After setting up and final characterization, which was only possible after final set up on the ship, the FTIR (Fourier Transform Infrared Radiation) instruments perform as expected. We had altogether four clear days to perform solar absorption measurements and many days to use the emission in the thermal infrared to perform a characterization of the thin cloud cover in the Arctic. Shown are two spectra, one measured during cloudy conditions, one at a clear day.

In Figure 1, one can clearly see the effect of a thin cloud on the observed infrared radiation. The upper envelope is caused by fully saturated emission and is basically black body radiation. The upward pointing lines are emissions from H2O, CO2 and Ozone. One can clearly see that a cloud has two effects; it attenuates the emission lines and adds additional broadband radiation. The form of the additional radiation depends on the properties of the cloud itself, notably mean radius of the droplets in a water cloud and the optical thickness, two properties, which are accessible in this wavelength region.

While drifting, attached to the floe, we conducted a variety of measurements from the helicopter and on the ice to characterise properties of melt ponds and the surrounding sea ice. Since the ponds alter the albedo of the sea ice, which means the amount of reflected sunlight, they tend to warm up the sea ice system. Conducting many measurements at and in melt ponds, we aim to learn more about how they alter the surface properties of the sea ice during the melting season. We have been lucky because melt ponds started to appear quite in time when we were occupying the floe. During a survey flight with the heli we found an area with some small pond forming; we therefore decided to conquer our “lake district” (see Fig. 2) for further measurement. We conducted airborne measurements using different cameras, i.e. a RGB camera and a hyperspectral sensor. On June 10, we had clear sky conditions perfect for remote sensing acquisitions and accompanying field measurements. To gather validation data for airborne and satellite data we measured radiance and irradiance above the pond surface and water depth. Since the ice bottom strongly influences the amount and spectral distribution of radiation they scatter back towards the atmosphere we also conduct drillings for assessing pond bottom depth. Additionally we took water samples; these samples are pre-processed in one of the laboratories of the ship, shock-frozen and then stored in a freezer until Polarstern arrives at Bremerhaven in October. To assess water constituents such as chlorophyll, particulate and suspended matter the samples will then be brought to a lab.

The oceanographic group has continuously carried out measurements with the ship Conductivity Temperature Depth (CTD) profiler.  This instrument provides high resolution data of temperature, salinity, chlorophyll and oxygen throughout the water column which helps us recognize which different types of water that are present at each site, and how their position in the water column changes from place to place or from time to time. With the 24 bottles attached on the steel frame, we can also collect water from any depth for further analyses. Most profiles have been made all way down to bottom depth, which often has been greater than 1 000 meters during our journey. During our weeks at sea we have followed the changes of Atlantic water and seen the seasonal melting of sea ice affect the surface waters.

During the ice floe drift, a 200 meter deep mooring line was deployed from the ice equipped with Acoustic Doppler Current Profilers and temperature/salinity sensors. The main information supplied by this mooring are the prevailing water velocities but it is also possible to analyze e.g. the daily patterns for vertically migrating organisms. If such patterns can be identified, we have a good chance of understanding what kind of organisms we see, by using the information collected by the biological groups during the cruise.

A particle analyzer (LISST) was several times deployed together with the CTD and separately under the ice (see Fig. 3). LISST determines the sizes of the particles present in the water. This can be used together with other measurements to understand processes such as vertical migration and sedimentation.

Best regards from Scientists and Crew,

Andreas Macke, chief scientist

With contributions from Simonas Kecorius, Marcel Nicolaus, Anna Nicolopoulos, Mathias Palm, Natascha Oppelt