Punta Arenas – Las Palmas – Bremerhaven
11 April – 24 May 2009

Since yesterday the half-year long mission of FS POLARSTERN on the southern hemisphere was terminated. Surrounded by a dark tropical sky and water temperatures of 30°C we crossed the equator at half past seven. We continue northbound along 23°W towards waypoint 20°N 23°W. The uneventful equator crossing has to be seen in view of the spectacular visit of King Neptune and his spouse Thetis on 1st May.  They returned only five months after their last visit to the ship and were received with a warm welcome by the Master, Kapitän Pahl. The following crossing-the-line ceremony was great fun as was the leisurely barbecue on the main deck later in the day.

Unfortunately we missed an unexpected rendez-vous with FS METEOR. Both ships were crossing the 23°W meridian within a few days.

All research works are accomplished without problems as planned. Depending on sun and cloud conditions meteorologist take measurements from the zodiac on our daily CTD station at 1 p.m. After dinner we often listed to interesting presentations and slides series in the ship’s seminar room. Most of us were deeply impressed by the first-hand reports about a research stay on the Argentine station “Jubany” by N Koschnik and about the newly erected German antarctic station “Neumayer III” by J Hofmann.

During the cruise Joachim Kuss and Martin Kunze from the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) study mercury in surface waters. The acronym of their research topic is “QueMar” (PI: Dr. Bernd Schneider). It is funded by the German Science Foundation (DFG). Here comes their report:

“Mercury is an element of natural origin. But, it is additionally mobilized and released to the atmosphere by anthropogenic activity, for example, by fossil fuel burning. It is distributed globally and is transported to the ocean attached to dust, by rain and/or by fluvial input. Since mercury changes its speciation under environmental conditions it is not finally deposited in the sea. It can be transformed to volatile elemental mercury and is re-emitted.

Each hour the concentration of elemental mercury is measured in surface water that is pumped into the lab. The analysis is similar to the determination of elemental mercury in the air using atomic fluorescence spectrometry. But the concentration of mercury cannot be directly determined with the spectrometer. Using additionally a so-called “equilibrator” the measurements can be done with the spectrometer. This equilibrator consists of large bottle with a showerhead. Water is dispersed into the bottle until the distribution of elemental mercury between the water and the air in the bottle is in equilibrium. This takes about one hour. Then the equilibrator air is analysed and the concentration in water is thus known. Alternately the concentration of elemental mercury in the marine atmosphere is analysed. Therefore air is pumped from the reeling of the uppermost deck of FS POLARSTERN in the lab. The air is then supplied to the spectrometer and is measured. From the concentration difference between the atmosphere and the seawater the mercury sea-air flux can be calculated. For the calculation the actual wind speed is needed. It determines the speed of exchange. The current study shows clear regional differences of mercury emissions. The amount of mercury released by the sea is small. It is in the range of a few tens to some 100 Nanograms (one of a billion gram) per square meter per day. But since oceans cover about 2/3 of earth surface, the total release of mercury by the ocean is assumed to be significant. Please note, that the mercury burden of the maritime air is clearly too small to make it harmful.”

First thoughts about packing and landing procedures for Bremerhaven are secure omens that one half of the journey lies behind us.

Warm greetings to everybody at home,

Walter Zenk
6°N 23°W, 6 May 2009