Misplaced Pages

#635364

50-529: The Tasman Sea is a marginal sea of the South Pacific Ocean , situated between Australia and New Zealand . It measures about 2,000 km (1,200 mi) across and about 2,800 km (1,700 mi) from north to south. The sea was named after the Dutch explorer Abel Janszoon Tasman , who in 1642 was the first known person to cross it. British explorer Lieutenant James Cook later extensively navigated

100-671: A megalodon , an extinct shark, was also found by researchers. In 1876, the first telegraph cable connecting Australia and New Zealand was laid in the Tasman Sea. The telegraph cable was made obsolete in 1963 when the Commonwealth Pacific Cable , New Zealand's first international telephone cable, was completed. Moncrieff and Hood were the first to attempt a trans-Tasman crossing by plane in January 1928. The aviators were never seen or heard of again. The first successful flight over

150-464: A common feature at oceanic spreading centers. A feature of the elevated ridges is their relatively high heat flow values, of about 1–10 μcal/cm s, or roughly 0.04–0.4 W/m . Most crust in the ocean basins is less than 200 million years old, which is much younger than the 4.54 billion year age of Earth . This fact reflects the process of lithosphere recycling into the Earth's mantle during subduction . As

200-546: A ship of the Lamont–Doherty Earth Observatory of Columbia University , traversed the Atlantic Ocean, recording echo sounder data on the depth of the ocean floor. A team led by Marie Tharp and Bruce Heezen concluded that there was an enormous mountain chain with a rift valley at its crest, running up the middle of the Atlantic Ocean. Scientists named it the 'Mid-Atlantic Ridge'. Other research showed that

250-408: A subduction zone drags the rest of the plate along behind it. The slab pull mechanism is considered to be contributing more than the ridge push. A process previously proposed to contribute to plate motion and the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor" due to deep convection (see image). However, some studies have shown that the upper mantle ( asthenosphere )

300-587: Is a seafloor mountain system formed by plate tectonics . It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin . This feature is where seafloor spreading takes place along a divergent plate boundary . The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at

350-420: Is a global scale ion-exchange system. Hydrothermal vents at spreading centers introduce various amounts of iron , sulfur , manganese , silicon , and other elements into the ocean, some of which are recycled into the ocean crust. Helium-3 , an isotope that accompanies volcanism from the mantle, is emitted by hydrothermal vents and can be detected in plumes within the ocean. Fast spreading rates will expand

400-747: Is diverted west in the Subtropical Front which collides with the western moving Subantarctic front of the Antarctic Circumpolar Current . The East Australian Current sheds eddies on its way south that move south-westward with some known as the Tasman Leakage making it as far westward as the Indian Ocean. A deep-sea research ship, the RV Tangaroa , explored the sea and found 500 species of fish and 1300 species of invertebrates. The tooth of

450-443: Is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks making up the crust below the seafloor are youngest along the axis of the ridge and age with increasing distance from that axis. New magma of basalt composition emerges at and near

500-540: Is sometimes also considered a marginal sea of the Atlantic. (coast-wise from north to south) (from east to west) While all other seas in the world are defined at least in part by land boundaries, there is only one sea which is defined only by ocean currents: Entities called "seas" which are not divisions of the World Ocean are not included in this list. Excluded are: Midocean ridge A mid-ocean ridge ( MOR )

550-470: Is the result of changes in the volume of the ocean basins which are, in turn, affected by rates of seafloor spreading along the mid-ocean ridges. The 100 to 170 meters higher sea level of the Cretaceous Period (144–65 Ma) is partly attributed to plate tectonics because thermal expansion and the absence of ice sheets only account for some of the extra sea level. Seafloor spreading on mid-ocean ridges

SECTION 10

#1732837215636

600-440: Is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi). On the other hand, some of the world's largest tectonic plates such as

650-451: Is underlain by denser material and is deeper. Spreading rate is the rate at which an ocean basin widens due to seafloor spreading. Rates can be computed by mapping marine magnetic anomalies that span mid-ocean ridges. As crystallized basalt extruded at a ridge axis cools below Curie points of appropriate iron-titanium oxides, magnetic field directions parallel to the Earth's magnetic field are recorded in those oxides. The orientations of

700-569: The North American plate and South American plate are in motion, yet only are being subducted in restricted locations such as the Lesser Antilles Arc and Scotia Arc , pointing to action by the ridge push body force on these plates. Computer modeling of the plates and mantle motions suggest that plate motion and mantle convection are not connected, and the main plate driving force is slab pull. Increased rates of seafloor spreading (i.e.

750-463: The Southwest Indian Ridge ). The spreading center or axis commonly connects to a transform fault oriented at right angles to the axis. The flanks of mid-ocean ridges are in many places marked by the inactive scars of transform faults called fracture zones . At faster spreading rates the axes often display overlapping spreading centers that lack connecting transform faults. The depth of

800-461: The longest mountain range in the world. The continuous mountain range is 65,000 km (40,400 mi) long (several times longer than the Andes , the longest continental mountain range), and the total length of the oceanic ridge system is 80,000 km (49,700 mi) long. At the spreading center on a mid-ocean ridge, the depth of the seafloor is approximately 2,600 meters (8,500 ft). On

850-712: The East Australian Current continues south in the western Tasman a branch flows east called the Tasman Front towards the north of New Zealand with most continuing eastward above New Zealand into the South Pacific Ocean. It transpires that while predominantly the location of westerly wind stress is a factor in how far north the formation of the Tasman Front occurs, so is the presence of the New Zealand land mass, as

900-730: The East Pacific Rise lack rift valleys. The spreading rate of the North Atlantic Ocean is ~ 25 mm/yr, while in the Pacific region, it is 80–145 mm/yr. The highest known rate is over 200 mm/yr in the Miocene on the East Pacific Rise. Ridges that spread at rates <20 mm/yr are referred to as ultraslow spreading ridges (e.g., the Gakkel Ridge in the Arctic Ocean and

950-664: The Mid-Atlantic Ridge have spread much less far (showing a steeper profile) than faster ridges such as the East Pacific Rise (gentle profile) for the same amount of time and cooling and consequent bathymetric deepening. Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys , sometimes as wide as 10–20 km (6.2–12.4 mi), and very rugged terrain at the ridge crest that can have relief of up to 1,000 m (3,300 ft). By contrast, fast-spreading ridges (greater than 90 mm/yr) such as

1000-815: The Northeast From the South East Rock to the north point of Three Kings Islands ( 34°10′S 172°10′E  /  34.167°S 172.167°E  / -34.167; 172.167 ), thence to North Cape in New Zealand. On the East On the Southeast A line running from South West Cape , Stewart Island, through the Snares (48°S, 166°30'E) to North West Cape, Auckland Island ( 50°30′S 166°10′E  /  50.500°S 166.167°E  / -50.500; 166.167 ), through this island to its southern point. On

1050-471: The South A line joining the southern point of Auckland Island ( 50°55′S 166°0′E  /  50.917°S 166.000°E  / -50.917; 166.000 ) to South East Cape, the southern point of Tasmania. The Tasman Sea's midocean ridge developed between 85 and 55 million years ago as Australia and Zealandia broke apart during the breakup of supercontinent Gondwana . It lies roughly midway between

SECTION 20

#1732837215636

1100-511: The Tasman Sea in the 1770s during his three voyages of exploration. The Tasman Sea is informally referred to in both Australian and New Zealand English as the Ditch ; for example, " crossing the Ditch " means travelling to Australia from New Zealand, or vice versa. The diminutive term "the Ditch" used for the Tasman Sea is comparable to referring to the North Atlantic Ocean as "the Pond". The south of

1150-427: The asthenosphere at ocean trenches . Two processes, ridge-push and slab pull , are thought to be responsible for spreading at mid-ocean ridges. Ridge push refers to the gravitational sliding of the ocean plate that is raised above the hotter asthenosphere, thus creating a body force causing sliding of the plate downslope. In slab pull the weight of a tectonic plate being subducted (pulled) below an overlying plate at

1200-478: The axis because of decompression melting in the underlying Earth's mantle . The isentropic upwelling solid mantle material exceeds the solidus temperature and melts. The crystallized magma forms a new crust of basalt known as MORB for mid-ocean ridge basalt, and gabbro below it in the lower oceanic crust . Mid-ocean ridge basalt is a tholeiitic basalt and is low in incompatible elements . Hydrothermal vents fueled by magmatic and volcanic heat are

1250-490: The axis changes in a systematic way with shallower depths between offsets such as transform faults and overlapping spreading centers dividing the axis into segments. One hypothesis for different along-axis depths is variations in magma supply to the spreading center. Ultra-slow spreading ridges form both magmatic and amagmatic (currently lack volcanic activity) ridge segments without transform faults. Mid-ocean ridges exhibit active volcanism and seismicity . The oceanic crust

1300-515: The continental margins of Australia and Zealandia. Much of Zealandia is submerged, so the ridge runs much closer to the Australian coast than New Zealand's. The Tasman Sea features a number of midsea island groups, quite apart from coastal islands located near the Australian and New Zealand mainlands: The East Australian Current that commences its flow southwards in the tropics of the Coral Sea, near

1350-407: The discovery of the worldwide extent of the mid-ocean ridge in the 1950s, geologists faced a new task: explaining how such an enormous geological structure could have formed. In the 1960s, geologists discovered and began to propose mechanisms for seafloor spreading . The discovery of mid-ocean ridges and the process of seafloor spreading allowed for Wegener's theory to be expanded so that it included

1400-489: The east coast to South East Cape , the southern point of Tasmania. On the North The parallel of 30°S from the Australian coast eastward as far as a line joining the east extremities of Elizabeth Reef and South East Rock ( 31°47′S 159°18′E  /  31.783°S 159.300°E  / -31.783; 159.300 ) then to the southward along this line to the South East Rock [an outlier of Lord Howe Island ]. On

1450-458: The eastern coast of Australia is the most energetic circulation feature in the south western Pacific Ocean and is a primary means of heat transport from the tropics to the middle latitudes between Australia and New Zealand. The East Australian Current is a return of the westward-flowing Pacific Equatorial Current (Pacific South Equatorial Current ). At the juncture between the Tasman and Coral seas while

1500-530: The field preserved in the oceanic crust comprise a record of directions of the Earth's magnetic field with time. Because the field has reversed directions at known intervals throughout its history, the pattern of geomagnetic reversals in the ocean crust can be used as an indicator of age; given the crustal age and distance from the ridge axis, spreading rates can be calculated. Spreading rates range from approximately 10–200 mm/yr. Slow-spreading ridges such as

1550-418: The floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot sima [rising] from depth". However, Wegener did not pursue this observation in his later works and his theory was dismissed by geologists because there was no mechanism to explain how continents could plow through ocean crust , and the theory became largely forgotten. Following

Tasman Sea - Misplaced Pages Continue

1600-478: The globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball . The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi). The mid-ocean ridges of the world are connected and form the Ocean Ridge, a single global mid-oceanic ridge system that is part of every ocean , making it

1650-600: The linear weakness between the separating plates, and emerges as lava , creating new oceanic crust and lithosphere upon cooling. The first discovered mid-ocean ridge was the Mid-Atlantic Ridge , which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around

1700-532: The mid-ocean ridge causing basalt reactions with seawater to happen more rapidly. The magnesium/calcium ratio will be lower because more magnesium ions are being removed from seawater and consumed by the rock, and more calcium ions are being removed from the rock and released into seawater. Hydrothermal activity at the ridge crest is efficient in removing magnesium. A lower Mg/Ca ratio favors the precipitation of low-Mg calcite polymorphs of calcium carbonate ( calcite seas ). Slow spreading at mid-ocean ridges has

1750-535: The mid-ocean ridge from the South Atlantic into the Indian Ocean early in the twentieth century. Although the first-discovered section of the ridge system runs down the middle of the Atlantic Ocean, it was found that most mid-ocean ridges are located away from the center of other ocean basins. Alfred Wegener proposed the theory of continental drift in 1912. He stated: "the Mid-Atlantic Ridge ... zone in which

1800-402: The movement of oceanic crust as well as the continents. Plate tectonics was a suitable explanation for seafloor spreading, and the acceptance of plate tectonics by the majority of geologists resulted in a major paradigm shift in geological thinking. It is estimated that along Earth's mid-ocean ridges every year 2.7 km (1.0 sq mi) of new seafloor is formed by this process. With

1850-403: The oceanic crust and lithosphere moves away from the ridge axis, the peridotite in the underlying mantle lithosphere cools and becomes more rigid. The crust and the relatively rigid peridotite below it make up the oceanic lithosphere , which sits above the less rigid and viscous asthenosphere . The oceanic lithosphere is formed at an oceanic ridge, while the lithosphere is subducted back into

1900-451: The opposite effect and will result in a higher Mg/Ca ratio favoring the precipitation of aragonite and high-Mg calcite polymorphs of calcium carbonate ( aragonite seas ). Experiments show that most modern high-Mg calcite organisms would have been low-Mg calcite in past calcite seas, meaning that the Mg/Ca ratio in an organism's skeleton varies with the Mg/Ca ratio of the seawater in which it

1950-574: The rate of expansion of the mid-ocean ridge) have caused the global ( eustatic ) sea level to rise over very long timescales (millions of years). Increased seafloor spreading means that the mid-ocean ridge will then expand and form a broader ridge with decreased average depth, taking up more space in the ocean basin. This displaces the overlying ocean and causes sea levels to rise. Sealevel change can be attributed to other factors ( thermal expansion , ice melting, and mantle convection creating dynamic topography ). Over very long timescales, however, it

2000-440: The ridge crest was seismically active and fresh lavas were found in the rift valley. Also, crustal heat flow was higher here than elsewhere in the Atlantic Ocean basin. At first, the ridge was thought to be a feature specific to the Atlantic Ocean. However, as surveys of the ocean floor continued around the world, it was discovered that every ocean contains parts of the mid-ocean ridge system. The German Meteor expedition traced

2050-416: The ridge flanks, the depth of the seafloor (or the height of a location on a mid-ocean ridge above a base-level) is correlated with its age (age of the lithosphere where depth is measured). The depth-age relation can be modeled by the cooling of a lithosphere plate or mantle half-space. A good approximation is that the depth of the seafloor at a location on a spreading mid-ocean ridge is proportional to

Tasman Sea - Misplaced Pages Continue

2100-427: The sea is passed over by depressions going from west to east. The northern limit of these westerly winds is near to 40°S . During the southern winter, from April to October, the northern branch of these winds from the west changes its direction toward the north and goes up against trade winds . Hence, the sea receives frequent winds from the southwest during this period. In the Australian summer (from November to March),

2150-739: The sea was accomplished by Charles Kingsford Smith and Charles Ulm later that year. The first person to row solo across the sea was Colin Quincey in 1977. The next successful solo crossing was completed by his son, Shaun Quincey, in 2010. Marginal sea There are several terms used for bulges of ocean that result from indentations of land, which overlap in definition, and which are not consistently differentiated: Many features could be considered to be more than one of these, and all of these terms are used in place names inconsistently; especially bays, gulfs, and bights, which can be very large or very small. This list includes large areas of water no matter

2200-431: The seafloor were analyzed by oceanographers Matthew Fontaine Maury and Charles Wyville Thomson and revealed a prominent rise in the seafloor that ran down the Atlantic basin from north to south. Sonar echo sounders confirmed this in the early twentieth century. It was not until after World War II , when the ocean floor was surveyed in more detail, that the full extent of mid-ocean ridges became known. The Vema ,

2250-428: The southern branch of the trade winds goes up against west winds and produces further wind activity in the area. The Tasman Sea is 2,250 km (1,400 mi) wide and has an area of 2,300,000 km (890,000 sq mi). The maximum depth of the sea is 5,943 m (19,498 ft). The base of the sea is made up of globigerina ooze. A small zone of pteropod ooze is found to the south of New Caledonia and to

2300-711: The southern extent of 30°S , siliceous ooze can be found. The International Hydrographic Organization defines the limits of the Tasman Sea as: On the West A line from Gabo Island (near Cape Howe , 37°30'S) to the northeast point of East Sister Island (148°E), thence along the 148th meridian to Flinders Island ; beyond this island a line running to the eastward of the Vansittart Shoals to [Cape] Barren Island , and from Cape Barren (the easternmost point of [Cape] Barren Island) to Eddystone Point (41°S) in Tasmania, thence along

2350-439: The square root of the age of the seafloor. The overall shape of ridges results from Pratt isostasy : close to the ridge axis, there is a hot, low-density mantle supporting the oceanic crust. As the oceanic plate cools, away from the ridge axis, the oceanic mantle lithosphere (the colder, denser part of the mantle that, together with the crust, comprises the oceanic plates) thickens, and the density increases. Thus older seafloor

2400-410: The term used in the name. The largest terrestrial seas, in decreasing order of area, are: Seas may be considered marginal between ocean and land, or between oceans in which case they may be treated as marginal parts of either. There is no single ultimate authority on the matter. (clockwise from 180°) In addition to the marginal seas listed in the three subsections below, the Arctic Ocean itself

2450-745: The top of New Zealand defines the furtherest south that the Tasman Front can be split off by the westerly winds. A boundary current called the East Auckland Current goes down the west coast of the North Island and further south the East Cape Current, that has been diverted towards the South Island by the shapes of the Lord Howe Rise and southern east coast of the North island continues to the south. The East Australian Current south of Tasmania also

2500-534: Was grown. The mineralogy of reef-building and sediment-producing organisms is thus regulated by chemical reactions occurring along the mid-ocean ridge, the rate of which is controlled by the rate of sea-floor spreading. The first indications that a ridge bisects the Atlantic Ocean basin came from the results of the British Challenger expedition in the nineteenth century. Soundings from lines dropped to

#635364