Sen Xu analyzed the changes in weathering fluxes from the headwaters of the Yangtze River over a period of seven years. During this time, climate warmed substantially, and Sen’s data show a substantial increases in solute fluxes from evaporite weathering (especially in the permafrost-rich headwaters of the JSR river). These changes could enhance secondary carbonate precipitation and lead to CO2 release. In addition, sulfide weathering becomes relatively more important than silicate and carbonate weathering reactions. This finding implies that warming and hydrological changes lead to a shift toward less CO2 drawdown and more CO2 release from rock weathering.
About: Xu, S., Bufe, A., Kemeny, P.C., Klaus, M., Zhong, J., Ma, T., Li, D., Li S.L., (2025). Climate warming and strengthened hydrologic cycle accelerate CO2 release from rock weathering. Geochimica et Cosmochimica Acta, 407, 174-192. Journal Link
A new paper on the fluxes and sources of CO2 outgassing from different floodplain deposits is out now. Sophia measured CO2 that is emitted from river channels, riverbank sediments and older floodplain deposits along the Rio Bermejo in Argentina. She found the highest fluxes occur away from the modern channel and riverbanks. Here, emissions are highly seasonal (highest fluxes during the wet season) and are influenced by the respiration of recent and old organic matter.
Based on her measurements, Sophie estimated that sediments and soils in the Rio Bermejo floodplains emit almost 450 tons of carbon per square kilometer and per year.
About: Dosch, S., Hovius, N., Bufe, A., Repasch, M., Scheingross, J., Vieth-Hillebrand, A., Sachse, D. (2025). CO2 Fluxes Driven by Floodplain Morphology and Seasonality at the Rio Bermejo, Argentina. Journal of Geophysical Research: Biogeosciences, 130(8), e2024JG008517. Journal Link
About: Erlanger et al., (2024), Nature Geosciences (link)
In our new paper, we use stream water chemistry in two river catchments of the central Apennines to infer the CO2 fluxes from surficial weathering reactions as well as the CO2 degassing from depths.
Photo Credit: Erica Erlanger
In the east, where the crust is thick and cold, carbon fluxes from silicate weathering dominate the carbon budget. In contrast, the western catchment is underlain by thin and hot crust. Here, carbon fluxes are dominated by CO2 degassing from the crust and mantle, and these fluxes are up to 50-times higher than the carbon drawdown from silicate weathering.
You can check out a more detailed press-release by the GFZ here.
About: Xu et al., (2024), Environmental Science & Technology (link)
Sampling in the Yangtze Headwaters. Copyright Sen Xu
In a new paper spearheaded by Sen Xu from Tianjin University, we investiagate the role of warming for the export of dissolved inorganic carbon (DIC) in two major rivers that drain the eastern Qinghai−Tibetan Plateau.
Warming trend in the Jinsha River Basin
In the Jinsha River that has 51% of its catchment underlain by continuous permafrost, DIC fluxes increase substantially over the past 40 years. Changes in river discharge play a negligible role for that increase in flux. Instead, the increase in DIC fluxes correlates most strongly with the temperature increase.
DIC fluxes: Pink points are the total flux and yellow points the flux normalized for variations in runoff.
The Yalong river that is situated at lower elevation and has only 14% permafrost cover does not show a substantial increase in DIC fluxes. This observation suggest that the presence or absence of permafrost may strongly modulate the sensitivity of inorganic carbon fluxes to global warming.
About: Turowski et al., (2024), Earth Surface Dynamics (link)
What sets the width of river valleys? In a paper published today, we propose a new model for the width of river valleys. It considers valley width as a competition of lateral channel motion and the uplift and erosion of valley walls. Here is the equation:
W is valley width qL is the lateral sediment transport capacity qH is the lateral input of sediment from hillslopes U is the uplift rate W0 is the channel belt width WC is the channel width
A dimensionless “mobility-uplift number, MU” expresses that competition where:
The model implies that valley width varies between two extremes: At a minimum, valleys are as wide as the channel. Such narrow valleys occur where rivers drain rapidly uplifting landscapes. At a maximum, valleys encompass wide channel belts. These two extremes are connected by a logarithmic function of the mobility-uplift number.
Despite its conceptual simplicity, the model compares surprisingly well to several datasets including experiments and a large compilation of valley widths in the Himalaya.
This model explains valley width in a landscape that has reached steady state. How do valleys evolve over time and what sets the maximum width of valleys? We are working on these questions in an upcoming publication.
In this new paper, we analysed weathering data from different mountain ranges. We found that silicates, carbonates and sulfides had different non-linear erosion sensitivities. The behaviors are very similar in all study areas. As a result, all datasets show that CO2 drawdown from rock-weathering is at a maximum at moderate erosion rates of ~0.07 mm/yr.
About: Xu et al., (2024), Geochimica et Cosmochimica Acta (link)
A multitude of different minerals are exposed at the surface of the Earth. Under the influence of acid waters, these minerals slowly dissolve and transform. These ‘chemical weathering’ reactions release nutrients, and they change move carbon between rocks, water, and the atmosphere. Rivers collect elements dissolved in soils. Therefore, we can use river chemistry to study the weathering reactions that occur within landscapes.
Deep Gorge carved by the Tongtian River – tributary to the Yangtze River – and located on the steep eastern margin of the Qinghai-Tibet Plateau
In large drainage basins that host many different rock-types, it can be a challenge to interpret the chemistry of rivers. In particular evaporite (“salt”) minerals can strongly dominate the weathering budget, and their contribution is difficult to distinguish from that of silicate, carbonate, or sulfide minerals.
Proportions of different minerals contributing to river solutes on the Qinghai-Tibet Plateau
In our work, we used a series of isotopes and major element chemistry to obtain a weathering budget in the headwaters of three of the largest rivers in the world – the Yangtze, Mekong, and Salween Rivers. We then analyzed how this weathering budget depends on erosion rates, rainfall and permafrost extent. We found that mountain building and attendant erosion play a major role in weathering of the studied rivers. Erosion boosts weathering reactions that may move CO2 from the rock-record to the atmosphere.
Chumar River with a high load of red suspended sediment located on the Qinghai-Tibet Plateau
About: Roda-Boluda et al., (2023), JGR-Earth Surface (link)
Spectacular view along the Poerua River showcasing steep hillslope and the high relief of the Southern Alps of New Zealand
Where rocks are uplifted, they get eroded by wind, water, ice, and gravity. Erosion creates large volumes of sediment that are transported from the mountains to sedimentary basins. The rates of erosion are fundamentally driven by mountain uplift. However, the climate can also impact the breakdown and movement of rock. For example, heavy and sustained precipitation can trigger landslides, glaciers grind their bases to a fine powder, and cycles of freezing and thawing can efficiently break down solid bedrock. Geologists currently debate how climate affects erosion on the scale of an entire mountain range.
Bare Hillslopes with scree – subject to periglacial erosion
The Southern Alps of New Zealand are a fantastic place to dig deeper into the link between climate and erosion. Along a narrow range, metamorphosed sandstones are lifted up at multiple millimeters per year – making the Southern Alps one of the fastest deforming mountain ranges on the planet. A relief of over 3000 m captures the westerly winds and leads to heavy rains on the Western Southern Alps with yearly precipitation of 2 – 10 meters. Moreover, the Southern Alps are subject to so-called “paraglacial” (conditioned by recently retreated glaciers) and “periglacial” (in a zone where temperatures fluctuate around 0ºC) erosion processes: Where glaciers recently retreated, hillslopes have become unstable and temperatures around freezing cause efficient freeze-thaw cycles.
During one month in the field, we sampled sand from a number of rivers that drain the Western Southern Alps. Measuring the concentration of cosmogenic beryllium-10, we estimated the average erosion rate upstream of each sample point. Then, we studied how erosion rates vary with different topographic and climatic parameters.
Plot suggesting a correlation between erosion and peri- and paraglacial erosion processes that are most active between ~1500 – 2000 m in the study area
We found that erosion rates were highest in those rivers that had a substantial portion of their catchment at an elevation of 1500 – 2000m. At these elevations para- and periglacial processes are particularly strong in the Southern Alps. In contrast, rainfall and erosion rates did not correlate well.
Overall, the pattern of erosion is set by the uplift of the rocks. However, our data suggest that these erosion rates can be modulated substantially by processes related to freeze-thaw and glacier retreat.
Moving 1000 kg of sand for analysis of cosmogenic nuclide concentrations
Valley shapes in the Morača river, Montenegro (left) and the Naryn river, Kyrgyzstan (right)
River valleys come with a wide range of shapes, from narrow canyons to wide plains. We know very little about what controls their width. To first order, wide valleys occur in big rivers. Indeed, compilations show a relationship between water discharge and valley width. They also show that valleys narrow as valley walls get harder to erode. However, widths scatter over multiple orders of magnitude for the same water discharge and valley-wall lithology. Something more controls the shape of valleys.
Valley width as a function of drainage area of streams in the French Alps with large scatter for a given drainage area. Adapted from Langston & Temme 2019, GRL
To investigate these additional controls, we turned to paired river terraces. Paired river terraces preserve the geometry of past valley shapes at a single point along the river. Moreover, many terrace sequences can be linked to cycles of wet and dry climate. In that case, all terrace levels preserve valleys that were formed under similar climatic and lithologic conditions.
Relationship between valley width and valley height
We compiled valley widths from 12 globally distributed – and climatically formed – terrace sequences. For all sequences, we find a very clear relationship between the height and width of the valley (The height refers to the height of the entire valley wall, not the height of individual terraces). This finding raises the following question: Does a process related to valley height impact the width of valleys?
A terrace sequence in the Quebrada del Toro, Argentina, showing sediment transport slopes from upper terrace levels into the stream
Based on our observation, we propose a new model for valley formation. Rivers widen valleys by lateral erosion of the valley walls. The eroded sediment has to be removed before erosion can continue. At the same time, valley hillslopes are eroding and deliver sediment to streams. A linear relationship between valley width and valley height can be explained only when sediment supply from hillslopes and sediment removal by streams are in balance. Hence, sediment supply from hillslopes may limit valley widths.
Valley width as a balance between sediment supply from hillslopes (Eh) and the transport capacity of the stream (qL)
The erosion of active mountain ranges exposes rocks to the surface of the Earth. Acidic rain- and soil waters slowly dissolve minerals in these rocks. Depending on the type of mineral, these “chemical weathering” reactions can either draw down CO2 from the atmosphere or release CO2. Therefore, uplift of different rock-types in mountain ranges can potentially affect Earth’s climate.
The steep peaks of the Gonga Shan erode at rates of almost 10 millimeters per year. Photo: Niels Hovius
In our recent study, we wanted to investigate how rock-type affects the balance of CO2 drawdown and release in mountains. We collected waters from small streams on the eastern Tibetan Plateau. These streams drain regions with either metasedimentary or granitoid rocks. Moreover, the erosion rates of the mountains vary by more than two orders of magnitude. This contrast can be clearly seen in the shape of the landscape.
Rolling hills on the Eastern Tibetan plateau are lowered at rates of less than 0.1 millimeters per year. Photo: Kristen Cook
Across the erosion rate gradient, we find that granitoid lithologies have generally lower weathering rates than metasedimentary rocks. Using a mixing model, we can infer the carbon balance of these weathering reactions. For all lithologies, increasing erosion shifts weathering from CO2 drawdown to CO2 release. This shift is most dramatic for metasedimentary rocks.
With increasing erosion, weathering shifts from drawing down CO2 to releasing CO2 for all lithologies. The shift is most prominent in the metasedimentary rocks.
Throughout the history of a mountain belt, different rock-types are exposed to the surface of the Earth. Our results suggest that changes in the exposure of rocks can alter the carbon cycle and earth’s climate in addition to changes in erosion rates.
Bufe, A., Cook, K.L., Galy, A., Wittmann, H., Hovius, N. (2022). The effect of lithology on the relationship between denudation rate and chemical weathering pathways. Evidence from the eastern Tibetan Plateau. Earth Surface Dynamics. 10(3), 513-530. Journal Link
