OOS2025-517, updated on 26 Mar 2025
https://doi.org/10.5194/oos2025-517
One Ocean Science Congress 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Effect of matter of glacial origin on Southern Ocean ecosystems: A Kerguelen Island case study
Rhea Thoppil, Ingrid Obernosterer, Philippe Catala, Olivier Crispi, Audrey Guéneuguès, Barbara Marie, and Stéphane Blain
Rhea Thoppil et al.
  • Laboratoire d'Océanographie Microbienne (LOMIC), CNRS, Sorbonne University, Banyuls sur Mer, France (rhea.thoppil@obs-banyuls.fr)

Being the largest high-nutrient-low-chlorophyll (HNLC) region, surface waters in the Southern Ocean (SO) hold a large potential for biological activity, with implications for carbon dioxide drawdown. However, the trace element iron (Fe) is a major constraint for microbially-mediated processes. During the past 40 years, the ice cap on Kerguelen Island (SO) has decreased in surface by 20% and its disappearance is predicted by the end of the century. This glacial erosion could be a significant new source of Fe, but whether Fe contained in matter of glacial origin (MGO) is bioavailable to microorganisms is not well understood. The main objective of the project MARGO (Matter of glacial origin and its fate in the ocean) is to quantify the input of Fe to the waters surrounding Kerguelen Island and to investigate its consequences on ecosystem functioning. We present here results from onboard incubation experiments carried out during a cruise in February 2024 to investigate the bioavailability of matter of glacial origin for marine bacteria and phytoplankton in Fe-limited HNLC waters. Our observations reveal that Fe in the form of glacial colloids (20-200 nm) stimulates phytoplankton and bacterial growth and leads to modifications in the composition of these microbial communities. Fe-related gene annotation analyses showed a higher abundance of siderophore synthesis and transport genes in communities growing in the presence of glacial colloids as compared to unamended controls. These observations suggest that siderophores, produced by bacteria, could be one mechanism rendering Fe of glacial origin bioavailable, and could potentially lead to strong interactions between bacteria and phytoplankton. Our results provide novel insights on the influence of glacial Fe on marine microbes and the consequences on the carbon cycle. They further highlight the importance of processes occurring along the glacier-to-ocean continuum for biogeochemical processes in the SO.

How to cite: Thoppil, R., Obernosterer, I., Catala, P., Crispi, O., Guéneuguès, A., Marie, B., and Blain, S.: Effect of matter of glacial origin on Southern Ocean ecosystems: A Kerguelen Island case study, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-517, https://doi.org/10.5194/oos2025-517, 2025.