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<p>The mesopelagic zone, between 100 m and 1,000 m depth, is a crucial layer in which carbon preliminary coming down from the surface is transformed before a portion makes it into the deep ocean. While eddies and their fronts influence surface productivity and carbon export, their effects deeper in the water column remain poorly understood. Here we show the importance and contribution of dark carbon fixation—the conversion of inorganic into organic carbon by prokaryotes—across five contrasting hydrological features in the North Atlantic, using isotopic tracers and quantification of chemoautotrophy genes. The approach allows simultaneous assessment of dark carbon fixation and heterotrophic activity of prokaryotes living suspended in seawater and attached to gravitationally settling particles. Our results highlight that heterotrophic prokaryotes attached to sinking particles contribute up to 21% of the total organic carbon required to sustain prokaryotic metabolism under the influence of eddy fronts. By contrast, dark carbon fixation by suspended prokaryotes can contribute up to half of the total carbon input to the mesopelagic zone in the cyclonic eddy. Our findings challenge the idea that carbon cycling in the mid-depth ocean is uniform and highlight the need to integrate microbial fractions and physical heterogeneity into ocean carbon models.</p>

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Distinct contributions of suspended and sinking prokaryotes to mesopelagic carbon budget

  • 期刊论文

  • 发表日期：

    2026年1月8日

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  • Pauline Le Coq,
  • Urania Christaki,
  • France Van Wambeke,
  • Elisabeth Chevillon,
  • Bruno Zakardjian,
  • Marc Garel,
  • Sophie Guasco,
  • Chloé M. J. Baumas,
  • Anne E. Dekas,
  • Patricia Bonin,
  • Badr Al Ali,
  • Maéva Gesson,
  • Frédéric Le Moigne,
  • Mireille Pujo-Pay,
  • Olivier Crispi,
  • Olivier Grosso,
  • Thierry Moutin,
  • Nagib Bhairy,
  • Emmanuel de Saint Léger,
  • Laurent Memery,
  • Lionel Guidi,
  • Fabrice Armougom,
  • Hans-Peter Grossart,
  • Christian Tamburini

摘要

The mesopelagic zone, between 100 m and 1,000 m depth, is a crucial layer in which carbon preliminary coming down from the surface is transformed before a portion makes it into the deep ocean. While eddies and their fronts influence surface productivity and carbon export, their effects deeper in the water column remain poorly understood. Here we show the importance and contribution of dark carbon fixation—the conversion of inorganic into organic carbon by prokaryotes—across five contrasting hydrological features in the North Atlantic, using isotopic tracers and quantification of chemoautotrophy genes. The approach allows simultaneous assessment of dark carbon fixation and heterotrophic activity of prokaryotes living suspended in seawater and attached to gravitationally settling particles. Our results highlight that heterotrophic prokaryotes attached to sinking particles contribute up to 21% of the total organic carbon required to sustain prokaryotic metabolism under the influence of eddy fronts. By contrast, dark carbon fixation by suspended prokaryotes can contribute up to half of the total carbon input to the mesopelagic zone in the cyclonic eddy. Our findings challenge the idea that carbon cycling in the mid-depth ocean is uniform and highlight the need to integrate microbial fractions and physical heterogeneity into ocean carbon models.