Cryogenic processes and fire activity in a high Atlantic mountain area in NW Iberia (Picos de Europa) during the Mid–Late Holocene

Mid–Late Holocene environmental changes in the Cantabrian Mountains are a consequence of both climate variability and human activity. A 182 cm-long sedimentary sequence was collected from Belbín depression, Western Massif of Picos de Europa (Cantabrian Mountains, NW Spain), in order to reconstruct Holocene environmental dynamics and the factors triggering landscape changes in the area. Using multi-proxy analysis of the uppermost 60 cm of the sediments (texture, organic matter content, quartz grains microstructures, charcoal deposition) together with three ¹⁴C AMS dates, a sequence of alternating warmer and colder phases has been inferred for the last ca. 6.7 ky cal BP. Warm stages are defined by low to moderate chemical weathering of the quartz grain particles with relative increases of the C/N ratio, while colder phases show a moderate to intense physical weathering of the quartz grains and lower C/N ratios. Warmer temperatures were recorded in Belbín area between: 6.7–5, 3.7–3, 2.6–1.1, 0.87–0.51 and since 0.01 ky cal BP. A colder regime occurred between 5–3.7, 3–2.6, 1.1–0.87 and 0.51 to 0.01 ky cal BP. The increasing organic matter content during the Late Holocene may be associated with increasing temperatures. The charcoal particles do not show a higher or lower concentration during prevailing colder or warmer conditions, and therefore may be linked to human-induced fire management of the landscape. The most intense period with fire activity occurred between 3.5 and 3 ky cal BP during the Bronze Age. - Highlights: • We analyse a high resolution sedimentary sequence from Picos de Europa, NW Spain. • Sediments reveal cryogenic processes and fire activity for the Mid–Late Holocene. • Climate variability was inferred based on quartz grain particles morphologies. • The most frequent fire events occurred during the Bronze Age (3.5–3 ky cal BP). • Fire severity influences physical/chemical weathering intensity on quartz grains.