Human imprints and final considerations

In addition to the dramatic increase in macro litter we have observed at the seafloor in the Fram Strait, this research has revealed that Arctic sea ice, sea surface, water column and deep-sea sediments also harbour high concentrations of microplastics. Significant quantities of microplastic in snow samples from ice flows indicate that atmospheric transport obviously plays an important role in determining sites of deposition. Therefore, to quantify airborne microplastic pollution throughout the cruise, active air-pumping devices were fitted near Polarstern’s “crow’s nest”, an observation post in the mast of the ship, high above the highest deck. The transit from Bremerhaven to the HAUSGARTEN area was of particular interest to delineate large-scale pollution patterns and transport processes. When combined with back trajectory particle transport analysis we can investigate where these plastic particles may have come from and which route of atmospheric transportation they take.

With this, we would like to complete our series of reports featuring the diverse scientific work conducted during Polarstern expedition PS126 and we hope that we could impart a comprehensive overview on our activities at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN and during the transits back and forth. On late Monday, June 21^st, we finished this year’s field campaign and set sail for Bremerhaven, where the expedition will come to an end on June 27^th in the late afternoon.

Compared to preceding cruises, the exceptional ice conditions in Fram Strait during PS126 constantly challenged our activities. Vast, dense (up to 100%) and almost stationary areas with smaller, one-year ice-flows in eastern parts, and huge multi-year ice-flows in western parts of the strait drifting in a southerly direction at awfully high drifting speeds of 1-2 knots, made the deployment of our Autonomous Underwater Vehicle (AUV) almost impossible, hampered the use of any kind of towed gear, such as the Ocean Floor Observation and Bathymetry System (OFOBS) and complicated the easy and secure recovery of our freefalling systems (Bottom-Lander). Generally, Polarstern had to reduce its speed while operating in the ice. As a result, we progressively lost valuable station time and finally had to skip some of the work from the original plans.

Still, during the cruise, we collected numerous samples and obtained a vast amount of physical, geochemical and biological data, which will extend our time-series at HAUSGARTEN observatory and finally help us to understand the effects of Global Change induced environmental changes in the Arctic Ocean. Moreover, we were able to recover the most expensive gear used for our long-term studies, i.e. our Benthic Crawlers TRAMPER and NOMAD. Both vehicles operated autonomously across the deep seafloor for two entire years and will now get a “breathing pause” and some maintenance, before they will be sent out again during the next expedition to HAUSGARTEN in 2022.

We would like to thank Captain Stefan Schwarze and his crew for their hospitality, the great team work and the pleasant atmosphere on board, and gratefully acknowledge the professional support by the HeliService team during our expedition.

We are now looking forward to see our families and beloved friends at home, and we hope that there are some warm summer days left after our return.

With best wishes from board Polarstern,

Thomas Soltwedel