High-precision U-Th dating of storm-transported coral blocks on Frankland Islands, northern Great Barrier Reef, Australia

High-energy storm-transported coral blocks are widespread on the reef flats of the Great Barrier Reef (GBR), Australia, and have the potential to be used as proxies for reconstructing past storm/cyclone events prior to historical or instrumental records. In this study, samples from 42 individual transported coral blocks were collected from the inshore Frankland Islands, northern GBR for high-precision MC-ICPMS U-Th dating with their surface mortality ages recording the timing of individual storms or cyclones responsible for their uplift from their original growth position. The dated mortality ages were found to match well with known historical storm/cyclone events in the last century, with 80% of them falling within episodes of increased storm activity (1910-1915, 1945-1950, 1955-1960, 1975-1990, 1995-2000 AD) captured by instrumental/historic records, confirming that transported coral blocks on inshore reefs can be used as proxies for past storm/cyclone occurrences. Using this approach, this study also identified 17 additional storm/cyclone events that occurred before European settlement in the 1850s, including three oldest events at 758.4 ± 3.7, 777.9 ± 4.9, and 985.2 ± 4.8 AD, respectively. Our results, despite still preliminary, suggest that the storm/cyclone activity in this region tends to broadly correlate with the positive modes of the Pacific Decadal Oscillation (PDO) during the last millennium. In addition, there appears to be a decreasing age trend from the shore to the reef edge (from 758.4 ± 3.7 AD to 1988.3 ± 1.6 AD), which can be attributed to sea-level fall and/or reef/island progradation over the last 2000 years.