Saturated CO2 inhibits microbial processes in CO2-vented deep-sea sediments

[摘要] This study focused on biogeochemical processes and microbial activity insediments of a natural deep-sea CO₂ seepage area (Yonaguni Knoll IVhydrothermal system, Japan). The aim was to assess the influence of thegeochemical conditions occurring in highly acidic and CO₂ saturatedsediments on sulfate reduction (SR) and anaerobic methane oxidation (AOM).Porewater chemistry was investigated from retrieved sediment cores and insitu by microsensor profiling. The sites sampled around a sediment-hostedhydrothermal CO₂ vent were very heterogeneous in porewater chemistry,indicating a complex leakage pattern. Near the vents, droplets of liquidCO₂ were observed emanating from the sediments, and the pH reachedapproximately 4.5 in a sediment depth > 6 cm, as determined in situ bymicrosensors. Methane and sulfate co-occurred in most sediment samples fromthe vicinity of the vents down to a depth of 3 m. However, SR and AOM wererestricted to the upper 7–15 cm below seafloor, although neithertemperature, low pH, nor the availability of methane and sulfate could belimiting microbial activity. We argue that the extremely high subsurfaceconcentrations of dissolved CO₂ (1000–1700 mM), which disrupt thecellular pH homeostasis, and lead to end-product inhibition. This limits lifeto the surface sediment horizons above the liquid CO₂ phase, where lessextreme conditions prevail. Our results may have to be taken intoconsideration in assessing the consequences of deep-sea CO₂sequestration on benthic element cycling and on the local ecosystem state.

[学科分类] 地球化学与岩石