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1. Chemical Weathering and Physical Erosion Fluxes From Serpentinite in Puerto Rico

   https://doi.org/10.1029/2024JF007776  

   Moore, Angus K; Méndez_Méndez, Kimberly; Hughes, K Stephen; Granger, Darryl E (January 2025, Journal of Geophysical Research: Earth Surface)

   Abstract Weathering of ultramafic rocks emplaced at low latitude during arc‐arc and arc‐continent collisions may provide an important sink for atmospheric CO₂over geologic timescales. Accurately modeling the effects of ultramafic rock weathering on Earth's carbon cycle and climate requires understanding mass fluxes from ultramafic landscapes. In this study, physical erosion and chemical weathering fluxes and weathering intensity are quantified in 15 watersheds across the Monte del Estado, a serpentinite massif in Puerto Rico, using measurements of in situ³⁶Cl in magnetite, stream solute fluxes, and sediment geochemistry. Despite high relief in the study watersheds, erosion fluxes are moderate (22–109 tons km⁻² yr⁻¹), chemical weathering fluxes are large (55–143 tons km⁻² yr⁻¹), and weathering intensities are among the highest yet reported for silicate‐rock weathering (up to 0.88). We use these data to parameterize power‐law relationships between weathering, erosion, and runoff. We interpret the relative importance of climate versus erosion in setting weathering fluxes and CO₂consumption from the best‐fit power‐law slopes. Weathering fluxes from tropical, montane serpentinite landscapes are found to be strongly controlled by runoff and weakly controlled by the supply of fresh rock to the weathering zone through physical erosion. The strong runoff dependence of weathering fluxes implies that, to the extent that precipitation rates are coupled to global temperature, ultramafic landscapes may be important participants in the negative silicate weathering feedback, increasing (decreasing) CO₂consumption in response to a warming (cooling) climate. Thus, serpentinite landscapes may help stabilize Earth's climate state through time. 

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2. 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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3. The rise of New Guinea and the fall of Neogene global temperatures

   https://doi.org/10.1073/pnas.2306492120  

   Martin, Peter E; Macdonald, Francis A; McQuarrie, Nadine; Flowers, Rebecca M; Maffre, Pierre_J Y (October 2023, Proceedings of the National Academy of Sciences)

   The ~2,000-km-long Central Range of New Guinea is a hotspot of modern carbon sequestration due to the chemical weathering of igneous rocks with steep topography in the warm wet tropics. These high mountains formed in a collision between the Australian plate and ophiolite-bearing volcanic arc terranes, but poor resolution of the uplift and exhumation history has precluded assessments of the impact on global climate change. Here, we develop a palinspastic reconstruction of the Central Range orogen with existing surface geological constraints and seismic data to generate time–temperature paths and estimate volumes of eroded material. New (U-Th)/He thermochronology data reveal rapid uplift and regional denudation between 10 and 6 Mya. Erosion fluxes from the palinspastic reconstruction, calibrated for time with the thermochronological data, were used as input to a coupled global climate and weathering model. This model estimates 0.6 to 1.2 °C of cooling associated with the Late Miocene rise of New Guinea due to increased silicate weathering alone, and this CO₂sink continues to the present. Our data and modeling experiments support the hypothesis that tropical arc-continent collision and the rise of New Guinea contributed to Neogene cooling due to increased silicate weathering. 

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4. Arc Heat Flow and Magmatic Heat Budgets

   https://doi.org/10.1029/2025RG000922  

   Ingebritsen, S E; Sawayama, Kazuki; Taran, Yuri; Chiodini, Giovanni; Kagiyama, Tsuneomi; Shinohara, Hiroshi; Rowland, Julie V; Black, Benjamin A (June 2026, Reviews of Geophysics)

   Abstract We evaluate hydrothermal heat loss from 11 volcanic‐arc segments (∼6,000 km of arc length, ∼10% of the global total), motivated by the observation that much magmatic heat ultimately crosses the land surface as heated aqueous fluid. Heat loss takes place by volcanic eruption, geothermal heat conduction to the surface, fumarolic (vapor) discharge, thermal springs, and discharge of groundwater that has been heated by only a few degrees. Heat loss by extrusion of volcanic products ranges from 0.1 to ∼4 MW/km. For some arc segments, the hydrothermal heat loss is dominated by “slightly thermal” springs (maximum ∼10 MW/km arc length) or thermal springs (maximum ∼21 MW/km), but more commonly by hydrothermal steam vents and volcanic fumaroles (maximum ∼7 MW/km). Total hydrothermal heat‐loss rates range from <2.5 MW/km (Southwest Japan, Cascade Range, Northeast Japan, Kurils) to ≥8 MW/km (Ryukyu, Apennines, Taupo Volcanic Zone). We use these hydrothermal heat losses to estimate rates of magma supply, and combine these estimates of magma supply with existing estimates of eruption rates to obtain intrusion:extrusion ratios. Potential causal influences include state‐of‐stress and the abundance of silicic magma in the midcrust. Likely causes of along‐arc variations range from the near‐surface (0–5 km) hydraulic architecture (Cascade Range) to the nature of the subducting plate (Ryukyu vs. the rest of southwest Japan). Inferred intrusion: extrusion ratios are generally between 0.5 and 9. Whole‐arc comparisons between heat‐flow‐based intrusion rates and those based on volatile fluxes and petrologic models are complicated by the wide range of along‐arc behavior and the fact that we sometimes rely on volatile fluxes (e.g., SO₂) to help calculate hydrothermal heat losses, so that the data sets are not fully independent. However, reasonable agreement can be demonstrated in some examples of arc subsections. 

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5. 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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