Baltic Sea's Dead Zone Pumps More Methane as Sediment Piles Up
Researchers have identified a critical mechanism driving methane emissions from the world's largest oxygen-depleted ocean zone: sediment accumulation rate. As mud builds up faster, more organic matter lingers in methane-producing zones, overwhelming the microbial processes that normally trap the gas—a finding with implications for carbon accounting and coastal management strategies.
Originaltitel: Near seafloor methane flux in the world's largest human-induced dead zone is regulated by sediment accumulation rate
<p>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.</p>