PS124 - Weekly Report No 2 | 08 - 14 February 2021

On the way into the ice!

[15. February 2021] 

It is quite unusual for an expedition to the southern Weddell Sea to do the first station already one week after departure. The test station, still away from sea ice, turns out to be a tough exercise, since parts of our equipment show peculiarities, which can cause problems during the cruise.

Still fixing the encountered problems, we continue steaming southwestward where we meet the first sea ice patches on 9 February. Though we pass through only loose sea ice, sometimes manned (Photo 1), we hear the metallic sound of scratches once in a while. As an icebreaker, however, Polarstern won’t start curving around the floes. This kind of shifting will be left for ‘real’ sea ice covers a few meters thick.

 

On the morning of 10 February, we leave behind the dense sea ice barrier in front of our area of research. We follow the coastal polynya – a Russian term for a large hole in a compact sea ice cover – southward to our first oceanographic station. On the way, one of the two helicopters on board, carries the sea ice physicists and biologists to a nearby floe for also testing their equipment (Photo 2).

Though our mooring site is covered by scattered floes, we press the button on 11 February at 6 o’clock to free a 2000-m long mooring from the iron grip of its anchor at the sea floor. After 30 minutes of tense waiting, what a relief to see the first witness of the mooring, a floatation, at the surface. What follows is routine of the experienced crew: a careful approach, maneuvering the working deck next to one of the floatations, picking up the line, and pulling instrument by instrument, meter by meter of mooring line on board using one of the ship’s large cranes.

It takes 2 hours and 15 minutes to bring in the first ’harvest’. Enough time is left to continue to the next nearby mooring of our French colleagues. This time, we plan to recover and deploy at the same location just close to an ice floe, which couches to prevent us from doing so. What a relief again, when the first floatation sees daylight after four years of darkness just 100 m away from the ship. The routine starts anew and ends at 6 pm, right in time for dinner (Photo 3).

Now it is time to move southward to our first BioGeo-station, where 10 different types of sampling are supposed to keep us busy for one day (Photo 4). It is a challenge to organize such station because sampling has to be done in blocks, limited and separated in time. The start is bumpy but with a high gain of experience. At the end, it is the approach of a strong low-pressure system, which stops our station work and forces us to escape to the northern sea ice where the sea is much calmer. However, we will return, since we leave back two landers, autonomous instruments measuring various parameters close to the sea floor, and one drifting trap.

We made the right decision to move towards the center of the cyclone, because slightly weaker winds cleared the area from sea ice such that we are able to deploy the second mooring in the morning of 13 February. Instruments from AWI as well as from our colleagues from Sweden and Norway will measure for several years temperature, salinity, and currents of a 2000-m thick water column. Since we are done at lunch time, we can slowly approach the two Norwegian moorings to the south, which will be recovered the next day and deployed again, when we leave the area beginning of March. On the way southward, we run several CTD (conductivity, temperature, and depth) casts across the slope front, separating the cold (-1.9 °C) waters of the continental shelf from the relatively warm (+ 0.75 °C) waters of the open ocean.

Needless to say that on 14 February the recovery of both moorings happens faster than calculated. Therefore, we can steam southward searching for the drifting trap, which sent its last position via telephone link to be 20 nm south of its deployment site. While writing this report, the little runaway safely gets on board again. 

PS124 sends regards from a calming Weddell Sea –a popular ground for Polarstern visits for more than 35 years.

 

Hartmut H. Hellmer (Chief Scientist)

Contact

Science

Hartmut Hellmer
+49(471)4831-1794
Hartmut.Hellmer@awi.de

Scientific Coordination

Ingo Schewe
+49(471)4831-1709
Ingo Schewe

Assistant

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