Corals are sensitive to changes in climate and, recently, high-latitude coral communities have received increased attention for their ability to act as refugia during global climate change. In this study, I report high resolution elemental ratio and stable isotope (δ18O, δ13C) time-series generated from the faviid coral Plesiastrea versipora to assess the fidelity of chemical variations in coral skeletons to reconstruct environmental conditions along the southern margin of Australia.

High resolution laser-ablation inductively-coupled plasma mass spectrometer (ICP-MS) analyses of established paleo-temperature proxies including B/Ca, Mg/Ca, Sr/Ca Ba/Ca and U/Ca, a suite of minor trace elements (Li, P, V, Mn, Cu, Zn, Y, Zr, Mo, Cd, Sn, Ba, Ce, Pr, Nd, Pb) and milled δ18O and δ13C analyses were obtained from seven cores of P. versipora from Gulf St Vincent and Spencer Gulf (35ºS), South Australia. Colony ages ranged from 100-400 years and annual extension rates for P. versipora varied from 1.2 to 8 mm yr-1 and these extension rates are among the slowest growth rates reported for hermatypic corals.

The potential of Plesiastrea versipora to capture the full seasonal cycle of sea surface temperature (SST) variation (10-24°C) in the South Australian gulfs was assessed by comparing skeletal chemistry with in situ SST data. Proxy/SST calibrations generated from the fast growing corals (> 3 mm yr-1) of Sr/Ca, U/Ca and δ18O were comparable to published SST calibrations for other species. Ba/Ca generally displayed a strong inverse correlation with SST and was the trace element which captured the full amplitude of the seasonal cycle with highest fidelity.

Trace metal analyses conducted on Plesiastrea versipora indicate substantial contamination in several sites in Spencer Gulf and Gulf St. Vincent. Trace metal contamination was associated with changes in urban and industrial development, and land use changes. The coastal corals from Seacliff reef recorded increased concentrations of lead, most likely due to the proliferation of automobiles in the 1960s. Increased concentrations of other heavy metals including Cu, Sn, Zn and Mn may be related to the discharge of treated sewage at a coastal site less than 10 km away. The corals from Whyalla indicated higher concentrations in the heavy metals Zn, Sn and Pb and the source of the contamination is likely to be nearby smelters. Light rare earth element (Y, La, Ce, Pr, Nd) enrichment occurred in three corals. This enrichment had a positive correlation with westerly winds suggesting an aeolian dust source.

Two coral colonies separated by less than 10 m display considerably different maximum concentrations of several metals including Cu, Mn, Zn, Sn and Pb. This suggests that distribution coefficients vary within a species, and are dependant on growth rate or another colony specific mechanism. Caution should be used when applying published distribution coefficients to different species and growth rates and estimating seawater concentrations from coral trace metal concentrations. δ13C analyses from a slow growing colony revealed a significant correlation with surface oceanic 13C depletion from fossil fuel CO2 (0.8‰) from the early 1930s to 2005 (the Suess effect).

The results from this study demonstrate that Plesiastrea versipora provides valuable paleoclimate information in high-latitude environments, recording seasonal and long-term variation in productivity regimes with high fidelity. This archive may be employed to reconstruct anthropogenic activity since European settlement and land-use changes not only in temperate Australia but other temperate regions in Asia and Africa.