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The oxidation of organic carbon contained within sedimentary rocks ("petrogenic" carbon, or hereafter OCpetro) emits nearly as much C2 as is released by volcanism, thereby playing a key role in the long-term global C budget. High erosion rates in mountains have been shown to increase OCpetro oxidation. However, these settings also export unweathered material that may continue to react in downstream floodplains. The relative importance of OCpetro oxidation in mountains versus floodplains remains difficult to assess as disparate methods have been used in the different environments. Here, we investigate the sources and fluxes of rhenium (Re) in the Rio Madre de Dios to quantify OCpetro oxidation from the Andes to the Amazon floodplain using a common approach. Dissolved rhenium concentrations (n = 131) range from 0.01 to 63 pmol L-1 and vary depending on lithology and geomorphic setting. We find that >75% of the dissolved Re derives from OCpetro oxidation and that this proportion increases downstream. We estimate that in the Andes, OCpetro oxidation releases 11.2+4.5/-2.8 tC km-2 y-1 of C2, which corresponds to ~41% of the total OCpetro denudation (sum of oxidized and solid OCpetro). A Re mass balance across the Rio Madre de Dios shows that 46% of OCpetro oxidation takes place in the Andes, 14% in the foreland-lowlands, and 40% in the Andean-fed floodplains. This doubling of OCpetro oxidation flux downstream of the Andes demonstrates that, when present, floodplains can greatly increase OCpetro oxidation and C2 release. [ABSTRACT FROM AUTHOR]

The balance between the burial of biospheric organic carbon (OC bio) in the ocean and the oxidation of rock-derived organic carbon across landscapes (OC petro) helps to regulate atmospheric CO 2 and O 2 over geological time. However, we lack reconstructions of these processes over the timescales necessary to properly understand the drivers and feedbacks operating. Here we use a sediment core from the Zhuoshui River delta in Taiwan, which receives sediments from a rapidly uplifting and eroding catchment, to reconstruct the variations in OC content and radiocarbon composition since the Last Glacial Maximum (LGM). We find that the export of OC bio and the oxidation of OC petro are both modulated by climate-driven changes in physical erosion and temperature. During cold and dry periods, such as the LGM and the Younger Dryas (YD), shallow erosion and low temperature enhanced the preservation of OC bio in the biosphere in catchment, while deep erosion and high temperature during warm and wet periods, such as the Holocene, favored the dilution and degradation of OC bio. The weathering intensity of OC petro (ω) was inversely related to physical erosion, suggesting a lower intensity of oxidation during the Holocene period while the overall oxidation flux was enhanced. This suggests that the degree of weathering was primarily controlled by physical erosion. We propose a proxy to estimate the ratio of fluxes of OC bio export and OC petro oxidation, and show that the net balance between these two processes shifted from a carbon sink during the late deglacial period to a carbon source during the mid-late Holocene. Our study reveals that with CO 2 rise, a warmer and wetter climate would promote the exposure and oxidation of OC petro by erosion in this mountain range, leading the organic carbon balance towards a CO 2 source to the atmosphere. • Erosion and temperature control carbon dynamic in erosive setting. • Cold, dry periods boost carbon preservation. • Warm, wet climate shifts mountains to carbon sources. [ABSTRACT FROM AUTHOR]

Earthquakes play a fundamental role in the evolution of Earth's topography through co-seismic uplift and subsidence, as well as erosion through widespread landslides induced by ground motion. Earthquake-induced landslides can result in exceptional increases in the transfer of mass from landscapes, supplying sediment to rivers where impacts can last for decades or longer. Landslides can also erode vegetation and soils, in addition to exposing freshly ground rock mass, which can both result in regionally significant carbon transfers. Recent work has sought to quantify the fluxes, rates, and temporal patterns of the impacts on earth surface processes generated by these tectonic events. In this review, we focus on the impacts of earthquake-induced landslides on erosion and sediment flux, river water chemistry, and carbon export through the lens of the well-studied 2008 Wenchuan earthquake. We then discuss these themes in the context of works from the 1999 Taiwan Chi-Chi earthquake, 2015 Nepalese Gorkha earthquake, and New Zealand historical earthquakes, altogether highlighting an important role of earthquake-induced landslides in erosion and weathering along tectonically active mountain ranges. We suggest that more monitoring, geochemical tracing, paleo-records, and/or modelling studies are needed to compare the processes and fluxes of catchment erosion and weathering before and after earthquake events, which will help to deepen our understanding not only of the impacts of earthquake-induced landslides on earth surface processes, but also the linkage among high magnitude events, continental erosion and weathering, and the long-term global carbon cycle. [ABSTRACT FROM AUTHOR]

In mountain ranges, earthquakes can trigger widespread landsliding and mobilize large amounts of organic carbon by eroding soil and vegetation from hillslopes. Following a major earthquake, the landslide-mobilized organic carbon can be exported from river catchments by physical sediment transport processes or stored within the landscape where it may be degraded by heterotrophic respiration. The competition between these physical and biogeochemical processes governs a net transfer of carbon between the atmosphere and sedimentary organic matter, yet their relative importance following a large landslide-triggering earthquake remains poorly constrained. Here, we propose a model framework to quantify the post-seismic redistribution of soil-derived organic carbon. The approach combines predictions based on empirical observations of co-seismic sediment mobilization with a description of the physical and biogeochemical processes involved after an earthquake. Earthquake-triggered landslide populations are generated by randomly sampling a landslide area distribution, a proportion of which is initially connected to the fluvial network. Initially disconnected landslide deposits are transported downslope and connected to rivers at a constant velocity in the post-seismic period. Disconnected landslide deposits lose organic carbon by heterotrophic oxidation, while connected deposits lose organic carbon synchronously by both oxidation and river export. The modeling approach is numerically efficient and allows us to explore a large range of parameter values that exert a control on the fate of organic carbon in the upland erosional system. We explore the role of the climatic context (in terms of mean annual runoff and runoff variability) and rates of organic matter degradation using single pool and multi-pool models. Our results highlight the fact that the redistribution of organic carbon is strongly controlled by the annual runoff and the extent of landslide connection, but less so by the choice of organic matter degradation model. In the context of mountain ranges typical of the southwestern Pacific region, we find that model configurations allow more than 90 % of the landslide-mobilized carbon to be exported from mountain catchments. A simulation of earthquake cycles suggests efficient transfer of organic carbon out of a mountain range during the first decade of the post-seismic period. Pulsed erosion of organic matter by earthquake-triggered landslides is therefore an effective process to promote carbon sequestration in sedimentary deposits over thousands of years. [ABSTRACT FROM AUTHOR]

Permafrost thaw in Arctic watersheds threatens to mobilize hitherto sequestered carbon. We examine the radiocarbon activity (F14C) of dissolved organic carbon (DOC) in the northern Mackenzie River basin. From 2003–2017, DOC‐F14C signatures (1.00 ± 0.04; n = 39) tracked atmospheric 14CO2, indicating export of "modern" carbon. This trend was interrupted in June 2018 by the widespread release of aged DOC (0.85 ± 0.16, n = 28) measured across three separate catchment areas. Increased nitrate concentrations in June 2018 lead us to attribute this pulse of 14C‐depleted DOC to mobilization of previously frozen soil organic matter. We propose export through lateral perennial thaw zones that occurred at the base of the active layer weakened by preceding warm summer and winter seasons. Although we are not yet able to ascertain the broader significance of this "anomalous" mobilization event, it highlights the potential for rapid and large‐scale release of aged carbon from permafrost. Plain Language Summary: The thaw of continuously frozen grounds in the Arctic induced by regional warming accelerates the release of carbon to the atmosphere and river systems. Of particular concern is the fate of dissolved organic carbon (DOC) due to its potential for rapid oxidation to carbon dioxide. In order to understand the ramifications of a warming climate, we analyze the radiocarbon age of DOC in the northern Mackenzie River—a major Arctic river basin. DOC in large Arctic rivers has been characterized by young radiocarbon ages, from modern vegetation and surface soils. In June 2018, we recorded a departure from long‐term observations: Older DOC was measured in three large catchments draining into the Mackenzie Delta. This release of aged DOC followed a warm summer and the second warmest winter on record. We infer that the aged DOC derived from thaw of deeper soil horizons and subsequent carbon mobilization and riverine export. This is the first time such an event has been documented; it highlights the potential for abrupt and widespread aged DOC export with important implications for regional and global carbon cycles. Key Points: A widespread pulse of aged dissolved organic carbon (DOC) occurred in the Mackenzie River and its tributaries in June 2018Export of aged DOC is consistent with a prolonged warming period and the formation of supra‐permafrost taliksMobilization of aged DOC and nitrate suggests percolation of supra‐permafrost groundwater through previously frozen soil layers [ABSTRACT FROM AUTHOR]

Rhenium (Re) is a trace element whose redox chemistry makes it an ideal candidate to trace a range of geochemical processes. In particular, fractionation of its isotopes 187Re (62.6% abundance) and 185Re (37.4%) may be used to improve our understanding of redox reactions during weathering, both in the modern day and in geological archives. Published methods for measurement of Re isotopic composition are limited by the requirements of Re mass to reach a desirable precision, making the analysis of many geological materials unfeasible at present. Here we develop new methods which allow us to measure Re isotope ratios (reported as δ187Re) with improved precision: ±0.10‰ (2σ) for a mass of Re of ∼1 ng to ±0.03‰ (2σ) for a mass of Re of >10 ng. This is possible due to the combination of a modified column chemistry procedure and the use of 1013 Ω amplifiers for measurement via multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). For river water samples (with Re concentrations typically ∼10−12 g g−1) we design a field-based pre-concentration of Re that can be used with large volumes of filtered water (5–20 L) shortly after sample collection to provide abundant Re for isotope analysis. As a result of these developments we provide new measurements of δ187Re in standards reference materials (δ187Re values range from −0.06 ± 0.07‰ to +0.19 ± 0.05‰) and a seawater standard (δ187Re = +0.10 ± 0.04‰), providing impetus for further exploration of the Re isotope system. [ABSTRACT FROM AUTHOR]

The article informs that Brantley et al. have studied the temperature dependence of silicate weathering, and its impact on Earth's climate. It mentions that the results showed that silicate weathering increased with temperature, with field rates increasing more than those from laboratory experiments, and highlights the complex interplay between temperature, minerals, and water in determining the rate of silicate weathering and its impact on the carbon cycle and Earth's climate.

Abstract Erosion of organic carbon from the terrestrial biosphere and sedimentary rocks plays an important role in the global carbon cycle across a range of timescales. Over geological timescales (>104 years), erosion and burial of particulate organic carbon (POC) from the terrestrial biosphere (POC biosphere) is an important CO 2 sink, while oxidation of organic carbon derived from sedimentary rocks (petrogenic, POC petro) releases CO 2 to the atmosphere. Over decadal to millennial timescales, the balance between POC biosphere production and degradation affects atmospheric CO 2 concentrations. To better constrain the controls on erosional carbon transfers, here we quantify POC biosphere and POC petro fluxes in a mountain range with relatively low runoff, the Longmen Shan, which drains the eastern margin of the Tibetan Plateau. We measure total organic carbon content ([OC total ]) and the carbon isotopic compositions (13C/12C expressed as δ13C; 14C/12C expressed as fraction modern or F mod) of organic matter in suspended sediments collected from six gauging stations on the Min Jiang, a tributary of the Yangtze River, from 2005 to 2012. We find that POC petro has a large range of δ13C, from −26.2‰ to −13.2‰. This POC petro mixes with POC biosphere to set the δ13C of POC in river sediments. Binary mixing models reveal the possibility of aged POC biosphere at two gauging stations which drain the high elevations of the eastern Tibetan Plateau, with modelled biospheric F mod values of 0.82 ± 0.09 and 0.84 ± 0.08. This is consistent with prior suggestions of aged biospheric carbon being eroded from the plateau. The annual POC petro yields range from 0.04 ± 0.02 tC km−2 yr−1 to 1.69 ± 0.56 tC km−2 yr−1 across the five study catchments, with basin average yield that appears to be linked to catchment average slope as a likely proxy for erosion rate. Here, the variability in the petrogenic organic carbon content of rocks masks the signal of the weathering and oxidation of this rock-derived organic carbon. The annual POC biosphere yields range from 0.21 ± 0.04 tC km−2 yr−1 to 3.33 ± 0.57 tC km−2 yr−1. These values are towards the lower end of those measured in mountain ranges around the world, which we suggest not only reflects the relatively low erosion rates of the Longman Shan, but also the low annual runoff (<1 m yr−1). Across this region, the river POC biosphere discharge is related to the intensity of runoff events. Our data suggest that a wetter (and/or stormier) climate could increase the erosional export of POC biosphere in this tectonically-active mountain range. Depending on the fate of POC biosphere downstream in larger river systems, this could act as carbon-cycle climate feedback over geological timescales. [ABSTRACT FROM AUTHOR]

Lithospheric organic carbon ( “ petrogenic ” ; OC petro ) is oxidized during exhumation and subsequent erosion of mountain ranges. This process is a considerable source of carbon dioxide (CO2) to the atmosphere over geologic time scales, but the mechanisms that govern oxidation rates in mountain landscapes are poorly constrained. We demonstrate that, on average, 67 ± 11% of the OC petro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized in soils, leading to CO2 emissions of 6.1 to 18.6 metric tons of carbon per square kilometer per year. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OC petro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emission fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial. [ABSTRACT FROM AUTHOR]

The article focuses on a study regarding impact of mountain glaciation on rapid oxidation of rock-bound organic carbon. It mentions the exposure of organic matter in rocks to oxidative weathering at the planet Earth's surface releases carbon dioxide. It also mentions th use of rhenium to track the oxidation of rock-bound organic carbon in the mountain watersheds.

Erosion drives the export of particulate organic carbon from the terrestrial biosphere (POC biosphere ) and its delivery to rivers. The carbon transfer is globally significant and can result in drawdown of atmospheric carbon dioxide (CO 2 ) if the eroded POC biosphere escapes degradation during river transfer and sedimentary deposition. Despite this recognition, we lack a global perspective on how the tectonic and climatic factors which govern physical erosion regulate POC biosphere discharge, obscuring linkages between mountain building, climate, and CO 2 drawdown. To fill this deficit, geochemical (δ 13 C, 14 C and C/N), hydrometric (water discharge, suspended sediment concentration) and geomorphic (slope) measurements are combined from 33 globally-distributed forested mountain catchments. Radiocarbon activity is used to account for rock-derived organic carbon and reveals that POC biosphere eroded from mountain forests is mostly < 1300 14 C years old. Annual POC biosphere yields are positively correlated with suspended sediment yields, confirming results from Taiwan and a recent global analysis, and are high in catchments with the steepest slopes. Based on these relationships and the global distribution of slope angles (3-arc-second), it is suggested that topography steeper than 10° (16% of the continental area) may contribute ~ 40% of global POC biosphere erosional flux. Climate is shown to regulate POC biosphere discharge by mountain rivers, by controlling hydrologically-driven erosion processes. In catchments where discharge measurements are available (8 of the 33) a significant relationship exists between daily runoff (mm day − 1 ) and POC biosphere concentration (mg L − 1 ) ( r = 0.53, P < 0.0001). The relationship can be described by a single power law and suggests a high connectivity between forested hillslopes and mountain river channels. As a result, annual POC biosphere yields are significantly correlated with mean annual runoff ( r = 0.64, P < 0.0001). A shear-stress POC biosphere erosion model is proposed which can explain the patterns in the data. The model allows the climate sensitivity of this carbon flux to be assessed for the first time. For a 1% increase in annual runoff, POC biosphere discharge is predicted to increase by ~ 4%. In steeper catchments, POC biosphere discharge increases more rapidly with an increase in annual runoff. For comparison, a 1% increase in annual runoff is predicted to increase carbon transfers by silicate weathering solute fluxes in mountains by 0.4–0.7%. Depending on the fate of the eroded POC biosphere , river export of POC biosphere from mountains may act as an important negative feedback on rising atmospheric CO 2 and increased global temperature. Erosion of carbon from the terrestrial biosphere links mountain building and climate to the geological evolution of atmospheric CO 2 , while the carbon fluxes are sensitive to predicted changes in runoff over the coming century. [ABSTRACT FROM AUTHOR]

Weathering of organic carbon contained in sedimentary rocks (petrogenic OC, OC petro) is an important control on the concentrations of carbon dioxide (CO 2) and oxygen in the atmosphere. Of particular significance are steep mountainous catchments, where high rates of physical erosion introduce OC petro to the surface, where oxygen in air and water can help drive oxidative weathering reactions, yet measurements of CO 2 emissions from OC petro oxidation are still scarce. Here, we use in situ gas accumulation chambers and show that CO 2 fluxes, and their environmental controls, can be determined during a stand-alone, short-term (8 days) field campaign, applied to a remote setting. In the rapidly eroding Waiapu River catchment, New Zealand, dominated by mudstones, we measured high rates of CO 2 release (222–1590 mgC m−2 d−1) in five accumulation chambers in the near-surface of naturally fractured and bedded rock outcrops. The corresponding CO 2 concentrations are very high (p CO 2 ~4700–27,100 ppmv), and such values could influence acid-hydrolysis reactions during chemical weathering of co-occurring silicate minerals. The CO 2 is radiocarbon depleted (fraction modern, F 14C = 0.0122–0.0547), confirming it is petrogenic in origin. Stable carbon isotopes suggest a source from OC petro , but δ13C values of the CO 2 are lower by ~3.5–3.7 ± 0.1 ‰ from those of OC petro (−25.9 ± 0.1 ‰), consistent with isotope fractionation associated with microbial respiration of OC petro. Over 6 days of measurement, we find that CO 2 fluxes respond quickly to changes in temperature and humidity, indicating an environmental regulation that is captured by our short-term installation. The approaches applied here mean that future research can now seek to constrain the climatic, lithological and biological controls on OC petro oxidation across regional to global scales. • CO 2 fluxes from oxidative weathering can be measured during short field campaigns. • Their size, regulated by temperature and humidity, reaches that of soil respiration. • Carbon isotopes reveal that measured CO 2 is sourced from petrogenic organic matter. • Microbial respiration is potentially associated with carbon isotope fractionation. • Partial pressures of CO 2 in rock can be high and induce silicate weathering. [ABSTRACT FROM AUTHOR]

Rapid erosion in mountain forests results in high rates of biospheric particulate organic carbon (POC) export by rivers, which can contribute to atmospheric carbon dioxide drawdown. However, coarse POC (CPOC) carried by particles >~1 mm is rarely quantified. In a forested pre-Alpine catchment, we measured CPOC transport rates and found that they increase more rapidly with water discharge than fine POC (<1 mm) and dissolved organic carbon (DOC). As a result, decadal estimates of CPOC yield of 12.3 ± 1.9 t C km^yr"1 are higher than for fine POC and DOC, even when excluding 4 extreme flood events. When including these floods, CPOC dominates organic carbon discharge (~80%). Most CPOC (69%) was water logged and denser than water, suggesting that CPOC has the potential to contribute to long-term sedimentary burial. Global fluxes remain poorly constrained, but if the transport behavior of CPOC shown here is common to other mountain streams and rivers, then neglecting CPOC discharge could lead to a large underestimation of the global transfer of biospheric POC from land to ocean. [ABSTRACT FROM AUTHOR]

Soils of the northern high latitudes store carbon over millennial timescales (thousands of years) and contain approximately double the carbon stock of the atmosphere. Warming and associated permafrost thaw can expose soil organic carbon and result in mineralization and carbon dioxide (CO2) release. However, some of this soil organic carbon may be eroded and transferred to rivers. If it escapes degradation during river transport and is buried in marine sediments, then it can contribute to a longer-term (more than ten thousand years), geological CO2 sink. Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers at high latitudes remains poorly constrained. Here, we quantify the source of POC in the Mackenzie River, the main sediment supplier to the Arctic Ocean, and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios to correct for rock-derived POC. Our samples reveal that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5,800 ± 800 years, much older than the POC in large tropical rivers. From the measured biospheric POC content and variability in annual sediment yield, we calculate a biospheric POC flux of teragrams of carbon per year from the Mackenzie River, which is three times the CO2 drawdown by silicate weathering in this basin. Offshore, we find evidence for efficient terrestrial organic carbon burial over the Holocene period, suggesting that erosion of organic carbon-rich, high-latitude soils may result in an important geological CO2 sink. [ABSTRACT FROM AUTHOR]

Oxidation of rock-derived, petrogenic, organic carbon (OC petro ) during weathering of sedimentary rocks is a major source of carbon dioxide (CO 2 ) to the atmosphere. This geological respiration is thought to be enhanced by physical erosion, suggesting that mountain belts could release large amounts of CO 2 to counter the CO 2 sequestration achieved by the erosion, riverine transfer and oceanic burial of organic carbon from the terrestrial biosphere. However, OC petro oxidation rates in mountain belts have not been quantified. Here we use rhenium (Re) as a proxy to track OC petro oxidation in mountain river catchments of Taiwan, where existing measurements of physical erosion rate allow the controls on OC petro oxidation to be assessed. Re has been shown to be closely associated with OC petro in rocks and following oxidation during chemical weathering forms a soluble oxyanion ( ReO 4 − ) which contributes to the dissolved load of rivers. Soils on meta-sedimentary rocks in Taiwan show that Re loss is coupled to OC petro loss during weathering, confirming previous observations from soil profiles on sedimentary rocks elsewhere. In Taiwan rivers, dissolved Re flux increases with the catchment-average sediment yield, suggesting that physical erosion rate is a major control on OC petro oxidation. Based on our current understanding of Re mobility during weathering, the dissolved Re flux can be used to quantify an upper bound on the OC petro oxidation rate and the associated CO 2 transfer. The estimated CO 2 release from this mountain belt by OC petro oxidation does not negate estimates of CO 2 sequestration by burial of biospheric OC offshore. The findings are compared to OC transfers estimated for the Himalaya, where OC petro oxidation in the mountain belt remains unconstrained. Together, these cases suggest that mountain building in the tropics can result in a net sink of OC which sequesters atmospheric CO 2 . [ABSTRACT FROM AUTHOR]

• 0.3‰ of δ 187 Re variation across rivers from the Mackenzie River basin. • For each river, the δ 187 Re of the dissolved load is higher than that of the corresponding river sediment • The δ 187 Re of river water and sediments is controlled by both provenance and modern oxidative weathering processes • The average δ 187 Re of Mackenzie bedrock (∼ − 0.05 ‰) and dissolved load (∼ − 0.01 ‰) are lower than Atlantic seawater δ 187 Re. Rhenium (Re) is a trace element whose redox chemistry makes it an ideal candidate to trace a range of geochemical processes. Here, we report the first rhenium isotopic measurements (δ 187 Re) from river-borne materials to assess the influence of chemical weathering on Re isotopes at continental scale. The δ 187 Re was measured in water, suspended sediments and bedloads from the Mackenzie River and its main Arctic tributaries in Northwestern Canada. We find that the δ 187 Re (relative to NIST SRM 989) of river waters ranges from −0.05‰ to +0.07‰, which is generally higher than the corresponding river sediment (−0.25‰ to +0.01‰). We show that the range of δ 187 Re in river sediments (∼0.30‰) is controlled by a combination of source bedrock isotopic variability (provenance) and modern oxidative weathering processes. After correcting for bedrock variability, the δ 187 Re of solids appear to be positively correlated with the amount of Re depletion related to oxidative weathering. This correlation, and the offset in δ 187 Re between river water and sediment, can be explained by preferential oxidation of reactive phases with high δ 187 Re (i.e. rock organic carbon, sulfide minerals), but could also result from fractionation during oxidation or the influence of secondary weathering processes. Overall, we find that both basin-average bedrock δ 187 Re (∼−0.05‰) and dissolved δ 187 Re (∼−0.01‰) in the Mackenzie River are lower than the δ 187 Re of Atlantic seawater (+0.12‰). These observations provide impetus for future work to constrain the Re isotope mass balance of seawater, and assess the potential for secular shifts in its δ 187 Re values over time, which could provide an additional isotopic proxy to trace current and past redox processes at Earth's Surface. [ABSTRACT FROM AUTHOR]

Abstract: Small rivers draining mountain islands are important in the transfer of terrestrial particulate organic carbon (POC) to the oceans. This input has implications for the geochemical stratigraphic record. We have investigated the stable isotopic composition of POC () in rivers draining the mountains of Taiwan. In 15 rivers, the suspended load has a mean that ranges from − to − (on average 37 samples per river) over the interval of our study. To investigate this variability we have supplemented suspended load data with measurements of POC in bedrock and river bed materials, and constraints on the composition of the terrestrial biomass. Fossil POC in bedrock has a range in from − to − between the major geological formations. Using coupled and N/C we have found evidence in the suspended load for mixing of fossil POC with non-fossil POC from the biosphere. In two rivers outside the Taiwan Central Range anthropogenic land use appears to influence , resulting in more variable and lower values than elsewhere. In all other catchments, we have found that variability in is not controlled by the variable composition of the biomass, but instead by heterogeneous fossil POC. In order to quantify the fraction of suspended load POC derived from non-fossil sources () as well as the isotopic composition of fossil POC () carried by rivers, we adapt an end-member mixing model. River suspended sediments and bed sediments indicate that mixing of fossil POC results in a negative trend between N/C and that is distinct from the addition of non-fossil POC, collapsing multiple fossil POC end-members onto a single mixing trend. As an independent test of the model, reproduces the fraction modern () in our samples, determined from measurements, to within 0.09 at the 95% confidence level. Over the sampling period, the mean of suspended load POC was low (0.29±0.02, n =459), in agreement with observations from other mountain rivers where physical erosion rates are high and fossil POC enters river channels. The mean in suspended POC varied between − and − from catchment to catchment. This variability is primarily controlled by the distribution of the major geological formations. It also covers entirely the range of found in marine sediments which is commonly thought to derive from mixing between marine and terrigenous POC. If land-sourced POC is preserved in marine sediments, then changes in the bulk observed offshore Taiwan could instead be explained by changes in the onshore provenance of sediment. The range in of fossil organic matter in sedimentary rocks exposed at the surface is large and given the importance of these rocks as a source of clastic sediment to the oceans, care should be taken in accounting for fossil POC in marine deposits supplied by active mountain belts. [Copyright &y& Elsevier]

Uranium (U) isotope signatures (δ238U) recorded in sedimentary archives provide insight into the paleo redox state of the ocean. But the robust interpretation of these sedimentary U isotope records requires characterisation of the U isotope signature of rivers, the main source of U to the ocean. The main controlling factors on riverine δ238U remain poorly constrained. Here, we investigate the elemental and isotope signatures of uranium in the dissolved and solid loads of a well-characterised river, the Mackenzie Basin (Canada). In the Mackenzie Basin, the solid load δ238U shows a positive relationship with U and vanadium (V) contents, consistent with the suggestion that particulate δ238U are explained by variable contributions via erosion of silicate and black shale. The δ238U of the dissolved and solid loads are correlated which, at first sight, suggests no U isotope fractionation during chemical weathering, and a purely lithological control on both the river dissolved and solid δ238U. Moreover, relationships between dissolved U and δ238U and major elements such as calcium and sulfate, also support the idea of a lithological control. However, the δ238U of end members inferred from mixing relationships are not consistent with binary mixing of two sources, suggesting some potential U isotope fractionation during weathering. In fact, the abundance of U in the river dissolved load is always lower than that predicted by silicate rock weathering. This suggests that 1) the weathering of silicate only can explain the abundance of U in the river dissolved load and 2) secondary weathering processes scavenge a proportion of the U released by primary mineral breakdown. The broad negative relationship between δ238U and the depletion of dissolved U is also consistent with the control of dissolved δ238U by secondary weathering processes following silicate mineral breakdown. The relationships observed between dissolved U, δ238U and the large-scale environmental controls on weathering processes (such as weathering intensity or runoff) support this hypothesis. Overall, our interpretations of the variation in the river dissolved δ238U challenge the common assumption of the control of dissolved U by black shale and carbonate weathering. In addition, we suggest that the extent of secondary weathering processes can imprint on the U isotope signature of rivers, now and in the past. [ABSTRACT FROM AUTHOR]

On geological time scales, the erosion of carbon from the terrestrial biosphere and its burial in sediments can counter CO2 emissions from the solid Earth. Earthquakes may increase the erosion of this biospheric carbon and supply it to mountain rivers by triggering landslides, which rapidly strip hillslopes of vegetation and soil. Over the long term, elevated river sediment loads may promote more efficient carbon burial. However, riverine export of earthquakemobilized carbon has remained poorly constrained. Here we quantify biospheric carbon discharge by the Zagunao River following a large earthquake with a unique set of samples collected before and after the A.D. 2008 Mw 7.9 Wenchuan (China) earthquake. Radioactive and stable carbon isotopes are used to isolate the biospheric carbon, accounting for rock-derived organic carbon inputs. River discharge of biospheric carbon doubled in the downstream reaches, characterized by moderate landslide impact, following the earthquake. The rapid export of carbon from earthquake-triggered landslides appears to outpace its degradation on hillslopes while sediment loads are elevated. This means that enhanced river discharge of biospheric carbon following large earthquakes can link active tectonics to CO2 drawdown. [ABSTRACT FROM AUTHOR]

Large earthquakes in active mountain belts can trigger landslides, which mobilize large volumes of clastic sediment. Delivery of this material to river channels may result in aggradation and flooding, while sediment residing on hillslopes may increase the likelihood of subsequent landslides and debris flows. Despite recognition of these processes, the controls on the residence time of coseismic landslide sediment in river catchments remain poorly understood. Here we assess the residence time of fine-grained (<0.25 mm) landslide sediment mobilized by the C.E. 2008 Mw 7.9 Wenchuan earthquake, China, using daily suspended sediment discharge measured in 16 river catchments from 2006-2012. Following the earthquake, suspended sediment discharge was elevated 3-7x compared to 2006-2007. However, the total 2008-2012 export (92.5 ± 9.3 Mt from 68,719 km²) was much less than estimates of fine-grained sediment input by coseismic landslides (480 +350/-338 Mt) determined by landslide area-volume scaling and deposit grain-size distributions. We estimate the residence time of fine-grained sediment in the affected river catchments using the post-earthquake rate of sediment export, and find that it ranges from one year to over a century. The first-order variability in fine-sediment residence time is proportional to the areal extent of coseismic landsliding, and is inversely proportional to the frequency of intense runoff events (>5 mm day-1). Together with previous observations from the C.E. 1999 Chi-Chi earthquake in Taiwan, our results demonstrate the importance of landslide density and runoff intensity in setting the duration of earthquake-triggered landslide impacts on river systems. [ABSTRACT FROM AUTHOR]

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy. [ABSTRACT FROM AUTHOR]

Abstract: In order to reveal particulate organic carbon (POC) source and mode of transport in the largest river basin on Earth, we sampled the main sediment-laden tributaries of the Amazon system (Solimões, Madeira and Amazon) during two sampling campaigns, following vertical depth-profiles. This sampling technique takes advantage of hydrodynamic sorting to access the full range of solid erosion products transported by the river. Using the Al/Si ratio of the river sediments as a proxy for grain size, we find a general increase in POC content with Al/Si, as sediments become finer. However, the sample set shows marked variability in the POC content for a given Al/Si ratio, with the Madeira River having lower POC content across the measured range in Al/Si. The POC content is not strongly related to the specific surface area (SSA) of the suspended load, and bed sediments have a much lower POC/SSA ratio. These data suggest that SSA exerts a significant, yet partial, control on POC transport in Amazon River suspended sediment. We suggest that the role of clay mineralogy, discrete POC particles and rock-derived POC warrant further attention in order to fully understand POC transport in large rivers. To examine the source of POC in the Amazon Basin in more detail, we use radiocarbon (14C) content and the stable isotope composition (δ13C) of POC. 14C activity demonstrates that rock-derived POC is a significant component of river bed sediments and contributes to POC across the river depth-profiles of suspended sediments. We estimate that the flux of rock-derived POC may reach 10% of the total POC export by the Amazon River. After correcting for rock-derived POC input, we find that POC from the terrestrial biosphere (biospheric POC) is mostly sourced from C3-plants. Higher biospheric POC δ13C values in the Madeira River (by 0.5–1‰) are best explained by a small (<5%) contribution of C4-grasses from Bolivian savannas. Finally, we use 14C to estimate the mean age of biospheric POC exported from the Amazon Basin. The data show that biospheric POC is younger in the Solimões River (1120years) than in the Madeira River (2850 years). These ages are much younger than the corresponding estimates of sediment residence time in the basin, suggesting that lowland areas and/or young POC from above-ground biomass may contribute disproportionately to the biomarker signals in terrigenous sediments of the Amazon delta. [Copyright &y& Elsevier]

Mineral weathering plays a primary role in the geologic carbon cycle. Silicate weathering by carbonic acid consumes CO² and stabilizes Earth's climate system. However, when sulfuric acid drives weathering, CO² can be released to the atmosphere. Recent work has established that sulfuric acid weathering resulting from sulfide mineral oxidation is globally significant and particularly important in rapidly eroding environments. In contrast, if SO4 ²-produced by sulfide oxidation is reduced during continental transit, then CO² release may be negated. Yet, little is known about how much SO4 ²-reduction takes place in terrestrial environments. We report oxygen and sulfur stable isotope ratios of SO4 ²-in river waters and mass budget calculations, which together suggest that SO4 ²-released from pyrite oxidation in the Peruvian Andes mountains is conservatively exported across ~300 km of the Amazon floodplain. In this system, floodplain SO4 ²-reduction does not counteract the large SO4 ²-flux from Andean pyrite weathering or measurably affect the stable isotope composition of riverine SO4 ²-. These findings support the hypothesis that uplift and erosion of sedimentary rocks drive release of CO² from the rock reservoir to the atmosphere. [ABSTRACT FROM AUTHOR]

Rivers carry the dissolved and solid products of silicate mineral weathering, a process that removes CO2 from the atmosphere and provides a key negative climate feedback over geological timescales. Here we show that, in some river systems, a reactive exchange pool on river suspended particulate matter, bonded weakly to mineral surfaces, increases the mobile cation flux by 50%. The chemistry of both river waters and the exchange pool demonstrates exchange equilibrium, confirmed by Sr isotopes. Global silicate weathering fluxes are calculated based on riverine dissolved sodium (Na+) from silicate minerals. The large exchange pool supplies Na+ of nonsilicate origin to the dissolved load, especially in catchments with widespread marine sediments, or where rocks have equilibrated with saline basement fluids. We quantify this by comparing the riverine sediment exchange pool and river water chemistry. In some basins, cation exchange could account for the majority of sodium in the river water, significantly reducing estimates of silicate weathering. At a global scale, we demonstrate that silicate weathering fluxes are overestimated by 12 to 28%. This overestimation is greatest in regions of high erosion and high sediment loads where the negative climate feedback has a maximum sensitivity to chemical weathering reactions. In the context of other recent findings that reduce the net CO2 consumption through chemical weathering, the magnitude of the continental silicate weathering fluxes and its implications for solid Earth CO2 degassing fluxes need to be further investigated. [ABSTRACT FROM AUTHOR]

Process-based, mechanistic investigations of organic matter transformation and diagenesis directly beneath the sediment–water interface (SWI) in Arctic continental shelves are vital as these regions are at greatest risk of future change. This is in part due to disruptions in benthic–pelagic coupling associated with ocean current change and sea ice retreat. Here, we focus on a high-resolution, multi-disciplinary set of measurements that illustrate how microbial processes involved in the degradation of organic matter are directly coupled with inorganic and organic geochemical sediment properties (measured and modelled) as well as the extent/depth of bioturbation. We find direct links between aerobic processes, reactive organic carbon and highest abundances of bacteria and archaea in the uppermost layer (0–4.5 cm depth) followed by dominance of microbes involved in nitrate/nitrite and iron/manganese reduction across the oxic-anoxic redox boundary (approx. 4.5–10.5 cm depth). Sulfate reducers dominate in the deeper (approx. 10.5–33 cm) anoxic sediments which is consistent with the modelled reactive transport framework. Importantly, organic matter reactivity as tracked by organic geochemical parameters (n-alkanes, n-alkanoic acids, n-alkanols and sterols) changes most dramatically at and directly below the SWI together with sedimentology and biological activity but remained relatively unchanged across deeper changes in sedimentology. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'. [ABSTRACT FROM AUTHOR]

The article discusses on long-term patterns of hillslope erosion by earthquake-induced landslides shape mountain landscapes. Topics discusses include information on erosion provenance using a novel combination of the isotopic and molecular composition of organic matter in Lake Paringa, New Zealand; shift in erosion provenance after four large earthquakes over 1000 years; and role of repeated large earthquakes in erosion at high elevations.

In tectonically active mountain ranges, landslides triggered by earthquakes mobilise large volumes of sediment that affect river dynamics. This sediment delivery can cause downstream changes in river geometry and transport capacity that affect the river efficiency to export this sediment out of the epicentre area. The subsequent propagation of landslide deposits in the fluvial network has implications for the management of hazards downstream and for the long-term evolution of topography over multiple seismic cycles. A full understanding of the processes and time scales associated with the removal of landslide sediment by rivers following earthquakes however, is still lacking. Here, we propose a nested numerical approach to investigate the processes controlling the post-seismic sediment evacuation at the mountain range scale, informed by results from a reach scale model. First, we explore the river morphodynamic response to a landslide cascade at the reach-scale using a 2D modelling approach. The results are then used to describe empirically the evacuation of a landslide volume which avoids using a computationally extensive model in catchments which may have thousands of co-seismic landslides. Second, we propose a reduced-complexity model to quantify evacuation times of earthquake-triggered landslide clusters at the scale of a mountain range, examining the hypothetical case of a M w 7.9 earthquake and its aftershocks occurring on the Alpine Fault, New Zealand. Our approach combines an empirical description of co-seismic landslide clusters with the sediment export processes involved during the post-seismic phase. Our results show that the inter-seismic capacity of the mountain range to evacuate co-seismic sediment is critical to assess the sediment budget of large earthquakes, over one to several seismic cycles. We show that sediment evacuation is controlled by two timescales, 1. the transfer time of material from hillslopes to channels and 2. the evacuation time of the landslide deposits once it has reached the fluvial network. In turn, post-seismic sediment evacuation can either be connectivity-limited, when sediment delivery along hillslopes is the main limiting process, or transport-limited, when the transport by rivers is the limiting process. Despite high values of runoff, we suggest that the Southern Alps of New Zealand are likely to be in connectivity-limited conditions, for connection velocities <10 m.yr−1. Connection velocities >2 m.yr−1 are sufficient to allow most of co-seismic sediments to be mobilised and potentially exported out of the range within less than one seismic cycle. Because of the poorly-constrained rate of sediment transfer along hillslopes, our results potentially raise the issue of co-seismic sediment accumulation within mountain ranges over several seismic cycles and of the imbalance between tectonic inputs and sediment export. We, therefore, call for renewed observational efforts to better describe and quantify the physical processes responsible for the redistribution and mobilization of sediment from landslide scars and deposits. [ABSTRACT FROM AUTHOR]

Earthquakes cause widespread landslides that can increase erosional fluxes observed over years to decades. However, the impact of earthquakes on denudation over the longer timescales relevant to orogenic evolution remains elusive. Here we assess erosion associated with earthquake-triggered landslides in the Longmen Shan range at the eastern margin of the Tibetan Plateau. We use the M w 7.9 2008 Wenchuan and M w 6.6 2013 Lushan earthquakes to evaluate how seismicity contributes to the erosional budget from short timescales (annual to decadal, as recorded by sediment fluxes) to long timescales (kyr to Myr, from cosmogenic nuclides and low temperature thermochronology). Over this wide range of timescales, the highest rates of denudation in the Longmen Shan coincide spatially with the region of most intense landsliding during the Wenchuan earthquake. Across sixteen gauged river catchments, sediment flux-derived denudation rates following the Wenchuan earthquake are closely correlated with seismic ground motion and the associated volume of Wenchuan-triggered landslides ( r 2 > 0.6 ), and to a lesser extent with the frequency of high intensity runoff events ( r 2 = 0.36 ). To assess whether earthquake-induced landsliding can contribute importantly to denudation over longer timescales, we model the total volume of landslides triggered by earthquakes of various magnitudes over multiple earthquake cycles. We combine models that predict the volumes of landslides triggered by earthquakes, calibrated against the Wenchuan and Lushan events, with an earthquake magnitude–frequency distribution. The long-term, landslide-sustained “seismic erosion rate” is similar in magnitude to regional long-term denudation rates (∼0.5–1 mm yr −1 ). The similar magnitude and spatial coincidence suggest that earthquake-triggered landslides are a primary mechanism of long-term denudation in the frontal Longmen Shan. We propose that the location and intensity of seismogenic faulting can contribute to focused denudation along a high-relief plateau margin. [ABSTRACT FROM AUTHOR]

Large earthquakes alter physical and chemical processes at Earth's surface, triggering landslides, fracturing rock, changing large-scale permeability, and influencing hydrologic pathways. The resulting effects on global chemical cycles are not fully known. Here we show changes in the dissolved chemistry of the Min Jiang, a river in the Yangtze River (China) headwaters, following the A.D. 2008 Mw 7.9 Wenchuan earthquake. Total solute fluxes transported by the Min Jiang increased after the earthquake, accompanied by an ~4x increase in Na*/Ca ratios (where Na* is Na+ corrected for atmospheric and evaporite contributions) and a 0.000644 ± 0.000146 increase in 87Sr/86Sr isotopic ratios. These changes are consistent with enhanced contribution from silicate sources. We infer that the CO2 consumption rate via silicate-derived alkalinity increased 4.3 ± 0.4 times. If similar changes are associated with other large earthquakes, enhanced solute export could directly link tectonic activity with weathering and alkalinity fluxes that supply nutrients to ecosystems, influence seawater chemistry evolution, and steer Earth's long-term carbon cycle and climate. [ABSTRACT FROM AUTHOR]

The erosion of major mountain ranges is thought to be largely cannibalistic, recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift. Despite this recognition, it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean. Here, we have analyzed the Li content and isotope composition (δ7Li) of suspended sediments sampled along river depth profiles and bed sands in three of the largest Earth's river systems (Amazon, Mackenzie and Ganga-Brahmaputra rivers). The δ7Li values of river-sediments transported by these rivers range from +5.3 to -3.6‰ and decrease with sediment grain size. We interpret these variations as reflecting a mixture of unweathered rock fragments (preferentially transported at depth in the coarse fraction) and present-day weathering products (preferentially transported at the surface in the finest fraction). Only the finest surface sediments contain the complementary reservoir of Li solubilized by water-rock interactions within the watersheds. Li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks. A mass budget approach, based on Li isotopes, Li/Al and Na/Al ratios, solved by an inverse method allows us to estimate that, for the large rivers analyzed here, the part of solid weathering products formed by present-day weathering reactions and transported to the ocean do not exceed 35%. Li isotopes also show that the sediments transported by the Amazon, Mackenzie and Ganga-Brahmaputra river systems are mostly sourced from sedimentary rocks (>60%) rather than igneous rocks. This study shows that Li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present-day weathering processes. Overall, Li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering. [ABSTRACT FROM AUTHOR]

Abstract: The concentration of 10Be in detrital quartz (10Beqtz) from river sediments is now widely used to quantify catchment-wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10Beqtz. Major landslide-triggering events can provide large amounts of low-concentration material to rivers in mountain catchments, but changes in river sediment 10Beqtz due to such events have not yet been measured directly. Here we examine the impact of widespread landslides triggered by the 2008 Wenchuan earthquake on 10Beqtz in sediment samples from the Min Jiang river basin, in Sichuan, China. Landslide deposit material associated with the Wenchuan earthquake has consistently lower 10Beqtz than in river sediment prior to the earthquake. River sediment 10Beqtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence (i.e., with greater than ∼0.3% of the upstream catchment area affected by landslides), because of input of the 10Be-depleted landslide material, but showed no systematic changes where landslide occurrence was low. Changes in river sediment 10Beqtz concentration were largest in small first-order catchments but were still significant in large river basins with areas of . Spatial and temporal variability in river sediment 10Beqtz has important implications for inferring representative denudation rates in tectonically active, landslide-dominated environments, even in large basins. Although the dilution of 10Beqtz in river sediment by landslide inputs may complicate interpretation of denudation rates, it also may provide a possible opportunity to track the transport of landslide sediment. The associated uncertainties are large, but in the Wenchuan case, calculations based on 10Be mixing proportions suggest that river sediment fluxes in the 2–3 years following the earthquake increased by a similar order of magnitude in the 0.25–1 mm and the <0.25 mm size fractions, as determined from 10Beqtz mixing calculations and hydrological gauging, respectively. Such information could provide new insight into sediment transfer, with implications for secondary sediment-related hazards and for understanding the removal of mass from mountains. [Copyright &y& Elsevier]

Abstract: Rapidly eroding, coastal mountain belts, where steep rivers and submarine channels connect upland sources to nearby marine sinks are hotspots of organic carbon transfer from life biomass, soil and exhumed bedrock into geological storage. Using observations from the Southern Alps of New Zealand, and Taiwan, we have mapped this organic pathway to geological carbon sequestration, and can evaluate the magnitude and efficiency of transfers between sources and sinks. We demonstrate that POC is harvested by landsliding, but importantly also by common and widespread surface runoff on steep hillslopes. Although terrestrially sourced POC is found in many sedimentary environments associated with mountain belts and frontier basins, it appears to be most abundantly trapped and preserved in marine turbidites. The loss of all forms of POC in onward transport through short, steep routing systems to this repository is limited. This is in marked contrast to larger routing systems, in which only the most resilient forms of POC survive into long-term deposition. [Copyright &y& Elsevier]

• Assessment of reactive phases in suspended particulates in a major Arctic river. • Neodymium isotopes show equilibration between Fe-Mn oxides and dissolved loads. • Reactive iron flux from the Mackenzie River is large; 0.21(+0.06,−0.05) Tg/yr. • Sedimentary rock weathering provides an important source of labile trace metals. Riverine suspended particulate matter (SPM) is essential for the delivery of micronutrients such as iron (Fe) to the oceans. SPM is known to consist of multiple phases with differing reactivity, but their role in the delivery of elements to the oceans is poorly constrained. Here we provide new constraints on the source and composition of reactive phases in SPM from the Mackenzie River, the largest sediment source to the Arctic Ocean. Sequential leaching of SPM shows that river sediments contain labile Fe phases. We estimate the labile Fe flux is substantial (0.21(+0.06,−0.05) Tg/yr) by quantifying Fe concentrations in weak leaches of the SPM. The labile Fe phase hosts a considerable amount of rare earth elements (REE), including neodymium (Nd). We demonstrate that the labile Fe phase and dissolved load have radiogenic Nd isotope ratios that are identical within uncertainty, but up to 8 epsilon units distinct from the silicate phase. We interpret this as evidence for dynamic cycling between Fe-oxide phases in SPM and the river water, demonstrating the high reactivity of the labile Fe phase. Nd isotope and elemental molar ratios suggest that a significant amount of labile Fe- and Nd-bearing phases are derived from Fe-oxides within the sedimentary source rock rather than silicate mineral dissolution. Thus, sedimentary rock erosion and weathering provides an important source of labile Fe, manganese (Mn) and by extension potentially other trace metals. Our results imply that both past and future environmental change in the Arctic, such as permafrost thaw, may trigger changes to the supply of reactive trace metals. These results demonstrate that a re-evaluation of sediment reactivity within rivers is required where uplifted sedimentary rocks are present. [ABSTRACT FROM AUTHOR]

Maintaining soil health is integral to agricultural production, and the archaeological record contains multiple lines of palaeoclimatic and palaeoenvironmental proxy evidence that can contribute to the understanding and analysis of long-term trajectories of change that are key for contextualizing 21st century global environmental challenges. Soil is a capital resource and its nutrient balance is modified by agricultural activities, making it necessary to ensure soil productivity is maintained and managed through human choices and actions. Since prehistory this has always been the case; soil is a non-renewable resource within a human lifetime. Here, we present and interpret carbon and nitrogen isotope analysis of charred cereals from southern Scandinavia. Anthropogenic effects on soils are evident from the initiation of farming 6000 years ago, as is amendment to counteract its effects. The earliest cereals were planted on pristine soils, and by the late Neolithic, agriculture extensified. By the Iron Age it was necessary to significantly amend depleted soils to maintain crop yields. We propose that these data provide a record of soil water retention, net precipitation and amendment. From the start of the Neolithic there is a concurrent decrease in both Δ13C and δ15N, mitigated only by the replacement of soil organic content in the form of manure in the Iron Age. The cereal isotopes provide a record of trajectories of agricultural sustainability and anthropogenic adaptation for nearly the entire history of farming in the region. • Isotope analyses of charred cereals are used to explore long-term soil health. • Soil amendment was practiced from the start of the Scandinavian Neolithic. • Anthropogenic soil depletion was only mitigated in the Iron Age. [ABSTRACT FROM AUTHOR]