Installation of Borehole Observatories at Reykjanes Ridge with the sea floor drill rig MARUM-MeBo70

Based on site-survey work during research expedition M183 (2022), the sea floor drill rig MARUM-MeBo70 was deployed in summer 2023 on the research vessel MARIA S. MERIAN (MSM119) in order to install observatories for the investigation of hydrothermal circulation in young oceanic crust. In-situ heat flow and fluid chemistry had inferred crustal fluid circulation along the ridge flank. The expedition went to the southernmost tip of Reykjanes Ridge – a part of the Mid-Atlantic Ridge. We were able to set two pairs of observatories in 1500 and 1700 m water depth, respectively. At each site two holes with 103 mm diameter were drilled through a 5 to 30 m sediment cover and an additional 5 to 13 m into the underlying ocean crust. The drill string was lifted by one drill pipe before a last prepared rod – the observatory rod - was screwed onto the drill string. The observatory rod sealed the drill pipe from sea water and was equipped with temperature sensors. One type – the injection observatory – also contained a system for releasing a tracer to the base of the borehole where it has contact to the fluid circulation system within the upper ocean crust. The second type – the monitoring observatory – was installed in a distance of a few tens of meters and contained an additional osmo-sampler for sampling the fluids from the upper crustal aquifer the base of the bore hole. The osmo-samplers will be recovered during an upcoming expedition in September 2025 (research expedition M213). This experiment will help to better understand the relevance of hydrothermal circulation in the flanks of ocean ridges for the exchange of elements and heat  between the ocean crust and the oceans.