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Land degradation resulting from increased continental surface erosion is a worldwide and systemic phenomenon due to human activities. Already fragile, the intertropical zone is likely to be further affected by climate change and increased aridity, an aggravating factor of soil erosion and land degradation. A major challenge is thus to provide the necessary knowledge to not only deepen our understanding of the Earth system and its critical thresholds but also to help achieving sustainable development goals. Understanding the factors that control the properties and processes of the critical zone, and especially what will be its responses to ongoing climate and land use changes, requires multidisciplinary efforts to tackle time scales that are compatible with morphogenesis and soil development as well as environmental disturbances of anthropogenic origin. Due to its prominent ecological importance, the Brazilian Cerrado biome is an ideal natural laboratory were to gauge the consequences of recent and strong human activities on continental surface erosion. We focused on the region of Brasília where our approach allows confronting the temporal scales of long-lived and stable cosmogenic nuclides with that of short-lived radioactive isotopes, through a comparison of natural and anthropogenically disturbed land surfaces. Our results indicate that long-term, background denudation rates are lower than 10 mm kyr-1whereas recent erosion rates due to human activities may reach rates at least 160 times higher, exceeding by far the sustainability rates of the soil resource.

To understand the timing of deglaciation of the northernmost marine-terminating glaciers of the Cordilleran Ice Sheet (CIS), we obtained 2610Be surface-exposure ages from glacially scoured bedrock surfaces in Prince William Sound (PWS), Alaska. We sampled six elevation transects between sea level and 620 m and spanning a distance of 14 to 70 km along ice flow paths. Most transect age–elevation patterns could not be explained by a simple model of thinning ice; the patterns provide evidence for lingering ice cover and possible inheritance. A reliable set of 20 ages ranges between 17.4 ± 2.0 and 11.6 ± 2.8 ka and indicates ice receded from northwestern PWS around 14.3 ± 1.6 ka, thinned at a rate of ~120–160 m/ka, and retreated from sea-level sites at 12.9 ± 1.1 ka at a rate of 20 m/yr. The retreat rate likely slowed as glaciers retreated into northern PWS. These results are consistent with the growing body of reported deglacial constraints on collapse of ice sheets along the Alaska margin indicating collapse of the CIS soon after 17 ka. These data are consistent with paleotemperature data indicating that a warming North Pacific Ocean caused catastrophic collapse of this part of the CIS.

Rock avalanches are voluminous debris instabilities originated from a fallen portion of bedrock that suffers pervasive disintegration [1]. Tough rock avalanches are foreseen as low-frequency events, their volume (>106 m3) and runout distance (kilometric scale) make them extremely hazardous processes in populated mountain settings and key contributors to landscape denudation [2]. Deciphering the timing of recurrent rock avalanches is crucial to understand the triggering factors involved in their origin (e.g., role of seismicity) and for risk assessment.This study focuses on a rock avalanche cluster preserved in the southern flank of Sierra de la Sobia; a limestone massif located in the Cantabrian Mountains (North Spain). The rock avalanche cluster analyzed is spatially related to the Marabio Fault trace, which shows unequivocal evidence of Quaternary activity [3]. Rock avalanches in this area have been interpreted as coseismic based on the following evidence [4]: (i) boulder populations show fractal block-size distributions consistently with dynamic fragmentation; (ii) the kinematic analysis of local minor transverse and parallel faults points to a horizontal N-S compression consistent with the regional stress field; and (iii) slope stability analysis indicates that headscarps will turn unstable if ground acceleration peak rises to 0.10–0.15 g during an earthquake, which is within the values expected according to the 2013 European Seismic Hazard Map. A first attempt of numerical dating was performed through the U-Th technique on calcite cements found in the oldest rock avalanches. Results suggest multiple episodes of cementation during the last ~280 ka, but age dispersion hinders the age bracketing of instability events4. Here we present a collection of twenty cosmic ray exposure ages relying on the isotope Cl-36 obtained from limestone boulders sampled in the youngest accumulation bodies of the Entrago and Carrea rock avalanches. Results allow to constrain up to 5 instability events spanning the last ~22 ka and occurring at average recurrence intervals of ~3.6 ka. The youngest rock avalanche event took place 8.5 ka ago and left boulder accumulations close to the headscarp of both rock avalanches. Boulder age dispersion increases accordingly with the increase in runout distance from the headscarp, possibly due to the spatial overlapping of accumulation bodies resulting from different instability events of seismic origin. These preliminary results are promising, because if extended to other rock avalanche clusters of the Cantabrian Mountains, they could help to decipher the recurrence time of severe earthquakes in mountain settings where tectonic deformation occurs at low to moderate rates.[1] Hermanns, R. L. Encyclopedia of Natural Hazards. vol. 2 (2013).[2] Davies, T. Rock Avalanches. In Oxford Research Encyclopedia of Natural Hazard Science 58 (Oxford University Press, 2018). doi:10.1093/acrefore/9780199389407.013.326.[3] Fernández, F. J., Alonso, J. L. & Pando, L. Evidence for quaternary tectonic activity in the western cantabrian Zone (Passes of Marabio, Sobia nappe). Geogaceta 64, 1–3 (2018).[4] Fernández, F. J., Menéndez-Duarte, R., Pando, L., Rodríguez-Rodríguez, L. & Iglesias, M. Gravitational slope processes triggered by past earthquakes on the Western Cantabrian Mountains (Sierra de la Sobia, Northern Spain ). Geomorphology 390, 107867 (2021).

The paper by E. Mendez-Quintas et al. (2020) aims to give an interdisciplinary overview of the lower Mino River terrace record in NW Iberia by combining geological and archaeological data. The authors also pretend to re-interpret the geological-geomorphological evolution of this river by presenting new data and by comparing them to data published in our five related papers. However, a wrong interpretation of the data they present as well as incorrect and selective citations of ours lead to the production of a publication containing numerous errors. The most flagrant ones are the mapping of fluvial terraces on one side of the river only and an incorrect interpretation of the sedimentological information used to correlate terrace remnants along-river. This results in incorrect longitudinal profile reconstructions and an improper proposal of the evolution of the Mino terraces that is even contradicted by the data they present. On the upside, the ages of the Porto Maior terrace site published by these authors confirm our previously published longitudinal profile reconstructions and evolutionary model of the Mino valley.

The Greenland Ice Sheet (GrIS) is a key component of the global climate system. However, our current understanding of the spatio-temporal oscillations and landscape transformation of the GrIS margins since the last glacial cycle is still incomplete. The objective of this work is to study the deglaciation of the Zackenberg Valley (74°N, 20°E), NE Greenland, and the origin of the derived landforms. Based on extensive fieldwork and high-detail geomorphological mapping we identified the different types of landforms, from which those of glacial and paraglacial origin were used to understand the processes driving regional environmental evolution. We applied cosmic-ray exposure (CRE) dating to 32 samples taken from erosive and depositional glacial landforms distributed across the valley. Geomorphological evidence shows that >800-m-thick Late Quaternary glacier filled the valleys and fjords and covered mountain summits. In subsequent phases, as ice thickness decreased, the glacier was limited to the interior of the valley, leaving several lateral moraines. The deglaciation of the Zackenberg Valley that started by ~13.7–12.5 ka also accelerated slope paraglacial processes. Many blocks from lateral moraines were remobilized and fell, reaching the valley floor where they covered the thinning glacier tongue; transforming it into a debris-covered glacier that subsequently melted gradually. By ca. 10.5 ka, the last remnants of glacial ice disappeared from the Zackenberg Valley floor, a chronology of deglaciation that is similar to that observed in other sites across NE Greenland. The results of this work must be considered in similar studies, reinforcing the need to support CRE ages of the different geomorphological phases with paleoclimatic data from other sedimentary records.

International audience; The aim of this work is to study the process of transformation of debris-free mountain glaciers into debris-covered glaciers and rock glaciers, and to examine the factors driving diverging evolution in similar glacial systems. The study area is the Hofsdalur valley, in the Trollaskagi peninsula (northern Iceland), where several cirques host a great diversity of glaciers and rock glaciers as well as various glacial landforms. Four adjacent cirques have been analysed through a multidisciplinary approach: geomorphological analysis, boulder surface displacement tracking, quantification of recent glacier changes, three dimensional palaeoglacier reconstruction, equilibrium-line altitude calculations and relative and direct dating methods applied to surface boulders. Dating methods included in situ Cl-36 cosmic-ray exposure dating, Schmidt hammer weathering measurements and lichenometric dating. The results confirm that glaciers in Hofsdalur followed an evolution pattern similar to that observed in other cirques in the Trollaskagi peninsula. During the Younger Dryas (12.9-11.7 ka) many of those cirques hosted debris-free glaciers, whose retreat started in the early Holocene. Distinct retreat dynamics and cirque floor elevation conditioned the subsequent glacial evolution. In some Trollaskagi cirques, the ice completely covered the headwalls, which consequently did not supply debris onto the glacier surface, which remained debris-free. In most of these cirques, however, glacier retreat enhanced paraglacial processes and the ice-free cirque walls generated a high debris supply onto the glacier surface. As a result, the glaciers evolved towards debris-covered glaciers or rock glaciers, depending on the local topographical setting. In the lower cirques they collapsed immediately after their formation. At higher altitudes, above the lower permafrost limit, these ice-cored landforms have survived until the present day, but they have been stagnant since the Holocene Thermal Maximum, while the heads of these cirques have hosted debris-free glaciers during the Late Holocene.

International audience; Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km(2)) and 1:15,000 (2.25 km(2)) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1-2 and br2) could be produced by erosion-sedimentation-consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31 degrees 59 ' 13.73"N, 5 degrees 30 ' 55.14"W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4-4.2 km in diameter. Cosmogenic nuclide data (Cl-36) constrain the local erosion rates between 220 +/- 22 m Ma(-1) and 430 +/- 43 m Ma(-1). These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3-1.9 Ma. This age is older than the Agoudal iron meteorite age (105 +/- 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.

The Kerguelen Archipelago (49°S, 69°E) is an excellent location for the study of multi-millennial glacier fluctuations, since it is the largest still glaciated emerged area (552 km2 in 2001) in the sub-Antarctic sector of the Indian Ocean, where many glacio-geomorphological formations such as moraines may be dated. To investigate the so-far little-known Late Glacial and the Holocene glacier fluctuations in Kerguelen, we apply cosmogenic nuclide dating of moraines in 3 glacial valleys: Val Travers valley, Ampere glacier valley and Arago glacier valley. We use in situ 36Cl dating of the basaltic moraine boulders at the first two sites, and 10Be dating of the quartz-bearing syenite boulders at the third site. The new 36Cl and 10Be exposure ages provide time constraints over the last 17,000 years. A glacial advance was highlighted during the Late Glacial at 14.4 ± 1.4 ka ago, probably linked to the Antarctic Cold Reversal event. These results are consistent with those previously obtained on the archipelago (Jomelli et al., 2017, 2018; Charton et al., 2020) and more generally those from other the sub-Antarctic regions (e.g. Sagredo et al., 2018). This suggests that all glaciers at this latitude were broadly sensitive to this specific climatic signal. No Early nor Mid Holocene advances were evidenced in Kerguelen glacier evolution during the Holocene due to missing moraines that may have formed in these specific periods. Radiocarbon-dated peat, published in the 1990s, provides evidence of less extensive glacier extents during the Early Holocene than during the Late Holocene (Frenot et al., 1997). Finally, glaciers seem to have re-advanced only during the Late Holocene, especially within the last millennium, at ⁓1 ka, ⁓620 years and ⁓390 years (Verfaillie et al., submitted). A comparison of this new dataset with the available 10Be ages from other sub-Antarctic regions allows for the identification of 3 different glacier evolution patterns during the Holocene. The glacial fluctuations experienced by Kerguelen glaciers seems particularly uncommon, and are likely due to its singular location in the Southern Indian Ocean. Finally, climatic factors that may explain the Kerguelen glacier evolution (temperature, precipitation) are discussed. To this end, we investigate the chronology of glacier advance/retreat periods with (i) the variation in atmospheric temperatures recorded in ice cores in Antarctica and (ii) the variation in precipitation (Southern Westerly Winds, Southern Annular Mode).Charton et al., 2020 : Ant. Sci. 1-13Frenot et al., 1997 : C.R. Acad. Sci. Paris Life Sciences 320, 567-573Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123Sagredo et al., 2018 : Quat Sci. Rev. 188, 160-166Verfaillie et al., submitted

The Cook Ice Cap (CIC) on the sub-Antarctic Kerguelen Islands recently experienced extremely negative surface mass balance. Further deglaciation could have important impacts on endemic and invasive fauna and flora. To put this exceptional glacier evolution into a multi-centennial-scale context, we refined the evolution of the CIC over the last millennium, investigated the associated climate conditions and explored its potential evolution by 2100 ce. A glaciological model, constrained by cosmic ray exposure dating of moraines, historical documents and recent direct mass balance observations, was used to simulate the ice-cap extents during different phases of advance and retreat between the last millennium and 2100 ce. Cosmogenic dating suggests glacial advance around the early Little Ice Age (LIA), consistent with findings from other sub-Antarctic studies, and the rather cold and humid conditions brought about by the negative phase of the Southern Annular Mode (SAM). This study contributes to our currently limited understanding of palaeoclimate for the early LIA in the southern Indian Ocean. Glaciological modelling and observations confirm the recent decrease in CIC extent linked to the intensification of the SAM. Although affected by large uncertainties, future simulations suggest a complete disappearance of CIC by the end of the century.

Reconstructions of the global production rate of the cosmogenic isotope 10Be from sedimentary records of authigenic 10Be/9Be ratios have been successfully used to obtain independent estimates of geomagnetic dipole moment variations caused by field excursions or reversals. In this study, we assess the reliability of 10Be/9Be as a proxy for the cosmogenic 10Be production rate by evaluating two potential biasing sources represented by sediment composition and climatic modulation. For this purpose, we compare five high-resolution 10Be/9Be records of the Matuyama-Brunhes (M-B) field reversal from sediment cores of the Indian, West Pacific, and North Atlantic oceans. Significant increase of 10Be/9Be ratios at ∼ 774 ka is explained in terms of the dominant control of geomagnetic modulation during the M-B reversal. Results do not support the existence of a direct proportionality between measured sedimentary 10Be/9Be ratio and cosmogenic 10Be production rate, as shown by 10Be/9Be records that offset relative to each other during and outside the M-B reversal. Residual differences between offset-corrected rescaled records do not appear to be related to an incomplete correction of variable sediment scavenging efficiencies by 9Be normalization. Instead, these differences can be explained by a common climatic modulation model, assuming a linear relation between 10Be/9Be and the global 10Be production rate with site- and time-dependent additive and multiplicative coefficients. These coefficients are linear functions of a single global climate proxy identified with the benthic δ 18 O record. Additive coefficients are almost constant in time and can represent up to ∼ 60% of the average 10Be/9Be value during periods of stable field polarity. Multiplicative coefficients are also site-specific, with mean values representing the bulk scavenging efficiency of the site, and variations about this mean expressing a multiplicative climatic modulation of the 10Be production rate. The amplitude of this modulation amounts to 10–15% of the maximum variations recorded during the M-B reversal and is sufficiently large to mask minor variations of the dipole moment during stable polarity periods. Reconstructions of the geomagnetic dipole intensity can benefit from the information about climatic modulation effects gained with our modelling approach. Best suited sites for magnetic field reconstructions should be characterized by minimal Be-recycling contributions from ancient 10Be reservoirs and minimal climatic modulation, as far as it can be determined from relative comparisons with other records. These conditions are most likely encountered in open basins at sites (1) with 2.8 km water depth, (2) > 200 km offshore, and (3) located underneath a large current system extending over regions with minimum terrigenous inputs. Scaling all records with respect to a chosen reference enables to produce 10Be/9Be stacks with reduced noise and short-term local environmental effects. Differences between stacks obtained in this manner highlight global climatic effects that need to be considered when generating calibrated reconstructions of the geomagnetic dipole moment.

Debris-covered glaciers constitute a substantial part of the worldwide cryosphere (Scherler et al. 2018). However, their long-term response to multi-millennial climate variability has rarely been studied, in particular in the Southern Hemisphere. The presence of both debris-covered and debris-free glaciers on Kerguelen Archipelago (49°S, 69°E) offers therefore an excellent opportunity to investigate and compare long-term evolution of these two types of glaciers. To do so, we used the cosmogenic 36Cl surface dating method on moraine boulders that allows to establish temporal constraints of glacier oscillation. We provide here the first Late Glacial and Holocene glacier chronology of a still active debris-covered glacier from the archipelago: the Gentil Glacier. Results show that the Gentil Glacier advanced once at ~14.3 ka, i.e. during the Late Glacial (19.0 – 11.6 ka), and re-advanced during the Late Holocene at ~2.6 ka (Charton et al., 2020). Both debris-covered and debris-free glaciers experienced a broadly synchronous advance during the Late Glacial, that may be assigned to the Antarctic Cold Reversal event (14.5 – 12.9 ka) (Jomelli et al., 2017; 2018). This suggests that both types (debris-covered and debris-free) of glaciers at Kerguelen were sensitive to large amplitude temperature fluctuations recorded in Antarctic ice cores (WAIS divide Project Members, 2013), associated with increased precipitations (Van der Putten, 2015). However, during the Late Holocene, the advance at about ~2.6 ka was not observed on other glaciers and seems to be a specific response of the debris-covered Gentil Glacier, either related to distinct ice dynamics or an individual response to precipitation changes. Charton et al., 2020 : Ant. Sci. 1-13Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123Scherler et al., 2018 : GRL. 45, 11,798-11,805Van der Putten et al., 2015 : Quat. Sci. Rev. 122, 142-157WAIS Divide Project Members, 2013: Nature. 500, 440-444

Denudation rates are routinely derived from concentrations of terrestrial in situ produced cosmogenic nuclides (TCN), particularly from 10Be concentrations in river sand. Denudation rates are calculated assuming that they remain steady throughout the integration time scale of the TCN. However, such an assumption is possibly unverified in settings with negligible tectonics, where rates typically range from 10 to 100 mm/ky. In those settings, the TCN conveys a signal that integrates denudation over a time span longer than a few thousand years. The signal may include periods when anthropogenic and climatic forcing on denudation was distinct from modern times. For instance, agricultural practices were limited before 6,000 years B.P. and climatic conditions were colder and drier before 10,000 years B.P. A variable forcing may produce variable and transient denudation rates. In that case, the assumption of steady denudation rates is invalid, and their derivation may introduce a bias.To detect transient landscapes and resolve such a bias, we can take advantage of the different sensitivity of the 14C and 10Be TCNs to recent and short-term changes in surface denudation. In situ 14C is more sensitive than 10Be to such changes, because of a shorter half-life (5,700 y compared to 1.4 My). This potential application of coupled 14C - 10Be measurements has recently been discussed in several theoretical studies (Hippe, 2017; Mudd, 2017; Skov et al., 2019). Despite the improvement of 14C extraction lines and measurement facilities (Hippe et al., 2009; Lupker et al., 2019), sensitivity tests remain limited on natural cases (Hippe et al., 2012).Here, we propose assessing this new application by in situ 14C - 10Be measurements on river sand from the Cevennes and the Monts Margeride within the Variscan Massif Central in France. With an average elevation of ~700 m, this mountain range presents an asymmetrical topography, composed of a low-relief surface reaching 1,700 m, and bordered by a gently sloping flank to the west and a steep escarpment to the southeast, along the Cevennes fault. This escarpment receives frequent and seasonal extreme precipitation events (300-700 mm in 48h) on its southeast flank.The range is subject to very limited seismic activity and appears relevant for an application of the 14C-10Be couple. Basins are rich in quartz and have homogeneous lithology. The recent paleoclimatic context is well constrained, with substantial climatic variations but with limited Pleistocene glaciations (e.g. Fauquette et al., 1999; Magny et al., 2003; Mayewski et al., 2004). The Massif Central is subject to active erosion processes, without major contribution from stochastic events such as landslides. Denudation rates are in the range of the theoretical study of Skov et al. 2019 (Schaller et al. 2001; Molliex et al. 2016; Olivetti et al. 2016; Desormeaux et al., 2021) and several studies have suggested transient denudation patterns (Schaller et al. 2001; Olivetti et al. 2016). With our new measurements, we will verify whether the 14C-10Be couple has sufficient resolution to detect such transience in natural cases.

International audience; 10 Be-derived catchment-wide denudation rates are positively correlated with topographic indices in the southern Longmen Shan.  Erosion rates are consistent over short-and long-term timescales across the Longmen Shan, suggesting an exhumational steady state.  Rock uplift pattern and topographic evolution across the Longmen Shan have been largely controlled by upper crustal shortening and fault geometry.

Denudation is one of the main processes that shapes landscapes. Because temperature, precipitation and glacial extents are key factors involved in denudation, climatic fluctuations are thought to exert a strong control on this parameter over geological timescales. However, the direct impacts of climatic variations on denudation remain controversial, particularly those involving the Quaternary glacial cycles in mountain environments. Here we measure in situ cosmogenic 10Be concentration in quartz in marine turbidites of two high-resolution cores collected in the Mediterranean Sea, providing a near-continuous (temporal resolution of ~1–2 kyr) reconstruction of denudation in the Southern Alps since 75 kyr ago (ka). This high-resolution palaeo-denudation record can be compared with well-constrained climatic variations over the last glacial cycle. Our results indicate that total denudation rates were approximately two times higher than present during the Last Glacial Maximum (26.5–19 ka), the glacial component of the denudation rates being $$1.5_{ - 1.0}^{ + 0.9}$$ mm yr−1. However, during moderately glaciated times (74–29 ka), denudation rates were similar to those today (0.24 ± 0.04 mm yr−1). This suggests a nonlinear forcing of climate on denudation, mainly controlled by the interplay between glacier velocity and basin topography. Hence, the onset of Quaternary glaciations, 2.6 million years ago, did not necessarily induce a synchronous global denudation pulse. Constraints on the denudation of the Southern Alps over the last glacial cycle indicate a nonlinear influence of climate on landscape evolution in glaciated areas, according to a beryllium isotope record measured from quartz in a sequence of Mediterranean turbidites.

ASTER Team: Georges Aumaître, Didier L. Bourlès and Karim Keddadouche; International audience; Debris-covered glaciers constitute a large part of the world's cryosphere. However, little is known about their long-term response to multi-millennial climate variability, in particular in the Southern Hemisphere. Here, we provide first insights into the response of a debris-covered glacier to multi-millennial climate variability in the sub-Antarctic Kerguelen Archipelago, which can be compared to that of recently investigated debris-free glaciers. We focus on the Gentil Glacier and present thirteen new 36 Cl cosmic-ray exposure ages from moraine boulders. The Gentil Glacier experienced at least two glacial advancesthe first one during the Late Glacial (19.0-11.6 ka) at ~14.3 ka and the second one during the Late Holocene at ~2.6 ka. Both debris-covered and debris-free glaciers advanced broadly synchronously during the Late Glacial, most probably during the Antarctic Cold Reversal event (14.5-12.9 ka). This suggests that both glacier types at Kerguelen were sensitive to abrupt temperature changes recorded in Antarctic ice cores, associated with increased moisture. However, during the late Holocene, the advance at about ~2.6 ka was not observed in other glaciers and seems to be an original feature of the debris-covered Gentil Glacier, either related to distinct dynamics or distinct sensitivity to precipitation changes.

Cereals are a central resource for the human diet and are traditionally assumed to have evolved from wild grasses at the onset of the Neolithic under the pressure of agriculture. Here we demonstrate that cereals may have a significantly longer and more diverse lineage, based on the study of a 0-2.3 Ma, 601 m long sedimentary core from Lake Acgol (South-West Anatolia). Pollen characteristic of cereals is abundant throughout the sedimentary sequence. The presence of large lakes within this arid bioclimatic zone led to the concentration of large herbivore herds, as indicated by the continuous occurrence of coprophilous fungi spores in the record. Our hypothesis is that the effects of overgrazing on soils and herbaceous stratum, during this long period, led to genetic modifications of the Poaceae taxa and to the appearance of proto-cereals. The simultaneous presence of hominins is attested as early as about 1.4 Ma in the lake vicinity, and 1.8 Ma in Georgia and Levant. These ancient hominins probably benefited from the availability of these proto-cereals, rich in nutrients, as well as various other edible plants, opening the way, in this region of the Middle East, to a process of domestication, which reached its full development during the Neolithic., TUBITAK-CNRS bilateral cooperation [114Y723]; ECCOREV (CNRS (ACIGoL project)); LABEX OT-MED (Bilat project); ANR (MRSEI, ACIGoL project); ALKM Company, This research was conducted as part of the TUBITAK-CNRS bilateral cooperation with the grant number of 114Y723 during 2015-2017. The researches were further funded by ECCOREV (CNRS (ACIGoL project), the LABEX OT-MED (Bilat project) and by the ANR (MRSEI, ACIGoL project). The long coring of Acgol (core 3) was funded by ALKM Company due to the Acgol Drilling Project signed between Cahit Helvac (DEU) and the ALKM and SODAS Companies. We are grateful to the companies of ALKM and SODAS, particularly to the courtesy of their respective owner and Mr Cihat Kora who permitted us to access and work on the Acgol Core-3. Moreover, Mr Huseyin unlu, the general director of ALKM Company during the coring, Mr. unal Ark director of ALKM and Mr. Mahmut Eser, the correspondent of the core is greatly appreciated as well as Mr. Serdar Salanc, the general director, and Mr. Necati Demirer the director of SODAS Cardak Plant. We thank Dahvya Belkacem for having extracted the pollen from the series of Acgol and Kocaba. We thank Michelle Leydet for storing our pollen data in EPD. We thank Alain Tonetto and the Platform for Analytical Technological and Imaging Research (PRATIM), from Aix Marseille University, for the confocal photographies of the pollen. Finally, we would like to thank Dr Chenglong Deng (Editorial Board Member of Scientific Reports) and the reviewer, Dr Li Quan, for very pertinent remarks, which helped to improve the manuscript significantly.

International audience; Despite a wealth of recent studies dealing with the evolution of the drainage network in the uplifted Ardennes massif (E. Belgium), especially from the Middle Pleistocene onwards, the Ardennian landscape evolution and long-term incision rates in the Meuse catchment remain poorly documented over the whole Plio-Quaternary. Alluvium-filled multilevel cave systems represent a relevant setting to unravel the Late Cenozoic history of regional river incision. We present here a dataset of 26 Al/ 10 Be concentration data obtained from fifteen pebble samples washed into the Chawresse system, one of the largest multi-level cave systems of Belgium, which developed in Devonian limestones of the lower Ourthe Valley, the main Ardennian tributary of the Meuse. The sample collection spans an elevation difference higher than 120 m and their depleted 26Al/10Be ratios yield burial ages ranging from ~0.25 to 3.28 Ma. After critical assessment of our dataset for intra-karstic reworking issues, the most striking outcome of the obtained burial ages is the acceleration by a factor five of the incision rates (from ~30to ~150 m/Ma) during the first half of the Middle Pleistocene. Integrating this incision peak and our pre-burial denudation rates, we then revisit the existing framework of Plio-Quaternary denudation and river incision in the Ardennian Meuse catchment. Whilst our 26Al/10Be concentration data shed new light on the temporal andspatial variability of the local river and hillslope system response to coupled tectonic and climatic forcings, it simultaneously highlights sampling issues and the need for further chronological data.

International audience; The respective impacts of Northern and Southern Hemispheric climatic changes on the Tropics during the last deglaciation remain poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) is better represented among morainic records than the Younger Dryas (12.9-11.7 ka BP). However, in the Altiplano basin (Bolivia), two cold periods of the Northern Hemisphere (Heinrich Stadial 1a, 16.5-14.5 ka BP, and the Younger Dryas) are synchronous with (i) major advances or standstills of paleoglaciers and (ii) the highstands of giant paleolakes Tauca and Coipasa. Here, we present new cosmic ray exposure (CRE) ages from glacial landforms of the Bolivian Andes that formed during the last deglaciation (Termination 1). We reconstruct the equilibrium line altitudes (ELA) associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation. Our temperature reconstruction (ΔT relative to present day) yields a consistent regional trend of progressive warming from ΔT = −5 to −2.5°C during 17-14.5 ka BP, followed by a return to colder conditions around −4°C during the ACR (14.5-12.9 ka BP). The Coipasa highstand (12.9-11.8 ka BP) is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (ca. 10 ka BP), around −3°C. Our results suggest that, during the last deglaciation (20-10 ka BP) atmospheric temperatures in the Tropical Andes mimicked Antarctic variability, whereas precipitation over the Altiplano was driven by changes in the Northern Hemisphere.

International audience; Late Cenozoic landscape evolution in intracratonic basins represents an illustrative example of the interaction between surface processes, climate, lithologic and tectonics factors. Here, we model the transition from endorheic to exorheic conditions for the intracratonic Madrid Basin (Tagus Basin, Central Spain). During the Late Cenozoic, this basin appears to have been the result of a prolonged period of similar to 4.0 Ma of headward erosion by the Atlantic external drainage system, local erosion and climatic oscillations. Determining the timing of this transition is crucial to understanding the principal mechanisms of the transition course of the intracratonic basins in or associated with pop-up ridges. We present a detailed geomorphic map of the north of the Tertiary Madrid basin and new age determinations of well-preserved pediments, alluvial fans, alluvial plains and strath terraces. By combining cosmogenic Be-10-Al-26-Ne-21 with magnetostratigraphic data, the sediments associated with the last endorheic phase yield an age of similar to 6.4 Ma. The earliest exorheic alluvial levels of the Madrid Cenozoic basin, explained here as the first fluvial terraces, have been dated through cosmogenic nuclides depth profiles (Be-10-Al-26) at 2.42 Ma and 2.36 Ma respectively.

International audience; Long considered to be a consequence of human antibiotics use by deduction, antibiotic resistance mechanisms appear to be in fact a much older phenomenon as antibiotic resistance genes have previously been detected from millions of year-old permafrost samples. As these specimens guarantee the viability of archaic bacteria, we herein propose to apply the culturomics approach to recover the bacterial content of a Siberian permafrost sample dated, using the in situ-produced cosmogenic nuclide chlorine36 (36 Cl), at 2.7 million years to study the dynamics of bacterial evolution in an evolutionary perspective. As a result, we cultured and sequenced the genomes of 28 ancient bacterial species including one new species. To perform genome comparison between permafrost strains and modern isolates we selected 7 of these species (i.e., Achromobacter insolitus, Bacillus idriensis, Brevundimonas aurantiaca, Janibacter melonis, Kocuria rhizophila, Microbacterium hydrocarbonoxydans and Paracoccus yeei). We observed a high level of variability in genomic content with a percentage of shared genes in the core genomes ranging from 21.23% to 55.59%. In addition, the Single Nucleotide Polymorphism (SNP) comparison between permafrost and modern strains for the same species did not allow a dating of ancient strains based on genomic content. There were no significant differences in antibiotic resistance profiles between modern and ancient isolates of each species. Acquired resistance to antibiotics was phenotypically detected in all gram-negative bacterial species recovered from permafrost, with a significant number of genes coding for antibiotic resistance detected. Taken together, these findings confirm previously obtained data that antibiotic resistance predates humanity as most of antimicrobial agents are natural weapons used in inter-microbial conflicts within the biosphere.

L’étude des nucléides cosmogéniques et leur application aux géosciences débutent dans les années 1980, avec le développement de spectromètres de masse par accélération dédiés. Depuis 2007, grâce à l’instrument national ASTER (Accélérateur pour les Sciences de la Terre, Environnement, Risques) du CEREGE, des progrès majeurs ont été réalisés. Ils ont permis la quantification jusqu’alors impossible de nombreux processus géophysiques. Parmi ces avancées, la restitution fidèle du champ magnétique terrestre pendant le dernier million d’années a été rendu possible par les mesures de concentration du béryllium-10 (10Be) atmosphérique.

International audience; Coarse debris accumulations cover large areas in high latitude and mountain environments, but their age and origin remain mostly unknown. Here we reassess the morphology of a prominent coarse debris accumulation in the Sudetes Mountain range in central Europe and constrain its timing with 10Be surface exposure data. Our observations indicate that the landform in the south-eastern slope of the Suť ridge appears consistent with the morphology of a block slope. The oldest minimum age of 150.1 ± 4.8 ka obtained for the tor at the upper limit of the block slope indicates the disintegration of the ridge and surface lowering under periglacial conditions prior to the last glacial-interglacial cycle. Four exposure ages retrieved for block samples range from 84.3 ± 3.8 to 26.8 ± 2.6 ka, providing evidence for block emplacement during the last cold period. The exposure ages extend existing chronological dataset for peri/glacial landforms in the Sudetes and constrain the timing of cold environments in the area prior the Last Glacial Maximum. The ages are also consistent with surface exposure data reported for block fields and block slopes in Western Europe and confirm the formation of similar landforms over the last glacial period in the Sudetes.

Sediment accumulation rates and thermal trackers suggest a substantial and global increase in erosion rates over the past few million years. That increase is commonly associated with the impact of the Northern Hemisphere glaciation, but methodological biases have led researchers to debate this hypothesis. Here, we test whether Himalayan erosion rates increased by measuring beryllium-10 (10Be) in the sediment of the Bengal Bay seabed. Sediment originated from rocks that produced 10Be under the impact of cosmic rays during erosion near surface. Thus, the 10Be concentrations indicate erosion rates. The 10Be concentration of the Bengal Bay sediment depends on the contributions of the Ganga and Brahmaputra rivers. Their sediments have distinct 10Be concentrations because of distinct elevations and erosion in their drainage basins. Variable contributions could thus complicate erosion-rate calculation. We traced these contributions by a provenance study using the strontium (Sr) and neodymium (Nd) isotopic sediment compositions. Within uncertainties of ±30%, our reconstructed past erosion rates show no long-term increase for the past six million years. This stability suggests that climatic changes during the late Cenozoic have an undetectable impact on the erosion patterns in the Himalayas, at least on the ten thousand to million year timescales accounted for by our dataset. Long-term Himalayan erosion rates remained stable through the global climatic changes of the past six million years, according to the cosmogenic nuclide composition of terrestrial sediments recovered from the Bay of Bengal.

The paleoclimatic changes that occurred in the Southern and Northern hemispheres during the last deglaciation are thought to have affected the continental tropical regions. However, the respective impact of North and Southern climatic changes in the tropics are still poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) was reported to be more represented than the Younger Dryas (12.9-11.7 ka BP) among morainic records. However, in the Altiplano basin (Bolivia), two cold periods of the North Hemisphere (Heinrich Stadial 1a (16.5-14.5 ka) and Younger Dryas) are synchronous with (i) major advances or stillstands of paleo-glaciers and with (ii) the highstands of the giant palaeo-lakes Tauca and Coipasa. Therefore, additional results are needed to disentangle between potential North and South Hemisphere climatic influence on the glacial dynamics in the region.We present new Cosmic Ray Exposure (CRE) ages from glacial landforms of the Bolivian Andes that extend pre-existing datasets for four different sites spreading from 16 to 21°S. We reconstruct the Equilibrium Line Altitudes (ELA) associated with each moraine with the AAR method and use them in an inverse algorithm that combines both the palaeo-glaciers and palaeo-lake budgets to derive temperature and precipitation reconstructions. Our temperature reconstruction (ΔT vs. Present) shows a consistent trend through the four glacial sites with a progressive warming from ΔT= -5°C (17 ka BP) to –2.5°C (15-14.5 ka BP, at the end of the Tauca highstand). This is followed by a return to colder conditions, around -4°C, during the ACR (15.5-12.9 ka BP). The Coipasa highstand is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (circa 10 ka BP), around -3°C. Precipitation is mainly characterized by increases during the lake highstands, modulated by the distance from the glacial sites to the center of the paleolakes that are moisture sources (recycling processes).These new results highlight the decorrelation of the glacier dynamics to the temperature signal in regions that are characterized by high precipitation variability. They also provide a theoretical frame to explain how both regional and global forcings can imprint the paleo-glacial records. Our results strongly suggest that during the last deglaciation (20 – 10 ka BP), in the Tropical Andes, atmospheric temperatures follow the Antarctic variability, while precipitation is driven by the changes occurring in the Northern Hemisphere.

The global production rate of the cosmogenic isotope 10Be by cosmic ray spallation is modulated by the activity of the sun and the intensity of the far-reaching component of the Earth magnetic field, which is in turn dominated by the dipolar term. Therefore, sedimentary 10Be records can be used to reconstruct past variations of the geomagnetic dipole moment. However, several environmental factors affect the transfer of 10Be atoms from the high atmosphere and soils, where it is produced, to the sediment, introducing a significant climatic modulation that can, in worst cases, completely obscure the paleomagnetic signal. These factors include variations of the continental runoff, oceanic circulation, sediment fluxes, and sediment scavenging effi­ciency. The latter is largely removed by normalizing the 10Be record with the concentration of authigenic 9Be, which is accumulated by sediment particles in the same manner as the cosmo­genic isotope. Even with this correction in place, individual 10Be/9Be records are significantly influenced by climate, to the point that only major geomagnetic events, such as the MB reversal, can be recognized. We present a model, which, for the first time, enables to deconvolve, at least partially, the climatic and magnetic components of 10Be/9Be records on a set of cores from the Atlantic, Indian, and Pacific Ocean. The climatic modulation is composed of an additive term, which reflects Be recycling through diagenetic release from sediments, and a multiplicative term, which is dominated by oceanic current patterns. Knowledge of these terms enables to remove, at least partially, site-specific environmental effects, obtaining a corrected 10Be/9Be stack that can be inverted to reconstruct variations of the dipole moment during the last geomagnetic reversal.

Multi-level cave systems record the history of regional river incision in abandoned alluvium-filled phreatic passages which, mimicking fluvial terrace sequences, represent former phases of fluvial base-level stability. In this respect, cosmogenic burial dating of in cave-deposited alluvium (usually via the nuclide pair 26Al/10Be) represents a suitable method to quantify the pace of long-term river incision. Here, we present a dataset of fifteen 26Al/10Be burial ages measured in fluvial pebbles washed into a multi-level cave system developed in Devonian limestone of the uplifted Ardenne massif (eastern Belgium). The large and well-documented Chawresse system is located along the lower Ourthe valley (i.e. the main Ardennian tributary of the Meuse river) and spans altogether an elevation difference exceeding 120 m.The depleted 26Al/10Be ratios measured in four individual caves show two main outcomes. Firstly, computed burial ages ranging from ~0.2 to 3.3 Ma allows highlighting an acceleration by almost one order of magnitude of the incision rates during the first half of the Middle Pleistocene (from ~25 to ~160 m/Ma). Secondly, according to the relative elevation above the present-day floodplain of the sampled material in the Manants cave (per descensum model of speleogenesis generally acknowledged for the regional multi-level cave systems and their abandoned phreatic galleries. In addition to its classical use for inferring long-term incision rates, cosmogenic burial dating can thus contribute to better understand specific and complex speleogenetic evolution.

International audience; Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif being located at the transition between the Alps and the Mediterranean Sea, its deglaciation chronology can be compared to the sediment budget of the Var River marine delta. In this paper, the deglaciation is constrained by 13 new and 22 reassessed Cosmic-Ray Exposure (CRE) 10Be datings of moraines and polished crystalline bedrocks. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif, in agreement with a major glacier recession at ca. 15 ka, at the onset of Bølling transition. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after ca. 15 ka. This major deglaciation is correlated with a 2.5 fold decrease of sediment discharge of rivers into the Mediterranean Sea. Main deglaciation of the massif upper slopes (2,700-2,800 m a.s.l.) occurred after the LGM at 20.8-18.6 ka, followed by the lower slopes (2,300 m a.s.l.) at 15.3-14.2 ka. Finally, the flat polished surfaces above 2,600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8-9 ka. At lower elevations, a sediment core in the Vens Lake located at 2,300 m a.s.l., shows onset of lake sedimentation at ca. 14 ka and a transition towards a vegetated environment after 8 ka. Final stabilization of moraines occurred at 5 ka, which might reflect denudation acceleration during the Holocene humid phase.

The central part of the Western Andes holds an exceptional concentration of giant paleolandslides involving very large volumes of rock material (v > km3). While those gravitational slope failures are interpreted consensually as an erosional response to the geodynamic activity of the Andes (relief formation and tectonic activity), the question of their triggering mechanisms remains enigmatic. To clarify the respective roles of climatic versus seismic forcing on the Andean landslides, new temporal constraints on paleo movements are essential. Here, we focus on one of those giant slope failures, the Aricota giant rockslide that damned the Locumba valley in southern Peru. We conducted fieldwork, high-resolution DEM analysis and cosmogenic nuclide dating to decipher its development history and failure mechanisms. Our results point to the occurrence of two successive events. A giant failure mobilizing a rock volume of ca. 2 km3 first produced a dam at 17.9 ± 0.7 ka. Considering its height of ca. 600 m, the Aricota rockslide dam is one of the three largest landslide dams worldwide. At 12.1 ± 0.2 ka, a second event produced ca. 0.2 km3 of material, and the rock-avalanche debris spread out over the dam. As the chronology of those two events is pointing to the two main paleoclimatic pluvial periods in this region (Heinrich Stadial 1a and Younger Dryas), we favor the interpretation of a climatic forcing. At a regional scale, the concomitant aggradation of alluvial terraces and fan systems along the nearby valleys highlights higher regional erosion, sediments supply and mass-wasting events during those paleoprecipitation events and strengthens this conclusion.

Assessing the impact of radioactive iodine on humans subsequent to a nuclear accident requires a better understanding of its behaviour in the environment. An original approach aimed at developing a model constrained by data collected during experimental campaigns has been developed. These experimental campaigns, named MIOSEC 2 and MIOSEC 3 respectively, were conducted in the middle of grassland. They are based on emissions of gaseous elemental iodine (I

International audience; The $^{10}$Be, $^{137}$Cs and $^{210}$Pb$_{xs}$ radionuclide fallout has been used for the last several decades to quantify various soil and geomorphological processes and their rates, on different time scales. However, a basic assumption of the studies relying on these radionuclides is that they have a strong affinity for soil particles and that their mobility in soil solution and losses through leaching can be neglected. Another area of the scientific literature deals with the radionuclide mobility in soils as solute. In that context, the objective of this work is to determine the pedological conditions under which this hypothesis of poor solute mobility of radionuclides is valid. To this end, meteoric $^{10}$Be, $^{137}$Cs and $^{210}$Pb$_{xs}$ concentrations were measured in six soil profiles representative of 5 soil types contrasted in terms of physico-chemical properties: an Andosol and a Luvisol under pasture, a Ferralsol and a Leptosol under forest and a Podzol both under forest and cultivation. The main soil properties (soil pH, organic carbon (OC) content, particle size distribution and specific extractions) were measured. The

International audience; Documenting accurately amplitude and rhythms of geomagnetic variations is a prerequisite to understand the mechanisms triggering geomagnetic excursions and reversals. We present new authigenic 10Be/9Be ratio (Be ratio) results covering the 60-20 ka time interval from equatorial core MD05-2920. The most significant Be ratio peak is located 18 cm above the main relative paleointensity (RPI) minimum recorded in this sequence. These are interpreted as two independent recordings of the geomagnetic dipole moment (GDM) decrease linked to the Laschamp excursion dated at ca 41 ka. The stratigraphic offset is assignable to post-depositional magnetization lock-in processes resulting in time delay of 1.6 ka. The Be ratio and RPI records show comparable asymmetric behavior before and after the dipole low. The Be ratio record is combined with three other series to construct a global record of 10Be paleoproduction variations. This compilation demonstrates the strong coherence of low and mid latitudes data sets and its comparison with 10Be-flux records from polar regions fully supports the hypothesis of a global atmospheric 10Be production doubling during the Laschamp. The Be ratio stack is converted in terms of GDM using both a theoretical model and a reconstruction of GDM values using absolute paleointensities measured on lava flows. Both methods provide similar results. The dipole moment record derived from this approach (BeDM 20-60) shows the following characteristics: high field values (> 11 × 1022 Am2) prior to a sharp two-steps dipole decrease until reaching minimum values (1.8 ± 0.7 × 1022 Am2) between 41.6 and 40.9 ka at the time of the Laschamp excursion. The GDM partly recovers up to values of ∼ 6.3 × 1022 Am2 , and oscillates in this range, without showing any sharp decreases that could be associated with excursions reported within the 38-20 ka time interval (e.g. the Mono Lake excursion).

International audience; Despite increasing knowledge on the orogenic phases of the Pyrenees, the Neogene evolution of the range remains poorly constrained. The central Pyrenees, particularly the Ariège River valley and its terrace systems and glacial extensions, are key to reconstructing Pyrenean evolution during the Neogene. However, few terrace relics remain on the piedmont edges. To overcome this limitation and temporally extend the dataset obtained from terraces, we focus on alluvium-filled horizontal epiphreatic passages developed in limestone karstic networks. These landforms record the transient position of former local base levels during the process of valley deepening, similar to fluvial terraces. The alluvium fills of the studied caves in the Tarascon-sur-Ariège area, in the transition zone between the upper range and the piedmont, therefore enable the reconstruction of the geodynamic evolution of the Ariège River valley. All studied caves are developed on at least eight levels. Based on burial durations determined by 26Al/10Be and 10Be/21Ne terrestrial cosmogenic nuclide dating of samples from epiphreatic levels, our results indicate Langhian to Messinian (~13–5 Ma) incision rates averaging 48 m Myr−1. However, the obtained record does not allow us to accurately retrace the Pliocene evolution of the area due to the lack of known caves at corresponding levels. Moreover, raised local base levels during glacial phases both make the record more complex and call into question the methodological approach in terms of potential internal sediment remobilization and mixing related to implied re-flooding periods.

International audience; The dynamics of carbonate-dominated landscapes is still debated, and first-order questions pertaining to the respective importance of chemical and mechanical weathering processes or the influence of climatic variability on denudation rates are largely open. To address these issues, we investigate the denudation pattern across a climatic gradient in Provence, SE France. We focused on a series of major carbonate mountain ranges with elevation spanning 200 to 2000 m and associated with >2-fold variations in mean annual temperature and precipitation. We collected 25 samples from 10 different mountain ranges and quantified denudation rates through the measurement of their Cl-36 concentrations in order to explore tectonic and climatic controls on these carbonate landscapes evolution. We observe that most of our samples experience denudation rates in the 30-60 mm/ka range (averaged over 5 to 40 ka), with no evident dependence on variations of mean annual temperature or precipitation. One range (Lure mountain) stands out as a significant outlier, with much higher denudation rates (>100 mm/ka) than adjacent sites (Ventoux mountain) at the same elevation and experiencing similar present-day environmental conditions. We explore in details the climatic, tectonic and geomorphological contexts of these two ranges in order to understand the reasons for this apparent 3-fold difference in denudation rates. A regionally-documented major Holocene hillslope destabilization event appears to be a likely candidate to explain the observed lower Cl-36 concentrations at the top of the Lure mountain. At longer wavelengths, our regional dataset shows no clear control of modem precipitation gradients on denudation rates, consistent with previous observations in landscapes underlain by other lithologies.

International audience; The knowledge of the eruptive history of volcanic centers allows for improving the evaluation of the related risks and hazards in populated areas, but substantially depends on the ability of dating the lava flows. However, traditional methods such as U-Th/He, 40 Ar-39 Ar, 40 K-40 Ar and radiocarbon dating are not always suitable. Therefore, an alternative approach based on the combination of in situ-produced 36 Cl based cosmic ray exposure dating, lichenometry and dendrochronology was tested on two lava flows (called Lava flow "A" and "B") from Pico de Orizaba (Mexico), previously attributed to 16th and 17th century eruptions, respectively. The presented results show that both lava flows are significantly older than their assumed 16th and 17th century ages. Regarding lava flow "A", the measured in situ-produced 36 Cl concentrations lead to a mean age of 3.03 ± 0.70 ka, while dendrochronology and lichenometry yield minimum ages of 834 and 1130 years, respectively. Regarding lava flow "B", the measured in situ-produced 36 Cl concentrations lead to a mean age of 1.45 ± 0.35 ka, whereas lichenometry gives a minimum age of ∼1000 years. Overall, this demonstrates that the combination of in situ-produced 36 Cl based cosmic ray exposure dating, lichenometry and dendrochronology has a considerable potential for dating purposes on young deposits and landforms, in particular on lava flows at high elevation sites.

International audience; In this study, we present a new glacial chronology based on 20 in situ-produced 36Cl-based cosmic ray exposure datings from moraine boulders and bedrock from the Throne of Zeus (TZ) and Megala Kazania (MK) cirques on Mount Olympus. The 36Cl derived ages of glacial landforms range from 15.6 ± 2.0 to 0.64 ± 0.08 ka, spanning the Late-glacial and the Holocene. The Late-glacial, recorded in both cirques, is partitioned in three distinct phases (LG1-3): an initial phase of moraine stabilization at 15.5 ± 2.0 ka with subsequent deglaciation starting at ∼14 ka (LG1), followed by a shift to marginal conditions for glaciation at 13.5 ± 2.0 ka (LG2), sustained by large amounts of wind-blown snow, despite regional warming. Glacial conditions returned at 12.5 ± 1.5 ka (LG3) and were characterized by low air temperatures and glacier shrinking. The Holocene glacial phases (HOL1-3) are recorded only in the MK cirque, likely due to its topographic attributes. An early Holocene glacier stillstand (HOL1) at 9.6 ± 1.1 ka follows the regional temperatures recovery. No glacier activity is observed during the mid-Holocene. The Late Holocene glacier expansions, include a moraine stabilization phase (HOL2) at 2.5 ± 0.3 ka, during wet conditions and solar insolation minima, while (HOL3) corresponds to the early part of the Little Ice Age (0.64 ± 0.08ka). Our glacial chronology is coherent with glacial chronologies from several cirques along the northeast Mediterranean mountains and in pace with numerous proxies from terrestrial and marine systems from the north Aegean Sea.

Terrestrial cosmogenic nuclide dating of ice-marginal moraines can provide unique insights into Quaternary glacial history. However, pre- and post-depositional exposure histories of moraine boulders can introduce geologic uncertainty to numerical landform ages. To avoid geologic outliers, boulders are typically selected based on their depositional context and individual characteristics but while these criteria have good qualitative reasoning, many have not been tested quantitatively. Of these, boulder location is critical, as boulders located on moraine crests are prioritised, while those on moraine slopes are typically rejected. This study provides the first quantitative assessment of the relative utility of moraine crest and moraine slope sampling using new and published 10Be and 36Cl ages (n = 19) and Schmidt hammer sampling (SH; n = 635 moraine boulders, ∼19,050 SH R-values) in the northern and southern Pyrenees. These data show that for many of the studied moraines, the spatial distribution of “good” boulders is effectively random, with no consistent clustering on moraine crests, ice-proximal or -distal slopes. In turn, and in contrast to prior work, there is no clear penalty to either moraine crest or moraine slope sampling. Instead, we argue that landform stability exerts a greater influence on exposure age distributions than the characteristics of individual boulders. For the studied landforms, post-depositional stability is strongly influenced by sedimentology, with prolonged degradation of matrix-rich unconsolidated moraines while boulder-rich, matrix-poor moraines stabilised rapidly after deposition. While this pattern is unlikely to hold true in all settings, these data indicate that differences between landforms can be more significant than differences at the intra-landform scale. As ad hoc assessment of landform stability is extremely challenging based on geomorphological evidence alone, preliminary SH sampling, as utilised here, is a useful method to assess the temporal distribution of boulder exposure ages and to prioritise individual boulders for subsequent analysis.

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; The possibility of quantifying surface processes in mafic or volcanic environment using the potentialities offered by the in situ-produced cosmogenic nuclides, and more specifically by the in situ-produced Be-10, is often hampered by the rarity of quartz minerals in the available lithologies. As an alternative to overcome this difficulty, we explore in this work the possibility of relying on feldspar minerals rather that on quartz to perform in situ-produced Be-10 measurements in such environments. Our strategy was to cross-calibrate the total production rate of Be-10 in feldspar (P-10fsp) against the total production rate of He-3 in pyroxene (P-3px) by measuring He-3 and Be-10 in cogenetic pyroxene (He-3(px)) and feldspar (Be-10(fsp)). The samples were collected from eight ignimbritic boulders, exposed from ca 120 to 600 ka at elevations ranging from 800 to 2500 m, along the preserved rock-avalanche deposits of the giant Caquilluco landslide (18 degrees S, 70 degrees W), Southern Peru. Along with data recently published by Blard et al. (2013a) at a close latitude (22 degrees S) but higher elevation (ca. 4000 m), the samples yield a remarkably tight cluster of He-3(px) - Be-10(fsp) total production ratios whose weighted-mean is 35.6 +/- 0.5 (1 sigma). The obtained weighted mean He-3(px) - Be-10(fsp) total production ratio combined with the local He-3(py) total production rate in the high tropical Andes published by Martin et al. (2017) allows to establish a total SLHL Be-10 in situ-production rate in feldspar mineral (P-10fsp) of 3.57 +/- 0.21 at.g(-1).yr(-1) (scaled for the LSD scaling scheme, the ERA40 atm model and the VDM of Lifton, 2016). Despite the large elevation range covered by the whole dataset (800-4300 m), no significant variation of the He-3(px) - Be-10(fsp) total production ratios in pyroxene and feldspar was evidenced. As an attempt to investigate the effect of the chemical composition of feldspar on the total Be-10 production rate, major and trace element concentrations of the studied feldspar samples were analyzed. Unfortunately, giving the low compositional variability of our dataset, this issue is still pending. (C) 2017 Elsevier B.V. All rights reserved.