Mud volcanoes in subduction-zone forearcs provide direct access to fluids generated at depth, yet their occurrence tens of kilometres landward of the deformation front poses several questions about the origin and nature of such fluids, since most of the fluid sources from sediment compaction and clay mineral dehydration are exhausted within a few 10s of km into the subduction system. Here we present a comprehensive pore-water geochemical and isotopic dataset from 12 submarine mud volcanoes in the Kumano Basin (SW Japan), located 42–85 km landward of the trench. More than 460 pore-fluid samples from gravity cores and seafloor drill cores were analysed for major and minor elements and for Li, B, and Sr isotopic compositions.Mud volcano fluids are strongly depleted in Cl, Na, Mg, and K and enriched in B and Li relative to seawater, indicating substantial freshening and deep fluid input. Elemental and isotopic systematics define a ternary mixing between seawater, a pristine deep fluid, and a shallowly overprinted deep fluid affected by volcanic ash alteration and ion exchange. Lithium and boron isotopes constrain fluid sources to a combination of sedimentary clay mineral dehydration and a higher-temperature component inconsistent with purely sedimentary origins. Inferred Li isotope compositions of the fluids sources indicate fluid–rock interaction temperatures of ~150–290 °C, exceeding the smectite-to-illite reaction window and pointing to dehydration of altered oceanic crust (saponite) beneath the forearc. Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr ≈ 0.708) further support mixing between sedimentary, volcanic, and crustal sources.Our results demonstrate that Kumano Basin mud volcanoes are fueled by multiple fluid sources spanning shallow diagenesis, deep accretionary prism dehydration, and subducting oceanic crust. These findings imply that crustal dehydration fluids can migrate into the overriding plate along inherited fault systems and play a major role in forearc hydrogeology. Mud volcanoes thus represent key natural observatories for integrating deep subduction-zone fluid processes beyond the reach of scientific drilling.

The basaltic crust attracts increasing attention as a promising lithology for CO2 storage, due to its common occurrence, its vast storage capacity in pores, and its chemical composition rich in divalent cations - required to bind the dissolved CO2 in form of carbonate minerals. The availability of divalent cations for carbonate mineralization critically depends on the dissolution kinetics of the basaltic host rock. Numerous laboratory experiments have been conducted on a variety of rock forming minerals to investigate these dissolution kinetics and mechanisms under various experimental conditions. In the case of heterogeneous materials, such as polymineralic rocks, the identification and quantification of rate determining parameters is challenging and requires further investigations.In our experiments, we analyze the dissolution behavior of an intact, micro-crystalline basalt sample, typical for mid ocean ridge basalts, in contact with CO2-charged water under temperature and pressure conditions relevant to offshore CO2 storage. We combine flow-through dissolution experiments with Raman coupled Vertical Scanning Interferometry (RcVSI) in order to obtain spatially resolved images of both the topography and the chemical composition of the rock surface. The consecutive topography measurements by VSI allow us to quantify spatial differences in surface reactivity and examine their relation to chemical and structural properties provided by Raman spectroscopy. The data show significant differences in dissolution rates both between the different minerals and within single phenocrysts. Furthermore, the spatial heterogeneities in surface reactivity indicate an important influence of the rock texture as well.This combination of measurements provides the means to investigate the dissolution kinetics of polymineralic rocks and to determine differences in the dissolution kinetics of different minerals simultaneously. The results provide important information about rock internal parameters that contribute to the overall dissolution behavior of the rock. The results improve our understanding of dissolution processes that are critical to the efficiency of carbonate mineralization for long-term CO2 storage in submarine basaltic aquifers.

Earthquakes are recognized as the primary cause of submarine landslides. These earthquake-induced submarine landslides can damage seafloor infrastructure (e.g. submarine cables, oil pipes and rigs) and trigger anomalous tsunamis that cannot be explained solely by coseismic deformation. However, due to their underwater occurrence, earthquake-induced submarine landslides are difficult to observe and measure directly, and current understanding of their characteristics and triggering mechanisms remains limited compared to earthquake-induced terrestrial landslides. Historical instances of anomalous tsunamis and submarine cable breaks following earthquakes provide valuable insights into earthquake-induced submarine landslides. This study reviewed 124 global events of anomalous tsunamis and submarine cable breaks following earthquake occurrences since 1900 using the National Oceanic and Atmospheric Administration tsunami database and systematic literature review. The study compiled key parameters of earthquake-induced submarine landslides associated with anomalous tsunamis and submarine cable breaks, such as locations, initial water depths of the headscarp, average seabed slope angles, volumes and landslide types. This study also obtained seismic parameters such as epicentral distances, peak ground acceleration (PGA) and Modified Mercalli Intensity (MMI) from the USGS-ShakeMap to establish a quantitative relationship between earthquake-induced submarine landslides and their seismic triggering parameters. Additionally, a comparison was made between earthquake-induced submarine landslides and earthquake-induced terrestrial landslides with emphasis on differences and similarities in landslide parameters, earthquake magnitudes, seismic parameters PGA and MMI, earthquake magnitude-maximum epicentral distance relationships and triggering mechanisms. It was observed that most of the earthquake-induced submarine landslides occur in shallow nearshore areas and generate tsunamis characterized by high local wave heights. This attribute leaves little or no time for warning and preventive measures. Earthquakes with onshore epicenters or strike-slip mechanisms that trigger submarine landslide tsunamis pose an additional challenge for early warning systems. Compared to earthquake-induced terrestrial landslides, earthquake-induced submarine landslides typically occur on gentler slopes, have larger volumes, are triggered by smaller earthquake magnitudes and exhibit distinct triggering mechanisms. However, they show more similarities than previously anticipated, particularly in terms of seismic parameters (PGA and MMI) and focal mechanisms. The findings of this study contribute to a better understanding of earthquake-induced submarine landslide characteristics and their quantitative relationship with seismic parameters. It highlights the necessity for further research on anomalous tsunamis and submarine cable breaks following earthquakes in order to improve current understanding of triggering mechanisms, frequencies and hazard potential of earthquake-induced submarine landslides. Moreover, given that studies on both earthquake-induced submarine landslides and earthquake-induced terrestrial landslides explore interconnected scientific questions within a unified framework, this study emphasizes the importance of comparing submarine and terrestrial environments in earthquake-induced geological disaster research.

Mud volcanoes (MVs) are important gateways for fluid migration, particularly in subduction zones. We investigate five MVs in the Gulf of Cadiz and the Mediterranean Ridge, revealing underappreciated fluid pathways responsible for fluid expulsion. By utilizing pore water geochemistry, advection-diffusion modeling, and high-resolution seismic profiles, we trace fluid origins, quantify fluxes, and constrain migration pathways, focusing on the Ginsburg MV. The Cl-depleted summit fluids originate from clay dehydration Cadiz (AUGC) and are channeled by central conduits, reaching high advection velocities (2.8-15 cm/yr). The Cl-enriched moat fluids exhibit slower advection velocities (0.3 cm/ yr) and show additional evaporite effects. To constrain moat fluid sources, fluid formation temperatures have been calculated using water isotopes and Mg-Li geothermometer. The resulting low temperatures suggest source depths atop the AUGC (-0.8 kmbsf), consistent with seismic data across the Ginsburg MV (showing high-amplitude reflections at the same depths) but different from the summit sites, where the source is deeper within the AUGC (-2.2 kmbsf). We relate moat seepage occurrence to fractures formed due to edifice subsidence, marked by stacked enhanced reflectors. Upon comparison with all analyzed pears in a specific evolutionary stage, during which it represents an important component of fluid budget. This phenomenon, which has been observed in terrestrial MVs, is rarely described for their submarine counterparts but has wide biogeochemical implications for fluid budget in subduction zones and the sustenance of seafloor biological communities.

To meet temperature goals that limit warming to well below 2°C requires the removal of hundreds of billions of tonnes of CO2 from the atmosphere over the course of this century. Effective Carbon Dioxide Removal (CDR) methodologies will be required to reduce net emissions in the near term, counterbalance residual CO2emissions to achieve net-zero in the medium term, and contribute to net-negative emissions in the longer term– all of this in a sustainable and safe manner. The AIMS3 project (www.aims3.cdrmare.de) will deliver new insights, monitoring tools and feasibility assessments for CO2 storage at oceanic Carbon Capture and Storage (CCS) sites, specifically in basalticrocks of the oceanic crust. The study forms a distinct progression of CO2 injection experiments carried out before (Sleipner gas release experiment, EU STEMM-CCS project, etc.) in former coastal subseafloor reservoirs or saline aquifers. Instead, AIMS3 focuses on the flanks of mid-ocean ridges where porous basaltic crust is overlain by thin sediment successions of low permeability as a cap. These basalts react quickly with injected CO2 (dissolved, liquid, or supercritical), which is fixed effectively in carbonate minerals without the risk of a later escape, ideally in deep water environments. Inflow of cold seawater and discharge of warmed hydrothermal fluids are focused and directed at such sites and help dispersing CO2 into wider areas, hence requiring fewer injection sites in case of future storage activities. The talk will present ongoing work at the Reykjanes Ridge south of Iceland. Together with industrial partners, AIMS3 is currently setting up a ridge flank observatory with a transect of boreholes through the fill of young sediment ponds into the upper oceanic crust. The boreholes are equipped with observatories, which will include a suite of cost-effective sensors, landers and robots to identify and quantify CO2 with high precision and accuracy. Here we outline the rationale of AIMS3, provide an overview of the activities, and highlight some of the expedition results, with the goal to stimulate communication and collaboration.

In the CDRmare research consortium AIMS³, experts have spent the past three years investigating under which conditions carbon dioxide (CO2) dissolved in seawater could be stored in the young basalt crust south of Iceland. In addition, they have developed new, deep-sea-capable sensors and monitoring systems for measuring the mineralisation of the stored CO2 and assessing the environmental soundness of such a potential deep-sea storage project.

Marine carbon dioxide removal (mCDR) and geological carbon storage in the marine environment (mCS) promise to help mitigate global climate change alongside drastic emission reductions. However, the implementable potential of mCDR and mCS depends, apart from technology readiness, also on site‐specific conditions. In this work, we explore different options for mCDR and mCS, using the German context as a case study. We challenge each option to remove 10 Mt CO2 yr−1, accounting for 8%–22% of projected hard‐to‐abate and residual emissions of Germany in 2045. We focus on the environmental, resource, and infrastructure requirements of individual mCDR and mCS options at specific sites, within the German jurisdiction when possible. This serves as an entry point to discuss main uncertainty factors and research needs beyond technology readiness, and, where possible, cost estimates, expected environmental effects, and monitoring approaches. In total, we describe 10 mCDR and mCS options; four aim at enhancing the chemical carbon uptake of the ocean through alkalinity enhancement, four aim at enhancing blue carbon ecosystems' sink capacity, and two employ geological off‐shore storage. Our results indicate that five out of 10 options would potentially be implementable within German jurisdiction, and three of them could potentially meet the challenge. Our exercise serves as an example on how the creation of more tangible and site‐specific CDR options can provide a basis for the assessment of socio‐economic, ethical, political, and legal aspects for such implementations. The approach presented here can easily be applied to other regional or national CDR capacity considerations.

Permanent carbonate mineralisation in basalt is a promising solution for Carbon Capture and Storage of anthropogenic greenhouse gases without the risk of leakage. While this process is known to occur at relatively low temperatures below 100°C, new research on Large Igneous Provinces (LIPs) and young rift basins suggests that much of the thermogenic gases mobilised during contact metamorphism can remain trapped and mineralised in the sills that mobilised them. This discovery is the result of two distinct drilling investigations on land (KARIN) and at sea (IODP Exp 385). It shows that basalts may not only trigger the sudden release of thermogenic gas, but also represent an important carbon sink. The two examples of carbonate trapping in sills presented here are from the Karoo and Guaymas basins. Results indicate that a large fraction of epimagmatic fluids charged with thermogenic gas systematically penetrated inside the sills during cooling. Our numerical solutions suggest that in both cases the higher permeability of the sill acquired during cooling and crystallisation compared to that of its host, ultimately dictates the fate of the thermogenic gas that accumulated in the igneous bodies.

Magma emplacement in the top unconsolidated sediments of rift basins is poorly understood. We compare two shallow sills from the Guaymas Basin (Gulf of California) using core data and analyses from IODP Expedition 385, and high‐resolution 2D seismic data. We show that magma stalling in the top uncemented sediment layer is controlled by the transition from siliceous claystone to uncemented silica‐rich sediment, favoring flat sill formation. Space is created through a combination of viscous indentation, magma‐sediment mingling and fluidization processes. We show that sills emplace above the opal‐A/CT diagenetic barrier. Our model suggests that in low magma input regions sills emplace at constant depth from the seafloor, while high magma input leads to upward stacking of sills, culminating in a funnel‐shaped intrusions. Our petrophysical, petrographic, and textural analyses show that magma‐sediment mingling creates significant porosity (up to 20%) through thermal cracking of the assimilated sediment. Stable isotope data suggest carbonate formation at 70–90°C, consistent with background geothermal gradient at 250–325 m depth. The unconsolidated, water‐rich host sediments produce little thermogenic gas through contact metamorphism, but deep diagenetically formed gas bypasses the low‐permeability top sediments via hydrothermal fluids flowing through the magma plumbing system. This hydrothermal system provides a steady supply of hydrocarbons at temperatures amendable for microbial life, serving as an incubator that may be abundant in magma‐rich young rift basins and play a key role in sustaining subseafloor ecosystems.

Extreme physical-oceanographic events, such as marine heatwaves, fluvial floods, droughts and storm surges, have major impacts on local communities, economic sectors and ecosystems, and their frequency, intensity and duration increase due to climate change. There is a lack of understanding of the systemic drivers of extreme events as well as of their interconnected impacts on estuarine and coastal ecosystems. This knowledge is essential for assessing future impacts on ecosystem services and the local communities that depend on them, and to inform robust risk assessments and develop comprehensive risk management and adaptation strategies including early warning systems. Considering this, the German Alliance for Marine Research (DAM)-funded programme “ElbeXtreme” focuses on an integrated approach utilizing stakeholder engagement, data mining, experimental and field observations to develop novel observational and modelling approaches for assessing and monitoring risks in the Elbe estuary. The programme will deliver new insights into risks and impacts of extreme events in the estuarine system of the Elbe and the adjacent region of the North Sea (German Bight) to build a systemic risk understanding and support adaptation planning for local communities and ecosystems. Here we outline the rationale of the ElbeXtreme project and its planned activities, with the aim of stimulating national and international collaboration in tackling the urgent issue of marine and coastal risks.

Natural radioactivity was measured and analyzed at the Nice Slope for over a month using radon daughters in order to trace groundwater movement from a coastal aquifer to a nearshore continental shelf. Such groundwater movement may have resulted in submarine groundwater discharge (SGD) and potentially sediment weakening and slope failure. The relationship among major hydrological parameters (precipitation, Var discharge, groundwater level, salinity and water origin) in the area is demonstrated in this study. Time series analyses also helped to detect tidal fluctuations in freshwater input, highlighting the crucial role SGD plays in the slope stability of the still failure-prone Nice Slope, parts of which collapsed in a tsunamigenic submarine landslide in 1979. Earlier deployments of the underwater mass spectrometer KATERINA showed that SGD is limited to the region of the 1979 landslide scar, suggesting that the spatially heterogenous lithologies do not support widespread groundwater charging. The calculated volumetric activities from groundwater tracing isotopes revealed peaks up to ca. 150 counts 214Bi, which is similar to those measured at other prominent SGD sites along the Mediterranean shoreline. Therefore, this rare long-term radioisotope dataset is a valuable contribution to the collaborative research at the Nice Slope and may not remain restricted to the unconfined landslide scar but may charge permeable sub-bottom areas nearby. Hence, it has to be taken into account for further slope stability studies.

Carbon Dioxide Removal (CDR) approaches are essential to achieve the Paris 2015 global warming targets, as emphasized by the Intergovernmental Panel on Climate Change (IPCC) in their reports from 2021 onwards. With European legislation and ethical constraints in mind, a desirable approach to contribute to meeting ambitious climate goals would require to find safe, effective and sustainable storage sites on European territory, e.g. to avoid additional CO2 footprint for transportation or other processing steps needed. Given that the (admittedly substantial) storage capacity of Mesozoic sandstones forming the continental socket of wider parts of Europe (with a potential to host 270 Gt of carbon dioxide) has been widely accepted, there still remain doubts that these deep, warm reservoirs are the ideal place for storage of supercritical CO2, in particular since the overburden strata are heavily fractured and far less impermeable than what would be ideal and safe – let alone the elevated temperatures in several kilometres where Buntsandstein formations encounter conditions where carbon dioxide remains in its supercritical state for geological times. In contrast, oceanic basalts have been demonstrated to host CO2 both as structural (pore volume) and mineral (precipitation as carbonate minerals) traps in a sustainable manner. In large water depth the CO2 is stable as pure carbon dioxide, and when dissolved in seawater, the carbonated equivalent is heavier than pure seawater and unlikely to escape. With that in mind various European regional scenarios have been (re-)visited in order to assess feasibility and potential of storage. We have focused on the North Atlantic Volcanic Province (NAVP) with an estimated volume of extrusives close to 1.8 Mill. km3. The NAVP comprises various mafic and ultramafic regions between Iceland, the UK and Norway, including ocean crust, vesicular basalt and other igneous rock originating from the opening of this part of the Atlantic Ocean. We identified various corridors using ArcGIS Pro in combination with the Carbfix Mineral Storage Atlas and quantified the storage potential and associated cost in case CDR was to be carried out in these areas. Despite the large uncertainty in such numbers, the study serves to compare (among others) the Vøring and Møre basins, the Aegir ridge, Shetland and Faroer islands and neighbouring facies, and the Rockall basin and ridge. Farther from industrial centres we also investigated Iceland and the Reykjanes ridge. The work carried out is part of the AIMS3 project as part of the research mission CDRmare (www.cdrmare.de).

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.

To meet temperature goals that limit warming to well below 2 °C requires the removal of hundreds of billions of tonnes of CO2 from the atmosphere over the course of this century. Effective Carbon Dioxide Removal (CDR) methodologies will be required to reduce net emissions in the near term, counterbalance residual CO2 emissions to achieve net-zero in the medium term, and contribute to net-negative emissions in the longer term – all of this in a sustainable and safe manner. This paper summarizes the research objectives and selected initial results of a collaborative project to assess CO2 storage in the upper ocean crust south of Iceland.The AIMS3 project (www.aims3.cdrmare.de) will deliver new insights, monitoring tools and feasibility assessments for CO2 storage in young, reactive basalts with little sedimentary cover. Along the flank of the Mid-Atlantic Ridge, we have done geophysical surveys and drilled a transect of boreholes in order to identify fluid migration in the upper ocean crust. Both in situ heat flow and geochemical signatures provide irrefutable evidence for such transport, which will help distributing injected CO2 in future experiments.In parallel, our project also has mineralization experiments to assess optimal conditions for injection dissolved, liquid, or supercritical CO2), numerical modelling for upscaling our results from seagoing work, and development of cost-effective sensors and smart robotic landers for long-term monitoring of the vicinity of the boreholes. We outline the rationale of AIMS3, provide an overview of the activities, and highlight some of the expedition results, with the goal to stimulate communication and collaboration.

Mud volcanoes in the Mediterranean Sea have been subject of scientific research since the 1970s and contributed to the understanding of these seafloor features and their role in the subduction budgets worldwide. Recently, the need to better characterize the connection of these mud volcanoes with the deeper lithologies of the accretionary prism and its implications led to expedition POS410 (2011) and SO278 (2020). During these expeditions, mud volcanoes which had been investigated in ODP Leg 160 (1996) were resampled and complemented with new sites along the Mediterranean Ridge accretionary complex. We present pore water data from six mud volcanoes and two brine pools in and around the Olimpi Mud Volcano Field (OMVF). The data highlight strong depletion in Cl (<200 mM), Na (∼200 mM), Mg and K (with concentrations ∼0 mM) and striking water isotope ratios (δ18O of +9.79‰ V-SMOW and δD of −26.33‰ V-SMOW), indicating dehydration of clay minerals at depth. At five locations, the interstitial waters are characterized by extremely high salinities (Cl > 5000 mM and Na >6500 mM), therefore drastically expanding the previous reports of highly saline pore waters in the OMVF. The measurements further reveal that Gelendzhik mud volcano, located in the western part of the OMVF along a major strike-slip fault, shows an unusual pore water downcore profile and its water isotopes signature differ strongly from the other structures (δ18O of +13.63‰ and δD of +1.83‰). Upon further investigation through XRF scans and hydrates stability calculations we tied the anomalous low salinity values of the Gelendzhik MV pore waters results from the presence of gas hydrates in the sediments. This is the first, indirect evidence of gas hydrates in the OMVF, several years after this hypothesis was formulated by De Lange and Brumsack (1998) and then quickly discarded.

Bottom trawling is a well-known global phenomenon and has significant physical impact on the seabed habitat, such as compression, displacement and mobilization of the sediment. Thus, it is necessary to examine how it alters the seabed, e.g., in order to support strategies in marine spatial planning and nature conservation. Numerous studies aim at quantifying the physical impact of bottom trawling on the seabed based on laboratory experiments and/or modeling approaches but, to our knowledge, none of them include in-situ techniques. The North Sea is heavily influenced by bottom trawling and thus, an area in the southern North Sea was selected where side scan sonar data identified areas showing the physical impact of bottom trawling by means of trawl marks. Here, the dynamic penetrometer Nimrod was deployed in order to determine the changes in sediment strength (quasi-static bearing capacity) compared to the reference sites (absent trawl marks). The results attest a higher penetration depth of Nimrod and a lower sediment strength in the trawled area compared to the un-trawled reference sites. This is likely related to an increase in water content and a decrease in bulk density of the sediment that was re-worked by bottom trawling.

The hadal trenches located on the subduction zone harbor unique deep-sea microbes, yet the mechanisms regulating the characteristics of the deep-sea microbial communities remain largely unknown. The frequent and unpredictable tectonic processes such as earthquakes triggered by plate subduction act as a lateral transport pathway for sediments, and may lead to redistribution and reburial of allochthonous microbes. However, such tectonically-triggered processes in the hadal trenches are not yet investigated. Here we demonstrate that distinctive allochthonous microbial communities are introduced into the Japan Trench by three historical earthquakes, with community structure transitions observed across the turbidite boundaries. The variations of the microbial community structures are linked to earthquake-driven organic carbon deposition and its characteristics, suggesting the potential impact of mass transport events on the microbial-mediated deep carbon cycles. Our calculations indicate that the Pacific trenches receive at least 5.1 Pg of earthquake-induced microbial biomass carbon during the past century, with spatial and temporal variations at different scales. These results suggest that pulsed tectonic events play a crucial role in introducing allochthonous microbes to the deep biosphere, potentially leading to substantial microbial biomass carbon export into the subduction zone.