PS106/2 - Weekly Report No. 6 | 26 June - 2 July 2017
Week 6: From East Svalbard towards the deep Arctic Ocean
The past week we started in the marginal sea ice zone east of Svalbard, and then set course north into the central Arctic Ocean.The marginal sea ice zone was mostly covered with decaying sea ice and some larger ice-free areas. On this side of Svalbard we saw a lot more wildlife than in the westerly part. A large number of birds are constantly circling around the ship looking for fish, which can be spotted on overturning ice floes during ice breaking.
While our bird and sea mammal observation team focuses on these charismatic animals, other scientists continuously monitor properties of the atmosphere using various automatic sensors.
In the framework of atmospheric characterization, the TROPOS remote sensing department utilizes a 35Ghz cloud radar as well as the OCEANET Container including the PollyXT lidar system, a multichannel microwave radiometer, and conducts long- and shortwave irradiance observations and meteorological measurements. Among other scientific applications, this set of observations produces key data to resolve two-dimensional cloud processes for comparison with high-resolution dynamical models.
For the investigation of local transfer processes of marine substances into the atmosphere, aerosols are collected permanently at the TROPOS container on the monkey deck of Polarstern. These samples were acquired either on quartz fibre filters, or size-resolved via five-stage BERNER impactors on aluminium foils. The sea surface microlayer works as a boundary layer between the oceanic water and the atmosphere and is highly enriched in several organic substances. From here, aerosols may enter the atmosphere. Polynyas, open leads and melt ponds as potential sources of these particles are investigated during PS 106. Samples from the sea surface microlayer are collected on a daily basis.
The group of the University of Trier performs measurements of vertical and horizontal profiles of wind, turbulence and aerosols. The knowledge of wind profiles is of great interest, since the coupling of the ocean and sea-ice surface with the atmospheric boundary layer (and the free atmosphere above) determines the wind-driven sea-ice export of the Arctic. A Doppler Wind LIDAR was installed on the lower Peildeck. It sends out an eye-safe laser beam that is backscattered at aerosol particles and clouds. Using the Doppler Effect, vertical and horizontal wind profiles can be calculated.
The group from the department “Integrative Ecophysiology” at AWI is primarily interested in living individuals of polar cod (Boreogadus saida) for experiments on the physiological resilience of this species to climate change. These experiments will be carried out at the AWI in Bremerhaven and will include analyses at different organismic levels, from molecules to the whole animal, in order to characterize processes limiting fish performance under increasing water temperatures and ocean acidification. In the first fishery attempts using the bottom trawl in about 200 m water depth, a number of benthic organisms was caught, but no polar cod. Some smaller octopuses in good condition were transferred into one of the aquariums in the aquaria container. The octopuses immediately turned the aquarium container into a new attraction on Polarstern, with many colleagues visiting. In spite of the absence of polar cod from the first hauls, the group of physiologists does not lose hope, as many more fishing hauls are planned in the course of the expedition.
In the night from 28th to 29th June it was time again for another ice station. Thanks to the ever-shining midnight sun, scientists spread out on the ice floe, sampling between 10 pm in the night and 6 am in the morning. The occupation of an ice floe by Polarstern scientists is always an interesting event watched by many eyes (Picture 1). This station had significantly less decayed ice. Again, numerous ice cores, water from melt ponds and snow were sampled, and the ROV accomplished several physical and biological under-ice transects.
During this second ice station of PS 106/2, the crew used the time to change the fishing gear of Polarstern from bottom trawl to a new set of trawls fit to sample polar cod and its prey both in the deeper water and directly under the ice. The Surface and Under Ice Trawl (SUIT) and Rectangular Midwater Trawl (RMT) were used to sample the ice-water interface and the upper 100 m of the water column, respectively (Pictures 2 and 3). The catch is used to study the distribution of species in the sea-ice habitat, the food web structure and the role of sea ice in the life cycle of different species. Our hope is that particularly the SUIT will catch polar cod, as the young individuals are known to dwell at the underside of the sea ice. Surprisingly, however, the first fish caught from under the ice was not a polar cod, but a closely related species. Besides polar cod, the biologists are interested in the many other ice-associated species, their diversity and their ecological importance. Hence, they sorted out and conserved specimens from numerous species for later in-depth investigations, such as stomach content analysis, molecular and biomarker studies.
Where the Barents Sea shelf drops into the Arctic deep-sea basin, water masses from the shelf encounter Atlantic water advected through the Fram Strait and Polar water from the central Arctic Ocean. To study the complex fine-scale hydrography of these interacting water masses, the physical oceanography team of the University of Gothenburg in collaboration with Aquabiota conducted a high-resolution oceanographic survey across the shelf slope. However, sea ice often blocked the carefully chosen sampling points of our trans-slope transect, and forced us to turn around and start over from the basin up onto the shelf, making this survey a true challenge to crew and scientists on Polarstern. Finally, after 30 hours of hard working, the transect was completed successfully on July 1st. After conclusion of the hydrographic shelf-slope transect, we resumed our sampling programme comprising ecosystem parameters and atmospheric studies. On Sunday 2nd July, a new ice station was started. Today, we are continuing north into the Arctic basin, sampling with CTD, SUIT and RMT.
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), Nils Koschnik (AWI) und Fokje Schaafsma (WMR)