Ross Sea
The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land and within the Ross Embayment, and is the southernmost sea on Earth. It derives its name from the British explorer James Clark Ross who visited this area in 1841. To the west of the sea lies Ross Island and Victoria Land, to the east Roosevelt Island and Edward VII Peninsula in Marie Byrd Land, while the southernmost part is covered by the Ross Ice Shelf, and is about from the South Pole. Its boundaries and area have been defined by the New Zealand National Institute of Water and Atmospheric Research as having an area of.
The circulation of the Ross Sea is dominated by a wind-driven ocean gyre and the flow is strongly influenced by three submarine ridges that run from southwest to northeast. The circumpolar deep water current is a relatively warm, salty and nutrient-rich water mass that flows onto the continental shelf at certain locations. The Ross Sea is covered with ice for most of the year.
The nutrient-laden water supports an abundance of plankton and this encourages a rich marine fauna. At least ten mammal species, six bird species and 95 fish species are found here, as well as many invertebrates, and the sea remains relatively unaffected by human activities. New Zealand insists that the sea comes under its jurisdiction as part of the Ross Dependency. Marine biologists consider the sea to have a high level of biological diversity and it is the site of much scientific research. It is also the focus of some environmentalist groups who have campaigned to have the area proclaimed as a world marine reserve. In 2016 an international agreement established the region as a marine park.
Description
The Ross Sea was discovered by the Ross expedition in 1841. In the west of the Ross Sea is Ross Island with the Mt. Erebus volcano; in the east is Roosevelt Island. The southern part is covered by the Ross Ice Shelf. Roald Amundsen started his South Pole expedition in 1911 from the Bay of Whales, which was located at the shelf. In the western parts of the Ross Sea, McMurdo Sound is a port that is usually free of ice during the summer. The southernmost part of the Ross Sea is Gould Coast, which is approximately from the geographic South Pole.Geology
The continental shelf
The Ross Sea overlies a deep continental shelf. Although the average depth of the world's continental shelves is about 130 meters, the Ross shelf average depth is about 500 meters. It is shallower in the western Ross Sea than the east. This over-deepened condition is due to cycles of erosion and deposition of sediments from expanding and contracting ice sheets overriding the shelf during Oligocene and later time, and is also found on other locations around Antarctica. Erosion was more focused on the inner parts of the shelf while deposition of sediment dominated the outer shelf, making the inner shelf deeper than the outer.Seismic studies in the latter half of the twentieth century defined the major features of the geology of the Ross Sea. The deepest or basement rocks, are faulted into four major north trending graben systems, which are basins for sedimentary fill. These basins include the Northern and Victoria Land Basin in the west, the Central Trough, and the Eastern Basin, which has approximately the same width as the other three. The Coulman High separates the Victoria Land Basin and Central Trough and the Central High separates the Central Trough and Eastern Basin. The majority of the faulting and accompanying graben formation along with crustal extension occurred during the rifting away of the Zealandia microcontinent from Antarctica in Gondwana during Cretaceous time. Paleogene and Neogene -age and faulting and extension is restricted to the Victoria Land Basin and Northern Basin.
Stratigraphy
grabens are filled with rift sediments of uncertain character and age. A widespread unconformity has cut into the basement and sedimentary fill of the large basins. Above this major unconformity are a series of glacial marine sedimentary units deposited during multiple advances and retreats of the Antarctic Ice Sheet across the sea floor of the Ross Sea during the Oligocene and later.Geologic drilling
Drill holes have recovered cores of rock from the western edges of the sea. The most ambitious recent efforts are the Cape Roberts Project and the ANDRILL project. Deep Sea Drilling Project Leg 28 completed several holes farther from land in the central and western portions of the sea. These resulted in defining a stratigraphy for most of the older glacial sequences, which comprise Oligocene and younger sediments. The Ross Sea-wide major unconformity RSU-6 has been proposed to mark a global climate event and the first appearance of the Antarctic Ice Sheet in the Oligocene.During 2018, Expedition 374 of the International Ocean Discovery Program, the latest successor to the DSDP, drilled additional holes in the central Ross Sea for determining Neogene and Quaternary ice sheet history.
Basement
The nature of the basement rocks and the fill within the grabens are known in few locations. Basement rocks have been sampled at DSDP Leg 28 drill site 270 where metamorphic rocks of unknown age were recovered, and in the eastern Ross Sea where a bottom dredge was collected. In both these locations the metamorphic rocks are mylonites deformed in the Cretaceous suggesting extreme stretching of the Ross Embayment during that time.Marie Byrd Land: Rocks exposed in western Marie Byrd Land on the Edward VII Peninsula and within the Ford Ranges are candidates for basement in the eastern Ross Sea. The oldest rocks are Permian sediments of the Swanson Formation, which is slightly metamorphosed. The Ford granodiorite of Devonian age intrudes these sediments. Cretaceous Byrd Coast granite in turn intrudes the older rocks. The Byrd Coast and older formations have been cut by basalt dikes. Scattered through the Ford Ranges and Fosdick Mountains are late Cenozoic volcanic rocks that are not found to the west on Edward VII Peninsula. Metamorphic rocks, migmatites, are found in the Fosdick Mountains and Alexandra Mountains. These were metamorphosed and deformed in the Cretaceous.
The Ross Supergroup system and Beacon Supergroup: Ross System rocks exposed in Victoria Land and in the Transantarctic Mountains on the western side of the Ross Sea are possible basement rock below the sedimentary cover of the sea floor. The rocks are of upper Precambrian to lower Paleozoic in age, deformed in many places during the Ross Orogeny in the Cambrian. These miogeosyncline metasedimentary rocks are partly composed of calcium carbonate, often including limestone. Groups within the Ross System include the Robertson Bay Group, Priestley Group, Skelton Group, Beardmore Group, Byrd Group, Queen Maud Group, and Koettlitz Group. The Robertson Bay Group compares closely with other Ross System members. The Priestley Group rocks are similar to those of the Robertson Bay Group and include dark slates, argillites, siltstones, fine sandstones and limestones. They can be found near the Priestley and Campbell glaciers. For thirty miles along the lower Skelton Glacier are the calcareous greywackes and argillites of the Skelton Group. The region between the lower Beardmore Glacier and the lower Shackelton Glacier sits the Beardmore Group. North of the Nimrod Glacier are four block faulted ranges that make up the Byrd Group. The contents of the Queen Maud Group area are mainly post-tectonic granite.
Beacon Sandstone of Devonian-Triassic age and the Ferarr volcanic rocks of Jurassic age are separated from the Ross Supergroup by the Kukri Peneplain. Beacon rocks are reported to have been recovered in the drill cores of the Cape Roberts Project at the western edge of the Ross Sea.