Mountain glacier evolution in the Iberian Peninsula during the Younger Dryas

Abstract

We review the evolution of glaciers in the Iberian Mountains during the Younger Dryas (12.9–11.7 ka, following the chronology of Greenland Stadial 1 – GS1) and compare with available environmental and climate data to investigate glacier dynamics during cold stadial episodes. The best examples of Younger Dryas moraines are found in the Central Pyrenees, involving short ice tongues up to 4 km in length in the highest massifs (above 3000 m a.s.l.) of the southern versant. Small cirque glaciers and rock glaciers formed during the YD occurred in other Pyrenean massifs, in the Cantabrian Range and in the Gredos and Guadarrama sierras (Central Range), as indicated by several rocky, polished thresholds that were ice-free at the beginning of the Holocene. Although some former rock glaciers were re-activated during the Younger Dryas, glacial activity was limited in the southernmost part of the Iberian Peninsula (Sierra Nevada).Most Iberian records show vegetation changes during the YD characterized by a forest decline and an expansion of shrubs (mainly Juniperus) and steppe herbs, although the vegetation response was not homogeneous because of variable resilience among ecosystems. Available records also document a variable lake response in terms of hydrology and productivity, with a decrease in sedimentation rates and organic productivity in most high altitude lakes and increases in salinity and relatively lower lake levels at lower altitudes. The impact of the Younger Dryas on the coastal environment was almost negligible, but it was responsible for a brief cessation in sea level rise. High-resolution analyses of new speleothem records have documented a double structure for the YD with an earlier drier phase followed by a relatively more humid period.The review of geomorphological evidence demonstrates a strong latitudinal control of glacial activity during the YD, with more intense development in the northern than in the southern regions. The increase in humidity during the second phase of the YD in southern latitudes could have been a decisive factor for glacier advance in the northern Iberian mountains.