Late Quaternary glacial phases in the Iberian Peninsula

Abstract

The only glaciers existing today in the Iberian Peninsula are small features located in the Pyrenees, though their number and extension has undergone significant changes over the Late Quaternary. The wide range of glacial landforms and deposits distributed across different Iberian ranges suggests the occurrence of several past periods with larger glacial systems. The objective of this research is to summarize the current knowledge on the spatial and temporal patterns of glacial activity in the Iberian mountains during the Late Quaternary. To this purpose, the chronological framework was divided in six periods: glaciations prior to the Last Glacial Cycle (Middle Pleistocene), Last Glacial Cycle (Late Pleistocene), Termination-1, Holocene, Little Ice Age (LIA) and present-day. The data were geographically divided considering the mountain systems where glacial evidence exists: Pyrenees, Cantabrian Range, NW ranges, Central Range, Iberian Range and Sierra Nevada. During Quaternary cold stages, ice accumulated in the head valleys of these mountain ranges and glaciers flowed down-valleys. In all cases, glaciers remained confined within the mountain systems and did not reach the surrounding lowlands. Depending on the combination of temperatures and moisture conditions, more or less ice was stored. In some ranges, there is evidence of Middle Pleistocene glaciations, one potentially correlating with marine isotope stage (MIS) 12 and another correlating with MIS 6 with glaciation dated to ca. 130-170 ka. However, most of the glacial records correspond to the Last Glacial Cycle and subsequent Termination. The maximum glacial expansion of this last Pleistocene glaciation stage occurred well before the global Last Glacial Maximum (LGM) between 30 and 60 ka in the Cantabrian Mountains and Pyrenees, at ca. 30 ka in Sierra Nevada and NW ranges, and (almost) synchronously to the LGM in the Central Range and Iberian Range. A massive glacial retreat occurred in all ranges at 19-20 ka, but the long-term deglaciation process was interrupted by cold intervals, such as the Oldest and Younger Dryas, which favoured glacial expansion in the highest mountains. Temperature increase recorded during the Holocene conditioned the melting of glaciers, which only reappeared in the highest massifs during the coldest periods, such as the LIA. However, post-LIA warming led to glacier disappearance in the Cantabrian Mountains, Sierra Nevada and most massifs of the Pyrenees, together with an accelerated shrinkage of the small glaciers still existing in this range at elevations near 3000 m.