Review and direct evidence of transgressive aeolian sand sheet and dunefield initiation

The multiple hypotheses which exist to explain the initiation of transgressive aeolian sand sheets and dunefields, are reviewed and discussed. Direct evidence supporting many of these hypotheses is largely lacking. In South Australia, the Younghusband Peninsula coastal barrier extends ~180 km and predominantly comprises transgressive and parabolic dunefields. The 42 Mile Crossing area on the barrier is undergoing significant erosion at variable rates of 0.5 to 5.0 m/yr, and a new transgressive aeolian sand sheet has rapidly developed in ~1 year and is extending landwards at an average rate of 13 m/yr. This research provides unequivocal evidence that large-scale shoreline and dunefield erosion does lead to the development of a new transgressive aeolian sand sheet (and eventual dunefield) phase thereby demonstrating an initiation mechanism that is likely linked to future sea level rise and climate change. We also show that the initiation process, and, in particular, the subsequent rate of sand sheet transgression occurs at an incredibly rapid rate (+100 m in 8 years). Plain Language Summary: Coastal sand dunes border many of the world's coastlines and are highly adapted to local climate and conditions. How coastal dunes transition from predominantly vegetated and stable systems to wind-blown sand sheets and dunefields transgressing prior terrain is a research area of pressing relevance due to forecasts of sea level rise and climate change. The factors or triggers that are considered to initiate transgressive aeolian sand sheets and dunefields are reviewed. The formation and evolution of a new transgressive aeolian sand sheet phase triggered by large-scale shoreline erosion in South Australia is presented. According to the results from historical and satellite images, local shoreline erosion began in the late 1970s and has continued at highly variable rates. We show that once the foredune was removed, the high scarp created by wave erosion of the relict, vegetated transgressive dunefield destabilized and was then eroded by wind processes leading to the rapid development of a transgressive aeolian sand sheet. The initiation and evolution of the sand sheet provides an excellent example of how dunefields might respond to future sea level rise and climate change.