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Free keywords:
PARTICULATE ORGANIC-CARBON; BENTHIC PRIMARY PRODUCTION; DIFFUSIVE
BOUNDARY-LAYER; IN-SITU MEASUREMENTS; DEEP-SEA SEDIMENTS; BALTIC SEA;
EQUATORIAL PACIFIC; NUTRIENT FLUXES; SOLUTE EXCHANGE; REACTION-RATESGeology; Organic carbon mineralization; Total oxygen uptake; Diffusive oxygen
uptake; Benthic fauna; Global budget; Database;
Abstract:
The seabed plays a key role in the marine carbon cycle as a) the terminal location of aerobic oxidation of organic matter, b) the greatest anaerobic bioreactor, and c) the greatest repository for reactive organic carbon on Earth. We compiled data on the oxygen uptake of marine sediments with the objective to understand the constraints on mineralization rates of deposited organic matter and their relation to key environmental parameters. The compiled database includes nearly 4000 O-2 uptake data and is available as supplementary material. It includes also information on bottom water O-2 concentration, O-2 penetration depth, geographic position, water depth, and full information on the data sources. We present the different in situ and ex situ approaches to measure the total oxygen uptake (TOU) and the diffusive oxygen uptake (DOU) of sediments and discuss their robustness towards methodological errors and statistical uncertainty. We discuss O-2 transport through the benthic and diffusive boundary layers, the diffusion-and fauna-mediated O-2 uptake, and the coupling of aerobic respiration to anaerobic processes. Five regional examples are presented to illustrate the diversity of the seabed: Eutrophic seas, oxygen minimum zones, abyssal plains, mid-oceanic gyres, and hadal trenches. A multiple correlation analysis shows that seabed O-2 uptake is primarily controlled by ocean depth and sea surface primary productivity. The O-2 penetration depth scales with the DOU according to a power law that breaks down under the abyssal ocean gyres. The developed multiple correlation model was used to draw a global map of seabed O-2 uptake rates. Respiratory coefficients, differentiated for depth regions of the ocean, were used to convert the global O-2 uptake to organic carbon oxidation. The resulting global budget shows an oxidation of 212 Tmol C yr(-1) in marine sediments with a 5-95% confidence interval of 175-260 Tmol C yr(-1). A comparison with the global flux of particulate organic carbon (POC) from photic surface waters to the deep sea, determined from multiple sediment trap studies, suggests a deficit in the sedimentation flux at 2000 m water depth of about 70% relative to the carbon turnover in the underlying seabed. At the ocean margins, the flux of organic carbon from rivers and from vegetated coastal ecosystems contributes greatly to the budget and may even exceed the phytoplankton production on the inner continental shelf.
