In addition to the annually repeated investigations in the water column and on the seafloor, the exchange of moorings is a central piece of the essential work for furthering the long-term observatory. During PS121, moorings are recovered and deployed, which carry out measurements and collect samples for physical, chemical, and biological questions. One important difference from classical measurements with a ship is that parameters of interest can be measured throughout the entire year. A lot happens in winter and spring, when there is hardly a ship in the area. In order to find out how fast and in what direction the water moves, current speed is measured with sensors deployed on the mooring. Because the moorings also sink a little in response to the current, the pressure is measured at different points, because it is important to know where in the vertical the measurements were recorded. Identifying water masses and their origins and transformations is possible with temperature and conductivity measurements (which is used to calculate salinity). In order to better understand the nutrient budget of the Arctic Ocean and the effects on the global carbon cycle, we use sensors on the moorings that can measure nitrate concentration as well as sensors that measure pH and CO2. In addition, we use instruments that pump 500 mL of seawater into separate containers every 8 days. The water samples can then be used for further chemical analyses and complex biological analyses can be conducted; for example, the abundances of DNA of microorganisms such as small algae are determined. In order to collect biomass of rare organisms, a larger amount of water is pumped through a filter every 16 days. At two places in the eastern and central Fram Strait, these measurements are conducted as close to the surface as technically possible, in this case ca. 20 m depth, in order to follow the growth of microalgae, specifically during the so-called “spring bloom.” We also measure the light transmittance in the ocean every hour, as well as the concentration of chlorophyll, the pigment that enables photosynthesis and makes plants green. After plankton die or are eaten in the upper ocean, some sinks through the water column to the seafloor and enables life there and takes carbon out of the atmosphere. This material is captured in different bottles in a sediment trap, such that all material falling over a ¼ square meter in one month is collected in a single bottle.

The mood and the comradery on board are overall very good. The scientists are sharing their results of their research in the HAUSGARTEN during regular evening seminars. Meanwhile, we find ourselves in the second half of the expedition, the start of which was marked with a fun grill fest.

With the best wishes of all expedition participants,

Katja Metfies

(Translation: Kirstin Meyer-Kaiser)