‘Polarstern’ Returns after Antarctic Mission

After year and a half in the Antarctic the research vessel Polarstern is expected back in its home port on 13 April.

Apart from the crew and scientists on board, there are lots of data, samples and animals from the Southern Ocean that will soon be examined more closely in the laboratories of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). They stem from the area of the Filchner-Ronne Ice Shelf in the very south of the Weddell Sea, where scientists conducted research on sea ice, oceanic currents and the biocoenoses on the last Antarctic cruise leg of the expedition.

Polarstern covered over 64,000 nautical miles in the past 18 months, which corresponds to about 120,000km and thus three times the circumference of the Earth at the equator. However, the icebreaker sailed through these tropical regions only on the way there and back.

The main research area was the Antarctic Weddell Sea. The last expedition prior to returning to Bremerhaven again took the vessel to the very south of Antarctica, to the marine region off the Filchner-Ronne Ice Shelf.

“Even in the Antarctic summer this area is not easily accessible and we had to struggle with very difficult ice conditions,” reports Dr. Rainer Knust, head of the expedition and biologist at the Alfred Wegener Institute. He coordinated a multidisciplinary team from eleven countries on board that conducted investigations on sea ice physics, hydrography and biology.

In close consultation with the captain, Knust laid down the work programme according to the ice conditions. The sea ice physicists were thus delighted about large ice floes on which they were able to place their measuring buoys. The latter measure whether an ice floe is growing or thawing and how quickly and in what direction it is drifting. The installed measuring buoys remain on the ice floes and transmit their data via satellite to the Alfred Wegener Institute in Bremerhaven.

The oceanographers were dependent on gaps in the ice to make use of their devices. They were able to conduct extensive oceanographic measurements of water depth, salinity, temperature and oceanic currents in the research area.

In addition to these measurements directly on board, they recovered long-term moorings and deployed new ones. They record oceanographic measurements over a period of more than two years. In this way it is possible to continuously measure changes in salinity and temperature of the seawater.

The objective of this work is to record and monitor the very cold melt water plume from the Filchner-Ronne Ice Shelf and its mixing with warmer water from the deeper Weddell Sea.

The work of the oceanographers is supported by Weddell Seals equipped with sensors and transmitters during the expedition. They not only supply measurements on diving behaviour during their dives, but also data on the salinity and water temperature under the ice that cannot be obtained otherwise. These data, too, are transmitted to AWI via satellite.

The initial results on the biocoenoses in this still extensively unexplored region show that settlement and species diversity on the seafloor are closely connected with the ice cover and hydrography. Wherever very cold water flows out or in areas that are covered with sea ice for a very long time, species diversity and settlement density are considerably lower than in open regions that are not as greatly influenced by glacier runoff.

“Earlier findings concerning the unexpected occurrence of elephant seals on the northern shelf slope of the Filchner Trench gave the impetus to study in more detail the previously only presumed connection between hydrographic conditions and increased food supply for seals in the course of our expedition with Polarstern,” reports Knust.

Prior to RV Polarstern, AWI’s research aircraft Polar 6 was also in operation on the edge of the Filchner-Ronne Ice Shelf in order to record the number of seals from the air. Using Polarstern’s on-board helicopters, biologists also undertook aerial counts. Their first impression before detailed evaluation appears to substantiate the hypothesis that there is indeed a connection between seal numbers and oceanographic conditions.

The Filchner-Ronne Ice Shelf is the second largest ice shelf in Antarctica. Coupled ocean-atmosphere model calculations at AWI indicate that dramatic changes with 20-fold higher melting rates can be expected there at the end of this century.

“This expedition is the first of a series of further Polarstern voyages aimed at gaining an understanding of the actual state of the Filchner-Ronne Ice Shelf system and measuring the water masses off and under the ice shelf. Then we will compare them to the little historical data available and can then check the calculated models,” says the head of the hydrographic team on board, Dr. Michael Schröder from AWI.

The future expeditions in this region will also be carried out on a multidisciplinary basis in order to examine the connection between ice, seawater and biology.

Polarstern will undergo scheduled maintenance and repair work at the Lloyd shipyard in the coming weeks before the Arctic season begins in mid-May.

AWI, April 11, 2014