Introduction

UV irradiance at the earth's surface is intimately related to stratospheric ozone. This gas tends to be concentrated in the lower stratosphere (hence the notion of an ozone layer) and is primarily responsible for the absorption of solar UV radiation (UVR). UVR has been recognised for many years (e.g. Worrest, Dyke & Thomson, 1978; Worrest et al., 1981; Calkins, 1982) as a potential stress for organisms in a variety of environments and as a factor in biogeochemical cycling (Zepp, Callaghan & Erickson, 1995). The trend in recent years of an intensifying, but periodic, anthropogenic-induced decline in stratospheric ozone concentrations with concurrent enhanced UV-B radiation is quite alarming. Altered solar radiation regimes can potentially upset established balances in marine ecosystems and thus presents a new problem. Most attention has been given to the ‘ozone hole’ over Antarctica that has been recorded annually since the 1980s. However, recent observations have confirmed measurable ozone losses over other regions, including the development of an Arctic ozone hole. The major factor responsible for the destruction of the ozone layer is anthropogenic emissions of chlorofluorocarbons (CFCs). These gases, having no natural sources, are non-toxic and inert in the troposphere, but are photolysed in the stratosphere, thereby releasing reactive chlorine atoms that catalytically destroy ozone. Other anthropogenic contributions to ozone depletion may include global changes in land use and the increased emission of nitrogen dioxide as a result of fertiliser applications (Bouwman, 1998). Paradoxically, the anthropogenic emissions of greenhouse gases that tend to cause a temperature increase at the earth's surface also produce a decrease in stratospheric temperatures.