Oxygen and carbon isotope ratios related to growth line patterns in skeletons ofLophelia pertusa(L) (Anthozoa, Scleractinia): Implications for determination of linear extension rate

Abstract

Abstract Patterns of growth lines and the composition of stable oxygen and carbon isotopes were studied in skeletons of the deep-water scleractinian Lophelia pertusa in longitudinal and transverse sections of corallites. δ180 showed a significant, positive linear correlation with δ13C. A gradual depletion of δ180 and BC was found in the theca, both towards the corallite edge within single growth layers, and across growth layers from the theca surface. δ18O was negatively correlated with the rate of linear extension. These results indicated that isotopic fractionation in Lophelia is controlled by kinetic isotope effects. The range of δ180 was 3.5 times larger than expected for aragonite precipitating in isotopic equilibrium with ambient sea water. However, the shape of the δ180 curve along the growth axis in the septa was almost parallel with the curve of sea water temperatures. This correspondence may be caused by a relation between growth rate and temperature or other environmental variables correlated with temperature. The δ180 curve fitted best with the temperature curve when the pronounced growth lines were assigned to the first quarter of the year. A 6 year growth line chronology was established for corallites in one colony. Between 10 and 14 fine lines were counted between pairs of the more pronounced annual lines in the septa. An average linear extension rate of 5.5 mm/yr was suggested based on measured distances between distal ends of adjacent growth layers in the theca. Colonies of Lophelia from one locality were kept alive in aquarium for 18 months before analysis. Direct measurements on these corallites showed that the linear extension decreased to 2.6 mm/yr.