Humans and flatulent cows have been blamed for global warming, but plankton may also be guilty. Now, German researchers have quantified the small, yet significant amounts of volatile organic contaminants (VOCs) - for example isoprene, dimethyl sulfide and halogenated compounds - emitted by various species of plankton into the atmosphere.

Aurélie Colomb from the Max-Planck Institute for Chemistry, Mainz, and co-workers looked at VOC emissions from five species of marine plankton using the technique head-space gas chromatography mass spectrometry.  Colomb found that different species emitted different amounts of pollutants, and that some pollutants were emitted only by certain species.  She also provided the first evidence of natural sources for pollutants such as chlorobenzene and dichlorobenzene, previously thought to be entirely human in origin.    

'The potential climate impacts of various trace organic gases have been established, and the terrestrial inputs are well studied, but little is known about which of these can be emitted from plankton,' said Noureddine Yassaa, one of Colomb's co-workers.  The emissions from plankton may influence global warming and the greenhouse effect in both negative and positive ways. The halogenated compounds are well known to cause the destruction of high atmosphere ozone, while isoprene oxidation produces aerosols which reflect some radiation away from the Earth.

Colomb's work is the first step towards assessing chemical emissions from marine sources on a global scale.  Next she plans to investigate the effects of temperature, pH, and growth stage of the plankton on the emission rates. 'Experiments with mixed species will also be necessary, since emissions from one species may be consumed by another,' explained Yassaa.  'It's important to realise that climate change may also change emission levels, since it may affect the distribution and relative amounts of these plankton in the environment.'

Stephen Davey