Evaluation of annual resolution coral geochemical records as climate proxies in the Great Barrier Reef of Australia

Sampling of annually banded massive coral skeletons at annual (or higher) resolutions is increasingly being used to obtain replicate long-term time series of changing seawater conditions. However, few of these studies have compared and calibrated the lower annual resolution records based on coral geochemical tracers with the corresponding instrumental climate records, although some studies have inferred the climatic significance of annual coral series derived from averages of monthly or sub-annual records. Here, we present annual resolution analysis of coral records of elemental and stable isotopic composition that are approximately 70 years long. These records were preserved in two coexisting colonies of Porites sp. from Arlington Reef, on the Great Barrier Reef in Australia, and are used to evaluate the climatic significance of annually resolved coral geochemical proxies. The geochemical records of coral sample 10AR2, with its faster and relatively constant annual growth rate, appear to have been independent of skeletal growth rate and other vital effects. The annual resolution of Sr/Ca and Delta delta O-18 time series was shown to be a good proxy for annual sea surface temperature (SST; r = -0.67, n = 73, p < 0.0000001) and rainfall records (r = -0.34, n = 67, p < 0.01). However, a slower growing coral sample, 10AR1 showed significantly lower correlations (r = -0.20, n = 71, p = 0.05 for Sr/Ca and SST; r = -0.19, n = 67, p = 0.06 for Delta delta O-18 and rainfall), indicating its greater susceptibility to biological/metabolic effects. Our results suggest that while annually resolved coral records are potentially a valuable tool for determining, in particular, long timescale climate variability such as Pacific Decadal Oscillation, Interdecadal Pacific Oscillation, and other climatic factors, the selection of the coral sample is important, and replication is essential.