High-precision chronologies by 14C wiggle matching on laminated lake sediments

Abstract

Radiocarbon (14C) dating is a widely applied technique for the establishment of robust lake sediment chronologies. However, the quality of these chronologies strongly depends on a plethora of important parameters such as the material used for radiocarbon dating, the sampling resolution, the size of the samples or even the choice of the coring site. Only short-lived (e.g. needles, bud scales, periderms, leaves, and seeds), taxonomically identified (e.g. terrestrial plants and invertebrates), and well-preserved remains should be used as sample material in order to avoid reservoir age effects or even uncorrectable biases caused e.g. by charcoal pieces or bulk sediment analyses. Furthermore, the choice of a thoughtful sampling resolution and the application of an appropriate Bayesian deposition model for data evaluation (Bronk Ramsey, 2008) are both crucial. A stringent selection of the dating material and a high sampling resolution often requires the analysis of small remains (<5 mg). Sometimes, the usage of a gas ion source is helpful for samples <0.2 mg (Szidat et al., 2014). In the current work, we investigated two varved lake sediment sequences from Moossee and Burgaschisee, both located on the Swiss Plateau (Rey et al., 2017) to test the ideal sampling strategy for high-precision dating. Constant-year sampling (e.g. always ca. 10 years within one sample) instead of constant-depth sampling (e.g. every cm) revealed to be important to reduce the age uncertainties (Rey et al., 2018). Radiocarbon dating was performed at the LARA laboratory at the University of Bern (Szidat et al., 2014). The mean 2σ age uncertainties were reduced to ±19 cal years for Moossee and to ±54 cal years for Burgaschisee over the entire period of 3000 years, with 2σ uncertainties of only ±13 cal years and ±18 cal years, respectively, for shorter time intervals (Rey et al., 2018). These results imply that a sophisticated subsampling strategy and a careful selection of short-lived and well-defined terrestrial plant remains are essential for the establishment of high-precision chronologies. Bronk Ramsey, C. (2008), Quaternary Science Reviews 27, 42-60. Rey, F., et al. (2017), Vegetation History and Archaeobotany 26, 571-586. Rey, F., et al. (2018), Radiocarbon 60, in review. Szidat, S., et al. (2014), Radiocarbon 56, 561-566.