Quantifying tidally driven benthic oxygen exchange across permeable sediments: An aquatic eddy correlation study

• Published in: Journal of geophysical research. Oceans Vol. 119; no. 10; pp. 6918 - 6932
• Main Authors: McGinnis, Daniel F., Sommer, Stefan, Lorke, Andreas, Glud, Ronnie N., Linke, Peter
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-10-2014
• Subjects: benthic oxygen exchange; Bottom currents; Boundary layer; Boundary layers; Computational fluid dynamics; Contaminated sediments; Continental shelves; eddy correlation; Exchange; Fluctuations; Fluid flow; Flux; Geophysics; Hydrodynamics; Hypoxia; Low flow; Mathematical models; Mineralization; North Sea; Nutrients; Ocean bottom; Oceanography; Organic matter; Oxygen; Oxygen uptake; permeable sediments; Pore water; Roughness coefficient; Sediments; Turbulence; Water exchange; ANE, North Sea
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2014JC010303

Continental shelves are predominately (70%) covered with permeable, sandy sediments. While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchange across permeable sediments remains poorly quantified. The central North Sea largely consists of permeable sediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigate the benthic O sub(2) exchange across the permeable North Sea sediments using a combination of in situ microprofiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sediment O sub(2) penetration depth (from 3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in the benthic sediment O sub(2) uptake. The O sub(2) flux and variability were reproduced using a simple 1-D model linking the benthic turbulence to the sediment pore water exchange. The high O sub(2) flux variability results from deeper sediment O sub(2) penetration depths and increased O sub(2) storage during high velocities, which is then utilized during low-flow periods. The study reveals that the benthic hydrodynamics, sediment permeability, and pore water redox oscillations are all intimately linked and crucial parameters determining the oxygen availability. These parameters must all be considered when evaluating mineralization pathways of organic matter and nutrients in permeable sediments. Key Points * Benthic oxygen fluxes vary by up to 25 times in North Sea permeable sediments * Bottom boundary layer turbulence drives sediment O sub(2) flux in permeable sediments * Bottom roughness coefficient varies as a function of velocity