Preface The expedition ARK XIX/3 with the German icebreaking RV ...

pH, resistivity, oxygen and HS - at the sediment-water interface were envisaged using the
ROV to deploy the microprofiler at selected spots within the above mentioned key
locations.
The first working day onboard was dominated by meetings and the assignment of
laboratories. The working schedules of the next days were presented and instruments
were tested. In the afternoon we reached our first station where the CTD was used to
obtain information about water salinity and temperature at different depths. This data was
necessary for the calibration of our sonar systems because among others the sound
velocity in water is determined by temperature and salinity. Afterwards we worked the
entire night on a small scale survey grid with the multi beam sonar system Hydrosweep,
the sediment profiling sonar system Parasound and the 38 kHz echosounder. With the
latter we obtained data where spots of high methane release were located. This kind of
information allowed us to collect afterwards samples in the water column at high spatial
precision.
On Saturday sediment sampling started by using the multicorer while in the evening two
free falling lander systems were deployed and soon after the first ROV station started. At
1250 m water depth a video survey was carried out during the night and the information
obtained by doing this was used on Sunday to select some sites of special scientific
interest where sediments covered by white bacterial mats were sampled using plastic
tubes (push corers) operated by the manipulator arms of "Victor 6000".
After the first succesful mission of "Victor 6000" at the Håkon Mosby Mud Volcano which
was finished shortly before midnight on Sunday, we released the lander which was
observed before by the ROV at more than 1200 m water depth. About thirty minutes later
the lander was sighted about 100 m distance in front of "Polarstern". At this moment we
had fog so the visibility was below 200 metres. However, the lander was equipped with a
radio beacon and flash lights providing safety systems for localization under such
conditions. After recovery of the lander we worked for about 12 hours on a heat flow
measurement programme. Therefore, a temperature lance of three metres length was
used with one of the ship‘s winches. The lance becomes rammed into the sediment and
measures the temperature at different depth strata. This procedure was repeated along a
given waypoint list. At the end of this work package we knew that the the temperature at
about 3 metres below the seabed might be much higher (close to 20 °C) than on deck of
- 13 -