Venting induced by magma-sediment interaction at Jøtul field – first discovery of hydrothermal seafloor venting along the 500-km-long Knipovich spreading ridge

During expedition MSM109 in July 2022, a new hydrothermal vent field was discovered, which is the first active field found along the 500-km-long ultra-slow spreading Knipovich Ridge. The so-called Jøtul hydrothermal field is not located on an axial volcanic ridge (AVR) but is associated with the eastern bounding fault of the rift valley. A hydrothermal plume with methane concentrations between 100-1000 nmol/L emits hot fluids into the water column above the hydrothermal field, and is being drifted north with the bottom current. These high methane emissions are likely related to interactions between magmatic intrusions and sediments of the Svalbard continental slope produce unusually high release of thermogenic methane. Further investigations during MSM109 using ROV Quest show a wide variety of fluid escape sites such as diffusive venting from sediments, as well as seepage from joints and cracks within igneous rocks. Additionally, new inactive and active mounds with abundant hydrothermal precipitates and chemosynthetic organisms were discovered. Fluids were sampled from an active black smoker emitting fluids with temperatures > 316°C, and from three other sites with venting temperatures between 8°C and 272°C. The fluids are characterized by high methane, carbon dioxide, and ammonium concentrations, as well as high ⁸⁷Sr/⁸⁶Sr isotope ratios, indicating a strong interaction of the fluids with sediments from the continental margin of Svalbard. Locations with such intense magma/sediment interactions are of particular importance for the carbon cycle, and a focus of the Bremen Cluster of Excellence "The Ocean Floor – Earth’s Uncharted Interface".