Seasonal temperature variability of the Neoglacial (3300–2500 BP) and Roman Warm Period (2500–1600 BP) reconstructed from oxygen isotope ratios of limpet shells (Patella vulgata), Northwest Scotland

Abstract

Seasonal sea-surface temperature variability for the Neoglacial (3300–2500BP) and Roman Warm Period (RWP; 2500–1600BP), which correspond to the Bronze and Iron Ages, respectively, was estimated using oxygen isotope ratios obtained from high-resolution samples micromilled from radiocarbon-dated, archaeological limpet (Patella vulgata) shells. The coldest winter months recorded in Neoglacial shells averaged 6.6±0.3°C, and the warmest summer months averaged 14.7±0.4°C. One Neoglacial shell captured a year without a summer, which may have resulted from a dust veil from a volcanic eruption in the Katla volcanic system in Iceland. RWP shells record average winter and summer monthly temperatures of 6.3±0.1°C and 13.3±0.3°C, respectively. These results capture a cooling transition from the Neoglacial to RWP, which is further supported by earlier studies of pine history in Scotland, pollen type analyses in northeast Scotland, and European glacial events. The cooling transition observed at the boundary between the Neoglacial and RWP in our study also agrees with the abrupt climate deterioration at 2800–2700BP (also referred to as the Subboreal/Subatlantic transition) and therefore may have been driven by decreased solar radiation and weakened North Atlantic Oscillation conditions.