South Tasman Rise

The South Tasman Rise is an area of seafloor that lies 550 km south of Hobart, Tasmania in the Southern Ocean where water depths are about 1,500 metres. The South Tasman Rise is also known as the Tasmania Ridge or South Tasmania Ridge. The South Tasman Rise is a sunken landbridge that used to connect Tasmania to Antarctica.

Exploration of this oceanic region has taken place via sonar, gravity field, magnetic field, a few drill holes and deliberate or accidental dredging of rocks up to the surface.

Geology

The rise forms a northern extension from the Macquarie-Balleny Ridge which extends to the subantarctic Balleny Islands. To east of the rise is the Tasman Basin, while the South Australian Basin extends westwards, south of the Great Australian Bight. The rise contains a number of seamounts, some of which have flat summits, indicating exposure above the sea surface at some time.[1]

The rise most probably originates from subsided continental crust that fragmented as Australia and Antarctica separated.[2]

This area of the seafloor is slated for exploration of offshore oil reserves. No oil has been recovered from the South Tasman Rise.[3]

Rocks

A quartz syenite sample has an age of 1119 Ma which is Grenville (geology) in age. This kind of rock resembles rocks from the Grenville magmatic province in the west of the United States. It supports the idea that Laurentia and eastern Australia, including the South Tasman Rise were once joined to each other during the time of the Rodinia supercontinent.[4]

Dolerite similar to the Jurassic dolerite in Tasmania has been recovered by dredging from the centre of the South Tasman Rise on RV Rig Seismic on its cruise 147.[5]

Glomar Challenger drilled a borehole on the southern slope of STR.[5] Hole 280 in oceanic crust resulted in basaltic intrusive of age 64.2 Ma. The hole at site 281 resulted in Precambrian quartz mica schist.[5]

RV Sonne did a cruise titled SO-36B in 1985 which did seismic profiles.[6]

Tertiary sediments

Bottle green coloured microtectites were found in borehole 1169 at around early Pliocene age, 202.14 meters below the seabed.[7]

Exploration

Ocean Drilling Program Leg 189 made a borehole into the sediments termed Site 1171.[8] Site 1169 was drilled at 145°14.2′E, 47°3.9′S.[7]

Fishery

The rise forms a sector of an international fishery managed by Australia and New Zealand.[9] New Zealand ceased fishing the area in the 2000-01 fishing season. By agreement between New Zealand and Australia the zone has been closed to commercial fishing since 2007. The principal species of fish sought after are the Orange Roughy and Oreo Dory using deepwater demersal trawlers.[10]

The northern part of the South Tasman Rise lies in the Australian Fishing Zone, in the exclusive economic zone of Australia, but the south end lies in international waters.[11]

Orange Roughy (Hoplostethus atlanticus) is an important fish found between 1 and 2 km deep on the South Tasman Rise. Fishing for orange roughy in international waters ramped up in late 1997.[11] 1998 saw the introduction of Arrangement Between the Government of Australia and the Government of New Zealand for the Conservation and Management of Orange Roughy on the South Tasman Rise.[12] This agreement set a research target of 150 tonnes per country, intended to input data to scientific research on the fish population structure.[11] Australian fishermen were allowed to catch three times as much fish as the New Zealanders. The quota was set at 2100 and then 2400 tonnes for 1999-2000. However it was exceeded so the fishing ground was closed till the end of February 2000. In June 1999 fishing boats from South Africa and one registered in Belize came in to fish the rise outside of the bilateral agreement. Diplomatic pressure from Australia caused the Belize government to deregister its vessel and for the South Africans to withdraw their boats.[11] A new agreement was made in 2000 about the orange roughy fishery. One feature of this new agreement was a 2:1 payback for over fishing: if the country's quota was exceeded, it had to pay back via a double reduction in its future fish allowance.[11]

Marine reserve

The South Tasman Rise Commonwealth Marine Reserve was declared in 2007.[1] The reserve seeks to protect unique environments for marine life which are of significant scientific interest.

See also

References
  1. "South Tasman Rise Commonwealth Marine Reserve". Department of Sustainability, Environment, Water, Population and Communities. 29 June 2011. Retrieved 22 December 2011.
  2. Glassby, G.P., ed. (1990). "Structure and Tectonics". Antarctic Sector of the Pacific. Amsterdam, The Netherlands: Elsevier Science Publishers. p. 153. ISBN 0-444-88510-2. Retrieved 22 December 2011.
  3. The American Association of Petroleum Geologists (2001). Petroleum Provinces of the 21st Century. p. 301. ISBN 0-89181-355-1. Retrieved 22 December 2011.
  4. Fioretti, A.M.; L.P. Black; J. Foden; D. Visonà (2005). "Grenville-age magmatism at the South Tasman Rise (Australia): A new piercing point for the reconstruction of Rodinia". Geology. 33 (10): 769. doi:10.1130/G21671.1. ISSN 0091-7613.
  5. Crawford, A. J.; R. Lanyon; M. Elmes; S. Eggins (1997). "Geochemistry and significance of basaltic rocks dredged from the South Tasman Rise and adjacent seamounts". Australian Journal of Earth Sciences. 44 (5): 621–632. doi:10.1080/08120099708728341. ISSN 0812-0099.
  6. Hinz, K.; M. Hemmerich; U. Salge; O. Eiken (1990). "Structures in Rift — Basin Sediments on the Conjugate Margins of Western Tasmania, South Tasman Rise, and Ross Sea, Antarctica". In Ulrich Bleil; Jörn Thiede (eds.). Geological History of the Polar Oceans: Arctic versus Antarctic. pp. 119–130. doi:10.1007/978-94-009-2029-3_7.
  7. Kelly, D. Clay; Linda T. Elkins-Tanton (2004). "Bottle-green microtektites from the South Tasman Rise: Deep-sea evidence for an impact event near the Miocene/Pliocene boundary". Meteoritics & Planetary Science. 39 (12): 1921–1929. doi:10.1111/j.1945-5100.2004.tb00087.x. ISSN 1086-9379.
  8. Pekar, Stephen F.; Audrey Hucks; Michael Fuller; Shawna Li (2005). "Glacioeustatic changes in the early and middle Eocene (51–42 Ma): Shallow-water stratigraphy from ODP Leg 189 Site 1171 (South Tasman Rise) and deep-sea δ18O records". Geological Society of America Bulletin. 117 (7): 1081. doi:10.1130/B25486.1. ISSN 0016-7606.
  9. "The Southern Remote Zone – South Tasman Rise Sector". Australian Fisheries Management Authority. Retrieved 22 December 2011.
  10. "South Tasman Rise : At a Glance". Australian Fisheries Management Authority. Retrieved 22 December 2011.
  11. Molenaar, Erik Jaap (January 2001). "The south Tasman rise arrangement of 2000 and other initiatives on management and conservation of orange roughy". International Journal of Marine & Coastal Law. 16 (1): 77. ISSN 0927-3522.
  12. Australian Department of Foreign Affairs and Trade (18 February 1998). "Arrangement Between the Government of Australia and the Government of New Zealand for the Conservation and Management of Orange Roughy on the South Tasman Rise" (PDF). Retrieved 22 July 2014.

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