Back to the Southern Ocean: taking a closer look at the complex climate system in the eastern Weddell Sea

4 December 2020

Following the German research icebreaker Polarstern’s fascinating year in the Arctic as the research platform for the MOSAiC expedition, it’s now time to return to the ice-covered Southern Ocean to gain a better understanding of local interactions between the ocean, sea ice and atmosphere. But this expedition won’t proceed entirely as planned, either – like so many things in the on-going coronavirus pandemic. In mid-December, the research ship Polarstern, with the new overwintering team, coordinators and helping hands for the German research station Neumayer III on board, will leave Bremerhaven, bound for the edge of the ice shelf near the Antarctic Neumayer Station. Once the supplies have been delivered and all the passengers have safely arrived at the station, RV Polarstern will set sail through the Waddell Sea to the Falkland Islands, where she is expected to arrive in late January 2021.

Prior to their departure, the research team for the PS124 expedition will spend two weeks in quarantine in Bremerhaven – so that they can be sure that they are healthy when they leave for the Falklands, and the expedition can start on time in early February.

In the subsequent two months, the research teams on board will investigate the complex interactions between the constantly changing climate and ecosystem in the eastern Weddell Sea. The exact research areas will essentially be dictated by mother nature: RV Polarstern will work her way southwards toward the Filchner ice shelf, as far as the sea ice permits. At the moment, we can’t say just how far this will be, since the sea-ice extent and concentration in the Weddell Sea are subject to substantial interannual fluctuations. At the same time, we have observed a slight increase in the summer sea-ice extent in recent years, which is thought to be largely driven by the wind. Therefore, one of the aims of the sea-ice fieldwork on the current expedition is to gain insights into the ice drift in the region in connection with potential changes in the ice and snow cover. To do so, we will make large-scale measurements of the sea-ice thickness using the EM-Bird, a sensor towed beneath a helicopter, as well as measurements of the thickness of several individual ice floes.

A major component of the Antarctic sea-ice mass balance is the snow cover, which not only varies spatially in terms of its thickness, but also in terms of its internal properties and processes. The latter include e.g. the characteristic melting and freezing processes in the snow, as well as snow metamorphosis. Analysing these processes can provide key insights into the timing of changes in the onset of the melting, depending on changing atmospheric conditions. “Therefore, as in previous expeditions, we will gauge the properties using so-called snow pits, and then compare our findings with remote satellite sea-ice observations, so that we can verify the current evaluation algorithms and gain a better understanding of the metamorphic snow processes and their regional variability,” explains Dr Stefanie Arndt, a sea-ice physicist at the AWI.  

Furthermore, internal snow melting processes lead to melt water seeping to the ice’s surface, where so-called intermediate layers consisting of slush, rising seawater and algae form. Large accumulations of organic compounds can be found in such habitats. “In the planned research area for the PS124 expedition, we expect to frequently encounter these conditions, which have rarely been examined with regard to the interplay of ice thickness, biomass and other biochemical processes in the intermediate layer. This is one reason for investigating these processes closely during our work at the ice station,” the researcher adds.

To allow us to continue observing the changes in the snow thickness, at least along the ice floes’ drift trajectories, like in previous expeditions, AWI sea-ice physicists will install autonomous measuring systems (buoys) on the ice. On an hourly basis, they will transmit data back home via satellite, so that the expedition participants can keep an eye on the ice conditions in the Weddell Sea even after their return. This data will be available on the portal shortly after the buoys have been installed.

Current sea-ice situation in the Antarctic:After reaching its absolute maximum extent of 19.4 million km² on 26 September this year, the Antarctic sea ice is now gradually decreasing again. In November, a total extent of 15.99 million km² was measured (see Fig. 1); roughly 150,000 km² below the long-term mean for 1981 – 2010 (see Fig. 2). The sea-ice extent is slightly above the long-term average in major areas of the Ross Sea, along the coast of Wilkes Land and in the western Weddell Sea. In the Amundsen and Bellingshausen Seas, it is slightly below the long-term average (see Fig. 3).

Dr. Stefanie Arndt
Dr. Renate Treffeisen
Dr. Klaus Grosfeld