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Glacial and fluvial landforms record the recent history of Earth’s surface, and hold information on the climatic or tectonic processes that shape the landscape. Southern Patagonia hosts uniquely well-preserved fluvial cut-and-fill terraces. A record of fluvial incision since 1.5–4 Ma is preserved from K-Ar dated basalt flows atop relict paleosurfaces, and published regional thermochronometric dating and modelling suggest an increased phase of exhumation in the last 1–3 Ma. However, few constraints exist on the onset of river incision, which might provide clues as to possible drivers of regional landscape change. To constrain the timing of Pleistocene incision and landscape evolution in southern Patagonia, we present new cosmogenic 10Be exposure ages of surface cobbles and amalgamated pebbles from fluvial terraces in the Tres Lagos region 50ºS) and the Río Santa Cruz. Locally, dated basalt flows set a maximum age of ~2.2 Ma for the Tres Lagos terraces, and between 2.2 and 1.7 Ma in the Condor Cliffs region of the Río Santa Cruz. Preliminary 10Be ages for terrace surfaces in the Tres Lagos region reveal ages between 45–845 ka. Ages of upstream fluvial terraces of the Río Santa Cruz reveal ages between 290–830 ka. The sequence of terrace ages shows that the phase of net incision started ca. 1 Ma after widespread emplacement of basalts, concomitant with enhanced climatic forcing following the Mid-Pleistocene Transition. Ages are also in agreement with the incision history recorded in dated fluvial terraces of other Patagonian rivers, notably the Río Deseado, where ages range from 400 ka–1 Ma (47ºS; Tobal et al., 2021). We argue that the combined results suggest that this net-incisional phase was widespread, therefore unlikely to result from local tectonic drivers, hence probably climatically driven. Our record of Pleistocene landscape evolution is similar to other records throughout the Andes, where the timing of fluvial incision has been linked with the transition to enhanced climatic forcing after ~1 Ma (e.g., Central Andes). Our results point a strong influence of the Mid-Pleistocene Transition on landscape evolution on a continental scale, and notably also in the southernmost regions of South America.

Alluvial surfaces like fluvial terraces can act as markers for past changes in sediment and water flux along alluvial rivers. By precisely dating terrace surfaces, we can begin to quantify how sedimentary signals propagate though river channels and better infer the paleo-climatic and tectonic conditions during their formation. However, collecting and processing geochronological samples along larger river systems can be costly and time consuming. Here, we extend alluvial landform age control along the Río Santa Cruz of southern Patagonia by applying a spectral surface characteristic model calibrated from a limited set of field samples and cosmogenic nuclide derived exposure ages. This quantitative method leverages the spectral response of surface weathering to ultimately improve age control of the region's fluvial landforms while reducing the time and cost associated with traditional field dating methods.Ages of alluvial surfaces may correlate with time-dependent geochemical weathering processes, such as clay mineral formation. Although previous surface-weathering studies have mostly focused on surface ages since the last or penultimate glaciation, we analyzed the change in weathering state for southern Patagonian fluvial terraces up to a million years old consisting of quarzitic and granitic source lithologies. We find that multispectral Landsat 8 data show a 20% increase in the band 6 to band 2 ratio with terrace elevation (and inferred age), highlighting the higher reflectance in the shortwave infrared band often associated with clay mineral formation. It is likely that weathering rates in the dry and cold Patagonian environment are slower compared to regions with less stable and warmer climate conditions or lithological sources, where age dependent weathering signals in multispectral data tend to saturate on much shorter time scales. Our new 10Be results from surface cobbles and amalgamated pebbles yield exposure ages roughly between 45 and 1000 ka for these surfaces, and the calibrated spectral model allows us to interpolate ages of additional 9 alluvial surface generations based on 11 dated surfaces in the region.Planned in-situ spectral surface measurements will provide robust ground-truthing to the satellite-based observations and allow for further investigation of the mineral changes driving the age-dependent spectral signal. Furthermore, additional terraces will be dated downstream to provide (1) a better understanding of how the weathering process may differ with downstream distance, and (2) a more reliable correlation of surfaces over long distances (> 100 km), enabling us to reconstruct the details of past climate forcing on alluvial-channel evolution.

Understanding the landscape evolution and potential geohazards of mountain landscapes requires quantifying the rates at which they uplift and erode, and the relative importance of different erosional processes. However, each of the available techniques to quantify rates of landscape change provides only a partial account of mountain erosion, given their inherent methodological biases and measuring timescales. Therefore, reconciling erosion and uplift rates estimated with different methods can be challenging, but can also provide insights into changes in erosion rates and dominant erosional processes.Here, we present a combination of new and compiled data from the western Southern Alps of New Zealand (WSA), one of the fastest-eroding ranges on Earth, which is believed to be in steady state. We present new data on: (a) 20 in-situ 10Be catchment-averaged denudation rates, which mostly range between ~0.6-9 mm/yr and represent erosion integrated over the last 275 years on average; (b) 17 10Be concentrations from recent landslide deposits, which together with drone photogrammetry of landslide scars, provide information about landslide recurrence intervals on millennial timescales; (c) the grain size distributions of sediment supplied from hillslopes and transported by rivers, which allows us to convert published suspended sediment load estimates (0.2-6.7 mm/yr, recorded over the 1960s-1990s) into total sediment flux estimates. Based on (b) and published landslide frequency-area data, we estimate landslide erosion rates on millennial timescales, and compare these to erosion rate estimates from (a), (c); and (d) modern published landslide erosion rates (1.8-18 mm/yr, 1948-1986), (e) published millennial soil erosion rates (up to 2.5 mm/yr), (f) compiled Late Quaternary fault throw rates (up to 12 mm/yr), and (g) recalculated thermochronological exhumation rates (up to ~6-9 mm/yr, Myr timescales).This comprehensive data set allows us to examine: (i) the proportion of total erosion driven by landslides versus other erosional processes; (ii) how modern denudation rates and landslide erosion rates compare to long-term erosion rate, rock uplift, and exhumation rate estimates; and (iii) the potential fluctuations of erosion rates and processes over seismic cycles and Holocene climate change.

The Vogelsberg area in Hessen, Germany, comprises the largest contiguous volcanic complex in Central Europe, covering an area of about 2300 km². After volcanic activity ceased during the mid-Miocene, the complex was subject to extensive erosion and weathering. Fluvial erosion has shaped the area, which is now characterised by Pleistocene valleys and a radial river system exposing primitive alkali basalts and basanites. However, the inference of catchment-wide weathering and erosion rates from the most commonly used cosmogenic nuclide – mineral pair (e.g. 10Be from quartz) remains challenging in such an environment due to the mafic nature and nominally quartz-free composition of the local bedrock. Due to these method-related obstacles only few cosmogenic studies have focused on basaltic regions until now, even though basalt weathering is globally an important CO2 sink.The development and establishment of the novel method using terrestrial cosmogenic krypton (Kr) in the weathering-resistant mineral zircon (Dunai et al. 2022) allows quantification of denudation on quartz-poor lithologies over hundreds of kyr timescales. We exploit the method’s advantage and sampled zircons from sediments of streams radially draining the Vogelsberg and measured Kr isotope abundances to assess the time-integrated erosion patterns shaping the volcanic complex. Integrating over millennial timescales, the 10Be(meteoric)/9Be system will be applied to the same catchments. The 10Be/9Be system can be measured on sediment of any type of lithology including mafic rock (Dannhaus et al. 2018), and thus presents an inter-method validation of the Kr method. We will present the krypton results and discuss basalt weathering in a currently temperate climate through the lens of the different methodological approaches applied. Dunai et al. (2022) Geochronology, https://doi.org/10.5194/gchron-4-65-2022Dannhaus et al. (2018) GCA, https://doi.org/10.1016/j.gca.2017.11.005

The hydrogen isotope composition of leaf wax biomarkers (δ2Hwax) is a valuable tool for reconstructing continental paleohydrology, as it serves as a proxy for the hydrogen isotope composition of precipitation (δ2Hpre). To yield robust palaeohydrological reconstructions using δ2Hwax in marine archives, it is necessary to examine the impacts of regional climate on δ2Hwax and assess the similarity between marine sedimentary δ2Hwax and the source of continental δ2Hwax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific, soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2Hwax values. We find that apparent fractionation between leaf waxes and source water is relatively constant in humid/semiarid regions (average: −121 ‰). However, it becomes less negative in hyperarid regions (average: −86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2H enrichment. We also observed that along strong aridity gradients, the 2H enrichment of δ2Hwax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicated that δ2Hwax values in marine surface sediments largely reflect δ2Hwax values from the continent, confirming the robustness of marine δ2Hwax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2Hwax values and pave the way for more quantitative paleohydrological reconstructions using δ2Hwax.

The denudation of rocks in mountain belts exposes a range of fresh minerals to the surface of the Earth that are chemically weathered by acidic and oxygenated fluids. The impact of the resulting coupling between denudation and weathering rates fundamentally depends on the types of minerals that are weathering. Whereas silicate weathering sequesters CO2, the combination of sulfide oxidation and carbonate dissolution emits CO2 to the atmosphere. Here, we combine the concentrations of dissolved major elements in stream waters with 10Be basin-wide denudation rates from 35 small catchments in eastern Tibet to elucidate the importance of lithology in modulating the relationships between denudation rate, chemical weathering pathways, and CO2 consumption or release. Our catchments span 3 orders of magnitude in denudation rate in low-grade flysch, high-grade metapelites, and granitoid rocks. For each stream, we estimate the concentrations of solutes sourced from silicate weathering, carbonate dissolution, and sulfide oxidation using a mixing model. We find that for all lithologies, cation concentrations from silicate weathering are largely independent of denudation rate, but solute concentrations from carbonates and, where present, sulfides increase with increasing denudation rate. With increasing denudation rates, weathering may therefore shift from consuming to releasing CO2 in both (meta)sedimentary and granitoid lithologies. For a given denudation rate, we report dissolved solid concentrations and inferred weathering fluxes in catchments underlain by (meta)sedimentary rock that are 2–10 times higher compared to catchments containing granitoid lithologies, even though climatic and topographic parameters do not vary systematically between these catchments. Thus, varying proportions of exposed (meta)sedimentary and igneous rocks during orogenesis could lead to changes in the sequestration and release of CO2 that are independent of denudation rate.

While landscapes are broadly sculpted by tectonics and climate, on a catchment scale, sediment size can regulate hillslope denudation rates and thereby influence the location of topographic highs and valleys. In this work, we used in situ 10Be cosmogenic radionuclide analysis to measure the denudation rates of bedrock, boulders, and soil in three granitic landscapes with different climates in Chile. We hypothesize that bedrock and boulders affect differential denudation by denuding more slowly than the surrounding soil; the null hypothesis is that no difference exists between soil and boulder or bedrock denudation rates. To evaluate denudation rates, we present a simple model that assesses differential denudation of boulders and the surrounding soil by evaluating boulder protrusion height against a two-stage erosion model and measured 10Be concentrations of boulder tops. We found that hillslope bedrock and boulders consistently denude more slowly than soil in two out of three of our field sites, which have a humid and a semi-arid climate: denudation rates range from ∼5 to 15 m Myr−1 for bedrock and boulders and from ∼8 to 20 m Myr−1 for soil. Furthermore, across a bedrock ridge at the humid site, denudation rates increase with increasing fracture density. At our lower-sloping field sites, boulders and bedrock appear to be similarly immobile based on similar 10Be concentrations. However, in the site with a Mediterranean climate, steeper slopes allow for higher denudation rates for both soil and boulders (∼40–140 m Myr−1), while the bedrock denudation rate remains low (∼22 m Myr−1). Our findings suggest that unfractured bedrock patches and large hillslope boulders affect landscape morphology by inducing differential denudation in lower-sloping landscapes. When occurring long enough, such differential denudation should lead to topographic highs and lows controlled by bedrock exposure and hillslope sediment size, which are both a function of fracture density. We further examined our field sites for fracture control on landscape morphology by comparing fracture, fault, and stream orientations, with the hypothesis that bedrock fracturing leaves bedrock more susceptible to denudation. Similar orientations of fractures, faults, and streams further support the idea that tectonically induced bedrock fracturing guides fluvial incision and accelerates denudation by reducing hillslope sediment size.

The interplay of tectonics, climate, and erosion controls mountain topography, modulates Earth’s climate, and regulates the fluxes of sediments and solutes across Earth’s surface. Understanding and quantifying the complex processes behind this interplay remains one of the key challenges in the Earth Sciences. At the scale of mountain ranges, glacial erosion, river incision, and landsliding are the only processes that have been observed to be capable of balancing rapid rock-uplift rates. These processes are thought to link tectonics and climate through the influence of mountain elevations on orographic precipitation or glaciation.The western Southern Alps of New Zealand (WSA) are one of the fastest-eroding ranges on Earth, where erosion has long been thought to be dominated by landsliding and glacial scouring. However, previous erosion studies in the WSA have been restricted to very few catchments, to decadal timescales, or to below the tree line, which has prevented evaluating the variables and processes controlling erosion at the orogen-scale over longer timescales. Here, 20 new in-situ 10Be catchment-averaged denudation rates, which mostly range between ~0.6-9 mm/yr, allow us to examine the controls and spatial distribution of denudation. We find that the proportion of catchment area within the 1500-2000 m elevation window explains >70% of the variability in denudation rates, more than any other variable. In the WSA, this elevation range is where temperatures most commonly fluctuate between -3ºC to -8ºC in the presence of water (the frost-cracking window), and includes the zone of recent glacial retreat and permafrost degradation. Our data hence suggests that temperature-controlled peri- and paraglacial erosional processes can balance some of the fastest rock-uplift rates on Earth, of several mm/yr. Therefore, these processes, which are also elevation-dependent, can play an important, but previously overlooked role in linking tectonics and climate and limiting mountain elevations.

Knowledge of the flux of material eroded and transported from mountains to oceans is a key factor across the Earth Sciences, for constraining global carbon cycling, interpreting the sediment record properly, and environmental management. The analysis of cosmogenic nuclides in sediment of large rivers has been shown to derive mean denudation rates of the sediment-producing areas, averaging out the local variations commonly found in small rivers. When analyzed in Earth largest rivers, cosmogenic nuclides provide the possibility to constrain global mean denudation rates that integrate over millennial time scales and to compare those longer-term fluxes to those from decadal-scale river monitoring. Using this approach, we measured in situ cosmogenic 26Al and 10Be in sand of >50 large rivers over a range of climatic and tectonic regimes covering 32% of the Earth’s terrestrial surface.In 35% of the analyzed rivers, we find 26Al/10Be ratios to be significantly lower than these nuclides´ surface-production-rate ratio of 6.75 in quartz, indicating radioactive decay over periods exceeding 0.5 Myr. We invoke a combination of slow erosion, shielding in the source area, and sediment storage and burial during long-distance transport to explain these low ratios. In the other 65% of studied rivers we find 26Al/10Be ratios to be within uncertainty of their surface production-rate ratio, indicating cosmogenic steady state. For these rivers, we obtain a global source area denudation rate of 141 t/km2/yr (54 mm/kyr of rock-equivalent) that translates to a flux of 3.07 +/- 0.56 Gt/yr. By assuming that this sub-dataset is representative of the global land surface, we upscale this value to the total surface area for exorheic basins, thereby obtaining a global denudation flux of 15.2 +/- 2.8 Gt/yr that integrates over the past 11 kyr. This value is slightly lower than published values from cosmogenic nuclides from small river basins (23 (+53/-16)) Gt/yr) upscaled using a global slope model, and also lower than modern sediment and dissolved loads exported to the oceans (24.0 Gt/yr). Our new approach confirms an estimate of global dissolved and solid matter transfer that converges to an encouragingly narrow range of within 35% of previous estimates. The use of paired nuclides in large rivers hence provides estimates of the buffering timescales of sediment transport. The Myr-scale duration of this buffering derived for rivers with low Al/Be ratios has important implications for interpreting the sediment record obtained from these mostly dry and slowly eroding river basins. Evidently in these basins, the eroding mountain source is not directly linked to downstream sediment archives, resulting in poor connectivity within the sediment routing system.

It has been proposed that at short timescales of 102–105 yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained. To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya. We compare past and present 10Be-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data. Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene. We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 ± 13°) erode at lower rates of 0.1–0.4 mm/yr compared to steeper (>40°) crestal regions of the Dhauladhar Range that erode at 0.8−1.3 mm/yr. In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed. Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas.