Holocene evolution of the Great Barrier Reef: Insights from 3D numerical modelling

Abstract

The Holocene reef in the outer Great Barrier Reef (GBR) represents an archetypal reef system, forming a thin veneer (10–30m) built upon an older Pleistocene reef surface. The morphology, stratigraphy and maturity (degree of lagoonal sediment infilling) of the modern reef results from the complex interplay between biologic and abiologic processes (reef accretion, sediment erosion, transport and deposition), basement substrate, and Holocene sea level rise. Combining 3D forward stratigraphic modelling (CARBONATE-3D) with a re-analysis of published observational data, we quantitatively simulate the Holocene evolution of One Tree Reef (Southern GBR) as a well constrained, model system, and explore the main processes affecting reef growth in the GBR and elsewhere. We test the influence of different basement substrate surfaces, sea level curves, reef accretion rates, sediment erosion and transport parameters and assess their relative importance in controlling reef evolution—particularly growth histories, 3D internal structure and stratigraphy and reef maturity. Quantitative comparisons between our “best estimate” model output and the observed data confirm that we are able to simulate a 75% match of the main morphologic and growth characteristics of One Tree Reef. The range of parameters tested produced the full spectrum of reef maturities from unfilled “juvenile” buckets to planar “senile” reefs with completely sediment infilled lagoons. We conclude that the shape and depth of the basement substrate has the strongest influence—significantly impacting reef evolution and final maturity including the shape of the “bucket”, the size of the reef margins and internal reef structure. In contrast, variations in sea level, sediment production, erosion and transport mainly controlled the degree of lagoonal sediment filling. This study has implications for better understanding the past evolution of the GBR and other reefs but also lays the foundation for improved predictions of possible trajectories of modern reefs in general in the face of future environmental changes.