island country or an island nation is a country A country ...

Seychelles
). The Atlantic Ocean has no large groups of atolls, other than eight atolls east of
Nicaragua Nicaragua (; ), officially the Republic of Nicaragua (), is the largest Sovereign state, country in the Central American isthmus, bordered by Honduras to the northwest, the Caribbean Sea, Caribbean to the east, Costa Rica to the south, and th ...

Nicaragua
that belong to the
Colombia Colombia ( , ; ), officially the Republic of Colombia, is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses. Generally identified by conv ...

Colombia
n department of San Andres and Providencia in the Caribbean. Reef-building corals will thrive only in warm
tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S; these latitudes correspond to ...

tropical
and
subtropical The subtropical zones or subtropics are geographical Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country locat ...

subtropical
waters of oceans and seas, and therefore atolls are found only in the tropics and subtropics. The northernmost atoll of the world is
Kure Atoll Kure Atoll (; haw, Mokupāpapa) or Ocean Island is an atoll in the Pacific Ocean west-northwest of Midway Atoll in the Northwestern Hawaiian Islands at . There is a coral ring six miles across that encloses a shallow lagoon several meters ...
at 28°24′ N, along with other atolls of the
Northwestern Hawaiian Islands The Northwestern Hawaiian Islands or Leeward Islands are the small island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent ...
. The southernmost atolls of the world are
Elizabeth Reef Elizabeth Reef is a coral reef in the Coral Sea. The reef is separated by a deep oceanic pass, some 45 km wide, from nearby Middleton Reef, both of which are part of the underwater plateau known as the Lord Howe Rise. It is around 1 ...
at 29°58′ S, and nearby
Middleton Reef Middleton Reef is a coral reef A coral reef is an underwater ecosystem An ecosystem is a community (ecology), community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. The ...
at 29°29′ S, in the
Tasman Sea The Tasman Sea (Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders ...

Tasman Sea
, both of which are part of the
Coral Sea Islands The Coral Sea Islands Territory is an external territory of Australia which comprises a group of small and mostly uninhabited tropical islands and reefs in the Coral Sea The Coral Sea () is a marginal sea of the Pacific Ocean, South Pac ...

Coral Sea Islands
Territory. The next southerly atoll is
Ducie Island Ducie Island is an uninhabited atoll in the Pitcairn Islands. It lies east of Pitcairn Island, and east of Henderson Island, and has a total area of , which includes the lagoon Garabogaz-Göl lagoon in Turkmenistan A lagoon is a sh ...
in the
Pitcairn Islands The Pitcairn Islands (; Pitkern: '), officially the Pitcairn, Henderson, Ducie and Oeno Islands, is a group of four volcanic islands in the southern Pacific Ocean that form the sole British Overseas Territories, British Overseas Territory in t ...
Group, at 24°40′ S. The atoll closest to the Equator is
Aranuka Aranuka is an atoll An atoll (), sometimes known as a coral atoll, is a ring-shaped coral reef A coral reef is an underwater ecosystem An ecosystem is a community (ecology), community of living organisms in conjunction with the nonli ...
of Kiribati. Its southern tip is just 12 km (7 miles) north of the Equator.
Bermuda ) , anthem = "God Save the Queen "God Save the Queen", alternatively "God Save the King" (dependent on the gender of the reigning monarch), is the or in most s, their territories, and the British . The author of the tune is unknown, ...

Bermuda
is sometimes claimed as the "northernmost atoll" at a
latitude In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the ...

latitude
of 32°24′ N. At this latitude, coral reefs would not develop without the warming waters of the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Drift The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current Boundary curren ...
. However, Bermuda is termed a ''
pseudo-atoll A pseudo-atoll, like an atoll, is an island upright=1.15, Great_Britain.html"_;"title="Ireland_(left)_and_Great_Britain">Ireland_(left)_and_Great_Britain_(right),_are_large_islands_of_north-west_Europe image:Small_Island_in_Lower_Saranac_Lake ...
'' because its general form, while resembling that of an atoll, has a very different mode of formation. In most cases, the land area of an atoll is very small in comparison to the total area. Atoll islands are low lying, with their elevations less than 5 meters (16'). Measured by total area,
Lifou Lifou is a commune A commune is an intentional community of people sharing living spaces, interests, values, beliefs, and often property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or wi ...
(1146 km2; 442 sq. mi.) is the largest
raised coral atoll A raised coral atoll or uplifted coral atoll is an atoll An atoll (), sometimes known as a coral atoll, is a ring-shaped coral reef A coral reef is an underwater ecosystems, ecosystem characterized by reef-building corals. Reefs are fo ...
of the world, followed by
Rennell Island Rennell Island, locally known as Mugaba, is the main island of two inhabited islands that make up the Rennell and Bellona Province in the Solomon Islands Solomon Islands is a sovereign state consisting of six major islands and over 900 s ...
(660 km2; 255 sq. mi.). More sources, however, list
Kiritimati Kiritimati (also known as Christmas Island) is a Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, t ...

Kiritimati
as the largest atoll in the world in terms of land area. It is also a raised coral atoll (321.37 km2; 125 sq. mi. land area; according to other sources even 575 km2; 2220 sq. mi.), 160 km2 (62 sq. mi.) main lagoon, 168 km2 (65 sq. mi.) other lagoons (according to other sources 319 km2 total lagoon size; 123 sq. mi.). The remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is
Aldabra Aldabra is the world's second-largest coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members ...
, with 155 km2 (60 sq. mi.). The largest atoll in terms of island numbers is
Huvadhu Atoll Huvadhu is a large atoll located south of the Suvadiva Channel the Republic of Maldives. Etymologically it was called Suvadhinmathi, Suvadiva or haddhun'mathi with a total area of 3152 km², of which 38.5 km² is dry land. The atoll cont ...
in the south of the Maldives, with 255 islands.


Formation

In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard HMS Beagle from 1831 to 1836. Darwin's explanation suggests that several tropical island types: from high volcanic island, through barrier reef island, to atoll, represented a sequence of gradual subsidence of what started as an oceanic volcano. He reasoned that a fringing coral reef surrounding a volcanic island in the tropical sea will grow upward as the island subsides (sinks), becoming an "almost atoll", or barrier reef island, as typified by an island such as Aitutaki in the Cook Islands, and Bora Bora and others in the Society Islands. The fringing reef becomes a barrier reef for the reason that the outer part of the reef maintains itself near sea level through biotic growth, while the inner part of the reef falls behind, becoming a lagoon because conditions are less favorable for the coral and calcareous algae responsible for most reef growth. In time, subsidence carries the old volcano below the ocean surface and the barrier reef remains. At this point, the island has become an atoll. As formulated by J. E. Hoffmeister, F. S. McNeil,MacNeil, F.S., 1954. ''The shape of atolls; an inheritance from subaerial erosion forms''. ''American Journal of Science'', 252(7), pp.402-427. E. G. Prudy, and others, the antecedent karst model argues that atolls are Pleistocene features that are the direct result of the interaction between subsidence and preferential karst dissolution that occurred in the interior of flat topped coral reefs during exposure during glacial lowstands of sea level. The elevated rims along an island created by this preferential karst dissolution become the sites of coral growth and islands of atolls when flooded during interglacial highstands. The research of A. W. Droxler and others supports the antecedent karst model as they found that the morphology of modern atolls are independent of any influence of an underlying submerged and buried island and are not rooted to an initial fringing reef /barrier reef attached to a slowly subsiding volcanic edifice. In fact, the Neogene reefs underlying the studied modern atolls overlie and completely bury the subsided island are all non-atoll, flat-topped reefs. In fact, they found that atolls did not form doing the subsidence of an island until MIS-11, Mid-Brunhes, long after the many the former islands had been completely submerged and buried by flat topped reefs during the Neogene. Atolls are the product of the growth of tropical marine organisms, and so these islands are found only in warm tropical waters. Volcanic islands located beyond the warm water temperature requirements of
hermatypic Hermatypic corals are those corals in the order Scleractinia which build reefs by depositing hard calcareous material for their skeletons, forming the stony framework of the reef. Corals that do not contribute to coral reef development are referred ...
(reef-building) organisms become
seamount A seamount is a large geologic landform that rises from the ocean floor The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
s as they subside, and are eroded away at the surface. An island that is located where the ocean water temperatures are just sufficiently warm for upward reef growth to keep pace with the rate of subsidence is said to be at the Darwin Point. Islands in colder, more polar regions evolve toward seamounts or
guyot In marine geology Marine geology or geological oceanography is the study of the history and structure of the ocean floor. It involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and co ...

guyot
s; warmer, more equatorial islands evolve toward atolls, for example
Kure Atoll Kure Atoll (; haw, Mokupāpapa) or Ocean Island is an atoll in the Pacific Ocean west-northwest of Midway Atoll in the Northwestern Hawaiian Islands at . There is a coral ring six miles across that encloses a shallow lagoon several meters ...
. Atoll forming-volcano.png, Darwin's theory starts with a
volcanic island Geologically, a high island or volcanic island is an island of volcano, volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the Tectonic uplift, uplifting of coral reefs (w ...
which becomes extinct Atoll forming-Fringing reef.png, As the island and ocean floor subside, coral growth builds a
fringing reef A fringing reef is one of the three main types of coral reef. It is distinguished from the other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows direct ...
, often including a shallow lagoon between the land and the main reef Atoll forming-Barrier reef.png, As the subsidence continues the fringing reef becomes a larger barrier reef farther from the shore with a bigger and deeper
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' and ''atoll lagoons''. They ...

lagoon
inside Atoll forming-Atoll.png, Ultimately the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon
Coral atolls are important as sites where
dolomitization Dolomitization is a geological process by which the carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salt ...
of calcite occurs. Several models have been proposed for the dolomitization of
calcite Calcite is a carbonate mineral Carbonate minerals are those mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid E ...

calcite
and
aragonite Aragonite is a , one of the three most common naturally occurring of , (the other forms being the s and ). It is formed by biological and physical processes, including precipitation from marine and freshwater environments. The of aragonite d ...

aragonite
within them. They are the evaporative, seepage-reflux, mixing-zone, burial, and seawater models. Although the origin of replacement
dolomites german: Dolomiten , photo=Val Gardena with Sella and Saslonch from Resciesa.JPG , photo_size= 285px , photo_caption=The Western Dolomites in Gherdëina , country= Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubbl ...
remains problematic and controversial, it is generally accepted that seawater was the source of magnesium for dolomitization and the fluid in which calcite was dolomitized to form the dolomites found within atolls. Various processes have been invoked to drive large amounts of seawater through an atoll in order for dolomitization to occur.Budd, D.A., 1997. ''Cenozoic dolomites of carbonate islands: their attributes and origin''. ''Earth-Science Reviews'', 42(1-2), pp.1-47.Wheeler, C.W., Aharon, P. and Ferrell, R.E., 1999. ''Successions of late Cenozoic platform dolomites distinguished by texture, geochemistry, and crystal chemistry; Niue, South Pacific''. ''Journal of Sedimentary Research'', 69(1), pp.239-255.Suzuki, Y., Iryu, Y., Inagaki, S., Yamada, T., Aizawa, S. and Budd, D.A., 2006. ''Origin of atoll dolomites distinguished by geochemistry and crystal chemistry: Kita-daito-jima, northern Philippine Sea''. ''Sedimentary Geology'', 183(3-4), pp.181-202.


Investigation by the Royal Society of London into the formation of coral reefs

In 1896, 1897 and 1898, the
Royal Society of London The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. Founded on 28 November 1660, it was granted a royal charter by Charles II of ...
carried out drilling on
Funafuti Funafuti is an atoll and the capital of the island nation of Tuvalu. It has a population of 6,320 people (2017 census), making it the country's most populous atoll, with 60.15 percent of Tuvalu's population. It consists of a narrow sweep of ...

Funafuti
atoll in
Tuvalu Tuvalu ( or ; formerly known as the Ellice Islands Tuvalu ( ; formerly known as the Ellice Islands) is an island country An island country or an island nation is a country A country is a distinct territory, territorial ...

Tuvalu
for the purpose of investigating the formation of coral reefs. They wanted to determine whether traces of shallow water organisms could be found at depth in the
coral Corals are marine invertebrates Marine invertebrates are the invertebrates that live in marine habitats. Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a ver ...

coral
of Pacific atolls. This investigation followed the work on
the structure and distribution of coral reefs ''The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836'', was published in 1842 as Charles Darwin Charles ...
conducted by
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
in the Pacific. The first expedition in 1896 was led by Professor
William Johnson Sollas Prof William Johnson Sollas PGS FRS FRSE Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and Literature, letters, judged to be ...
of the
University of Oxford The University of Oxford is a collegiate university, collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the List of oldest universit ...
. Geologists included Walter George Woolnough and
Edgeworth David Sir Tannatt William Edgeworth David (28 January 1858 – 28 August 1934) was a Welsh Australian geologist and Heroic Age of Antarctic Exploration, Antarctic explorer. A household name in his lifetime, David's most significant achievements ...

Edgeworth David
of the
University of Sydney The University of Sydney (USYD, or informally Sydney Uni) is a public In public relations Public relations (PR) is the practice of managing and disseminating information from an individual or an organization An organization, ...

University of Sydney
. Professor Edgeworth David led the expedition in 1897. The third expedition in 1898 was led by Alfred Edmund Finckh.


United States national monuments

On January 6, 2009, U.S. President
George W. Bush George Walker Bush (born July 6, 1946) is an American politician and businessman who served as the 43rd president of the United States The president of the United States (POTUS) is the head of state and head of government of the Un ...

George W. Bush
announced the creation of the
Pacific Remote Islands Marine National Monument The Pacific Remote Islands Marine National Monument is a group of unorganized, mostly unincorporated United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguou ...
, covering several islands and atolls under U.S. jurisdiction.


See also

* *
Low island Geologically, a low island is an island of coral origin. The term applies whether the island was formed as a result of sedimentation upon a coral reef or of the tectonic uplift, uplifting of such islands. The term is used to distinguish such is ...
* Nukuoro Atoll * Kapingamarangi Atoll


References

* Dobbs, David. 2005. ''Reef Madness: Charles Darwin, Alexander Agassiz, and the Meaning of Coral''. Pantheon. * Fairbridge, R. W. 1950. "Recent and Pleistocene coral reefs of Australia". ''J. Geol.'', 58(4): 330–401. * McNeil, F. S. 1954. "Organic reefs and banks and associated detrital sediments". ''Amer. J. Sci.'', 252(7): 385–401.


External links


Formation of Bermuda reefs


– a short video discussing Darwin and Agassiz' coral reef formation debate

* ttps://oceanservice.noaa.gov/facts/threecorals.html NOAA National Ocean Service - What are the three main types of coral reefs?
Research Article: Predicting Coral Recruitment in Palau’s Complex Reef Archipelago

World Atolls, Goldberg 2016: A global map containing all atolls
{{coastal geography Coastal and oceanic landforms Oceanographical terminology Biogeomorphology Islands by type