Birds close to Oden during one of our sampling stations. This sampling station was the last we made in the very loose pack ice at about 80°30’N, 154ºE before we headed for the southern Lomonosov Ridge working area of Box 4. The birds to the left are Kittiwakes and to the right an Ivory Gull is sitting. Photo: Martin Jakobsson

The work in the area of the southern Lomonosov Ridge comprised the last part of the SWERUS-C3 Leg 2 cruise plan. The main idea with this working area, called Box 4, was to link all the research we had done on the shallow shelf to the deep Arctic Ocean setting. One of my personal research goals was to map bathymetric highs on the southern Lomonosov Ridge shallower than 1000 m to see if they had been scoured by deep drafting ice during past glacier periods. I have since my first Oden expedition in 1996 worked on the Arctic Ocean glacial history. During the Arctic Ocean 96 expedition with Oden we discovered that the Lomonosov Ridge near the North Pole had been scoured by icebergs that reached as deep as 1000 m below present sea level. This means that icebergs as thick as 880 m (the sea level was about 120 m lower at the peaks of some previous glacial periods) existed in the Arctic Ocean. The result was kind of a breakthrough because there had been several speculations in the scientific literature about huge 1 km thick ice shelf complexes that existed in the deep Arctic Ocean during the last glacial maximum at about 20,000 years ago. But lack of mapping data did not permit that any of the proposed theories could be tested. Since 1996 more data containing evidences of very extensive marine glaciers have been collected. But we still need more systematic mapping to find out how large the past marine ice sheets really were. Perhaps most interesting is how fast these huge ice shelf complexes and their feeding glaciers from the surrounding continental margins broke up and disintegrated. The time this took is of interest because we presently see that the largest marine portion of Antarctic ice sheets, the West Antarctic Ice Sheet, has lost mass quite rapidly.

Tom Cronin from US Geological Survey loading the multi corer. Photo: Martin Jakobsson

Mapping of the southern Lomonosov Ridge started September 13 with the acquisition of a seismic line. Tom and Arne were sure eager to put their gear into the water once again. The weather was really nice with low winds. A long successful seismic line was acquired from outside of the Russian Economic Zone to the peak of the southern Lomonosov Ridge. Sediments draped the underlying bedrock beautifully. We have proposed to do drill within the program Integrated Ocean Drilling Program (IODP) in this area of the Lomonosov Ridge. For this reason, the German research vessel Polarstern was here to do so-called site surveying. They towed a 3 km long hydrophone streamer and collected seismic profiles over the proposed drill sites. Their seismic penetrates much deeper than ours, but the resolution is on the other a lot less. This means that we can see thinner sediment layers but not as deep. The two complements each other well. We took contact with each other in order to meet and coordinate our efforts and avoid unnecessary overall with our surveys. Rüdiger Stein from Alfred Wegener Institute of Marine and Polar Research (AWI) is chief scientist onboard Polarstern. Since they had a helicopter onboard and we did not, we decided that Rüdiger and two of his scientific colleagues would come over to meet us. The helicopter landing on Oden became the big happening of the day, all that did not have instruments to watch peaked out to see. We discussed and coordinated our plans for about 45 minutes. This was truly well invested 45 minutes. Together our data will contribute to select the best drilling target for the future IODP expedition.

The helicopter from Polarstern landing on Oden. Photo: Martin Jakobsson

Photo: Martin Jakobsson

The oceanographers were also happy since we managed to map out the bottom topography and take several CTD (Conductivity, Temperature, Depth) profiles from key locations. This will allow them to sort out how the Atlantic water circulates and passes over the Lomonosov Ridge to move forward into the Amerasian part of the Arctic. The Atlantic water inflow to the Arctic Ocean is an important heat source with effects on the entire circulation system, the slope-methane story, and likely also on sea ice.

During the evening of the 17, the wind began to pick up quite a lot. It became impossible to do any station work and even too rough to acquire good quality multibeam data. But we had to endure a bit since there were still some critical parts we wanted to map. Eventually we decided to go north towards the pack ice and begin new work at 84–85°N. The last thing to do was to pass through one of the planned IODP drill sites on the way. The waves grew more and more and Oden rolled quite heavily. Just when we passed over the drill site, the multibeam acquisition software crashed; aaarrg! It was late in the evening and I had to convince our captain Erik to turn the boat, go back one nautical mile or so, and pass over the site again. Erik said, “Martin, this will not be fun and I’m not at all keen to do this, is this really necessary?”. What could I say? We had promised to go through the site since it not was a detour for us, and I knew how important our data could prove to be for the scientific community. So I said “Yes, it is necessary”. “Well, Erik muttered and turned Oden around”. I could never imagine how bad the rolling would be during the turn. Stuff including cameras, note books, bags, flew to right and left up on the bridge were the motion was worse. After the turn, we had to do one more, which for some reason was much smoother. Puh, the maneuver was done, and we could acquire the critical data. I’m very glad we did it, but I will make sure I have a good reason to ask to turn Oden around in bad weather again in the future.

Bad weather during the last part of our work over southern Lomonosov Ridge. Photo: Martin Jakobsson

When I write this, we steam north and the waves are coming in from behind so the ride is quite pleasant. There is information that we could potentially get from the Lomonosov Ridge area around 84–85°N that could help us understand results from surveys we have done during SWERUS. Few previous expeditions, if any, have had the opportunity we now have to work all the way from the shallow shelf out into the deep Arctic Ocean over a large area! During our trip north the Russian geophysics team onboard led by Andrey Korschurnikov ran an electromagnetic survey line. This invloves towing an 800 m long signal cable behind Oden and transmitting 400 ampere into the water through another cable. While I looked at the cable, I noticed a piece of driftwood floating by.

Drift wood floating by the transmitting cable of the electromagnetic survey equipment. Photo: Martin Jakobsson