Variability in North Atlantic marine radiocarbon reservoir effects at c. AD 1000

C-14 age measurements made on samples from three archaeological sites located on North Atlantic coasts were used to investigate the marine reservoir effect (MRE) at c. AD 1000. This is an important period within human cultural and palaeoenvironmental research as it is a time when Norse expansion to the North Atlantic islands occurred, during what appears to be a period of ameliorating climatic conditions. This makes improved chronological precision and accuracy at this time highly desirable. The data indicate a potential latitudinal variation in M RE at c. AD 1000 from a Delta R of - 142 +/- 16 C-14 yr at Omey Island (53 degrees 32' N) to 64 +/- 13 C-14 yr at Undir Junkarinsflotti (61 degrees 51' N). The results are compared with modern assessments of MRE values within the context of oceanographic and climatic regimes that provide a possible driving mechanism for spatial and temporal variation in MRE.