Terrestrial Palaeoecology and Global Change

Chapter 7. Climate change
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pletions are much greater, up to 50% over Antarctica at altitudes 20-50 km. This phenomenon,
first observed in 1985, became known as the “ozone hole”. It is now considered
as a major environmental hazard.
Episodic attenuation of the ozone layer is caused by solar flares, as well as by cold
winters (Müller et al., 1997). The ongoing ozone depletion is ascribed to industrial emissions
of chlorofluorocarbons (CFCs), a source of chlorine that is engaged in heterogeneous
reactions on the stratospheric ice clouds. Naturally such compounds are produced
by decaying red algae (Wever, 1988). The ozone-destructive aerosols are metabolically
produced by terrestrial vegetation (Kavoures et al., 1998) and by phytoplankton. Bacterial
nitrification is a substantial source of atmospheric nitrous oxide, enhanced by warm
SST (incidentally by El Niño) bolstering a dominance of nitrogen-fixing cyanobacteria
(Dore et al., 1998).
Volcanic eruptions are a source of chlorides far exceeding the present-day industrial
emissions. Concomitantly, the ozone-destroying reactions are enhanced by injections of
sulfur acid aerosols (Arnold et al., 1990; Brasseur et al., 1990; Brasseur, 1991).
Critical for the stratospheric ozone layer are the tropospheric processes affecting
circulation of ozone-destructive compounds (Fig. 95). These are conducted by ascending
air, primarily at the tropopause and through the polar vortices. Thus, aerosols from
Fig. 95. A Watson circle scheme (Coughlan & Armour, 1992) of variables affecting the stratospheric ozone
layer, including chlorofluorocarbons (CFC), their derived chlorine, nitrous oxides, sulfur acid aerosols,
water vapour, hydroxyl, temperature and the vorticity of the polar area (right margin symbol). The relative
importance of these factors is reflected in the number of departing arrows, maximal for the vorticity of
polar air.