Question: When did the ocean where Sidmouth Rock is located become a thing?

full_context: Document 1: Pedra Branca (Tasmania): Pedra Branca is a rock islet or small island, located in the Southern Ocean, off the southern coast of Tasmania, Australia. The island is situated approximately south southeast of South East Cape and is contained within the Southwest National Park, part of the Tasmanian Wilderness World Heritage Site. An erosional remnant of the Tasmanian mainland, the island is approximately long, wide, with an elevation of above sea level. The island is estimated to have separated from the Tasmanian mainland at least 15,000 years ago.
Document 2: Sidmouth Rock: The Sidmouth Rock is a rock islet or small island, located in the Southern Ocean, off the southern coast of Tasmania, Australia. The island is situated approximately south-east of South East Cape and is contained within the Southwest National Park, part of the Tasmanian Wilderness World Heritage Site. An erosional remnant of the Tasmanian mainland with a diameter of , the island is estimated to have separated from the Tasmanian mainland at least 15,000 years ago.
Document 3: Southern Ocean: By way of his voyages in the 1770s, Captain James Cook proved that waters encompassed the southern latitudes of the globe. Since then, geographers have disagreed on the Southern Ocean's northern boundary or even existence, considering the waters as various parts of the Pacific, Atlantic, and Indian Oceans, instead. However, according to Commodore John Leech of the International Hydrographic Organization (IHO), this situation has no scientific sense since it has different ecosystem and life from the three oceans mentioned before and is located on a southern portion of Earth, hence the name of an ocean. This remains the current official policy of the IHO, since a 2000 revision of its definitions including the Southern Ocean as the waters south of the 60th parallel has not yet been adopted. Others regard the seasonally - fluctuating Antarctic Convergence as the natural boundary.
Document 4: Twin Islets: The Twin Islets form a close pair of small, steep-sided, granite islands, with a combined area of 5.61 ha, in south-eastern Australia. They are part of Tasmania’s Hogan Group, lying in northern Bass Strait between the Furneaux Group and Wilsons Promontory in Victoria.
Document 5: Tasman Island: The Tasman Island, part of the Tasman Island Group, is an oval island with an area of , lying close to the south-eastern coast of Tasmania, Australia. The island is located in the Tasman Sea, situated off the Tasman Peninsula and is contained within the Tasman National Park.
Document 6: Rocky Cape National Park: Rocky Cape National Park is a national park on the North West Coast of Tasmania, Australia. It is located at a geographical headland and surrounds the town of Sisters Beach. It is located approximately 365 km by car northwest of State Capital Hobart.
Document 7: Cape of Good Hope: A common misconception is that the Cape of Good Hope is the southern tip of Africa. This misconception was based on the misbelief that the Cape was the dividing point between the Atlantic and Indian Oceans. Contemporary geographic knowledge instead states the southernmost point of Africa is Cape Agulhas about 150 kilometres (90 mi) to the east - southeast. The currents of the two oceans meet at the point where the warm - water Agulhas current meets the cold water Benguela current and turns back on itself. That oceanic meeting point fluctuates between Cape Agulhas and Cape Point (about 1.2 kilometres (0.75 mi) east of the Cape of Good Hope).
Document 8: Antarctica: Positioned asymmetrically around the South Pole and largely south of the Antarctic Circle, Antarctica is the southernmost continent and is surrounded by the Southern Ocean; alternatively, it may be considered to be surrounded by the southern Pacific, Atlantic, and Indian Oceans, or by the southern waters of the World Ocean. It covers more than 14,000,000 km2 (5,400,000 sq mi), making it the fifth-largest continent, about 1.3 times as large as Europe. The coastline measures 17,968 km (11,165 mi) and is mostly characterized by ice formations, as the following table shows:
Document 9: Amundsen Sea: The Amundsen Sea, an arm of the Southern Ocean off Marie Byrd Land in western Antarctica, lies between Cape Flying Fish (the northwestern tip of Thurston Island) to the east and Cape Dart on Siple Island to the west. Cape Flying Fish marks the boundary between the Amundsen Sea and the Bellingshausen Sea. West of Cape Dart there is no named marginal sea of the Southern Ocean between the Amundsen and Ross Seas. The Norwegian expedition of 1928–1929 under Captain Nils Larsen named the body of water for the Norwegian polar explorer Roald Amundsen while exploring this area in February 1929.
Document 10: Borders of the oceans: The Southern Ocean did not appear in the 1953 third edition because ``... the northern limits... are difficult to lay down owing to their seasonal change... Hydrographic Offices who issue separate publications dealing with this area are therefore left to decide their own northern limits. (Great Britain uses the Latitude of 55 ° South) ''. Instead, in the IHO 1953 publication, the Atlantic, Indian and Pacific Oceans were extended southward, the Indian and Pacific Oceans (which had not previously touched pre 1953, as per the first and second editions) now abutted at the meridian of South East Cape, and the southern limits of the Great Australian Bight and the Tasman Sea were moved northwards.
Document 11: Cooperation Sea: The Cooperation Sea was named in 1962 by the Soviet Antarctic Expedition in honor of international science cooperation in Antarctica. The name first appeared as a proposal to the IHO in the IHO 2002 draft. This draft was never approved by the IHO (or any other organization), and the 1953 IHO document (which does not contain the name) remains currently in force. Leading geographic authorities and atlases do not use the name, including the 2014 10th edition of the World Atlas from the United States' National Geographic Society and the 2014 12th edition of the British Times Atlas of the World. But Soviet and Russian-issued maps do.
Document 12: Breaksea Islands (Tasmania): The Breaksea Islands Group is a group of six islands, located in the Southern Ocean, off the south western coast of Tasmania, Australia.
Document 13: Saint Helena: There are several rocks and islets off the coast, including: Castle Rock, Speery Island, the Needle, Lower Black Rock, Upper Black Rock (South), Bird Island (Southwest), Black Rock, Thompson's Valley Island, Peaked Island, Egg Island, Lady's Chair, Lighter Rock (West), Long Ledge (Northwest), Shore Island, George Island, Rough Rock Island, Flat Rock (East), the Buoys, Sandy Bay Island, the Chimney, White Bird Island and Frightus Rock (Southeast), all of which are within one kilometre (0.62 miles) of the shore.
Document 14: Southern Ocean: The Southern Ocean, geologically the youngest of the oceans, was formed when Antarctica and South America moved apart, opening the Drake Passage, roughly 30 million years ago. The separation of the continents allowed the formation of the Antarctic Circumpolar Current.
Document 15: Wilkes Land: Wilkes Land is a large district of land in eastern Antarctica, formally claimed by Australia as part of the Australian Antarctic Territory, though the validity of this claim has been placed for the period of the operation of the Antarctic Treaty, to which Australia is a signatory. It fronts on the southern Indian Ocean between Queen Mary Coast and Adelie Land, extending from Cape Hordern in 100°31' E to Pourquoi Pas Point, in 136°11' E. The region extends as a sector about 2600 km towards the South Pole, with an estimated land area of 2,600,000 km², mostly glaciated. It is further subdivided in the following coastal areas which can also be thought of as sectors extending to the South Pole:
ground_truth: the 1770s
sub_queries: Sidmouth Rock >> located in or next to body of water Answer: Southern Ocean
when did Southern Ocean become a thing Answer: the 1770s