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To provide insights into glacier-climate dynamics of the South Shetland Islands (SSI), NW Antarctic Peninsula, we present a new deglaciation and readvance model for the Bellingshausen Ice Cap (BIC) on Fildes Peninsula and for King George Island/Isla 25 de Mayo (KGI) ~62°S. Deglaciation on KGI began after c. 15 cal. ka BP and had progressed to within present-day limits on the Fildes Peninsula, its largest ice-free peninsula, by c. 6.6–5.3 cal. ka BP. Probability density phase analysis of chronological data constraining Holocene glacier advances on KGI revealed up to eight 95% probability ‘gaps’ during which readvances could have occurred. These are grouped into four stages – Stage 1: a readvance and marine transgression, well-constrained by field data, between c. 7.4 and 6.6 cal. ka BP; Stage 2: four probability ‘gaps’, less well-constrained by field data, between c. 5.3 and 2.2 cal. ka BP; Stage 3: a well-constrained but restricted ‘readvance’ between c. 1.7 and 1.5 cal. ka BP; Stage 4: two further minor ‘readvances’, one less well-constrained by field data between c. 1.3 and 0.7 cal. ka BP (68% probability), and a ‘final’ well-constrained ‘readvance’ after

The Early to Mid-Pleistocene Transition (MPT) between ~ 1.2 Ma to ~500 ka (also termed as ‘900 ka event’) marks a change in climatic periodicity, from 41 ka cycles to 100 ka cycles of increased intensity. In non-glaciated areas of Europe this climatic shift has been associated with pronounced acceleration of river incision, in part driven by increased sediment loads from periglacial hillslope processes. Until the Pleistocene, low-relief landscapes are thought to have dominated throughout Europe. Utilizing novel in-situ cosmogenic Krypton in zircon methodology (Dunai et al. 2022), we find direct evidence that this was indeed the case, and that these landscapes were profoundly transformed during the MPT.Our study area (Vogtland, Saxony, Germany) was never glaciated but was within 50 km of the ice margins during the largest Quaternary glaciations. For our study, we utilize a unique source of megacryst zircons (Ebersbrunn diatreme), whose exhumation, dispersal and burial history is recorded by cosmogenic Krypton. The megacryst zircons are found in the fluvial sediments of the current catchments downstream of the source (Raumbach, Göltzsch, Weiße Elster), however, also in a distal catchment (Weida), now disconnected from the source due to late Pleistocene superimposed drainage (Weiße Elster valley).The cosmogenic Krypton data from the megacryst zircons is commensurate with a long (1 to 3 Myr) exposure at or near the surface, or exhumation at a very low rate (

Understanding long-term soil and landscape evolution can help us understand the threats to current-day soils, landscapes and their functions. The temporal evolution of soils and landscapes can be studied using geochronometers, such as optically stimulated luminescence (OSL) particle ages or radionuclide inventories. Also, soil–landscape evolution models (SLEMs) can be used to study the spatial and temporal evolution of soils and landscapes through numerical modelling of the processes responsible for the evolution. SLEMs and geochronometers have been combined in the past, but often these couplings focus on a single geochronometer, are designed for specific idealized landscape positions, or do not consider multiple transport processes or post-depositional mixing processes that can disturb the geochronometers in sedimentary archives. We present ChronoLorica, a coupling of the soil–landscape evolution model Lorica with a geochronological module. The module traces spatiotemporal patterns of particle ages, analogous to OSL ages, and radionuclide inventories during the simulations of soil and landscape evolution. The geochronological module opens rich possibilities for data-based calibration of simulated model processes, which include natural processes, such as bioturbation and soil creep, as well as anthropogenic processes, such as tillage. Moreover, ChronoLorica can be applied to transient landscapes that are subject to complex, non-linear boundary conditions, such as land use intensification, and processes of post-depositional disturbance which often result in complex geo-archives. In this contribution, we illustrate the model functionality and applicability by simulating soil and landscape evolution along a two-dimensional hillslope. We show how the model simulates the development of the following three geochronometers: OSL particle ages, meteoric 10Be inventories and in situ 10Be inventories. The results are compared with field observations from comparable landscapes. We also discuss the limitations of the model and highlight its potential applications in pedogenical, geomorphological or geological studies.

The Atacama Desert is the driest and oldest desert on Earth. Despite the abundance evidence for long-term landscape stability, there are subtle signs of localised fluvial erosion and deposition since the onset of hyperaridity in the rock record. In the dry core of the Atacama Desert, pluvial episodes allowed antecedent drainage to incise into uplifting fault scarps, which in turn generated sinuous to meandering channels. Incision of ancient alluvial fan surfaces occurred during intermittent fluvial periods, albeit without signs of surface erosion. Fluvial incision during predominantly hyperarid climate periods is evident from these channels in unconsolidated alluvium. The absence of dense vegetation to provide bank stability and strength led us to investigate the potential role of regionally ubiquitous CaSO

Understanding long-term soil and landscape evolution can help us understand the threats to current-day soils, landscapes and their functions. The temporal evolution of soils and landscapes can be studied using geochronometers, such as optically stimulated luminescence (OSL) particle ages or radionuclide inventories. Also, soil–landscape evolution models (SLEMs) can be used to study the spatial and temporal evolution of soils and landscapes through numerical modelling of the processes responsible for the evolution. SLEMs and geochronometers have been combined in the past, but often these couplings focus on a single geochronometer, are designed for specific idealized landscape positions, or do not consider multiple transport processes or post-depositional mixing processes that can disturb the geochronometers in sedimentary archives. We present ChronoLorica, a coupling of the soil–landscape evolution model Lorica with a geochronological module. The module traces spatiotemporal patterns of particle ages, analogous to OSL ages, and radionuclide inventories during the simulations of soil and landscape evolution. The geochronological module opens rich possibilities for data-based calibration of simulated model processes, which include natural processes, such as bioturbation and soil creep, as well as anthropogenic processes, such as tillage. Moreover, ChronoLorica can be applied to transient landscapes that are subject to complex, non-linear boundary conditions, such as land use intensification, and processes of post-depositional disturbance which often result in complex geo-archives. In this contribution, we illustrate the model functionality and applicability by simulating soil and landscape evolution along a two-dimensional hillslope. We show how the model simulates the development of the following three geochronometers: OSL particle ages, meteoric 10Be inventories and in situ 10Be inventories. The results are compared with field observations from comparable landscapes. We also discuss the limitations of the model and highlight its potential applications in pedogenical, geomorphological or geological studies.

Concentrations of cosmogenic nuclides in rocks at the Earth’s surface are routinely measured by AMS (accelerator mass spectrometry) to obtain exposure ages. One particular application of this technique has been to derive ages for the formation of marine terraces, thus allowing constraints to be placed on rates of tectonic uplift. However, multiple rock samples from the same terrace surface have typically shown an amount of scatter in cosmogenic nuclide concentrations in excess of analytical uncertainties, potentially undermining the confidence in the resulting uplift rates. In addition, earlier works have considered the application of bedrock samples for exposure age dating marine terraces, but little attention has been directed towards the validity of sampling clasts exposed on terrace surfaces. Here, we use 10Be and 26Al measurements from a flight of marine terraces in northern Chile to compare the results from pebbles with those from bedrock samples and to investigate assumptions that sample pre-exposure and burial are negligible. We examine the influence that processes of surface deflation and pebble erosion will have on cosmogenic nuclide concentrations using a Monte Carlo model, the results of which are compared to our 10Be measurements. We find good agreement of 10Be concentrations between bedrock and pebble samples. At the sampled location, sample burial is rare and 10Be inheritance in pebble samples is low relative to the age of the terraces. Our modelling suggests that in arid environments, such as northern Chile, pebble erosion will be a secondary effect compared to surface deflation and that multiple periods of deflation will result in multimodal distributions of 10Be concentrations. More broadly, our findings show that measuring multiple surface clasts from a single marine terrace reveals the geomorphological processes influencing exposure ages, and may also be used to help identify the operation of past surface processes such as episodic deflation.

Although fluvial erosion is predominantly governed by surface driven fluvial incision, more exotic erosional processes can significantly contribute to the fluvial shaping of landscapes. To this group belongs sapping caused by concentrated groundwater discharge, which can form a very distinct type of topography (characterised e.g. by the development of theatre-shaped channel heads). Fluvial erosion through sapping occurs where groundwater encounters a rapid change in elevation (i.e. across scarps, cliffs), and it is highly modulated by the physical properties of the solid. Groundwater sapping is, for example, promoted by inhomogeneities of permeability and/or lithological composition of the subsurface, which is often prevalent in sedimentary deposits and along contact boundaries between different lithological units. Consequently, topography shaped by groundwater sapping can be found in many places on Earth and even on Mars, and the formation of these landscapes can integrate over thousands to millions of years. However, in some regions, such as coastal areas, groundwater sapping has been reported to be associated with severe soil loss and high erosion rates on the order of tens of metres per day.A similar magnitude of soil loss could be observed close to the village of Erftstadt-Blessem, Germany, as caused by severe flooding, peaking the 15th of July 2021. Here, intense rain events caused the formation of local drainage networks towards a gravel pit located to the north of the village. As a consequence, adjacent arable land was subject to intense backward incision, thereby eroding the underlying Quaternary sediments. The erosion formed drainage networks that appear to resemble characteristic groundwater sapping. This fluvial topography was largely preserved after the flooding, thus providing the opportunity to decipher the processes involved in the formation of these features. We use Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry to reconstruct the drainage geometry based on drone imagery (provided by the Kreisverbindungskommando Köln, M. Wiese; additional SfM-MVS photogrammetry data provided by ESRI Deutschland GmbH, T. Gersthofer) and photographs taken in the field using a handheld camera. The data is subsequently used to characterise the drainage networks and to compare the topography to other groundwater sapping landscapes on Earth and on Mars. Additionally, we intend to perform grain size analyses of the different sediment layers and to quantify fallout 239+240Pu in selected samples to asses the physical properties of the substratum and to trace the fate of the radionuclides during the flood event. Our aim is that our data will contribute to a better understanding of how groundwater sapping processes operate over time and to assess the importance of individual factors (e.g. substrate properties, vegetation cover and -type) on the severity of erosion. The outcome could thus not only be important for modelling terrestrial and extra-terrestrial processes but has also practical applications to the loss of arable land and the effects of outburst flooding.

Analysis of cosmogenic nuclides produced in surface rocks and sediments is a valuable tool for assessing rates of processes and the timing of events that shaped the Earth surface. The various nuclides that are used have specific advantages and limitations that depend on the time-range over which they are useful, the type of material they are produced in, and not least the feasibility of the analytical effort. Anticipating novel applications in Earth surface sciences, we develop in-situ produced terrestrial cosmogenic krypton (Krit) as a new tool; the motivation being the availability of six stable and one radioactive isotope (81Kr, half-life 229 kyr) and of an extremely weathering-resistant target mineral (zircon). We provide proof of principle that terrestrial Krit can be quantified and used to unravel Earth surface processes.

The shape of soil‐mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1‐m LiDAR data, and the erosion rates have also been determined via a single method, in‐situ cosmogenic 10Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6 – 922 mm/kyr), mean annual precipitation (39 – 320 cm/yr), and aridity index (0.08 – 1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil‐mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that processes occurding in the bedrock (e.g., fracture generation) may play a role in the shape of hillslope profiles at our sites.

The shape of soil-mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1-m LiDAR data, and the erosion rates have also been determined via a single method, in-situ ­cosmogenic 10Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6 – 1373 mm/kyr), annual precipitation (31 – 320 cm/yr), and aridity index (0.08 – 1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil-mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that bedrock processes may be responsible for the shape of hillslope profiles at our sites.

s & presentations : EGU General Assembly 2021 EGU General Assembly 2021, vEGU21, online, 19 Apr 2021 - 30 Apr 2021; G��ttingen : Copernicus Gesellschaft mbH EGU21-13578, 2 Seiten (2021). doi:10.5194/egusphere-egu21-13578, Published by Copernicus Gesellschaft mbH, G��ttingen

Active intraplate deformation as a far-field effect of the India-Eurasia convergence has led to four Mw∼8 earthquakes in western and southern Mongolia in the past century. Palaeoseismological and morphotectonic studies have shown that these earthquakes are characteristic events along transpressive fault systems with cumulative offsets. The tectonically active Gobi Altai and Hangay mountains are separated by the seismically quiescent Valley of Gobi Lakes, which consists of major perennial rivers draining into endorheic lakes. Despite the scarcity of recorded earthquakes, Quaternary deposits in the Valley of Gobi Lakes are crosscut by multiple fault scarps with significant, landscape-altering displacements. To assess past earthquakes and the potential seismic hazard of this area, we apply remote sensing, tectono-morphometric techniques and cosmogenic nuclide dating to estimate the amount of deformation the faults in the Valley of Gobi Lakes are accommodating, and to determine the effect of these faults on local landscape evolution. The Tuyn Gol (gol = Mongolian for river) is crosscut by four E-W to NE-SW trending fault scarps that display variable fault kinematics due to scarp orientation differences relative to a stable NE-SW principle stress direction. Mapping of the >40–90 km long Valley of Gobi Lake faults shows that they can accommodate M ∼ 7 earthquakes. Offset measurements of the Tuyn Gol deposits allow Middle Pleistocene to modern vertical slip rate estimates and M ∼ 7 earthquake recurrence intervals of 0.012 ± 0.007–0.13 ± 0.07 mm/yr and 5.24 ± 2.61–81.57 ± 46.05 kyr, respectively. Cumulative vertical displacement amounts to 0.27 ± 0.08 mm/yr, which is similar to that of major tectonic structures such as the Bogd fault in the Gobi Altai. This implies that the total active deformation accommodated by southern Mongolian faults may be larger than previously expected and distributed across more faults between the Hangay and the (Gobi) Altai mountain ranges. Geomorphological observations and surface exposure dating indicate that the Tuyn Gol drainage system developed over four to five 100 kyr climate cycles, during which active deformation played an important role in drainage reorganization. Our results demonstrate the dominant role of tectonics on local landscape dynamics, indicating the importance of studying regional geomorphology to adequately estimate the earthquake potential of faults that were considered inactive.

High-mountain environments in an active tectonic setting are prone to landsliding. The triggering mechanisms are still a challenge as these areas are influenced by several pre-conditioning factors coupled with active seismicity and climatic forcings. Understanding the intrinsic and external mechanisms in which these events are influenced would help to establish better constraints onto their timing and periodicity and, eventually, hazard assessment and prediction. Glacially eroded valleys are especially prone as they deeply incise mountain ranges leaving unstable slopes once they retreat. Establishing the timing of such events enables to link the causality and comprehend in a deeper level the triggering and pre-conditioning factors of landslides. To this aim, ¹⁰Be and ²⁶Al cosmogenic age determinations were performed in three landslide deposits in a poorly studied area of San Juan province, all of which are novel to the area. Coupled with remote sensing techniques, field observations and detailed stratigraphic and sedimentological studies, these new large landslides represent a first approach to understand this dynamic environment. The three landslides were categorized as rock avalanches found in the middle and lower reaches of the Blanco River, sourced from the Choiyoi Group with evidence of hydrothermal alteration and including/deforming moraine deposits during their fall. Ages range from 20.9±1.4, 10.8±0.7 and 12.8±0.9 ka from the lowermost deposit to the highest, respectively. Even though one sample per deposit is not enough to have statistically significant exposure ages, these values, along with the established chronostratigraphy, allow first order assumptions on the link between deglaciation processes and readjustment of the slopes via large landslide events.

Processes contributing to soil creep dominate the downslope movement of soil particles in many regions, and climate is generally hypothesized to have an important influence on the efficiency of the...

Measurements of cosmogenic 10Be, 26Al and 36Cl in Apollo 16 double drive core 68002/68001 are combined with a high resolution digital surface model of the sampling site to investigate the surface processes on the Moon. We find both a significant deficit of solar cosmic ray (SCR)-produced 26Al and a lack of SCR-produced 36Cl in the top 3–5 g/cm2 of the lunar regolith. The topographic model shows the core was taken from just inside a crater with a rim diameter of 25–30 cm. These observations are consistent with regolith removal and displacement by a shallow impact that occurred on the order of 100 kyr ago, or less. Our findings are also compatible with shallow mixing, or gardening, of the lunar regolith to depths of a few cm, a value often found in other lunar cores over the ∼106 yr averaging times of 26Al and 53Mn measurements. More definitive regolith mixing depth estimates are not possible due to the likelihood of disturbance in the top of the core as a result of sampling and/or handling. Our results support the hypothesis that the lunar surface experiences more frequent disturbances by small primary and secondary impacts than has previously been assumed. Additionally, we find no evidence that fine-grained ejecta from the 2.0 Myr old South Ray Crater impact reached this site. If the layer of fine-grained ejecta that reached the sampling site from the South Ray Crater was no more than a few cm thick, this absence can be explained by the erosion that formed the small, relatively recent crater at the coring location.

In the hyperarid environment of the Atacama Desert, alluvial fans are the principle fluvial geo-archive reflecting variations in climate and tectonics in their architecture. While they have been studied in the core of the desert to reconstruct long-term palaeoenvironmental changes from the Oligocene to the Quaternary and, in particular, to constrain the onset of hyperaridity, alluvial fans along the coast (20.5°S – 25.5°S) are younger and show a much higher activity; thus, they can serve as archives during the Pleistocene to Holocene evolution. However, past and recent morphodynamics of the coastal alluvial fans (CAF) are yet poorly reconstructed so that the understanding of an interplay between climatic, geologic, and biotic controls is still challenging.We related climatic, lithologic, and tectonic source-area characteristics to geomorphometric parameters of the CAF and their catchments. Geomorphometric analyses were conducted based on the 12.5 m TanDEM‑X WorldDEM™, lithological and tectonic data were extracted from regional geological maps, and the frequency of heavy rainfall events derived from a regional Weather Research and Forecasting (WRF) model was used as a climate parameter. We further combined luminescence dating, cosmogenic nuclide exposure dating, and existing chronological data to constrain the timing of Pleistocene alluvial fan deposition as well as the ages of interbedded marine terraces.Results indicate a primary climatic control on CAF dynamics shown in the functional relationships with catchment hydromorphometrics that mirror a high susceptibility to debris-flows as well as in the temporal pattern of CAF activity. Distinct phases of CAF activity occurred during the late Pleistocene (95–80 ka, 60–45 ka, and 35-20 ka) and the Holocene – driven by atmospheric changes from the Pacific Ocean. The primary source of precipitation is reflected along the latitudinal gradient: frontal systems and cut-off lows mainly originating from the extratropics. Towards the south, an increasing density of Loma vegetation can be observed so that also possible feedback mechanisms of biota on sediment supply need to be considered. While source-area lithology is of negligible relevance for CAF morphodynamics, an important long-term influence of tectonics can be seen in the regional uplift, which in turn controls the catchment shape and relief. From the numerical dating of the marine terraces, uplift rates ranging between ~0.06 and ~0.57 m/ka were derived for the late Pleistocene period.Acknowledgement: TanDEM-X WorldDEM™ data is provided by a DLR Science grant, 2017.References: Bartz, M., Walk, J., Binnie, S.A., Brill, D., Stauch, G., Lehmkuhl, F., Hoffmeister, D., Brückner, H., in press. Late Pleistocene alluvial fan evolution along the coastal Atacama Desert (N Chile). Global and Planetary Change, 103091. https://doi.org/10.1016/j.gloplacha.2019.103091Walk, J., Stauch, G., Reyers, M., Vásquez, P., Sepúlveda, F.A., Bartz, M., Hoffmeister, D., Brückner, H., Lehmkuhl, F., 2020. Gradients in climate, geology, and topography affecting coastal alluvial fan morphodynamics in hyperarid regions – The Atacama perspective. Global and Planetary Change 185, 102994. https://doi.org/10.1016/j.gloplacha.2019.102994

The hyperarid parts of the Atacama Desert, N Chile, are among the driest places on Earth, and a number of studies have emphasized the remarkable slowness of Earth surface processes since the late Tertiary. Despite episodic overland flow or flash flood activity, salt-driven shrink-swell processes, dust deposition, and seismic shaking have significantly contributed to the formation of the characteristic landscape. The enigmatic and Atacama-specific zebra stripes are contour-parallel, thin lateral bands of rather angular gravels on hillslopes, characterized by grain sorting, a lateral succession of 1-3 m-wide frontal lobes, and specific wavelengths, occurring generally in areas with lowest rainfall and low to no fog occurrence. While previous investigations suggest that zebra stripes represent fossil evidence of overland flow, a recent study challenged their water-related evolution and emphasized the role of seismicity in their formation, and in shaping the Atacama landscape in general. Similar landforms may also be found on Mars, although related processes may be different to those on Earth.We use UAV-derived orthophotos and digital elevation models, geomorphological surveys and sediment sampling, as well as OSL rock surface dating and cosmogenic nuclide (21Ne, 10Be) analysis of surface clasts to provide new insights into zebra stripe activity and stability in the Atacama Desert. Our investigations show that zebra stripes are found in numerous areas in the hyperarid core of the Atacama, implying a wider distribution of zebra-striped hillslopes than previously suggested. Inter-site comparison illustrates considerable differences between individual zebra stripe sites, and geomorphological characteristics suggest that zebra stripes may be active or inactive forms, depending on their location. Active forms are indicated by well-developed frontal lobes, reduced dust contents, and clearly developed downslope sorting trends with a high percentage of freely floating clasts, whereas inactivity seems to be indicated by poorly visible frontal lobes, high dust contents, poor sorting trends and a high proportion of clasts embedded into the underlying vesicular soil horizon. At the same time, preliminary chronological data based on OSL rock surface dating suggests that active stripes contain clasts with active bleaching fronts at top and bottom sides, pointing to late Pleistocene to Holocene activity and clast overturning. Inactivity, in contrast, is indicated by similar IR50 and pIR225 bleaching curves (equilibrium of bleaching and dosing) in upper clast surfaces and the lack of a bleaching front at the bottom side, pointing to long exposures without clast overturning. Combined with cosmogenic nuclide concentrations, our results allow for inter-site comparisons and a better understanding of (relative) stripe chronologies and activity-stability patterns. Alongside further investigations on the significance of fog, wind, rain and seismicity, future work will aim at constraining time scales on which active/young and inactive/old forms have developed. If these forms are seismicity-related, our study contributes important information on the paleoseismic evolution of the central Atacama.

The formally named SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt flow that is preserved in the desert climate of northern Arizona, USA. The flow is independently dated with an 40Ar/39Ar age of 72 ± 4 ka (2σ) and has undergone negligible erosion and/or burial, making its surface an ideal site for direct calibration of cosmogenic nuclide production rates. Production rates for cosmogenic 26Al have been determined from SP flow quartz in this study and are combined with production rates for 10Be, 14C, and 21Ne (Fenton et al., 2019) to yield a suite of production rate ratios. The error-weighted mean, sea-level, high latitude (SLHL) total reference production rate of 26Al is 25.8 ± 2.5 at/g/yr (2 σ x ‾ ; standard error) using time-independent Lal (1991)/Stone (2000) (St) scaling factors. The St scaled spallogenic 26Al rate is 25.0 ± 2.4 at/g/yr integrated over the past 72 ka. This rate overlaps within 2σ uncertainty with other St-scaled production rates in the literature. SLHL spallogenic 26Al production rates in SPICE quartz (SP Flow Production-Rate Inter-Calibration Site for Cosmogenic-Nuclide Evaluations) are nominally lower if time- dependent Sf, Sa, and Lm scaling factors are used, yielding values of 22.9 ± 2.2 at/g/yr, 22.6 ± 2.2 at/g/yr, and 24.1 ± 2.2 at/g/yr (2 σ x ‾ ), respectively. All 26Al production rates in SP flow quartz overlap within 2σ uncertainty, regardless of time independent or time dependent scaling. Production rate ratios for cosmogenic 26Al/10Be, 26Al/14C, and 26Al/21Ne are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2 σ x ‾ ; standard error) of 6.7 ± 0.6, 2.23 ± 0.20, and 1.51 ± 0.13, respectively. This study suggests that, similar to cosmogenic 21Ne and 10Be production rates in SP flow quartz, production rates of cosmogenic 26Al in quartz do not significantly increase when integrated over 72 ka, a time span which includes the period of decreased magnetic strength from 20 to 50 ka.

A new accelerator mass spectrometer was successfully designed for the Cologne FN accelerator to enlarge the measurement capability of CologneAMS to medium mass radionuclides. With this AMS-system (53Mn/55Mn) isotopic ratios are measurable at a 10 MV tandem accelerator in the range of 10 - 9 to 10 - 10 for the first time, with a detection limit of C L = 5.0 × 10 - 12 . A high 53Cr suppression in the (53Mn/55Mn) isotopic ratio measurement was achieved by using the optimal silicon nitride degrader foil thickness in combination with an electrostatic analyzer (ESA). The new system opens the field of research for CologneAMS users to the medium mass region of cosmogenic nuclides, like 53Mn for geological applications of long term erosion, exposure and burial dating and 60Fe for nuclear astrophysical models. The presented definition of an error normalized sensitivity S x allows an inter laboratory comparison of isotopic ratio measurements.

The timing, structure, and landscape change during the Patagonian Ice Sheet deglaciation remains unresolved. In this article, we provide a geomorphic, stratigraphic, and geochronological deglacial record of Río Cisnes Glacier at 44°S and also from the nearby Río Ñirehuao and Río El Toqui valleys (45°S) in Chilean Patagonia. Our 14C, 10Be, and optically stimulated luminescence data indicate that after the last glacial maximum, Río Cisnes Glacier experienced ~100 km deglaciation between >19.0 and 12.3 ka, accompanied by the formation of large glacial paleolakes. Deglaciation was interrupted by several ice readvances, and by 16.9±0.3 ka, Río Cisnes Glacier extended only ~40% of its full glacial extent. The deglaciation of Río Cisnes Glacier and other sensitive Patagonian glaciers occurred at least 1 ka earlier than the ca. 17.8 ka normally assumed for the local termination, coincident with West Antarctic isotope records. This early deglaciation can be linked to an orbital forcing–driven decline of Southern Ocean sea ice associated with a distinct atmospheric warming that is apparent for West Antarctica through Patagonia.

Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic 10Be and 21Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2–3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered.

Cosmogenic nuclide exposure dating of ancient shoreline terraces of the Quillagua-Llamara Soledad Lake in the central Atacama Desert of northern Chile provides new insights in the paleohydrology of the driest desert on Earth. The lake developed in a paleo-endorheic drainage system in the Central Depression prior to draining into the Pacific due to incision of the Rio Loa canyon. The durations of lake stages were sufficiently long to form wave-erosion induced shoreline terraces on the wind-exposed slopes of former islands. Successively younger shoreline levels are preserved over an elevation range of 250 m due to progressive uplift of the islands coeval with the lake stages. Cosmogenic 10Be- and 21Ne-derived exposure ages of the shorelines reveals that the hyperarid conditions in the Rio Loa catchment were interspersed by several pluvial stages during the Pliocene and Pleistocene, which generated a large and persistent lake in the Quillagua-Llamara basin. The exposure ages of the final lake stage provide the maximum age for the incision of the Rio Loa canyon (274 ± 74 ka) and the subsequent breaching of the Coastal Cordillera.

Preserved remnants of fluvial activity in deserts constitute evidence for changing boundary conditions. The Atacama Desert of northern Chile is the global end-member for aridity, so the history of relict stream networks in this region is a record of how landscapes develop under extreme conditions. On Pampa de Tana in northern Chile (19.4°S), a series of channel forms that are presently inactive but in the past flowed westward are incised into the surface of a fault bounded, topographically elevated portion of the El Diablo Formation, a regionally extensive, relict pediment. We measure cosmic-ray produced 10Be, 26Al and 21Ne in fluvial deposits to date the timing of abandonment of three channels and couple this with topographic profile information from a SPOT-6 derived, 2 m resolution digital elevation model. We find two of the channels were abandoned approximately >5.6 Myr and 2.0 Myr ago. One channel is still capable of flow and has ages suggesting it was fluvially active within the last few hundred thousand years. Using the paleochannel ages measured here and published ages for the end of aggradation of the El Diablo Formation we estimate the rates of fluvial channel incision before channel abandonment, and uplift rates on the faults after channel abandonment. Maximum uplift rates of ~12 m/Myr over the last 2 Myr are found. In general, while rates of uplift are relatively low they are several-fold more rapid than the rates of fluvial incision prior to channel abandonment. This implies that westward channel flow was interrupted by uplift of topography above a blind NW-SE striking reverse fault that affects the Central Depression, an alluvial forearc basin. We consider also that shrinkage of the upstream catchment area by stream capture, promoted via headward erosion and lateral expansion of adjacent canyons (quebradas) could be a factor in the abandonment of the channels on Pampa de Tana. Our results highlight the polygenetic nature of this landscape and show that relatively minor amounts of fault displacement in hyperarid regions can have implications for stream network evolution. Even subtle topographic uplift upstream should be taken into account when fluvial deposits are used as proxies for long-term environmental conditions.

Citation: Schildgen, T. F., Robinson, R. A. J., Savi, S., Phillips, W. M., Spencer, J. Q. G., Bookhagen, B., . . . Strecker, M. R. (2016). Landscape response to late Pleistocene climate change in NW Argentina: Sediment flux modulated by basin geometry and connectivity. Journal of Geophysical Research-Earth Surface, 121(2), 392-414. doi:10.1002/2015jf003607

Due to their sensitivity to both tectonic activity and climatic variations, coastal alluvial fans (CAF) along the western flank of the Coastal Cordillera in the Atacama Desert (northern Chile) are important geo-archives for unravelling Quaternary environmental change. Our study focuses on terrestrial and marine deposits of five CAF complexes between 20° and 25°S along the coastal zone of the Atacama to identify phases of alluvial fan activity during the Late Quaternary. Based on a combination of luminescence dating and 10Be cosmogenic nuclide exposure dating as well as existing chronological data in the area, insights into climatic variations along the hyper-arid coast are presented for the Late Pleistocene derived from CAF morphodynamics. Activity of alluvial fans could be documented during time spans 95–80 ka, 60–45 ka, 35–20 ka, as well as the Holocene. Numerical dating of marine terrace deposits gives insights into the tectonic uplift of the Coastal Plain in northern Chile during the Late Quaternary period, for which estimated uplift rates between ~0.06 and ~0.57 m/ka were derived. While tectonic activity induces base-level changes, long-term tectonic activity rather indirectly controls alluvial fan activity. We suggest that alluvial fan activity is mainly controlled by atmospheric changes from the Pacific Ocean. Based on our observations, CAF in the hyper-arid Atacama Desert serve as suitable geo-archives for reconstructing climate changes during the Quaternary. In particular, the usefulness of alluvial fan systems in a water-limited environment is important for understanding the palaeoenvironmental evolution in a coastal desert.

The SP lava flow is a quartz-, olivine- and pyroxene-bearing basalt with an 40Ar/39Ar age of 72 ± 4 ka (2σ). The flow is preserved in the desert climate of northern Arizona, USA. Its unweathered appearance and the lack of soil development indicate it has undergone negligible erosion and/or burial, making it an ideal site for direct calibration of cosmogenic nuclide production rates. Cross-calibrated production rates and production rate ratios for cosmogenic 21Ne, 10Be, and 14C have been determined from SP flow quartz. Production rate ratios for 21Ne/10Be, 21Ne/14C, and 14C/10Be are based on the total, local production rates of each cosmogenic nuclide, independent of scaling models, and have error-weighted means (±2σ uncertainty) of 4.44 ± 0.32, 1.43 ± 0.10, and 2.85 ± 0.21, respectively. Error-weighted mean, sea-level, high latitude (SLHL) total reference production rates of 21Ne, 10Be, and 14C are 17.0 ± 1.1, 3.84 ± 0.27, and 11.2 ± 0.6 at/g/yr (2σ), respectively, using time-independent Lal (1991)/Stone (2000) (St) scaling factors. St scaled spallogenic 10Be and 14C rates are 3.73 ± 0.26 and 9.2 ± 0.6 at/g/yr, respectively. 21Ne and 10Be production rates are integrated over the past 72 ka, whereas 14C production rates are integrated over 25 ka, the time at which SP flow quartz has reached saturation with respect to 14C. These rates overlap within 2σ uncertainty with other St-scaled production rates in the literature, including the total reference SLHL 21Ne production rate of Niedermann (2000), which is revised in this paper to 16.8 ± 3.3 at/g/yr (2σ; St scaling) to reflect a recent change in age control at the Sierra Nevada sites. All SLHL production rates are lower if time- dependent Sf, Sa, and Lm scaling factors are used. For example, error-weighted mean, sea-level, high latitude (SLHL) total reference production rates for 10Be as calculated in the CREp online calculator range from 3.49 ± 0.23 to 3.74 ± 0.25 at/g/yr (2σ), using time-dependent Lm scaling factors. Commonly used SLHL 10Be and 14C production rates in the literature were calibrated on surfaces that have been exposed to cosmic rays for less than 20 ka. Between 20 and 50 ka, the geomagnetic field is proposed to have been weaker than it is today. Production rates of cosmogenic nuclides increase during periods of weaker geomagnetic field strength. However, our study finds no measureable difference between St-scaled production rates of cosmogenic 21Ne and 10Be over the past 20 ka and St-scaled 21Ne and 10Be production rates over the past 72 ka. As such, the study suggests that 21Ne and 10Be production rates in quartz were not significantly greater during the proposed period of decreased magnetic strength from 20 to 50 ka.

There is growing interest in geochronological applications of terrestrial in situ-produced cosmogenic nuclides, with the most commonly measured being 10Be and 26Al in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N 10Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their 26Al targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) 10Be and that it has low concentrations of the major elements that can interfere with Be and Al extraction chemistry and AMS measurements. We derive preliminary concentrations for 10Be and 26Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit.

The timing, structure and termination of the last southern mountain glaciation and its forcing remains unclear. Most studies have focused on the global Last Glacial Maximum (LGM; 26.5–19 ka) time period, which is just part of the extensive time-frame within the last glacial period, including Marine Isotope Stages 3 and 4. Understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change. Here, we present an extensive (n = 65) cosmogenic 10Be glacier chronology derived from moraine belts marking the pre-global LGM extent of the former Patagonian Ice Sheet in southernmost South America. Our results show the mountain ice sheet reached its maximum extent at 48.0 ± 1.8 ka during the local LGM, but attained just half this extent at 21.5 ± 1.8 ka during the global LGM. This finding, supported by nearby glacier chronologies, indicates that at orbital time scales, the southern mid-latitude glaciers fluctuated out-of-phase with northern hemisphere ice sheets. At millennial time-scales, our data suggest that Patagonian and New Zealand glaciers advanced in unison with cold Antarctic stadials and reductions in Southern Ocean sea surface temperatures. This implies a southern middle latitudes-wide millennial rhythm of climate change throughout the last glacial period linked to the north Atlantic by the bipolar seesaw. We suggest that winter insolation, acting alongside other drivers such as the strength and/or position of the southern westerlies, controlled the extents of major southern mountain glaciers such as those in southernmost South America.

With the aim of simplifying AMS target preparation procedures for TCN measurements we tested a new extraction chromatography approach which couples an anion exchange resin (WBEC) to a chelating resin (Beryllium resin) to separate Be and Al from dissolved quartz samples. Results show that WBEC–Beryllium resin stacks can be used to provide high purity Be and Al separations using a combination of hydrochloric/oxalic and nitric acid elutions. 10Be and 26Al concentrations from quartz samples prepared using more standard procedures are compared with results from replicate samples prepared using the coupled WBEC–Beryllium resin approach and show good agreement. The new column procedure is performed in a single step, reducing sample preparation times relative to more traditional methods of TCN target production.

Terrestrial cosmogenic nuclide exposure ages for the Wohlthat Massif (Antarctica), have previously been determined. This was done with 10Be and 26Al measurements by accelerator mass spectrometry (AMS) at the AMS facility at the ETH Zurich. In order to determine the extent to which the results from the Wohlthat Massif are of regional significance, additional samples were collected during the 2007 BGR-expedition “Queenmet”. Two of the Steingarden Nunataks (isolated mountain peaks) were chosen as sampling locations, approximately 100 km south-east of the Wohlthat Massif/Queen Maud Land, at the edge of the Polar Plateau. Quartz rich samples were collected at different elevations on the nunataks to reconstruct an elevation-dependent exposure history. The in situ produced cosmogenic nuclides 10Be and 26Al in these samples were measured by AMS. During sample processing the quartz separates were prepared by two different methods (Kohl and Nishiizumi, 1992, Altmaier, 2000) and measurements were performed at two different facilities (CologneAMS und Zurich AMS) to confirm the reproducibility of the results. The new results of rock surface exposure ages reveal that the exposure of the lower nunatak to cosmic radiation started between 0.65 and 1.1 Ma ago, while the more elevated regions of the second nunatak were apparently above the ice 3–4 Ma ago.

Short-term geomorphic processes (fluvial, glacial, and hillslope erosion) and long-term exhumation control transient alpine landscapes. Long-term measurements of exhumation are not sufficient to capture the processes driving transient responses associated with short-term climatic oscillations, because of high variability of individual processes across space and time. This study compares the efficacy of different erosional agents to assess the importance of variability in tectonically active landscapes responding to fluctuations in Quaternary climate. We focus on the Teton Range, where erosional mechanisms include hillslope, glacial, and fluvial processes. Erosion rates were quantified using sediment accumulation and cosmogenic dating (bedrock and stream sediments). Results show that rates of erosion are highly variable, with average short-term rockfall rates (0.8 mm/y) occurring faster than either apparent basin-averaged (0.2 mm/y) and long-term ridge erosion rates (0.02 mm/y). Examining erosion rates separately also demonstrates the coupling between glacial, fluvial, and hillslope processes. Apparent basin-averaged erosion rates amalgamate valley wall and ridge erosion with stream and glacial rates. Climate oscillations drive the short-term response of a single erosional process (e.g., rockfalls or other mass wasting) that may enhance or limit the erosional efficiency of other processes (glacial or fluvial). While the Teton landscape may approach long-term equilibrium, stochastic processes and rapid response to short-term climate change actively perpetuate the transient ruggedness of the topography.

Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (104 yr; 102 km) but over shorter timescales most of the deformation may be accommodated by

Accelerator mass spectrometry (AMS) has a great potential for various geological applications. The precision and sensitivity is directly linked to technical developments. Therefore CologneAMS, the center for accelerator mass spectrometry of the University of Cologne ( Dewald et al., 2013a , Dewald et al., 2013b ), does extensive work on method developments for isotopic ratio measurement, for new applications and to improve the precision. We present two important technical developments: (1) dating of sediments with 53Mn and (2) ultra-small 14CO2 samples. (1) The age determination of discontinuously deposited sediments by measurement of cosmogenic 53Mn and 3He concentration in iron‑titaniumoxides (hematite, magnetite, titanomagnetite, ilmenite), where the measurement of the medium mass isotope 53Mn is difficult because of the interfering isobar 53Cr. It can be measured at only 2 laboratories worldwide. The new AMS system at the Cologne 10 MV FN tandem accelerator is therefore designed especially for the measurement of medium mass isotopes, e.g. 53Mn. It provides the opportunity to use several detector systems in different combinations: degrader foils with an electrostatic analyzer, a 4 m time-of-flight system, a new 135∘ gas-filled magnet, different gas ionization detectors and a projectile x-ray detector. With the implementation of the new 135∘ gas-filled magnet to the 10 MV FN-Tandem accelerator AMS beamline the first tests have shown an increase in transmission and reduction of blank value in comparrison to the measurement with the degrader foil technique (Schiffer et al. 2018). The background level was reduced by a factor of 3.3 and the error normalized sensitivity (Schiffer et al. 2018) was increased by a factor of 1.6. (2) For the measurement of extremely low carbon from cosmogenic in-situ produced 14C or from 14C content of bulk sediments, with 0.01% carbon, technical developments are required to measure low concentrations in terrestrial rocks of 100,000 atoms g−1 in quartz and to trace organic compounds with 10–50 μg of 14CO2 samples. It turned out, that the measurement of 14CO2 micro-samples with the gas-ion source of the Cologne 6 MV AMS system in combination with a gas-handling system is an alternative to the development of a micro-scale graphitization. Modern 1 μg CO2 samples, (14C/12C) = 1.18×10−12, can be measured with this system with a precision of 2.8%. The overall efficiency is 4%–6% and the reproducibility of standard samples is 0.9% with a blank level of 3–6×10−15.

We present results of thermal neutron flux measurements in experimental granite piles that were tailored to study the effect of hydrogen-rich covers on that flux. We find that hydrogen-rich covers (polyethylene, water), used as proxies for snow, dead and/or live plant matter, increase the thermal neutron flux in an underlying rock surface significantly, as compared to the state without cover. The rock serves as the main source for thermal neutrons, the hydrogen-rich cover as a neutron reflector. In situations where the thickness of such a cover would be negligible in terms of high-energy neutron (>10 MeV) attenuation, e.g. 2–3 cm water equivalent cover, a significant enhancement of the thermal neutron flux (factor >2.5 ± 0.5) can be achieved. This increase is made up of three components ( Masarik et al., 2007 ): (1) reflected thermal neutrons (albedo neutrons), (2) moderated fast neutrons from the ground, and (3) moderated fast neutrons from the atmospheric cascade ( Masarik et al., 2007 ). The higher thermal neutron flux increases the production rates of those cosmogenic nuclides that have a significant thermal neutron production pathway ( 3 He, 36 Cl, 41 Ca). Ignoring this effect in situations where target nuclei ( 6 Li, 35 Cl, 40 Ca) are abundant will severely underestimate production rates. The effect of hydrogen-rich ground cover on the thermal neutron flux has the potential to be used for studies that are aimed at reconstructing the persistence of past plant/snow cover. Isotopic ratios of spallogenic versus predominantly thermal neutron produced nuclides, would reveal the presence or absence of hydrogen-rich cover in the past as compared to the present-day situation.

Cosmogenic 36Cl analysis by accelerator mass spectrometry (AMS) is a valuable environmental and geological sciences research tool. Overcoming the stable nuclide 36S isobar interfering with measurement is challenging, however. Traditionally this has required large accelerators, but following recent technical advances it is now possible with ∼ 30 MeV ion energies. Consequently 5 MV or even smaller modern bespoke spectrometers are now 36Cl-capable, increasing accessibility and promoting wider and more varied 36Cl use. However, the technical ability to identify 36Cl ions is quite distinct from demonstrated high-performance AMS. Such is the theme of this paper. We present a systematic analysis of the accurate measurement of sample radioisotope relative to the stable chlorine, the normalisation of the measured ratio and correction for remaining 36S interference, all combined with the use of stable-isotope dilution to determine sample Cl concentration to begin with. We conclude by showing that repeated analyses support our claims for routine 3% 36Cl-AMS data. Accordingly, the modest SUERC spectrometer well competes with the performance of larger longer-established instruments, and the results may be quite generic for modern bespoke instruments.

Cosmogenic nuclide surface exposure ages are determined from in situ 10 Be and 36 Cl analysis of 38 rock surfaces found in different glacial landforms in Denmark. Dating of erratic boulders and adjacent ice-sculpted bedrock on the island of Bornholm in the western Baltic Sea reveals almost identical values. This suggests that little if any inherited nuclides are present in the sampled boulders. West of the Last Glacial Maximum (LGM) ice margin in Denmark ages reflect exposure from the Middle Weichselian. East of the LGM margin exposure ages from 35 samples show Late Weichselian ages in a range between 20.6–11.9 ka. To test to what extent these dates reflect the onset of deglaciation immediately after cessation of active glacier flow, surface exposure ages are evaluated against independent chronologies of Late Weichselian ice-sheet fluctuations in southwestern Scandinavia. The Bornholm dates agree with the independent age model, however, in the data set for eastern Denmark only less than half the surface exposure ages lie within the expected age envelope. This apparent mismatch is most likely due to post-glaciation shielding and delayed surface stabilisation compared to the timing of ice-margin retreat. Thus ages from boulders resting in dead-ice moraines and mass wasting landscapes underestimate deglaciation by 3–6 thousand years. The results quantify the impact of exhumation and landform stabilisation on cosmogenic surface exposure ages on millennial scales. We conclude, that interpretation of cosmogenic exposure ages should include careful evaluation of possible post-depositional landform transformation in attempts to fine tune ages of e.g. end moraine features. With reference to independent age models we critically evaluate glacier advance – retreat scenarios from regions around the southern Baltic that alone are based on weighted average ages of cosmogenic exposure dating.

The northeast Antarctic Peninsula (NEAP) region is currently showing signs of significant environmental change, evidenced by acceleration of glacial retreat and collapse of both Larsen-A and -B ice shelves within the past 15 years. However, data on the past extent of the eastern margin of the Antarctic Peninsula Ice Sheet (APIS) and its Holocene retreat history are sparse, and hence we cannot yet put the recent changes into a long-term context. In order to investigate the timing of deglaciation, we present 16 new cosmogenic 10Be surface exposure ages from sites on northern James Ross Island (Cape Lachman, Johnson Mesa and Terrapin Hill) and Seymour Island. The majority of the ages cluster around 6e10 ka, with three significantly older (25e31 ka). We combine these ages with existing terrestrial and marine radiocarbon deglaciation ages, and a compilation of existing swath bathymetry data, to quantify the temporal and spatial character of the regional glacial history. Ice had begun to retreat from the outer shelf by 18.3 ka, reaching Seymour Island by w8 ka. Northern James Ross Island began to deglaciate around the time of the Early Holocene Climatic Optimum (c. 11e9.5 ka). Deglaciation continued, and a transition from grounded to floating ice in Prince Gustav Channel occurred around 8 ka, separating the James Ross Island ice cap from the APIS. This occurred shortly before Prince Gustav Channel ice shelf began to disintegrate at 6.2 ka. Our results suggest there may be a bathymetric control on the spatial pattern of deglaciation in the NEAP.

The relative importance of climatic and tectonic factors in driving rates of denudation in mountain ranges has long been debated, with both precipitation and rates of crustal uplift cited as first order controls in a variety of different mountainous settings. Few studies, however, have explicitly considered the influence of climatic and tectonic processes on denudation rates during the early stages of orogenesis. Using basin-wide denudation rates derived from in-situ cosmogenic 10Be, and published modern precipitation rate data, the significance of rainfall and snowfall on rates of denudation is evaluated for the San Bernardino Mountains, California. Denudation rates vary between 52 mm ka− 1 in the arid northern regions of the mountains and 2700 mm ka− 1 in the more humid southern sector. We select three basins where the influence of precipitation on denudation rates can be isolated from the effects of crustal uplift and find that there is no apparent relationship between denudation rates and precipitation. Denudation rates differ more than five-fold on the opposing slopes of Mill Creek, a valley bisected by a major splay of the San Andreas Fault, and we propose that this denudation rate disparity can be best explained by variations in uplift rates across the fault. The results suggest that crustal uplift is the mechanism that underpins the ∼ 50-fold variability in denudation rates we have measured in the San Bernardino Mountains, but that this must be facilitated by sufficient precipitation to remove valley-fill deposits.

Basin-averaged cosmogenic 10 Be concentrations, apatite (U–Th)/He thermochronometry and incision into a dated palaeosurface constrain spatial and temporal variations in the rates of denudation experienced during the early-stages of orogenesis in the San Bernardino Mountains, California. Cosmogenic 10 Be analysis measures denudation over intermediate (∼ 10 2 –10 4 years) time scales and records rates which decrease from a maximum of 2700 ± 500 mm ka − 1 in the south to a minimum of 52 ± 5 mm ka − 1 in northern catchments. Corresponding rates from (U–Th)/He and incision into a dated palaeosurface measure long-term (∼ 10 6 years) denudation rates which decrease from between 1200 ± 400 mm ka − 1 in the south to a minimum of 30 ± 20 mm ka − 1 in the north. The temporal consistency observed in the broad-scale patterns of denudation rates probably results from the persistent imprint of the initial crustal architecture and drainage network. These have maintained an influence on slope distributions, and are thus fundamental factors controlling the gross patterns of denudation throughout the early stages of orogenesis. Where variations between the denudation rates measured over different time scales are apparent the intermediate-term rates are found to be consistently greater than the long-term, with the increase being more pronounced around the fault bounded peripheries of crustal blocks relative to quiescent block interiors. This provides empirical support for a model of mountain building whereby topographic development is dictated by the headward retreat of drainage systems that propagate away from zones of displacement. Our findings indicate that recent localised increases in denudation rates in young fault block orogens may be explained by a progressive denudational response to prior tectonic uplift, rather than a consequence of climatic change.

The Institute (formerly Department) of Geography of the University of Edinburgh has been active in the rejuvenation of the sub-discipline of geomorphology over the past two decades with its emphasis on addressing macroscale questions of long-term landscape development. In addition to interdisciplinary collaborations in the fields of low-temperature thermochronology and numerical landscape modelling, researchers there have played a key role both nationally and, more recently, internationally in applying cosmogenic isotope analysis to landform dating and the estimation of denudation rates. Some examples of research are discussed from the passive margin setting of southern Africa, the active tectonic setting of southern California, and the arid environments of Chile and Namibia.

The extent of the last British–Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23–19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright © 2008 John Wiley & Sons, Ltd.

Synopsis Geomorphological mapping provides evidence for two former low-level corrie glaciers on Hoy, both defined by end moraines. Five 10 Be exposure ages obtained from sandstone boulders on moraine crests fall within the range 12.4 ± 1.5 ka to 10.4 ± 1.7 ka (weighted mean 11.7 ± 0.6 ka), confirming that these glaciers developed during the Loch Lomond (Younger Dryas) Stade (LLS) of 12.9–11.5 cal. ka bp, and demonstrate the feasibility of using this approach to establish the age of LLS glacier limits. The equilibrium line altitude (ELA) of one of the glaciers (99 m) is the lowest recorded for any LLS glacier, and the area-weighted mean ELA for both (141 m) is consistent with a general northward ELA decrease along the west coast of Britain. The size of moraines fronting these small (≤0.75 km 2 ) glaciers implies that glacier termini remained at or close to their limits for a prolonged period. The apparent restriction of LLS glaciers to only two sites on Hoy probably reflects topographic favourability, and particularly the extent of snow-contributing areas.