PS114 - Weekly Report No. 3 | 23 - 29 July 2018

Mooring Work on Foggy Days

[30. July 2018] After two long weeks of intense work we can be more than happy with what we have achieved! All our instruments worked really well, we took and analysed lots of water and sediment samples, recorded hundreds of pictures from the water column and of the sea floor so as to document life in the deep sea and we recovered almost a hundred instruments which were continuously recording water mass and current properties for the past two years.

The only factor which did not always play along was the weather. Whilst people at home reported brilliant sunshine, we saw nothing but fog, fog and fog for days on end (Picture 2). This made recovering moorings especially difficult. Thankfully we have a sophisticated positioning system called POSIDONIA.

Abb. 1: Ein Wasserprobennehmer und ein Gerät, das autonom Partikel aus der Wassersäule filtriert, werden verankert. Die orangen Kugeln oben leisten Auftrieb, damit die Geräte möglichst nahe an der Oberfläche arbeiten können.
Fig. 2: A water sampler and an instrument which can autonomously filter particles from the water column are being moored. The orange balls at the top provide the necessary buoyancy for the instruments to work close to the surface. — Mooring Work (Photo: Alfred-Wegener-Institut)

Abb. 2: Das Eis vor Polarstern verschwindet im Nebel. Wenn Verankerungen auftauchen, müssen sie zunächst gesichtet werden, was sich an manchen Tagen recht schwierig darstellte.
Fig. 2: The ice in front of Polarstern is swallowed up by the fog. When moorings surface they have to be sighted, which was rather difficult on some days. — Looking for Moorings (Photo: Alfred-Wegener-Institut)

With this system we can “wake up” the mooring from our ship to get its exact position. We than edge up to that position and give a signal to the mooring to release its anchor weight and rise to the surface. After a while the mooring appears a couple hundred meters away, directly in front of the ship and we can recover it. This meant that even with the fog we could always find the orange floatation packs quite well (Pictures 1 and 3).

Even so, our recoveries did not always run smoothly. At our northernmost mooring position, at 80°50’N, we were met with lots of large ice floes. At first, we tried to break a hole in to the ice cover by sailing in circles above the mooring position. But the ice drift was too strong, and the hole was closed again in a thrice. That meant: wait. The ice radar showed that a hole in the ice should drift right over our mooring site in the next one or two hours. Of course, we used the time to do other station work. But then, a couple of hours later, the hole had passed by us and still our mooring was covered by a huge expanse of ice. Bad luck. Since we had further station work planned at this site we changed our schedule leaving the mooring to last. But nothing helped, still there was too much ice. Finally, the ice radar showed a larger hole in the ice which was predicted to drift across our mooring site in a couple hours. And the prediction came true! We quickly sent the signal to release the mooring and then all eyes were searching the water in front of us. One minute passed…two minutes…there it is! The day of waiting was worth it!

Abb. 3: Strömungsmesser und Auftrieb sind an Deck gekommen und müssen von Bewuchs gereinigt werden. Das ist eine nasse Angelegenheit. Im Hintergrund sind andere autonome Probennahmegeräte.
Fig. 3: A current meter and floatation devices have been pulled on deck and the growth on them has to be scrubbed off. A rather wet task! Other autonomous samplers can be seen in the background. — Working on Deck (Photo: Alfred-Wegener-Institut)

Abb. 4: Polarstern fährt durch Meereis vor dem 79Nord Gletscher. Wenige Tage zuvor war dieses Eis noch Festeis und ist entsprechend hart, weshalb wir uns einen Weg entlang der Spalte zwischen den Schollen gesucht haben.
Fig. 4: Polarstern sails through sea ice in front of 79 North Glacier. A couple of days earlier, the ice was still fast-ice and accordingly it was quite hard, which is why we made our way through the cracks between the floes. — RV Polarstern in front of 79 North Glacier (Photo: Alfred-Wegener-Institut)

In eastern Fram Strait warm Atlantic water is at or relatively close to the surface. There we recovered and deployed moorings which will help us to understand ecosystem processes. They measure nutrient concentrations, light intensity, chlorophyll concentration (which is related to the amount of algae in the water column), amongst other things. The instruments also took and will take water samples in the upper ocean year-round (Picture 1). This is a great advancement, since water sampling would otherwise only take place during summer when research vessels are in the area. But interesting things still happen during the remainder of the year. To be able to know what the currents and water masses in the entire water column are like during all seasons, moorings are deployed in the shape of a triangle at two sites. At these sites three moorings are spaced exactly as far apart as the water is deep. We took some risks with these, because some of the instruments sit only 25 m below the surface. But so far, the risk has payed off.

We recovered five moorings from central Fram Strait. All of them were deployed along the prime meridian between 78°10’N and 80°50’N. With the help of these time series of temperature, salinity and velocity we will try to understand the recirculation of warm Atlantic Water better. The warm and salty Atlantic Water is transported northward through the North Atlantic, along the Norwegian coast into the eastern Fram Strait. There, part of the water flows eastward into the Arctic Ocean and the remainder turns westward (it recirculates) in Fram Strait before returning southward along the eastern coast of Greenland. This circulation can however not be pictured as a well-defined current but is rather made up of numerous small and large eddies. A first look at the data, that our moorings collected during the last two years, shows many events with strong velocities. Whether theses are the proposed eddies remains to be seen during the more detailed data analysis later on.

Abb. 5: Die Fahrtroute von Polarstern vor dem 79Nord Gletscher in rot. Helles grau deutet auf Eis hin, während schwarz offenes Wasser zeigt durch das wir uns geschlängelt haben. Die Verankerungspositionen sind in blau. Ganz im Westen (links) liegt die Verankerung direkt vor dem Gletscher an die wir nicht kommen konnten.
Fig. 5: The cruise track of Polarstern in front of the 79 North Glacier is shown in red. Lighter gray shows ice, whereas black denotes open water through which we maneuvered. The mooring locations are shown in blue. One mooring, which we could not reach, lies directly in front of the glacier, on the western side (on the far left). — Cruise Track of RV Polarstern (Graphic: Alfred-Wegener-Institut)

After our work in the eastern, central and western Fram Strait we yesterday went to the east coast of Greenland. There, we had also deployed four moorings which we now wanted to recover. The 80 km long floating ice tongue of the 79 North Glacier flows into the ocean there, making this a particularly interesting region. The warm Atlantic water from Fram Strait can also be found beneath the floating ice tongue. Thus, a rise in the ocean temperatures can play a key part in melting the ice tongue.

But the ice situation in front northeast Greenland was complicated. In particular, we had to grapple with fast-ice. Fast-ice is sea ice which cannot be moved by currents or wind because it is frozen either to the coast or the seafloor or grounded ice bergs. In front of the glacier the fast ice covers a large area for most of the year. With the help of satellite pictures (Picture 5) we have been keeping an eye on the ice during the last three weeks and although we saw that some movement was starting to take place, the part where our moorings were located was still covered by fast ice. Because we saw some cracks in the ice, we decided to give it a try. Yesterday morning we were only a couple hundred meters from the coast and still fog, fog, fog. Slowly we moved forward through a thin lead between the coast and a large ice floe towards our mooring. At the same time the sun finally burnt off the fog. All of a sudden, we had a clear view (Picture 4) and after weeks of fog and nightshifts the mood on board lifted together with the fog! Everyone enjoyed the view of the beautiful Greenland coast with glaciers and as an added bonus we also saw a polar bear, a walrus and a whale! The sun also made it possible to navigate through different ice cracks to three of our four moorings, which we recovered successfully.

Now we are on our way to the shelfbreak where we want to recover another four moorings. The sun shines, the mood is great and soon we will be on our way back home.

Best greetings and see you soon,

Janin Schaffer, Maren Richter, and Wilken-Jon von Appen on behalf of the scientists of PS114

Contact

Science

Uta Krebs-Kanzow
+49(471)4831-1052
uta.krebs-kanzow@awi.de

Scientific Coordination

Rainer Knust
+49(471)4831-1709
Rainer Knust

Assistant

Sanne Bochert
+49(471)4831-1859
Sanne Bochert

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