With high-tech in the deep sea

During the recent expedition, the 3000 m depth-rated 5 m long Autonomous Underwater Vehicle PAUL, which we have been operating for many years to conduct research in the ocean waters, will mainly be used to map the deep-sea bed at the LTER observatory HAUSGARTEN. For this purpose, PAUL is now equipped with a special camera system to take high-resolution seafloor images as well as a side-scan sonar to assess the topography and larger objects at the seabed across wider areas. During each dive, PAUL’s camera system captures thousands of images, which allow us to assess the density and biodiversity of larger epifauna in the area. A comparison with data from 20 years of observations allows us to assess natural and anthropogenically-induced variations in deep-sea benthic communities at the HAUSGARTEN observatory. In contrast to the camera system, the side-scan sonar is able to cover much larger areas. We also use the sonar to get a “picture” of our own “foot-print”, which we certainly have left after two decades of extensive research at HAUSGARTEN. The background information gained from these surveys allows us to spatially relate the data we generate for all the different parameters with increasing accuracy.

Complementary to the work carried out with the AUV, we deploy an entire fleet of free-falling devices, so-called bottom-landers, to conduct various physical and biogeochemical measurements, to do experiments, and to collect deep-sea organisms at the seabed. Such devices consist of a metal frame, weights for the descent, and floats to bring the gear back to the surface after releasing the weights after experiments or a period of monitoring are completed. Bottom-landers may be equipped with a variety of instruments. During this cruise, we use landers carrying a range of systems, including a microprofiler to study re-mineralization processes at the sediment-water interface, a pumping system to collect larvae of seafloor organisms drifting within the bottom currents, to attract and collect scavenging organisms, and to carry out experimental work at the deep seafloor. Within the framework of a European project (Integrated Arctic Observation System, INTAROS), we use one of the landers to conduct a mesocosm experiment to study the effects of ocean acidification on the small sediment-inhabiting biota, the so-called meiobenthos. This is the first time that such experiments have been conducted at deep water depths (>1000 m) and the technical requirements of the experiment are certainly a challenge for our technicians and engineers – however, they will find a way to realise this study.

With great excitement we are looking forward for the recovery of two deep-sea rovers (Benthic Crawlers), which were deployed two years ago at approx. 900 m water depth off Northeast-Greenland, and at about 2500 m to the west of Spitsbergen. Both crawlers, TRAMPER in western parts and NOMAD in eastern parts of the Fram Strait, are equipped with microprofilers to repeatedly conduct high-resolution oxygen profiles at the seafloor, to move forward for a short distance and take another measurement a week later, and so on, and so on. The oxygen profiles frequently taken at the sediment-water interface for two years allow us to assess seasonal variations in remineralisation rates at the seafloor. In addition, NOMAD carries incubation chambers, which were repeatedly lowered to the seafloor, enclosing a certain volume of sediment-overlying water and register the oxygen consumption of sediment-inhabiting microorganisms. Moreover, the rover is equipped with a special scanning system, which assesses the organic matter (i.e. food) availability on the seabed. A first trial to recover “our nomad” went wrong. However, on Wednesday next week we will try again, and we are certain that – this time – we will succeed. Both Benthic Crawlers will get some maintenance during the expedition and then will be redeployed for new journeys across the cold and dark arctic deep seafloor.

The next weekly report will provide details about the work of the phyto-opticians, biogeochemists and planktologists during this expedition.

Everybody on board feels well and is in a good mood.

With best regards from all participants,

Thomas Soltwedel