Penetration of ultraviolet B, blue and quanta irradiance into Svalbard waters

Observations from August 1991 and 1993 of downward UV-B, blue and quanta irradiances, and of colour indices and Secchi disc depths in the Greenland Sea and the northern part of the Barents Sea, are presented. The UV-B irradiance (306 nm) is on average reduced to 10% of its surface value at 5 metres depth, and to 1% at 10 m. Blue irradiance (465 nm) is reduced to 10% at 21 m, and to 1% at 41 m. The integrated quanta irradiance obtains the same reductions at 16 m and 35 m, respectively. These penetration depths correspond to Ocean Water Type III in Jerlov's classification. They are about twice the values of May-June 1973 observed by Aas & Berge, but they are half the values observed in September 1979 by Hojerslev. This variability may partly be seasonal, caused by the hydrological and light-climate cycles. The UV-B transparency of the Svalbard waters seems to be influenced by yellow substance from different freshwater run-offs, and there is probably no single relation between salinity and yellow substance content in this region. Statistical relations between the quanta irradiance and the colour index, the Secchi disc depth and the blue irradiance differ from one region to another, and from year to year.