Expedition Diary

Three earlier attempts were defeated by foul weather. Just when Polarstern should have covered this position, storms raged there, making a recovery impossible.  However, luck strikes this time and the sea is sufficiently calm.  A big question lingers in the air though: will the batteries – after 6 years of operation – still bear sufficient power to trigger the release in response to our hydroacoustic commands?  A few release attempts later we are relieved. The underwater tracking system shows that the PIES slowly surfaces at a pace of 3km/h.  Once recovered, we find the batteries about empty, yet the instrument is in a mint condition, having recorded data for a 4½ years.  This completes a data set from 14 PIES (Fig. 1), which monitored the watermass transport across the Antarctic Circumpolar Current for more than 4 years, a treat for our colleagues from the fields of satellite altimetry and gravimetry, which helps evaluating and improving their global analyses.

22. December, 6^th day at sea

After yesterday’s cliff-hanger recovery of the PIES, less nerve wrecking activities fill today’s station plan.  CTD and net-catches only require the scientific standard watch and are being conducted routinely after a short break-in period.

28. December, 1 week and 5 days at sea

Today, the pelagic team from the University of Bremen is on night shift.  Benefitting from the daily vertical migration of zooplankton, Bongo-nets are deployed at 2 AM to catch copepods and amphipods which then occur at shallow depths.  However, this time the catch contains only few amphipods but rather much Krill and Pteropods (Fig.3).

Later today another mooring is being recovered. Of particular interest this time: The sequel mooring carries multiple underwater recorders which match in configuration and depth those of a mooring in the AWI’s Arctic FRAM observatory.  Both locations feature similar topography yet quite different acoustic environments.  While the southern hemisphere mooring resides in an acoustically pristine environment, the northern one is frequently exposed to anthropogenic sounds.  With this bi-polar deployment, we aim for a direct, vertically resolved comparison of the pre-industrial and industrial acoustic marine environments.

The nautical officers’ unwavering attention facilitates a special sampling this evening.  Passing a school of krill nearby, which shows up as a patch of brownish water, they alert the scientific party who quickly get their nets ready for deployment.  Polarstern circles back and passes the patch close by for a successful sampling.  Our biologists aboard are thrilled to have caught abundant numbers of krill to start experiments aimed at understanding its sensitivity to water temperatures.  By exposing specimen caught in warmer and colder oceanographic temperature regimes to increased water temperatures (in the aquaria) they measure the krill’s origin-specific stress response to explore its ability to adapt to a changing environment.

30. December, 2 weeks at sea

Strong winds and high waves still render a recovery of mooring AWI232-10 unfeasible.  However, with conditions easing up during the day (Fig. 6) we can start recovering mooring AWI232-12 after a deep CTD.  Roping the mooring in is yet still difficult during the strong gusts, a challenge aptly faced by the professional commitment of the crew.  Two hours later all instruments are on board, ready for downloading of data.

31. December, 2 weeks and 1 day at sea

The last day of the year.  Finally the weather conditions are suitable to recover mooring AWI232-10.  As it continues to fail to release, we decide for a rather laborious manoeuvre, called tucking.  At a depth of 700m, a rope is stretched out horizontally between the ship and a buoy.  Circling the presumed mooring location, we attempt to wind the tucking-rope around the mooring, trying to get them entangled.  Not until five and a half hours after the start of the manoeuvre it becomes clear that we have succeeded:  the acoustic tracking system unveils the mooring being slowly lifted from the sea-floor.  Another 3 hours later the last instrument is wrested from the abyss (Fig. 7) and a 2 year data gap, 2010-2012, is closed, providing important knowledge on the evolution of the Weddell Sea’s watermass properties.  Why the double releases did not open their clutches to the anchor will remain a mystery until closer inspection – nothing unusual is immediately apparent with the release units.

1. January 2017, 2 weeks and 2 days at sea

After yesterday’s short distraction in form of a splendid New Year’s Eve menu (suckling and ice cream cake) and the New Year reception on the bridge, we resume our work just before 9 AM.  Another mooring recovery is planned, running smoothly this time.  Ten minutes after the release command the colourful buoyancy elements are spotted at the sea surface and the roping-in can commence.  

2. January 2017, 2 weeks & 3 days at sea

Originally we had planned to berth today near Neumayer Station, yet yesterday’s weather forecast (which has proven true by now) predicted strong winds which would have significantly impeded the cargo operations.  To avoid losing valuable time, Polarstern hence first detours to the North to recover and redeploy a mooring there.  Visiting Neumayer has now been shifted to the 4th of January - with hopes high for sunshine on January 5.

3. January 2017, 2 weeks & 4 days at sea

No station work is planned for today, yet work in the labs continuous full throttle.  The mooring team even started to pack the return freight: storing, labelling and documenting the first set of recovered instruments.  Coming next spring, these have to be turned around in less than a month in Bremerhaven, to be ready for the next expeditions to the Arctic in summer.

Having arrived at Atka bay early this morning, after the first serious breaking of ice, all expedition participants (healthy and cheerful) extend their greetings home.  We look forward to finally set foot onto Antarctica, if only on its northernmost, floating rim.

Olaf Boebel