Among the participants in PS121 is the PEBCAO group (Plankton Ecology and Biogeochemistry in a Changing Arctic Ocean), which has been a constant participant in the research program in the long-term observatory HAUSGARTEN. The group’s focus is investigations of plankton communities and microbial processes in the research area, which is influenced by rapid changes in the surrounding climate conditions. It is expected that changes in the temperature and ice cover will lead to changes in the biodiversity, ecology, and biogeochemical cycles in the Arctic Ocean, which can only be detected by long-term observation programs. The investigations of the PEBCAO group are based on combined investigations of various parameters, which in sum contribute to understanding process and changes in the Arctic marine ecosystem. The chlorophyll concentration in the water is measured as an indicator of current photosynthetic biomass. In addition, the biodiversity of plankton is investigated using classical light microscopy and modern optical and molecular methods. During the last 10 years, the PEBCAO group has collected complementary information regarding the annual variability in the plankton assemblage, primary production, and bacterial activity. The results show that the phytoplankton assemblage, the smallest organisms at the base of the food web, have changed in the summer months in the eastern Fram Strait during the investigation period.

During PS121, light profile measurements are being measured as part of a PEBCAO project. In addition to nutrients, light is one of the important limiting factors for biological growth in the ocean, especially for photo-synthetically active organisms like phytoplankton. Sediment and dissolved particles limit light penetration depth in the water. Exact knowledge of how the light color changes in the ocean is necessary to develop robust algorithms to build continuous global maps of the amount and assemblage of phytoplankton and associated by-products from satellite measurements at high temporal (daily) and spatial (300 m) resolution. In addition, our light measurements must be validated, for which we also measure specific values such as the absorption and diffraction of seawater continually, along with all components of the pigment assemblage of phytoplankton from water samples at six different depths. This way, we receive continuous information along the ship’s route at the surface and for the whole water column at our stations about the abundance and assemblage of phytoplankton and by-products, which are very different in different regions of the Fram Strait.

In addition to primary producers, which are at the base of the marine food web, assemblages of small animals, the zooplankton, are also studied in the long-term observatory HAUSGARTEN. These investigations are part of a multi-year cooperation between the PEBCAO group and zoo-planktologists at the University of Bremen. In the Fram Strait, zooplankton species from the Arctic Ocean and the Atlantic mix. Animals with different origins are carried into the area by the opposing ocean currents, the polar East Greenland Current and the Atlantic West Spitsbergen Current. As an effect of global warming, which is strongly felt here in the Arctic, zooplankton species of southern, Atlantic origin advance every further and push back the native polar fauna. Biologists from the University of Bremen are investigating how the various zooplankton species react to increases in temperature. For this purpose, amphipods just a few millimeters long to krill a few centimeters long are kept at various water temperatures in climate-controlled chambers on board, and their metabolisms are measured over multiple hours. The results will show at what temperature Atlantic “warm-water species” begin to have an advantage over their polar relatives and how the plankton community will change in species assemblage and biodiversity in the context of climate change.

The mood and comradery on board have thus far been very good. The scientists have continued their presentation series with results from their own research in HAUSGARTEN during the past week, and there are always lively scientific discussions afterwards.

With warm greetings from all expedition participants,

Katja Metfies

(Translation: Kirstin Meyer-Kaiser)