Five weeks after setting sail from Tromsø, Norway, the Alfred Wegener Institute's research vessel Polarstern makes a stop at the northernmost point on Earth. Here, too, the international team of researchers is investigating the coupling between sea ice, the ocean and its life, including within the deep sea. So far, the Arcwatch-1 expedition, launched on August 3, 2023, has delivered some surprising discoveries: For example, 2023 is characterized by unusual ice drift, which is affecting communities under the ice. In addition, the team has discovered an amazing biodiversity at a previously unmapped seamount at 1500 meters depth, under the ice.
On August 3, 2023, the research icebreaker Polarstern set sail from Tromsø, Norway, to conduct two months of research in the Arctic Ocean. The goal of the current ArcWatch-1 expedition is to study the biology, chemistry and physics of sea ice as well as the effects of sea ice retreat on the entire ocean system, from the surface to the deep sea.
After a short stopover on Spitsbergen, Polarstern reached the ice edge at 81.5°N and 17°E on August 6. In the following weeks, ice stations were conducted first along 85°N latitude in the Nansen and Amundsen Basins of the Arctic Ocean, and then north along 130°E longitude. During these weeks, the expedition reached the region where the MOSAiC Drift Expedition started in autumn 2019. More than 50 buoys and autonomous monitoring stations were deployed over thousands of square kilometers. In addition, the helicopter-towed sensor system "IceBird" conducted sea ice thickness measurements, and remote sensing methods were used to study the dynamics of sea ice cover over large areas . For the ice stations, which lasted several days, the ship docked at a particular ice floe in each location, allowing researchers to walk from the ship onto the ice, to set up autonomous observation stations, to explore the underside of the floe with a robot, and drill out ice cores to study life in the network of tiny sea ice channels. From the ship, they sampled the ocean beneath the ice down to the seafloor using a variety of deep-sea technologies, such as the Ocean Floor Observation and Bathymetry System (OFOBS) camera and sonar system developed at AWI.
On August 21, the OFOBS provided one of the many highlights of the expedition so far on August 21. The AWI researchers were able to survey a 2500 meter high, previously unmapped seamount. Its base lies at a depth of 4000 meters, and its peak reaches 1500 meters below the sea surface. "The top of the seamount was teeming with life," says Antje Boetius, director of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), who is leading the expedition. "We found huge sponges here, some close to half a meter in size, which were over and over populated with worms, crabs and soft corals. But very surprisingly for us, we also came across countless fish, eelpout and snailfish, which are known for their antifreeze proteins. We were delighted by the beautiful apricot-colored and almost half-meter sea anemones."
Another goal of the expedition is to make comparisons with earlier studies from 2012, as well as with studies from the MOSAiC expedition 2019-2020. In 2012, the team - also led by AWI Director Antje Boetius - was underway with Polarstern during the largest sea ice melt since satellite records began. Over a huge area, sea ice life fell into the water and sank into the deep sea - especially the filamentous endemic sea ice diatom algaeMelosira arctica. Decomposition of these algal carpets by seafloor bacteria created oxygen minima in the Arctic seafloor. The team has now been able to determine, eleven years later, that the repeated melting of sea ice algae in recent years has changed the composition of the seafloor community: formerly dominant species such as brittle stars have disappeared, but there are significantly more annelids, bristle worms and sea cucumbers. However, this year the ice algae Melosira arctica is absent from large areas of the study area, both under the ice and on the seafloor. Antje Boetius summarizes, "Returning to the places we first studied in 2012 and following up on the climate change phenomena recorded then is the essential goal of the expedition. We are very surprised by this year's change in the coupling between sea ice, ocean and seafloor. And glad that the world's hottest summer in 2023 did not lead to a new record melt, as the central Arctic was protected by a special weather condition."
Results from sea ice physics explain the observations: For example, an anomaly in ice drift became apparent early this year, pushing thicker ice southward from the west central Arctic. In regions where young ice from the Siberian shelf with their algae carpets was found in 2012 and 2020, heavily melted two-year-old ice dominated this year. As a result, there was hardly any input of material from the ice into the sediment traps and to the seafloor. Oceanographers also noticed an anomaly: The stratification of seawater beneath the ice was locally determined by melting processes or mixing by strong winds, but showed comparatively high salinity. This possibly resulted from overall low melting and reduced input from the freshwater-rich Siberian Shelf Seas. Directly under the ice, at each station planktologists encountered other swarms of animals -such as various jellies, winged snails, amphipods, and copepods. Unlike in 2012, hardly any export of biomass to the deep sea was observed. Even at the end of the melt season, there is still a distinct layer of snow on the sea ice. This makes the ice and ocean below quite dark and leads to the rise of phyto- and zooplankton from deeper water layers to the brighter underside of the ice. In addition, there are hardly any melt ponds on the sea ice, which are otherwise characteristic of the Arctic summer.
Comparisons with sea ice extent during the 2019-2020 MOSAiC Drift Expedition also show that in 2023 more will be left than during the record minima of 2012 and 2020. Despite 2023 being the hottest summer in the world - since weather observations began- sea ice shows an even higher average thicknesses than in previous years. The sea ice physicists and climate modelers explain this phenomenon with a strong low-pressure system influencing the central Arctic weather patterns this year. It remains to be seen how the ice melt will develop until mid-September towards the annual minimum sea ice extent. The first autumn storms are currently transporting warm air towards the Arctic.
Yesterday, the AWI research vessel reached the North Pole on schedule. It is the seventh time in total that in its 42-year history the research icebreaker Polarstern visits the northernmost point of Earth. The ship last reached the North Pole on August 18, 2020, during the MOSAiC expedition lead by Markus Rex. The work, which will last several days, began with a dive to the geographic pole at 90°N in 4224 m water depth. Currently, the scientists are setting up their observatories on the ice floe, in the ocean and on the seafloor. They will then continue their research southwards along 60°E longitude. Polarstern is expected back in Bremerhaven on October 1, 2023.
A camera team from UFA Documentary GmbH will be filming the expedition. The television documentary, which is being produced in cooperation with NDR, is scheduled to be broadcast on ARD at the turn of the year. Already during the expedition, impressions from on board are available by tuning in to the expedition-associated radio program on Radio Bremen and of course anyone may follow the expedition in the Polarstern web app and on the social media channels of the Alfred Wegener Institute.
Participating institutes and companies on board:
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
Albert Ludwig University Freiburg
Dartmouth College
DRF Luftrettung gAG
Fielax - Gesellschaft für wissenschaftliche Datenverarbeitung mbH
German Weather Service
MARUM - Center for Marine Environmental Sciences of the University of Bremen
Max Planck Institute for Marine Microbiology
Northern HeliCopter GmbH
Otto von Guericke University Magdeburg
Senckenberg Society for Nature Research
Tim Kalvelage (Freelance science journalist)
UFA Documentary GmbH
University of Bremen
University of Colorado Boulder
University of Exeter
University of Southern Denmark
University of Tasmania (UTAS)
University of Tokyo
