Response of the Great Barrier Reef to sea level and environmental changes over the past 30,000 yearsCitation for published version:

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The shelf of the Great Barrier Reef (GBR) was progressively marine flooded from the last glaciation maximum (LGM) (ca 20 ka BP) until the last sea-level highstand (ca 6 ka BP), affecting the depositional evolution of the GBR margin and associated deposits. However, the physiographic variables related to this process have not been fully characterized, especially in relation to the sedimentary processes at the shelf margin. For this study, we used a bathymetric model of the entire shelf and a shelf margin sub-set, divided into 33 latitudinal zones. Postglacial marine flooding was simulated and flooded area (km 2 ), flooding magnitude (km 2 per sea-level increment), flooding rate (km 2 . ky -1 ) and coastline length (km) were estimated for each zone, from 130 m to 0 m below present sea level, representing the period from 20 ka to 6 ka BP. Our results show that the postglacial marine flooding did not occur uniformly and that some sub-regions (e.g. the southern-central GBR) had early and rapid flooding. Coastal complexity increased in the mid-postglacial, reaching maximum values at around 9 ka BP. This reflects a coastal landscape evolving from a linear, laterally connected coast to a complex coast dominated by estuaries and lagoons, partly returning to its initial linearity during highstand. Flooding trends and geological evidence make two depositional relationships apparent. Firstly, the timing and magnitude of the off-shelf sediment flux appears linked to the presence and orientation of a shelf-edge rim, and to the extension and morphology of the evolving drainage network. Secondly, the periods of shelf-edge reef

Shallow (<200 m) submarine landslides influence margin evolution and can produce devastating tsunamis, yet little is known about these processes on mixed siliciclasticcarbonate margins. We have discovered seven landslides along the shelf edge and upper slope of the central Great Barrier Reef (GBR), Australia. The largest shelf edge landslide is investigated in detail and represents a collapse of a 7 km long section of the shelf edge at 90 m water depth with coarse debris deposited up to 5.5 km away on the upper slope down to 250 m. The precise timing and triggering mechanisms are uncertain but available chronologic and seismic stratigraphic evidence suggest this event occurred during the last deglacial sea-level rise between 20 and 14 ka. Regional bathymetric data confirms that these shelf edge and upper slope slides are restricted to the central GBR between latitude 18° and 19°S, suggesting a spatial relationship between the extensive Burdekin paleo-fluvial/delta system and shallow landslide activity. This study highlights an important local mechanism for the generation of tsunamis on this margin type, and numerical simulations under present conditions confirm a 2 to 3 m tsunami wave could be produced locally. However, we consider that the risk of such slides, and their resulting tsunamis, to the modern coastline is negligible due to their relatively small size and the capacity of the GBR to dissipate the wave energy.