Global Emiliania Modelling Initiative (GEM)
a model study for the investigation of geosphere-biosphere interactions
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.