Growth-limiting size of atoll-islets: Morphodynamics in nature

Several linear models have been proposed for islet evolution. These models do not address the non-linear processes contributing to islet evolution or account for feedback between islet morphology and the fluid dynamics leading to sediment sequestration. The non-linear Sediment Allocation Model (SAM) has also been proposed for atoll-islet evolution. The SAM is a quantitative model of atoll-islet development implemented assuming that there is morphodynamic feedback between islet topography and the fluid dynamics leading to sediment sequestration in islet sinks. The SAM requires measurements of islet volume to recover parameters in the model using a data inversion algorithm. The SAM was developed and tested using synthetic data in order to determine the effect of errors in the islet volume measurements on model parameters. In this study the model parameters are estimated using radiocarbon-dated samples from published field studies of islet development on atolls. These calibration procedures involved reanalysis of the data using methods consistent with the morphodynamic principles of islet growth underlying the SAM. The results support a pattern of islet growth characterized by rapid lateral expansion followed by diminishing vertical accretion and shoreface rotation due to morphodynamic feedback.