Linking climate variability and growth in coral skeletal records from the Great Barrier Reef

Abstract

The remoteness of the northern Great Barrier Reef makes observations of environmental change and coral health sparse, but provides opportunities for paleoclimate and paleoecology proxies to contribute new insights into coral health in a changing climate. These proxies include geochemical measures (δ18O, δ13C, and Sr/Ca) that track sea surface temperature (SST), salinity, and physiological processes; luminescence, which records freshwater input; and annual growth parameters (density, extension, and calcification). Merging these approaches provides insight into the historical role of environmental variability in coral health. This study uses Porites spp. corals from five sites on the northern Great Barrier Reef (12–13.5°S) to produce combined monthly resolved records of geochemistry, growth banding, and luminescence between 1972 and 2008. We demonstrate that SST reconstructed from Sr/Ca accurately captures Indo-Pacific Warm Pool variability, and hydrological proxies (luminescence and seawater δ18O) accurately reconstruct summer rainfall and river discharge in nearshore corals. Concurrent Sr/Ca minima and density and luminescence peaks from two sites demonstrate that high-density bands are generally formed during summer at these sites, which aids the development of future coral paleoclimate and paleoecology chronologies. Regional hydrological proxies showed more consistent responses to El Nino–Southern Oscillation (ENSO) events than SST proxies, in agreement with instrumental data. Because these corals, like instrumental records, show no consistently large ENSO heat extremes, we find no consistent growth anomalies during historical ENSO events. Our results highlight the unusual nature of recent widespread and severe coral bleaching and establish groundwork for exploring the response of northern GBR corals to past climate variations.