Tropical river flow and rainfall reconstructions from coral luminescence: Great Barrier Reef, Australia

Rainfall and river flow in northeast Queensland, Australia, are highly seasonal and show high interannual and decadal variability that is modulated by El Nino-Southern Oscillation (ENSO) events and the Pacific Decadal Oscillation (PDO). Reconstructions of October-September freshwater input to the Great Barrier Reef lagoon and October-September Queensland rainfall are developed from visual assessment of the occurrence and intensity of luminescent lines in massive Porites from up to 25 coral cores from 15 nearshore reefs regularly influenced by river flood plumes. Separate reconstructions are developed for four rivers (Herbert, Burdekin, Pioneer, and Fitzroy), and these are used to reconstruct total annual freshwater flow into the Great Barrier Reef (69-74% variance calibrated) and an index of Queensland rainfall (53-57% variance calibrated). The reconstructions extend back to 1631 but are most reliable from 1661 and capture significant decadal variability. The reconstructions provide insights into long-term tropical rainfall and river flow variability and the behavior of ENSO and the PDO over several centuries. Significant, though weak, relationships are found between these reconstructions and an independent reconstruction of ENSO. The reconstructions highlight that observations from the instrumental records of high interannual and decadal rainfall and river flow variability in northeast Australia also characterize the past few centuries. Although there appears to be no overall trend toward wetter or drier conditions, the reconstructions suggest that the variability of rainfall and river flow has increased during the twentieth century with more very wet and very dry extremes than in earlier centuries, as projected for the region as a consequence of global warming.