Coral record of harbour dredging: Townsville, Australia

Concentrations of Ba/Ca, Cu/Ca, Sr/Ca and Zn/Ca were measured by secondary ion mass spectrometry in a branching coral, Pocillopora damicornis, from a coral reef receiving suspended sediments from Townsville Harbour dredging activities. The Sr/Ca record correlated with observed sea surface temperatures (SST), which allowed pulse inclusions of barium, copper and zinc to be dated and compared with various environmental records. Copper and zinc concentrations in this coral skeleton correlated with short exposures to labile metals in resuspended fine sediment. The biota–sediment accumulation factor (BSAF) indicated that concentrations of these metals in the coral skeleton were lower than the labile fraction in the sediment (BSAF=0.15 and 0.18, respectively). Distortions to the timing and amplitude of pulse-records in the coral record may have been caused by seasonal variation in skeleton growth. High barium concentrations in the coral skeleton recorded during a dry period corresponded with weather events that resuspended fine, inner-shelf sediment, specifically local winds interacting with swells driven by offshore trade winds, and dredging of the harbour's access channel. This coral has recorded entry of resuspended fine sediment into the reef. Irregularities in the strontium paleothermometer were similar to the solar radiation profile, which preceded variation of seawater temperature by about a month. When coral records were temporally adjusted to fit variation in solar radiation, the correlation between strontium and solar radiation was greater than the strontium–temperature correlation used to date the coral