Plankton Cool The Southern Hemisphere

Mtinkheni Gondwe used satellite observations to follow the distribution of phytoplankton in the oceans. Although the majority of plankton are found between the middle and high latitudes in the northern hemisphere, the effect of these on the climate is greatest in the southern hemisphere.

Plankton can influence the climate by producing the gas dimethyl sulphide (DMS). This gas is a source of small sulphur particles in the atmosphere, which act as condensation nuclei for the water vapour. The miniscule water drops formed in the air as a result of this, reflect the sunlight back before it reaches the Earth, causing the Earth to cool.

There are various reasons why plankton exert a greater influence on the climate in the southern hemisphere than in the northern hemisphere. For example, the plankton species in the southern hemisphere produce more DMS than their northern counterparts. Also in the southern hemisphere there is a higher DMS flux from the sea to the atmosphere and the sea surface area is greater. Finally, the atmosphere has a lower oxidation capacity in the southern hemisphere than in the northern hemisphere, which means that less DMS is broken down in the atmosphere. In the more industrialised northern atmosphere, there is a far greater emission of radical precursors which increase this oxidation capacity.

However, Gondwe concludes that the production of DMS by plankton only has a small effect on the Earth's temperature. Other compounds, such as carbon dioxide and CFCs have a far greater effect on the Earth's climate. The effects of the DMS production by plankton are particularly noticeable at a regional level.

The research was funded by the Netherlands Organisation for Scientific Research.