ANT-XXIV/3 Weekly Report No. 2

Sunday, 24  February 2008

 
We have crossed the Polar Front and reached the Antarctic in an oceanographic sense. However, in a legal context, we will not be there until tomorrow after having crossed 60° of Southern latitude. We are now in the northern limb of the Weddell gyre, the large-scale bean- shaped current system which covers the Antarctic sector of the Atlantic Ocean. East of the Greenwich meridian warm and salty water from the Antarctic Circumpolar Current, the Circumpolar Deep Water, flows to the south.  In the west newly formed Weddell Sea Bottom Water returns at great depth to the north. In the south the Antarctic Coastal Current follows as the southern boundary current the continental slope and the ice shelf front from east to west. In the coming weeks we will cross the Weddell gyre twice, first from north to south along the Greenwich meridian, and then from east to west across the Weddell Sea proper. The latter will take us from Kapp Norvegia to the northern tip of the Antarctic Peninsula.

The weather is getting closer to Antarctic conditions with air temperatures near to 0°C and scattered snowfall. The wind fluctuates from 6 to 8 Bft. The first icebergs sighted were met with a great deal of attention but now their presence has become normal. They drift with the northern limb of the Weddell gyre from the Antarctic Peninsula into our operation area. However, so far we have only met highly weathered remnants and not the impressive table icebergs for which Antarctica is famous.

Our work is progressing well. The station distances decreased from about 100 nm to 30 nm since we had reached our main operational area. At each station a CTD probe (Conductivity, Temperature Depth) is lowered to depth to measure the vertical profiles of temperature, salinity, oxygen, transmissivity and fluorescence. The data are transmitted onboard, displayed and stored.  In addition a current profile is obtained from the lowered acoustic Doppler current profiler (LADCP) which is mounted on the CTD frame. At super stations a full suite of water sampling devices is operated. Up to now we achieved four super stations with the tendency of increasing numbers of casts including the rosette water sampler, the ultra-clean sampler and in-situ pumps. They all are needed to fulfil the requirements of the GEOTRACES community and take up to 18 hours per station. In later reports we will describe the variety and application of the substances the concentration of which will be measured.

The physical oceanographers added to the world wide network of vertically profiling floats (Argo-Floats) with 14 Floats provided by Stephen Riser from the University of Washington. These floats are supposed to drift with the Antarctic Circumpolar Current into the Indian Ocean. Underway we recovered 6 and redeployed 5 inverted echo sounders with bottom pressure recorders (PIES). Unfortunately one of the instruments was lost upon recovery. These instruments measure the fluctuations of sea level height and the velocity of sound in the water column which allows the determination of variability in the Antarctic Circumpolar Current. The mooring work started with the successful recovery of three moorings in the transition zone from the Antarctic Circumpolar Current to the Weddell gyre, which were supposed to measure the exchanges between the two current systems. Unfortunately these moorings could not be redeployed because of the critical funding situation and the project has to be terminated. We got the impression that we are not the only ones deploring this loss because we had a visit from several Humpback whales during and after the mooring work who strived with great interest around the ship as if they had noticed the loss of a well known point of repair. To us the visit of these giants so close to the ship was an unforgettable experience which resulted in many MB of digital slides.

During the coming week we will keep on with our work along the Greenwich meridian and by the weekend we will reach the Neumayer Station.

With the best regards from everybody onboard

Eberhard Fahrbach