Calibration and performance of the stirred flux chamber from the benthic lander Elinor

Flow velocities and O2 microgradients were measured by use of minithermistors and O2 microelectrodes inside a laboratory model of the chamber from the benthic lander, Elinor. The sensors were introduced from below through small holes in the chamber bottom and penetrated up through the sediment. Flow velocities and the diffusive boundary layer (DBL) could thereby be studied with a minimum of disturbance. In the central part of the chamber covering 9% of the area, the DBL was thicker and the flow rates significantly lower than in the rest of the hydrodynamically uniform chamber. Average flow velocities of 2.4–4.6 cm s−1 and average DBL thicknesses of 220–625 em were measured at stirring rates of 8–15 rpm and water column heights of 10–15 cm. In homogeneous impermeable sediments, the average diffusive O2 uptake calculated from O2, microprofiles was equal to the total O2 uptake within ±3%. Radial pressure gradients in the stirred chamber were 1–3 Pa. Such pressure gradients may induce advective pore water transport in permeable sediments and increase the flushing of animal burrows in bioturbated sediments.