MARINE RADIOCARBON RESERVOIR EFFECTS FOR THE MESOLITHIC AND MEDIEVAL PERIODS IN THE WESTERN ISLES OF SCOTLAND

This article presents new values for the Scottish marine radiocarbon reservoir effect (MRE) during the Mesolithic at 4540-4240 BC (6490-6190 BP) and the Medieval period at AD 1460-1630 (490-320 BP). The results give a R of -126 +/- 39 C-14 yr for the Mesolithic and of -130 +/- 36 C-14 yr for the Medieval. We recalculate previously published MRE values for the earlier Holocene in this region, at 6480-6290 BC (8430-8180 BP). Here, MRE values are slightly elevated, with a R of 64 +/- 41 C-14 yr, possibly relating to the 8.2ka BP cold event. New values for the Mesolithic and Medieval indicate lower MRE values, broadly consistent with an existing data set of 37 mid- to late Holocene assessments for Scottish waters, indicating stable ocean conditions. We compare the intercept and probability density function (PDF) methods for assessing R. The R values are indistinguishable, but confidence intervals are slightly larger with the PDF method. We therefore apply this more conservative method to calculate R. The MRE values presented fill important gaps in understanding Scottish marine C-14 dynamics, providing confidence when calibrating material from critical periods in Scotland's prehistory, particularly the Mesolithic, when the use of marine resources by coastal populations was high.