The ocean in action – key terms
Find out about the physical and chemical properties of the ocean and explore the ocean’s role in transporting heat, water, salt and carbon around the Earth.
This resource provides explanations of the key concepts encountered when exploring the ocean in action – the ‘basics’ that every student should understand.
Ocean
The ocean is a continuous body of salty water covering two-thirds of our planet. Five main regions of the ocean have been given the names Pacific, Atlantic, Indian, Arctic and Southern Oceans.
Sea
Smaller parts of the larger oceans are named seas, such as the Tasman Sea between New Zealand and Australia. Other seas are almost surrounded by land but are still connected to an ocean.
Oceanography
The study of the physical, chemical and biological processes of the ocean. Scientists who study these aspects of the ocean are called oceanographers.
Seawater
Seawater contains chemicals that make it different to freshwater. It has important properties that vary from place to place – for example, parts of the ocean are more or less salty, warmer or cooler.
Salinity
Salinity is a measure of the saltiness of seawater. It is caused mostly by the chemical sodium chloride. Salinity is an important property – salt makes seawater denser than freshwater.
Ocean current
There are two main causes for the large-scale movements of ocean water called currents. Surface currents are mostly pushed by the wind. Deep currents are caused by changes in the density of the water.
Earth systems
The Earth functions as a dynamic system of many interrelated parts. There are 4 main subsystems – the hydrosphere (water), atmosphere (air), geosphere (solid Earth) and biosphere (living things).
Carbon cycle
Carbon is a chemical element vital to all living things and is also present in many non-living things. Carbon circulates around the planet in what is called the carbon cycle. It moves through the carbon cycle in stops and starts. An individual atom might pass through plants, animals and the atmosphere in a matter of days, yet stay trapped in rocks for millions of years.
Carbon dioxide
Carbon dioxide (CO2)is a gas that plays an important part in the carbon cycle. It makes up just 0.004% of the atmosphere, yet with the more abundant water vapour, it soaks up infrared radiation (heat) from the Earth’s surface and stops it from escaping into space.
Density
Density is a measure of how tightly a certain amount of matter is packed into a given volume. The more the matter is packed in, the higher the density. Density can be calculated by dividing an object’s mass by its volume.
