Plattform Platform	Reise-Nr. Cruise-No.	Zeitraum Period	Projekt Project	Arbeitsgebiet Working area
Maria S. Merian	MSM98-VARIOSEEP	08.01.2021 - 23.01.2021		North Sea

Fahrtleiter Chief Scientist	Institut Institute	Auslaufhafen Port of departure	Einlaufhafen Port of return	Stationskarte Station map	Schiffsroute Trackchart
Romer Miriam	Universitat Bremen, Zentrum fur Marine Umweltwissenschaften	Emden	Emden

Ziel der Reise / Objectives of Cruise:

Methane seeping from the seafloor, particularly in shallow shelf-regions, is one source of atmospheric methane, but exact amounts are still discussed. During cruise HE537 (July 2019) we studied the seafloor at the German EEZ of the North Sea for gas seepage. While none of the nine studied abandoned wells released obviously gas, we found hundreds flares in the study area. Salt dome Berta exhibited 10-fold enriched methane concentrations, but the intensity, temporal variation, rates, local atmospheric methane concentrations, microbial fate and isotopic nature of the gas remained unknown. In the frame of this cruise, we intended to answer these open questions by an interdisciplinary approach using hydroacoustic and electromagnetic measurements, gas geochemistry and microbiology. Our studies should also base on gas samples taken by a small-size ROV. We planned to characterize the nature of the active gas system and further test, whether yet unstudied abandoned wells release gas. Narrative At the start of our expedition, we reached our working area in relatively calm seas on the evening of 8.1. Our initial hydroacoustic mapping confirmed the activity of gas bubble seeps in our main study area and we started our sampling program on 9.1. The Golden Eye was first successfully deployed to image electromagnetic indications of gases in the upper sediment layers. Subsequently, the use of a small ROV gave us our first visual impressions of the gas bubble seeps and our sonar lander was deployed in the afternoon. The lander stayed on the seafloor for five days and observed the temporal variability of the gas bubble seeps. The first working day at sea was completed with a CTD water sampling program and sediment sampling with a multicorer. We used the night for more hydroacoustic mapping and were able to complete all of our planned stations on 10.1. An EK60 echosounder was calibrated in the morning. Further water samples and sediment samples were taken using the CTD and multicorer, and the ROV was deployed again. On the morning of 11 January, a known flare location was mapped in high resolution with the echosounder. We were able to conduct systematic CTD samplings with the aid of ADCP profiles. We also observed three flare locations over a tidal cycle. During the night of 14.1., we recovered the sonar lander. After obtaining sediment samples in the area of the gas bubble seeps with the multicorer, we deployed the ROV to sample successfully the gas seeps. At the end of the day, the Golden Eye was used again. On the following 15.1., more sediment samples were taken with the multicorer and the sonar lander was deployed a second time. In the afternoon we moved to our second work area where we discovered some depressions on the seafloor in 2019. Here we started with Golden Eye surveys. A gravity core deployment on 16.1. showed us the presence of peat. A ROV dive in the afternoon completed our impressions of the peats. Furthermore, we sampled the water column of a nearby old borehole with a CTD and mapped the surrounding area with hydroacoustics during the night. On 17.1., we finished our investigations in the area of the depressions with another Golden Eye mission and a ROV dive. On 18.1., the multicorer was used to sample two old drill sites and water samples were taken using the CTD. On 19.1., the sonar lander has been recovered. Subsequently, the ROV completed two important tasks: the recovery of a transponder and sampling gas bubbles. Finally, a detailed hydroacoustic survey was conducted. The winds started to pick-up on 20.1., but conditions still allowed surveying the last remaining working area: The Schillgrund Fault. Completing three long profiles, we decided to escape the approaching storm and focus the remaining two days on hydroacoustic surveys of possible gas emissions at old drill sites near the shore. One site has also been sampled with the CTD on 22.1. The scientific program ended just before midnight.

Messungen / Measurements

Verankerungen / Moorings