No abstract

Abstract. IODP Expedition 357 utilized seabed drills for the first time in the history of the ocean drilling program, with the aim of collecting intact sequences of shallow mantle core from the Atlantis Massif to examine serpentinization processes and the deep biosphere. This novel drilling approach required the development of a new remote seafloor system for delivering synthetic tracers during drilling to assess for possible sample contamination. Here, we describe this new tracer delivery system, assess the performance of the system during the expedition, provide an overview of the quality of the core samples collected for deep biosphere investigations based on tracer concentrations, and make recommendations for future applications of the system.

In der Tiefsee ist die letzte Eiszeit noch nicht vorbeiGashydratvorkommen im Schwarzen Meer reagieren auf postglaziale Klimaänderungen 30.03.2021/Kiel/Bremen. Bei der Untersuchung von Gashydratvorkommen im westlichen Schwarzen Meer machte ein Team von Forschenden vom GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel und dem MARUM -Zentrum für Marine Umweltwissenschaften der Universität Bremen überraschende Entdeckungen. Entgegen bisheriger Erkenntnisse und Theorien fanden die Wissenschaftler*innen freies Methangas in Schichten, wo diese eigentlich nicht auftauchen dürften. In der jetzt in der internationalen Fachzeitschrift Earth and Planetary Science Letters veröffentlichten Studie schließen sie, dass sich das Gashydratsystem im Tiefseefächer der Donau durch die Klimaänderungen seit dem letzten glazialen Maximums weiterhin verändert.

During expedition MARIA S. MERIAN MSM57/2 to the Svalbard margin offshore Prins Karls Forland, the seafloor drill rig MARUM‐MeBo70 was used to assess the landward termination of the gas hydrate system in water depths between 340 and 446 m. The study region shows abundant seafloor gas vents, clustered at a water depth of ∼400 m. The sedimentary environment within the upper 100 m below seafloor (mbsf) is dominated by ice‐berg scours and glacial unconformities. Sediments cored included glacial diamictons and sheet‐sands interbedded with mud. Seismic data show a bottom simulating reflector terminating ∼30 km seaward in ∼760 m water depth before it reaches the theoretical limit of the gas hydrate stability zone (GHSZ) at the drilling transect. We present results of the first in situ temperature measurements conducted with MeBo70 down to 28 mbsf. The data yield temperature gradients between ∼38°C km−1 at the deepest site (446 m) and ∼41°C km−1 at a shallower drill site (390 m). These data constrain combined with in situ pore‐fluid data, sediment porosities, and thermal conductivities the dynamic evolution of the GHSZ during the past 70 years for which bottom water temperature records exist. Gas hydrate is not stable in the sediments at sites shallower than 390 m water depth at the time of acquisition (August 2016). Only at the drill site in 446 m water depth, favorable gas hydrate stability conditions are met (maximum vertical extent of ∼60 mbsf); however, coring did not encounter any gas hydrates.

CMOVE is a wheel driven underwater vehicle that has been developed to conduct measurements at the sediment/water interface. It can be either operated as an autonomous vehicle or tethered with a fibre optic cable. In the current configuration the power supply allows for covering a range of the order of 100's of meter and a deployment time of about 12 hours using the type of scientific payload that is currently installed. During a cruise with the German research vessel MERIAN in the Black Sea in April 2010 ten deployments of the system has been carried out. All missions were completed successful and a significant amount of technical data to judge about the performance of the system has been collected. As a general conclusion it can be said that the vehicle concept has been proven to be very successful in regard to the payload integration and steering capability. The later characteristic is very important as one of the main scientific goals is to investigate the spatial variability of biological activity which is reflected in the patchiness of the sediment surface structure. To probe the actual spot of interest and not just following a preprogrammed pattern is of utmost importance as the spatial variability of the processes that occur at the sediment/water interface is largely unknown up to now. It is very important that the vehicle does not disturb the anticipated measurements for instance by exerting too much force on the sediment or by dispersing extensive amounts of dust with the propulsion system. It could be verified by visual inspection with a high resolution camera that the amount of redeposited sediment was negligible. In regard to the performance of the developed wheels the underwater images of the tracks showed that the slip of the wheels was very low. This demonstrates a high power efficiency of the propulsion system. Also the weight distribution is critical as this will influence the wheel performance and the steering of the vehicle. The individual dive was carried out by deploying the system with a depressor weight which decoupled the vehicle from the ship motion and the cable drag. The operation range was limited to a diameter of 50 m around the depressor. For reaching areas outside the range the ship followed the vehicle in the direction of motion making use of a very precise operating dynamic positioning system.In this paper the basic vehicle concept will be recapitulated and compared with the achieved results. Furthermore, the range of applications where this vehicle concept is best suited and outperforms other approaches are described.