Rapid reef island formation and stability over an emerging reef flat: Bewick Cay, northern Great Barrier Reef, Australia
P.S. Kench et al., School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand. Published online 2 Mar. 2012, doi: 10.1130/G32816.1.
The study presents new and significant scientific findings on the conditions necessary for the formation of reef islands on the western boundary of the Pacific Ocean during the Holocene. P.S. Kench of the University of Auckland and colleagues present a model that resolves reef island formation in relation to both reef platform substrate development and mid-Holocene sea level change for Bewick Island, northern Great Barrier Reef (GBR), based on morphostratigraphic analysis and radiocarbon dated island sediments and reef corals. On Bewick, elevated and fossil corals record reef flat development at higher sea level (1.5 m) by 6,500 years before present. Island building began on a partially emergent reef flat 5,000,000 years before present, when sea level was 0.5 m above present. As sea level fell to its present level, the reef platform closed the process window and the island core stabilized. Results present the first unequivocal evidence of island building directly over a reef flat comprising micro-atolls, and the first detailed model of island formation from the GBR. The model demonstrates that the interplay of sea level and reef surface elevation can vary between sites but their convergence is critical for island initiation. Future trajectories of island change will vary dependent on the unique relative sea level and substrate depth conditions that govern island formation.
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