ARK-XXVI/2, Weekly Report No. 3
25 July - 31 July 2011
Let’s start with this week from the end, with Sunday, 31 July. On this day, the last station work was ended. Our previously-used towed camera and video system was used in the night from Saturday to Sunday for its last time on this trip. The camera system was towed in about 300 m water depth in the vicinity of Spitsbergen. Following this photo transect, we travelled early on Sunday morning about 13 miles west to a new position. Here, our colleagues from the first leg had tried to recover a mooring which was deployed last year. All signs indicate that a fishing boat threw out its nets at the mooring’s location and dredged parts of the instrument. The acoustic receiver still answered to the signal from “Polarstern,” but indicators showed that the mooring lay on the sea floor instead of standing erect in the water column.
We had a tool on board that could help save this otherwise lost instrument, along with all the data it collected over the last year: the ROV “KIEL 6000” from IFM-GEOMAR. A recovery plan was discussed between the ship leadership and the ROV team the day before and carried out on Sunday morning. Shortly after reaching the sea floor, the one-ton anchor, acoustic release pair, and an expensive instrument were all found. It only took a few more minutes to bring up the recovered equipment from 230 m depth. The ROV waited a safe distance from the equipment so that we could observe through the camera as the equipment slowly righted itself and began to float to the surface.
We left the last of our southern HAUSGARTEN stations on Saturday afternoon. At this point, all intended station work was 100% finished. One more AUV dive was planned to parallel to the course of “Polarstern” towards Spitsbergen. Outfitted with a water sample collector developed at AWI, optical sensors for photosynthetically active radiation and planktonic pigments in the water column, as well as CO2, temperature, and conductivity sensors, the autonomous vehicle followed its pre-programmed course; about 10 miles long at varying depth between 300-500 m. The “Polarstern” travelled at about 3 knots adjacent the submerged vehicle, so that we could always control its underwater position via Posidonia. After about 4 hours, the AUV was brought back on board, just in time because the wind in the vicinity of Spitsbergen was much stronger. All components of the vehicle worked perfectly, including the scientific payload. Together with an under-ice deployment of the vehicle on Tuesday afternoon, during which the vehicle went many kilometres under the nearly-solid field of sea ice and collected data, this dive was one more step toward operational use of the AUV.
Just as we were visited by “Polar 5” last week, we were contacted by radio on Wednesday, 27 July, by a cruise ship that would pass by us. We were near the ice edge at a station when the captain of “C. Columbus” asked if it would be possible for him to drive around us so he and his passengers to take pictures of “Polarstern.” Since the multi-corer had just been brought up, nothing stood in the way, and more than several hundreds cruise ship passengers had the chance to see a polar research ship on the ocean with their own eyes. Just how many pictures were taken in the next half hour by both ships will forever remain a mystery.
The first days of the last week were used for finishing up station work. The last moorings and free-fall landers were deployed to be recovered next year. Water samples with the CTD, diverse multi- and bongo net stations were successfully accomplished as well as multi-corer samples, so that the working groups on board were loaded down with samples and data on the journey home. On Sunday afternoon about 4:15, a short blast of the ship’s horn (“Typhon”) signaled the official end of station work for this leg of the expedition. Since then, we have been on a southerly course to Norway. Smooth seas and a light wind have made it easy to pack our equipment and load the containers. We are all looking ahead and planning for when we arrive in the port of Tromsø early in the morning on 3 August and bring the expedition leg ARK-XXVI/2 to an end.
I must speak a word of thanks to Captain Pahl and his wonderful crew. Without their untiring and competent work around the clock, this expedition, which was packed full both in terms of time and technicalities, could never have been successfully carried out.
We are all looking forward to being home, to what looks like a coming summer, and send our heart-felt greetings from on board.
(Translated by Kirstin Meyer)