ANT XXV/1, Weekly Report No. 4
The rosette water sampler is being deployed... (photo: Norbert Hertkorn)
24 November - 3 December 2008
This week, the weather still remained friendly with a lot of sunshine. This weather is not a given because this region can often be affected by strong southeasterly trade winds and an overcast sky. The research is going on smoothly and the water sample systems work fine, which means there is still plenty of work to do within this last week. On the 29th of November, the last deep CTD was sent into the abyss to get water samples from great depths. Here in the Cape Basin, the water is 4,600 m deep. Close to the sea floor, the Antarctic bottom water is already present with temperatures of 0.7° C. On the 30th of November, the last CTD station took place. The nice weather with a lot of sunshine makes it possible to use the rubber boat for irradiation measurements without the influence from the vessel.
Beside the chemical characterization of dissolved organic matter, a biological program is also under way. The particulate organic matter is characterized in detail. Samples are taken to determine the pigment composition of various algae and cyanobacteria communities across the different climatic zones.
...and is in the water. (photo: Norbert Hertkorn)
This data will be used to verify chlorophyll and biomass data from satellites. The microbiological work on board tries to answer the question how chitin is degraded. Chitin is one of the most abundant compounds in the ocean and is particularly important for the utilization by bacteria of the strain Vibrio. It is not known what kind of products is formed during this degradation pathway and to what extend dissolved organic compounds are produced.
Over the course of the last week it has been evident that biological production in the surface seawater has been the highest encountered over the cruise track. Bacterial production in the surface water has continued to increase. Dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) levels have also been increasing. DMS concentrations have been 10 times higher than the oceanic average. DMS is created when DMSP, which is produced in the cells of certain phytoplankton, is cleaved. It is believed that oceanic bacteria play a major role in this process. Interestingly, preliminary evidence from this cruise suggests that when DMS levels were the highest, phytoplankton levels were the lowest of this past week and bacterial production the highest. DMS draws interest, because its atmospheric oxidation products can go on to influence the radiative budget of the Earth reflecting radiation out to space. This interaction illustrates how the smallest marine life can affect atmospheric trace gas chemistry and even the global climate system.
Finally, toward the end of the cruise, on the 30th of November, the wind picked up to wind force 7. At night, there was the final barbeque on deck, and the research work will stop on the following day. Everything has to be packed up and on the 3rd of December we will arrive in port in Cape Town.
Thanks to the very nice collaboration between all scientists and the very friendly and professional support of the crew of the Polarstern; all work has been performed very successfully. We would like to say good-bye with this last weekly report, and we can look back to a very successful and enjoyable research cruise.
Best wishes and greetings,
Gerhard Kattner.
Scientific team of ANT-XXV/1 (photo: Holger Uhlig)
