16 - 25 July 2007 (Week 29)

The week started off with intense station work. A multiple corer, giant box corer, CTD, and bottom water sampler were used to fill the gaps in our HAUSGARTEN station programme.

Another mooring which had been deployed in the previous year was recovered and it turned out that all instruments had worked flawlessly. Even during the Arctic winter, our northernmost mooring station was not covered with ice in the last few years. Therefore, we shifted it further north. The latest satellite images indicated that the ice margin in the summer lay around 78°45’ N. Much to the pleasure of all cruise participants who have never been on an icebreaker before, Polarstern steamed towards the location chosen. In the morning the crew deployed the mooring with three sediment traps at 2700 m depth with the precision and reliability of a clock work, as we say in Germany.  Unfortunately, no polar bears were seen during our passage through the ice.  Although we observed quite a few seals (favourite prey of bears) in the water and on the ice, we only saw bear tracks some of which were quite big!

For Wednesday, we planned a special dive with the ROV QUEST to recover the remains a lost mooring. In the previous year, the upper part of a mooring of some 2 km length had surfaced due to flaws in the material. Fortunately, the British research vessel "James Clark Ross” was in the area at the time and rescued the better part of the mooring for us. Left on the sea floor remained a sediment trap, a current meter, two acoustic releasers and a pack of buoyancy glass spheres. We calculated that the buoyancy left would not have sufficed to allow the remaining 200 m of the mooring to ascend to the water surface.  Therefore, we had discussed and prepared different rescue scenarios with the ROV team over the past few months.
Such operations with floating ropes or parts on the sea floor are not without risk to ROVs. The underwater positioning system of Polarstern thus had to be fine-tuned through a calibration course. This activity was only completed in the afternoon. Therefore, the dive had to be postponed to the next day.

In the morning of the 19th July, the rescue mission began: QUEST brought a buoyancy pack to the sea floor and attached it to the mooring that lay on the sea floor. This took quite some nerves and concentration but was performed with ease and elegance! After the ROV had been recovered the ship activated the acoustic releasers of the mooring which had been on the sea floor for two years. Would the batteries after all this time have enough power left to trigger the motor mechanics such that the hook of the mooring would disengage? A few minutes later, this question was answered: our recalibrated underwater positioning system indicated that the mooring was ascending. The added buoyancy as calculated by the engineers of the Deep-Sea Research Group was sufficient to bring the instruments back to the water surface. Not only could we rescue 100,000 Euro worth of equipment but also invaluable data- the sediment trap had worked! Upon recovery the cause of the debacle could be seen: a thick metal ring made of stainless steel had corroded. Minute impurities during fabrication can lead to such effects.

In the following days we completed our station programme at the deeper stations of the HAUSGARTEN observatory. Sediment samples were taken from the deepest point of HAUSGARTEN, the Molloy Deep (5500 m), and a lander was also deployed at this depth. This deployment, prepared by Swedish Scientists from Gothenburg University, led the instruments attached to the lander to the limits of their pressure grading. Twenty-four hours after deployment at the sea floor, Polarstern positioned above the lander. All sonar systems of the ship were switched off temporarily so as to avoid acoustic interferences. After a few acoustic release commands, the underwater positioning system indicated once again that the lander was ascending much to the relieve of all involved! The 3-D micro-profiler was also deployed once more with great success: the pre-programmed course of the electrodes was performed without flaw at 2500m depth.

In the mean time, all station work has been completed. On Sunday night, the ship took a southerly course. A long signal of the tyfon (the ship’s horn) which marked the end of our work at HAUSGARTEN was sent out as a last greeting to our colleague, Jan Wegner, who had passed away last December and had been very involved in our research at HAUSGARTEN.

On our way to Tromsø, two more multiple corer stations were done. Furthermore, we searched for the upper part of a drifting long-term mooring deployed in the previous year by AWI oceanographers. It was found and recovered in the early hours of Monday morning at 77° N! Ever since, we took course towards the Norwegian coast.

On Wednesday morning at 10 o’clock, we will take our berth at the pier of Tromsø.
This will be the end of Polarstern-Expedition ARK-XXII/1. It was the first contribution to the international activities in the Arctic within the framework of the International Polar Year. At the same time, the expedition was a “show case cruise“ of the EU-funded project HERMES (Hotspot Ecosystem Research along the Margins of European Seas). Polarstern has contributed important new scientific results to both programmes. For the first time, Polarstern had a manned submersible (JAGO, IFM-GEOMAR Institute in Kiel) and the remotely operated vehicle QUEST (Research Centre MARUM, Bremen University) on board. Not only was the ship able to deploy these underwater vehicles very successfully but the size of Polarstern also allowed us to perform a variety of logistically demanding tasks using a range of state-of-the-art technologies.

Favoured by almost constant calm weather and sea conditions, we were able to achieve more than we expected. But this would not have been possible without the excellent work of the ship’s crew! We are indebted to Capitan Pahl and his exceptional officers and crew who remained enthusiastic throughout the expedition although it included three different study areas with three almost entire changes of scientists. It could not have been better!

The crew and some scientific cruise participants have been onboard since Polarstern left Bremerhaven on the 29th of May. We really look forward to returning home and to enjoying what is left of the summer with family and friends.

All onboard are healthy and send their best regards home,

Michael Klages