Long Mediterranean expedition of the Bremen ocean floor cluster finished

Nov 26, 2020

Research vessel SONNE returns to Germany

Ship's crew and scientists recovering the autonomous diving robot AUV MARUM-SEAL 5000 after its first operation on the Bergamo mud volcano. Photo: Heike Dugge

Next Tuesday, December 1st, after 50 days, this year's Mediterranean expedition of the MARUM with research vessel SONNE SO278 will end in the port of Emden. Within the framework of the Cluster of Excellence "The Ocean Floor - the Earth's uncharted interface", the research unit "The Ocean Floor as a Reactor" carried out investigations on the ocean floor along the Mediterranean Ridge from the Calabrian Arc to southern Crete.

In this collision zone between Africa and Europe, a multitude of mud volcanoes have formed, which transport mud, rocks, gases and fluids from greater depths to the sea floor. Along with magmatic volcanoes, they are the most active structures on the sea floor, responsible for numerous exchange processes with seawater. Of the more than 500 counted mud volcanoes of the eastern Mediterranean, 16 volcanoes in 4 different provinces have been studied. A precise sampling of the mud breccias in the volcanic chimney was possible because in many cases high-resolution maps were previously acquired with the MARUM AUV SEAL. In addition to surveying the seafloor with the echo-sounders of the vessel and the AUV, sediment cores were sampled, direct observations on the seafloor with a TV sled, and profiles for heat transport in the sediments were carried out. A previously unnamed mud volcano, which was surveyed with the AUV and sampled with a gravity corer and multicorer, has been given the name Helios Mud Volcano (Greek for sun) by the researchers. A peculiarity of mud volcanoes in the Mediterranean Sea are interactions with salt deposits under the seabed and so three of the investigated mud volcanoes had up to 7 times higher salt concentrations in the pore water of the mud flow deposits. In the surroundings of the mud volcanoes circular sinkholes were discovered for the first time, which probably developed by dissolution of the underground salts and subsidence of the seabed and do not seem to be a rarity according to the AUV mapping.

The MARUM AUV SEAL returns to the sea surface from a dive. Photo: Tabea King

Newly discovered mud volcano Helios. Graphic: Miriam Römer

Group photo of the expedition members. Picture: Tabea King

Full concentration on deck of the research vessel SONNE. Photo: Heike Dugge

Ten of the sampled mud volcanoes showed up to 4-fold depleted concentrations in salinity. These low salinities of the pore water can be explained by the release of water from mineral reactions in very deep layers that dilute the marine pore water. From which depths and from which rock units the pore waters and gases originate are investigated by further analyses of different isotope systems at the Cluster of Excellence of the University of Bremen. The expedition brings back a large collection of very well selected samples, whose analyses and interpretations will keep the researchers intensively occupied in the coming years.