CALIBRATION AND PERFORMANCE OF THE STIRRED FLUX CHAMBER FROM THE BENTHIC LANDER ELINOR

Flow velocities and O-2 microgradients were measured by use of minithe rmistors and O-2 microelectrodes inside a laboratory model of the cham ber from the benthic lander, Elinor. The sensors were introduced from below through small holes in the chamber bottom and penetrated up thro ugh the sediment. Flow velocities and the diffusive boundary layer (DB L) could thereby be studied with a minimum of disturbance. In the cent ral part of the chamber covering 9% of the area, the DBL was thicker a nd the flow rates significantly lower than in the rest of the hydrodyn amically uniform chamber. Average flow velocities of 2.4-4.6 cm s(-1) and average DBL thicknesses of 220-625 mu m were measured at stirring rates of 8-15 rpm and water column heights of 10-15 cm. In homogeneous impermeable sediments, the average diffusive O-2 uptake calculated fr om O-2 microprofiles was equal to the total O-2 uptake within +/- 3%. Radial pressure gradients in the stirred chamber were 1-3 Pa. Such pre ssure gradients may induce advective pore water transport in permeable sediments and increase the flushing of animal burrows in bioturbated sediments.