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1. Erosion and weathering in carbonate regions reveal climatic and tectonic drivers of carbonate landscape evolution

   https://doi.org/10.5194/esurf-11-247-2023  

   Ott, Richard; Gallen, Sean F.; Helman, David (January 2023, Earth Surface Dynamics)

   Abstract. Carbonate rocks are highly reactive and can have higher ratios of chemical weathering to total denudation relative to most other rock types. Their chemical reactivity affects the first-order morphology of carbonate-dominated landscapes and their climate sensitivity to weathering.However, there have been few efforts to quantify the partitioning ofdenudation into mechanical erosion and chemical weathering in carbonatelandscapes such that their sensitivity to changing climatic and tectonicconditions remains elusive. Here, we compile bedrock and catchment-averagedcosmogenic calcite–36Cl denudation rates and compare them to weathering rates derived from stream water chemistry from the same regions. Local bedrock denudation and weathering rates are comparable, ∼20–40 mm ka−1, whereas catchment-averaged denudation rates are ∼2.7 times higher. The discrepancy between bedrock and catchment-averaged denudation is 5 times lower compared to silicate-rich rocks, illustrating that elevated weathering rates make denudation more spatially uniform in carbonate-dominated landscapes. Catchment-averaged denudation rates correlate well with topographic relief and hillslope gradients, and moderate correlations with runoff can be explained by concurrent increases in weathering rates. Comparing denudation rates with weathering rates shows that mechanical erosion processes contribute ∼50 % of denudation in southern France and ∼70 % in Greece and Israel. Our results indicate that the partitioning between largely slope-independent chemical weathering and slope-dependent mechanical erosion varies based on climate and tectonics and impacts the landscape morphology. This leads us to propose a conceptual model whereby in humid, slowly uplifting regions, carbonates are associated with low-lying, flat topography because slope-independent chemical weathering dominates denudation. In contrast, in arid climates with rapid rock uplift rates, carbonate rocks form steep mountains that facilitate rapid, slope-dependent mechanical erosion required to compensate for inefficient chemical weathering and runoff loss to groundwater systems. This result suggests that carbonates represent an end member for interactions between climate, tectonics, and lithology. 

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2. Climatic controls on soil production, transport and chemical erosion: Insights from modelling topography, soils and cosmogenic nuclides at Little Lake, Oregon

   https://doi.org/10.1002/esp.70197  

   Reed, Miles M; Ferrier, Ken L; Marshall, Jill A; Roering, Josh J; Perron, J Taylor (November 2025, Earth Surface Processes and Landforms)

   Abstract Predicting physical and chemical erosion rate responses to climate change are an ongoing challenge in geomorphology. A promising approach for investigating this is by measuring transient variations in physical and chemical erosion rates during climatically variable time periods, which can be accomplished by measuring cosmogenic nuclide concentrations and chemical depletion in sedimentary deposits. Interpreting such measurements warrants applying landscape evolution models that track variations in topography, cosmogenic nuclide concentrations and chemical depletion in soils. We applied a recently developed model that tracks these quantities at Little Lake, Oregon. Previous studies documented variations in cosmogenic nuclide concentrations and chemical depletion in paleo‐lake sediments from 50 ka BP to the present, a time interval that includes cooling before the Last Glacial Maximum and warming after it. We extended the model by adding climate‐sensitive parameterizations for mineral dissolution, soil transport by frost heave and soil production by frost cracking. We conducted simulations driven by a paleo‐temperature time series applicable to Little Lake. Simulations showed that a shift to frost heave, frost cracking and temperature‐controlled mineral weathering and alteration elevated¹⁰Be‐inferred denudation rates and lowered chemical depletion fraction (CDF) values comparable to those observed in cores from paleo‐Little Lake. In contrast, introducing a lake with no changes to process operation led to a decline in denudation rates. No single climate‐sensitive process could reproduce both high inferred denudation rates and low CDF, indicating that all of the climate‐sensitive processes modelled in our simulations are needed to explain observed values. Modelled denudation rates increased when the connection between frost cracking intensity and maximum soil production rate was strengthened. The integration of climate‐sensitive processes showed that a handoff from biotically driven processes to frost‐driven ones could induce large, detectable changes in both inferred denudation rate from¹⁰Be and CDF, signalling the potential for globally heterogeneous climate‐denudation rate linkages. 

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3. The influence of erosion and vegetation on soil production and chemical weathering rates in the Southern Alps, New Zealand

   https://doi.org/10.1016/j.epsl.2023.118036  

   Larsen, Isaac J; Eger, Andre; Almond, Peter C; Thaler, Evan A; Rhodes, J Michael; Prasicek, Günther (April 2023, Earth and Planetary Science Letters)

   Chemical weathering influences many aspects of the Earth system, including biogeochemical cycling, climate, and ecosystem function. Physical erosion influences chemical weathering rates by setting the supply of fresh minerals to the critical zone. Vegetation also influences chemical weathering rates, both by physical processes that expose mineral surfaces and via production of acids that contribute to mineral dissolution. However, the role of vegetation in setting surface process rates in different landscapes is unclear. Here we use 10Be and geochemical mass balance to quantify soil production, physical erosion, and chemical weathering rates in a landscape where a migrating drainage divide separates catchments with an order-of magnitude contrast in erosion rates and where vegetation spans temperate rainforest, tussock grassland, and unvegetated alpine ecosystems in the western Southern Alps of New Zealand. Soil production, physical erosion, and chemical weathering rates are significantly higher on the rapidly eroding versus the slowly eroding side of the drainage divide. However, chemical weathering intensity does not vary significantly across the divide or as a function of vegetation type. Soil production rates are correlated with ridgetop curvature, and ridgetops are more convex on the rapidly eroding side of the divide, where soil mineral residence times are lowest. Hence our findings suggest fluvially-driven erosion rates control soil production and soil chemical weathering rates by influencing the relationship between hillslope topography and mineral residence times. In the western Southern Alps, soil production and chemical weathering rates are more strongly mediated by physical rock breakdown driven by landscape response to tectonics, than by vegetation. 

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4. Biogeochemical reactivity in the unsaturated zone revealed by in-situ measurements

   https://doi.org/10.3897/aca.8.e155241  

   Osorio-Leon, Ivan; Rempe, Daniella; Bouchez, Julien; Druhan, Jennifer (May 2025, ARPHA Conference Abstracts)

   Bedrock mineral breakdown in mountainous landscapes sustains long-term atmospheric CO₂ drawdown and releases solutes that sustain ecosystems and set the chemistry of upland stream water. In the unsaturated Bedrock Vadose Zone (BVZ) of hillslopes, minerals, water, reactive gases, and deep roots interact to produce a hotspot of these weathering reactions. New evidence suggests that, in the BVZ, rock moisture sustains evapotranspiration, while deep roots drive deep CO₂ production. However, the contribution of the BVZ to catchment-scale chemical weathering fluxes, and particularly the role of deep roots as drivers of this reactivity, remains poorly constrained due to the difficulty of direct access and measurement of fluids in this compartment. Quantifying this BVZ chemical reactivity is crucial to advance our understanding of upland landscapes' influence on the global carbon cycle and river solute fluxes. Here, we leverage an innovative Vadose-zone Monitoring System (VMS) to investigate these processes and their biogeochemical implications. We present four years of in-situ monitoring of water and pore gas composition in a ~16-meter weathered bedrock profile at the Eel River Critical Zone Observatory (ERCZO) in California. Using this novel instrumentation, we show that the average geogenic chemical solute efflux from the BVZ is 80 ± 34 t km⁻² yr⁻¹, representing approximately 68% of the solute flux measured in the creek draining the hillslope. This highlights the substantial role of the BVZ in catchment-scale weathering. To further interpret these data, we develop a multi-component reactive transport model (RTM) calibrated with batch-reactor experiments using drilling cuttings from the hillslope. Results indicate that solute concentrations arise from a coupled set of primary mineral dissolution and secondary mineral precipitation reactions, which evolve with depth and align with the mineralogical composition gradient from soil to fresh bedrock. Our RTM demonstrates that water storage and drainage timescales in the vadose zone are sufficient to allow significant evolution of pore water due to chemical weathering. However, the model cannot reproduce observed solute concentrations unless elevated CO₂ from deep rhizosphere respiration is incorporated. We find that organic carbon respiration in the deep rhizosphere enhances chemical weathering fluxes at the ERCZO by a factor of ~1.8 ± 0.5, providing direct evidence of accelerated chemical weathering in the Critical Zone due to the presence and function of deeply rooted vegetation. A key characteristic of the linkage between deep rhizosphere respiration and weathering reactions is that, despite strong seasonal variations in water content and O₂ profiles, CO₂ concentrations in the BVZ remain stable, leading to steady weathering rates across seasons and years. Sensitivity analyses with our calibrated RTM reveal that this stability results from the interplay between labile organic carbon oxidation and seasonal hydrological conditions. During dry periods, O₂ is abundant throughout the BVZ due to opening of pore space, but DOC availability is constrained by low water content. Conversely, wet periods enhance availability of labile organic carbon, but O₂ becomes limiting. This balance maintains stable CO₂ profiles and, ultimately, steady weathering rates. We propose that this buffering mechanism allows watersheds to modulate seasonal variability in ecological, hydrological, and climatic inputs, contributing to the pervasive observation of stable concentrations of geogenic solutes in streams draining these landscapes despite their strong variations in discharge. These findings underscore the critical role of the BVZ in regulating solute fluxes from hillslopes, and suggest that deep vadose zone processes must be integrated into biogeochemical and hydrological models to accurately predict catchment responses to environmental change. 

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5. Volcanic Arc Weathering Rates in the Humid Tropics Controlled by the Interplay Between Physical Erosion and Precipitation

   https://doi.org/10.1029/2023AV001066  

   Moore, Angus K.; Méndez Méndez, Kimberly; Hughes, K. Stephen; Granger, Darryl E. (April 2024, AGU Advances)

   Abstract Volcanic arcs are chemical weathering hotspots that may contribute disproportionately to global CO₂consumption through silicate weathering. Accurately modeling the impact of volcanic‐arc landscapes on the Earth's long‐term carbon cycle requires understanding how climate and physical erosion control weathering fluxes from arc landscapes. We evaluate these controls by examining the covariation of stream solutes, sediment geochemistry, and long‐term physical erosion fluxes inferred from cosmogenic³⁶Cl in magnetite in volcanic watersheds in Puerto Rico that span a ca. 15‐fold gradient in specific discharge. Analysis of this data using power‐law relationships demonstrates that CO₂consumption from arc‐rock weathering in the humid tropics is more strongly limited by physical erosion and the supply of primary minerals to the weathering zone than by temperature or the flux of fresh, chemically reactive waters through the critical zone. However, a positive correlation between long‐term physical erosion fluxes and specific discharge is also observed. This indicates that fresh mineral supply in arc environments may ultimately depend on precipitation rates, which may maintain a coupling between arc‐rock weathering fluxes and climate under principally supply limited weathering conditions. 

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