Deep-Sourced Fluids From a Convergent Margin Host Distinct Subseafloor Microbial Communities That Change Upon Mud Flow Expulsion

Abstract

Submarine mud volcanoes (MVs) along continental margins emit mud breccia and globally significant amounts of hydrocarbon-rich fluids from the subsurface, and host distinct chemosynthetic communities of microbes and macrofauna. Venere MV lies at 1,600 m water depth in the Ionian Sea offshore Italy and is located in a forearc basin of the Calabrian accretionary prism. Porewaters of recently extruded mud breccia flowing from its west summit are considerably fresher than seawater (10 PSU), high in Li + and B (up to 300 and 8,000 μM, respectively), and strongly depleted in K + (<1 mM) at depths as shallow as 20 cm below seafloor. These properties document upward transport of fluids sourced from >3 km below seafloor. 16S rRNA gene and metagenomic sequencing were used to characterize microbial community composition and gene content within deep-sourced mud breccia flow deposits as they become exposed to seawater along a downslope transect of Venere MV. Summit samples showed consistency in microbial community composition. However, beta-diversity increased markedly in communities from downslope cores, which were dominated by methyl- and methanotrophic genera of Gammaproteobacteria . Methane, sulfate, and chloride concentrations were minor but significant contributors to variation in community composition. Metagenomic analyses revealed differences in relative abundances of predicted protein categories between Venere MV and other subsurface microbial communities, characterizing MVs as windows into distinct deep biosphere habitats.

Sulfur and Methane-Oxidizing Microbial Community in a Terrestrial Mud Volcano Revealed by Metagenomics

“…Mud volcanoes attracted the attention of microbiologists because they provide easy access to the deep subsurface biosphere since relatively rapid fluid transport in a fracture network enables limited alteration of fluid and gas until it is discharged to the surface [ 2 ]. Microbial communities associated with mud volcanoes located at the seafloor have been extensively studied [ 7 , 8 , 9 , 10 , 11 , 12 ]. More limited number of studies has focused on microbial communities in terrestrial mud volcanoes [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”

Microbial communities from Arctic marine sediments respond slowly to methane addition during ex situ enrichments

“…Their global ubiquity and distribution within methane‐rich sediments (Nunoura et al ., ; Ruff et al ., ) shapes microbial community structures in these zones (Harrison et al ., ), and in situ observations suggest that these methanotrophic communities develop over timescales of years (Ruff et al ., ). Processes that contribute to the spatiotemporally variable distribution of methane and sulfate throughout the sediment column include increases in subseafloor methane flux (Hong et al ., ), gas hydrate destabilization (Westbrook et al ., ), emission of mud breccia flows through mud volcanism (Ruff et al ., ; Klasek et al ., ) and sediment gravity flows (Hensen et al ., ). These all presumably impact microbial community structure, ANME/SRB populations, and ultimately AOM rates.…”

Focused fluid flow and methane venting along the Queen Charlotte fault, offshore Alaska (USA) and British Columbia (Canada)

“…The incorporation of shells also indicates in situ cementation of chemosynthetic communities that live at the sediment-water interface. In contrast, the depleted radiogenic Sr-isotope composition from samples 2011-STN43 (seep 16) and 2017-STN03 (seep 11) suggests mixing with fluids other than modern seawater, such as deep-sourced mud breccia flow (e.g., Klasek et al, 2019) and meteoric fluids from groundwater circulating at depth due to changes in hydraulic head linked to ice-sheet dynamics (e.g., Person et al, 2007).…”