Online first articles

Understanding how climate change and human activity affect fragile mountain ecosystems is key to managing these environments under future climate scenarios, including global warming and increased aridity. Paleoecological records provide long-term insights into how ecosystems responded to past climate shifts and human impacts, especially during warm and/or dry phases. We present a multiproxy study of wetland sediments from the Sierra Nevada, southern Spain, using biotic (pollen, charcoal, biomarkers, chironomids, cladocerans) and abiotic (physical, geochemical) analyses to reconstruct environmental, climatic, and anthropogenic changes over the past ~20 000 years. The coldest conditions occurred during the Last Glacial Maximum and the last deglaciation. A marked warming phase in the Early Holocene coincided with maximum summer insolation, with peak humidity and precipitation between ~10 500 and 7000 cal yr BP, indicated by high water runoff, abundant forest taxa, algae, and elevated total organic carbon. Since ~7000 cal yr BP, especially after a transition around 7000–5000 cal yr BP, progressive cooling and aridification became dominant. This is reflected in shifts in aquatic invertebrate assemblages, declining tree cover, increased xerophytic herbs, reduced runoff, and decreased sediment influx. Geochemical evidence also shows increased Saharan dust input, likely linked to vegetation degradation in North Africa. Superimposed on this long-term aridification trend are millennial-scale cold/arid events at ~7500–7200, 6500, 5200, 4500–4200, 3000, and 1200–1000 cal yr BP. Several of these coincide with known Mediterranean droughts and may relate to persistent positive phases of the North Atlantic Oscillation (NAO+), such as during the Medieval Climate Anomaly. Over the past ~3000 years, human impacts have intensified, with evidence of increased fire activity, grazing, cultivation, atmospheric pollution, and reforestation with Pinus, along with widespread Olea cultivation at lower elevations.