ARK-XXVI/3, Weekly Report No. 1

5 August - 13 August 2011

On Friday, August 5, at 18:00 we left sunny Tromsoe. The beautiful fjord landscape distracted us from the worry if all last minute freight sent to Tromsoe really had made its way onboard - but of course everything was already safely stored by the cargo officer and the crew.

The summer accompanied us for a little while on our way to the Arctic, but we did not see much of it because unpacking had become the main priority. The start of every cruise is typically governed by mild chaos: labs are distributed and then traded again, as there is never enough space for everyone’s needs. The containers are unloaded, and boxes are missing - just to be later found where they were supposed to be. Instruments are set up and usually do not function on first tests until after some minutes of calm troubleshooting. One day later, the chaos all over the working deck and labs has eased considerably, our comfort supported by a small low-pressure system that turned the sea surface from a mirror into smooth waves. Soon we conducted a test station for the CTD system and two plankton nets: everything went well.

The expedition “TransArc” (Transarctic survey of an ocean in transition) will take us for the next two months to the central Arctic Ocean. This ocean is one of the least explored regions on earth; still the heavy sea ice around the North Pole allows only ice-breaking vessels to get to the region, thus the grid of observations is still very sparse. At the same time, the Arctic hosts the strongest signals of climate change: its warming is twice as large as the global mean, and the sea ice cover is reducing rapidly.

With this expedition, 50 scientists, students and technicians intend to tackle the complex system jointly in an interdisciplinary approach. Participants come from Germany, Russia, France, Finland, Sweden and the USA. We are supported by 43 experienced crew members and an equally experienced helicopter team.

The focus of our work is the physical, biological and chemical changes of the Arctic Ocean. The decreasing ice cover, the warming of the ocean water and the shifting ocean circulation affect the heat and gas exchange between water, ice and atmosphere. These processes drive changes of the ecosystem of the sea ice and in the water column, from the surface to the sea floor. Four years after the International Polar Year 2007/08 (IPY 2007/08) we are repeating a large scale synoptic survey of the state of the Arctic Ocean. We will sample water, ice and sea floor from the shallow Siberian shelf seas up to the Canadian Basin, and from the open ocean into the pack ice. Additionally, we want to take sediment cores in the vicinity of the North Pole to provide insight to the long-term climate history of the Arctic.

The first oceanographic section started north of Franz-Josef-Land. Here the sea floor slopes steeply from 100 m to 3500 m depth. Along the steep slope flows a narrow band of warm Atlantic Water, coming from the Nordic Seas, through the Arctic Ocean. This very final weak extension of The North Atlantic current system that began in the Gulf Stream is an important heat source for the Arctic Ocean. We want to know how strong - and how warm - this current is, and how it changes with time. Therefore a team of Russian and American colleagues deployed a mooring north of Franz Josef Land two years ago. We have responded to the request of our colleagues to recover their mooring during our cruise, as international co-operation is essential in the Arctic.

Moorings such as the one we recovered record the variability of velocity and water properties at a fixed location over an extended period. The instruments are attached to a rope that is anchored at the bottom with a heavy ground weight, stretched tight upright by floats on the top. To recover the mooring an acoustic signal is sent to a trigger which releases the ground weight so that the mooring can rise to the surface. Although we transmitted the release signal several times, no mooring appeared at the surface. Through an echo sounder survey we finally determined that the mooring was still sitting on the ground and obviously the release had not worked! This was the big moment for the crew: with a sophisticated manoeuvre using a line, towed between Polarstern and a small boat, the mooring was snagged, all instruments were recovered and two years of measurements were safely brought on board

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At 82°N we passed the ice edge and within the next hours we saw the first Polar Bear; an iconic reminder of the need for being cautious at the ice station work which started on Thursday.

Friday was the last day for submitting a proposal to our ice bet: What will be the value of the 2011 minimum of the sea ice extent? In September 2007 it has been only 4.14 Millions of square kilometres – the lowest ever observed value. Will it be even smaller this year?  About half of the scientists are betting it will be!

Best regards by the whole team!

Ursula Schauer