Tasman Sea

May 13, 2013, 11:29 pm
Content Cover Image

Southern tip of New Zealand, southeastern limit of Tasman Sea. @ C.Michael Hogan

The Tasman Sea is the sizable saline water body separating New Zealand from Australia.

The southern boundary of the Tasman Sea is the Subtropical Convergence Zone at about 45 degrees southern latitude, and the northern boundary is the Tasman Front at the edge of the Coral Sea at about 32 degrees southern latitude. The Tasman Sea is a southwestern arm of the southern Pacific Ocean.

caption Tasman Sea. Source: OMC

The Tasman Sea is commonly referred to in both Australia and New Zealand as The Ditch; in fact, crossing the Ditch implies traveling between Australia and New Zealand. In the native M?ori language, the Tasman Sea is called Te Tai-o-Rehua.

Early exploration

caption Dutch explorer Abel Tasman. Attributed to Jacob Gerritsz Cuyp, 1637 The earliest European to explore Tasmania and New Zealand and Tasmania the Dutch explorer Abel Janszoon Tasman, for whom the water body was named. The British explorer Captain James Cook later extensively navigated the Tasman Sea in the 1770s as part of his first voyage of exploration. It has been suggested that Chinese navigators reached the Tasman Sea as early as the first quarter of the fifteenth century, although no written records of such voyages are extant.

Geography

The Tasman Sea measures approximately 2000 kilometres wide in its separation of New Zealand from Australia; the sea’s north south dimension is reckoned at about 2800 km. The International Hydrographic Organization defines the limits of the Tasman Sea as follows:

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 east 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 the east coast to South East Cape, the Southern point of Tasmania.

On the north. The 30th parallel south from the Australia in coast eastward as far as a line joining the east extremities of Elizabeth Reef and South East Rock (31 degrees 47 minutes S; 159 degrees 18 minutes E) then to the southward along this line to the South East Rock

On the northeast. From the South East Rock to the North point of Three Kings Islands (34 degrees 10 minutes S; 172 degrees 10 minutes E) thence to North Cape, New Zealand.

On the east.

  • In Cook Strait. A line joining the southern extreme of the foul ground off Cape Palliser, Ngawi, New Zealand and the Cape Campbell Lighthouse (Te Karaka).
  • In Foveaux Strait (46°45' S). A line joining the light on Waipapapa Point [sic] (168° 33' E) with East Head (47'02'S) of Stewart Island. On the southeast. A line running from South West Cape, New Zealand, Stewart Island, through The Snares (48°S, 166°30'E) to North West Cape, Auckland Island (50 degrees 30 minutes S; 166 degrees 10 minutes E), through this island to its southern point. ''On the South. A line joining the Southern point of Auckland Island (50 degrees 55 minutes S; 166 degrees 0 minutes E) to South East Cape, the southern point of Tasmania.

Hydrology

caption Northwest Tasman Sea along the Australian coast
@ C.Michael Hogan
According to Longhurst there is virtually no continental shelf associated with the Tasman Sea; where shelf-edge fronts occur, they are essentially the landward boundaries in both Australia and New Zealand. These edges are particlularly prominent along the Westland region of South Island, New Zealand, wher significant upwelling occurs.

The Tasman Sea is a region of disproportionately high winds for its latitude; correspondingly the seasonal cycle of summer stratification and winter vertical water column mixing is quite strong. In fact, wind stress and convection cause the summer mixing zone to reach a depth of 300 metres (m); the winter vertical mixing zone is correspondingly only about 125 m. 

Another key characteristic of the Tasman Sea is the profusion of eddies; this eddy zone extends as far south as below Tasmania and the Snares Bank.

Mid-sea ridge

The Tasman Sea's mid-sea ridge was formed approximately 85 and 55 million years before present at a time when Zealandia broke off from Australia and Zealandia, as part of the larger disintegration of the supercontinent Gondwana. The ridge is situated about midway between the continental margins of Australia and Zealandia, such that the ridge itself lies considerably to Australia compared to the distance to New Zealand.

Islands

The Tasman Sea features a number of mid-sea island groupings, totally distinct from coastal islands located near the Australian and New Zealand mainlands:

  • Lord Howe Island (an element of New South Wales)
  • Ball's Pyramid (an element of New South Wales)
  • Norfolk Island, in the extreme north of the Tasman Sea, on the border with the Coral Sea (External Territory)
  • Middleton Reef (an element of the Coral Sea Islands Territory)
  • Elizabeth Reef (an element of the Coral Sea Islands Territory)

Ecology

caption New Zealand fur seals basking on skerries at mouth of
Doubtful Sound, Tasman Sea. @ C.Michael Hogan
The southern portion of the Tasman Sea manifests a characteristic spring bloom such within the south and central Tasman Sea achieves a maximal chlorophyll biomass in the late September/ early October time frame. Haswell reports on the first micro-flora and micro-fauna assays of the Tasman Sea in his 1907 work, noting that the surfaces samples yielded a rich assortment of radiolarians, dinoflagellates, foraminifers, polycaeta, crustacea, heteropoda, pteropoda, chaetognatha, urochorda and a single species of vorticellid and and polychlad. Benthic dredging found mostly calcareous polyzopolyzoa.

Larger animals found in the Tasman Sea include such notable species as the New Zealand fur seal and the Fjordland crested penguin. This penguin can be observed in the vast fjord extents such as Doubtful Sound; correspondingly there is a notable occurrence of the New Zealand fur seals at the mouth of Doubtful Sound. Cetaceans found in the Tasman Sea include the Humpback whale and Spinner dolphin, both commonly seen at Hervey Bay.

Some seabirds found in the Tasman Sea are: Brown Booby, Brown Tern, Black-naped Tern, Bridled Tern, Crested Tern, Roseate Tern, Sooty Tern, Black Noddy, Red-tailed Tropicbird, Silver Gull, Wedge-tailed Shearwater and Eastern Reef Egret.

A number of endangered Kiwi species can be found along the New Zealand margin ot the Tasman Sea including Apteryx haastii, A. rowi, A. owenii and A. australis.

References

  • William Aitcheson Haswell. 1907. The colonial Radiolaria of the Tasman Sea.
  • Alan R.Longhurst. 2007. Ecological geography of the sea. Academic Press. 542 pages
  • New Zealand Journal of Zoology. 1989. vol. 16. no 4. 350 pages
  • R?wiri Taonui. Te Ara - the Encyclopedia of New Zealand, Ministry for Culture and Heritage. ISBN 978-0-478-18451-8
  • International Hydrographic Organization. 1953. Limits of Oceans and Seas, 3rd edition
Glossary

Citation

Hogan, C. (2013). Tasman Sea. Retrieved from http://www.eoearth.org/view/article/156417

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