Polarstern Returns to Bremerhaven

Upon departing from Bremerhaven, the Polarstern and teams under expedition leader Prof Torsten Kanzow from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), initially headed for Fram Strait. Here they worked to continue the interdisciplinary time series of the West Spitsbergen Current, which, thanks to observatories moored on the sea floor, consists of continuously gathered observations reaching back to 1997. The West Spitsbergen Current transports warm water originating from the subtropical North Atlantic toward the Arctic Ocean, thus representing the Arctic Ocean’s most important oceanic heat source .

Next, the vessel steamed on to the expedition’s main area – the marginal ice zone in north of Svalbard. Over the course of three weeks, the researchers documented the summertime decay of selected floes. In this regard, they also studied energy and matter fluxes between the ocean, sea ice and atmosphere. The teams also measured the sea-ice thickness and characteristics and deployed new instruments in the water and on the sea floor, which will gather data directly below the sea ice for the next year. A related project in the region examined how small-scale ocean fronts, eddies and the ice edge itself influence carbon export in the ocean. In this context, the experts documented the spatial changes in oceanic stratification and the sea ice, from the open water near Svalbard across the marginal ice zone and into the pack ice. In the process, they also recorded data on the nutrient supply and distribution of phytoplankton and zooplankton.

From the marginal ice zone, the teams ventured a foray to the only confirmed field of black smokers in the Arctic Ocean, located at the seamount “Aurora”, which they managed to reach after passing through dense ice cover. Here, they deployed high-sensitivity seismometers on the sea floor, which can detect magma flows beneath the seabed and the presence of fracture zones, along which water circulated through the rock, is warmed, and then makes its way back to the sea floor, carrying dissolved materials with it.

Once the fieldwork in the marginal ice zone was done, the ship proceeded to the coast of Northeast Greenland, where the researchers explored oceanic influences on the melting of marine glaciers. In response to oceanic warming, the inland ice of the two major glaciers found there (79 N Glacier and Zachariae Isstrøm) is in decline. As a result, the glaciers’ flow speeds have increased, which contributes to sea-level rise. Although the combination of a stable barrier of fast ice off the coast and permanent fog made taking measurements near the glaciers impossible – both from the ship and by helicopter – the teams still succeeded in characterising the oceanic inflow of warm water. The last phase of the fieldwork took place in the glacial fjord system of the Scoresby Sund in East Greenland, where they recovered observatories from the depths of the fjord that had been recording data for the past four years.

All told, the researchers can look back on a highly successful journey, as expedition leader Torsten Kanzow confirms: “One of the greatest successes while taking measurements in the ice zone was the first-ever deployment of the TOP-AWI sensor platform below the sea ice, which allowed us to document the interplay of sea-ice cover, ocean stratification, nutrient and plankton distribution at unprecedented resolution.” During the three weeks the Polarstern remained in the marginal ice zone, the teams used ice buoy and ocean buoy-based measurements to continuously observe the pronounced changes in the ice floes: “It was impressive to see how, at one station, the swell from the open ocean came in, and how the floe we were working on moved in time with the waves, and ultimately broke into pieces beneath our feet,” Kanzow recalls. “Later, from the ship we could see that the sea ice floe over a wide range of our working area had suffered the same fate. We posit that the erosion of sea ice in the marginal ice zone, produced by the swell, has a major effect on ice melting, and on the ecosystem connected to the sea ice.”

The crew of the Polarstern will spend the next two weeks preparing for the next expedition, which will take them to the Antarctic at the end of August. Anyone interested in the ship’s route, the weather conditions, and snapshots and testimonials from on board is welcome to check out the Polarstern Web App: https://follow-polarstern.awi.de/