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

Continental shelves are predominately (70%) covered with permeable, sandy sediments.While identified as critical sites for intense oxygen, carbon, and nutrient turnover, constituent exchangeacross permeable sediments remains poorly quantified. The central North Sea largely consists of permeablesediments and has been identified as increasingly at risk for developing hypoxia. Therefore, we investigatethe benthic O2exchange across the permeable North Sea sediments using a combination of in situ micro-profiles, a benthic chamber, and aquatic eddy correlation. Tidal bottom currents drive the variable sedimentO2penetration depth (from 3 to 8 mm) and the concurrent turbulence-driven 25-fold variation in thebenthic sediment O2uptake. The O2flux and variability were reproduced using a simple 1-D model linkingthe benthic turbulence to the sediment pore water exchange. The high O2flux variability results fromdeeper sediment O2penetration depths and increased O2storage during high velocities, which is then uti-lized 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 oxygenavailability. These parameters must all be considered when evaluating mineralization pathways of organicmatter and nutrients in permeable sediments.