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Graphic: An Encyclopaedia of New Zealand 1966.

Warning

This information was published in 1966 in An Encyclopaedia of New Zealand, edited by A. H. McLintock. It has not been corrected and will not be updated.

Up-to-date information can be found elsewhere in Te Ara.

OCEAN CURRENTS AROUND NEW ZEALAND

Contents


Sub-surface Water Masses Around New Zealand

Immediately below the upper water masses there is another water mass, the Antarctic Intermediate Water. This is derived from a mixture of Antarctic and Sub-Antarctic Waters which sink at the Antarctic Convergence and spread north almost as far as the Equator. The vertical distribution of salinity shows a minimum value at depths somewhere between 800 and 1,200 metres, and this salinity minimum marks the core of the Antarctic Intermediate Water. As this water moves towards the north it mixes with the over and underlying waters and the salinity minimum becomes less and less pronounced.

Two water masses present below the intermediate layer are Deep Water and Antarctic Bottom Water. The Antarctic Bottom Water is formed near the Antarctic continent and, being very cold and dense, it sinks and spreads northwards. This water has been traced well north of the Equator. The Deep Water originates mainly in the high latitudes of the North Atlantic Ocean where surface waters are cooled. The consequent increase in density causes the cooled water to sink and it spreads southwards. South of the Equator the Deep Water continues in southward movement above the northgoing Antarctic Bottom Water and below the northgoing Antarctic Intermediate Water, and eventually helps to replace the water that is moving away from the Antarctic Ocean. It may be seen, therefore, that a huge process of turnover operates within the ocean. The rates involved in this turnover process are not yet known, but long-term studies involving the radioactive carbon-dating of sea water are being carried out both in New Zealand and overseas.

by Norman MacKillop Ridgeway, New Zealand Oceanographic Institute, Wellington.