2. Participants

3. Activities

3.1 General

We visited seven stations, three less than envisioned in the cruise plan. One full day was lost due to bad weather conditions. Furthermore, malfunctioning of both lander systems forced us to stay longer at station 5 than planned. The original plan was to investigate stations with increasing grain size and permeability, starting at the muddy Friesian Front and ending in the Broad Fourteens where sand dunes dominate bed form. During the cruise we decided to refrain from the stations planned in the coarsest sands in the south, because the change for successful deployment of the oxygen profiler would be minimal there. At the now coarsest station 5 the microelectrodes were broken due to the shell fragments intermixed with the sand grains. Station 4 appeared promising to evidence the effect of pore water percolation on the organic carbon mineralization rates and was therefore revisited twice (Stations 6, 7). The storm at the first of October gave us the opportunity to investigate the effect of increased current and wave activity on permeability and early diagenetic activity in the sandy sediment.

At the Friesian Front we deployed the recruitment lander of Magda Bergman (NIOZ) as part of the ongoing "Friesian Front/Beef to fish" study. The first 3 stations were within the target area of the NWO/ALW-funded Plume and Bloom program.

3.2 Stations

One additional station (22; 53:20.01 N, 4:75 E, depth 29 m) was visited on 22 September to collect sand to be used in the experimental set-up to measure permeability. Station 1 was revisited on 25 Sep to recover the TROL lander.

3.3 Experiments

1. The TROL lander was deployed at stations 1, 5, 6 and 7. The ALBEX chambers, albeit not all, functioned well at the last 4 stations. The oxygen profiler did not function until station 7 ? The ALBEX modules were programmed to inject a bromide solution into the water in the chambers, allowing diffusion of the bromide into the pore water. Thereafter two of the three cambers were withdrawn, allowing free exchange of the bromide in the pore water into the water column. Finally the chambers were closed again and sediment cores were taken to measure the bromide profiles in the two cores with and the one core without free exchange. With these experiments we hope to get insight in the difference between the diffusive and advection-stimulated exchange rates.
   The oxygen-profiling unit of the TROL showed mechanical and electronical problems, which could be overcome just in time to have a last deployment at St. 7.
2. The PULS C-ADP lander from IOW-Warnemünde is equipped with a video camera and a down-looking puls coherent ADCP measuring in bins of 1.7 cm in the lower 2.5 m of the water column. The lander was deployed at stations 3, 5, 6 and 7. As for the TROL the PULS C-ADP lander caused problems at the first stations and several test deployments were needed to collect good data at stations 5 and 7.