The surface temperature changes for the last 4000. years in northern inland Iberia (an area particularly sensitive to climate change) are determined by a high resolution study of carbon stable isotope records of stalagmites from three caves (Kaite, Cueva del Cobre, and Cueva Mayor) separated several tens of kilometers away in N Spain. Despite the local conditions of each cave, the isotopic series show a good overall coherence, and resulted to be strongly sensitive to surface temperature changes.The record reflects alternating warmer and colder intervals, always within a temperature range of 1.6°C. The timing and duration of the intervals were provided by 43 230Th-234U (ICP-MS) ages. Main climatic recognized periods are: (1) 3950-3000yrBP: warm period punctuated by cool events around ~3950, 3550 and 3250yrBP; (2) 2850-2500yrBP cold interval (Iron Age Cold Period); (3) 2500-1650yrBP moderate warm period (Roman Warm Period), with maximum temperatures between 2150 and 1750yrBP; (4) 1650-1350yrBP cold interval (Dark Ages Cold Period), with a thermal minimum at ~1500yrBP; (5) 1350-750yrBP warm period (Medieval Warm Period) punctuated by two cooler events at ~1250 and ~850yrBP; (6) 750-100yrBP cold period (Little Ice Age) with extremes occurring at 600-500yrBP, 350-300yrBP, and 150-100yrBP; and (7) the last 150years, characterized by rapid but no linear warming (Modern Warming). Remarkably, the presented records allow direct comparison of recent warming with former warm intervals such as the Roman or the Medieval periods. That comparison reveals the 20th century as the time with highest surface temperatures of the last 4000years for the studied area.Spectral analysis of the time series shows consistent climatic cycles of ~ 400, ~ 900 and ~ 1300 yr, comparable with those recognized in the North Atlantic marine record, the Greenland ice cores, and other terrestrial records for the middle-late Holocene, suggesting common climate forcing mechanisms related to changes in solar irradiance and North Atlantic circulation patterns.
- Climate change
- Stable isotopes