Pore-water advection and organic matter mineralization in North Sea shelf sands

Advective pore-water transport and its effect on sediment metabolism was studied in sandy sediments north of the Island of Spiekeroog in situ. Natural pressure gradients as estimated from sediment topography and bottom flow indicated significant advection in medium and coarse sands. This was confirmed by time series of oxygen micro profiles, showing an advective supply of oxygen to the sediment. The contribution of this supply to the sediment oxygen uptake was investigated with benthic chambers that exposed the enclosed sediments to defined pressure gradients to induce pore-water advection at natural rates. At high permeabilities the oxygen uptake increased significantly in the presence of advection, indicating its potential to favor aerobic degradation of organic matter in permeable sands. Combining these measurements with larger scale estimates of sediment permeabilities, pore-water advection was expected to promote sediment oxygen consumption in up to 60 % of the German Bight area.