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 supports the hypothesis that the clear and definite bandings of these shells are annual rings. The pulse of C-14 around 1960, resulting from atmospheric 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 growth bands. This variation, at least for O-18, agreed with annual temperature variations and suggests that growth bands are a reflection of seasonally determined differential growth rates. The longevity of individuals of this species, coupled with variations in band width, may provide important information regarding growth and productivity, as well as a record of past environmental conditions.