Optically stimulated luminescence dating of young estuarine sediments:: a comparison with 210Pb and 137Cs dating

A sediment core taken from a tidal mudflat in Ho Bugt in the northernmost part of the Wadden Sea in Denmark is used to explore the application of optically stimulated luminescence (OSL) dating to young fine-grained estuarine sediments, using Pb-210 dating and the Cs-137 Sellafield peak from 1980 as independent age control. Despite the anticipated difficulties of weak luminescence signals and incomplete resetting of residual radiation dose prior to deposition, the OSL ages from the sediment core ranged from 7.0+/-1.5 at the surface to 305+/-16 years (68 cm depth). OSL- and Pb-210-dates were in good agreement back to similar to1975, and even as far back as similar to1945 using the CRS-model. The average OSL age of 9+/-3 years for the surface mixing zone indicates that the OSL signal of the quartz grains was well zeroed at deposition. The OSL ages give new information on past deposition regimes on the Ho Bugt mudflat: fine-grained sediment started to deposit at similar to0.5 mm year(-1) approximately 300 years ago, when a terrestrial reed-swamp was transgressed. About 100 years ago, the sedimentation rate increased to similar to4 mm year(-1). Approximately 40 years ago, the sediment became more fine-grained, perhaps because of emergence of the tidal flat; the accretion rate at that time was already well above the local rate of sea-level rise of similar to1 mm year(-1). The post-1980 accretion rate was found to be similar to16 mm year(-1) with OSL dating and similar to9-12 turn year(-1) with Pb-210 and Cs-137 dating. Advantages of the OSL method include applicability over a much larger time-span (similar to125 ka compared to similar to120 years for Pb-210) and a lack of significant dependence on changes in mean grain size or Pb-210 supply. With this method, it is also possible to date sediment cores from sand flats, providing a new approach to the problem of evaluation of stability and calculation of sediment budgets for estuaries and coastal lagoons. (C) 2004 Elsevier B.V. All rights reserved.