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<p>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&#xa0;m and extending to the basin floor (~ 160&#xa0;m), was shown to exhibit elevated temperatures and high concentrations of H<sub>2</sub>S, consistent with inputs of volcanically derived fluids. A bubble-like acoustic scattering and the detection of CH<sub>4</sub> 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&#xa0;μm) and ammonium (25&#xa0;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 (C1<sub>245(350)-440</sub> and C3<sub>270(400)-505</sub>) 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 H<sub>2</sub>S from the seabed and microbial sulfate reduction may contribute to the observed H<sub>2</sub>S 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.</p>

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Euxinic conditions and altered biogeochemical cycles in a Patagonian fjord influenced by volcanic activity

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月18日

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  • Iván Pérez-Santos,
  • Paulina Montero,
  • Marcelo H. Gutiérrez,
  • Gerdhard L. Jessen,
  • Alexander Galán,
  • Laura Farías,
  • Leonardo Castro,
  • Camilo Rodriguéz-Villegas,
  • Patricio A. Díaz,
  • Claudia Aracena,
  • Elías Pinilla,
  • Karen Sanzana,
  • Aranza L. Pérez,
  • Karina Fuentes,
  • Constanza Asmut,
  • Guido Mancilla-Gutiérrez,
  • Gabriel Soto,
  • Cynthia Urrutia,
  • Claudio Navarro,
  • Matías Castro,
  • David Silva,
  • Salma Espinoza,
  • Laura A. Bristow,
  • Morten Larsen,
  • Osvaldo Ulloa

摘要

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.