Last glacial termination in Andorra, southeastern Pyrenees

This study provides new, comprehensive chronological constraints on the final deglaciation of the two major valleys in Andorra. Between 2002 and 2023, numerous targeted sampling campaigns were conducted on glacially polished bedrock surfaces and morainic boulders in the Valira del Nord and Valira d’Orient valleys, which preserve abundant evidence of extensive Late Pleistocene glaciation. Thirty-two terrestrial cosmogenic nuclide (TCN) surface exposure ages were obtained, ranging from ca. 21 to 10 ka. These data, along with previously reported AMS ¹⁴C dates from glaciolacustrine sediments, enable a better-constrained reconstruction of glacier retreat dynamics in Andorra and align with glacial chronologies from nearby Pyrenean regions. The resulting chronology shows a pattern of glacial culmination followed by retreat during the Last Glacial Maximum (LGM), marked by several stabilization phases and minor re-advances, as evidenced by the remains of the terminal moraine complex at the southern limit of Andorra la Vella and by lateral moraines at ca. 500 m above the main Valira d’Orient Valley. Here, the glacier reached a maximum ice thickness of ca. 500 m during the LGM. It thinned and disappeared during the Oldest Dryas ca. 16 ka ago, as indicated by several polished bedrock TCN ages from the main Valira d’Orient Valley floor. This was immediately followed by the deglaciation of the tributary Valira del Nord Valley ca. 15 ka ago, during the transition from the Oldest Dryas to the Bølling–Allerød Interstadial, a period marked by massive glacial retreat in the Pyrenees. Glaciers retreated into cirques during the Younger Dryas and disappeared in the Early Holocene, thereby facilitating the formation of rock glaciers in the recently exposed ice-free regions. Complementary to TCN surface-exposure dating, we also used Parallel Ice Sheet Modeling (PISM) to reconstruct maximum paleo-ice extents and paleoclimate conditions during the LGM. By matching the location of moraine fronts with modeled maximum ice extents, we suggest that the paleoclimate supporting Andorran glaciers during the LGM should be between 5 and 6°C colder than today, assuming either 10% wetter or 10% drier than today's precipitation, respectively. Modeling Andorran glaciation provides new insights into the Iberian Peninsula's paleoclimate and contributes to an improved regional framework for the Last Glacial Termination.