Global Emiliania Modelling Initiative (GEM)

a model study for the investigation of geosphere-biosphere interactions

P. Westbroek,
LIC/NSG, Department of Chemistry,
University of Leiden,
P.O. Box 9502, 2300 RA Leiden, the Netherlands

There is no doubt that geosphere-biosphere interactions play an important role in global climate, but it is very difficult to model these interactions. Major discrepancies exist between the characteristics of sound mechanistic models and the nature of life in the real world. In the first place, mechanistic models must be simple in order to be useful, while living systems are highly complex and diverse. Furthermore, a good model can only operate over a narrow range of scales in time and space, while this range is huge in biological systems, varying from milliseconds and nanometers to megayears and the periphery of the planet.

There are three reasons why these difficulties may be overcome, at least in principle. Firstly, instead of a single model, hierarchically nested modules may be constructed, which, like a set of russian dolls, represent the geosphere-biosphere interactions at successive levels of organisation. The second argument relies on the fact that nature tends to repeat itself. Underlying the immense diversity of living beings is a striking uniformity. The third reason follows from the observation that at specific 'levels of organisation' the behaviour of biological systems is highly ordered and relatively easy to model. For example, a handful of simple rules adequately describes the major physiological properties of individual organisms, despite the fact that this behaviour results from a multitude of biochemical reactions inside. Other levels of biological organisation would include the molecular, the ecological and the global levels.

In conclusion, we believe that eventually models of geosphere-biosphere interactions will consist of a hierarchy of compatible modules, together representing the full range of biological levels of organisation. Modelling will have to be organised around a limited number of representative model systems. The Global Emiliania Modelling Initiative (GEM) explores this hypothetical strategy for the modelling of geosphere-biosphere interactions by studying the marine alga Emiliania huxleyi from many different angles. This tiny organism (~1 x 10-5 m in diameter) occurs in all the world oceans, forms huge blooms, particularly in the North Atlantic, and is a major producer of three climate-forcing substances - calcium carbonate, organic carbon and dimethyl sulphide (DMS). The organism can be easily cultivated and is studied at the individual and the molecular biological levels in the laboratory; its blooms are studied in the field and by satellite imagery, and its geological history by sediment traps and deep-sea cores.

GEM is unique because these very diverse investigations are aspects of a single modelling initiative. Presently, integrated modelling and experimental projects concentrate on the individual and geological levels of organisation, while complementary molecular biological and ecological studies, building on from previous experience, are in preparation. Presently, GEM combines the research of about 50 investigators worldwide.

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