Amy J. Dougherty

Towards more robust chronologies of coastal progradation: Optically stimulated luminescence ages for the coastal plain at Moruya, south-eastern Australia

Accurate chronologies are fundamental for detailed analysis of palaeoenvironmental conditions, archaeological reconstructions and investigations of Holocene coastal morphological changes. Chronological data enable estimation of rates of shoreline progradation, and provide appropriate context for forecasting future coastal changes. A previously reported radiocarbon chronology for the Moruya coastal plain in south-eastern Australia indicated a decelerating overall rate of progradation with minimal net seaward shoreline movement in the past ~2500 years. Single-grain and multi-grain aliquot optically stimulated luminescence (OSL) analyses demonstrate that marine sands from this region have excellent luminescence characteristics. A series of OSL ages across this coastal barrier indicates a remarkably linear trend of Holocene shoreline progradation. The linear trend of seaward shoreline movement indicates that the barrier has grown at an average rate of 0.27 m/yr with successive ridge formation every ~110 years. The oldest ridge on the barrier appears to correspond to cessation of rapid post-glacial sea-level rise, and the large foredune at the seaward margin of the barrier is <400 years old. The contrast between the existing radiocarbon chronology and the OSL ages reported in this study implies the need for a more cautious interpretation of coastal barrier chronologies, in Australia and around the world, where they have been based on radiocarbon dating of shell hash.

Prograded Barriers + GPR + OSL = Insight on Coastal Change over Intermediate Spatial and Temporal Scales

ABSTRACT Dougherty, A.J.; Choi, J-H., and Dosseto, A., 2016. Prograded Barriers + GPR + OSL = Insight on coastal change over intermediate spatial and temporal scales. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 368–372. Coconut Creek (Florida), ISSN 0749-0208. Sea level is predicted to rise ∼1m by the next century but the response of sandy shorelines is unknown. Understanding past centennial-scale coastal change is crucial to forecast erosion and prepare vulnerable communities/infrastructure for the impact of climate change. To predict intermediate-scale shoreline behavior, models of short-term morphodynamics along beaches and longer-term coastal landscape evolution are integrated. However, limitations exist as process-based engineering models depend on wave climate and beach profile data restricted to historical records (decadal at best), while large-scale coastal behavior models are based on general stratigraphic data inferring evolutionary trends over millennia. Detailing the stratigraphy of paleo-beachfaces preserved beneath Holocene beach ridges, and accurately dating them, could fill this gap by allowing short-term records of present-day beach morphodynamics to be extended over hundreds and thousands of years. This paper aims to demonstrate how using Ground-Penetrating Radar (GPR) and Optically Stimulated Luminescence (OSL) on prograded barriers can achieve this. To illustrate the potential of these methods, decades of research from strandplains in North America, New Zealand and Australia are synthesized to show how: 1) mapping the geometry of paleo-beachfaces can provide Holocene storm records, 2) digitizing the height of paleo-beachfaces could reconstruct sea-level curves, and 3) calculating barrier lithesome area/volume will quantify sediment supply with respect to accommodation space. Storms, sea level, and sediment supply are essential components determining beach behavior; this proposed methodology can yield empirical data on these mechanisms over the centennial-scale providing insight, and input to models, critical for protecting coasts threatened by global warming.

Mapping grapevine vigour, topographic changes and lateral variation in soils

Direct mapping of variability in soils can be a complex, time-consuming and costly process. Consequently, maps of geophysical data such as ground penetrating radar (GPR) and electromagnetic induction (EMI) are commonly used as proxies for soil maps, and these geophysical maps are most useful if they relate to variations in plant attributes such as grapevine trunk circumference. This article demonstrates that vine trunk circumference in five pinot noir vineyards is primarily influenced by changes in slope, elevation and aspect. Variability in GPR maps shows mixed correlations with vine trunk circumference data. In contrast, multi-frequency EMI surveys yield soil apparent electrical conductivity data that commonly show significant correlations with variations in vine trunk circumference data, especially when coupled with global positioning system surveys, suggesting that this is the preferred geophysical tool for mapping variability in soils.