EFFECTS OF ULTRAVIOLET-B RADIATION ON PRIMARY PRODUCTION ALONG LATITUDINAL TRANSECTS IN THE SOUTH-PACIFIC OCEAN

Ambient intensities of solar ultraviolet radiation inhibit photosynthe sis in the upper layers of the oceans. In this study the effect of ult raviolet-B radiation (UVBR) (290-320 nm) on marine phytoplankton carbo n fixation during two latitudinal transects through the South Pacific ocean were measured to determine a dose-response model for estimating UVBR effects in natural surface populations and to identify latitudina l variation in UVBR sensitivity. Photoinhibition increased linearly wi th increasing doses of UVBR as weighted by the DNA action spectrum, wi th no apparent threshold for effect. The dose-rate response was nearly constant at low latitudes but varied at higher latitudes. Ambient int ensities of UVBR cause photoinhibition and it is likely that even smal l increases in surface UVBR will cause additional photodamage. A quant itative estimate of the long-term effect of UVBR on marine phytoplankt on, however, cannot be made from short-term measurements of photoinhib ition since factors such as vertical mixing, photorepair, and photoada ptation will modify the final expression of UVBR damage.