Marine radiocarbon reservoir effects (MRE) in archaeology : temporal and spatial changes through the Holocene within the UK coastal environment

• Main Author: Russell, Nicola
• Published: University of Glasgow 2011
• Subjects: 930.1; QE Geology : CC Archaeology
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.541012

The purpose of this research was to investigate temporal and spatial trends in the Marine Radiocarbon Reservoir Effect (MRE) on the North Sea coast of Scotland throughout the Holocene. The MRE is a 14C age offset between contemporaneous marine derived carbon and its terrestrial counterpart, owing to the extended residence time of 14C in oceanic environments. This results in marine samples being depleted in 14C relative to contemporaneous terrestrial samples and consequently, the production of 14C ages that are erroneously old. The offset between contemporaneous marine and terrestrial entities varies through space and time on a global scale and so a single correction factor cannot be universally applied. In order to gain a coherent understanding of the MRE, its variability and its full impact on the radiocarbon dating of samples containing marine derived carbon, a brief background to the fundamental principles of radiocarbon dating is presented. This is followed by a global overview of variability in the MRE before focussing on the UK coastal environment, and in particular the North Sea coast of Scotland. Using contemporaneous multiple terrestrial and marine entities from secure archaeological contexts, this thesis investigates the MRE as represented by 13 contexts from 9 archaeological sites spanning a geographical range from Aberdeen in the north to Dunbar in the south. The sites are predominantly Medieval in age, owing to sample availability, and cover a calendar age range of c. 600 – 1500 AD. This thesis recommends the use of the multiple paired sample approach for ΔR calculations and the publication of ΔR using histograms alongside weighted mean values and the standard error for predicted values in order to provide a more accurate estimate of where ΔR values measured in the future for a similar site and location may lie. In so doing, a weighted mean for the sites studied in this thesis has produced a ΔR for the period described above of -19 ± 52 14C yrs. This thesis also compared ΔR values calculated using mollusc shell with those calculated from fish bone and found that although fish bone produces a slightly increased ΔR, this offset is not significant using the standard error for predicted values. When the fish bone results are included in the weighted mean for the study region; ΔR = -29 ± 51 14C years. This thesis highlights the variability inherent within the calculation of ΔR values and places caution on drawing definitive conclusions using ΔR as a proxy for large scale changes in oceanographic/climatic regimes. It also provides new methods of interpreting and presenting ΔR values and their associated errors for publication, alongside recommending best practice statistical treatment of the data used in ΔR calculations. Previous MRE research in this geographic area is limited and therefore this thesis contributes significantly to the understanding of the temporal and spatial trends in the MRE on the North Sea coast of Scotland within the Medieval period.