Saturated CO<sub>2</sub> inhibits microbial processes in CO<sub>2</sub>-vented deep-sea sediments

Abstract

Abstract. This study focused on biogeochemical processes and microbial activity in sediments of a natural deep-sea CO2 seepage area (Yonaguni Knoll IV hydrothermal system, Japan). The aim was to assess the influence of the geochemical conditions occurring in highly acidic and CO2 saturated sediments on sulfate reduction (SR) and anaerobic methane oxidation (AOM). Porewater chemistry was investigated from retrieved sediment cores and in situ by microsensor profiling. The sites sampled around a sediment-hosted hydrothermal CO2 vent were very heterogeneous in porewater chemistry, indicating a complex leakage pattern. Near the vents, droplets of liquid CO2 were observed emanating from the sediments, and the pH reached approximately 4.5 in a sediment depth > 6 cm, as determined in situ by microsensors. Methane and sulfate co-occurred in most sediment samples from the vicinity of the vents down to a depth of 3 m. However, SR and AOM were restricted to the upper 7–15 cm below seafloor, although neither temperature, low pH, nor the availability of methane and sulfate could be limiting microbial activity. We argue that the extremely high subsurface concentrations of dissolved CO2 (1000–1700 mM), which disrupt the cellular pH homeostasis, and lead to end-product inhibition. This limits life to the surface sediment horizons above the liquid CO2 phase, where less extreme conditions prevail. Our results may have to be taken into consideration in assessing the consequences of deep-sea CO2 sequestration on benthic element cycling and on the local ecosystem state.

Geochemical observations within the water column at the CO2‐rich hydrothermal systems Hatoma Knoll and Yonaguni Knoll IV, in the southern Okinawa Trough

“…However, it cannot be excluded that diffuse flow of liquid or supercritical CO 2 leads to pronounced CaCO 3 dissolution in the sediment and that these processes affect the geochemistry of the near‐bottom layer of both systems (lowermost 10 m of the water column) which have not been investigated geochemically in this study. Very high A T values measured in pore waters of the upper sediment close to active sites in YK [ de Beer et al ., ; Neumann , ] support this assumption, however, further investigations are required.…”

“…The seafloor at YK is mainly covered with muddy sediments of terrigenous origin [ Suzuki et al ., ] and is strongly affected by carbonate and silicate weathering at the vent sites [ de Beer et al ., ; Häckel et al ., ].…”

“…During a cruise with the German R/V SONNE (SO 196‐2, SUMSUN) in March 2008, both CO 2 ‐rich systems were investigated by applying an interdisciplinary approach including chemical and physical oceanography, marine geochemistry, and microbiology. Objectives of the cruise included investigations of strongly enhanced CO 2 concentrations on biological processes and microbial activity in the sediment and pore water geochemistry [ de Beer et al ., ; Neumann , ; Yanagawa et al ., ].…”

Influence of impurities (nitrogen and methane) on the CO2 storage capacity as sediment-hosted gas hydrates – Application in the area of the Celtic Sea and the Bay of Biscay

“…The second stream CO2-97 is representative of a fluid mixture coming from a gas-fired plant using the pre-combustion 8 capture process and contains 3% of impurities with about 1% of N 2 and less than 2% of CH 4 (Table 1) (Metz et al, 2005). Submarine venting of natural liquid CO 2 has been recently observed and it has been shown that CO 2 -saturated seawater should inhibit sulfate reduction and anaerobic methane oxidation (AOM) in deep-sea sediments (de Beer et al, 2013).…”

“…Submarine venting of natural liquid CO 2 has been previously observed only at a few submarine volcanoes (Lupton et al, 2006;de Beer et al, 2013). The study in laboratory of the dynamics of the gas hydrates in sedimentary medium (namely formation, accumulation and destabilization processes) is still at its beginnings.…”