Science: Space-eye view: The tiny plankton that keep the Earth alive

Just another satellite image? No - this picture, taken last weekend, shows in minute detail the density of vegetation on land and in the oceans. Charles Arthur, Science Editor, explains how the blue patches, areas of plankton, stop our atmosphere becoming a sauna.

British and American scientists got their first views yesterday of new satellite data that will provide a vital insight into interactions between the atmosphere and the oceans, which cover the majority of the Earth's surface.

They hope it can help answer two essential questions troubling atmospheric scientists: how do the oceans and continents "breathe"? And, how important are the oceans in regulating global warming caused by the build-up of carbon dioxide in the atmosphere?

The SeaStar satellite, launched by the US space agency Nasa on 1 August, uses state-of-the-art instruments to map the amount and colour of light reflected from the world's oceans.

Though the sea may look much the same colour from the ground, from space its colour is largely determined by the amount of microscopic plant life - called phytoplankton - living close to the surface. SeaStar's instruments, can detect subtle variations in sea colour and interpret them in terms of density of plankton.

The study of plankton, a favourite food of fish and marine mammals such as whales, may seem esoteric. But the spread of this tiny organism, and of chlorophyll contained in them, has a direct and crucial effect on global warming. As plankton proliferates, it takes up carbon dioxide from the sea and converts it into carbohydrates. The sea then makes up the imbalance by absorbing carbon dioxide from the atmosphere.

This simple system absorbs 5,000 billion tonnes (5 gigatonnes) of carbon from the atmosphere every year, and some of the carbon taken up by the plankton becomes fixed into deep-sea sediments and eventually rocks such as limestone. In this way, plankton are crucial to the regulation of global temperature.

SeaStar's data will be assessed at sites such as the Southampton Oceanography Centre and Plymouth Laboratory to see what they reveal about global vegetation patterns, both on land and in the oceans.