Effects of UV on the terrestrial and aquatic biosphere

1. Resumé

In order to assess the influence of ultraviolet radiation on terrestrial and aquatic ecosystems in the Antarctic, quantitative information is required on the spectral ultraviolet irradiance at sites of biological interest. Temporal variations in the ultraviolet radiation dose, weighted by relevant biological action spectra, will be determined using a radiative transfer model together with available measurements.

2. Scientific background

The development of Antarctic ozone depletion has given rise to increased fluxes of ultraviolet radiation at wavelengths of biological importance. Increased levels of ultraviolet exposure may result in reduced primary production, genetic damage, elimination of sensitive species, and changes in community structure. Within the Antarctic region affected by the ozone hole, colonisation of soils and aquatic ecosystems is dominated by microbial primary producers (cyanobacteria and microalgae) which are inevitably exposed to UV while absorbing light for photosynthesis. These and subsequent macroscopic colonists (mosses, lichens, two higher plants, and associated invertebrate animals) often occupy habitats which receive minimal protection by winter snow, resulting in their exposure to high UVB levels at the time of maximum ozone depletion in the Antarctic spring, prior to the commencement of the growing season.

Experimental studies of Antarctic flora therefore require reliable information regarding the ultraviolet irradiance at sites where field investigations are carried out. The biological effects of ultraviolet radiation are highly dependent on wavelength, and on the seasonal development of the species concerned. Spectral data are therefore needed as a function of time, throughout the period of biological study. The ultraviolet irradiance received at the Earth's surface depends on a number of factors, including solar zenith angle, ozone, atmospheric aerosols, cloud cover, and surface albedo. However, few measurements of spectral irradiance are available, and those are generally not at the required sites of biological interest. There is therefore a need to establish quantitative methods to enable the spectral ultraviolet irradiance to be inferred at sites for which data are not directly available.

3. Research and methodology

The aim of the work will be to calculate the spectral and temporal distribution of the ultraviolet irradiance at the Earth's surface, at sites chosen for their relevance to biological investigations carried out in the Antarctic. The sites will be selected along a north-south transect extending from the northern edge of the ozone hole to near the southern limits of biological survival.

The calculations will combine theoretical and empirical techniques in order to achieve the widest applicability of the available experimental data. The relationships between measured ultraviolet irradiances and the controlling influences of the atmospheric regime will be established from experimental data drawn from Arctic and Antarctic stations of the NSF ultraviolet spectroradiometer network, together with data from Arctic field campaigns of the European spectroradiometer network in which BAS scientists have played a central role. Experience already gained from analyses of laboratory and field studies in ultraviolet spectroradiometry will allow instrumental characteristics to be taken into account when interpreting the available data.

A discrete-ordinate radiative transfer model will be used as a framework for the generalisation of observational data to atmospheric conditions at the times and locations where calculated irradiances are required. In particular, it will be possible to vary the ozone column, aerosol loading, cloud cover, and surface albedo, and to establish the spectral ultraviolet irradiance as a function of solar zenith angle for the specified atmospheric and surface regimes. The calculations will be related to observed conditions at Antarctic stations by making use of ozone, solar radiation, and cloud data drawn from the results of the BAS long-term climatological monitoring programmes.

Particular attention will be paid to the selective effects of different wavelengths, intensities and doses on biochemicals and metabolic processes which are susceptible to ultraviolet damage. The irradiance spectra from the radiative transfer model will be convolved with the action spectra for UV damage to the organisms and the protective pigment spectra to calculate the net biological effect of the incident UV radiation.

4. Wider implications

The methods and algorithms developed in this work will assist in the interpretation and application of spectral ultraviolet irradiance data from other parts of the world, and will provide guidance in the criteria to be applied when specifying ultraviolet spectroradiometer characteristics.

This project will also complement proposed studies of protection mechanisms developed by the relevant organisms to minimise or rectify damage caused to their diverse metabolic and reproductive systems by UV radiation.

5. References

Frederick, J.E. and A.D. Alberts. 1991. Prolonged enhancement in surface ultraviolet radiation during the Antarctic spring of 1990. Geophys. Res. Lett. 18(10), 1869-1871.

Garcia-Pichel, F. and R.W. Castenholz. 1993. Occurrence of UV-absorbing, mycosporine-like compounds among cyanobacterial isolates and an estimate of their screening capacity. Appl. and Env. Microbiol. 59, 163-169.

Garcia-Pichel, F., C.E. Wingard and R.W. Castenholz. 1993. Evidence regarding the UV sunscreen role of a mycosporine-like compound in the cyanobacterium Gloeocaspa sp. Appl. and Env. Microbiol., 59, 170-176.

Holm-Hansen, O., E.W. Helbling and D. Lubin. 1993. Ultraviolet radiation in Antarctica: inhibition of primary production. Photochem. and Photobiol., 58, 567-570.

Karentz, D. 1994. Ultraviolet tolerance mechanisms in Antarctic marine organisms. In Ultraviolet Radiation in Antarctica: Measurements and Biological Effects. Eds. Weiler, C.S. and P.A. Penhale. American Geophysical Union, Washington, D.C. Antarctic Research Series, 62.

Lubin, D., J.E. Frederick, C.R. Booth, T. Lucas and D. Neuschuler. 1989. Measurements of enhanced springtime ultraviolet radiation at Palmer Station, Antarctica. Geophys. Res. Lett. 16(8), 783-785.

Lubin, D., B.G. Mitchell, J.E. Frederick, A.D. Alberts, C.R. Booth, T. Lucas and D. Neuschuler. 1992. A contribution toward understanding the biospherical significance of Antarctic ozone depletion. J. Geophys. Res. 97(D8), 7817-7828.

Pentecost, A. 1993. Field relationships between Scytonemin density, growth, and irradiance in cyanobacteria occurring in low illumination regimes. Microbial Ecology 26, 101-110.

Post, A. and A.W.D. Larkum. 1993. UV-absorbing pigments, photosynthesis and UV exposure in Antarctica: comparison of terrestrial and marine algae. Aquatic Botany 45, 231-243.

Stamnes, K., Z.H. Jin, J. Slusser, C. Booth and T. Lucas. 1992. Several-fold enhancement of biologically effective ultraviolet radiation levels at McMurdo Station, Antarctica, during the 1990 ozone "hole". Geophys. Res. Lett. 19, 1013-1016.

Wynn-Williams, D.D. 1994. Potential effects of UV radiation on Antarctic primary terrestrial colonizers: cyanobacteria, algae and cryptogams. In Ultraviolet Radiation in Antarctica: Measurements and Biological Effects. Eds. Weiler C.S. and P.A. Penhale. American Geophysical Union, Washington, D.C., 243-257. Antarctic Research Series 62.