ANT-XXVI/3, Weekly Report No. 8

22 March - 28 March 2010

A thin veneer of fresh sea-ice covers the calm ocean. Ideal conditions for seismic profiling. Then seals appear – not just two or three as observed at many other times – no, it is hundreds of crab-eater seals approaching Polarstern from all directions. The seismic airguns are shut down. Again and again, groups of seals swim close to the stern of Polarstern and play in the turbulent water of the propeller. One group goes, the next comes. It is an impressive sight all day long, which also excites our marine mammal experts, because such behaviour has hardly been observed before.

Having almost completed our research activities on the shelf, we decide to go first to the Marie Byrd Seamounts for geological sampling due to an upcoming storm. It is worth the detour: The marine geologists are happily collecting cold-water corals with a dredge sampler. These fossil corals contain information about the composition of the sea-water at the time of their growth and are, therefore, invaluable for the scientists who – like Marcus Gutjahr – work on the relationship between changes of southern Pacific water masses and climate change.

The end of the expedition is approaching. Many groups are working on the final cruise report. For instance, the two smallest groups come up with their following resumes:

Quite unexpected information was revealed from the measurements of the geothermal heat flux in the seafloor. Although measured with a robust looking gradient thermometer, the temperatures of the sub-surface provide normally information on the structure of the continental margin and younger tectonic and volcanic events. Not always were the measurements successful with this aim in mind, but we have learned instead how dynamic the water mass exchange takes place between the deep-water Pacific and the continental shelf. At depths of 600-800 m, the sea-floor keeps the temperature information of the water masses moving in and out during the last weeks and months. In comparison with CTD data of the oceanographers, this is a new gain of knowledge in a totally unexpected direction.

The biologists of the Polar Biological Oceanography investigate the changes in phytoplankton biodiversity and distribution in the Southern Ocean due to climate change. Samples from the surface water were taken during the whole cruise to complete a north-south-profile from New Zealand to the Antarctic coast and a west-east-profile parallel to the Antarctic coast. Additional depth profiles were taken in the Amundsen Sea Embayment from water samples of the CTD casts. Due to the end of the summer and the big phytoplankton blooms the main interests are the species composition and distribution during the post summer bloom phase. At this time a relative low phytoplankton density can be detected in the Southern Ocean.  But rests of summer blooms and autumn blooms can be found as patches. Such a patch was found during a CTD profile last week. One station out of 11 showed a significant higher phytoplankton density than the other 10. It will be very interesting to analyze and compare the composition of the “patch” and the other stations when we are back in Bremerhaven.

Antarctica at its best on our last day on the shelf of the Amundsen Sea: Polarstern cruises through a milky-white sea of freshly frozen pancake ice on a sunny day for our farewell. An event for photographers and for pure enjoyment ….

This is now the last weekly report before our arrival in Punta Arenas on Easter Monday. I hope the readers got a small impression of our research activities in this very exciting and interesting region of West Antarctica. All groups made a good catch of samples and data and are now looking forward to returning home.

Our very special thanks go to the crew of Polarstern and the helicopter team. Their support in all of our work – with its frequent changes of the work plan – has been phenomenal. Our sincere thanks!

With best regards and best wishes for the Easter holidays from all participants

Karsten Gohl  (with contributions by Norbert Kaul and Christian Wolf)