On Tuesday August 22 at 19:00 POLARSTERN left Tromsö with an unusual freight on board into direction of Svalbard. Unusual, because 10 of the 40 scientists on board are space experts and special are also the new and innovative robotic systems, which should improve our capabilities in deep-sea research. The new technologies include 3 different types of benthic crawler, each designed for its specific scientific purpose on the bottom of the sea, a glider for water column studies, unmanned aerial vehicles (UAVs) to support AUV operations under sea ice and an underwater mass-spectrometer.
The robotic systems have been developed since 2012 within the Helmholtz-Alliance ROBEX (Robotic Exploration of Extreme Environments) where 120 scientists and engineers from 16 space and deep-sea institutions all over Germany are working together. On the one hand expedition PS108 is aiming to verify mission critical robotic technology required to operate in extreme environments, on the other hand PS108 will contribute to investigations in Arctic ecosystems: long-term experiments at the HAUSGARTEN deep sea observatory and research at the gas hydrate stability zone (GHSZ). The “Remotely Operated Vehicle, ROV” KIEL6000 (GEOMAR) will support our scientific investigations as well as the verification of the robotic developments.
The journey to the first destination at the HAUSGARTEN observatory was used to become familiar with life on board and also for preparation of the different units and instruments for their first deployments. In addition regular observations of litter were performed in order to understand the distribution of litter at the surface of the Arctic Ocean.
On Thursday, August 24, we reached our working area and started the research program with the deployment of two bottom lander systems capable to measure oxygen consumption rates at the seafloor. These measurements are part of the long-term investigations performed at HAUSGARTEN since 1999. During the night a “Catamaran”, an instrument that is dragged over the surface of the sea, was used in order to collect litter and micro plastic. Some of the plastic pieces could already be recognized with the naked eyes.
In the morning of August 25 the ROV „KIEL6000“ (GEOMAR) was deployed, directly at the start position of the crawler TRAMPER deployment one year ago. During its one year operation TRAMPER should perform measurements of the oxygen distribution in the seafloor. The search for the starting point was quite short and then the observers were able to recognize the tracks of TRAMPER in the sediment. The ROV followed them and after 20 minutes TRAMPER was recognized standing there vertically to its tracks. The reason was that after around 350 m and 24 weeks of traveling at the seafloor the right caterpillar didn´t work anymore and TRAMPER stayed the rest of the year in a mode of circling. Because of the weather recovery of the crawler was not possible at this time. The rest of the ROV dive was used for collecting animals and taking pictures of the seafloor.
With the towed video and photo system OFOS a survey transect to the deepest point of the Arctic Ocean, the Molly Deep (5.500 m depth), was performed. The last operation in this area was 20 years ago. On the photos a bustle of life was recognized with countless small sea cucumbers and sea anemones. Furthermore a lot of wood and unfortunately much more litter could be seen. The new dataset will be compared with the data from 1997 and might provide hints about the change of this ecosystem.
The second ROV dive focused on a biological long-term experiment, which was started last year. A common feature in polar deep-sea regions is the occurrence of so-called “dropstones” at the seafloor, which enhance the topographic heterogeneity and alter related hydrodynamic patterns. These dropstones of different sizes are transported by sea ice and after melting of the ice they finally sink to the bottom of the ocean. There is abundant evidence that habitat structures have important effects on spatial distribution patterns of benthic fauna populations in deep-sea environments. Changed flow regimes around dropstones can have a direct effect on colonization and settlement of benthic individual organisms and indirect effects on community structures by the amount of potential food trapped around dropstones and changing sediment characteristics. Until now we do not know how fast benthic communities react on new dropstones. Therefore 9 artificial dropstones of different shapes were deployed at 2500 m water depth in 2016. During the ROV-dive sediment cores were retrieved from surface sediments influenced by the dropstone and nearby undisturbed areas as controls. The cores will be sub-sampled for meiofauna/nematode analyses and different biochemical parameters indicating food availability. At the end of the ROV dive the artificial dropstones were moved to different places nearby and will be sampled again in 2019.
During the night of August 26 until the afternoon of August 27 the intermixed water of the Arctic and Atlantic Ocean was in the focus of interest. In terms of biological activity, the polar marginal ice zones (MIZ) are among the most relevant regions in the world. Previous observations suggest the high biological activity to be triggered by physical and chemical processes, which take place in the upper water column in the MIZ. Obvious differences in temperature and salinity can be observed. This effect is maybe intensified by melting ice. Thus the influence on biological processes near the surface seems to be evidently. With ship-based sensors for temperature, salinity, chlorophyll a, pressure and flow velocity the zone were both water bodies start to mix was identified. Afterwards the AUV PAUL, equipped with a chlorophyll a fluorometer, a fluorometer for colored dissolved organic matter (CDOM), oxygen and nitrate sensor, a microstructure probe (MSP) and a sensor for photosynthetically active radiation (PAR), was used to investigate this mixed layer more in detail. Because of communication problems between PAUL and the control station on board POLARSTERN at the beginning of the dive, the rest of the timeslot was too short for the completion of the planned investigations. But the performed measurements seem anyhow to be promising.
In the afternoon of August 27 we were able to get TRAMPER back on board after its one-year mission at the seafloor. The first investigations showed that Tramper did an almost perfect job until the deadlock of the right caterpillar. The crawler performed 24 measurements during the first half-year of its mission which will improve our knowledge about the seasonal variations of the oxygen distribution in the seafloor.
In the next weekly report we will give an overview about the other new robotic systems and instruments used during this expedition as well as our investigations in the gas hydrate stability zone.
Everyone on POLARSTERN is feeling very well and we send the best greetings!
Frank Wenzhöfer
(with support of Martina Wilde, Thomas Soltwedel, Melanie Bergmann, Thorben Wulff and Sandra Tippenhauer)
