Late Pleistocene glacial chronology and paleoclimate of the Cadí Massif, SE Pyrenees, Spain: Insights from 36Cl cosmogenic surface exposure dating and glacier modelling

Abstract

The cold and dry Younger Dryas (YD) stadial (ca. 12.9 to 11.7 ka) generated glacial deposits in the Iberian Mountains, often restricted to high altitudes in cirque areas. Contrary to expectations, we encountered well-developed YD moraines at relatively low altitudes on the northern slopes of the Cadí Massif in the Southeastern Pyrenees, Spain. We applied the ³⁶Cl terrestrial cosmogenic nuclides (TCN) surface exposure dating method on 11 limestone boulders collected from three moraines to assess the glacial geochronology and paleoclimate conditions associated with their formation. We report a small but well-preserved moraine at an unusually high altitude for the Southeastern Pyrenees (between 2160 m and 2120 m above sea level; asl) fed by a small hanging glacier that formed at 23.0 ± 1.5 ka during the global Last Glacial Maximum (LGM). Four kilometres west of the LGM moraine, a ca. 2.5 km long glacier originating from one of the largest cirques of the Cadí Massif deposited a ca. 700 m long moraine preserved between 1760 m and 1600 m. As alluvial and periglacial processes heavily modified this moraine, we cautiously attribute its age to 12.9 ± 1.0 ka. This age represents the onset of the YD period following the Bølling-Allerød warming, widespread in the Pyrenees. On the other hand, another ca. 1.7 km long glacier sourced from the adjacent cirques deposited a pair of well-preserved lateral moraines and a terminal moraine ca. 1150 m long. The samples collected from the moraines yielded tightly clustered boulder ages (average age = 12.1 ± 1.1 ka). Although they developed at relatively low elevations (1830–2100 m) with an Equilibrium Line Altitude (ELA) of 2175 m, which is exceptional for the Southeastern Pyrenees, these moraines were formed during the YD stadial. Our study suggests that despite increased glacier retreat in the Mediterranean region, local relief is crucial in preserving ice masses far below the modern glacial belt with ample snow accumulation. We also used the Parallel Ice Sheet Model (PISM) to reconstruct the paleo-ice extents and paleoclimate regime. We propose two equally possible best-fit scenarios for the maximum ice extent of the YD period. The first foresees a 4 °C temperature decline with today's precipitation values, and the second predicts a 5 °C cooling if precipitation were 20% lower than today. Identifying and dating this unexpected YD glaciation on Cadí Massif provides new insights into understanding the Iberian Peninsula's paleoclimate.