On the inclusion of trace materials into massive coral skeletons .2. Distortions in skeletal records of annual climate cycles due to growth processes

Numerical models of skeletal growth in Porites (Taylor et al., 1993, 1995) are extended to examine the likely distribution of trace materials which become included in skeleton as the result of a continuous, annual cycle in their environmental concentration or in their uptake from the environment. Modelling suggests that the amplitude, profile and apparent timing of variations in the concentration of trace materials along skeletal growth axes may differ greatly from the amplitude, profile and timing of causative variations in the environment. Alterations of the recorded signal are associated with coral growth parameters such as annual extension rate and the depth of skeleton occupied by tissue, and with annual cycles in the density at which skeleton is deposited and annual cycles in skeletal extension rate. The models also indicate that the annual average obtained for the signal recorded in coral skeletons will vary from the annual average of the causative, environmental signal. Examples of recording of continuous, annual, environmental cycles by corals are temperature-related variations in skeletal concentration of O-18 and strontium. Published information about these coral thermometers is examined in terms of output from the models. The models are used to examine errors that may result from overly simplistic interpretation of temperature information stored in coral skeletons.