Meta-Study of Carbonate Sediment Delivery Rates to Indo-Pacific Coral Reef Islands

Coral reef islands are amongst the most vulnerable environments to sea-level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m-1 yr-1, but with substantial inter-island variability. Comparison with carbonate sediment production rates from census-based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR. Low-lying coral reef islands are under threat of sea-level rise (SLR). However, when these islands are flooded, ocean waves can bring in sediment that can increase the island elevation. This would enable coral reef islands to better withstand flooding in the future. Knowing how much sediment is brought in will help in our understanding of future changes to these islands due to SLR. In this paper, we use data from 28 Indo-Pacific coral reef islands to compute sediment supply to the islands. We find that on average 0.1 m3 of sediment (roughly 100 kg) is delivered each year for every meter of island shoreline. We further suggest that this implies that only one quarter of the sediments produced by the coral reef system is delivered to the island shoreline. Most of the sediment produced remains on the reef flat or is exported to the ocean or the lagoon. Our results will help future studies to predict more accurately how coral reef islands will adjust to SLR. We provide the first estimates of carbonate sediment delivery rates to 28 coral reef islands using all data available from the literature Sediment delivery to the reef islands occurs at a rate of c. 0.1 m3 m-1 yr-1, but with substantial inter-island variability Where island building has been continuous through island history, long-term delivery rates provide valuable estimates for contemporary rates