Comparative studies of pelagic microbial methane oxidation within the redox zones of the Gotland Deep and Landsort Deep (central Baltic Sea)

[摘要] Pelagic methane oxidation was investigated in dependence on differinghydrographic conditions within the redox zone of the Gotland Deep (GD) andLandsort Deep (LD), central Baltic Sea. The redox zone of both deeps, whichindicates the transition between oxic and anoxic conditions, wascharacterized by a pronounced methane concentration gradient between the deepwater (GD: 1233 nM, 223 m; LD: 2935 nM, 422 m) and the surface water (GDand LD < 10 nM). This gradient together with a ¹³C CH₄enrichment (δ¹³C CH₄ deep water: GD −84‰, LD−71‰; redox zone: GD −60‰, LD −20‰;surface water: GD −47‰, LD −50‰; δ¹³CCH₄ vs. Vienna Pee Dee Belemnite standard), clearly indicating microbialmethane consumption within the redox zone. Expression analysis of the methanemonooxygenase identified one active type I methanotrophic bacterium inboth redox zones. In contrast, the turnover of methane within the redox zonesshowed strong differences between the two basins (GD: max. 0.12 nM d⁻¹, LD: max. 0.61 nM d⁻¹), with a nearly four-times-lower turnovertime of methane in the LD (GD: 455 d, LD: 127 d). Vertical mixing rates forboth deeps were calculated on the base of the methane concentration profileand the consumption of methane in the redox zone (GD:2.5 × 10^–6 m² s⁻¹, LD:1.6 × 10^–5 m² s⁻¹). Our study identified verticaltransport of methane from the deep-water body towards the redox zone as wellas differing hydrographic conditions (lateral intrusions and vertical mixing)within the redox zone of these deeps as major factors that determine thepelagic methane oxidation.

[学科分类] 地球化学与岩石