Nikumaroro, previously known as Kemins Island or Gardner Island, is a part of the Phoenix Islands, Kiribati, in the western Pacific Ocean. It is a remote, elongated, triangular coral atoll with profuse vegetation and a large central marine lagoon. Nikumaroro is about 7.5 km (4.7 mi) long by 2.5 km (1.6 mi) wide. The rim has two narrow entrances, both of which are blocked by a wide reef, which is dry at low tide. The ocean beyond the reef is very deep, and the only anchorage is at the island's west end, across the reef from the ruins of a mid-20th-century British colonial village, but this is safe only with the southeast trade winds. Landing has always been difficult and is most often done south of the anchorage. Although occupied at various times during the past, the island is uninhabited today.

Kiribati declared the Phoenix Islands Protected Area in 2006, with the park being expanded in 2008. The 425,300-km (164,200-mi) marine reserve contains eight coral atolls including Nikumaroro.

Nikumaroro has notably been the focus of considerable speculation and exploration as a possible location where pilot Amelia Earhart and navigator Fred Noonan might have landed in July 1937 when they vanished during their ill-fated flight to circumnavigate the globe. However, to date, no conclusive evidence of her plane has been found on or in the vicinity of the island.

Thick scrub and Pisonia forest cover the land surface. The trees grow 15 m (49 ft) in height and result in decomposing leaf material in the soil. Coconut palms remain from the attempts to operate a plantation on the island from 1893 to 1894 and later from 1938 to 1963.

The scarcity of fresh water on Nikumaroro has proven problematic for residents in the past, and contributed directly to the failure of a British project to colonize the island from 1938 to 1963.

Nikumaroro is sporadically visited by biologists attracted to its extensive marine and avian ecosystems. The atoll has populations of coconut crabs and migratory birds, and rats abound. Several species of sharks and bottlenose dolphins have been observed in the surrounding waters.

The island is part of the Phoenix Islands Protected Area, and as such, has been named an Important Bird Area, especially for its breeding colony of red-tailed tropicbirds.

The 2000 surveys (Obura, et al.) identified that the leeward sites on the reef had 25-40% Live Coral Cover (LCC), in some places exceeding 75% LCC on the shallow reef platforms. Coralline algae, Halimeda and coral rubble were the three other dominant cover categories. The windward sites on the reef had an estimated 70% LCC and the lower cover on the reef slope was 30% LCC. The steep slope was dominated by Halimeda with plates of Porites rus. In contrast to the leeward side, very little loose coral rubble was found with the majority of bare surfaces covered by encrusting coralline algae in shallow water. The most abundant coral species at Nikumaroro included: Acroporidae (staghorn corals); Acropora cytherea; Montipora efflorescens; Favites pentagona; Leptastrea purpurea; Pocillopora verrucosa; Pavona minuta and Pavona varians.

Nikumaroro is in a naturally iron-poor region. The introduction of iron to this environment from shipwrecks and anchor gear is linked to proliferation of turf algae and benthic bacterial communities, and degraded ‘black reefs’. Monitoring from 2000 to 2015 recorded the black reef originating at the 1929 wreck of the SS Norwich City on Nikumaroro progressing northward to sites 1 kilometre (1 mi) away.

Little is known of habitation on the island prior to 1824. What evidence there is for pre-historic occupation is slim and unsubstantiated.

In 1989, an expedition to the island by TIGHAR suggested that what they believed to be fish traps on the shore of the island was indeed evidence of long forgotten pacific natives. Also found by TIGHAR's work party was what was believed to be a basalt adze.

The ancient settlements on nearby Manra and Orona Island were probably founded around 1000 BC, when eastern Melanesians are known to have travelled northwards across the water. These have yielded basalt artifacts that originated in Samoa, the Marquesas, and the Cook Islands, and were transported to the Phoenix and Line Islands during the 12th–14th centuries AD. There is evidence to suggest that Howland Island was the site of a prehistoric settlement, which may have extended down to Rawaki, Canton, Manra and Orona - and possibly Nikumaroro. Archaeological sites have been discovered on Manra and Orona that suggest there were two distinct groups of settlers in the area, one from eastern Polynesia, and one from Micronesia.

Nikumaroro was known by sundry names during the early 19th century: Kemins' Island, Kemis Island, Motu Oonga, Motu Oona, and Mary Letitia's Island. The first record of a European sighting was made by Capt. C. Kemiss (or Kemin, Kemish) from the British whaling ship Eliza Ann in 1824. On 19 August 1840, the USS Vincennes of the U.S. Exploring Expedition confirmed its position and recorded the atoll's name as Gardner Island, originally given in 1825 by Joshua Coffin of the Nantucket whaler Ganges. Some sources say the island was named after U.S. Congressman Gideon Gardner, who owned the Ganges.

In 1856, Nikumaroro was claimed as "Kemins Island" by CA Williams & Co. of New London, Connecticut, under the American Guano Islands Act. No record exists of guano deposits ever being exploited, however. On 28 May 1892, the island was claimed by the United Kingdom during a call by HMS Curacoa. Almost immediately, a license was granted to Pacific entrepreneur John T. Arundel for planting coconuts. Twenty-nine islanders were settled there and some structures with corrugated iron roofs were constructed, but a severe drought resulted in the failure of this project within a year. In 1916, it was leased to a Captain E.F.H. Allen of the Samoa Shipping Trading Co Ltd, but remained uninhabited until 1938.

During a storm on 29 November 1929, the SS Norwich City, a large unladen British freighter with a crew of 35 men, ran aground on the reef at the island's northwest corner. A fire broke out in the engine room and all hands abandoned ship in darkness through storm waves across the dangerous coral reef. There were 11 fatalities. The survivors camped near collapsed structures from the abortive Arundel coconut plantation and were rescued after several days on the island. The devastated wreck of the Norwich City was a prominent landmark on the reef for 70 years, although by 2007, only the ship's keel, engine, and two large tanks remained. A Digital Globe satellite image taken 15 November 2016 shows one of the two tanks pushed inland by wave action, and the engine is now gone.

Amelia Earhart attempted her world flight in 1937, but she and navigator Fred Noonan disappeared after the plane left Lae, New Guinea, and headed for Howland Island. Nikumaroro Island—then called Gardner Island—is about 640 kilometres (400 mi) southeast of Howland Island. During the subsequent search for them and their plane, the United States Navy checked several nearby islands, and flew over Gardner Island, noting "signs of recent habitation", though they presumed the island was uninhabited. A British exploratory expedition visited Gardner Island in October 1937 but found nothing. In 1938, recent skeletal remains were found on the island, but they were not linked to Earhart's flight.

The International Group for Historic Aircraft Recovery (TIGHAR) made several expeditions to Nikumaroro during the 1990s, 2000s, and 2010s. The group investigated the renewed hypothesis that Earhart and Noonan had landed on Gardner Island after they had failed to find Howland Island, and died as castaways. TIGHAR found and cataloged artifacts: U.S. beauty and skin-care products that may have dated to the 1930s, such as flakes of rouge and a shattered mirror from a woman's cosmetic compact, parts of a folding pocket knife, traces of campfires bearing bird and fish bones, clams opened in the same way as oysters in New England, "empty shells laid out as if to collect rain water", and U.S. bottles dating from before World War II. What appeared to be the phalanx bone of a human finger had DNA tests done, but the tests were inconclusive as to whether it was turtle or human bone. A piece of aircraft-grade aluminum found on the island closely resembles a patch that is in photographs of Earhart's airplane.

The TIGHAR hypothesis has various critics, with TIGHAR's founder and executive director, Richard Gillespie, described as a good showman who lacks credible results. A curator at the Smithsonian Institution's Air and Space Museum said: "Not to impugn [Gillespie], but I don't think he's found anything on any expedition." To date, TIGHAR has failed to connect any of their artifacts to Earhart, Noonan, or to any specific person or people known to have been on the island from 1929 to present. TIGHAR has failed to provide any dating to establish how long any of the artifacts were in the ground, nor has it provided evidence as to when the artifacts may have arrived on the island.

Ocean explorer Robert Ballard led a 2019 expedition to locate Earhart's Lockheed Model 10-E Electra or evidence that it landed on Nikumaroro. After days of searching the deep cliffs supporting the island and the nearby ocean, Ballard did not find any evidence of the plane or any associated wreckage of it. Allison Fundis, Ballard's chief operating officer stated: "We felt like if her plane was there, we would have found it pretty early in the expedition."

In their October 2019 documentary, "Expedition Amelia" tracing Robert Ballard's efforts, National Geographic stated regarding the Gardner Island (Nikumaroro) hypothesis, "It’s a nice story. But like all the other evidence obtained here over the decades, there is no provable link to Amelia or her plane."

On 1 December 1938, members of the British Pacific Islands Survey Expedition arrived to evaluate the island as a possible location for either seaplane landings or an airfield. On 20 December, more British officials arrived with 20 Gilbertese settlers in the last colonial expansion of the British Empire (other than formal annexations preparatory to withdrawal, etc.).

The British colonial officer Gerald Gallagher established a headquarters of the Phoenix Islands Settlement Scheme in the village located on the island's western end, on the south side of the largest entrance to the lagoon. Efforts to clear land and plant coconuts were hindered by a lack of drinking water. By June 1939, a few wells had been successfully established and 58 I-Kiribati were on Gardner, comprising 16 men, 16 women, and 26 children. Wide coral-gravel streets and a parade ground were laid out and important structures included a thatched administration house, a wood-frame cooperative store, and a radio shack. Gallagher died and was buried on the island in 1941.

At his mother's request, Gallagher's remains were moved to Tarawa for reburial and the memorial plaque was retrieved. Although reasons cited for giving up on the struggling colony included unstable water lenses and uncertain copra markets, observers familiar with the colony's history remarked that after Gallagher's death a "will" or "nerve" to succeed seemed to vanish from the settlements.

From 1944 through 1945, the United States Coast Guard operated a navigational LORAN station with 25 crewmen on the southeastern tip of Gardner, installing an antenna system, quonset huts, and some smaller structures. Only scattered debris remains on the site.

The island's population reached a high of about 100 by the mid-1950s, but by the early 1960s, periodic drought and an unstable freshwater lens had thwarted the struggling colony. Nikumaroro (together with Manra and Orona) was evacuated by the British government in 1963. Its residents were evacuated to the Solomon Islands by the British, and by 1965, Gardner was officially uninhabited.

The Gardner Island Post Office opened around 1939 and closed around January 1964.

In 1971, the UK granted self-rule to the Gilbert Islands, which achieved complete independence in 1979 as Kiribati. That same year, the United States, after having recently surveyed the island for possible weapons testing, relinquished any claims to Gardner through the Treaty of Tarawa. The island was officially renamed Nikumaroro, a name inspired by Gilbertese legends and used by the settlers during the 1940s and 1950s.

The current name for the Island, Nikumaroro, comes from the name of a legendary goddess of the Gilbertese people, "Nei Manganibuka". It is said that she comes from Samoa, is associated with the Buka tree, and first taught the Gilbertese canoe craft along with the lore of ocean navigation. Nikumaroro was named by the natives who accomanied the British during a visit to the island in 1938. In Tungaru (Gilbertese), “Nei” is roughly the equivalent of Miss or Ms, and “Manganibuka” means “old woman of the Buka trees.”

In an interview in 1997, Risasi Finikaso, who lived in Nikumaroro as a child, remarked of a place called Niurabo which was sacred to Nei Manganibuka.

According to legend, the wife of Teng Koata, the first island leader of Nikumaroro, had been walking along the north-western part of the island when she saw a "great and perfect maneaba". It is said that this was the maneaba of Nei Manganibuka who she saw sitting under its high thatched roof. Nei Manganibuka was seated with two children, and conversing with three ancients about the happy future of Nikumaroro and how it would one day support thousands of inhabitants. In later years this spot became known as Ghost Maneaba, though the area is now known as Kanawa Point.

• List of Guano Island claims
• List of islands
• Desert island
• Phoenix Islands

• Geographical map of Nikumaroro (Earhart related)
• Earhart Project Hypothesis, Summer 2009
• Forensic Imaging Project II (Earhart related)
• Miamiherald.com: Planned July 2012 search for Earhart
• Tighar.org: Hydrographic Office Chart 125
• Natlib.govt.nz: 1889 Survey catalog entry
• http://www.loran-history.info/Gardner_Island/gardner.htm