Turbulent recirculation

During nighttime both hydrographic measurements combined with water sampling targeting trace element analyses and biological sampling using nets were carried out, while the recovery and deployment of stationary, autonomous observatories – subsequently referred to as moorings – took place during daytime.

In this report I will mostly focus on the mooring-related work. The West Spitsbergen Current represents the extension of the Gulf Stream – North Atlantic Current System and carries warm, saline waters to the north along the continental slope of Spitsbergen. The heat carried by the current keeps the waters near the eastern boundary of Fram Strait free of sea ice all year round.

While a part of this water subsequently enters the Arctic Ocean, a sizable fraction of it leaves the boundary current and moves to the west within Fram Strait - only to flow back southward along its western side. This recirculation is highly turbulent and surprisingly so far has received very little scientific attention. Ultimately, the strength of the recirculation determines the amount of oceanic heat that can penetrate into the Arctic Ocean.

Both the northward transport of warm water within the West Spitsbergen Current and the recirculation occurring in Fram Strait represent research foci of the expedition. The Alfred Wegener Institute for Polar and Marine Research has been operating an array of moorings in the West Spitsbergen Current. Sensors attached to the mooring rope record current velocities, temperature, salinities and underwater sound in the different water layers between the sea surface and the sea floor all year round. The longest of these moorings exceed a length of 2000 m.

Concerted action

By the concerted action of the bridge personnel, deck crew, mooring technicians and  scientists, we were able to recover the moorings safely which were deployed last year. In turn, we replaced them by re-deploying the array of moorings and we expect to recover them in two years time. Moored measurements of this kind have been maintain for almost 20 years, and by now represent an important time series at this gateway to the Arctic Ocean. 

After completion of the work in the West Spitsbergen Current, R/V Polarstern crossed the Greenwich Meridian at 79°N, on the western side of which we caught sight of sea ice for the first time during the expedition. Meanwhile we have worked our way along in a northerly direction. Four more moorings have so far been deployed along the south – north transect. During the next two years they will make continuous observations of the above-mentioned recirculating branch of the warm water for the first time.

After having reached this important intermediate goal of the expedition, the kitchen personnel did a tremendous job in preparing a rich barbecue, that left no wishes open. In good weather and with a sight of the sea ice this change was highly welcome.

Best wishes on behalf of all participants,

Torsten Kanzow