PS106/2 - Weekly Report No. 7 | 2 - 9 July 2017
Week 7: In the deep Arctic Ocean
During our northward transect, Polarstern bit its way through heavy sea ice, hard as concrete and covered with a thick layer of snow. This altogether slowed down our progress into the north significantly. During our journey in the thick ice across the deepening Arctic Ocean, wildlife became scarcer and scarcer. Patches of Melosira arctica were only spotted rarely.
Our standard sampling consists of CTD casts, zooplankton nets, SUIT, and sampling of the surface microlayer from Polarstern’s zodiac Laura. The perceived drop in the abundance of seabirds and mammals was mirrored at the lower and mid trophic levels of the high-Arctic marine food web: zooplankton and under-ice fauna abundances in the nets appeared to decrease considerably the more we went towards the North Pole.
On this expedition, zooplankton of about 0.2 mm to 2 cm length, such as copepods, amphipods or jellyfish is collected with the multinet by the zooplankton group of AWI. The multinet is equipped with five fine-mesh zooplankton nets, which can be opened and closed at pre-defined depths. The organisms sampled by these nets are stored in preservation fluid on board, and will later be analysed in the home laboratory. A taxonomic analysis gives insight in the diversity of the zooplankton community, its vertical structure, and horizontal distribution patterns. In addition, the zooplankton group investigates the vertical and the horizontal distribution of abundant species with the Lightframe Onsight Key species Investigation device (LOKI). The heart of LOKI is a high-resolution digital camera, which takes about 20 pictures per second. LOKI can be either towed vertically up from 1000 meter water depth, or towed horizontally from AWI’s ROV BEAST. While sampling photographs of zooplankton, LOKI records salinity, temperature and chlorophyll a fluorescence. In this way, the fine-scale distribution of the species recorded by LOKI can be correlated to the hydrographical structure of each cast. During PS 106/2, LOKI is also equipped with an Aquascat. This device is a mini echo sounder, emitting sound at various frequencies. From the reflection pattern at each of these frequencies, zooplankton biomass and size structure can be estimated at high spatial resolution.
A major aim of the work of the Sea Ice Physics team on PS 106/2 is to investigate the optical properties of snow and sea ice: How much sunlight is reflected to the atmosphere, how much contributes to warming and melting of sea ice, and how much reaches the upper Ocean as an energy source for the ecosystem? Our most important tool to address these questions is the ROV BEAST (Picture 1). BEAST, operated through a hole in the sea ice, can investigate the sea ice and underlying water up to a distance of about 200 m. Hyper-spectral radiation sensors, multi-beam sonar and cameras constitute the standard sensor equipment of the ROV. Furthermore, extensive sampling of snow- and ice thickness and manual measurements of optical properties are conducted during each ice station. The range of our ice thickness measurements is significantly extended by measurements of an electromagnetic ice thickness probe (EM-Bird, Picture 2) from the helicopter. EM-bird flights provide an important insight in the regional-scale distribution of ice thickness.
Operated by the atmospheric scientists on PS 106/2, a number of optical and other remote sensing instruments are working continuously day and night. The instruments are measuring parameters to characterize the atmosphere and the interface to the surface. These parameters are important inputs for example for climate models, to improve the accuracy of the parametrization or to validate measurements of satellites. With the FTIR system (Fourier Transform Infrared Radiometer, Picture 3) of the University of Bremen, a large number of trace gases can be derived. The optical up- and downwelling radiance is measured by the Freie Universität Berlin with two optical systems. A scanning DOAS (Differential Optical Absorption Spectrometer) instrument (Pandora-2s) mounted at the Peildeck, and a scanning Hyperspectral Polarimeter (URMS/AMSSP: Universal Radiation Measurement System / Airborne Multi-Spectral Sun- and Polarimeter) installed at the crow’s nest of Polarstern. The Pandora-2s performs vertical scans of the atmosphere with two high-resolution spectrometers in the spectral range from 320 to 1000nm. Profiles and horizontal distribution of the trace gases NO2, O3 and H2O can be retrieved. The second instrument scans the atmosphere on the left side of the ship.
The aim of the measurements and data analysis is the retrieval of aerosol parameters and the measurement of the up- and downwelling polarized light coming from the Sun. The light gets scattered by the atmosphere and reflected by the surface. For this cruise reflectance measurements of ice, snow and water during different atmospheric conditions were performed. Together with the standard radio soundings, the vertical profiles of temperature and pressure, will drive radiative transfer models to characterize the status of the atmosphere. The results of the radiative transfer model and the measurements can be compared to find differences between model and measurements of the calculated light field to improve the existing retrieval methods used e.g. by satellites and to develop new methods with the additional information of the polarized state of light.
In the evening of July 6th we arrived at the northernmost point of our sampling at 83°40’N 31°35’E. Here, we deployed our full range of sampling gear and performed a 10-hour ice station. As this station marked about half the cruise time, scientists and crew enjoyed a well-deserved barbeque on board in the evening of July 7th. Everybody had been working extremely hard, many of us day and night, making these first two and a half weeks of PS 106/2 a great success. Since the barbeque commenced, we have been heading south.
Yesterday night, however, our daily sampling routine was interrupted by a medical incident. One of the scientists had an inflammatory disease demanding immediate action. After a successful surgery by our doctor Claus Rudde-Teufel in the ship’s hospital, the patient is now well and recovering. Further complications are not expected, and therefore Polarstern resumed scientific work already shortly after its medical stop last night.
Whereas ice melt has only just begun in the deep Arctic Ocean where we have been sampling last week, we expect a more advanced stage of melting in the coming days, when we approach the marginal ice zone in the south. There, another visit to the ice drift station of PS 106/1 is planned. We will recollect the automatic devices left there to collect data, and sample this ice floe intensively 5 weeks after we had left it behind. We are curious to see how ‘our’ floe looks like now, and how the sea ice has changed.
Best regards from Scientists and Crew,
Hauke Flores, chief scientist
With contributions from Thomas Ruhtz (Freie Universität Berlin), Ulrich Küster (FU-Berlin), Jonas Witthuhn (Tropos), Martin Radenz (Tropos), Sebastian Zeppenfeld (Tropos), Simonas Kecorius (Tropos), Hannes Schulz (Tropos), Teresa Vogl (Tropos), Andre Wetli (Tropos), Xianda Gong (Tropos), Svenja Kohnemann (Uni Trier), Gerit Birnbaum (AWI), Marcel König (CAU), Peter Gege (DLR), Philipp Richter (Uni Bremen), Christine Weinzierl (Uni Bremen), Marcel Nicolaus (AWI) Barbara Niehoff (AWI) und Nicole Hildebrandt (AWI)