EGU24-2143, updated on 08 Mar 2024
https://doi.org/10.5194/egusphere-egu24-2143
EGU General Assembly 2024
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Time matters: photosynthetic vs. weathering-induced C drawdown and the role of dust inputs along a one-million-year soil weathering gradient on the Galápagos Islands

Franz Zehetner1,2, Martin H. Gerzabek1, J. Gregory Shellnutt3, Pei-Hao Chen1,4, I Nyoman Candra5, Kuo-Fang Huang6, and Der-Chuen Lee6
Franz Zehetner et al.
  • 1Institute of Soil Research, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria
  • 2Galápagos National Park Directorate, Galápagos, Ecuador
  • 3Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan
  • 4Department of Geography, National Taiwan University, Taipei, Taiwan
  • 5Institute of Chemistry Education, University of Bengkulu, Indonesia
  • 6Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan

The Galápagos archipelago, a chain of islands formed by hotspot volcanism on the Nazca tectonic plate, exhibits a pronounced rock age gradient with distance from the volcanic hotspot from west to east. Here, we investigate chemical weathering along a soil chronosequence (1.5 to 1070 ka) under humid conditions. Our results show considerable loss of base cations already in the early to intermediate phases of weathering (e.g. 95% of Na and 78% of Mg lost from the topsoil after 26 ka) and almost complete loss from the entire profile in soils older than 800 ka. Depletion of Si was less pronounced, with topsoil losses of 24% and 63-68% after 26 ka and >800 ka, respectively. Total weathering flux and associated CO2 consumption rates estimated from profile-scale element losses in this study exceeded catchment-scale estimates reported for other volcanic islands or global averages during the early weathering phase, but were much lower in the intermediate and late phases. Nevertheless, total C drawdown was dominated by soil organic C sequestration (70-90% share) rather than inorganic, weathering-induced CO2 consumption during early pedogenesis (≤4.3 ka), and the relative importance switched in the intermediate and late phases (90-95% share of weathering-induced C drawdown at ≥166 ka). Dust deposition derived from a nearby ocean sediment core was <20% of total basalt mass loss at the young and intermediate-aged sites, but reached 40-60% at the older sites (>800 ka). Our results suggest that (1) young volcanic surfaces are very efficient (inorganic and organic) C sinks, (2) the development of thick soil covers at advanced pedogenic stages effectively shields the underlying rocks from further weathering, and (3) dust inputs become an increasingly important biogeochemical factor in such highly weathered environments.

How to cite: Zehetner, F., Gerzabek, M. H., Shellnutt, J. G., Chen, P.-H., Candra, I. N., Huang, K.-F., and Lee, D.-C.: Time matters: photosynthetic vs. weathering-induced C drawdown and the role of dust inputs along a one-million-year soil weathering gradient on the Galápagos Islands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2143, https://doi.org/10.5194/egusphere-egu24-2143, 2024.