Sunday, 16 March 2008
 
We have reached the eastern Weddell Sea. The work on the Greenwich meridian is finalized.  We are glad, that in spite of tragic events at the Neumayer Station and the time we spent waiting in Cape Town for the container that this first part of the cruise could be brought to an end, which will clearly permit us to obtain the results which were expected when planning the cruise. A longer phase with relatively weak winds was favourable to this progress. We completed 6 „Super stations“ in the context of the GEOTRACES-Programme, 24 ultra-clean CTD and 64 normal CTD stations to cover all hydrographic regions on the Greenwich meridian with all the relevant parameters. We have recovered 9 moorings and redeployed 5 of them. The grid of vertically profiling floats was extended by 40 and these will now drift under the sea ice of the forthcoming autumn and winter.

At the last mooring at about 12 nm north of the edge of the Fimbul Ice Shelf, we encountered a new challenge. When we tried to interrogate the acoustic releases with the Posidonia system onboard POLARSTERN no reply was received. So we released blindly and waited for the mooring to show up at the surface. However no float was sighted and no signal was detected with the radio receiver onboard from the satellite transmitter, which is mounted on the uppermost part of the mooring. We started to search with the ship and with the helicopter, but with no result.  When we were sure that the mooring was not longer at its position, we stopped searching and resumed water sampling stations towards the ice shelf edge. However, shortly after, we were surprised by a message from Optimare in Bremerhaven who are surveying for us the satellite transmitters of the moorings. They informed us that the transmitter had reached the surface shortly after the release signal, though 7 nm away from the expected position. We turned immediately towards the indicated position; the helicopter started again and was able to identify the mooring in an ice field in a few miles distance.  With this information from the helicopter it was easily possible to approach the mooring with the ship and to recover it quickly. It had damages which clearly indicated that it was removed by an iceberg to a position which was still within the reach of the Posidonia transmitter on board to receive the release command, but too far distant for the reply from the less powerful releaser to be received onboard. The satellite beacon was pushed by the iceberg so deep into the float assembly that it was hidden for the quasi-horizontal view from a distance on the ship, but still visible to the satellite which was on top of it.  We are glad about the happy end of the recovery. Unfortunately the upward looking sonar was damaged by the iceberg encounter so that the recorded data were lost. However, it is a great success that all moorings on the Greenwich meridian were recovered after the first 3-year-mooring period, which proves that our mooring technology has reached a standard which allows us to plan such long deployment periods in future.

The hydrographic survey is currently being evaluated. However even a quick look at the preliminary data indicates that the cooling of the Warm Deep Water since the mid 90ties has come to a halt. Together with the observation of an earlier warming until the mid 90ties this suggests that decadal fluctuations dominate the variability. Now we can compare the atmospheric forcing during the last years with the one in the early nineties to better understand the forcing mechanism of the fluctuations. The bottom water temperature is still increasing. Either its properties are completely independent from the fluctuations of the source water or the response is so slow that it smoothed out the decadal changes.

With my best regards from all on board

Eberhard Fahrbach