Hydrothermal mercury: the natural history of a contaminant

, ,

Our colleague Hélène Planquette participated in an international study coordinated by the CNRS aiming to estimate the contribution of hydrothermal sources to the mercury stock present in the oceans.

This study has just been published in the journal Nature Geoscience and is the subject of a CNRS press release:

An international team of researchers, coordinated by the CNRS (see inset), has established the first global estimate of hydrothermal mercury (Hg) emissions from mid-ocean ridges. The UN Minamata Convention on Mercury aims to reduce human exposure to toxic mercury by reducing anthropogenic emissions. We are primarily exposed through the consumption of fish that bioaccumulate Hg from the ocean. The current paradigm is that anthropogenic mercury emissions (currently 3,100 tons per year) are responsible for a 21% increase in the global oceanic mercury reservoir. This estimate is inaccurate because we do not know how much natural mercury was present in the ocean before the start of anthropogenic emissions.

We are also unable to quantify the impact of anthropogenic emissions on Hg levels in fish. Hydrothermalism is the only direct source of natural Hg to the ocean. Previous studies, based solely on hydrothermal fluid measurements, suggested that hydrothermal Hg inputs could range from 20 to 2,000 tons per year. This new study used measurements of hydrothermal plumes, seawater, and rock cores in addition to fluid measurements from the Trans-Atlantic Geotraverse (TAG) hydrothermal source on the Mid-Atlantic Ridge.

The combination of observations suggests that the majority of enriched Hg in the fluids would be diluted in seawater, and a small fraction would precipitate locally. Extrapolation of the results indicates that the overall hydrothermal Hg flux from mid-ocean ridges is low (1.5 to 65 tons per year) compared to anthropogenic Hg emissions. Although this suggests that the majority of Hg in the ocean is of anthropogenic origin, it also raises hope that strict implementation of emission reductions under the Minamata Convention will reduce mercury levels in fish and human exposure.


Article Reference:

Torres-Rodriguez, N., Yuan, J., Petersen, S. et al. Mercury fluxes from hydrothermal venting at mid-ocean ridges constrained by measurements. Nat. Geosci. (2023).

The ocean may be storing more carbon than estimated in previous studies

, , , ,

Our colleague Frédéric Le Moigne contributed to an international study on the efficiency of the oceanic carbon pump. The study, published this week in Nature magazine, reassesses the ocean’s capacity to store carbon, particularly through ‘marine snow’. The CNRS issued a press release about this publication :

The ocean’s capacity to store atmospheric carbon dioxide is almost 20% higher than the estimates presented in the latest IPCC report. These are the findings of a study published in the journal Nature on 6 December 2023 by an international team including a biologist from the CNRS. The scientists looked at the role played by plankton in the natural transport of carbon from the surface to the seabed.

Plankton is fond of this gas, which it transforms into organic tissue through photosynthesis during its development, and some of it is transformed into marine particles at the end of its life. Denser than seawater, this ‘marine snow’ sinks to the seabed, storing carbon and providing essential nutrients for many deep-sea creatures, from tiny bacteria to deep-sea fish.

Based on the study of a database collected from around the world since the 1970s using oceanographic vessels, the team of seven scientists were able to digitally map the fluxes of organic matter throughout the oceans. The resulting new estimate of storage capacity is 15 gigatonnes per year, an increase of around 20% on the previous studies (11 gigatonnes per year) reported by the IPCC in its 2021 report.

This reassessment of the seabed’s storage capacity represents a significant advance in our understanding of carbon exchanges between the atmosphere and the ocean at a global level. While the team stresses that this absorption process takes place over tens of thousands of years, and is therefore not sufficient to offset the exponential increase in CO2 emissions generated by global industrial activity since 1750, this study nevertheless reinforces the importance of the ocean ecosystem as a major player in regulating the global climate in the long term.

Global distribution of organic carbon flux from the surface layer of the open ocean.
© Wang et al., 2023, Nature.



Biological carbon pump estimate based on multi-decadal hydrographic data. Wei-Lei Wang, Weiwei Fu, Frédéric A. C. Le Moigne, Robert T. Letscher, Yi Liu, Jin-Ming Tang, and François W. Primeau. Nature, le 6 décembre 2023.
DOI : https://doi.org/10.1038/s41586-023-06772-4

PAMPAS project exhibition: Coastal marsh heritage

, , ,

The PAMPAS project – Évolution de l’identité PAtrimoniale des Marais des Pertuis charentais en réponse à l’Aléa de Submersion marine, 2019-2023 – is a collaborative research project funded by the French National Research Agency (ANR) and led by the Littoral Environnement et Sociétés de La Rochelle laboratory (LIENSs, CNRS – La Rochelle University). It aims to understand the future of coastal wetlands, focusing on the evolution of the heritage identity of the marshes of the Pertuis Charentais in response to flooding over half a century.
The marshes of Charente-Maritime: a unique study area presenting:

  • A strong heritage identity – landscape, biodiversity, architectural heritage
  • Vulnerability to submersions,
  • Contrasted management methods and a concentration of numerous economic activities – agriculture, shellfish farming, tourism … whose sustainability can be questioned.

In a context of increasing populations and activities in coastal areas, the preservation and maintenance of these socio-ecosystems are essential to safeguard the quality and functions of these constrained environments. The project has expanded the concept of heritage identity to include the ecological and environmental functions of marshes, such as:

  • Their adaptation to the overall rise in sea level through sedimentation,
  • Their role as a buffer against marine submersions limiting the rise in sea level in adjacent areas,
  • Their role in water filtration, nutrient recycling, carbon sequestration, habitat provision, and nursery functions for numerous species.

This project chose to go beyond traditional approaches to the assessment of conservation ecology, economics, and cultural heritage management, all considered insufficient to comprehend heritage as the entirety of components contributing to the collective identity of a marsh.


  • Adopted an interdisciplinary approach applied to three study areas (the marshes of Brouage, Fier d’Ars, and Tasdon), contrasting in terms of natural, cultural, and landscape heritage, as well as management practices: in debate between laissez-faire and embankment, heavily embanked, and reconnected to the sea, respectively.
  • Built a collective approach and participatory engineering, crossing expertise in Humanities and Social Sciences, Life and Earth Sciences, and involving marsh managers, with 48 people from 13 research units and 9 disciplines.

The 3 major objectives of PAMPAS are to:

  • Characterize the natural, cultural, and landscape functions of the marshes and spatially represent these different components of heritage identity;
  • Represent the socio-ecosystem of marshes in terms of functionality, services, resilience, or adaptability to hazards;
  • Define scenarios for the evolution of the heritage identity of the three study sites facing submersion hazards and assess their adaptive potential. These results will be discussed through an interactive mapping tool.

In conclusion, based on a revised definition of heritage identity adapted to marsh areas, PAMPAS provides a new vision for sustainable marsh management by transmitting economic, cultural, and ecological knowledge. The challenges and issues of this project thus far exceed the local level and concern wetlands globally, for which it is now necessary to reconsider analysis and management frameworks, integrating heritage in its various socio-ecosystemic dimensions.

This heritage is not always visible or recognized as such by the entire population. Therefore, this exhibition aims to reveal to the general public not only the results of a research project but also the objects (animals, plants, structures, landscapes, activities, etc.) that could be recognized as full-fledged heritage in the marshes. Showing the invisible, less easily perceived objects, and highlighting the ecological functions of the marshes is the objective of this exhibition.

The exhibition will be visible from September 30 to November 4 at the Ecomuseum of Loix en Ré (Ile de Ré)

Claire Hellio, awarded the CNRS Innovation Medal

, , ,

Congratulations to our colleague Claire HELLIO, who has been awarded the 2023 CNRS Innovation Medal!

Claire, a University Professor at UBO, is in charge of the BIODIMAR platform. The platform is dedicated to biotechnology research, and develops solutions for producing more environmentally-friendly products, mainly from molecules of marine origin.

Extract from the CNRS press release:

Claire Hellio, drawing inspiration from natural molecules for environmentally-friendly products

Claire Hellio develops innovative bioinspired solutions based on active molecules produced by algae and microorganisms. Conducted at the Laboratoire des sciences de l’environnement marin, this work, at the interface between chemistry, biology, biochemistry and ecology, is carried out via the Biodimar bioprospecting platform, which this professor heads up.

Her team responds to the problems and R&D needs of manufacturers, developing specific biotests and innovative biotechnological solutions based on natural substances of marine origin. Applications are mainly in the fields of cosmetics (antioxidants and preservatives) and antifouling coatings (protection of boat hulls against colonization). These solutions are made as environmentally-friendly as possible. This collaboration with companies has, for example, taken the form of a joint laboratory called BiotechALg in partnership with Green Sea, the European leader in microalgae production.

15th conference of the French Association of Halieutics in Brest

, ,

The 15th conference of the French Association of Halieutics, will take place at the end of June in Brest, on the theme “Fisheries systems facing crises“.

Workshops will be held on 27 (at IUEM in Plouzané) and 28 June 2022 (at Pôle numérique du Bouguen, in Brest).

The conference itself will be held from 29 June to 1 July 2022, also at the Pôle numérique du Bouguen in Brest.

The programme can be downloaded here, and the registration file here.

Link to the AFH website (take the opportunity to join AFH!).