Objectives

The main objective is to mechanistically understand Hg species dynamics in the coastal and open ocean. Specific objectives are to (1) implement mechanistic and quantitative assessments of methyl-Hg (MMHg, including monomethyl-Hg and dimethyl-Hg) origin and transformation; (2) to better characterise the production and exchange flux of dissolved gaseous Hg species (DGM = Hg(0) + DMHg) at the ocean-atmosphere interface, (3) to provide new high quality observational data of all marine Hg species for the development of better 3D coupled ocean-atmosphere models of the global and regional Hg cycles, in order to predict how Hg emission and global change scenarios will affect MMHg formation and bioaccumulation in marine ecosystems.

Description of Work

WP2 will investigate Hg methylation under controlled laboratory conditions, semi-controlled field mesocosm experiments, and oceanographic field campaigns in coastal, shelf and open marine environments. Findings will be integrated in WP5 and WP6 modelling.

Task 2.1: ESR3 at CNRS will develop novel (δ13C) and hydrogen (δD) isotopic tracers of the ’methyl’ group in MMHg compounds using state-of-the-art gas chromatography – combustion – isotope ratio mass spectrometry (GC-C-IRMS). The obtained C/H isotope signatures will provide information about the hydrocarbon source (terrestrial/marine, labile/refractory) in MMHg formation. This will be coupled with Hg stable isotopic analysis (δ202Hg/Δ199Hg) of MMHg using MC-ICP-MS. 3D (δ13C-δD-δ202Hg/Δ199Hg) isotopic analysis will be implemented in lab experiments and in biological tissues from plankton to top marine predators, with a particular focus on the Peruvian Humboldt Current System (PHCS), a highly productive coastal upwelling, which represents only 0.1% of the ocean surface, but concentrates more than 10% of fish global catches, and where Peruvian anchovy contributes to more than half of world landings used for fishmeal production and then fuels a critical portion of world aquaculture production. ESR3 will also work with ESRs 5 and 6 to characterise MMHg Hg/C/H isotopic signatures during controlled laboratory Hg methylation and with analysing food web samples originating from different ocean basins. Findings will be integrated in WP5 ecosystem modelling (ESR13).

Task 2.2: ESR4 at AMU will investigate open ocean Hg methylation. High-resolution marine maps of all Hg species and other biogeochemical parameters will be produced for a better understanding of marine methylHg production. Experimental results of ESR6 will be combined with field observations of ESR4 and ESR5 and will be integrated into regional ecosystem models developed in WP5 (ESR13). ESR 4 will benefit from ongoing projects involving sampling in the Arctic Ocean, the Mediterranean Sea in including monthly cruises. Furthermore, for the period of ITN-GMOS-Train project the following cruise participations for ESR 3-6 are planned: Peruvian Humboldt Current System, South Pacific, Southern Ocean Indian Sector, and the Arctic shelf seas, most of which within the international GEOTRACES program. Sampling on oceanographic cruises will be planned in concert with all other ESR projects to provide additional samples for numerical modelling, test novel sensors (ESR11) and improve sampling/measurements (ESR10).

Task 2.3: ESR5 at UPPA will investigate MMHg formation and degradation processes in coastal marine environments by conducting innovative experiments during oceanographic research cruises in selected coastal and shelf areas of the Atlantic Ocean, the Mediterranean Sea and the Baltic costal sites in collaboration with WP3 (ESR7). The experimental techniques target photochemical, biotic and abiotic MMHg transformations, and include enriched stable isotope incubations in the water column from coastal, shelf and margin stations. IOS, SU, CNRS and AMU will second ESR5 in terms of oceanographic logistics during field campaigns.

Task 2.4: ESR6 at IFREMER will investigate the sorption and uptake rates of dissolved Hg and MMHg species by key marine particles (colloidal, particulate organic matter, microbes, phytoplankton, and zooplankton) using controlled laboratory and mesocosm experiments. State-of-the-art analytical and isotope tracing techniques will be used to trace Hg and MMHg dynamics, seconded by AMU and CNRS. ESR6 will collaborate especially with ESRs in WP1 to incorporate atmospherically driven reactions, and with ESRs 4 and 5 in WP2 on joint marine sampling cruises during open ocean and coastal cruises. Work with WP3 ESR’s will incorporate laboratory rates and field knowledge of methylation processes in the marine context, and with WP5 to improve modelling of Hg uptake in food webs.

Task 2.5: ESR7 will study the reactivity of terrestrial Hg along land to sea transects by applying novel approaches to study desorption kinetics and refractory concentrations of Hg from contrasting terrestrial study sites and to study the reactivity of Hg and MeHg complexed to DOM from land to sea transects. Field sites will be shared with other WP2 ESR allowing transects to be included and comparison of experimental data on biological uptake to biological reactivity of Hg-TDOM reactivity measured in experiments and using the biosensors developed in WP4.

Expected Results

ESR3

(i) to validate methodologies for the 3D (δ13C-δD-δ202Hg/Δ199Hg) isotopic analysis of MMHg in natural samples at low concentrations (sediment, zooplankton) (paper 1); (ii) to study 3D (δ13C-δD-δ202Hg/Δ199Hg) isotopic variations of MMHg during biotic Hg methylation experiments & laboratory conditions (paper 2);  (iii) to document the 3D isotopic variations of MMHg in marine organisms collected from different study sites of ESR 4, 5, 6, 7, but with large focus on the highly productive coastal oxygen minimum zone off Peru. The trophic ecology and habitat of these organisms will also be documented by complementary analysis of δ13C, and δ15N signatures on individual amino acids (paper 3).

ESR4

Provide a DGM time-series to better constrain the large exchange flux at the ocean-atmosphere interface (paper 1). Provide high-resolution full depth open ocean description of all Hg species (tHg, MMHg, DMHg, Hg(0), DGM), and methylation/demethylation rates for uncharted open ocean basins (2 papers). New observations will feed the GEOTRACES global database and be used to confront and update state-of-the-art numerical global open ocean models.

ESR5

Methylation, di-methylation or demethylation rates in various environmental compartments as defined by critical biogeochemical parameters (e.g., microbial diversity and hgcA “methylation” genes; sunlight irradiance and DOM chromophoric properties) affecting Hg transformations in coastal, shelf and/or margin stations. Provide new molecular and isotopic information on transformations of the methylated Hg species in coastal environments (3 papers).

ESR6

New Hg speciation data and uptake rates between different marine particle size classes ranging from field-flow fractionated organic matter, bacteria- and phytoplankton, and zooplankton. (2 papers) and joint paper defined in D2.1.2

ESR7

Improved understanding of the fate and reactivity of terrestrial Hg along land to sea transects by i) applying novel approaches currently developed at SU to study desorption kinetics and refractory concentrations of Hg transported on particulate matter from contrasting terrestrial sources, and ii) study the reactivity (i.e. availability of Hg for photochemical and bacterial transformation reactions, and biological uptake) of Hg and MeHg complexed to TDOM and MDOM from contrasting land-to-sea transects (including Swedish Baltic coast, French Atlantic and Mediterranean coast and Northern Adriatic coasts), a coastal Mediterranean  time-series station, and ocean basins (within the framework of ESR 4, 5, 6) and iii) comparison of experimental and field derived data on the availability of Hg-TDOM and MDOM complexes for biological uptake with the biological reactivity of Hg-TDOM complexes measured using the biosensors (in collaboration with ESR 5 and 11) (2 papers).

Deliverables

Del. Deliverable Title – Science deliverables WP Lead Type Diss. Due
D2.1 ESR3: 3 papers on (i) validated methodologies for isotopic analysis of MMHg in natural samples at low concentration,(ii) 3D (δ13C-δD-δ202Hg/Δ199Hg) isotopic variations of MMHg during biotic Hg methylation experiments, (iii) 3D isotopic variations in marine food webs 2, 3, 5 CNRS R PU M45
D2.2 ESR4: 3 papers on (i) new spatial and temporal Hg speciation in sea water and (ii) use of new data in global modelling (joint paper with Harvard) (ii) joint paper on isotopic signatures in DGM, jointly with JSI 2,5 AMU R PU M46
D2.3 ESR5: 3 papers (i) paper on microbial and photochemical processes; revised coastal biogeochemical cycling; (ii) Joint paper with ESR3 on isotopic fractionation; (iii) Joint paper on novel experimental data with models developed by ESR13 2,5 UPPA R PU M45
D2.4 ESR6: 2 papers on (i) Hg speciation and uptake rates in different marine particle size classes (ii) isotope tracing of Hg and MeHg dynamics in coastal regions 2 Ifremer R PU M43
D2.5 Desorption kinetics and refractory concentrations of Hg transported on particulate matter from terrestrial sources and reactivity of Hg and MeHg complexed to TDOM and MDOM 2 SU R PU M46

Milestones

No Title WP(s) Lead Benef. Due Date Means of Verification
2 Validated Hg speciation method in seawater 2 AMU M16 Interlaboratory comparison: AMU; CNRS; UPPA; JSI; IFREMER (ESR4)
6 Developed and validated methodologies for 3D MMHg C/H/Hg CSIA 2 CNRS M48 Interlaboratory comparison with JSI (ESR3)
10 Successful implementation of lab methylation experiments 2 CNRS M42 Data verified and reported
11 A selection of appropriate sentinel organisms for 3D MMHg C/H/Hg CSIA 2 AMU M48 Hg analysis and speciation in sentinel organisms (ESR4, 5, 6)
12 New cruises and data on marine Hg speciation 2, 5 AMU M42 Cruises completed, data verified
13 New data on coastal Hg speciation 2, 5 UPPA M36 Measurements completed and validated