Business as usual.

A few day later, on 24 January, mooring AWI 250-1 is up for recovery, which has been waiting in the frosty abyss for 6 year by now. A first attempt of its recovery after the common two-year long deployment period had been foiled by the need to abort the expedition then due to damage to the ship’s propulsion system. Two years ago, during our second attempt, we discovered that the release would not let go of the anchor, the mooring simply preferred to stay where she was, at the sea floor. Having anticipated the possibility of such complications after a mooring period of 4 years, we had then brought our little ROV Fiona (Fig. 3) to try hooking a recovery rope to the mooring rope (at a notable depth of 230m!). It worked, but – being our first ever such attempt of using Fiona – the chosen recovery rope was too thin, as it broke when trying to lift the anchor. With then no time to spare for a second try we wanted to give it another chance this time, using a slightly thicker, but much more robust special rope.

Not unlike to the displays of a video game (Fig. 4) the two pilots steer the ROV using an electronic chart, a sonar and a video display to the presumed location of the mooring. However, to our dismay, no mooring is to be seen, neither in the sonar nor in the video and that in spite of being right on the spot and scanning all directions. 

However, we only have a very limited field of view. Up to 30m distance in the sonar, 10m in the video – not unlike driving a car at night in thick fog. Following a short discussion, we decide to follow the line from the original mooring position to the place where we successfully had docked with the mooring two years ago. However, to no avail, no sign of the mooring is to be seen. We decided to head back, parallel to the ship, somewhat offset to the side of the original track.  Suddenly we see a clear echo in the sonar, then a thin rope in the video: the recovery rope from 2 years ago. We follow it down, past the top floatation and hook the new recovery rope to the mooring rope (Fig. 4). A few tense minutes later – the ROV is being pulled back aboard but is the recovery rope long enough? – We keep the latter in our hand. When the deck’s crew is starting to pull on the recovery rope minutes later, the releaser at the sea floor lets go of the anchor, apparently 1 t of anchor weight was too much, and the mooring surfaces. Sediment or biotic material might have jammed the release’s hook, which apparently refused open on its own. The mooring is then pulled by the recovery rope (pink) to the ship, along with a clew of the early recovery rope (grey) (Fig. 5) and hoisted aboard.

After having deployed our last SUIT today in thick ice, tonight we set off for our one but last part of our expedition, a dense sequence of CTD profiles uphill the slope of the Antarctic Peninsula, along with many mooring recoveries and deployments, 17 in total.  We are curious if we will be able to complete fully this important component of our expedition, noting that time is running out by the hour, with only half a day to spare in our planning.

A most busy crew and scientific party send their best greetings from aboard Polarstern.

Olaf Boebel