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International audience; The Upper Garonne Basin included the largest glacial system in the Pyrenees during the last glacial cycle. Within the long-term glacial retreat during Termination-1 (T-1), glacier fluctuations left geomorphic evidence in the area. However, the chronology of T-1 glacial oscillations on the northern slope of the Central Pyrenees is still poorly constrained. Here, we introduce new geomorphological observations and a 12-sample dataset of 10Be Cosmic-Ray Exposure (CRE) ages from the Ruda Valley. This U-shaped valley, surrounded by peaks exceeding 2800 m a.s.l., includes a sequence of moraines and polished surfaces that enabled to reconstruct the chronology of the last deglaciation. Following the maximum ice extent, warmer conditions prevailing at ~15-14 ka, during the Bølling-Allerød (B-A) Interstadial, favoured glacial retreat in the Ruda Valley. Within the B-A, glaciers experienced two phases of advance/stillstand with moraine formation at 13.5 and 13.0 ka. During the early YD, glacial retreat exposed the highest surfaces of the Saboredo Cirque (~2300-2350 m) at 12.7 ka. Small glaciers persisted only inside the highest cirques (~2470 m), such as in Sendrosa Cirque, with moraines stabilizing at 12.6 ka. The results of this work present the most complete chronology for Pyrenean glacial oscillations from the B-A to the YD.

International audience; The Upper Garonne Basin included the longest glacier in the Pyrenees during the Late Pleistocene. During major glacial advances, the Garonne palaeoglacier flowed northwards along similar to 80 km from peaks of the axial Pyrenees exceeding 2800-3000 m until the foreland of this mountain range at the Loures-Barousse-Barbazan basin (LBBb), at 420-440 m. Here, the palaeoglacier formed a terminal moraine complex that is examined in this work. Based on geomorphological observations and a 12-sample data set of Be-10 Cosmic-Ray Exposure (CRE) ages, the timing of the maximum glacial extent was constrained as well as the onset of the deglaciation from the end of the Last Glacial Cycle (LGC). Chronological data shows evidence that the external moraines in this basin were abandoned by the ice at the end of the Penultimate Glacial Cycle (PGC) and the onset of the Eemian Interglacial, at similar to 129 ka. No evidence of subsequent glacial advances or standstills occurred during the LGC in this basin were found, as the few existing datable boulders provided in the internal moraine showed inconsistent ages, thus probably being affected by post-glacial processes. The terminal basin was already deglaciated during the global Last Glacial Maximum at 24-21 ka, as revealed by exposure ages of polished surfaces at the confluence of the Garonne-La Pique valleys, 13 km south of the entrance of the LBBb. This study introduces the first CRE ages in the Pyrenees for the glacial advance occurred during the PGC and provides also new evidence that glaciers had already significantly shrunk during the LGM.

Through a detailed geomorphological study, including thourough mapping of the geomorphic features as well as Be-10 Cosmic-Ray Exposure (CRE) dating, the geomorphological evolution of the Mulhacen cirque since the maximum ice extent of the last glacial cycle until nowadays was determined. This glacial cirque is shaped on the northern face of the Mulhacen peak (3479 m a.s.l. 37 degrees 03'12 ' N/3 degrees 18'41 ' W), Sierra Nevada, southern Spain. It includes several depositional and erosional glacial landforms that allowed reconstructing its environmental evolution since the last glacial cycle. Furthermore, the sequence of glacial oscillations from this site was compared to that of other cirques of the massif, evidencing that: (i) new glaciers formed in these cirques during the Younger Dryas (YD), and (ii) disappeared at 11.7 +/- 1.0 ka. Depending on the altitude, orientation and height of the cirque walls, the final deglaciation of the cirques generated a diversity of landscapes, including a wide range of glacial and periglacial landforms, such as polished surfaces, sequences of moraines, proto-rock glaciers or large rock glacier systems. No glaciers existed in the Sierra Nevada during the Middle Holocene. Only the cirques whose summits exceed 3300 m, are north-exposed and whose walls exceed 300 m high (i.e. Mulhacen and Veleta) hosted glaciers during Neoglacial phases, including the Little Ice Age (LIA) (approx.1300-1850 CE). During these periods, climate oscillations favoured the formation of small glaciers in these cirques, which generated large moraine systems with either one polygenic ridge or a sequence of spaced frontal arcs. The existence of glaciers impeded the formation of permafrost-related landforms, such as rock glaciers and protalus lobes until the end of the LIA, when they started to form. These results are compared with the deglacial evolution in 55 cirques from Iberian mountains as well as from glacial cirques from other mid-latitude mountains and subpolar regions. The chronology of their deglaciation as well as the landforms generated during glacial retreat followed similar patterns, with no significant differences at regional scale. For each mountain range, the geomorphological diversity existing in each cirque depends on the local topographic characteristics although they formed during the same climatic phases.

International audience; The Central Pyrenees hosted a large ice cap during the Late Pleistocene. The cirques under relatively low-altitude peaks (2200–2800 m) include the greatest variety of glacial landforms (moraines, fossil debris-covered glaciers and rock glaciers), but their age and formation process are poorly known. Here, we focus on the headwaters of the Garonne River, namely on the low-altitude Bacivèr Cirque (highest peaks at ~2600 m), with widespread erosive and depositional glacial and periglacial landforms. We reconstruct the pattern of deglaciation from geomorphological observations and a 17-sample dataset of 10Be Cosmic-Ray Exposure (CRE) ages. Ice thickness in the Bacivèr Cirque must have reached ~200 m during the maximum ice extent of the last glacial cycle, when it flowed down towards the Garonne paleoglacier. However, by ~15 ka, during the Bølling-Allerød (B-A) Interstadial, the mouth of the cirque was deglaciated as the tributary glacier shrank and disconnected from the Garonne paleoglacier. Glacial retreat was rapid, and the whole cirque was likely to have been deglaciated in only a few centuries, while paraglacial processes accelerated, leading to the transformation of debris-free glaciers into debris-covered and rock glaciers in their final stages. Climate conditions prevailing at the transition between the B-A and the Younger Dryas (YD) favored glacial growth and the likely development of small moraines within the slopes of the cirque walls by ~12.9 ka, but the dating uncertainties make it impossible to state whether these moraines formed during the B-A or the YD. The melting of these glaciers favored paraglacial dynamics, which promoted the development of rock glaciers as well as debris-covered glaciers. These remained active throughout the Early Holocene until at least ~7 ka. Since then, the landscape of the Bacivèr Cirque has seen a period of relative stability. A similar chronological sequence of deglaciation has been also detected in other cirques of the Pyrenees below 3000 m. As in other mid-latitude mountain regions, the B-A triggered the complete deglaciation of the Garonne paleoglacier and promoted the development of the wide variety of glacial and periglacial landforms existing in the Bacivèr cirque.

International audience; An accurate review of the literature on surface exposure dating methods shows evidence of the difficulty in applying cosmogenic dating methods to old moraines because of the intensity of Late Quaternary erosion processes. Moreover, as in some previous cases, we found also special difficulties in applying these methods to LIA moraines, due to the intensity of current paraglacial processes. The objective of this study is to apply cosmogenic dating methods to very old and very young moraines, which in both cases have been or are being affected intensively by erosion. With this purpose, we collected samples of boulders from moraines corresponding to: (a) the penultimate glaciation, and (b) the Little Ice Age (LIA), both from Sierra Nevada, in the south of the Iberian Peninsula. The sampling strategy was based on a preliminary accurate analysis of the geomorphological settings of two valley sites that Manuscript with line numbering and double line spacing Click here to view linked References resulted in the collection of only four boulder samples from an old moraine and three more from a very recent moraine. Using in situ produced cosmogenic 10 Be to date these boulders, the old samples yielded an age of ca. 130-135 ka for moraine stabilization. The younger samples indicate that the LIA moraine accretion probably occurred between the 14 th and 17 th centuries, with a subsequent stage of accumulation during the 19 th century as suggested by historical documents. Both, dating a glaciation that occurred prior to the last Pleistocene glacial cycle and dating LIA glacial stages are novel in the context of Iberian glaciations and agree with other palaeoenvironmental studies in Iberian and in other European mountains. The limited number of boulders adequate for cosmic-ray exposure dating prevents statistical methods to be applied, and therefore highlights the need to improve geomorphological criteria in sample selection.