Trace element Porites coral records of recent marine heat wave events from the northwest shelf of Australia

The ability of massive corals to record the impacts of marine heat wave events provides a unique perspective into the variable responses of corals to anthropogenic climate change. In this study, coral cores (Porites sp.) were collected from 7 different reef environments across the NW shelf of Australia to examine the seasonal pattern of trace element (TE) Sr/Ca and Li/Mg ratios, and extension rate signatures associated with past marine heat waves in the region. Trace element anomalies and declines in linear extension rate were observed in the records during the late 1990s (1 of 5 records) and more recently during the summers of 2011 (3 of 7 records) and 2013 (5 of 7 records), indicating the impacts of marine heat waves have become increasingly widespread in the region. However, for the summers of 2011 and 2013, no significant relationships were observed between the magnitude of these TE ratio anomalies in the core records, and maximum thermal stresses predicted at the reef sites from high-resolution satellite records. We show that the strongest individual reductions in linear extension rates and associated ratio anomalies occurred during the 2011 heat wave, rather than during the subsequent and more intense (~ 1 °C warmer) 2013 event. Together these observations suggest that at the local reef-scale Porites colonies and their symbionts exhibit differential responses to heat wave events, with the prior exposure to less intense events probably playing an important role in acclimatisation.