48 research outputs found
The Biogeochemistry of Hydrogen Sulfide: Phytoplankton Production in the Surface Ocean
Hydrogen sulfide can exist in oxic waters in the form of a dissolved gas, dissociated ions, dissolved metal sulfide complexes, and particulate metal sulfides. The sum of the dissolved species is termed total dissolved sulfide (TDS). In addition to the hydrolysis of carbonyl sulfide, it has been speculated that phytoplankton may produce TDS. We present results from preliminary culture studies which demonstrate that phytoplankton produce TDS and particulate acid-volatile sulfide (pAVS). The phylogenetic order of TDS + pAVS production (per unit cell volume) for the oceanic species examined is Synechococcus sp. \u3e Emiliania huxleyi â Pyramimonas obovata \u3e Thalassiosira oceanica. Moreover, TDS and pAVS production increases when the concentrations of uncomplexed trace metals in culture media are also increased, suggesting metal detoxification via the formation of metal sulfide complexes
Modeling the influence of eutrophication and redox conditions on mercury cycling at the sediment-water interface in the Berre Lagoon
This study presents a specifically designed Mercury module in a coupled benthic-pelagic reactive-transport model - Bottom RedOx Model (BROM) that allows to study mercury (Hg) biogeochemistry under different conditions. This module considers the transformation of elemental mercury (Hg(0)), divalent mercury (Hg(II)) and methylmercury (MeHg). The behavior of mercury species in the model is interconnected with changes of oxygen, hydrogen sulfide, iron oxides, organic matter, and biota. We simulated the transformation and transport of Hg species in the water column and upper sediment layer under five different scenarios, combining various levels of oxygenation and trophic state in the Berre lagoon, a shallow eutrophic lagoon of the French Mediterranean coast subjected to seasonal anoxia. The first scenario represents the conditions in the lagoon that are compared with experimental data. The four other scenarios were produced by varying the biological productivity, using low and high nutrient (N and P) concentrations, and by varying the redox conditions using different intensity of vertical mixing in the water column. The results of the simulation show that both oxidized and reduced sediments can accumulate Hg, but any shifts in redox conditions in bottom water and upper sediment layer lead to the release of Hg species into the water column. Eutrophication and/or restricted vertical mixing lead to reducing conditions and intensify MeHg formation in the sediment with periodic release to the water column. Oxygenation of an anoxic water body can lead to the appearance of Hg species in the water column and uptake by organisms, whereby Hg may enter into the food web. The comparison of studied scenarios shows that a well-oxygenated eutrophic system favors the conditions for Hg species bioaccumulation with a potential adverse effect on the ecosystem. The research is relevant to the UN Minimata convention, EU policies on water, environmental quality standards and Mercury in particular.publishedVersio
Multidisciplinary investigation on cold seeps with vigorous gas emissions in the Sea of Marmara (MarsiteCruise): Strategy for site detection and sampling and first scientific outcome
MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 ÎŒmol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems
Impacts des substances chimiques sur lâĂ©cosystĂšme. Sous-rĂ©gion marine Manche - Mer du Nord. Evaluation initiale DCSMM.
Impacts des substances chimiques sur lâĂ©cosystĂšme. Sous-rĂ©gion marine Golfe de Gascogne. Evaluation initiale DCSMM.
Impacts des substances chimiques sur lâĂ©cosystĂšme. Sous-rĂ©gion marine Mers celtiques. Evaluation initiale DCSMM.
Impacts des substances chimiques sur lâĂ©cosystĂšme. Sous-rĂ©gion marine MĂ©diterranĂ©e occidentale. Evaluation initiale DCSMM.
Programme de surveillance chimique sanitaire 2018. Bilan scientifique et technique définitif
Le ROCCH produit les donnĂ©es chimiques nĂ©cessaires Ă lâĂ©valuation de la qualitĂ© chimique des eaux marines, et notamment la qualitĂ© sanitaire des zones conchylicoles françaises. En 2018, 76 Ă©chantillons de mollusques ont Ă©tĂ© collectĂ©s et analysĂ©s dans ce cadre, complĂ©tĂ©s de 46 points hors suivi sanitaire. Trois secteurs apparaissent prĂ©occupants en fĂ©vrier 2018: le sud de la rade de Brest (fortes teneurs en plomb dans les moules et teneurs Ă©levĂ©es en cadmium dans les huĂźtres), la baie de Marseille ((fortes teneurs en plomb dans les moules et teneurs Ă©levĂ©es en HAP) et lâestuaire de la Gironde (fortes teneur en cadmium dans les huĂźtres), la baie de Toulon (teneurs Ă©levĂ©es en plomb des moules), le pertuis charentais (teneurs Ă©levĂ©es en cadmium des huĂźtres), le nord de la rade de Brest (teneurs Ă©levĂ©es en HAP dans les huĂźtres), lâembouchure de la Seine (teneurs Ă©levĂ©es en HAP et composĂ©s de type dioxine dans les moules), la cĂŽte nord normande (teneurs Ă©levĂ©es en composĂ©s de type dioxine dans les huĂźtres et les moules).  Â
Avis scientifique de l'Ifremer sur les conséquences sur le milieu marin de l'immersion de la cargaison d'oxyde de fer suite au naufrage du navire Union Neptune
Distribution and behavior of dissolved hydrogen sulfide in hydrothermal plumes
Through the deep ocean, hydrothermal plumes disperse high concentrations of key chemical tracers including He-3, CH4, Mn, Fe, H2S, etc. This paper focuses on the distribution and behavior of total dissolved sulfide (sulfide hereafter) in hydrothermal plumes to show that its plume concentration decreases to subnanomolar a few kilometers from the vents. We also report on sulfide removal rates determined at in situ conditions; we observe that they are two orders of magnitude greater than for open ocean seawater, consistent with sulfide being detected only in the vicinity of hydrothermal vents. From our observations, we infer that the sole presence of sulfide in hydrothermal plumes locates active venting at the kilometer scale