Building of shore-oblique transverse dune ridges revealed by ground-penetrating radar and optical dating over the last 500years on Tottori coast, Japan Sea

Coastal dunes provide valuable information on the past aeolian activity. Better characterization of internal dune structures and their chronology potentially can greatly improve the interpretation of past environmental changes. Ground-penetrating radar (GPR) and optically-stimulated luminescence (OSL) dating was applied to two transverse dune ridges which are arranged obliquely to the shoreline on the Tottori coast, Japan Sea. Data shows that the inner ridge has a core of Pleistocene dune draped with Holocene sand, while the outer ridge consists only of Holocene sand. The Holocene dune is generally dominated by landward migration, but the outer ridge shows a clear seaward accretion during the 18th century AD. OSL dating showed concordant results with radar stratigraphy and topographic changes since AD 1932 revealed by maps. From this we were able to present the first detailed report of the multi-decadal- to centennial-scale dune formation for the last 500. years in East Asia, contemporaneous with the Little Ice Age, during which many European coastal and inland dunes were activated. In East Asia, it is thought that the winter monsoon plays an important role for aeolian processes. The seaward migration during the 18th century reflects a decrease in wind capacity, which restricted sand transport nearshore, being related to decline in winter monsoon revealed by Chinese historical documents. In contrast, two remarkable events of landward accretion occurred in AD 1580-1640 and around AD 1840, respectively, corresponding to periods of increased dust fall in China, which suggest enhanced winter monsoon. The zone of maximum sedimentation shifted through time from the inner to outer ridges, and also towards the seaward end of the shore-oblique dune ridge, reflecting an expansion of the dune field caused by shoreline progradation. These suggest that the effective combination of GPR and OSL dating was critical in detailed characterization of the complicated depositional pattern of the transverse dune ridge, and thus in reconstruction of the past aeolian activity.