Eastern Australian Current

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The East Australian Current as part of the South Pacific Vortex in an older illustration from 1943. Direction of flow: blue = cold, red = warm

The East Australian Current (Engl. "East Australian Current" or shortly "EAC" ) is a warm ocean current in the Pacific , by the South Sea extends to the southeast coast of Australia and the north coast of New Zealand. With its warm water, it ensures a warm, humid climate in Australia and New Zealand ( subtropical to tropical ).

Physical oceanography

The east australian current forms, together with the poleward currents along the east coast of New Zealand , the western edge current of the south pacific vortex . It thus occupies a position in the South Pacific analogous to the Kuroshio in the North Pacific, the Gulf Stream in the North Atlantic or the Brazil Current in the South Atlantic .

The East Australian Current is fed by the Pacific South Equatorial Current , which splits into three branches in the area between the island chains of New Caledonia and the Solomon Islands . The northern branch probably runs east of the Solomon Islands towards the equator. The middle one crosses the Coral Sea and splits again into a northern and a southern branch when it hits the Australian coast. The southern branch initially runs south of New Caledonia and turns south when it meets the Australian coast as an eastern Australian current.

The current follows the east Australian coast to the south and divides at about 32 ° -34 °  south latitude into a main branch branching off to the east (“Tasman Front”) and a residual current (“EAC extended "). The “Tasman Front” essentially forms a continuous, albeit extremely variable and strongly meandering current that extends to the north coast of New Zealand, where it merges into the East Auckland Current and a series of semi-permanent currents. The south-facing residual current, on the other hand, often dissolves immediately into a series of individual eddies and can reach beyond the southern tip of Tasmania .

Compared to other western marginal currents, the Eastern Australian Current is relatively weak. It also shows significant seasonal, annual and decade-long fluctuations in terms of characteristics, speed and volume flow . The volume flow is lowest in the southern winter at 27.4  Sv and reaches a maximum of up to 36.3 Sv in the southern summer. At a latitude of 30 ° S, the flow velocity reaches values ​​of up to 1.3 m / s in the southern summer and only up to 0.7 m / s in the southern winter. In the area around the junction of the “Tasman Front”, the flow velocity can reach peak values ​​of up to 2 m / s in southern summer.

Historical

The temperature distribution of the sea surface on April 19, 2016 shows a vortex of the residual current of the East Australian Current southeast of Tasmania.

The southward current along the Australian east coast was already noticed by James Cook during his First South Sea voyage (1768–1771). It was first described in detail in 1814 by Matthew Flinders . Heinrich Berghaus published the first map showing the course of the current, dated 1837.

Effects

The East Australian Current transports large amounts of warm surface water from the equatorial region to the mid-southern latitudes and thus influences the climate along the east coast of Australia.

The waters of the East Australian Current are basically poor in nutrients. However, the current itself is able to transport locally cold, nutrient-rich deep water into the euphotic zone , especially in the area where the “Tasman Front” branches off and in the area of ​​larger eddies . This upwelling leads to increased bioproductivity in the area of ​​the current and, in extreme cases, triggers algal blooms , often involving the dinoflagellate species Noctiluca scintillans . Normally, however, the total biomass is dominated by large diatoms such as Dactyliosolen or Guinardia . They form the nutritional basis of the rich fish fauna in the area of ​​the current. The stocks of yellowfin tuna ( Thunnus albacares ), which like to hunt in warmer waters and near the sea surface, are of particular economic importance .

An increased residual current ("EAC extended"), on the other hand, caused an intense and, with 251 days, extremely long marine heatwave (MHW) off the east coast of Tasmania in the southern summer of 2015/16 . The MHW had a massive impact, especially on sessile sea ​​creatures. In particular, the numerous aquacultures of the Pacific oyster ( Magallana gigas ) were severely damaged by the temperature-dependent Ostreavirus .

Trivia

Wide notoriety gained the East Australian Current by Pixar - animated film " Finding Nemo " in which he said clownfish "Marlin" makes his home in the Great Barrier Reef to Sydney to go.

In fact, numerous tropical coral fish are found in the waters off Sydney and other coastal stretches of the mid-latitudes of Eastern Australia in the southern summer months , far from their usual distribution areas. Although the fish reach these areas via the East Australian Current, unlike in the film, they are mostly juvenile fish that have already made the journey, driving passively, in the larval stage. The speed of the East Australian current is also shown in a far exaggerated manner in the film.

Individual evidence

  1. ↑ East Australian Current in geodz.com
  2. ↑ a b M. Bowen, JL Wilkin & WJ Emery: Variability and forcing of the East Australian Current. In: Journal of Geophysical Research: Oceans , Volume 110, 2005, C03019, doi : 10.1029 / 2004JC002533 .
  3. ^ A b P. Marchesiello & JH Middleton: Modeling the East Australian Current in the Western Tasman Sea. In: Journal of Physical Oceanography , Volume 30, 2000, pp. 2956-2971, ( digitized version ).
  4. ^ WS Kessler & S. Cravatte: ENSO and Short-Term Variability of the South Equatorial Current Entering the Coral Sea. In: Journal of Physical Oceanography , Volume 43, 2013, pp. 956-969, ( digitized version ).
  5. ^ NV Zilberman, DH Roemmich, ST Gille & J. Gilson: Estimating the Velocity and Transport of Western Boundary Current Systems: A Case Study of the East Australian Current near Brisbane. In: Journal of Atmospheric and Oceanic Technology , Volume 35, 2018, pp. 1313-1329, ( digitized ).
  6. ^ A b S. L. Ypma, E. van Sebille, AE Kiss & P. ​​Spence: The separation of the East Australian Current: A Lagrangian approach to potential vorticity and upstream control. In: Journal of Geophysical Research: Oceans , Volume 121, 2016, pp. 758-774, ( digitized ).
  7. ^ Ch. E. Tilburg, HE Hurlburt, JJ O'Brien & JF Shriver: The Dynamics of the East Australian Current System: The Tasman Front, the East Auckland Current, and the East Cape Current. In: Journal of Physical Oceanography , Volume 31, 2001, pp. 2917-2943, ( digitized version ).
  8. ^ K. Ridgway & K. Hill: The East Australian Current. In: ES Poloczanska, AJ Hobday & AJ Richardson (eds.): A Marine Climate Change Impacts and Adaptation Report Card for Australia 2009 , NCCARF Publication 05/09, 2009, ISBN 978-1-921609-03-9 , 16 pp. , ( Digitized version ).
  9. ^ St. R. Massel: Fluid Mechanics for Marine Ecologists. Springer Science & Business Media, 1999, ISBN 978-3-642-64305-7 , p. 236, ( reading sample ).
  10. ^ A b P. R. Oke & JH Middleton: Nutrient enrichment off Port Stephens: the role of the East Australian Current. In: Continental Shelf Research , Volume 21, 2001, pp. 587-606, ( digitized version ).
  11. ^ JE Jones & ISF Jones: The Western Boundary Current in the Pacific: The Development of Our Oceanographic Knowledge. In: KR Benson & Ph. F. Rehbock: Oceanographic History: The Pacific and Beyond , University of Washington Press, Seattle & London, 2002, ISBN 0-295-98239-X , pp. 86-95, ( reading sample ).
  12. ↑ a b K. R. Ridgway: Long-term trend and decadal variability of the southward penetration of the East Australian Current. In: Geophysical Research Letters , Volume 34, 2007, L13613, doi : 10.1029 / 2007GL030393 .
  13. ↑ JW Young, AJ Hobday, RA Campbell, RJ Kloser, PI Bonham, LA Clementson & MJ Lansdell: The biological oceanography of the East Australian Current and surrounding waters in relation to tuna and billfish catches off eastern Australia. In: Deep-Sea Research II: Topical Studies in Oceanography , Volume 58, Number 5, 2011, pp. 720-733, ( digitized version ).
  14. ↑ ECJ Oliver, JA Benthuysen, NL Bindoff, AJ Hobday, NJ Holbrook, CN Mundy & SE Perkins-Kirkpatrick: The unprecedented 2015/16 Tasman Sea marine heatwave. In: Nature Communications , Volume 8, 2017, 16101, doi : 10.1038 / ncomms16101 .
  15. ↑ DJ Booth, WF Figueira, MA Gregson, L. Brown & G. Beretta: Occurrence of tropical fishes in temperate southeastern Australia: Role of the East Australian Current. In: Estuarine, Coastal and Shelf Science , Volume 72, 2007, pp. 102-114, ( digitized ).