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Near seafloor methane flux in the world's largest human-induced dead zone is regulated by sediment accumulation rate.

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Title: Near seafloor methane flux in the world's largest human-induced dead zone is regulated by sediment accumulation rate.
Authors: Ketzer, M.1 (AUTHOR) marcelo.ketzer@lnu.se, Stranne, C.2 (AUTHOR), Rahmati-Abkenar, M.1,3 (AUTHOR), Shahabi-Ghahfarokhi, S.1,4 (AUTHOR), Jaeger, L.1,5 (AUTHOR), Pivel, M.A.G.6 (AUTHOR), Josefsson, S.7 (AUTHOR), Zillén, L.7 (AUTHOR)
Source: Marine Geology. Feb2024, Vol. 468, pN.PAG-N.PAG. 1p.
Subjects: Sediments, Methane, Supply & demand, Organic compounds, Sedimentation & deposition, Sediment-water interfaces
Geographic Terms: Gulf of Mexico
Abstract: The vast oxygen-depleted area of the central Baltic Sea is the largest human-induced dead zone in the world with 70,000 km2 or approximately three times the second largest one in the Gulf of Mexico. Methane occurs in high concentrations in bottom waters (3200 nM) and sediments (30 mM), and its dynamics is better constrained for the water column, but still poorly understood on sediments. Here we show that sediment accumulation rate plays a major role in regulating the quantity of organic matter and its residence time in the sulphate reduction and methanogenesis zones and, therefore, affects methane generation, consumption, and diffusive flux in sediments near the seafloor (< 1 m). High fluxes found in high sediment accumulation rate areas and competition for substrate (organoclastic sulphate reduction vs. anaerobic oxidation of methane with sulphate), compromise the ability of the thin microbial filter to consume and prevent methane diffusion through the seafloor. • A coring campaign compared methane concentrations in sediments and bottom waters in the Baltic Proper and Bothnian Bay. • High near-seafloor methane fluxes in sediments in the Baltic Proper occur in areas with high sediment accumulation rate. • High supply of labile organic matter diminishes the ability of the sulphate reduction microbial filter to oxidise methane. • High sedimentation quickly buries organic matter below the sulphate reduction zone leaving labile material for methanogenesis. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:The vast oxygen-depleted area of the central Baltic Sea is the largest human-induced dead zone in the world with 70,000 km2 or approximately three times the second largest one in the Gulf of Mexico. Methane occurs in high concentrations in bottom waters (3200 nM) and sediments (30 mM), and its dynamics is better constrained for the water column, but still poorly understood on sediments. Here we show that sediment accumulation rate plays a major role in regulating the quantity of organic matter and its residence time in the sulphate reduction and methanogenesis zones and, therefore, affects methane generation, consumption, and diffusive flux in sediments near the seafloor (< 1 m). High fluxes found in high sediment accumulation rate areas and competition for substrate (organoclastic sulphate reduction vs. anaerobic oxidation of methane with sulphate), compromise the ability of the thin microbial filter to consume and prevent methane diffusion through the seafloor. • A coring campaign compared methane concentrations in sediments and bottom waters in the Baltic Proper and Bothnian Bay. • High near-seafloor methane fluxes in sediments in the Baltic Proper occur in areas with high sediment accumulation rate. • High supply of labile organic matter diminishes the ability of the sulphate reduction microbial filter to oxidise methane. • High sedimentation quickly buries organic matter below the sulphate reduction zone leaving labile material for methanogenesis. [ABSTRACT FROM AUTHOR]
ISSN:00253227
DOI:10.1016/j.margeo.2024.107220