ANT-XXVIII/2, Weekly Report No. 2
10 December - 16 December 2011
Welcome in the ice. (Photo: Sebastian Richter)
On 10th December in the evening we arrived at 53°S and continued our programme with stations about every 2°. We are now routinely deploying larger plankton nets to sample phyto- and zooplankton. On 11th December we could observe the first penguins (chinstrap penguins), which passed the ship in small groups. First small ice floes, remains of icebergs, slowly prepared us for the arrival in ice-covered regions.
At water and air temperatures below -1°C we swiftly approached the marginal ice zone, which we reached in the afternoon of 12th December. At noontime we had cut through the first small ice field and passed a small iceberg carrying about 100 chinstrap penguins. Occasionally larger icebergs appeared. The ice coverage became slowly denser. However, it was not easy to determine the transition area from open waters to ice-covered areas, the change was quite gradual. The increasing occurrence of humpback and fin whales, crabeater seals and one leopard seal, many chinstrap penguins and hundreds of petrels indicated that this was a very productive area, as expected from ice edge zones. We slowed down and completed a so-called ice zone station at 58°S.
Chinstrap penguins on an ice flow. (Photo: Jan Haelters, PolE)
The zooplanktologists were very enthusiastic about this “hotspot”. A krill swarm and many zooplankton specimens were encountered and sampled with the nets. The Antarctic krill, Euphausia superba, was in excellent condition, their midgut glands, similar to a stomach, showed a dark green colour, due to intense feeding on microalgae. Krill plays a key role as food source for e.g. many marine mammals and seabirds in the Antarctic. Of special interest to our scientists are also copepods, tiny crustaceans between 1 and 10 mm length. Copepods are very important members of the food web comprising up to 80% of the zooplankton biomass. The two dominant Antarctic, algae-eating copepod species, Calanus propinquus and Calanoides acutus, have to cope with extended periods of food shortage during the long and dark winter season, when phytoplankton algae cannot grow. However, their life-cycle strategies and adaptations differ substantially. Calanoides acutus descends to great depths of more than 1000 m in autumn and survives the winter time in an inactive state called diapause. In contrast, Calanus propinquus remains active during winter, and switches from its algae-based summer diet to a wider food spectrum in winter. Both species accumulate large fat reserves, although of different chemical compositions. We aim to elucidate the mechanisms controlling diapause and regulating buoyancy in Calanoides acutus and other species. To study these processes under almost natural conditions, the scientists “take a part of the Antarctic environment onboard Polarstern”. They work in temperature-controlled lab containers under challenging, simulated field conditions including freezing temperatures.
On 13th December we were surrounded by ice. It was still very thin and every once in a while interrupted by large open leads. This ice is no challenge for Polarstern. We made very good progress, better than expected. The weather was also fine, even the sun appeared frequently, but also light snow showers.
The copepod Calanus propinquus. (Photo: Jenny Huggett)
On the next day, 14th December, we intended to recover a small mooring. Since 2008 MARU (Marine Autonomous Recording Unit) has recorded acoustic signals, sounds of animals (whales, seals) and icebergs. We were all anxious to see what the ice conditions would be like in this area. The position of the mooring was quickly identified, but large ice floes covered the spot. Since the ice also drifted with wind and current, we carried out another station with CTD and nets and observed in the meantime, in what direction the ice drifted. Unfortunately, the drift was not as required, and therefore we had to postpone the recovery of the mooring. We still have another chance on our way back. The next two days we proceeded without interruption, apart from a small boat manoeuvre, in the direction of the Neumayer III Station, which is still more than 400 nautical miles away. Our route is a rather crooked line, since we keep bypassing larger ice areas.
The visit and supply of the Neumayer III Station are well in preparation. Every morning we have contact with the station and exchange newest information about weather and ice conditions. Many things cannot be planned as yet, since they depend on weather and time of arrival of Polarstern.
Everybody is looking forward to visiting the station, and the preparations for our Christmas celebration are also developing slowly but surely. We wish you all a nice week before Christmas and send our sincere greetings to everybody,
Gerhard Kattner