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  • Rights: The University of Waikato Te Whare Wānanga o Waikato
    Published 30 June 2010 Referencing Hub media
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    Dr Phil Sutton of NIWA explains how New Zealand sits at the boundary between warm, salty subtropical water and cool, less salty subantarctic water. Argo and Jason have shown that changes in ocean heat1 content are focused in this region. Dr Sutton also describes how Argo can be used in local studies, such as fish distribution.

    Transcript

    Dr Phil Sutton

    New Zealand is in a very interesting part of the world as far as most oceanography is concerned, but we span two ocean current regimes. The north of New Zealand, north of Chatham Rise, basically, or north of a line between Banks Peninsula2 and Chatham Islands, is all in subtropical water, which is relatively warm and salty water, and then south of Chatham Rise, you get into subantarctic water, which is relatively cold and fresh.

    Subtropical water is connected to a big current system that flows anticlockwise around the South Pacific all the way across to South America and then westward south of the equator, southward along the coast of Australia, and then ultimately along the north-east coast of New Zealand and then a general eastward trend at about 40° south.

    The subantarctic system is associated with the Antarctic Circumpolar3 Current, which is a strong current that flows eastward all the way around Antarctica, driven by the strong winds at those latitudes.

    The thing that we have learnt since the Argo deployment and the Jason satellites is that the changes in the world’s oceans in the last decade or so have been focused really on the 40° south latitude4 – so the South Pacific, South Indian Ocean and South Atlantic – and the largest changes in heat content have been seen centred on about 40° south, in other words, right around the New Zealand region. We think that is because of the changes in the large-scale wind field in the Southern Hemisphere, and we are just keeping an eye on what is happening exactly and still trying to work out what it all means. But in terms of heat content, changes globally, the Southern Hemisphere is dominating the current picture.

    There have been a number of detailed smaller process studies using Argo data5. Argo is relatively young and so I think people are still learning what they can do with Argo data. A couple of the examples around New Zealand are looking at what is happening at the parking – the depth where the float parks at about 1,000 metres6 – where it’s freely drifting.

    And the reason that has been interesting is because a number of our fish stock hangs out at about those depths – so orange roughy and hoki are a bit shallower than that. And we have used float trajectory7 data from around Chatham Rise to look at what is happening with the water mass movements near the orange roughy breeding grounds.

    It turns out that, where the orange roughy – their spawning8 ground is really in a region where the warm water from the subtropical side, the north side of Chatham Rise is coming around a little bit, around the southern side of Chatham Rise, and meeting the cold water coming north in the subantarctic system – and so the next question is whether the orange roughy really care about that or not, and we still have to work on that.

    Acknowledgements
    NIWA
    Google Earth
    NASA/Goddard Space Flight Centre Scientific Visualization Studio/courtesy of nasaimages.org.
    Public domain
    Argo data in this video clip was collected and made freely available by the International Argo Project and the national programmes that contribute to it. (www.argo.ucsd.edu, www.ocean-ops.org). Argo is a pilot programme of the Global Ocean Observing System.
    Scripps Institution of Oceanography, UCSD
    Diarmuid Toman
    Google Earth, ©2010 Map Data Sciences Pty Ltd, PSMA,

    1. heat energy (heat): Heat energy: the transfer of energy in materials from the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.
      Heat: the flow of energy from a warm object to a cooler object.
    2. peninsula: A large section of land that juts out into a body of water.
    3. circumpolar: Located around a polar region (e.g. a water current travelling around the South Pole is called a circumpolar current).
    4. latitude: A geographic co-ordinate that specifies the north-south position of a point on the Earth’s surface. Lines of constant latitude (or parallels) run east-west as circles parallel to the equator. Latitude is used with longitude to specify the precise location of features on the surface of the Earth.
    5. data: The unprocessed information we analyse to gain knowledge.
    6. metre: The base unit of length in the International System of Units (SI).
    7. trajectory: An arc (path) made (or likely to be made) by an object, such as a bullet or a launched rocket, as it moves from its launch position to its point of impact. The moving object has had some force applied to it to set it moving on its path.
    8. spawning: The laying of eggs by aquatic animals like fish, frogs, crustaceans or mollusks.
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      heat energy (heat)

    1. + Create new collection
    2. Heat energy: the transfer of energy in materials from the random movement of the particles in that material. The greater the random movement of particles the more heat energy the material has. Temperature is a measure of the heat energy of a material.
      Heat: the flow of energy from a warm object to a cooler object.

      latitude

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    4. A geographic co-ordinate that specifies the north-south position of a point on the Earth’s surface. Lines of constant latitude (or parallels) run east-west as circles parallel to the equator. Latitude is used with longitude to specify the precise location of features on the surface of the Earth.

      trajectory

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    6. An arc (path) made (or likely to be made) by an object, such as a bullet or a launched rocket, as it moves from its launch position to its point of impact. The moving object has had some force applied to it to set it moving on its path.

      peninsula

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    8. A large section of land that juts out into a body of water.

      data

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    10. The unprocessed information we analyse to gain knowledge.

      spawning

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    12. The laying of eggs by aquatic animals like fish, frogs, crustaceans or mollusks.

      circumpolar

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    14. Located around a polar region (e.g. a water current travelling around the South Pole is called a circumpolar current).

      metre

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    16. The base unit of length in the International System of Units (SI).