Gomez-Saez Gonzalo V.

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Gonzalo V.

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  • Article
    Soothsaying DOM: A current perspective on the future of oceanic dissolved organic carbon
    (Frontiers Media, 2020-05-25) Wagner, Sasha ; Schubotz, Florence ; Kaiser, Karl ; Hallmann, Christian ; Waska, Hannelore ; Rossel, Pamela ; Hansman, Roberta L. ; Elvert, Marcus ; Middelburg, Jack J. ; Engel, Anja ; Blattmann, Thomas M. ; Catalá, Teresa S. ; Lennartz, Sinikka T. ; Gomez-Saez, Gonzalo V. ; Pantoja-Gutiérrez, Silvio ; Bao, Rui ; Galy, Valier
    The vast majority of freshly produced oceanic dissolved organic carbon (DOC) is derived from marine phytoplankton, then rapidly recycled by heterotrophic microbes. A small fraction of this DOC survives long enough to be routed to the interior ocean, which houses the largest and oldest DOC reservoir. DOC reactivity depends upon its intrinsic chemical composition and extrinsic environmental conditions. Therefore, recalcitrance is an emergent property of DOC that is analytically difficult to constrain. New isotopic techniques that track the flow of carbon through individual organic molecules show promise in unveiling specific biosynthetic or degradation pathways that control the metabolic turnover of DOC and its accumulation in the deep ocean. However, a multivariate approach is required to constrain current carbon fluxes so that we may better predict how the cycling of oceanic DOC will be altered with continued climate change. Ocean warming, acidification, and oxygen depletion may upset the balance between the primary production and heterotrophic reworking of DOC, thus modifying the amount and/or composition of recalcitrant DOC. Climate change and anthropogenic activities may enhance mobilization of terrestrial DOC and/or stimulate DOC production in coastal waters, but it is unclear how this would affect the flux of DOC to the open ocean. Here, we assess current knowledge on the oceanic DOC cycle and identify research gaps that must be addressed to successfully implement its use in global scale carbon models.
  • Article
    Relative importance of chemoautotrophy for primary production in a light exposed marine shallow hydrothermal system
    (Frontiers Media, 2017-04-21) Gomez-Saez, Gonzalo V. ; Pop Ristova, Petra ; Sievert, Stefan M. ; Elvert, Marcus ; Hinrichs, Kai-Uwe ; Bühring, Solveig I.
    The unique geochemistry of marine shallow-water hydrothermal systems promotes the establishment of diverse microbial communities with a range of metabolic pathways. In contrast to deep-sea vents, shallow-water vents not only support chemosynthesis, but also phototrophic primary production due to the availability of light. However, comprehensive studies targeting the predominant biogeochemical processes are rare, and consequently a holistic understanding of the functioning of these ecosystems is currently lacking. To this end, we combined stable isotope probing of lipid biomarkers with an analysis of the bacterial communities to investigate if chemoautotrophy, in parallel to photoautotrophy, plays an important role in autotrophic carbon fixation and to identify the key players. The study was carried out at a marine shallow-water hydrothermal system located at 5 m water depth off Dominica Island (Lesser Antilles), characterized by up to 55°C warm hydrothermal fluids that contain high amounts of dissolved Fe2+. Analysis of the bacterial diversity revealed Anaerolineae of the Chloroflexi as the most abundant bacterial class. Furthermore, the presence of key players involved in iron cycling generally known from deep-sea hydrothermal vents (e.g., Zetaproteobacteria and Geothermobacter), supported the importance of iron-driven redox processes in this hydrothermal system. Uptake of 13C-bicarbonate into bacterial fatty acids under light and dark conditions revealed active photo- and chemoautotrophic communities, with chemoautotrophy accounting for up to 65% of the observed autotrophic carbon fixation. Relatively increased 13C-incorporation in the dark allowed the classification of aiC15:0, C15:0, and iC16:0 as potential lipid biomarkers for bacterial chemoautotrophy in this ecosystem. Highest total 13C-incorporation into fatty acids took place at the sediment surface, but chemosynthesis was found to be active down to 8 cm sediment depth. In conclusion, this study highlights the relative importance of chemoautotrophy compared to photoautotrophy in a shallow-water hydrothermal system, emphasizing chemosynthesis as a prominent process for biomass production in marine coastal environments influenced by hydrothermalism.
  • Article
    Fluid flow stimulates chemoautotrophy in hydrothermally influenced coastal sediments
    (Nature Research, 2022-04-22) Sievert, Stefan M. ; Bühring, Solveig I. ; Gulmann, Lara K. ; Hinrichs, Kai-Uwe ; Pop Ristova, Petra ; Gomez-Saez, Gonzalo V.
    Hydrothermalism in coastal sediments strongly impacts biogeochemical processes and supports chemoautotrophy. Yet, the effect of fluid flow on microbial community composition and rates of chemoautotrophic production is unknown because rate measurements under natural conditions are difficult, impeding an assessment of the importance of these systems. Here, in situ incubations controlling fluid flow along a transect of three geochemically distinct locations at a shallow-water hydrothermal system off Milos (Greece) show that Campylobacteria dominated chemoautotrophy in the presence of fluid flow. Based on injected 13C-labelled dissolved inorganic carbon and its incorporation into fatty acids, we constrained carbon fixation to be as high as 12 µmol C cm−3 d−1, corresponding to areal rates up to 10-times higher than previously reported for coastal sediments, and showed the importance of fluid flow for supplying the necessary substrates to support chemoautotrophy. Without flow, rates were substantially lower and microbial community composition markedly shifted. Our results highlight the importance of fluid flow in shaping the composition and activity of microbial communities of shallow-water hydrothermal vents, identifying them as hotspots of microbial productivity.