Marine shallow hydrothermal systems: imprint of their exclusive biogeochemistry on dissolved organic matter and chemosynthesis

• Main Author: Gómez Sáez, Gonzalo Vicente
• Other Authors: Bühring, Solveig I., Dittmar, Thorsten
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2016
• Subjects: Marine shallow hydrothermal systems; dissolved organic matter (DOM); dissolved organic sulfur (DOS); iron-carbon co-precipitation; chemoautotrophy; 550; 550 Earth sciences and geology; ddc:550; Iceland; North Atlantic
• Online Access: https://media.suub.uni-bremen.de/handle/elib/999; https://nbn-resolving.org/urn:nbn:de:gbv:46-00105043-12

Shallow submarine hydrothermal systems are extreme environments with unique biogeochemical conditions, originating from (1) the interaction of hot, reduced fluids and cold, oxygenated seawater, and (2) the possibility of simultaneous primary production by photo- and chemosynthesis. The flux of carbon, reduced molecules and trace elements from hydrothermal vents is mainly controlled by dissolved organic matter (DOM), which is one of the largest pools of organic carbon in the oceans and therefore plays a major role in key biogeochemical cycles. However, the influence of hydrothermal activity on DOM at a molecular level has not been investigated, and an holistic understanding of the functioning of marine shallow systems is currently lacking. The aim of this thesis was to investigate the imprint of the exclusive biogeochemistry of marine shallow hydrothermal systems on (1) the DOM molecular signature and associated redox processes at the interface between fluids and seawater (Chapters 3, 4, S8), and (2) the role of chemoautotrophy in carbon fixation at hydrothermally influenced sediments (Chapters 5, S7). The study sites were three contrasting shallow systems off Dominica (Caribbean Sea), Milos (Eastern Mediterranean) and Iceland (North Atlantic). In contrast to the predominantly meteoric fluids from Dominica and Iceland, hydrothermal fluids from Milos were mainly fed by recirculating seawater. Milos fluids were also strongly enriched in hydrogen sulfide (H2S) and dissolved organic sulfur (DOS), as indicated by high DOS/DOC ratios and by the fact that 93% of all assigned DOM molecular formulas exclusively present in the fluids contained sulfur. Evaluation of hypothetical pathways suggested DOM reduction and sulfurization during seawater recirculation in Milos seafloor. The four most effective pathways were those exchanging an O atom by one S atom in the formula or the equivalent H2S reaction. In all three systems, low O/C molar ratios in the fluids suggested shallow hydrothermal systems as a source of reduced DOM ...