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  • The ocean is part of our lives – we may swim in it, sail on it or eat food from it. Many aspects of the ocean affect us – it controls climate, supports life, wears away land, and provides resources.

    The ocean is a system of chemical, physical and biological processes. Some of these processes are driven by basic science concepts – temperature, density and salinity (saltiness) – that help cause currents and affect climate.

    Oceans and seas

    The ocean is a continuous body of salty water that covers two-thirds of our planet. Five main regions of the ocean have been given the names Pacific, Atlantic, Indian, Arctic and Southern Oceans. There are also smaller areas called seas. Some of these are part of a larger ocean – for example, the Tasman Sea between New Zealand and Australia is part of the Pacific Ocean. Other seas are almost surrounded by land but are still connected to an ocean – an example is the Mediterranean Sea, which is connected to the Atlantic Ocean only by a small gap between Europe and Africa.

    Find out more about ocean motion and the important role the ocean plays in several Earth systems and cycles.

    Seawater properties

    Seawater is not pure water – one sip tells you there is something in it that makes it salty. If you’ve swum in the ocean, you’ll know that seawater is denser than freshwater, as it helps you float better than the water in the pool. Saltiness (scientists call this saltiness ‘salinity’) and density are just two properties of seawater that affect many aspects of life on Earth.

    The ocean is not the same everywhere. Seawater properties vary from place to place – for example, some parts of the ocean are more or less salty, warmer or cooler, more or less dense. Properties also change over time, from season to season and year to year, as well as over much longer timescales.

    Some properties of seawater influence the climate of Earth and the ability of life to survive. The ocean is a complex system, and there are close links between the different properties. To understand how this works, we need to look at these properties – what they are, what causes the properties to vary around the world and what happens when they change.

    Oceanography – the young science

    Since the ocean is so big, and so important to our lives, you’d think that we’d know a lot about it, but oceanography – the study of the physical, chemical and biological processes of the ocean – is quite a young science. The sheer size of the ocean makes it hard to measure more than a tiny part of it, and much of it is inaccessible below the surface.

    Scientists now have new technology that lets them collect information from parts of the ocean they can’t actually see or touch. Sound has been used to map the mountains and valleys of the ocean floor, automatic sensors probe below the surface and satellites collect data over the whole surface. Powerful computers can handle the vast amounts of data being collected.

    One result of these advances is that scientists now know that the ocean plays an important part in controlling climate. The role of the atmosphere in climate control has been studied for a long time, but the urgency of climate change has helped drive the study of the ocean and its relationship with climate. Find out more in the article, The ocean and the carbon cycle.

    Meet some New Zealand oceanographers

    New Zealand is surrounded by ocean, so it is not surprising that its scientists play an important part in the international effort to understand the ocean and its processes. Find out about the work of two oceanographers and hear from others explaining how some ocean processes work.

    Dr Phil Sutton is involved in the international Argo project, which uses thousands of automatic floats to monitor global ocean currents and chemistry. Data is available free on the internet and is updated every day, allowing scientists all round the world to build models of how the ocean works.

    Dr Kim Currie studies the role of the ocean in the carbon cycle – the movement of the element carbon around the Earth. She’s particularly interested in the exchange of carbon dioxide between the ocean and the atmosphere. Her tools include ships and satellites with equipment to collect and analyse seawater and air. Find out more about this in the articles Carbon dioxide in the ocean and Carbon dioxide in the atmosphere.

    Take up the challenge

    The following activities can help students deepen their understanding of the ocean’s role in transporting heat, water, salt and carbon around the Earth.

    • Buoyancy in water – make a Cartesian diver with your class to demonstrate the relationship between volume, mass and density.
    • Using radiocarbon carbon dioxide data – students interpret graphs showing carbon dioxide in the atmosphere of New Zealand and explore how sampling intervals affect the conclusions we are able to make.

    Question bank

    The The ocean in action – question bank provides an initial list of questions about the physical and chemical properties of the ocean and places where their answers can be found. The questions support an inquiry approach.

    Key terms

    For explanations of key concepts, see The ocean in action – key terms.


    Explore the timeline to see some important historical dates in the history of ocean studies, including the interaction of the ocean with climate and atmospheric carbon dioxide.

      Published 16 June 2010 Referencing Hub articles
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