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During the scientific expedition GAZCOGNE2 at the Bay of Biscay nine gas seeps were sampled for the first time and their flux was measured using an in situ pressure-preservation sampler (PEGAZ, © IFREMER). Overall, three sites were investigated to determine the nature and the origin of the gases bubbling at the seafloor and forming acoustic plumes into the water column, as this was the question raised from the first geologic study of the area. This has guided our study and accordingly corresponds to the main purpose of the present article. Thus, the molecular and isotopic ( D and 13 C) analyses revealed that the gas seeps were primarily composed of methane. Both methane and ethane are of microbial origin, and the former has been generated by microbial reduction of carbon dioxide. Heavier hydrocarbons accounted for less than 0.06% mol of the total amount. Despite the microbial origin of methane, the samples exhibit subtle differences with respect to the 13 C CH 4 values, which varied between −72.7 and −66.1‰. It has been suggested that such a discrepancy was predominantly governed by the occurrence of anaerobic methane oxidation. The PEGAZ sampler also enabled us to estimate the local gas fluxes from the sampled streams. The resulting values are extremely heterogeneous between seeps, ranging from 35 to 368 mLn⋅min −1 . Assuming a steady discharge, the mean calculated methane emission for the nine seeps is of 38 kmol⋅yr −1 . Considering the extent of the seep area, this very local estimate suggests that the Aquitaine Shelf is a very appropriate place to study methane discharge and its fate on continental shelves.

Ocean chemistry and marine biogeochemical cycles depend strongly on the exchanges at the deep-sea floor. Mineralization processes within sediments and the exchange of compounds across the sediment-water interface are, however, regulated by a balance between chemical and biological processes. Turnover between particulate and dissolved states is characteristic of bioactive element cycles, and this process is particularly rapid on the deep sea floor (Jahnke et al. 1989). The diffusive and advective transfer of chemical compounds across the sediment represents significant sources or sinks in oceanic budgets. The coupling between sediment and the water column interface have been done by several authors, and the aim of their studies was to calculate the rates of chemical exchanges (Smith Jr. et al. 1983;Patching et al. 1986;Jahnke et al. 1989;Pfannkuche 1993; Jahnke et al. 1994). Over the last 20 years, benthic landers have been developed to estimate these deep benthic exchanges. Two approaches are generally used. The first approach uses core-sampled sediments to extract interstitial waters or to measure with microprobe the chemical gradients, and then calculate advective-diffusive fluxes within the sediment. This approach has limitations because nutrient concentrations are difficult to measure with precision at fine scale and transport coefficients are rarely accurately determined. A possible re-equilibration of the system during its recovery can also affect the distribution of porewater components. The second approach uses in situ benthic chambers in which a known volume of seawater is placed in contact with the sediment and incubated. This approach directly measures the solute flux, and contrary to the other method, does not need calculation using model or coefficient. The incubation is made on a great sediment surface and the AbstractA new submersible-operated benthic chamber has been developed to measure benthic organism metabolism and chemical exchange rates at the sediment-water interface up to 6000 m depth. This equipment can be used everywhere on soft sediment, but particularly to deploy it on small area reached only by submersible-like cold seep. The chamber, 41 cm diameter cylinder, includes six 100 mL-sampling cells to isolate aliquots, which are sampled at predetermined intervals and an oxygen-optode probe. This chamber named CALMAR (Chambre Autonome Légère MAnipulable par ROV) was used for the first time during the Medeco cruise (2007) in Eastern Mediterranean Sea. It allowed measurement of fluxes of oxygen, dissolved inorganic carbon, and methane on the Napoli mud volcano site. Two benthic chambers were deployed with the ROV Victor, respectively, on small, active, cold seep colonized by Siboglinidae worms and mussels (Station A), and at about 3 m from the first where no visible animals were observed (Station B). The oxygen flux was 35 mmol O 2 m -2 d -1 in sediment colonized by large organisms (Station A) and 13.5 mmol O 2 m -2 d -1 on the inactive area (CALMAR B). In terms of inorganic carbon, the flu...

The European Multidisciplinary Seafloor and water-column Observatory (EMSO) European Research Infrastructure Consortium (ERIC) provides power, communications, sensors, and data infrastructure for continuous, high-resolution, (near-)real-time, interactive ocean observations across a multidisciplinary and interdisciplinary range of research areas including biology, geology, chemistry, physics, engineering, and computer science, from polar to subtropical environments, through the water column down to the abyss. Eleven deep-sea and four shallow nodes span from the Arctic through the Atlantic and Mediterranean, to the Black Sea. Coordination among the consortium nodes is being strengthened through the EMSOdev project (H2020), which will produce the EMSO Generic Instrument Module (EGIM). Early installations are now being upgraded, for example, at the Ligurian, Ionian, Azores, and Porcupine Abyssal Plain (PAP) nodes. Significant findings have been flowing in over the years; for example, high-frequency surface and subsurface water-column measurements of the PAP node show an increase in seawater pCO2 (from 339 μatm in 2003 to 353 μatm in 2011) with little variability in the mean air-sea CO2 flux. In the Central Eastern Atlantic, the Oceanic Platform of the Canary Islands open-ocean canary node (aka ESTOC station) has a long-standing time series on water column physical, biogeochemical, and acidification processes that have contributed to the assessment efforts of Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site.the Intergovernmental Panel on Climate Change (IPCC). EMSO not only brings together countries and disciplines but also allows the pooling of resources and coordination to assemble harmonized data into a comprehensive regional ocean picture, which will then be made available to researchers and stakeholders worldwide on an open and interoperable access basis.