ANT XXV/1, Weekly Report No. 1
Water sampling at the rosette sampler. (photo: Dieter Peterke)
31 October - 9 November 2008
We left Bremerhaven in the afternoon on the 31st of October. The sea was calm and supported a quick and smooth unpacking of the first boxes and the deployment of some equipment. At 9.00 pm of the following day, the refuelling began in Rotterdam and lasted until the next morning. On the 1st of November at noon, we were back at sea steaming towards the English Channel.
At midday of the 3rd of November, we stopped to proceed with the first measurements using the CTD profiler and water samplers in the English Channel. This stop was the start of daily CTD casts to measure salinity, temperature, depth and some additional parameters and to perform seawater sampling at distinct depths. The ship has a permanently deployed seawater supply, which is used to continuously measure chemical, biological and oceanographic parameters.
Additionally, a metal- and organic-free online water sampling device (“fish”) was deployed alongside the vessel to continuously pump water from the ocean surface on board. A third source of seawater is supplied by the moonpool. The water is pumped through a “snorkel” from this moonpool at about 12 m depth into one of the wet laboratories. The biggest wet lab on board is packed with a diversity of scientific equipment and researchers, because the water from the “fish” sampler is pumped continuously into this lab. Almost everybody needs a steady water flow to run continuous measurements. Most measurements are undertaken while the vessel is moving.
The “fish” for continuous water pumping. (photo: Boris Koch)
On the 4th of November, the Polarstern was located west of Bretagne/France. The weather remained friendly. It was overcast but the sea was calm. The reputation of a stormy Gulf of Biscay in autumn did not hold up, and even the sun came out on the following day while we were still crossing the Gulf. During the station times and CTD casts, everybody was very busy. Some people sampled water from various depths; others measured sunlight intensities aboard a small rubber boat or used a second winch to test sensors.
On the 6th of November, we arrived west of the northern tip of Spain, and a longer Posidonia test was scheduled. Posidonia is an acoustic positioning system to recover instruments, which are deployed at great depths. To find these instruments, a series of distinct acoustic signals is send through the water using a hydrophone. After the reception of this signal, a short pulse is send back from the instrument. The distance of the instrument relative to the vessel can be calculated using the time difference between transmitting and receiving of the signal. A minimum of two hydrophones at different locations on board is needed to be able to find the instrument. This procedure is similar to the human ears to locate the exact position of a sound. Modern systems are transducer arrays containing 4 “ears” integrated into a 60 cm disc.
This Posidonia system calculates the depth and horizontal distance of the instrument, which need to be recovered, relative to the vessel. Recently, a new transducer array was permanently mounted into the Polarstern. The new system was tested and compared to the old one. This system is expected to further improve the recovery of temporarily deployed deep-sea instruments (e.g. moorings).
The big wet lab full of instruments (photo: Boris Koch)
The wind slightly increased and so did the swell. The movement of the vessel is now noticeable with its rocking and rolling, but everybody is already used to it, and hence nobody is affected. The really bad weather just hit the Gulf of Biscay, but fortunately we are already further south.
Today, Sunday the 9th of November, we are west of Gibraltar. The air and water temperatures are increasing daily reaching already 18ºC. We are definitely getting closer to the tropics.
Everybody is doing great and best wishes from the Polarstern,
Gerhard Kattner