Cartier Island is an uninhabited and unvegetated sand cay in a platform reef in the Timor Sea north of Australia and south of Indonesia. According to the Commonwealth of Nations, the land area of the Cartier Islands is 0.004 square kilometers (0.4 hectares). It is located at 12°31'S 123°33'E, on the edge of the Sahul Shelf, about 300 kilometres off the north west coast of Western Australia, 200 kilometres south of the Indonesian island of Roti, and 70 kilometres south-east of Ashmore Reef. It is within the Territory of Ashmore and Cartier Islands, an external territory of Australia.
The area within 4 nautical miles (7 km) of the centre of the reef is protected as the Cartier Island Marine Reserve. It was declared a Marine Reserve in June 2000. At the southern edge of the reef is a shipwreck of the Ann Millicent, an iron-hulled barge of 944 tons wrecked in 1888. The remains of an RAAF Beaufighter can also be seen at low tide. Formerly used as a bombing range, access to the island is prohibited because of the risk of unexploded ordnances. The area is still a gazetted Defence Practice Area, but is no longer in active use.
The island was charted in 1800 and named after the ship Cartier. Its charted position was somewhat inaccurate until corrected in 1878 during a hydrographic survey by Lieutenant William Tooker in the Airlie. On 5 January 1888 the Ann Millicent was wrecked on the island during a voyage from the Gulf of Carpentaria to Adelaide, South Australia. In 1909 it was annexed by the United Kingdom, but on 23 July 1931 both Ashmore Reef and Cartier Island was transferred to Australia. During World War II it was used as a bombing range.
The Cartier Island Marine Reserve is in an area subject to a Memorandum of Understanding (MOU) signed by Australia and Indonesia in 1974 and reviewed in 1989, which provided for continued Indonesian traditional fishing within limits.
In 2003, environmental authorities closed maritime access to the island and its surrounding reef to build up depleted fish stocks and for safety reasons. Announced as a seven-year closure, Environment Australia planned to monitor levels of marine wildlife, and determine the presence of unexploded ordnance. Prior to that time, the area was frequented by yachts, and fished by Indonesian boats.
- "Ashmore and Cartier Islands". Commonwealth of Nations. Retrieved 2014-04-03.
- Domaschenz, Phil (2001). "Management arrangements for the Ashmore Reef Nature Reserve & Cartier Island Marine Reserve" (PDF). Understanding the Cultural and Natural Heritage Values and Management Challenges of the Ashmore Region (Department of the Environment, Australian Government): 11.
- "Authorities close off Cartier Island". ABC News (Australian Broadcasting Corporation). 2003-06-06.
- Beech, Graeme (2001). "Balancing the cultural and natural heritage values of the Ashmore region" (PDF). Understanding the Cultural and Natural Heritage Values and Management Challenges of the Ashmore Region (Department of the Environment, Australian Government): 7.
- Cartier Island at the Gazetteer of Australia online
- Ashmore and Cartier Islands at CIA - The World Factbook
- Kenneally, Kevin F. (1993). "Ashmore Reef and Cartier Island". Flora of Australia: Volume 50: Oceanic Islands 2. Canberra: AGPS Press. pp. 43–47. ISBN 0-644-14446-7.