The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation–biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report.
KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This study was undertaken with the support of CSIRO Oceans and Atmosphere, and through resources made available through the eReefs project, the CSIRO Marine and Coastal Carbon Biogeochemistry Cluster, and the Australian Climate Change Science Program. The observations at Yongala were sourced as part of the Integrated Marine Observing System (IMOS)—IMOS is supported by the Australian Government through the National Collaborative Research Infrastructure Strategy and the Super Science Initiative. We thank Sven Uthicke for making his observations publically available, Professorss Tom Trull and Sabina Belli for their constructive comments on the manuscript, Miles Furnas who willingly shared his knowledge of the region and provided observations and three anonymous reviewers.