Tag Archive for: contaminants

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).

Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Abstract

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

 

Graphical abstract


Spatial variability of skipjack mercury concentrations. Smoothed spatial contour maps of (A) observed and (B) standardized Hg concentrations (micrograms ⋅ grams−1, dw) in skipjack white muscle samples from the Pacific Ocean. The black dots represent the location of skipjack samples. Ocean areas correspond to the sample origin: NWPO, CNPO, NEPO, EPO, SWPO, and WCPO. The transparent dots represent the location of seawater samples with available and published MeHg data

 

Highlights

Humans are exposed to toxic methylmercury mainly by consuming marine fish. New environmental policies under the Minamata Convention rely on a yet-poorly-known understanding of how mercury emissions translate into fish methylmercury levels. Here, we provide the first detailed map of mercury concentrations from skipjack tuna across the Pacific. Our study shows that the natural functioning of the global ocean has an important influence on tuna mercury concentrations, specifically in relation to the depth at which methylmercury concentrations peak in the water column. However, mercury inputs originating from anthropogenic sources are also detectable, leading to enhanced tuna mercury levels in the northwestern Pacific Ocean that cannot be explained solely by oceanic processes.

 

Reference

Anaïs Médieu, David Point, Takaaki Itai, Hélène Angot, Pearse J. Buchanan, Valérie Allain, Leanne Fuller, Shane Griffiths, David P. Gillikin, Jeroen E. Sonke, Lars-Eric Heimbürger-Boavida, Marie-Maëlle Desgranges, Christophe E. Menkes, Daniel J. Madigan, Pablo Brosset, Olivier Gauthier, Alessandro Tagliabue, Laurent Bopp, Anouk Verheyden, Anne Lorrain. Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs. Proceedings of the National Academy of Sciences Jan 2022, 119 (2) e2113032119; DOI: 10.1073/pnas.2113032119

Read the article on PNAS website

Tag Archive for: contaminants

MERTOX

,

Tag Archive for: contaminants

Chibido team

Team

Chibido

Marine chemistry, biogeochemical cycles and ocean dynamics

The marine biogeochemical cycles of the major and trace elements play fundamental roles in both the biological and chemical functioning of the ocean but also in terrestrial climatic regulation. Marine ecosystems (phytoplankton, zooplankton, bacteria, fish, predators) occupy a central place within these cycles and contribute by various processes (assimilation-degradation-trophic transfer-sedimentation) to transform, store and redistribute the chemical elements in the column. of ocean water. These transformations favor different levels of coupling between the element cycles and interact directly on the climate by modifying the gas exchanges involved in the radiative balance of the atmosphere (CO2, CH4, N2O, DMS). Despite significant progress made in recent decades, this essential role of marine ecosystems on biogeochemical cycles and ultimately on the climate remains poorly quantified and is still a scientific issue.

This issue is all the more important in the current context in which anthropogenic pressures on the ocean and marine organisms continue to increase and multiply. Climate change and modification of environmental forcings (T, pH, pCO2, currents, extension of sea ice), releases of polluting substances (toxic metals, pesticides, microplastics, etc.), intensive exploitation of biological resources or the degradation of natural habitats are all factors that can profoundly alter the structure, functioning and biodiversity of marine ecosystems. What will be the impacts of these modifications on biogeochemical cycles, ocean productivity, gas exchanges? What will be the climate feedbacks and organizations’ response to these changes? These are all questions that the scientific community must answer if it intends to reduce the uncertainties associated with climate simulations and anticipate the joint evolution of marine ecosystems.

It is around these questions that our research team (CHIBIDO) develops its activities. Our objects of study are the biogeochemical cycles of the major elements (C, N, P, S, Si) and metallic traces (Fe, Mn, Cu, Ni, Zn, Co, Cd, Mo, Pb) and we try, by multidisciplinary approaches involving physicists, biologists, chemists and modelers to contribute to the improvement of knowledge on the interactions between oceanic dynamics, biogeochemical cycles, ecosystems and climate. Our research actions combine a wide spectrum of approaches associating the development of new methods of analysis (multi-elementary, isotopic and speciation), the implementation of tracers / geochemical proxies (Baxs, 234Th, δ30Si, δ11B), in situ observation at different scales (microcosms, mesocosms, basin, global), laboratory experimentation and the use of numerical modeling. These approaches are part of the international (IMBER, GEOTRACES, SOLAS) and national (LEFE-CYBER, EC2CO / DRIL, LABEX Sea) programmatic framework and are structured along three lines of research:

chibido - Axes des recherche

Axes de recherche de l’équipe Chibido.


Animation: Olivier Ragueneau & Gabriel Dulaquais

A better understanding of oceanic biogeochemical cycles requires describing and understanding input and output, and their variability. To this end, we are working on the different interfaces with the ocean, since these interfaces are external sources and sinks of matter whose intensity and importance vary according to the element considered. These interfaces are generally the site of strong physico-chemical gradients and are extremely sensitive to different anthropogenic pressures.

Sediments, the ocean-atmosphere interface, and hydrothermal springs are the sources of metals for the ocean. Our findings showing that bacterial concentrations in rainwater samples are related to the increase in iron-specific ligand concentrations that can impact organic speciation of iron, our objective is to better understand the interactions between iron and bioaerosols and their fate in the ocean water column. In hydrothermal environments, our objective is to identify and describe the chemical reactions that determine the organic complexing of metals.

The land-sea continuum is an interface strongly impacted by anthropogenic pressures. The physico-chemical gradients in estuaries control river inputs of biogenic (Si, N) and metallic elements. Our team continues to improve our understanding of the dynamics of these elements along the land-sea continuum by studying the changes that occur through adsorption/desorption, coagulation, complexing or degradation processes and by characterizing the composition and physico-chemical role of organic matter that influences their bioavailability/toxicity.

In addition, our work in the Bay of Vilaine should lead us to participate in the development of a nutrient limitation scheme that could restore eutrophic ecosystems. By improving our knowledge of the Brest Rade we wish to use climate change scenarios to model the evolution of nutrient fluxes in the coastal zone. These scenarios can be combined with scenarios of changes in agricultural practices in the watersheds in collaboration with AMURE’s team of economists.

 

Animation: Pascal Rivière & Eva Bucciarelli 

In this RA, we are seeking to better understand the spatial and temporal variability of phytoplankton production in relation to cycle dynamics and small-scale hydrodynamic structures. To do this, we have targeted several objectives

(1) to observe and describe the distributions and chemical speciation of dissolved and particulate trace metals during major international oceanographic cruises

(2) to study factors such as limitations or toxicity and pressures that will control the internal dynamics of biogenic elements (N, Si, metals) in relation to phytoplankton physiology and phytoplankton community structure in collaboration with Team 2

(3) to link small-scale dynamic structures and planktonic biodiversity.

To achieve these objectives, we combine different approaches involving in situ observation within the framework of international (GEOTRACES) and national programs (biologging and sea elephants CNES-TOSCA ) or from the LAbexMer and EUR ISblue (M2BIPAT), laboratory and natural environment process studies (isotopic techniques), as well as 3D ocean circulation models (NEMO, CROCO) coupled with biogeochemical models (PISCES, DARWIN, DARWIN-QUOTA) to understand planktonic diversity.

Animation : Laurent Mémery

In close connection with ISBLUE Theme 1, the objectives of this axis are to study the factors controlling the nature, amplitude, and mitigation of carbon export fluxes from the surface to the deep ocean. Emphasis is placed on the processes of particle formation (biological and physical aggregation), vertical export (proxy 234Th), mesopelagic remineralization (proxy Baxs) and trophic interactions with microbial and zooplankton communities. Despite the progress made by recent models that increasingly take into account the processes controlling export, such as size classes and zooplankton behaviour, there is still a need to improve our understanding of particle dynamics and the factors affecting particle size and number, their sink rate and their fate in the mesopalagic zone. To this end, our approach includes in situ measurement campaigns using geochemical proxies, as well as process studies more specifically related to processes impacting particle dynamics in mesopelagic zones and various modelling tools.

Team leaders


Researchers and teachers


Paul Treguer

engineers and technicians


PhD students


Post-doctoral positions


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).

Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs

Abstract

Pacific Ocean tuna is among the most-consumed seafood products but contains relatively high levels of the neurotoxin methylmercury. Limited observations suggest tuna mercury levels vary in space and time, yet the drivers are not well understood. Here, we map mercury concentrations in skipjack tuna across the Pacific Ocean and build generalized additive models to quantify the anthropogenic, ecological, and biogeochemical drivers. Skipjack mercury levels display a fivefold spatial gradient, with maximum concentrations in the northwest near Asia, intermediate values in the east, and the lowest levels in the west, southwest, and central Pacific. Large spatial differences can be explained by the depth of the seawater methylmercury peak near low-oxygen zones, leading to enhanced tuna mercury concentrations in regions where oxygen depletion is shallow. Despite this natural biogeochemical control, the mercury hotspot in tuna caught near Asia is explained by elevated atmospheric mercury concentrations and/or mercury river inputs to the coastal shelf. While we cannot ignore the legacy mercury contribution from other regions to the Pacific Ocean (e.g., North America and Europe), our results suggest that recent anthropogenic mercury release, which is currently largest in Asia, contributes directly to present-day human mercury exposure.

 

Graphical abstract


Spatial variability of skipjack mercury concentrations. Smoothed spatial contour maps of (A) observed and (B) standardized Hg concentrations (micrograms ⋅ grams−1, dw) in skipjack white muscle samples from the Pacific Ocean. The black dots represent the location of skipjack samples. Ocean areas correspond to the sample origin: NWPO, CNPO, NEPO, EPO, SWPO, and WCPO. The transparent dots represent the location of seawater samples with available and published MeHg data

 

Highlights

Humans are exposed to toxic methylmercury mainly by consuming marine fish. New environmental policies under the Minamata Convention rely on a yet-poorly-known understanding of how mercury emissions translate into fish methylmercury levels. Here, we provide the first detailed map of mercury concentrations from skipjack tuna across the Pacific. Our study shows that the natural functioning of the global ocean has an important influence on tuna mercury concentrations, specifically in relation to the depth at which methylmercury concentrations peak in the water column. However, mercury inputs originating from anthropogenic sources are also detectable, leading to enhanced tuna mercury levels in the northwestern Pacific Ocean that cannot be explained solely by oceanic processes.

 

Reference

Anaïs Médieu, David Point, Takaaki Itai, Hélène Angot, Pearse J. Buchanan, Valérie Allain, Leanne Fuller, Shane Griffiths, David P. Gillikin, Jeroen E. Sonke, Lars-Eric Heimbürger-Boavida, Marie-Maëlle Desgranges, Christophe E. Menkes, Daniel J. Madigan, Pablo Brosset, Olivier Gauthier, Alessandro Tagliabue, Laurent Bopp, Anouk Verheyden, Anne Lorrain. Evidence that Pacific tuna mercury levels are driven by marine methylmercury production and anthropogenic inputs. Proceedings of the National Academy of Sciences Jan 2022, 119 (2) e2113032119; DOI: 10.1073/pnas.2113032119

Read the article on PNAS website

MERTOX

,

Chibido team

Team

Chibido

Marine chemistry, biogeochemical cycles and ocean dynamics

The marine biogeochemical cycles of the major and trace elements play fundamental roles in both the biological and chemical functioning of the ocean but also in terrestrial climatic regulation. Marine ecosystems (phytoplankton, zooplankton, bacteria, fish, predators) occupy a central place within these cycles and contribute by various processes (assimilation-degradation-trophic transfer-sedimentation) to transform, store and redistribute the chemical elements in the column. of ocean water. These transformations favor different levels of coupling between the element cycles and interact directly on the climate by modifying the gas exchanges involved in the radiative balance of the atmosphere (CO2, CH4, N2O, DMS). Despite significant progress made in recent decades, this essential role of marine ecosystems on biogeochemical cycles and ultimately on the climate remains poorly quantified and is still a scientific issue.

This issue is all the more important in the current context in which anthropogenic pressures on the ocean and marine organisms continue to increase and multiply. Climate change and modification of environmental forcings (T, pH, pCO2, currents, extension of sea ice), releases of polluting substances (toxic metals, pesticides, microplastics, etc.), intensive exploitation of biological resources or the degradation of natural habitats are all factors that can profoundly alter the structure, functioning and biodiversity of marine ecosystems. What will be the impacts of these modifications on biogeochemical cycles, ocean productivity, gas exchanges? What will be the climate feedbacks and organizations’ response to these changes? These are all questions that the scientific community must answer if it intends to reduce the uncertainties associated with climate simulations and anticipate the joint evolution of marine ecosystems.

It is around these questions that our research team (CHIBIDO) develops its activities. Our objects of study are the biogeochemical cycles of the major elements (C, N, P, S, Si) and metallic traces (Fe, Mn, Cu, Ni, Zn, Co, Cd, Mo, Pb) and we try, by multidisciplinary approaches involving physicists, biologists, chemists and modelers to contribute to the improvement of knowledge on the interactions between oceanic dynamics, biogeochemical cycles, ecosystems and climate. Our research actions combine a wide spectrum of approaches associating the development of new methods of analysis (multi-elementary, isotopic and speciation), the implementation of tracers / geochemical proxies (Baxs, 234Th, δ30Si, δ11B), in situ observation at different scales (microcosms, mesocosms, basin, global), laboratory experimentation and the use of numerical modeling. These approaches are part of the international (IMBER, GEOTRACES, SOLAS) and national (LEFE-CYBER, EC2CO / DRIL, LABEX Sea) programmatic framework and are structured along three lines of research:

chibido - Axes des recherche

Axes de recherche de l’équipe Chibido.


Animation: Olivier Ragueneau & Gabriel Dulaquais

A better understanding of oceanic biogeochemical cycles requires describing and understanding input and output, and their variability. To this end, we are working on the different interfaces with the ocean, since these interfaces are external sources and sinks of matter whose intensity and importance vary according to the element considered. These interfaces are generally the site of strong physico-chemical gradients and are extremely sensitive to different anthropogenic pressures.

Sediments, the ocean-atmosphere interface, and hydrothermal springs are the sources of metals for the ocean. Our findings showing that bacterial concentrations in rainwater samples are related to the increase in iron-specific ligand concentrations that can impact organic speciation of iron, our objective is to better understand the interactions between iron and bioaerosols and their fate in the ocean water column. In hydrothermal environments, our objective is to identify and describe the chemical reactions that determine the organic complexing of metals.

The land-sea continuum is an interface strongly impacted by anthropogenic pressures. The physico-chemical gradients in estuaries control river inputs of biogenic (Si, N) and metallic elements. Our team continues to improve our understanding of the dynamics of these elements along the land-sea continuum by studying the changes that occur through adsorption/desorption, coagulation, complexing or degradation processes and by characterizing the composition and physico-chemical role of organic matter that influences their bioavailability/toxicity.

In addition, our work in the Bay of Vilaine should lead us to participate in the development of a nutrient limitation scheme that could restore eutrophic ecosystems. By improving our knowledge of the Brest Rade we wish to use climate change scenarios to model the evolution of nutrient fluxes in the coastal zone. These scenarios can be combined with scenarios of changes in agricultural practices in the watersheds in collaboration with AMURE’s team of economists.

 

Animation: Pascal Rivière & Eva Bucciarelli 

In this RA, we are seeking to better understand the spatial and temporal variability of phytoplankton production in relation to cycle dynamics and small-scale hydrodynamic structures. To do this, we have targeted several objectives

(1) to observe and describe the distributions and chemical speciation of dissolved and particulate trace metals during major international oceanographic cruises

(2) to study factors such as limitations or toxicity and pressures that will control the internal dynamics of biogenic elements (N, Si, metals) in relation to phytoplankton physiology and phytoplankton community structure in collaboration with Team 2

(3) to link small-scale dynamic structures and planktonic biodiversity.

To achieve these objectives, we combine different approaches involving in situ observation within the framework of international (GEOTRACES) and national programs (biologging and sea elephants CNES-TOSCA ) or from the LAbexMer and EUR ISblue (M2BIPAT), laboratory and natural environment process studies (isotopic techniques), as well as 3D ocean circulation models (NEMO, CROCO) coupled with biogeochemical models (PISCES, DARWIN, DARWIN-QUOTA) to understand planktonic diversity.

Animation : Laurent Mémery

In close connection with ISBLUE Theme 1, the objectives of this axis are to study the factors controlling the nature, amplitude, and mitigation of carbon export fluxes from the surface to the deep ocean. Emphasis is placed on the processes of particle formation (biological and physical aggregation), vertical export (proxy 234Th), mesopelagic remineralization (proxy Baxs) and trophic interactions with microbial and zooplankton communities. Despite the progress made by recent models that increasingly take into account the processes controlling export, such as size classes and zooplankton behaviour, there is still a need to improve our understanding of particle dynamics and the factors affecting particle size and number, their sink rate and their fate in the mesopalagic zone. To this end, our approach includes in situ measurement campaigns using geochemical proxies, as well as process studies more specifically related to processes impacting particle dynamics in mesopelagic zones and various modelling tools.

Team leaders


Researchers and teachers


Paul Treguer

engineers and technicians


PhD students


Post-doctoral positions