VERIFICATION OF ANNUAL GROWTH INCREMENTS IN ARCTICA-ISLANDICA L FROM THE NORTH-SEA BY MEANS OF OXYGEN AND CARBON ISOTOPES

C-14 analysis of material from the shells of Arctica islandica support s the hypothesis that the clear and definite bandings of these shells are annual rings. The pulse of C-14 around 1960, resulting from atmosp heric nuclear-bomb testing was recorded in the shell at a location in concurrence with that expected from band counting. The observed cyclic variation in stable isotopes of oxygen and carbon coincided with grow th bands. This variation, at least for O-18, agreed with annual temper ature variations and suggests that growth bands are a reflection of se asonally determined differential growth rates. The longevity of indivi duals of this species, coupled with variations in band width, may prov ide important information regarding growth and productivity, as well a s a record of past environmental conditions.