Ship's log M190

FS METEOR on course for the Mid-Atlantic Ridge

No two black smokers are alike - this applies to the geology as well as to the fluids that emerge from the hydrothermal vents. Now an approximately four-week research cruise is starting, led by Prof. Wolfgang Bach from MARUM. The aim of the expedition with the research vessel METEOR is to investigate differences between the individual vents and discharge points. This applies both to the chemical composition of the escaping fluids and to the geological framework conditions. In addition, the microorganisms living here, which live either freely or in symbioses at the smokers, will also be studied.

From June 8 to July 10, the 28-member expedition team will also go in search of previously unknown hydrothermal vents, in addition to already known hydrothermal vents. On board will be the diving robot MARUM-QUEST 4000 as well as other scientific equipment for detecting and sampling hydrothermal plumes, i.e. the "plumes" of hot springs.

The target area is the Mid-Atlantic Ridge south of the Azores. Expedition M 190 is expected to provide key results for the Cluster of Excellence "Ocean Floor" based at MARUM, especially in the question of how geosphere and biosphere interact with each other on the ocean floor.

The transmission technology is highly dependent on the conditions at sea. Therefore, dives can be canceled or postponed at short notice.

Day 2 - the R/V METEOR sails along a westerly course on its way to the submarine hydrothermal vent systems at the Mid-Atlantic Ridge. From Las Palmas to our first working area, a distance of 1,500 nautical miles has to be covered. At 10 nautical miles per hour, we have a bit over six days of transit before reaching our first study site. Time to look at some details.

The Mid-Atlantic Ridge (MAR) is part of the longest mountain range on Earth. With a total length of around 60,000 km, these so called mid-ocean ridges are found in all oceans. Here is where the major tectonic plates of Earth spread apart and new seafloor forms. In the northern Atlantic Ocean, the plates spread apart at rates of 2-3 cm/year, thereby enlarging the distance between Europe and North America. Most of this seafloor is composed of basaltic rocks that form when the upper mantle comes up underneath the MAR and undergoes partial melting. This upflow of the mantle happens in response to the divergent movement of the plates along the MAR. Because hot material of relatively low densely moves up underneath the MAR, the seafloor rides higher there than elsewhere in the middle of the Atlantic. This crest of MAR lies between 2,500 and 3,500 m water depth. Away from the ridge crest, crust and mantle cool and turn denser, which causes the seafloor to subside to water depths > 4,000 to 5,000 m in the deep-sea basins on either side of the MAR.

Along with the movement of basaltic magma that fills the gap between the diverging plates tremendous amounts of heat are brought to the seafloor. This high heat flow initiates the circulation of seawater through the newly formed and highly fractured ocean floor. Cold seawater percolates through cracks in between the rocks of the ocean floor, where it is heated up. Interactions with hot rocks in the basement change the chemical composition and physical properties of the circulating seawater which is turned into a hot fluid, with temperatures as high as 400°C and more! These fluids are enriched in a variety of dissolved metals, sulfide, and different gases. They rise up quickly through cracks in the ocean floor and are injected into the oceans through hydrothermal vents. Upon contact with the 2°C-cold sea water, the dissolved metals and sulfide immediately precipitate as minerals, which form tall chimney structures at the seafloor. Most of the minerals, however, are expelled from the top of the chimneys into the ocean as black smoke, forming particle plumes that rise to hundreds of meters above the seafloor before the spread out sideways.