Description: In near-shore and coastal margin sediments remineralization of organic carbon is significantlyaffected by biologically mediated solute exchange caused by burrow-dwelling infauna. Although irrigationrates have been determined for various environments, little is known about their seasonal variations and theircoupling to the food-supply or the oxygen level in bottom waters. These aspects have been investigated at twosites in the Kiel Bight by modelling pore water concentrations of Cl, which is a suitable tracer for transportprocesses. A very similar temporal pattern of irrigation was determined at both sites. In spring and fall theeffect of bioirrigation on the pore water concentration of Cl is important at both sites, and a more than twoto five fold enhancement of solute exchange, relative to diffusional transport, was calculated. The temporalpattern of bioirrigation correlates with that of the Chl.-a (eq) inventory of the surface sediments. Enhancedirrigation rates follow the settling of plankton blooms in this region. During the summer, when low oxygenlevels were observed in bottom waters, overall irrigation rates are low. Furthermore, the relative importanceof irrigation processes operating close to the sediment surface increases suggesting an upward movement andmigration of burrow-dwelling organisms in response to low O2-concentrations. Because bioirrigation is animportant transport process coupling organic carbon flux, remineralization at the seafloor, and redox zonationin the sediment quantifying the seasonal cycle of the irrigation intensity represents a step forward in thedynamic understanding of benthic processes.