The oceans play an extremely important role in controlling the climate of our Earth by transporting heat from the equator to the polar regions. If it wasn't for the oceans, most of the planet would be too cold for humans to live on. The sea is also an important source of food and of energy, both as non-renewable oil and gas and as renewable wind and wave power. The coastal area is particularly important for humans since over 60% of the Earth's population live within 100 km of the sea.
In this Basic Introduction to The Oceans, we will look at how oceans move heat around the globe and how the special properties of water help regulate to the climate of the Earth. We will look at the most important life form in the oceans, the phytoplankton, showing how they grow and what their sources of food are. We will also look at how these single celled marine plants affect climate by taking up carbon dioxide and by producing gases which enter the air and help to form clouds.
Water has amazing properties which help to control our climate and make life on Earth possible. Although we call our planet Earth, only 29% of its area is actually land; the rest is covered by water and almost all of this water is in the oceans. Ocean waters continuously move around the globe as if they were on a huge conveyor belt, moving from the surface waters to the deep and back again. Wind, the saltiness of the water and temperature all control this movement. This ocean circulation helps to spread the heat from the Sun throughout the Earth.
The oceans also take up huge amounts of carbon dioxide from the atmosphere. Around a quarter of the carbon dioxide we humans produce by burning fossil fuels ends up being stored in the oceans. In some ocean areas this carbon can be stored for centuries, helping to reduce the effects of global warming.
On land it's easy to see that different areas have very different amounts of plant growth. The tropical rain forests have the most biological growth and the deserts have the least. Although it's not so easy to see, it's similar in the oceans. Oceanographers call the desert areas of the oceans the OLIGOTROPHIC regions. Oligo is the Greek word for small and troph is derived from the Greek for "to feed" so the name oligotrophic simply means an area with little food. Low levels of the major plant nutrients, nitrogen and phosphorous, in these areas means that little grows. In this unit we will look at where these nutrients come from and how phytoplankton grow in the oceans.
Large inputs of nitrogen and phosphorous from land make coastal waters the most biologically active region of the ocean. Most of these nutrients come from human activities. Areas with excess nutrients are known as EUTROPHIC regions (based on the Greek for "to nourish"). Large amounts of phytoplankton growth in these areas can cause eutrophication problems and we will discuss these in this Unit.
We use chlorophyll (the photosynthetic pigment in plants) as a measure of how much biological growth there is in the oceans. The blue areas with little chlorophyll are the deserts of the oceans. The red areas, which are generally around the coasts, are the most biologically active. Image taken by the NASA SeaWiFS satellite.
It was originally thought that the oceans and the atmosphere acted independently but we now know that both have a huge influence on each other. In this Unit we look at how phytoplankton living in the oceans affect our climate. We think that these tiny single celled plants emit almost as much sulphur into the air as do all the power stations on Earth put together! We concentrate on the gas dimethyl sulphide (DMS) which is probably the most important gas produced biologically. We look at how and why this gas is produced and why it is so important to our climate. We also look at other climatically important gases which are formed in seawater and how these are involved in global warming and ozone depletion in the stratosphere.