Search

In situ cosmogenic nuclides are an important tool for quantifying landscape evolution and dating fossil-bearing deposits in the Cradle of Humankind (CoH), South Africa. This technique mainly employs cosmogenic 10-Beryllium (Be-10) in river sediments to estimate denudation rates and the ratio of 26-Aluminium (Al-26) to Be-10 (Al-26/Be-10), to constrain ages of sediment burial. Here, we use Be-10 and Al-26 concentrations in bedrock and soil above the Rising Star Cave (the discovery site of Homo naledi) to constrain the denudation rate and the exposure history of soil on the surface. Apparent Be-10-derived denudation rates obtained from pebble- to cobble-sized clasts and coarse-sand in soil (on average 3.59 +/- 0.27 m/Ma and 3.05 +/- 0.25 m/Ma, respectively) are 2-3 times lower than the bedrock denudation rates (on average 9.46 +/- 0.68 m/Ma). In addition, soil samples yield an average Al-26/Be-10 ratio (5.12 +/- 0.27) that is significantly lower than the surface production ratio of 6.75, which suggests complex exposure histories. These results are consistent with prolonged surface residence of up to 1.5 Ma in vertically mixed soils that are up to 3 m thick. We conclude that the Be-10 concentrations accumulated in soils during the long near-surface residence times can potentially cause underestimation of single-nuclide (Be-10) catchment-wide denudation rates in the CoH. Further, burial ages of cave sediment samples that consist of an amalgamation of sand-size quartz grains could be overestimated if a pre-burial Al-26/Be-10 ratio calculated from the surface production is assumed.

Quantifying the time scales of sediment transport and storage through river systems is fundamental for understanding weathering processes, biogeochemical cycling, and improving watershed management, but measuring sediment transit time is challenging. Here we provide the first systematic test of measuring cosmogenic meteoric Beryllium-10 (10Bem) in the sediment load of a large alluvial river to quantify sediment transit times. We take advantage of a natural experiment in the Rio Bermejo, a lowland alluvial river traversing the east Andean foreland basin in northern Argentina. This river has no tributaries along its trunk channel for nearly 1,300 km downstream from the mountain front. We sampled suspended sediment depth profiles along the channel and measured the concentrations of 10Bem in the chemically extracted grain coatings. We calculated depth-integrated 10Bem concentrations using sediment flux data and found that 10Bem concentrations increase 230% from upstream to downstream, indicating a mean total sediment transit time of 8.4 ± 2.2 kyr. Bulk sediment budget-based estimates of channel belt and fan storage times suggest that the 10Bem tracer records mixing of old and young sediment reservoirs. On a reach scale, 10Bem transit times are shorter where the channel is braided and superelevated above the floodplain, and longer where the channel is incised and meandering, suggesting that transit time is controlled by channel morphodynamics. This is the first systematic application of 10Bem as a sediment transit time tracer and highlights the method's potential for inferring sediment routing and storage dynamics in large river systems., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1119

We compile detrital 10Be concentrations of Alpine rivers, representing the denudation rates pattern for 375 catchments across the entire European Alps. Using a homogeneized framework, we employ state-of-the-art techniques for inverting in-situ 10Be concentrations into denudation rates. From our compilation, we find that (i) while lithologic properties and precipitation/runoff do influence erosion mechanisms and rates at the scale of individual catchments and in some specific Alpine regions, such controls do not directly stand for the entire Alps, (ii) as also previously suggested, catchment-wide denudation rates across the entire European Alps closely follow first-order Alpine topographic metrics at the scale of individual catchments or selected Alpine sub-regions. However, in addition to previous local-scale studies conducted in the European Alps, our large-scale compilation highlights a functional relationship between catchment-wide denudation and mean catchment slope angle. Catchment-wide denudation positively correlates with mean catchment slope up to a threshold angle (25–30°). Above this threshold, any correlation between catchment-wide denudation and slope as well as other catchment metrics breaks apart. We can reconcile these systematic patterns by proposing a regional erosion model based on diffusive-transport laws for catchments located below the slope threshold angle. In oversteepened catchments situated above-threshold slopes, erosion is stochastic in nature, as glacial carving likely caused a partial decoupling between hillslope and fluvial domains with complex topographic relationships and sediment connectivity patterns. Finally, we identify a first-order positive relationship between modern geodetic rock uplift and catchment-wide denudation for the European Alps. The observed spatial pattern is highly variable and possibly reflects the surface response to deep geodynamic mechanisms prevailing in the different Alpine regions. We conclude that today's topography and geomorphic features of the entire Alps are the result of a millenial-scale geomorphic response to past glacial processes and active rock uplift, highlighting a link between external and internal drivers for mountain erosion. ISSN:0012-8252 ISSN:1872-6828

Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 103 to 105 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We re-calculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance—an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ∼25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.

As reverse weathering has been shown to impact long‐term changes in atmospheric CO2 levels, it is crucial to develop quantitative tools to reconstruct marine authigenic clay formation. We explored the potential of the beryllium (Be) isotope ratio (10Be/9Be) recorded in marine clay‐sized sediment to track neoformation of authigenic clays. The power of such proxy relies on the orders‐of‐magnitude difference in 10Be/9Be ratios between continental Be and Be dissolved in seawater. On marine sediments collected along a Chilean margin transect we chemically extracted reactive phases and separated the clay‐sized fraction to compare the riverine and marine 10Be/9Be ratio of this fraction. 10Be/9Be ratios increase fourfold from riverine to marine sediment. We attribute this increase to the incorporation of Be high in 10Be/9Be from dissolved biogenic opal, which also serves as a Si‐source for the precipitation of marine authigenic clays. 10Be/9Be ratios thus sensitively track reverse‐weathering reactions forming marine authigenic clays., Plain Language Summary: Clay minerals can form on land by the chemical breakdown of rock‐forming minerals, but clays can also form in the ocean. When clay formation takes place in the ocean, CO2 is released. To date, there is no method that can easily measure the amount of clay minerals formed in the ocean. We used two isotopes of the same element, beryllium (Be), with the atomic mass of 9 and 10 to test whether this isotope system can be used to measure marine clay formation. The abundance of these isotopes differs majorly on land and in the ocean. We measured beryllium isotopes in river sediment and ocean‐bottom sediment offshore the Chile coast and compared the ratios of the isotopes (10Be/9Be). The ratio is four times higher in ocean sediment, when compared to river sediment. We interpret this increase to be due to the formation of clay minerals in the ocean, which include the high 10Be/9Be ratio during their formation. We conclude that the beryllium‐isotope system can be used to measure the formation of even very small amounts (less than 2%) of marine clay minerals. This is important, as the clay‐forming chemical reactions release CO2 which has a long‐term effect on global climate., Key Points: We explored the potential of the beryllium isotope ratio to track neoformation of marine authigenic clays. Beryllium isotope ratios increase fourfold from riverine to marine sediment due to the presence of marine Be incorporated in authigenic clay. Beryllium isotope ratios sensitively track reverse‐weathering reactions forming marine authigenic clays., Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659, IPGP multidisciplinary program PARI and by Paris‐IdF region SESAME Grant 12015903

The lower Amazon basin contains vast floodplains that exchange sediment with the main river. The exchange of sediment between the floodplain and the channel follows a seasonal cycle that is anticorrelated with the hydrological cycle. At low water stages, sediment that has been stored in the floodplain for potentially several thousands of years is eroded and transferred from the floodplain to the mainstem. During high water stages, most sediment transported in the main channel stems directly from the eroding source with little intermittent storage. We apply the meteoric cosmogenic 10Be to stable 9Be ratio (10Be/9Be) as a denudation and weathering proxy to investigate this seasonality in sediment transport. Single meteoric 10Be concentrations ([10Be]) have previously been shown to record floodplain storage; whereas fractions of mobilized 9Be, a trace metal released during weathering, provide degrees of weathering. The resulting 10Be/9Be ratio provides denudation rates of the sediment sources. We compare 10Be/9Be measured on suspended sediment from river depth profiles at two sites (Obidos/Macapa) and during two hydrological seasons (high/low water stage in 2013). We show that careful construction of river depth profiles in combination with Rouse modeling is necessary to exclude the grain size dependence that together with hydrodynamic sorting introduces a bias into single [10Be] and [9Be]. In contrast, the 10Be/9Be is largely uniform across grain sizes and is thus unaffected by sorting. Our 10Be/9Be ratios, the denudation rates derived from them, and mobilized 9Be fractions do not show variations outside their uncertainties across seasons or sites. Thus, 10Be/9Be show that upstream sediment sources were well mixed by multiple cycles of storage and remobilization in the floodplain.

Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from seismic disturbances, depending on how recovery is defined. We examine three principal proxies of river recovery after earthquake-induced sediment pulses around Pokhara, Nepal's second largest city. Freshly exhumed cohorts of floodplain trees in growth position indicate rapid and pulsed sedimentation that formed a fan covering 150 km2 in a Lesser Himalayan basin with tens of metres of debris between the 11th and 15th centuries AD. Radiocarbon dates of buried trees are consistent with those of nearby valley deposits linked to major medieval earthquakes, such that we can estimate average rates of re-incision since. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos, and dated tree trunks to reconstruct geomorphic marker surfaces. The volumes of sediment relative to these surfaces require average net sediment yields of up to 4200 t km–2 yr–1 for the 650 years since the last inferred earthquake-triggered sediment pulse. The lithological composition of channel bedload differs from that of local bedrock, confirming that rivers are still mostly evacuating medieval valley fills, locally incising at rates of up to 0.2 m yr–1. Pronounced knickpoints and epigenetic gorges at tributary junctions further illustrate the protracted fluvial response; only the distal portions of the earthquake-derived sediment wedges have been cut to near their base. Our results challenge the notion that mountain rivers recover speedily from earthquakes within years to decades. The valley fills around Pokhara show that even highly erosive Himalayan rivers may need more than several centuries to adjust to catastrophic perturbations. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in active mountain regions.

The uplift of the Shillong Plateau, in northeast India between the Bengal floodplain and the Himalaya Mountains, has had a significant impact on regional precipitation patterns, strain partitioning, and the path of the Brahmaputra River. Today, the plateau receives the highest measured yearly rainfall in the world and is tectonically active, having hosted one of the strongest intra-plate earthquakes ever recorded. Despite the unique tectonic and climatic setting of this prominent landscape feature, its exhumation and surface uplift history are poorly constrained. We collected 14 detrital river sand and 3 bedrock samples from the southern margin of the Shillong Plateau to measure erosion rates using the terrestrial cosmogenic nuclide 10Be. The calculated bedrock erosion rates range from 2.0 to 5.6 m My−1, whereas catchment average erosion rates from detrital river sands range from 48 to 214 m My−1. These rates are surprisingly low in the context of steep, tectonically active slopes and extreme rainfall. Moreover, the highest among these rates, which occur on the low-relief plateau surface, appear to have been affected by anthropogenic land-use change. To determine the onset of surface uplift, we coupled the catchment averaged erosion rates with topographic analyses of the plateau's southern margin. We interpolated an inclined, pre-incision surface from minimally eroded remnants along the valley interfluves and calculated the eroded volume of the valleys carved beneath the surface. The missing volume was then divided by the volume flux derived from the erosion rates to obtain the onset of uplift. The results of this calculation, ranging from 3.0 to 5.0 Ma for individual valleys, are in agreement with several lines of stratigraphic evidence from the Brahmaputra and Bengal basin that constrain the onset of topographic uplift, specifically the onset of flexural loading and the transgression from deltaic to marine deposition. Ultimately, our data corroborate the hypothesis that surface uplift was decoupled from the onset of rapid exhumation, which occurred several millions of years earlier.

The Labrador Sector of the Laurentide Ice Sheet is characterized by a complex network of ice divides and an extensive landform record outlining two broad and opposing ice flows that are separated by a narrow Horseshoe Intersection Zone (HIZ). This geomorphic system gave rise to contrasting reconstructions, which reflect uncertainties on the temporal evolution of ice divides, the nature and age of the main landform systems and the overall pattern of ice retreat during the last deglaciation. Here, we address these issues through systematic mapping of glacial landforms and ice-flow indicators in a large area of northeastern Quebec and Labrador. The application of cosmogenic (10Be and 26Al) dating to esker-fed glaciomarine deltas and different rock surfaces brings new constraints on the chronological framework and insights on the subglacial thermal regime. Our results outline four main landform assemblages, two of which relating to a major system of opposite ice flows that delineate the position of the eastern Ancestral Labrador ice divide. Our reconstruction shows that the HIZ occurs several tens of km to the west of this divide and that these two features are genetically distinct. The HIZ relates to the late-glacial development of ice streams showing a massive convergent ice flow into Ungava Bay. The upstream extent of this ice flow system shows a strong coupling with the outline of Ungava Bay drainage divide, suggesting that the configuration of the HIZ could be the expression of a topographic control on the late-glacial ice sheet dynamics. Landforms also indicate a significant shift in the deglaciation mode, which evolved from an overall warm-based to an areally-confined cold-based ice retreat near the center of the former ice mass – a change in dynamics that also played a role in the configuration of the HIZ. Overall, areas indicative of cold-based ice conditions are limited to highly elevated terrains, thus ruling out models arguing for an extensive cold-based ice cover over Ungava Bay throughout the last deglaciation.

At an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic 10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the marine authigenic phase in surface sediments along a coast-perpendicular transect and compared to samples from their riverine source. We find evidence for growth of authigenic rims through coprecipitation, not via reversible adsorption, that incorporate an open ocean 10Be/9Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10Be/9Be signatures. Together with increasing 10Be/9Be ratios, particulate-bound Fe concentrations increase, which we attribute to release of Fe-rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleodenudation flux reconstructions are the following: in coast-proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater, whereas sites beneath well-mixed seawater will preserve global flux signatures.

Terrestrial cosmogenic nuclide concentrations in fluvial deposits allow estimation of paleo-erosion rates and reconstruction of the response of landscapes to climatic perturbations. In partly ice-covered landscapes, however, incorporation of subglacially-derived sediments that were shielded by ice from cosmic can lead to erroneous erosion rate calculations. Here, we combine in situ-produced 10Be-derived erosion rates, based on sand and pebbles from a fluvial fill terrace and the modern riverbed in the upper Yamuna catchment, with numerical ice flow modelling to quantify this bias. New luminescence and surface exposure ages suggest that aggradation of the exposed deposits occurred between 29.9 ± 2.5 ka and 14.8 ± 2.8 ka. During most of the deposition, glaciers probably covered ∼19% of the catchment. 10Be concentrations of terrace sand samples differ from those of pebble samples. We obtained the lowest erosion rates from quartzite pebbles, which stem from low elevations, and the highest erosion rates from crystalline pebbles, which stem from high elevations in the Yamuna catchment. We explain these different erosion rates by differences in the steepness of the source areas, an effect that prevails throughout the entire aggradation period despite significant former ice-cover. Sand samples, which are thought to be derived from all elevation parts of the catchment, however show lower 10Be concentrations during the aggradation compared to present-day. We argue that this difference is due to a substantial subglacial origin of the sand during the aggradation period, and not necessarily related to enhanced erosion. We conclude that aggradation of the valley fill in the Yamuna catchment is most likely due to reduced discharge, and only marginally related to higher erosion rates during the late Pleistocene.

Recent developments in terrestrial cosmogenic nuclide (TCN) exposure dating and the reinterpretation of TCN boulder ages from moraines have improved our understanding of the glacial chronology in the Central Andes. According to these records, glacial advances throughout the region correlate with insolation-driven changes in the intensity of the South American Summer Monsoon and millennial-scale climate events such as Heinrich Stadials and the Younger Dryas. Quantifying the temperature and precipitation shifts during these events helps to constrain past moisture pathways and associated changes in atmospheric circulation patterns. Yet, particularly in the southern Central Andes, where a wealth of glacigenic landforms attests to formerly cooler and/or wetter conditions, the magnitudes of past temperature and precipitation changes are only loosely constrained at a few sites. Here, we present results from TCN-dated moraines combined with the reconstruction of former glaciers and paleolakes within the eastern sector of the southern Central Andes (24°–27°S) for the Last Glacial Maximum (LGM), Heinrich Stadial 1 (HS1), and the Younger Dryas (YD). We performed Monte-Carlo simulations with 2-dimensional models of ice flow and lake hydrology that are forced by a spatially-distributed surface energy balance model. Our results indicate that temperatures were 3.0–4.2 °C, 2.0–3.3 °C and 1.3–2.5 °C cooler during the LGM, HS1 and YD, respectively, in agreement with previous estimates elsewhere in the Central Andes. We find that temperature changes during the late glacial are compatible with sea-surface temperature anomalies derived from the tropical Atlantic. Precipitation was only 5–27% greater than today, which contrasts with larger anomalies reconstructed for the Bolivian part of the Andean Plateau (Altiplano). We attribute this discrepancy to the southerly position of our study region with respect to the Bolivian High, supporting the hypothesis that this atmospheric pressure system played a prominent role for South American Summer Monsoon dynamics during glacial episodes.

The southernmost thrust of the Himalayan orogenic wedge that separates the foreland from the orogen, the Main Frontal Thrust (MFT), is thought to accommodate most of the ongoing crustal shortening in the Sub-Himalaya. Steepened longitudinal river-profile segments, terrace offsets, and back-tilted fluvial terraces within the Kangra re-entrant of the NW Sub-Himalaya suggest Holocene activity of the Jwalamukhi Thrust (JMT) and other thrust faults that may be associated with strain partitioning along the toe of the Himalayan wedge. To assess the shortening accommodated by the JMT, we combine morphometric terrain analyses with in-situ 10Be-based surface exposure dating of the deformed terraces. Incision into upper Pleistocene sediments within the Kangra Basin created two late Pleistocene terrace levels (T1 and T2). Subsequent early Holocene aggradation shortly before ~10 ka was followed by episodic re-incision, which created four cut-and-fill terrace levels, the oldest of which (T3) was formed at 10.1 ± 0.9 ka. A vertical offset of 44 ± 5 m of terrace T3 across the JMT indicates a shortening rate of 5.6 ± 0.8 to 7.5 ± 1.1 mm.a-1 over the last ~10 ka. This result suggests that thrusting along the JMT accommodates 40-60% of the total Sub-Himalayan shortening in the Kangra re-entrant over the Holocene. We speculate that this out-of-sequence shortening may have been triggered or at least enhanced by late Pleistocene and Holocene erosion of sediments from the Kangra Basin.

We analyze the source-to-sink variations of in situ 10Be, 26Al and 21Ne concentrations in modern sediment of the Po river catchment, from Alpine, Apennine, floodplain, and delta samples, in order to investigate how the cosmogenic record of orogenic erosion is transmitted across a fast-subsiding foreland basin. The in situ 10Be concentrations in the analyzed samples range from ∼ 0.8 × 10 4 at / g QTZ to ∼ 6.5 × 10 4 at / g QTZ . The 10Be-derived denudation rates range from 0.1 to 1.5 mm/yr in the Alpine source areas and from 0.3 to 0.5 mm/yr in the Apenninic source areas. The highest 10Be-derived denudation rates are found in the western Central Alps (1.5 mm/yr). From these data, we constrain a sediment flux leaving the Alpine and the Apenninic source areas (>27 Mt/yr and ca. 5 Mt/yr, respectively) that is notably higher than the estimates of sediment export provided by gauging (∼10 Mt/yr at the Po delta). We observe a high variability in 10Be concentrations and 10Be-derived denudation rates in the source areas. In the Po Plain, little variability is observed, and at the same time, the area-weighed 10Be concentration of ( 2.29 ± 1.57 ) × 10 4 at / g QTZ (±1 SD of the dataset) from both the Alps and the Apennines is poorly modified (by tributary input) in sediment of the Po Plain ( ( 2.68 ± 0.78 , ± 1 SD ) × 10 4 at / g QTZ ). The buffering effect of the Po floodplain largely removes scatter in 10Be signals. We test for several potential perturbations of the cosmogenic nuclide record during source to sink transfer in the Po basin. We find that sediment trapping in deep glacial lakes or behind dams does not significantly change the 10Be-mountain record. For example, similar 10Be concentrations are measured upstream and downstream of the postglacial Lake Maggiore, suggesting that denudation rates prior to lake formation were similar to today's. On the scale of the entire basin, the 10Be concentration of basins with major dams is similar to those without major dams. A potential modification of the 10Be-mountain record during sediment storage in the subsiding Po Plain can be excluded as measured 26Al/10Be ratios do not show the addition of deeply buried material. A barely resolvable excess 21Ne signal in the Po plain indicates recycling of previously eroded sediment rather than accumulation of cosmogenic nuclides during surficial floodplain transport. Our results demonstrate that the cosmogenic record of mountain erosion is effectively transmitted from the source areas to the sediment sink, even across a strongly subsiding foreland basin. We show that this record is poorly influenced by a range of potential geological and anthropogenic sources of bias, and is largely independent from upstream sediment interception and sediment storage in the floodplain.

Meteoric cosmogenic 10Be is a powerful tracer to quantify dates and rates of Earth surface processes over timescales of 103-105 yrs. A prerequisite for its applications is knowledge of the flux at which 10Be, produced in the atmosphere, is delivered to the Earth surface. Four entirely independent approaches are available to quantify this flux: 1) General Circulation Models (GCM) combined with 10Be production functions and aerosol dynamics; 2) 10Be in precipitation collections; 3) 10Be inventories in dated soil profiles; 4) riverine 10Be exported in solid and dissolved forms. We compiled and reprocessed published globally distributed 10Be flux data from each of these methods and compared them with each other after normalization to a common atmospheric production rate. Based on precipitation records, we propose a simple framework to discriminate between two delivery effects on 10Be fluxes. In the additive effect water vapor and 10Be are continuously accumulating during long-distance transport, leading to an increase in 10Be flux with precipitation rate. In the dilution effect, the 10Be flux is delivered from proximal vapor sources, limited by the rate of 10Be introduction from the stratosphere and independent of precipitation rate. Both effects are mostly present in combination, and the relative weight of either effect depends on vapor condensation rate and on the ratio of vapor condensation area to precipitation area. A comparison between precipitation-derived fluxes and GCM-derived fluxes shows that half of the precipitation estimates are >2 times greater than GCM-derived fluxes. By comparison, soil- and GCM-derived fluxes agree within a factor of 2 for more than half (∼57%) of the dataset, and the remaining soil estimates (∼43%) are much lower than GCM-derived fluxes. 71% of 10Be flux estimates from riverine export using 10Be (meteoric)/9Be ratios also agree with GCM-derived fluxes within a factor of 2. We explain the precipitation-derived fluxes that commonly exceed all other estimates by short-term stochasticity in precipitation events that might introduce a measurement time-interval bias towards higher fluxes. This bias is not present over longer-term (103-105 yrs) flux estimates like those from soil profiles. Soil-derived fluxes might still present an underestimation when retention of 10Be in soil is incomplete. We recommend producing more 10Be depositional flux data from soil inventories with full Be retention, as these generate in our view the most relevant estimates for applications of meteoric 10Be on millennial-scale Earth surface processes.

Cosmogenic nuclide analysis in sediment from the Earth's largest rivers yields mean denudation rates of the sediment-producing areas that average out the local variations commonly found in small rivers. 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 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 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%; whereas the use of paired nuclides in large rivers provides estimates of the buffering timescales of sediment transport.

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.

We present an extensive investigation of a new erosion and weathering proxy derived from the 10Be(meteoric)/9Be(stable) ratio in the Amazon River basin. This new proxy combines a radioactive atmospheric flux tracer, meteoric cosmogenic 10Be, with 9Be, a trace metal released by weathering. Results show that meteoric 10Be concentrations ([10Be]) and 10Be/9Be ratios increase by >30% from the Andes to the lowlands. We can calculate floodplain transfer times of 2–30 kyr from this increase. Intriguingly however, the riverine exported flux of meteoric 10Be shows a deficit with respect to the atmospheric depositional 10Be flux. Most likely, the actual area from which the 10Be flux is being delivered into the mainstream is smaller than the basin-wide one. Despite this imbalance, denudation rates calculated from 10Be/9Be ratios from bed load, suspended sediment, and water samples from Amazon Rivers agree within a factor of 2 with published in situ 10Be denudation rates. Erosion rates calculated from meteoric [10Be], measured from depth-integrated suspended sediment samples, agree with denudation rates, suggesting that grain size-induced variations in [10Be] are minimized when using such sampling material instead of bed load. In addition, the agreement between erosion and denudation rates implies minor chemical weathering intensity in most Amazon tributaries. Indeed, the Be-specific weathering intensity, calculated from mobilized 9Be comprising reactive and dissolved fractions that are released during weathering, is constant at approximately 40% of the total denudation from the Andes across the lowlands to the Amazon mouth. Therefore, weathering in the Amazon floodplain is not detected.

Field geologists and geomorphologists are increasingly looking to numerical modelling to understand landscape change over time, particularly in river catchments. The application of landscape evolution models (LEMs) started with abstract research questions in synthetic landscapes. Now, however, studies using LEMs on real-world catchments are becoming increasingly common. This development has philosophical implications for model specification and evaluation using geological and geomorphological data, besides practical implications for fieldwork targets and strategy. The type of data produced to drive and constrain LEM simulations has very little in common with that used to calibrate and validate models operating over shorter timescales, making a new approach necessary. Here we argue that catchment fieldwork and LEM studies are best synchronized by complementing the Pattern Oriented Modelling (POM) approach of most fluvial LEMs with Pattern Oriented Sampling (POS) fieldwork approaches. POS can embrace a wide range of field data types, without overly increasing the burden of data collection. In our approach, both POM output and POS field data for a specific catchment are used to quantify key characteristics of a catchment. These are then compared to provide an evaluation of the performance of the model. Early identification of these key characteristics should be undertaken to drive focused POS data collection and POM model specification. Once models are evaluated using this POM/POS approach, conclusions drawn from LEM studies can be used with greater confidence to improve understanding of landscape change.

Quantifying rates of weathering and erosion of mafic rocks is essential for estimating changes to the oceans alkalinity budget that plays a significant role in regulating atmospheric CO2 levels. In this study, we present catchment-wide rates of weathering, erosion, and denudation measured with cosmogenic nuclides in mafic and ultramafic rock. We use the ratio of the meteoric cosmogenic nuclide 10Be, deposited from the atmosphere onto the weathering zone, to stable 9Be, a trace metal released by silicate weathering. We tested this approach in stream sediment and water from three upland forested catchments in the north-west Czech Republic. The catchments are underlain by felsic (granite), mafic (amphibolite) and ultramafic (serpentinite) lithologies. Due to acid rain deposition in the 20th century, the waters in the granite catchment exhibit acidic pH, whereas waters in the mafic catchments exhibit neutral to alkaline pH values due to their acid buffering capability. The atmospheric depositional 10Be flux is estimated to be balanced with the streams’ dissolved and particulate meteoric 10Be export flux to within a factor of two. We suggest a correlation method to derive bedrock Be concentrations, required as an input parameter, which are highly heterogeneous in these small catchments. Derived Earth surface metrics comprise (1) Denudation rates calculated from the 10Be/9Be ratio of the “reactive” Be (meaning sorbed to mineral surfaces) range between 110 and 185 t km−2 y−1 (40 and 70 mm ky−1). These rates are similar to denudation rates we obtained from in situ-cosmogenic 10Be in quartz minerals present in the bedrock or in quartz veins in the felsic and the mafic catchment. (2) The degree of weathering, calculated from the fraction of 9Be released from primary minerals as a new proxy, is about 40–50% in the mafic catchments, and 10% in the granitic catchment. Lastly, (3) erosion rates were calculated from 10Be concentrations in river sediment and corrected for sorting and dissolved loss. These amount to 50% of denudation rates from 10Be/9Be in the mafic and ultramafic catchments, the remainder being mass loss in the dissolved form by weathering. In contrast, erosion comprises most of the mass loss in the granitic catchment. These first results are encouraging, given that we find overall good agreement between in situ and meteoric cosmogenic methods, that our denudation rates are in the range of those published for middle European river catchments, and that degrees of weathering are as expected for these diverse lithologies. This method allows quantifying rates of erosion and weathering in mafic rock over the time scale of weathering that are, unlike in situ cosmogenic 10Be, independent from the presence of quartz. 10Be/9Be therefore offers to quantify Earth surface processes in a wide range of landscapes underlain by mafic rock – rates that are of high importance for exploring climate-weathering feedbacks but that have been inaccessible to date.

Erosion and tectonic uplift are widely thought to be coupled through feedbacks involving orographic precipitation, relief development, and crustal weakening. In many orogenic systems, it can be difficult to distinguish whether true feedbacks exist, or whether observed features are a consequence of tectonic forcing. To help elucidate these interactions, we examine Gongga Shan, a 7556 m peak on the eastern margin of the Tibetan Plateau where cosmogenic 10Be basin-wide erosion rates reach >5 mm/yr, defining a region of localized rapid erosion associated with a restraining bend in the left-lateral Xianshuihe Fault. Erosion rates are consistent with topography, thermochronometry, and geodetic data, suggesting a stable pattern of uplift and exhumation over at least the past 2–3 My. Transpression along the Xianshuihe Fault, orographically enhanced precipitation, thermally weakened crust, and substantial local relief all developed independently in the Gongga region and existed there prior to the uplift of Gongga Shan. However, only where all of these conditions are present do the observed topographic and erosional extremes exist, and their relative timing indicates that these conditions are not a consequence of rapid uplift. We conclude that their collocation at 3–4 Ma set into motion a series of feedbacks between erosion and uplift that has resulted in the exceptionally high topography and rapid erosion rates observed today.

When using cosmogenic nuclides to determine exposure ages or denudation rates in rapidly evolving landscapes, challenges arise related to the small number of nuclides that have accumulated in surface materials. Improvements in accelerator mass spectrometry have enabled analysis of samples with low 10Be content (

Understanding past changes in the Antarctic ice sheets provides insight into how they might respond to future climate warming. During the Pliocene and Pleistocene, geological data show that the East Antarctic Ice Sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior, but oscillating at its marine-based margin. It is currently not clear how outlet glaciers, which connect the ice sheet interior to its margin, responded to these orbitally-paced climate cycles. Here we report new ice surface constraints from Skelton Glacier, an outlet of the East Antarctic ice sheet, which drains into the Ross Ice Shelf. Our multiple-isotope (10Be and 26Al) cosmogenic nuclide data indicate that currently ice-free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past. We use an exposure-burial model driven by orbitally-paced glacial–interglacial cycles to determine the probable ice surface history implied by our data. This analysis shows that: 1) the glacier surface has likely fluctuated since at least the Pliocene; 2) the ice surface was >200 m higher than today during glacial periods, and the glacier has been thicker than present for ∼75–90% of each glacial–interglacial cycle; and 3) ice cover at higher elevations possibly occurred for a relatively shorter time per Pliocene cycle than Pleistocene cycle. Our multiple-nuclide approach demonstrates the magnitude of ice surface fluctuations during the Pliocene and Pleistocene that are linked to marine-based ice margin variability.

The Song Gianh is a small-sized (~3500 km2), monsoon-dominated river in northern central Vietnam that can be used to understand how topography and climate control continental erosion. We present major element concentrations, together with Sr and Nd isotopic compositions, of siliciclastic bulk sediments to define sediment provenance and chemical weathering intensity. These data indicate preferential sediment generation in the steep, wetter upper reaches of the Song Gianh. In contrast, detrital zircon U-Pb ages argue for significant flux from the drier, northern Rao Tro tributary. We propose that this mismatch represents disequilibrium in basin erosion patterns driven by changing monsoon strength and the onset of agriculture across the region. Detrital apatite fission track and 10Be data from modern sediment support slowing of regional bedrock exhumation rates through the Cenozoic. If the Song Gianh is representative of coastal Vietnam then the coastal mountains may have produced around 132 000–158 000 km3 of the sediment now preserved in the Song Hong-Yinggehai Basin (17–21 of the total), the primary depocenter of the Red River. This flux does not negate the need for drainage capture in the Red River to explain the large Cenozoic sediment volumes in that basin but does partly account for the discrepancy between preserved and eroded sediment volumes. OSL ages from terraces cluster in the Early Holocene (7.4–8.5 ka), Pre-Industrial (550–320 year BP) and in the recent past (ca. 150 year BP). The older terraces reflect high sediment production driven by a strong monsoon, whereas the younger are the product of anthropogenic impact on the landscape caused by farming. Modern river sediment is consistently more weathered than terrace sediment consistent with reworking of old weathered soils by agricultural disruption.

Fluvial fill terraces in intermontane basins are valuable geomorphic archives that can record tectonically and/or climatically driven changes of the Earth-surface process system. However, often the preservation of fill terrace sequences is incomplete and/or they may form far away from their source areas, complicating the identification of causal links between forcing mechanisms and landscape response, especially over multi-millennial timescales. The intermontane Toro Basin in the southern Central Andes exhibits at least five generations of fluvial terraces that have been sculpted into several-hundred-meter-thick Quaternary valley-fill conglomerates. New surface-exposure dating using nine cosmogenic 10Be depth profiles reveals the successive abandonment of these terraces with a 100 kyr cyclicity between 75±7 and 487±34 ka. Depositional ages of the conglomerates, determined by four 26Al/10Be burial samples and U–Pb zircon ages of three intercalated volcanic ash beds, range from 18±141 to 936±170 ka, indicating that there were multiple cut-and-fill episodes. Although the initial onset of aggradation at ∼1 Ma and the overall net incision since ca. 500 ka can be linked to tectonic processes at the narrow basin outlet, the superimposed 100 kyr cycles of aggradation and incision are best explained by eccentricity-driven climate change. Within these cycles, the onset of river incision can be correlated with global cold periods and enhanced humid phases recorded in paleoclimate archives on the adjacent Bolivian Altiplano, whereas deposition occurred mainly during more arid phases on the Altiplano and global interglacial periods. We suggest that enhanced runoff during global cold phases – due to increased regional precipitation rates, reduced evapotranspiration, or both – resulted in an increased sediment-transport capacity in the Toro Basin, which outweighed any possible increases in upstream sediment supply and thus triggered incision. Compared with two nearby basins that record precessional (21-kyr) and long-eccentricity (400-kyr) forcing within sedimentary and geomorphic archives, the recorded cyclicity scales with the square of the drainage basin length. Fil: Tofelde, Stefanie. Universitat Potsdam; Alemania. Deutsches Geo Forschungs Zentrum; Alemania Fil: Schildgen, Taylor F.. Universitat Potsdam; Alemania. Deutsches Geo Forschungs Zentrum; Alemania Fil: Savi, Sara. Universitat Potsdam; Alemania Fil: Pingel, Heiko. Universitat Potsdam; Alemania Fil: Wickert, Andrew D.. University of Minnesota; Estados Unidos Fil: Bookhagen, Bodo. Universitat Potsdam; Alemania Fil: Wittmann, Hella. Deutsches Geo Forschungs Zentrum; Alemania Fil: Alonso, Ricardo Narciso. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentina Fil: Cottle, John. University of California; Estados Unidos Fil: Strecker, Manfred R.. Universitat Potsdam; Alemania

The ratio of the meteoric cosmogenic nuclide 10Be, precipitated from the atmosphere, to the stable nuclide 9Be, released by silicate weathering, was measured in suspended sediment of the Ganga River basin to determine denudation rates, degrees of weathering, and sediment storage in the floodplain. The 10Be precipitated and the 9Be released are carried to ca. 90% by amorphous and to 10% by crystalline Fe-hydroxides, as revealed by chemical extractions, whereas the dissolved Be transport is negligible due to the river pH of 8. Resulting 10Be/9Be ratios increase from 0.75 × 10 − 9 for the northern and Himalaya-draining rivers to 1.7 × 10 − 9 in the downstream basin. The increase in 10Be/9Be ratios results from two compounding effects: with 1) average denudation rates decrease from 0.5 mm yr−1 in the Himalayas to 0.17 mm yr−1 for the Ganga main stem in the lowlands, 2) the southern tributaries draining the low-relief craton contribute sediment with a ratio of 2.0 × 10 − 9 , corresponding to a denudation rate of 0.03 mm yr−1. We find that at the spatial scale of the entire basin, the atmospheric delivery flux of 10Be equals its sedimentary export flux. Hence fluxes can be considered to be at steady state and radioactive decay of 10Be during sediment storage is not discernible. The lack of a resolvable increase in 10Be concentration during sediment transfer along the floodplain stretch furthermore suggests that the sediment transfer time is indeed short. We also cannot resolve any additional release of silicate-bound 9Be there, testifying to the lower degree of weathering there. When multiplied with the basin area the 10Be/9Be-derived denudation rate of 0.14 mm yr−1 corresponds to a sediment flux of 350 Mt yr−1 which is in good agreement with gauging-derived sediment fluxes (ca. 400 Mt yr−1). Because they integrate over the entire basin, denudation rates from 10Be/9Be are lower than floodplain-corrected denudation rates from in situ cosmogenic 10Be that reflect the rates of the sediment-producing mountain areas.

Concentrations of meteoric 10 Be extracted from detrital Amazon River sediment are strongly particle size-dependent. Such grain size dependency presents a formidable obstacle to routine applications of meteoric cosmogenic 10 Be to basin-wide erosion studies. In this study, we explore means to eliminate these grain size effects in bedload from rivers of the Amazon basin by measuring 10 Be/ 9 Be ratios after selective chemical extraction of reactive authigenic phases. These phases mainly comprise Fe–Mn-(hydr)oxides that are the main carriers of 9 Be and 10 Be. We explore the distribution of 10 Be and its stable 9 Be counterpart between these phases and the partitioning of Be into remaining silicate fractions. This extraction procedure was carried out on bedload samples comprising the three main tectonic units of the Amazon basin, namely the Andes, the Guyana and Brazilian Shields, and the central Amazonian lowlands. For all samples, extracted 10 Be concentrations show a strong decrease with increasing particle size, with up to 20 times more 10 Be extracted from the finest analyzed ( 10 Be concentrations mostly to subsequent dilution by quartz in coarse bedload. However, when normalized to stable 9 Be concentrations that are also extracted from reactive phases, grain size effects are effectively removed and the resulting “reactive” 10 Be/ 9 Be ratio is uniform for all particle sizes. The reactive 10 Be/ 9 Be ratio thus offers important advantages over methods employing single meteoric 10 Be concentrations, such that this ratio can now be developed as quantitative tracer for Earth surface processes.

In the Central Andes, several studies on alluvial terraces and valley fills have linked sediment aggradation to periods of enhanced sediment supply. However, debate continues over whether tectonic or climatic factors are most important in triggering the enhanced supply. The Del Medio catchment in the Humahuaca Basin (Eastern Cordillera, NW Argentina) is located within a transition zone between subhumid and arid climates and hosts the only active debris‐flow fan within this intermontane valley. By combining 10Be analyses of boulder and sediment samples within the Del Medio catchment, with regional morphometric measurements of nearby catchments, we identify the surface processes responsible for aggradation in the Del Medio fan and their likely triggers. We find that the fan surface has been shaped by debris flows and channel avulsions during the last 400 years. Among potential tectonic, climatic, and autogenic factors that might influence deposition, our analyses point to a combination of several favorable factors that drive aggradation. These are in particular the impact of occasional abundant rainfall on steep slopes in rock types prone to failure, located in a region characterized by relatively low rainfall amounts and limited transport capacity. These characteristics are primarily associated with the climatic transition zone between the humid foreland and the arid orogen interior, which creates an imbalance between sediment supply and sediment transfer. The conditions and processes that drive aggradation in the Del Medio catchment today may provide a modern analog for the conditions and processes that drove aggradation in other nearby tributaries in the past. Fil: Savi, Sara. Universitat Potsdam; Alemania Fil: Schildgen, Taylor F.. Universitat Potsdam; Alemania. German Research Centre for Geosciences; Alemania Fil: Tofelde, Stefanie. Universitat Potsdam; Alemania Fil: Wittmann, Hella. German Research Centre for Geosciences; Alemania Fil: Scherler, Dirk. German Research Centre for Geosciences; Alemania. Freie Universität Berlin; Alemania Fil: Mey, Jürgen. Universitat Potsdam; Alemania Fil: Alonso, Ricardo Narciso. Universidad Nacional de Salta. Facultad de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Strecker, Manfred R.. Universitat Potsdam; Alemania

Measured from a bag of sand taken in large rivers, the concentration of cosmogenic nuclides such as in situ-produced 10Be, 26Al, and 14C can be used to constrain the mean sediment flux of the headwaters and assess the duration of sediment storage from source to sink. We revisit these principles, with examples from the Amazon and Ganga basins. We identify two end member cases controlling the concentration of cosmogenic nuclides in lowland river sediment: 1) if the time scale of floodplain sediment storage is short compared to the half-life of the nuclide, in situ cosmogenic nuclide concentrations are not significantly altered in lowland basins. In this case the concentration of e.g. in situ-produced 10Be in the sediment taken in the lowland basin equals in most cases that exported from the sediment source area, but the variability in nuclide concentrations between headwater streams is significantly averaged-out. Thus to convert the measured river sediments' in situ cosmogenic nuclide concentration into a catchment-wide denudation rate, production rates are scaled to include those of the sediment-producing mountainous areas only, rather than the entire catchment area. Nuclide production in the lowlands, where no sediment is being produced, is hence excluded. This correction is termed “floodplain correction”. 2) If sediment buried for periods of the order of the nuclides´ half-life is episodically re-entrained into the active river, paired nuclides, for example the ratio of 26Al/10Be, through the differential decay of these isotopes, constrain the the storage duration and re-mixing of floodplain sediment. As in-situ cosmogenic nuclides measure denudation rates over longer time scales, typically integrating between 103 and 105 years, their combination with modern estimates of sediment fluxes from river load gauging offers a rich potential of deciphering the controls of Earth surface fluxes across large basins. From this combination, we can assess how river systems react to external perturbations such as climate change or human interference, and how such signals are transmitted through the alluvial reaches of lowland basins. The most important results in both basins are that i) lowland Amazon and Ganga nuclide concentrations indeed broadly reflect the spatial average of Andean and Himalayan denudation, respectively, ii) the thus calculated sediment fluxes are within uncertainty of modern fluxes from sediment gauging, indicating complete sediment delivery to the sea without net loss into the basin, and iii) only the Amazon basin, given its size, contains a substantial fraction of sediment buried temporarily in the Quaternary. Finally, we provide a short introduction to the use of meteoric cosmogenic nuclide 10Be and its ratio to stable 9Be, released by rock weathering, in lowlands. In the Amazon basin we show that 10Be concentrations in fine-grained suspended loads, depth-integrated over the water column using Al/Si ratios, provide erosion rates whereas the 10Be/9Be ratio on Be adsorbed to particles provides the denudation rate. Both are similar to denudation rates from in situ 10Be. We show that this system responds more sensitively to sediment storage than the in situ system, and both accumulation and decay of meteoric concentrations may thus be used to determine sediment residence time.

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives. New surface-exposure dating of six terrace levels with in-situ cosmogenic 10Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4 ± 3.2 ka and 43.0 ± 2.7 ka (1σ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6 ± 1.2 ka and 15.3 ± 0.9 ka , while terraces sculpted into the upper Pleistocene–Holocene fan (AF2) provide ages of 9.3 ± 0.4 ka (T3), 7.1 ± 0.4 ka (T4), 5.2 ± 0.4 ka (T5) and 3.6 ± 0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision.

New developments in Geochemistry during the last two decades have revolutionized our understanding of the processes that shape Earth's surface. Here, complex interactions occur between the tectonic forces acting from within the Earth and the exogenic forces like climate that are strongly modulated by biota and, increasingly today, by human activity. Within the Helmholtz Laboratory for the Geochemistry of the Earth Surface (HELGES) of the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, it is our goal to quantify the rates and fluxes of these processes in detail and to develop new techniques to fingerprint them over various temporal and spatial scales. We use mass spectrometry facilities to analyze metal stable isotopes, element concentrations and cosmogenic nuclides to fingerprint and quantify geomorphological changes driven by erosion and weathering processes. We use these novel geochemical tools, to quantify, for example, the recycling of metals in plants after their release during weathering of rocks and soils, soil formation and its erosion rates, and mechanisms and speed of sediment transport through drainage basins. Our research is thus dedicated towards understanding material turnover rates at the Earth's surface by using geochemical fingerprints.

The isotope ratio of the meteoric cosmogenic nuclide 10 Be to the mineral-derived stable isotope 9 Be discloses both the Earth surface denudation rate and its weathering intensity. We develop a set of steady state mass balance equations that describes this system from a soil column over the hillslope scale to an entire river basin. The prerequisites making this new approach possible are: (1) the 9 Be concentration of parent rock (typically 2.5±0.5 ppm in granitic and clastic sedimentary lithologies) is known; (2) both Be isotopes equilibrate between the fluids decomposing rock and reactive solids formed during weathering; and (3) a critical spatial scale is exceeded at which the fluxes of both isotopes into and out of the weathering zone are at steady state over the time scale of weathering (typically ∼10 kyr). For these cases the isotope ratios can be determined in bulk sediment or soil, on leachates from the reactive (adsorbed and pedogenic mineral-bound) phase in sediment or soil, and even on the dissolved phase in river water. The 10 Be/ 9 Be ratio offers substantial advantages over the single-isotope system of meteoric 10 Be. The latter system allows to directly determine erosion rates only in the case that 10 Be is fully retentive in the weathering zone and that riverine sorting has not introduced grain size-dependent 10 Be concentration gradients in sediments. We show the feasibility of the 10 Be/ 9 Be tracer approach at the river scale for sediment and water samples in the Amazon basin, where independent estimates of denudation rates from in situ -produced 10 Be exist. We furthermore calculate meaningful denudation rates from a set of published 10 Be/ 9 Be ratios measured in the dissolved load of globally distributed rivers. We conclude that this isotope ratio can be used to reconstruct global paleo-denudation from sedimentary records.

In the Wadi Haymiliyah of the Oman ophiolite (Haylayn block), discordant wehrlite bodies ranging in size from tens to hundreds of meters intrude the lower crust at different levels. We combined investigations on natural wehrlites from the Wadi In the Wadi Haymiliyah of the Oman ophiolite (Haylayn block), discordant wehrlite bodies ranging in size from tens to hundreds of meters intrude the lower crust at different levels. We combined investigations on natural wehrlites from the Wadi Haymiliyah section with an experimental study on the phase relations in a wehrlitic system in order to constrain the petrogenesis of the crustal wehrlites of the Oman ophiolite. Secondary ion mass spectrometry analyses of clinopyroxenes from different wehrlite bodies imply that the clinopyroxenes were crystallized from tholeiitic, mid-ocean ridge (MORB)-type melts. The presence of primary magmatic amphiboles in some wehrlites suggests a formation under hydrous conditions. Significantly enhanced Sr-87/Sr-86 isotope ratios of separates from these amphiboles imply that the source of the corresponding magmatic fluids was either seawater or subduction zone-related. The experiments revealed that under wet conditions at relatively low temperatures, a MORB magma has the potential to produce wehrlite in the ocean crust by accumulation of early olivine and clinopyroxene. These show typically high Mg# which is a consequence of the oxidizing effect of the prevailing high aH(2)O. First plagioclases crystallizing after clinopyroxene under wet conditions are high in An content, in contrast to the corresponding dry system. Trace element compositions of clinopyroxenes of those wehrlites from the Moho transition zone are too depleted in HREE to be in equilibrium with present-day MORB, implying a genetic relation to the V2 lavas of the Oman ophiolite, which are interpreted to be the result of fluid-enhanced melting of previously depleted mantle. We present a model on the petrogenesis of the crustal wehrlites in an upper mantle wedge above an initial, shallow subduction zone at the beginning of the intraoceanic thrusting.