PS124 - Weekly Reort No. 5 | 1 - 7 March 2021
Research in the Southern Ocean
[08. March 2021]
The last weekly report talked about weather and even though weather is applicable to almost everyone’s work on board, it is critically important to those whose research activities rely on Polarstern’s two helicopters. On this expedition, two teams alternate use of the helicopters: the sea ice team and the seal team.
Both teams, the pilots, captain and chief scientist meet at the ship’s weather bureau every morning at 8:15 a.m. to hear what the weather will be doing during the day, and then organise their flights and map their desired routes.
Sea ice research in the Southern Ocean
In contrast to the sea ice cover in the Arctic, which has shrunk dramatically, Antarctic sea ice has changed little. The reasons for this striking difference are still little understood. In addition, most observations rely on satellite data only, while extensive in-situ observations in the southeastern Weddell Sea have not been performed for more than 20 years. Therefore, the objectives of the bio-physical sea ice research program during COSMUS are to investigate the state of sea ice directly and with modern observational methods, and to better understand its role in the Antarctic ecosystem. To this end, observations of snow and ice thickness change, snow metamorphism, as well as biological diversity and carbon fluxes are of particular importance. The latter is also very relevant in the context of all other studies during this cruise, which are concerned with processes and fluxes in the water column and at the sea floor that are strongly influenced by sea ice.
Due to the tight and rigid ship schedule we are unable to enter the ice from the ship. Instead, we rely on the use of helicopters to bring us to the ice. This has the advantage that from the air we can very well select representative, level ice. In addition, using the helicopters allows us to find ice farther away from the ship, which mostly sails in open water. As the ice team includes five people and uses a lot of scientific and safety equipment (Fig. 1), we have to carry out at least two flights to transport everything to the ice. Due to relatively poor weather conditions with thick and low clouds there are often flat-light conditions on the snow covered ice which makes the landing very challenging. However, our experienced helicopter team meets those challenges with ease.
First results show that snow and ice thickness in the southeastern Weddell Sea are quite similar to conditions more than twenty years ago. The ice floes are quite variable, which results from their origin in various source regions of the Weddell Sea and their drift with winds and currents. This can also be concluded from variable composition of biological microorganisms living in the ice. In addition, and despite being in late summer, we have found only little evidence for sea ice and snow surface melt during the previous summer. Our in-situ measurements are also very important for the better understanding and utilization of satellite imagery from microwave sensors. In the future, those satellite sensors will allow us to observe sea ice processes year-round, and when no in-situ observations can be carried out. More specific results of the biological and bio-geochemical ice studies will only be available later, when our extensive ice core samples have been analyzed in our labs at home.
Seals and Oceanography
Although the Southern Ocean covers about 20 million km2 – only 10 % of the World Ocean – it is home to more than 50 % of the world’s biomass of marine mammals. This includes the six Antarctic seal species: the Weddell, Ross, crabeater, leopard, southern elephant, and Antarctic fur seal. The comparatively low diversity is caused by the isolation of Antarctica by the Antarctic Circumpolar Current (ACC), which acts like an invisible barrier separating the water and land masses south of the ACC towards the north with water temperature differences of more than 10 °C. The unique oceanographic conditions of the Southern Ocean play an important role for the highly adapted Antarctic seal species that live, breed and eat in these waters.
In addition to the oceanographic work from aboard the Polarstern, Weddell seals are used to collect oceanographic data and complement the oceanographic work. The seal team, a small group of scientists from South Africa, Norway, and Germany, equips Weddell seals with miniatured sensors and satellite transmitters that collect data on temperature, salinity, and pressure of the sea water in which the seals dive. During the breathing and resting periods of the seals at the sea surface or on the ice, the data is transmitted via satellite. We plan to instrument twelve Weddell seals with transmitters that continue collecting data up to one year after deployment. Aside from the oceanographic questions, the data also allows us to understand the movement and diving behaviour of Weddell seals and how they interact with their environment.
Aboard Polarstern, satellite images are used to identify pack-ice flows several kilometres of length to fly to and search for Weddell seals. Once a seal has been identified, the helicopter lands on the ice and sets out the seal team to deploy the transmitter on the seal (Fig. 2). It is always a surrealistic, almost magic moment, when the helicopter leaves and you find yourself on an ice floe more than hundred kilometers away from the ship. The greatness of nature and the relative smallness of human being is overwhelming. This sensation will forever influence our perception of the Earth we live on.
PS124 sends regards from our southernmost position (77° 12‘ S 34° 01‘ W) in a fall-like Weddell Sea – one of the few Antarctic marginal seas which are covered in part by sea ice all year round.
Hartmut H. Hellmer (Chief Scientist)
Contact
Science
Hanna Sophie Knahl
hanna.knahl@awi.de
Scientific Coordination
Ingo Schewe
+49(471)4831-1709
Ingo Schewe
Assistant
Sanne Bochert
+49(471)4831-1859
Sanne Bochert