20 Dec to 27 Dec 2007

The scientific core programme really began four days before Christmas. After successful completion of our logistic duties and a struggle through strong sea-ice fields we started sampling on the southernmost station of the 3° West transect at 70°04´S and 1550 m water depth. The location of this station is well in the centre of the Antarctic Coastal Current, a strong band of icy cold water circulating westward around the shelves of the Antarctic continent. To retrieve the necessary information about the structure in the water column, the physical oceanographers deploy their CTD probe. CTD stands for conductivity, temperature and depth from which salinity and density is calculated. All those parameters are measured and transmitted back into the lab on-line while the probe is lowered at one meter per second to depths as close as 10 m above the see floor. In the coastal current we find slightly less saline water (34.415; the oceanographers care about the third decimal after the dot) with temperatures close to the freezing point of -1.82°C. In addition a fluorometer measures algal pigments with depth and a turbidity sensor records light attenuation from particles (e.g. dead or live algal cells and zooplankton or detritus) passing a 25 cm long, and a few millimetres wide. The operator can remotely close 24 bottles, holding 12 litres of water each, in distinct depth layers. The water is then analysed for oxygen, plant nutrients and pigments, plankton species composition and abundance and the amount of total organic carbon and biogenic silica. The first results indicate that down far south the water is still in winter condition, meaning very little unicellular algae – the phytoplankton – and few animals in the water – the zooplankton. Only the underside of the sea-ice shows the bright green-brownish colour of ice algae. As we penetrate our way north with such a CTD-station every 30 nautical miles, the picture of an end-of-winter situation sharpens. But north of about 64°S where the ice is disintegrating more and more, algae are released from the melting ice into the water. Also a phytoplankton spring bloom starts developing. The zooplankton abundance also increases and we find increasing numbers of krill in the plankton nets.

As we make our way north along the first transect, the sampling at each position becomes a routine. We fish for our pelagic target species Antarctic krill (Euphausia superba) with a big net, the rectangular mid-water trawl. The term “krill” originated from the Norwegian language and means „what the whale eats“. That can be a large variety of organisms including zooplankton, euphausiids and other swimming crustaceans. Six euphausiid species live in Antarctic waters; five of these species are found in the Lazarev Sea. We use the term krill explicitly for the largest euphausiid (E. superba) that dominates the others in biomass and abundance.

Several geographical locations of high krill abundance have been known around Antarctica since the early observations from the 1930s. The last 40 years of international research have concentrated on areas located north of the Antarctic Peninsula (Scotia Sea), around South Georgia, Elephant Island, and South Shetland Islands and in the Bellingshausen Sea. Krill is commercially harvested in these areas for 30 years, especially by fleets originating from Ukraine (former USSR), Japan and during the last years with increasing effort also from Korea, Poland, Chile, Argentina and the USA. Total catch in 2002 was around 120 000 tonnes, well below the limit of 4 Mill. tonnes set by an international body in charge of fishing activities in the Antarctic: The Convention for Conservation of Antarctic Marine Living Resources - CCAMLR.

Krill holds a central role in the pelagic Antarctic ecosystem as it serves as food organism for many vertebrates including whales, seals, penguins, flying birds and fish. Also the food spectrum of krill is highly diverse, reaching from minute plankton organisms to the biota living under and in the sea ice. Krill can live for 7 years and reach 50 to a maximum of 63 mm in body length; they only grow during the few summer months that are rich in food. Krill matures in their 3rd year; they can reproduce for up to 4 years allowing the stock to sustain several unfavourable years. Investigations from the Antarctic Peninsula indicate years of high sea ice concentration are also years of high krill production and vice versa.

To catch krill, we deploy the 8 m² big RMT (Rectangular Midwater Trawl) from the ship´s stern and fish for about 40 minutes with a ship´s speed of 2.5 knots obliquely down to 200 m. After retrieval, the catch is preserved, examined under the stereomicroscope; specimens are identified to species and developmental stage, sex and stage of maturity and counted. From the database obtained, population dynamic parameters will be derived including age structure of the population, hatching success and the regional distribution of krill. With additional data from other expeditions we will be able to predict krill production for our investigation area.

The Dutch group on board has constructed a net system to catch the under ice biota quantitatively. Sea ice provides a suitable feeding and hiding ground for krill. As Polarstern turns around the ice floes their under side is covered with red sparkling dots of various species of krill in different developmental stages. The Dutch Surface Under Ice Trawl (SUIT) net can be trawled under the sea ice with a speed high enough to get the fast swimming krill. The net really has to be robust to do so. The 4 square metre wide and 4 m long frame is made of 9 cm wide steel tubes. On the upper front bar, 9 car wheel tires help the net to slide and roll under the ice. A spout is attached to one side of the frame that also serves as otter doors. Thus, once towed with 1.5 knots speed, the net slides aside under the undisturbed sea ice as it leaves the wake produced by Polarstern steaming through the ice. The top is open to allow big pieces of ice to leave the frame again, as they are bushed upward by steel bars the width of a man’s arm. The fine mesh sized 14 m long net itself is attached to the lower end of the frame and is protected on the outside by a coarse strong additional fishing net.

Crew and scientists are working as a team to lower this prototype sampling gear into the water, where it slides under the ice at a distance of 120m aside from the ship. To ensure that ice floes do not entangle with the towing cable, an additional lead weight of 1000 kg suppresses the 18 mm wire deep enough to slide freely under the ice floes that are up to 2 m thick. 8 people work hard and hand in hand to operate the net that nickname has become „chariot“.

Of course we recognised Christmas and had both, a respectful and an enjoyable celebration. Instead of telling you these stories here, I would like to redirect you to the various sites of our Education and Outreach programme that the participants of our expedition are feeding with detailed information, daily logbooks and many pictures. On www.awi.de , www.caml.aq and www.cedamar.org you will find information about our cruise, and all about our Christmas activities.

An extra source of information is at the AWI ftp-server ( ftp://ftp.awi.de/ ). For log-in please use "anonymous" as user name, and your own e-mail-address as password. On the first level of the ftp-server choose the directory called "pub" ("public"). Therein you will find a second directory called "ANT24-2". Good luck.

Momentarily we are busy completing the last stations on our 3°W transect to spend Sylvester night steaming and dancing the 169.1 nautical miles or 313.2 km to 3°E where we intend to proceed south again. In the hope that 2007 is closing well for all of you and that you will experience a fabulous start into a splendid 2008, I will see you then “as young as ever”.

Uli Bathmann (27.12.2007)