Holocene evolution of the Ninety Mile Beach sand barrier, Victoria, Australia: The role of sea level, sediment supply and climate.

Abstract

The Ninety-Mile Beach (NMB) barrier system in southeastern Australia is the largest active barrier island system in Australia. The response of a sandy barrier system to a warming climate is dependent on the boundary conditions of sediment supply and sea level. Deposition during the Holocene can therefore provide an indication of how these barriers may change in the future. In this study airborne LiDAR, ground penetrating radar and subsurface coring were combined with 46 optically-stimulated luminescence and 32 radiocarbon ages to provide a detailed understanding of sedimentation of NMB through the Holocene. The barrier complex formed in three distinct phases dating back to the earliest stabilisation of sea level after the Postglacial Marine Transgression. First, restriction of the flooded open-ocean embayment that had formed around a Last Interglacial beach-barrier sequence occurred with accretion of an island complex at around 8000 years BP, sourced from transgressive sands reworked from the shelf. In the second phase, at around 6000 years BP, a second barrier island formed seaward of the Last Interglacial barrier but disconnected from the earlier Holocene barrier islands by a large tidal inlet. Waning sediment supply from the shelf meant that aggradation of these islands slowed by 4000 years BP. The third and final phase occurred after 3000 years with the initiation of sediment supply at the southwestern end of the barrier. The island system which formed seaward of the Last Interglacial barrier then prograded by several hundred metres and elongated in a northeasterly direction by tens of kilometres infilling the tidal inlet and enclosing the earliest Holocene barrier landward of a newly created lake. Sediment supply appears to be the primary limiting factor in the development of NMB with indications of a change in wave climate and sea level have an influence on barrier evolution.