ANT XXV/1, Weekly Report No. 3
Meeting of RV Polarstern with RV Maria S. Merian (photo: Holger Uhlig)
17 November - 23 November 2008
This week we crossed the equator at 12°04, 25’W, and we are now on the Southern hemisphere.
On the 18th of November, a random meeting with the research vessel Maria S. Merian took place. Polarstern crossed the cruise track of the Merian at 8.00 am. The rubber boats of both vessels were launched, and a busy boat shuttle service started with exchange of researchers and crew between the two German research vessels. The sea was calm and the thermometers showed 29°C (more info under www.ifm-geomar.de). At lunch the two ships separated again and moved on. This visit took place right in the middle of the inner tropical convergence zone (ITCZ), which is famous for its heavy tropical rain showers and lightning storms. However, we crossed this area without any rain, but some scientists would have preferred to collect rain and to investigate the contribution of substances to the ocean via rainfall.
A float is deployed and drifts away. (photo: Dieter Peterke)
In ocean surface water and in atmosphere volatile elemental mercury is continuously measured. Different processes are responsible for the formation of this mercury species, and to date there are no data available within the investigated area. Mercury in air is analyzed using fluorescence spectroscopy with a pre-concentration of mercury present in 5.5 litre of air. To be able to measure mercury in the ocean surface water a continuously operating equilibrator is used establishing an equilibrium between the concentration of mercury in the water and in the air. The mercury content in the air is then analyzed, and the content in the water can be calculated. First results showed elevated levels of mercury at the European continental shelf, which decreased slightly with direction south until they started to significantly increase again at a latitude of 15°N. Hence, the ocean within the ITCZ seems to be a source of mercury.
Polyfluorinated compounds are also measured in air and water. These anthropogenic substances are wide spread around the globe. They are accumulating in the marine environment, e.g. in fish and mammals, but also in human blood. To be able to detect these chemicals, 1000 L water and/or 1000 m3 air have to be extracted.
The so-called fish is towed for water pumping. (photo: Dieter Peterke)
During the week, a rumour persisted that Neptune will visit the Polarstern when crossing the equator. And indeed on the 20th of November, Neptune’s ambassador Triton arrived on board and on the next day Neptune was welcomed on Polarstern. The traditional equator baptism was a great success, and everybody had a lot of fun.
South of the equator, every three degrees of latitude a float is deployed. These drifting devices regularly dive to a specific depth and collect data as part of the worldwide Argo monitoring program. During the next surfacing of the float, the data is transmitted to the headquarters for this program. This approach allows a continuous monitoring of oceanographic data for several years.
Not only in Germany but also here on board the Polarstern, the temperature decreased slightly to a pleasant temperature of 24°C. Three weeks of this expedition already passed, and first preparations are underway as well as thoughts about the end of the cruise.
We all send again our warmest greetings to everybody at home,
Gerhard Kattner