9:45 AM - 10:00 AM
[ACG42-04] Sediment transport in the Kujukuri coast revealed by luminescence
Keywords:OSL, sediment transport, Kujukuri
Luminescence signals of sediment particles have the potential for tracing sediment transport. In this study, sediment transport in the Kujukuri coast was investigated by measuring OSL signals of sediments. Residual doses of foredune, beach, and offshore sediments were evaluated from OSL signals, which are supposed to reflect the exposure conditions during sediment transport. OSL signals of offshore core samples, collected at water depths of 10 m, 15 m, 20 m, and 25 m, were also measured to determine depositional ages.
Residual doses of surface sediments were higher on the northern beach near the eroded sea cliff of Byobugaura, which is the main source of sediment supply, and lower on the central beach. The residual doses also decrease by a few Gy from the foreshore to adjacent foredune. These trends are interpreted as reflecting the increasing exposure to sunlight during sediment transport by longshore currents and wind. Residual doses of the offshore samples were not significantly different from those of the beach samples immediately landward regardless of the water depth, suggesting that surface sediment transport may extend offshore to a hundred and a few tens of meters in water depth. The offshore cores show that equivalent doses of samples from the surface to several tens of centimeter were almost equal to or slightly higher than the residual doses in the surface. It is indicated that sediment transport of several tens of centimeters from the surface occurs on the annual to decadal scales. Such information may provide criteria for the depth-of-closure. The results of this study could be improved with further constraints, such as the rate of OSL signal resetting and additional data of deeper sediment cores, which leads to a quantitative assessment of sediment transport.
Residual doses of surface sediments were higher on the northern beach near the eroded sea cliff of Byobugaura, which is the main source of sediment supply, and lower on the central beach. The residual doses also decrease by a few Gy from the foreshore to adjacent foredune. These trends are interpreted as reflecting the increasing exposure to sunlight during sediment transport by longshore currents and wind. Residual doses of the offshore samples were not significantly different from those of the beach samples immediately landward regardless of the water depth, suggesting that surface sediment transport may extend offshore to a hundred and a few tens of meters in water depth. The offshore cores show that equivalent doses of samples from the surface to several tens of centimeter were almost equal to or slightly higher than the residual doses in the surface. It is indicated that sediment transport of several tens of centimeters from the surface occurs on the annual to decadal scales. Such information may provide criteria for the depth-of-closure. The results of this study could be improved with further constraints, such as the rate of OSL signal resetting and additional data of deeper sediment cores, which leads to a quantitative assessment of sediment transport.