Holocene variations in the North Atlantic marine radiocarbon reservoir effect

This thesis aims to examine the spatial and temporal characteristics of the ¹⁴C marine reservoir effect (MRE) in the North Atlantic over the Holocene. The MRE is a time dependant offset in ¹⁴C age between the atmospheric and ocean carbon reservoirs and accurate quantification of MRE correction values is crucial for radiocarbon chronologies. In a specific ocean area the MRE may show a deviation (known as ΔR) from the average value for the global average surface oceans given by the marine calibration curve (currently MARINE04). This occurs as a function of local oceanographic and climatic variables and current research has identified the potential for both spatial and temporal variations in ΔR values. A new and rigorous sample selection protocol was developed for this study to produce a large number of ΔR determinations that have a high degree of accuracy and precision. This involved selection of multiple single entity samples of both marine and terrestrial material from 30 clearly-defined deposits at 20 archaeological sites in Western Ireland, the island belts ofNorthern and Western Scotland, the western and northern Scottish mainland coast and the Faroe Isles. A total of 301 radiocarbon (¹⁴C) measurements were made of sample material and the overall results demonstrate observable spatial and temporal variability in ΔR within the study area over the past c.8000 years. These can be related to climate and oceanographic changes previously identified as potential mechanisms for producing variation in ΔR. The interpretations drawn from this study were as follows:1. At sites selected according to the study protocol a range of marine mollusc species can be used to accurately determine ΔR. || 2. In the Early Holocene (c.6480-1940 BC) ΔR values were greater relative to that of later periods. || 3. During the periods c.400 BC - 60 AD and c. 1000-1200 AD, ΔR values were reduced relative to those of the present day || 4. During the period c.1200-1400 AD, ΔR values were higher compared to the present. || 5. In addition, there is evidence for spatial variation in ΔR within the study area over the Holocene. This is illustrated at c. 1000-1200 AD when a large number of measurements indicate an increase in ΔR value northwards from the west coast of Ireland to the Faroe IslesThe results of this study have important implications for our understanding of the MRE and the effective application of correction values to marine samples for ¹⁴C measurement within both paleoenvironmental and archaeological research