| Summary: | Memoria de tesis doctoral presentada por Federico Baltar González para obtener el grado de Doctor en Oceanografía por la Universidad de las Palmas de Gran Canaria (ULPGC), bieno (2005-2007), realizada bajo la dirección del Dr. Javier Arístegui Ruiz, del Dr. Gerhard Herndl y del Dr. Josep Maria Gasol Piqué del Institut de Ciències del Mar (ICM-CSIC).-- 317 pages [EN] Prokaryotes are the cornerstone mediating the oceanic biogeochemical cycles. Due to the typical extreme abiotic conditions (e.g. high pressure, low temperature, low availability of organic matter) found in the dark ocean (> 200 m depth), it was generally assumed to be a site holding negligible, homogeneously-distributed biological activity. That is why most of the research done concerning the ecology ofprokaryotes have been carried out in surface waters, further leaving behind the study of the largest habitat in the biosphere: the dark ocean. In this study we assessed the actual role of the deep-sea prokaryotes in the marine biogeochemical cycles. The distribution of the organic matter pool (dissolved and particulate), the prokaryotic assemblage structure, abundance and metabolism (heterotrophic production, respiration, extracellular enzymatic activity) were analyzed along the water column of the North Atlantic, in six different research cruises. We found that the dark ocean plays a key role in the carbon mineralization processes (sometimes being, on a per-cell level, as active as the epipelagic waters), being far from a homogenously-distributed non-active ecosystem. The heterogeneity found in the dark ocean seemed to be controlled by a “bottom-up” effect, where the suspended particulate organic matter distribution modulates the prokaryotic activity. This stronger association between suspended particles and deepsea prokaryotes than assumed hitherto, would facilitate synergistic interactions in the cycling of matter in the dark ocean. Finally, we also found that the enigmatic imbalance between the organic carbon supply to the dark ocean and the ...
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