2 July - 8 July 2007 (Week 27)

During the night from Sunday to Monday sediment samples were taken by a multiple corer followed by gravity cores in the early hours of the morning. Some gravity cores were taken in the vicinity of the mud volcano so as to assess changes in the mud flow of the Håkon Mosby.

On Monday at six o’clock in the morning, the lift which carried various instruments was carefully lowered by the ship’s winches and was disconnected from the rope at 20 m above the sea bed – the last few meters the lift falls freely to the sea floor.

A very accurate underwater navigation system allows us to locate the system at a precision of a few meters. This enables the ROV QUEST to fly towards the lift without delay and to pick up instruments. At a water depth of 1300 m the descent of QUEST takes an hour. The average bottom time is ca 10 hours which has to be divided such that each research team on board has sufficient time for their measurements and sampling. In the early hours of the evening both the lift and the ROV were back on deck and the geological sampling proceeded. The weather had calmed down considerably and according to the (excellent!) weather forecasts of the board meteorologist it was to remain calm during the week. We were therefore able to establish a routine of conducting QUEST dives during the day and using winch operated gears during the night for the days to come.

In the middle of the week, we carried out further measurements with the temperature lance: for this purpose, temperature sensors are attached at defined intervals along a 6 m steel pipe which measure the ambient temperature at an accuracy of 0.002 °C and logs the result every 5 seconds. At the centre of the mud volcano, the lance which weighs just above 1 t sank 80 m deep into an almost liquid mud which has a temperature of 25°C in the upper meters (the temperature of the bottom water is -0.8°C – this is an enormous temperature gradient!). This coincidence allowed us to obtain one of the deepest temperature profiles ever measured at a mud volcano. It should be noted that during this procedure “Polarstern” has to maintain its position precisely above the point where the lance penetrates the sea floor. As the temperature lance sank forever deeper into the mud the whole measurement took an hour. During all this time the nautical officers at the bridge succeeded in maintaining the ship’s position within a range of less than 10 m. This does not only take technical aptitude but also great nautical skills!

The fish trap which had been deployed during the first few days was not as successful as hoped. Rather than fish, the traps caught several dozens of scavenging deep-sea crustaceans (amphipods). Even after modification of the trap design and using different types of bait only few fish were caught. The disappointment and nervousity of the scientists increased with every trap deployment which did not yield the fish hoped for, especially as a grant proposal had been accepted by the Deutsche Forschungsgemeinschaft this week. This project relies on alive fish from the Arctic deep sea. Therefore, the slurp gun (hoover) of QUEST was used to catch fish. In the evening the cavity of the slurp gun was placed above the bottom-dwelling fish by one of the robotic arms and the hydraulic pump activated: Although some of the fish managed to escape a considerable number of fish was sucked up and spat out into fish containers. In the meantime, some 20 fish have settled down in our aquaria.

The last two ROV dives were planned for Thursday and Friday. Last gaps in the sampling programmes were filled and it is not without pride that we can now announce that we have completed 10 successful dives in total with QUEST. This is a surprisingly high number given the short duration of this cruise leg (less than 14 days). This could only be achieved because there were no significant technical problems and because of the excellent team work between the bridge, the deck’s crew and the ROV team during the deployment and recovery of QUEST.
 
On Friday night, we left the Håkon Mosby Mud Volcano taking a westerly course so as to take a sediment sample with a multiple corer at 2000m water depth. In the early hours of Saturday morning, we reached the sampling position and managed to complete the sampling rapidly.  Afterwards, we headed north towards Svalbard but stopped briefly at 74 ° north to take the last multiple corer sample of this cruise leg.

After that, all station work was stopped and we proceeded towards Longyearbyen (Svalbard), where 23 scientists will have to say good-bye and 30 scientists will be welcomed onboard. The packing and stowing of instruments in the freight containers took the better part of Saturday and Sunday. At the same time the contributions to the cruise report had to be completed and the laboratories cleaned. These activities were disrupted only briefly by a barbecue party on Saturday, where „Håkon Mosby“ pollack which had been caught by angling during the preceding week was grilled in foil or fried.

To sum up the final presentations of the scientists on Sunday afternoon we can say that the cruise ARK XX/1b of „Polarstern“ has yielded a wealth of new knowledge on the geology and biology of the Håkon Mosby Mud Volcano which will contribute significantly to the rating of the EU project HERMES.

Our estimated time of arrival in Longyearbyen is Monday at 9 o’ clock. After lunch, the leaving cruise participants will be transferred to the shore by zodiacs and should reach their home over the next few days where they will be able to tell their families, friends and colleagues about this expedition themselves.

Kind regards from Polarstern on behalf of all remaining cruise participants and those who have just left.


Michael Klages