Incremental accretion of a sandy reef island over the past 3000 years indicated by component-specific radiocarbon dating

Low-lying reef islands appear particularly threatened by anticipated sea-level rise, and determining how they formed and whether they are continuing to accumulate sediment is essential for their sustainable management. Depositional chronology of Warraber Island, a small sand cay in Torres Strait, Australia, is re-examined based on AMS radiocarbon dating of specific skeletal components. Whereas radiometric dating of bulk sand samples indicated one or more discrete phases of mid-late Holocene deposition, component-specific AMS radiocarbon dating of sand grains indicates sustained incremental growth over the past 3000 years. Ages on gastropods that lived on the reef flat around the island indicate continuing sediment production and island progradation, in contrast to bulk ages and other components produced at greater distances. Growth of sand cays depends on the rate and pattern of sediment supply, which are functions of the local ecology of the surrounding reef and reef flat, and hydrodynamic constraints.