Global estimates on the number of submarine mud volcanoes are highly uncertain, as well as their role in the deep-sea biosphere and methane budgets. Several expeditions have been conducted in the Norwegian sector of the Barents Sea over the last two decades, with hundreds of hydrocarbon seeps being mapped and investigated. Still, the only mud volcanoes known so far are the Håkon Møsby Mud Volcano (confirmed in 1995) and Borealis (2023). I will report on the recent discovery of ten mud volcanoes in the Southwestern Barents Sea. They form flat-topped mounds which are connected to seismic chimneys rooted within the infilling of a buried Pleistocene mega-slide scar. I will show ROV seafloor imagery depicting sedimentary features and chemosynthetic habitats, and discuss the 3D seismics and gas geochemistry. Methane-derived carbonates collected from the top of the mud volcanoes exhibit various facies linked to fluid seepage, providing evidence of prolonged activity.

We present results from our seagoing mission MSM131 aboard R/V Maria S. Merian to the Jøtul hydrothermal field, located on the ultraslow-spreading northern Knipovich Ridge. In autumn 2024, we conducted water column surveys, geological investigations, and collected hydrothermal vent fluids using isobaric gas-tight samplers. The Jøtul hydrothermal field lies near the continental shelf of Svalbard, where clastic sediments are deposited within the rift valley. The hydrothermal vent fluids are metal-poor, alkaline and exhibit the highest methane concentrations ever recorded at mid-ocean ridge hydrothermal vent sites, all indicating the importance of fluid-sediment interactions in the subsurface of this vent site. Unexpectedly, the vent fluids also contain hydrogen (H₂) concentrations that are substantially higher than those found in other sediment-hosted vent systems. Together with low hydrogen sulfide (H₂S) concentrations, this composition is typically associated with fluids that have interacted with ultramafic rocks. The presence of altered ultramafic rocks on the seafloor near the Jøtul field suggests that such interaction may have contributed to the fluid composition. However, our thermodynamic calculations indicate the high H₂/H₂S ratios are not necessarily related to ultramafic rock alteration, but rather may arise from thermal degradation of organic matter, followed by abiotic oxidation of methane at reaction-zone temperatures around 400°C. While high H₂ concentrations are often considered indicative of fluid-rock reactions with ultramafic rocks, our findings demonstrate that high-pressure, high-temperature fluid sediment interactions can also be a significant source of H₂ emissions into the ocean.

Cold-water corals (CWC) have been identified as a geochemical proxy archive for paleo-oceanographic reconstructions of intermediate water masses, due to their long lifespan (several hundred years) and their globally widespread occurrence. To date, the descriptions of CWC appearances in the Indian Ocean are only sparse and therefore require comprehensive geochemical investigations of these taxa within this region. In this study, we compare the spatial and temporal variations in the chemical composition to the structural and growth-related features of CWCs to assess their application as proxy archives to reconstruct recent changes in the intermediate water masses in the West Indian Ocean.

During research cruise SO306 with RV Sonne two living CWC colonies of Enallopsammia rostrata (Pourtalès, 1878) were collected in the northern part of the Mozambique Channel around the island of Mayotte. The corals originate from intermediate water depths (600 to 900 m) within the transition zone of South Indian Central Water (SICW) and the underlying Red Sea Water (RSW).

The chemical composition of different branches from each colony was analysed using EPMA mapping (Mg, Ca, S, Sr) and LA-ICP-MS line scans (Li, Mg, Ca, Sr, U). U/Th dating enable the determination of ages and growth rates of the individual colonial parts, allowing the sclerochronological alignment of the geochemical data. The obtained long-term (> 100 years) and spatially high-resolution data reveal pronounced cyclic variability in E/Ca ratios (e.g. Sr/Ca). However, using existing proxy calibrations along these data do not meet recorded environmental observations, emphasising the necessity for species-specific adjustments.

Crustose coralline algae (CCA) precipitate high-Mg calcite, contributing to carbonate sediment budgets and benthic habitat complexity. Rhodoliths formed by CCA are key bioconstructors in high-latitude photic zones, playing a role analogous to coral reefs in tropical systems, albeit with markedly slower accretion rates—on the order of micrometers per year. Their sensitivity to environmental change makes them valuable archives for assessing long-term climatic and oceanographic variability, but also challenges their future role as calcifying ecosystem engineers.

This study integrates historical temperature records with a temporally explicit model to reconstruct rhodolith growth trends over ~90 years in Arctic waters. Our results reveal a significant inverse relationship between summer seawater temperatures and rhodolith accretion at 11 and 27 m depths, with an average decline in growth of 8.9 μm per °C (95% CI: 1.32–16.60 μm °C⁻¹; p < 0.05). At 46 m depth and under mesophotic conditions, no significant trend was observed. These findings suggest that increasing ocean temperatures—potentially compounded by acidification and turbidity—are suppressing the calcification rates of CCA beyond their thermal optimum, thus reducing their net carbonate production.

Given the global distribution and ecological importance of CCA-generated rhodolith beds, our findings highlight a geologically significant reduction in biogenic carbonate formation in polar regions. This decline not only alters present-day benthic systems but also has implications for interpreting past climate signals recorded in high-latitude carbonate deposits.

After the discovery of an approximately 1 km² area of ​​solidified asphalt on a seamount (knoll) in the southern Gulf of Mexico, scientists defined the term asphalt volcanism for the process of formation because of the numerous other signs of eruptive deposition on the seafloor. They named the structure Chapopote, after the word asphalt in the Aztec language. Subsequent visual examinations of the seafloor revealed extensive surface deposits of solidified asphalt and light crude oil seeping from locations along the rim of a crater-like structure at 2,900 m water depth. Large areas of the asphalt deposits were colonized by vestimentifera tubeworms, bacterial mats, and other biological communities. Further seafloor mapping showed that most of these knolls have crater-like areas associated with seepage. During recent expeditions, the crater structures of Mictlan Knoll and Tsanyao Yang Knoll were mapped in high resolution, sampled in detail and visually examined with MARUM ROV QUEST4000. Although large areas are also covered with lava-like asphalt sheets, the asphalt seems not to be flown at higher temperatures. Extrusion of heavy liquid oil in form of whips or sheets were observed at several locations which indicate a slow consolidation of the liquid oil to form firm asphalt. After extrusion, chemical and physical changes in the asphalt generate increasing viscosity gradients both along the flow path and between the flow’s surface and core. This allows the asphalt to form pāhoehoe lava-like shapes and to support dense chemosynthetic communities over timescales of hundreds of years.