PS108 - Weekly Report No. 2 | 29 August - 6 September 2017

New technical possibilities in the deep sea

[08. September 2017] The second week of our expedition was in focus of the in ROBEX new developed robotic systems.

Fig.1: Echo-sounding record of methane flares in the water column at the GHSZ off Spitzbergen. (Photo: Alfred-Wegener-Institut)

During the past nights and early morning hours an under-water-membrane-inlet-mass-spectrometer (UW_MIMS) has been deployed to detect dissolved gases in the gas hydrate stability zone (GHSZ) off Spitsbergen. In this region along a 25 km long stretch methane is released from the seafloor into the water column at the upper boundary of the GHSZ at about 400 m water depth. In echo-soundings gas release can be easily detected and hence is used for the detection and mapping of gas release (Fig.1).

Fig.2: The underwater mass spectrometer in front of the fascinating landscape off Spitzbergen. (Photo: Alfred-Wegener-Institut)

The UW-MIMS has been developed within the Helmholtz Alliance ROBEX at the GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel and has been deployed for the first time during this expedition under harsh in situ and ship operation conditions. The UW-MIMS has been integrated within a steel frame, which further hosts sensors for the measurement of temperature, pH, pressure, carbon dioxide, methane as well as a camera system for seafloor observation and imaging, (Fig.2). Overcoming first difficulties to run the system at the beginning of the cruise, during the third deployment we were able to successfully measure methane simultaneously to other dissolved gases. The next deployment will take place at shallow water methane seep sites off Spitsbergen in a water depth of about 90 m.

Fig. 3: Recovery of the Glider MAPPA after successful completion of dive at position Lat N 78° 36.380’ Lon E 05° 03.055’. (Photo: Alfred-Wegener-Institut)

Within the framework of the HGF-Alliance ROBEX a new type of underwater glider has been developed (Partners involved – MARUM, AIRBUS, DLR, University of Wuerzburg) – MAPPA - that has been investigated as part of numerous tests in lakes and now for the first time has been deployed from board a vessel during the POLARSTERN cruise PS108. The first step in this process was the weight trim in the operation area FRAM Strait where the vehicle was deployed via crane into the sea and the buoyancy engine has been set to the end points „Dive“ and „Resurface“ to check for proper operation. After successful completion of this critical test the glider that is based on a blended wing design was deployed and pulled to the operation area with the help of a zodiac (Fig. 3). The dive command was sent via a RF link and about 30 min later the vehicle has reached its maximum depth of 105 m. The Guidance Navigation and Control system then initiated the ascent and about 20 min later the glider reached the surface again. Using the ship’s GAPS sonar system the trajectory of the underwater flight could be tracked in real-time. The entire operation including recovery took 3h. After analysing the recorded flight data another deployment is planned.

Fig. 4: Sponge, Cladorhiza gelida, on a plate oft he long-term experiment. (Photo: Alfred-Wegener-Institut)

During our work at the ice edge at 80°N the AUV Paul was able to dive for 3 hours, without contact to the control room at POLARSTERN for track control, under the sea ice and back. This successful dive will provide new and valuable data for studies of the sea ice – ocean interface.

On the evening of August 31, there was an ROV dive to recover a long-term experiment on settlement in the deep sea. The experiment consisted of a weighted frame and 46 attached plates made from hard materials. In the HAUSGARTEN area, there are not just soft sediments but also stones (drop stones) on the seafloor and a steep reef, which are inhabited by sessile benthic animals. The experiment was begun in 1999 to show how animal communities on similar hard substrata develop over time. In 2005 and 2011, the frame was visited with a ROV, and in 2005, a few plates were also cut off of the frame and recovered. The current recovery ends the time-series and brings new information on deep-sea growth to the surface.

The growth on the plates and the frame have already been analyzed on board POLARSTERN. Altogether, there were 4 species of Foraminifera (single-celled organisms) and about 10 species of animals. The most abundant animals were a sponge (Fig. 4) and a sea lily, both of which are common on stones and the reef in the Fram Strait. Samples from the settlement frame allow for an analysis of growth rates of these deep-sea animals and also development of animal communities in the Arctic.

Fig. 5: The robotic System MANSIO-VIATOR shortly before the deployment. (Photo: Alfred-Wegener-Institut)

On the evening of September 4 we had a second test mission of the new robotic system MANSIO-VIATOR (Fig. 5). The system was developed within the HGF-Alliance ROBEX and consists out of a deep-sea crawler „VIATOR“ and a non-mobile lander „MANSIO“. This was the first time the system was deployed in a water depth of 1276 m at Vestnessa Ridge, western Svalbard (Fig. 6). After a thorough survey with GEOMAR’s ROV Kiel6000 we could position the device accurately at the seafloor.

Fig. 6: MANSIO-VIATOR at the seafloor (Photo: Alfred-Wegener-Institut)

After waiting for the programmed sleep mode to end VIATOR started to move autonomously. While leaving the hangar we encountered several issues with the drive train that could be partially fixed by aborting the mission via an acoustic link (USBL). The ROV was imported piece to recover the system and to perform additional test that led to the final successful docking (the return oft he crawler into the hangar) of the crawler into the lander.

For the last four years and after many land-based as well as shallow water tests the team of AIRBUS, the DFKI (German center for artificial intelligence) and Kraken Robotics performed an important step towards the use of this system under deep-sea conditions during scientific missions. Apart from reaching the technical and robotic goals of this deep-sea test the partners collected valuable information regarding the operation during deployment and recovery – a true team effort.

After the recovery of Tramper last week, the system was renewed and deployed again this week for its second 12-month mission at the Arctic seafloor. We will recovery Tramper next year. A second crawler, NOMAD, which will additionally study seasonal variations in biogeochemcial processes at the seafloor, was successfully tested. Besides measuring oxygen consumption rates, NOMAD is able to take images of the spatial distribution of the settling labile organic matter.

Today, in the afternoon of September 6, our research activities come to an end and we will start our return to Tromsö. Everyone is looking at a successful cruise with many new scientific and technical insights. For many participants this POLARSTERN expedition was a remarkable experience.

Everyone on POLARSTERN is feeling very well and we send the best greetings!

Frank Wenzhöfer

(with support of Kirstin Meyer, Stefan Sommer, Christoph Waldmann und Sascha Flögel)