ARK-XXVI/2, Weekly Report No. 2
18 July - 24 July 2011
The second week on board was characterized by rotating station work, which included not only standard sampling methods like CTD, multi-net, and bongo-net, which were already used throughout the first leg, but also the multi-corer for sediment samples. The remotely operated underwater vehicle “KIEL 6000” from IFM-GEOMAR was used a total of three times, and also a torpedo-shaped diving vehicle from AWI was put to use. On Monday morning, a dive was completed with the Remotely Operated Vehicle (ROV) from Kiel on the so-named Vestnessa Ridge, located west of Spitsbergen. The goals of the dive at a depth of 1400 m were to find gas seepage on the sea floor and to take sediment samples with the community of organisms living therein kept under in-situ pressure in specially designed pressure containers.
After 11 hours in use, the ROV was brought back on board in early evening, and stations on the Spitsbergen shelf at less than 300 m deep were worked on. Problems had already existed with our satellite communication system since the departure from Longyearbyen, so that the exchange of data and information over telephone and e-mail was significantly difficult. Partially due to the situation with the satellite and also for other equipment on board, a systems technician was met by our agents at Longyearbyen and brought along with spare parts aboard by helicopter as part of an already-planned transport of people. The ship waited at the entrance of the Isfjord for several hours while the technician, working together with the board electrician, confirmed the successful connection between the ship, AWI, and the shipping company. Afterwards, the station plan took us on a northwesterly and later a westerly course back into the main working area. Water samples, CTD, net collections, and sediment samples with the multi-corer quickly followed. At selected stations, so-called free-fall landers with various instruments were deployed. They were to stay on the sea floor for two or three days and follow through with previously programmed measurements.
Early on Friday morning, the ROV was used for its first time at the most important HAUSGARTEN station – the so called central deep sea station of our observatory consisting out of a total of seventeen of such stations. But here, at the so-called central station, we had, among many other in-situ experiments, placed four metal cages about 2 x 2 m at 2500 m depth three years ago, in order to reduce the food supply under the metal structures to a minimum.
We predict that the deep-sea biological community in the Fram Strait will experience a decreasing food supply as the Arctic continues to warm. By this type of simulation experiment, we hope to improve our forecast capabilities how the future development of benthic biological communities in the Arctic may look like. Two years ago, we searched for these cages on the sea floor with another ROV type but were only were able to find one of four despite the use of precise location data. At the time, we took all possible samples at this one location. This year, we were very lucky and found all of the cages that had been placed in 2008 right after each other using the Sonar of the ROV.
On Saturday afternoon, “Polarstern” went on a westerly course that took us almost 20 nautical miles into the ice in the outer portions of the East Greenland Current. For a number of participants on this leg, the last few days were quite an experience because they had never experienced the ship’s abilities as an icebreaker. We were only hoping to see maybe a seal or a polar bear, but there was quite a highlight in the ice: besides countless seals, a total of four polar bears were seen from the ship, three of which were in the immediate vicinity of the ship – so close, in fact, that recognizable photos could be taken with a normal camera, without the use of a telescopic lens.
During the night leading to Sunday, we again assumed a course to the central HAUSGARTEN station, where ROV dive number four are to take place. In the pre-dive briefing on Saturday afternoon, which involved the ship’s command, the chief scientist, ROV team leaders, and responsible scientists, it was decided to have a simultaneous use of the ROV and the autonomous underwater vehicle (AUV). Obviously, the simultaneous use of these two vehicles is a huge advantage time-wise. The ship must be concerned with the ROV, which is connected by a cable, but the AUV can complete its pre-programmed mission independently. Naturally, this autonomy brings a great risk in the open ocean at about 2.5 km depth, because in the case of any unforeseen events underwater, the vehicle must make independent calculations and decisions.
As a last resort, the mission can be aborted, and the vehicle will float to the surface. Before the use of these two underwater vehicles, another free-fall lander with fish bait was recovered. The bait served to capture one small decapod crustacean, dozens of scavenging amphipods and nine demersal deep sea fishes, relatives of eel pouts we know from the North and Baltic seas. Actually, at least 10 fish were caught. However one individual was the victim of captured crustaceans. This event shows the drama that unfolds in the deep sea – every scrap of the body was gone, as the fish was eaten alive by a hundred or even a thousand crustaceans.
Back to the use of the ROV and AUV. Both vehicles communicated with the ship constantly throughout the dive via underwater acoustics, so that at every point, the exact position of the vehicles with relation to the ship was known on the bridge and in the control container. During the dive, we also received a short visit from another important research platform at AWI – our polar airplane, “Polar 5,” had successfully completed a major campaign on Greenland on Saturday and was on its way home from the Greenland north station to Bremerhaven with a stop in Longyearbyen. The on-board weather station on “Polarstern” had sent important information and weather predictions the past few days to our colleagues.
Shortly after lunch, we received the news from the bridge that “Polar 5” would fly over us in 8 minutes. Those that were not bound to their working station used the opportunity to see the airplane circle the ship. While “Polar 5” vanished in the clouds, both our underwater vehicles collected data in the Arctic Ocean at 500 and 2500 metres of water below “Polarstern.” About 10 pm, both vehicles were on board, and a new course along the northern transect of HAUSGARTEN was set. Today and this week, free-fall landers will be recovered and re-deployed for a new year – among all the other station work, of course. The weather is treating all workers well; almost all day Sunday, we had calm seas and blue sun in the afternoon and this is also predicted for Monday.
Despite the tight schedule and the therefore large work load, everyone on board is doing well. Heart-felt greetings from on board on behalf of all expedition participants.
(Translated by Kirstin Meyer)