A high resolution delta C-13 record in a modern Porites lobata coral: Insights into controls on skeletal delta C-13

delta C-13 was determined at a high spatial resolution by secondary ion mass spectrometry (SIMS) across a 1 year section of a modern Porites lobata coral skeleton from Hawaii. Skeletal delta C-13 is dominated by large oscillations of 5-7 parts per thousand that typically cover skeletal distances equivalent to periods of similar to 14-40 days. These variations do not reflect seawater temperature and it is unlikely that they reflect variations in the delta C-13 of local seawater. We observe no correlation between skeletal delta C-13 and the pH of the calcification fluid (estimated from previous measurements of skeletal delta B-11). We conclude that either the proportion of skeletal carbon derived from metabolic CO2 is not reflected by estimated ECF pH (as the [CO2] in the overlying coral tissue varies) and/or the delta C-13 composition of the metabolic CO2 is highly variable. We also observe no correlation between skeletal delta C-13 and previous delta O-18 SIMS measurements. Variations in skeletal delta C-13 and delta O-18 do not have a common timing, providing no evidence that skeletal delta C-13 and delta O-18 vary in response to a single factor. This suggests that skeletal delta C-13 is principally driven by variations in the delta C-13 composition of metabolic CO2 rather than by the abundance of metabolic CO2, which would also affect skeletal delta O-18. The delta C-13 composition of metabolic CO2 reflects the processes of photosynthesis, heterotrophic feeding and respiration in the overlying coral tissue. Corals catabolise stored lipid reserves to meet energetic demands when photosynthesis conditions are sub-optimal. Variations in the amounts and types of reserves utilised could induce changes in the delta C-13 composition of metabolic CO2 and the resultant skeleton which are temporally offset from skeletal delta O-18 records. (C) 2012 Elsevier Ltd. All rights reserved.