Figure 4.

A conceptual biogeochemical model of the Loki's Castle Vent Field. (1) The high-temperature vent fluid is characterized by high CH₄, H₂, and ${\text{NH}}_4^{+}$ concentrations in addition to H₂S (Pedersen et al., 2010). (2) The H₂S, H₂and CH₄ support growth of Epsilonproteobacteria of the genera Sulfurimonas and Sulfurovum and gammaproteobacterial Methylococcales, respectively, in biofilms covering the black smoker chimneys (Dahle et al., 2013, 2015). (3) Sulfurovum forms large filamentous structures with sheaths of a heat resistant biopolymer (Stokke et al., 2015). (4) Subsurface mixing with percolating seawater and associated geochemical and microbial processes lead to sulfate reduction (Eickmann et al., 2014) and depletion of H₂ in the low-temperature fluids discharged in the barite field. H₂S in the diffuse venting fluids in the barite field supports microorganisms in the microbial mat on top of the barite chimneys (5), in the chimney exterior (6), interior (7), and in the hydrothermal sediment (8). CH₄ supports microorganisms in the sediment and in the chimney interior and exterior, whereas ${\text{NH}}_4^{+}$ may be utilized in the surface sediment densely colonized by the tubeworm Sclerolinum contortum (Kongsrud and Rapp, 2012). The moderate fluid flow through the barite chimneys support biofilms of Sulfurimonas (5) forming delicate networks of single cells interconnected with EPS.