| Title: |
Controls on Weathering Zone Thickness in a Rapidly Eroding Mountain Range, Western Southern Alps/Ka Tiritiri o te Moana, New Zealand/Aotearoa. |
| Authors: |
Eger, A.1 (AUTHOR) egera@landcareresearch.co.nz; Winnick, M. J.2 (AUTHOR); Larsen, I. J.2 (AUTHOR); Condron, L. M.3 (AUTHOR); Boitt, G.3 (AUTHOR); Hynek, S. A.4 (AUTHOR); Jercinovic, M. J.2 (AUTHOR); Rhodes, J. M.2 (AUTHOR) |
| Source: |
Journal of Geophysical Research. Earth Surface. Nov2025, Vol. 130 Issue 11, p1-20. 20p. |
| Subject Terms: |
*Chemical weathering; *Soil depth; *Weathering; *Erosion; *Carbon sequestration; Water-rock interaction; Analytical geochemistry |
| Geographic Terms: |
Southern Alps/Kā Tiritiri o te Moana (N.Z.); New Zealand |
| Abstract: |
Tectonic fracturing in uplifting mountains facilitates fluid‐rock interactions, causing downward propagation of chemical weathering fronts. In contrast, erosion in uplifting mountains removes fractured and chemically altered bedrock, thinning the weathering zone. The interplay of these processes sets weathering zone thickness, but despite the disproportionate influence of chemical weathering in mountains on global biogeochemical cycles, it is unclear where within the weathering zone those chemical reactions predominantly occur. Here we present geochemical data from a 300 m‐deep drill core and results from reactive transport modeling to assess weathering zone characteristics in the Southern Alps/Kā Tiritiri o te Moana of New Zealand/Aotearoa. Our findings indicate that soil is thin and chemical weathering fronts are shallow, with only apatite (and likely calcite) weathering extending below the soil‐bedrock boundary. Simulations indicate that soil thickness is primarily controlled by porosity‐generating plagioclase weathering and that simulated soil thicknesses are consistent with local precipitation and denudation rates. However, simulations also show that if all 6 m of annual precipitation infiltrated bedrock, chemical weathering fronts would extend substantially deeper than observed. We infer that the porosity contrast between soil and rock limits bedrock fluid flow, slowing the propagation of chemical weathering. Erosion and limited fluid‐mineral interaction in deep fractures result in a thin weathering zone, suggesting that silicate weathering in uplifting mountains occurs primarily within soil, rather than bedrock. Our measurements suggest that oxidative weathering of petrogenic carbon has been overestimated previously, but, consistent with prior work, surface processes in the study area result in net consumption of atmospheric CO2. Plain Language Summary: Earth's geochemical cycles and long‐term climate are strongly influenced by the dissolution of minerals in mountain landscapes. However, it is unclear whether these chemical reactions occur primarily within soil, deep bedrock, or in other parts of the landscape. We conducted geochemical measurements on a 300 m‐long drill core from western Southern Alps/Kā Tiritiri o te Moana, Aotearoa/New Zealand and simulated the depth at which different minerals were removed due to dissolution by infiltrating rainfall. Even though the rock has been fractured by plate tectonics, we found that soils were thin and that only the most soluble minerals have been depleted from the bedrock and only at shallow depths. Our simulations predict the observed soil thicknesses and mineral dissolution depths when all 6 m of annual rainfall infiltrates into the soil, but only a fraction percolates into bedrock. Even though mineral dissolution occurs primarily at shallow depths within the soil, it contributes to sequestration of atmospheric CO2. The findings show how the interaction of water and rock in rapidly uplifting mountains influences climate on geological timescales. Key Points: In the study region soil is thin and weathering fronts are shallow with very limited weathering extending below the soil‐bedrock boundaryIf reduced bedrock infiltration is considered, reactive transport modeling can reproduce the observed soil thickness and weathering frontsSilicate weathering primarily occurs in soils, and surface processes consume atmospheric CO2, while oxidation of petrogenic carbon is minor [ABSTRACT FROM AUTHOR] |
| : |
Copyright of Journal of Geophysical Research. Earth Surface is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) |
| Database: |
GreenFILE |