The vast majority of the mid-ocean ridge system and of the continental margins around the globe have not yet been explored. A relatively small number of vent and seep sites have been analysed and are the focus of long-term research programmes. However, the exploration of new areas will certainly provide the discovery of new vent and seep sites. Furthermore, the study of these key locations will lead to the description of new species and improve our understanding of the abundance, diversity, and distribution of species from chemosynthetically-driven systems around the world's oceans. It is the aim of ChEss to develop an exploration field phase to discover new deep-water hydrothermal vents and cold seeps at key locations, to describe their fauna, and to study the processes driving these ecosystems. The main objective is to obtain a thorough understanding of the biogeography of chemosynthetic ecosystems at a global scale.

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Mineralizing processes at shallow submarine hydrothermal vents: examples from Mexico. Therefore, shallow submarine vents may be considered as modern analogues of some economic ore deposits. The boundary between shallow and deep hydrothermal vents can be established at a depth of mbsl, which represents an abrupt change in the environmental parameters and in the structure of the biotic communities.

In addition, this depth corresponds to an increase of the slope of the boiling curve of seawater with respect to pressure. Shallow submarine vents support complex specialized biotic communities, characterized by the coexistence and competition of chemosynthetic and photosynthetic organisms. Some biogeochemical and biomineralization processes related to chemosynthesis are similar to those described in deep ocean hydrothermal vents and in cold seeps.

Hydrothermal shallow vent fluids show intermediate chemical and isotopic characteristics between those of deep vents and of continental geothermal systems. Commonly, vent water has lower salinities than seawater. This fact, along with isotopic compositions, is evidence for large contributions of meteoric water in these vents. Venting of exsolved gas, evidenced by continuous bubbling, is a striking feature of shallow submarine hydrothermal systems.

In most cases vent gas is rich in C O 2, but it can be rich in N 2 and CH 4 in vent systems related to thick sedimentary series, and rich in H 2 S in vents related to volcanic fumaroles. The tectonic setting of these hydrothermal systems corresponds to continental margins affected by extension, with anomalously high geothermal gradients.

These vents do not show obvious links with volcanic activity. Their study has contributed to the understanding of mineralogical and geochemical processes in shallow submarine hydrothermal vents. These systems, in addition, may be a potential source of geothermal energy. Asimismo, los comentarios de Jordi Tritlla fueron muy beneficiosos para la mejora del manuscrito.

Agradecemos a A. Dando, P. Dando, M. Forrest, J. Melwani, A. Torres Vera y R. Villanueva Estrada el apoyo proporcionado en el trabajo de campo. Agradecemos a S. Franco sus observaciones sobre el manuscrito. Fontarnau, C. Reyes Salas, respectivamente.

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Life at Vents & Seeps

In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules usually carbon dioxide or methane and nutrients into organic matter using the oxidation of inorganic compounds e. Chemoautotrophs , organisms that obtain carbon from carbon dioxide through chemosynthesis, are phylogenetically diverse, but also groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria , the Aquificae , the methanogenic archaea and the neutrophilic iron-oxidizing bacteria. Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites where hydrogen molecules H 2 are available, the energy available from the reaction between CO 2 and H 2 leading to production of methane, CH 4 can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized.



Hydrothermal vents and cold seeps are places where chemical-rich fluids emanate from the seafloor, often providing the energy to sustain lush communities of life in some very harsh environments. Cold seeps and hydrothermal vents differ from one another in the underlying conditions that form and drive them. This has implications for the kinds of animals that are able to survive at each. On land and near the ocean surface, sunlight provides the energy that allows photosynthetic plants to convert carbon dioxide and water into the organic carbon, the fundamental source of nutrients for animals higher up the food chain. Below the photic zone—the sunlit, upper reaches of the ocean—many microbes have evolved chemosynthetic instead of photosynthetic processes that create organic matter by using oxygen in seawater to oxidize hydrogen sulfide, methane, and other chemicals present in vent and seep fluids.





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