Iron (hydr)oxide formation in Andosols under extreme climate conditions
Klaes, Bjoern
Universitat Trier
Thiele-Bruhn, Soeren
Universitat Trier
Woerner, Gerhard
University of Gottingen
Hoeschen, Carmen
Technical University of Munich
Mueller, Carsten W.
Technical University of Munich
Marx, Philipp
Universitat Trier
Arz, Helge Wolfgang
Leibniz Institut fur Ostseeforschung Warnemunde
Breuer, Sonja
Fed Inst Geosci & Nat Resources BGR
Kilian, Rolf
Journal
Scientific Reports
ISSN
2045-2322
Open Access
gold
Volume
13
Redox-driven biogeochemical cycling of iron plays an integral role in the complex process network of ecosystems, such as carbon cycling, the fate of nutrients and greenhouse gas emissions. We investigate Fe-(hydr)oxide (trans)formation pathways from rhyolitic tephra in acidic topsoils of South Patagonian Andosols to evaluate the ecological relevance of terrestrial iron cycling for this sensitive fjord ecosystem. Using bulk geochemical analyses combined with micrometer-scale-measurements on individual soil aggregates and tephra pumice, we document biotic and abiotic pathways of Fe released from the glassy tephra matrix and titanomagnetite phenocrysts. During successive redox cycles that are controlled by frequent hydrological perturbations under hyper-humid climate, (trans)formations of ferrihydrite-organic matter coprecipitates, maghemite and hematite are closely linked to tephra weathering and organic matter turnover. These Fe-(hydr)oxides nucleate after glass dissolution and complexation with organic ligands, through maghemitization or dissolution-(re)crystallization processes from metastable precursors. Ultimately, hematite represents the most thermodynamically stable Fe-(hydr)oxide formed under these conditions and physically accumulates at redox interfaces, whereas the ferrihydrite coprecipitates represent a so far underappreciated terrestrial source of bio-available iron for fjord bioproductivity. The insights into Fe-(hydr)oxide (trans)formation in Andosols have implications for a better understanding of biogeochemical cycling of iron in this unique Patagonian fjord ecosystem.
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