Optical dating of dune ridges on Romo, a barrier island in the Wadden Sea, Denmark

The application of optically stimulated luminescence (OSL) to the dating of recent aeolian sand ridges on Romo, an island off the southwest coast of Denmark, is tested. These sand ridges began to form approximately 300 years ago, and estimates of the ages are available from historical records. Samples for OSL dating were taken similar to 0.5 m below the crests of four different dune ridges; at least five samples were recovered from each ridge to test the internal consistency of the ages. Additional samples were recovered from the low lying areas in the swales and from the scattered dune formations in a broad hummocky area landward of the well-defined ridges. Despite low luminescence signals, we were able to obtain a mean age for the youngest ridge of 17 +/- 2 years, consistent with the known age of < 28 years. Optical ages of individual samples in our study ranged between 10 +/- 3 years and 690 +/- 50 years, and all ages were broadly consistent with those expected from historical information. The oldest aeolian surface on Romo appears to be 370 +/- 30 years. This is built on what we interpret as a marine sandbank, whose surface is similar to 700 years old. The sand ridges seaward of the hummocky dune field have well-defined building phases separated by inactive periods and the first major ridge formed similar to 235 years ago. This study demonstrates that optical dating can be successfully applied to these young aeolian sand deposits, and we conclude that OSL dating is a powerful chronological tool in studies of coastal change.