It seems that the large aggregations of fin whales are sustained by krill, which in turn feed on phytoplankton. In many regions of the Southern Ocean, however, trace elements such as iron limit primary production. The goals of the trace metal group on board (Photo 3), led by Florian Koch, are to elucidate the impact of iron limitation and trace nutrient (iron, zinc, and vitamin B12) cycling around the waters of the Western Antarctic Peninsula. In addition, the impacts of salp and krill fecal pellets and various dust sources on trace metal concentrations and their bioavailability are being investigated. Since the Polarstern consists of 11,820 tons of metal, special care needs to be taken not to contaminate the samples. A Teflon membrane pump, connected to a polyethylene line was used to pump surface seawater from 20 m depth directly into a trace metal clean container where the seawater could be sampled. Over a period of 6 hours, ~3000L of clean seawater were pumped onto Polarstern. Three stations, one in off-shore high nutrient low chlorophyll (HNLC) waters, and two in coastal low chlorophyll regions, were sampled in this manner and a total of ten experiments with this water were conducted, looking at the impacts of fecal pellets, dust and grazing on phytoplankton/trace metal dynamics.  Another way to collect water using ‘trace metal clean techniques’ is via a specialized collection bottle called a ‘GoFlo’ (Photo 4). Unlike regular bottles on a CTD Rosette, which enter the water in the open position and are closed at depth, a ‘GoFlo’ has a specialized mechanism. This enables the bottle to enter the water in the closed position and minimizes contamination from the ship. Using the ‘GoFlo’, water was collected at ten stations in order to measure trace metal and vitamin removal and recycling processes with the help of isotopic tracers. Radioisotopes are a powerful tool to measure various rate processes in the marine environment and the Polarstern has a state of the art isotope container in which these compounds can be safely used. Concurrently, bacterial production and primary production rates were assessed and water samples collected in order to characterize the plankton community composition as well as the water chemistry (trace metals, ligands, nutrients, vitamins).

On the 30th April we finished our activities at our last process study station and left Elephant Island in northerly direction in order to complete our krill and salp abundance transect. At present all working groups are busy packing their scientific equipment and organizing the storage of the scientific samples that were generated during the expedition. Everybody hopes for a smooth crossing of the Drake Passage in moderate weather conditions because this area is notorious for the high frequency of low pressure systems.

PS112 was a very successful expedition. For the first time, experiments were conducted with the salp species Salpa thompsoni in pristine condition, their interaction with the Antarctic krill Euphausia superba as well as the impact of both organisms on the biological carbon pump and the phytoplankton composition. In addition, we were able to observe a large fin whale aggregation and their foraging behavior on krill, which was not observed before. We are looking forward to analyze the large dataset and the hundreds of samples that were generated during the expedition at our home institutes and to combine the results fulfill the aims of our projects.

With best wishes from all expedition participants from Polarstern

Helena Herr, Florian Koch, and Bettina Meyer (Chief Scientist)