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The lateral migration of a river meander is driven by erosion on the outer bank and deposition on the inner bank, both of which are affected by shear stress (and therefore channel slope) through complex morphodynamic feedbacks. To test the sensitivity of lateral migration to channel slope, we quantify slope change induced by glacial isostatic adjustment along the Red River (North Dakota, USA and Manitoba, Canada) and two of its tributaries over the past 8.5 ka. We demonstrate a statistically significant, positive relationship between normalized cutoff count, which we interpret as a proxy for channel lateral migration rate, and slope change. We interpret this relationship as the signature of slope change modulating the magnitude of shear stress on riverbanks, suggesting that slope changes that occur over thousands of years are recorded in river floodplain morphology. Plain Language Summary: Rivers move through the landscape by eroding river bank material on their outer bank and depositing sediment on their inner bank, a process that forms meander bends. Understanding what factors drive river meandering is important for interpreting how rivers interact with landscapes. One factor that could impact river meandering is river slope. To understand the impact of slope on river meandering we quantify how slope has changed along the Red River (North Dakota, USA and Manitoba, Canada) over the past 8.5 Kyr. Over this time, vertical land movement substantially reduced the slope of the river, through the ongoing solid Earth response to the retreat of massive North American ice sheets in a process known as glacial isostatic adjustment (GIA). We find that change in slope, induced by GIA, positively correlates with river migration rate along the Red River, suggesting that slope plays an important role in determining the pace of river meandering. Key Points: Glacial isostatic adjustment (GIA) is the primary control on slope change for the Red River (ND, USA and MB, Canada) since it began to flow 8.5 kaSlope change caused by GIA significantly correlates with river cutoff frequency, a proxy for lateral migration rateWe infer that slope change modulates the magnitude of shear stress on the riverbank, driving changes in lateral migration rate [ABSTRACT FROM AUTHOR]

The crest of the Andes--the trace of the highest mountain topography--weaves back and forth, in places near the coastline, in others farther inland. Its position reflects the asymmetric distribution of orogen mass and coincides with asymmetry of orographic precipitation. This coincidence is thought to reflect a primary influence of orographic precipitation on accumulated orogenic mass whereby the more erosive (wetter) side promotes crest migration toward the less erosive (drier) side. However, whether this remains the case after excluding tectonic controls on the size and asymmetry of the wedge is an open question. We assessed relationships between precipitation, erosion rates, and the macromorphology of the Andes. We find that precipitation rates cannot sufficiently explain orogen asymmetry after statistically controlling for the age or dip of the Nazca slab. Slab age and dip are known to primarily affect mountain building in the Andes by impacting stress and strain propagation into the retro-arc region, thus better explaining the position of the mountain chain within the orogenic wedge. Accordingly, using basin-wide erosion rate, topographic, and precipitation data, we find that precipitation possibly influences erosional efficiency in semi-arid Andean landscapes but falls short in explaining the variability of erosion rates in regions of high orographic precipitation. We conclude that the orographic effect cannot change the Andean macromorphology that is set by bottom-up tectonic processes. [ABSTRACT FROM AUTHOR]

Over geologic timescales, C[O.sub.2] is emitted from the Earth's interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial. This balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions (1). Changes in this balance have been attributed to changes in topographic relief, where varying rates of continental rock weathering and erosion (1,2) are superimposed on fluctuations in organic carbon burial (3). Geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation (1,2,4). Widespread observations of a recent (0-5-Myr) fourfold increase in global sedimentation rates require a global mechanism to explain them (4-6). Accelerated uplift and global cooling have been given as possible causes (2,4,6,7), but because of the links between rates of erosion and the correlated rate of weathering (8,9), an increase in the drawdown of C[O.sub.2] that is predicted to follow may be the cause of global climate change instead (2). However, globally, rates of uplift cannot increase every where in the way that apparent sedimentation rates do (4,10). Moreover, proxy records of past atmospheric C[O.sub.2] provide no evidence for this large reduction in recent C[O.sub.2] concentrations (11,12). Here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record (13). As evidence, we recast the ocean dissolved [sup.10]Be/[sup.9]Be isotope system as a weathering proxy spanning the past ~12 Myr (ref. 14). This proxy indicates stable weathering fluxes during the late-Cenozoic era. The sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean. We conclude that processes different from an increase in denudation caused Cenozoic global cooling, and that global cooling had no profound effect on spatially and temporally averaged weathering rates., Studies of both the suspended and the dissolved loads of the world's largest rivers and of hill-slope denudation have shown a strong link between physical erosion and chemical weathering (8,9). [...]

Along the South Fork of the Eel River in northern California, paleoerosion rates derived from [sup.10]Be concentrations in late Pleistocene strath terrace sediment are a factor of 2 greater than erosion rates derived from modern stream sediment and 3.5 times greater than paleoerosion rates from the Pleistocene-Holocene transition. Using these results as a proxy for sediment supply, we provide quantitative field-based evidence that extensive strath planation is linked to elevated sediment supply conditions. We have used optically stimulated luminescence (OSL) to date strath terrace sediment and find that the highest erosion rates and most extensive period of strath planation occurred during a period of increased precipitation in the late Pleistocene. Based on our OSL data, we estimate that bedrock channel lowering rates have outpaced basin-averaged erosion rates by a factor of three since abandonment of the extensive late Pleistocene strath surface. Thus, our data indicate that hillslope relief has been increasing for the past ~20 ka.

Measuring rates of valley head migration and determining the timing of canyon‐opening are insightful for the evolution of planetary surfaces. Spatial gradients of in situ‐produced cosmogenic nuclide concentrations along horizontal transects provide a framework for assessing the migration of valley networks and similar topographic features. We developed a new derivation for valley head retreat rates from the concentrations of in situ‐produced cosmogenic radionuclides in valley walls. The retreat rate is inversely proportional to the magnitude of the spatial concentration gradient and proportional to local nuclide production rates. By solving for a spatial gradient in concentration along a valley parallel transect, we created an expression for the explicit determination of valley head retreat, which we refer to herein as unzipping. We applied this expression to a seepage‐derived drainage network developing along the Apalachicola River, Florida, USA. Sample concentrations along a valley margin transect varied systematically from 2.9 × 105 to 3.5 × 105 atoms/g resulting in a gradient of 160 atoms/g/m, and from this value a valley head retreat rate of 0.025 m/y was found. The discrepancy between overall network age and current rates of valley head migration suggests intermittent network growth which is consistent with glacial‐interglacial precipitation variations during the Pleistocene. This method can be applied to a wide range of Earth‐surface environments. For the 10Be system, this method should be sensitive to unzipping rates bounded between 10−6 and 100 m/y. Plain Language Summary: The pace at which landforms develop is an important control on many biological, chemical, and physical processes operating at Earth's surface. Rates of landscape change are often quantified by measuring the accumulation of cosmogenic radionuclides in near‐surface Earth materials, as an indicator of the erosion rate and age of landforms. In this study, we advance a method for querying the rate of horizontal topographic changes, such as valley growth or ice margin retreat, by sampling material in a horizontal transect and observing patterns in the nuclide concentrations in a spatial gradient. We present the results of numerical modeling that describe the limits of this approach due to the rate and consistency of ongoing landscape evolution processes. We present the first empirical data on the growth rate of a well‐studied seepage channel network in Florida, which suggests that the time‐averaged channel advance rate is 0.025 m/y. Furthermore, our measurements indicate that the age of the incising plateau surface is between 2 and 2.5 My and that the regional uplift rate is between 27 and 38 m/My. Key Points: Propagation rates of morphologic features determined by nuclide concentration gradients along a horizontal transectUplift rate of the Florida panhandle estimated between 0.027 and 0.038 mm/y from a nuclide depth profileChanges in climate over the Quaternary likely drove variable growth rates of seepage valleys along the Apalachicola River [ABSTRACT FROM AUTHOR]

Drainages reorganise in landscapes under diverse conditions and process dynamics that impact biotic distributions and evolution. We first investigated the relative control that Earth surface process parameters have on divide migration and stream capture in scenarios of base-level fall and heterogeneous uplift. A model built with the Landlab toolkit was run 51 200 times in sensitivity analyses that used globally observed values. Large-scale drainage reorganisation occurred only in the model runs within a limited combination of parameters and conditions. Uplift rate, rock erodibility, and the magnitude of perturbation (base-level fall or fault displacement) had the greatest influence on drainage reorganisation. The relative magnitudes of perturbation and topographic relief limited landscape susceptibility to reorganisation. Stream captures occurred more often when the channel head distance to divide was low. Stream topology set by initial conditions strongly affected capture occurrence when the imposed uplift was spatially heterogeneous. We also integrated simulations of geomorphic and biologic processes to investigate relationships among topographic relief, drainage reorganisation, and riverine species diversification in the two scenarios described above. We used a new Landlab component called SpeciesEvolver that models species at landscape scale following macroevolutionary process rules. More frequent stream capture and less frequent stream network disappearance due to divide migration increased speciation and decreased extinction, respectively, especially in the heterogeneous uplift scenario in which final species diversity was often greater than the base-level fall scenario. Under both scenarios, the landscape conditions that led to drainage reorganisation also controlled diversification. Across the model trials, the climatic or tectonic perturbation was more likely in low-relief landscapes to drive more extensive drainage reorganisation that in turn increased the diversity of riverine species lineages, especially for the species that evolved more rapidly. This model result supports recent research on natural systems that implicates drainage reorganisation as a mechanism of riverine species diversification in lowland basins. Future research applications of SpeciesEvolver software can incorporate complex climatic and tectonic forcings as they relate to macroevolution and surface processes, as well as region- and taxon-specific organisms based in rivers and those on continents at large. [ABSTRACT FROM AUTHOR]

Meteoric 10Be (10Bemet) concentrations in soil profiles have great potential as a geochronometer and a tracer of Earth surface processes, particularly in fine-grained soils lacking quartz that would preclude the use of in situ produced 10Be (10Bein situ). One prerequisite for using this technique for accurately calculating rates and dates is constraining the delivery, or flux, of 10Bemet to a site. However, few studies to date have quantified long-term (i.e., millennial) delivery rates, and none have determined a delivery rate for an eroding soil. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in eroding soils sampled from the same depth profiles to calibrate a long-term 10Bemet delivery rate. We did so on the Pinedale (~21-25 kyr) and Bull Lake (~140 kyr) glacial moraines at Fremont Lake, Wyoming (USA), where age, grain sizes, weathering indices, and soil properties are known, as are erosion and denudation rates calculated from 10Bein situ. After ensuring sufficient beryllium retention in each profile, solving for the delivery rate of 10Bemet, and normalizing for paleomagnetic and solar intensity variations over the Holocene, we calculate 10Bemet fluxes of 1.46 (±0.20) x 106 atoms cm-2 yr-1 and 1.30 (±0.48) x 106 atoms cm-2 yr-1 to the Pinedale and Bull Lake moraines, respectively, and compare these values to two widely used 10Bemet delivery rate estimation methods that substantially differ for this site. Accurately estimating the 10Bemet flux using these methods requires a consideration of spatial scale and temporally varying parameters (i.e., paleomagnetic field intensity, solar modulation) to ensure the most realistic estimates of 10Bemet-derived erosion rates in future studies. [ABSTRACT FROM AUTHOR]

Meteoric beryllium‐10 (10Bem, t1/2 = 1.4 Myr) is a cosmogenic radionuclide that remains largely underutilized for deriving hillslope‐scale estimates of erosion on uplands under conditions of land use change. We applied two different models for estimating erosion rates from observed 10Bem concentrations (a one‐dimensional model predicting vertical profiles of 10Bem within hillslope soils [loss only, diffusion only, LODO] and a two‐dimensional model predicting the concurrent evolution of hillslope topography and 10Bem distributions via bioturbation, chemical mobility, and surface erosion [Be2D]). Both models were used to derive pre‐European and post‐European settlement erosion rates (Enat and Epost, respectively) across paired cultivated and uncultivated hillslopes in west‐central Minnesota, USA. Epost estimates from 10Bem were compared to Epost estimates derived from 137Cs inventories and the process‐based Water and Tillage Erosion Model (WaTEM). The results from these models suggest that erosion rates from upper positions on the cultivated hillslope have increased from an average of 0.047 mm/year under natural conditions to Epost values of 3.09 mm/year. The Be2D and LODO models, on average, produced Epost estimates that were similar in magnitude to WaTEM and 137Cs conversion models. This numerical convergence does not imply absolute 10Bem model accuracy, particularly when considering the uncertainties inherent in each approach, but it does suggest that the orders of magnitude increase in estimated erosion rates from Enat to Epost is robust. Additionally, the pattern of Epost estimates produced using 10Bem conversion models is supported by the distribution of soil inorganic carbon at the study site. Our results demonstrate that 10Bem can provide reasonable estimates of both predisturbance and postdisturbance erosion rates in landscapes that have undergone extensive human modification. Plain Language Summary: Agricultural practices have substantially changed soil erosion rates in the Midwestern United States. Although much work has been devoted to understanding the changes in soil erosion rates with land cover change, the ability to quantify those changes at discrete locations on the landscape over long periods of time has been limited. We use a set of tracers and models to estimate presettlement and postsettlement erosion rates on a hillslope in west‐central Minnesota, USA, and show that soil erosion has increased by approximately 1 to 2 orders of magnitude over a period of approximately 110 years. This has implications for how we view our current agricultural landscapes and how we think about soil sustainability in the future. Key Points: Meteoric beryllium‐10 is used to generate point‐based estimates of long‐term erosion on paired hillslopesThese estimates suggest that erosion rates have increased by 2 orders of magnitude under agricultural managementModel choice influences erosion rate magnitude, but average rates are similar to estimates from process‐based models and cesium‐137 [ABSTRACT FROM AUTHOR]

Along glaciated margins, ratios of meteoric cosmogenic beryllium-10, 10Be, normalized to its stable isotope, 9Be, reflect an environmental signal, driven ultimately by climatic change. We explore the application of this isotopic pair as a proxy for East Antarctic Ice Sheet dynamics. We analyze 10Be/9Be in middle Pliocene glaciomarine sediments offshore the Wilkes Land Region (Integrated Ocean Drilling Program (IODP) Site U1361A) and examine our new record alongside existing biochemical/geochemical records (Ba/Al, opal %wt, εNd, and 87Sr/86Sr). 10Be/9Be ratios reach local maxima during pulsed, mild warming events and are strongly correlated with existing records that indicate concurrent ice sheet retraction and increased bioproductivity. We suggest climate change as the primary driver of the 10Be/9Be record near glaciated margins, whereby increased warming drives ice sheet retraction, discharging freshwaters and diluting the open ocean 10Be/9Be signal recorded in authigenic minerals. Plain Language Summary: If the entire Antarctic Ice Sheet collapsed, it would raise global sea level by about 60 m (200 feet). How sensitive is the ice sheet to warming temperatures? Should we expect extreme sea level rise by the middle to late century, when global average temperatures could warm by about 2 °C (3.6 °F) or more? To answer these questions, earth scientists design numerical models to simulate ice sheet behavior and improve those models using physical evidence. High-quality physical evidence is found in the marine sedimentary record deposited in the past under analogous warm conditions, such as during the Pliocene period (2.6–5.3 million years ago). The elemental and isotopic composition of these marine sediments gives clues as to how the ice sheet has reacted to warming temperatures. One such isotope is beryllium-10 (10Be), which, in specific environments, fluctuates in tandem with glacial-interglacial transitions. As additional marine sediment records identify specific mechanisms of ice mass loss at work, we begin to strengthen predictions of sea level rise from numerical simulations. Key Points: 10Be/9Be in Pliocene-age glaciomarine sediments offshore the Wilkes Subglacial Basin (WSB) reflect oscillations in the East Antarctic Ice Sheet (EAIS)Freshwater discharge via basal ice melt can account for the observed 10Be inventory entering Adélie Land Bottom Water (ALBW)Variation in the 10Be/9Be ratio is used to estimate freshwater discharge and deep water dilution [ABSTRACT FROM AUTHOR]

Understanding the chemical controls on beryllium sorption is fundamental when assessing its mobility as a pollutant and interpreting its concentration as a geochemical tracer of erosion, weathering and landscape surface stability. In order to evaluate the interactions of beryllium with soil- and aquatic-related materials, we selected model organic compounds and minerals to perform sorption experiments. The retention of beryllium by each of these compounds and minerals was evaluated over a pH range of 3-6 and at various equilibration times to determine which conditions allowed the greatest retention of beryllium. We conclude that most beryllium sorption occurred within 24 h for both organic and mineral materials. However, equilibration required longer periods of time and was dependent on the solution pH and sorbent material. The pH exhibited a strong control on beryllium sorption with distribution coefficient (Kd) values increasing non-linearly with increasing pH. A system with a pH of 6 is likely to retain 79-2270% more beryllium than the same system at a pH of 4. Phosphonate retained the greatest amount of beryllium, with Kd values 2-30x greater than all other materials tested at a pH of 6. Therefore, soils containing larger amounts of phosphorus-bearing minerals could result in greater retention of beryllium relative to phosphorus-limited soils. Overall, soil composition, with an emphasis on phosphorus oxide content and pH, is an important property to consider when evaluating the capacity of a system to retain beryllium. [ABSTRACT FROM AUTHOR]

At the largest time and space scales, the pace of erosion and chemical weathering is determined by tectonic uplift rates. Deviations from equilibrium arise from the transient response of landscape denudation to climatic and tectonic perturbations. We posit that the constraint of mass balance, however, makes it unlikely that such disequilibrium persists at the global scale over millions of years, as has been proposed for late Cenozoic erosion. We synthesize weathering fluxes, global sedimentation rates, sediment yields and tectonic motions to show a remarkable constancy in the pace of Earth-surface evolution over the last 10 Ma and support the null hypothesis - that global rates of landscape change have remained constant over this time period, despite global climate change and mountain building events. This work undermines the hypothesis that increased weathering due to mountain building or climate change was the primary agent for a decrease in global temperatures. [ABSTRACT FROM AUTHOR]

In equilibrium landscapes, 10Be concentrations within detrital quartz grains are expected to quantitatively reflect basin-wide denudation rates. In transient landscapes, though detrital quartz is derived from both the incising, adjusting lowland and the unadjusted, relict upland, the integrated 10Be concentrations still provide a denudation rate averaged across the two domains. Because fi eld samples can provide only a snapshot of the current upstream-averaged erosion rate, we employ a numerical landscape evolution model to explore how 10Be-derived denudation rates vary over time and space during transient adjustment. Model results suggest that the longitudinal pattern of mean denudation rates is generated by the river's progressive dilution of low-volume, high-concentration detritus from relict uplands by the integration of high-volume, low-concentration detritus from adjusting lowlands. The proportion of these materials in any detrital sample depends on what fraction of the upstream area remains unadjusted. Because the boundary of the adjusting part of the landscape changes over time, the longitudinal trend in cosmogenic nuclide-derived erosion rates changes over time. These insights are then used to guide our interpretation of geomorphic and longitudinal cosmogenic nuclide data from the South Fork Eel River (SFER) in the California Coast Range (United States). The northward-propagating crustal thickening and rock uplift associated with the passage of the Mendocino triple junction generates a mobile wave of uplift that progressively sweeps longitudinally down the SFER. The consequences of this forcing can be both replicated in the model environment and observed in the fi eld. The SFER contains transient landforms including knickpoints and river terraces along mainstem and tributary channels that define a clear boundary between an incised, adjusting lowland and an unadjusted, relict upland. We report nine nested, basin-wide denudation rates in the mainstem of the SFER using terrestrial cosmogenic 10Be in river-borne sediment. We fi nd that denudation rates increase in the downstream direction from ~0.2 mm/yr in the upper catchment to ~0.5 mm/yr at the outlet. Using comparisons to the modeled landscape, we show that this pattern of denudation rates, paired with the distribution of relict topography throughout the watershed, reflect the immaturity of the landscape's transient adjustment. Later in this modeled transient, the predicted erosion rates decrease downstream before they become uniform. This interpretation of our data has potentially far-reaching implications for quantifying the uplift history and response time of transient landscapes using cosmogenic nuclides. [ABSTRACT FROM AUTHOR]

We use a new compilation of global denudation estimates from cosmogenic nuclides to calculate the apportionment and the sum of all sediment produced on Earth by extrapolation of a statistically significant correlation between denudation rates and basin slopes to watersheds without denudation rate data. This robust relationship can explain approximately half of the variance in denudation from quartz-bearing topography drained by rivers using only mean slopes as the predictive tool and matches a similar fit for large river basins. At slopes >200 m/km, topography controls denudation rates. Controls on denudation in landscapes where average slopes are <~200 m/km are unclear, but sediment production rates in these areas average ~45 mm/k.y., 75% of the denudation rates being >10 mm/k.y. We use global topographic data to show that the vast majority of the Earth's surface consists of these gently sloping surfaces with modest, but positive, gross denudation rates, and that these areas contribute the most sediment to the oceans. Because of the links between silicate weathering rates and denudation rates, the predominance of low sloping areas on the Earth's surface compared to areas of steep mountainous topography implies that mountain uplift contributes little to drawdown of CO2 at cosmogenic nuclide time scales of 10³-106 yr. The poorly understood environmental controls that set the pace of denudation for the largest portion of Earth's surface hold the key to understanding the feedbacks between erosion and climate. [ABSTRACT FROM AUTHOR]

We present cospatial, contemporary archival records of biotic and abiotic terrestrial processes operating over the past ∼25 ky within the Rio Fajardo watershed, in northeastern Puerto Rico. The proxy records were derived from a 5-m-thick stratigraphic section exposed by cut bank incision. We interpreted ecosystem dynamics from changes in the stable carbon isotopic ratio of sedimentary organic material compared to δ 13C ratios of contemporary carbon sources. Sedimentary organic material had δ 13C values ranging from −29.715 to −15.291. We derived a record of paleo-erosion rates in the catchment from the concentration of meteoric 10Be in layers of the floodplain sediments. Paleo-erosion rates ranged from 13 to 356 mm ky−1. The chronology of the sediments was constrained with the radiocarbon ages of organic deposits, the oldest age was calibrated to ∼22.4 ky BP (thousand years before present) and retrieved at 440 cm depth. We collected grain size data, clay mineralogies, and analyzed geochemical indices including the chemical weathering index, salinization, and base cation loss down profile. This stratigraphic sequence captures major shifts in the Caribbean climate, the intensification of the El Nino-Southern Oscillation, and the arrival of humans on the island. During the last glacial and early Holocene epochs both biotic (δ 13C) and abiotic proxies (10Be met and geochemical data) indicated dynamic equilibrium with climate. The past five thousand years (ky) of record are characterized instead by pulsed responses to disturbances in both systems. Colonial-era land use drove changes that significantly exceeded natural variability in any proxy over the period of record. [ABSTRACT FROM AUTHOR]

The article discusses the geormophology study on the role of rain in the mountain erosion rate which are exposed on the deposits of porphyry copper that are depthly emplaced. Topics mentioned include the link between erosion and precipitation where high amount of precipitation may lead to rapid erosion, the use of natural speedometer in measuring the crustal conveyor belt pace, and the offer of the mineral deposits in clarifying the muddy waters.

Terrestrial cosmogenic nuclides, produced by secondary cosmic-ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere, are widely used to date surface exposure of rocks and sediments, to estimate erosion and weathering rates, and to date sediment deposition or burial. Their use has transformed geomorphology and Quaternary geology, for the first time allowing landforms to be dated and denudation rates to be measured over soil-forming time scales. The application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry (AMS) in 1977 and increased dramatically with the measurement of in situ-produced nuclides in mineral grains near Earth's surface in the 1980s. The past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool. This review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today, and by identifying key advances in that period that moved the field forward. We emphasize the most commonly used in situ-produced nuclides measured by AMS for geological applications, but we also discuss other nuclides where their applications overlap. Our review covers AMS instrumentation, cosmogenic nuclide production rates, the methods of surface exposure dating, measurement of erosion and weathering, and burial dating, and meteoric 10Be. [ABSTRACT FROM AUTHOR]