The 14C depletion in the oceanic carbon reservoir relative to the atmosphere that results in the Marine Reservoir Effect (MRE) varies on both temporal and spatial scales. The MARINE04 curve provides a time-series of MRE values for the global average surface and deep oceans where temporal MRE variations are shown in the curve as the oceans respond to solar-derived fluctuations in atmospheric 14C content. However MRE values for a specific ocean area may deviate from this global average as a function of specific local oceanographic and climatic variables. This deviation (known as ΔR) is determined by empirical measurement of local samples and modern (pre-bomb) ΔR values show considerable spatial variations. In addition to spatial variations, current research interest also focuses on the potential for temporal changes in MRE as a function of climatic and ocean changes identified in paleoclimatic data.
In the North Atlantic, major paleoclimatic changes occurred c.10, 000 14C y BP, at the onset of the current Holocene period. A body of research indicates that North Atlantic MRE offsets were significantly greater during the Early Holocene and preceding Younger Dryas climatic phase than they are currently. Here we present results from Scottish coastal sites that may support the interpretation of increased early MRE offsets in the North Atlantic. These results were obtained using paired samples from Scottish coastal archaeological sites. These data and their implications are used to identify important questions concerning current approaches to quantifying the MRE, both for the modern surface ocean and for pre-modern periods. This is particularly relevant given the current interest in defining MRE values in a range of global locations on both spatial and temporal scales. Questions raised include our ability to define accurate and precise MRE values using available samples, and the level to which underlying causes of MRE variability can be identified. The need for an agreed approach to correction and to coordinate with the requirements of paleoclimatic and archaeological researchers for accurate 14C correction values is discussed, together with suggestions for how research could be coordinated to produce the most useful assessments.
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