(18)O/(16)O and (13)C/(12)C in an ahermatypic deepwater coral Lophelia pertusa from the North Atlantic: A case of disequilibrium isotope fractionation

The numerous stable isotope studies of scleractinian photosynthetic reef-building corals in tropical seas have demonstrated the complexity of the biological and environmental factors that give rise to their isotopic composition. Scleractinian non-photosynthetic corals of the deep cold water environment might be expected to reflect the more stable physical environment in the deep sea. However, in comparison, little is known about their isotope systematics. The present study concentrates on specimens of Lophelia pertusa from the north-eastern Atlantic, the Norwegian Shelf and Fjord. Aliquots taken from the theca represent time series and show variations in δ(13)C and δ(18)O of up to 4.7 and 2.4‰, respectively. The variations seem to be related to morphological features of branching. The tendency of higher values near the tip of the polyps reported previously was detected only in some samples. The δ(18)O of the corals are in all cases more negative than the equilibrium values. There is a strong correlation between δ(13)C and δ(18)O forming linear arrays. The difference between these arrays is more pronounced in δ(13)C. The covariation of δ(13)C and δ(18)O indicates an overruling 'kinetic isotope effect'. This is in line with the behaviour of some trace elements. This isotope effect should be regarded as one manifestation of variations in partition coefficients dictated by a biological control on mineralisation (such as food or reproduction) rather than changes in the relative contribution of metabolic carbon affecting δ(13)C, and changes in temperature affecting δ(18)O. (C) 2000 John Wiley and Sons, Ltd.