Abstract
Fjords in Chilean Patagonia are highly dynamic systems shaped by land-derived inputs, oceanic exchange, and volcanic activity. Prior to the elaboration of the present article, no in-depth investigation had been undertaken into the anoxic or euxinic conditions of fjords in this region. Consequently, the present research represents an interdisciplinary oceanographic approach to studying Quitralco Fjord (45.6° S, 73.1° W; 2022–2025) and provides the first evidence of a volcanically influenced euxinic fjord in Chilean Patagonia. A subsurface anoxic layer, beginning between 90 and 120 m and extending to the basin floor (~ 160 m), was shown to exhibit elevated temperatures and high concentrations of H2S, consistent with inputs of volcanically derived fluids. A bubble-like acoustic scattering and the detection of CH4 within this layer suggest an external input of the gas into the water column. Although largely stagnant, this layer shifted vertically over time, likely driven by interannual deep-water renewal. Within the euxinic layer, nitrate was completely depleted, while high phosphate (20 μm) and ammonium (25 μm) concentrations indicated an active sulfur cycle. A pronounced deep fluorescence maximum was also detected in the dark, anoxic basin, attributed to fluorescent dissolved organic matter (fDOM) dominated by two humic-like components (C1245(350)-440 and C3270(400)-505) with high aromaticity. Microbial community composition changed markedly across the redox gradient, while geochemical and microbiological fingerprints exhibited shifts in metabolic potential through the water column. Geological emissions of H2S from the seabed and microbial sulfate reduction may contribute to the observed H2S accumulation, enhancing and sustaining euxinic conditions, thereby strongly influencing the basin’s biogeochemical cycles. Overall, the present study reveals a previously unrecognized link between volcanic activity and fjord biogeochemistry, documenting for the first time the development of euxinic conditions in a Patagonian fjord in Chile.
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Acknowledgements
We thank the chemical and microbiological laboratories of the Patagonia Ecosystem Research Center (CIEP) and the University of Concepción for the biogeochemical analyses presented in this manuscript. Special thanks to the crews of the Jürgen Winter, Antiqua, and Don Felipe III vessels for supporting data collection in the Quitralco Fjord.
Funding
Iván Pérez-Santos was funded by FONDECYT 1211037, 1251038, 1230152, COPAS COASTAL FB210021, and CIEP R20F002. Alexander Galán has been partially supported by ANID, Concurso de Fortalecimiento al Desarrollo Científico de Centros Regionales 2020 CLAP-R20F0008. Paulina Montero was funded by FONDECYT 11230763, COPAS COASTAL FB210021, and PATSER R20F002. Marcelo Gutiérrez was funded by COPAS COASTAL FB210021. Gerdhard Jessen was funded by FONDECYT 1251543 and COPAS COASTAL FB210021. Laura Farias would like to thank the Instituto Milenios Secos ICM 2019–015, CR2 FONDAP-ANID 1522A0001, and FONDECYT 1250210. Morten Larsen and Laura Bristow were supported by the European Union’s Horizon Europe ERC Synergy Grant program under grant agreement No. 101167445 (RECLESS). Matías Castro and Osvaldo Ulloa were supported by the Millenium Institute of Oceanography, grant ICN2025_030.
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Pérez-Santos, I., Montero, P., Gutiérrez, M.H. et al. Euxinic conditions and altered biogeochemical cycles in a Patagonian fjord influenced by volcanic activity.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-58650-4
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DOI: https://doi.org/10.1038/s41598-026-58650-4
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