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The Role of Salt Tectonics in the 2021 Central Adriatic Seismic Sequence
No full textOn 27 March 2021 a 3‐months lasting seismic sequence struck the Central Adriatic Basin that is part of the Adria plate, a relatively undeformed plate since recent times. Analyzing the waveform data acquired by the Italian and Croatian seismic networks, we computed the location parameters of 160 earthquakes and the focal mechanisms of the M w 5.2 mainshock and the larger aftershocks. Most events align along a WNW‐ESE trending, 30 km long, narrow belt. The depth distribution of events indicates that the mainshock and a few aftershocks occurred within the upper 4 km, while most aftershocks were located below 5 km within the carbonate platform. We propose that the evolution of the 2021 earthquake distribution is primarily ruled by the top ductile salt layer. Moreover, the presence of a salt layer explains the relatively high V P /V S ratio of 1.83 in the sediment rocks surrounding the salt bodies, as also observed in similar tectonic settings. We suggest that the seismogenic fault likely responsible for the 2021 events is an inherited SW‐dipping normal fault, reactivated by reverse kinematics in response to the regional compressive stress. These results, and the understanding that salt deposits play a key role in focusing deformation and seismogenesis, represent a novel contribution to the long‐standing challenge of seismic hazard assessment of the Central Adriatic Basin, where moderate to large events could have devastating impacts along the densely populated coasts.
Plain Language Summary
The analysis of a seismic sequence that hit the Central Adriatic Basin on 27 March 2021 enabled us to shed light on tectonic processes and seismogenesis of this complex and poorly constrained geodynamic domain in the Mediterranean basin. We used the waveform data acquired by the Italian and Croatian seismic networks to compute the location parameters of 160 earthquakes as well as the focal mechanism solutions of 7 events with moment magnitudes, M w , larger than 3.6. We suggest that the seismic sequence originated on a WNW‐ESE oriented and SW‐dipping fault with reverse kinematics that interacts at shallow depth with a salt layer. Understanding the interplay between seismicity and local tectonics contributes to assessing seismic hazard in the Adriatic region.
Key Points
Hypocentral parameters of the 2021 central Adriatic seismic sequence and focal mechanisms of the larger events are computed
The 2021 seismicity is distributed along SW dipping inherited fault reactivated by salt diapirs with reverse kinematics
Salt tectonics controls the evolution of the seismicit
Thriving Through Synergy: Fostering a SOLAS Science Community Built on Equity, International Connections, and the Integration of Early Career Scientists
No full textThe Surface Ocean-Lower Atmosphere Study (SOLAS) is a global research network dedicated to advancing coupled oceanographic and atmospheric science, a field that requires both interdisciplinary and globally distributed expertise. Since 2004, SOLAS has fostered an international interdisciplinary scientific community through coordinated science and capacity sharing activities. This paper outlines how SOLAS 3.0 (2026–2035) will build on this legacy by further prioritizing diversity, equity, and inclusion, and expanding and strengthening research at the ocean-atmosphere interface. SOLAS 3.0 new initiatives include a mentorship program, skill enhancement workshops, increasing access to resources, and a network of observation and training centers. By learning from past successes and challenges, SOLAS 3.0 aims to inspire scientists from around the world, as well as the next generation, to address complex transdisciplinary research and tackle present and future societal challenges in a truly global way
A Lagrangian perspective reveals the carbon and oxygen budget of an oceanic eddy
No full textQuantifying the ocean's ability to sequester atmospheric carbon is essential in a climate change context. Measurements of gravitational carbon export to the mesopelagic seldom balance the carbon demand or the oxygen consumption there, suggesting the potential presence of other mechanisms of carbon export. We deployed a biogeochemical Argo float in a cyclone in the Benguela upwelling system for five months, and estimated vertical carbon export and respiration in the eddy via particle imagery with an underwater vision profiler 6 in a quasi Lagrangian way. A sensitivity analysis shows that, under certain assumptions, oxygen consumption rates could match the carbon supply and carbon demand. We furthermore identified a mechanism of vertical particulate carbon export, the full eddy core submergence pump. Our analysis suggests that at 450 m depth, within this eddy, this pump exports about one fourth to half of the total carbon compared to the biological gravitational pump
Mineral phases and growth conditions of morphologically diverse shelfal ferromanganese concretions
No full textFerromanganese concretions in the shelf sea regions, such as the Baltic Sea, are of significant interest due to their geochemical properties, economic resource potential, and roles in benthic ecosystems. This study analyses the authigenic and detrital mineral phases and their provenance in the Baltic Sea concretions, as well as their formation mechanisms and diagenetic evolution. These concretions exist in three distinct morphotypes: crust, discoidal, and spheroidal. Using synchrotron-based techniques (µ-XRF and µ-XAS) paired with XRD, stable Pb isotope, and bulk geochemical analyses, we found that discoidal and spheroidal concretions consist of alternating Fe- and Mn-rich layers, whereas crust concretions are predominantly Fe-rich. The Mn phases primarily consist of birnessite-like phyllomanganates with columnar and branched dendritic growth patterns, indicative of microbially-mediated precipitation. In contrast, the Fe phases are represented by poorly crystalline ferrihydrite, the formation of which is influenced by admixing of detrital minerals. The three main components (Fe-rich, Mn-rich and detrital), each exhibit distinct trace element associations. The geochemical composition and morphology of the Baltic Sea concretions resembles other shelfal precipitates, indicating consistency in formation mechanisms across different shelf environments. Slightly negative to intermediate Ce anomaly values and the range in Nd contents in the samples suggest that early diagenetic processes contribute to the formation of all the morphotypes. The lateral distribution and morphology of concretions are influenced by local hydrodynamic conditions, sedimentation dynamics, and redox fluctuations. An important factor is the periodic cover of a very organic-rich “fluffy” mud layer, which is driven by near-bottom currents, imports detrital minerals and modifies redox conditions, impacting microbial activity within the concretions. The higher occurrence of detrital minerals in Fe-rich concretions, particularly in the crust morphotype, suggests formation under stronger terrigenous influence in high-energy sedimentation conditions as opposed to more Mn containing concretions (mainly discoidal and spheroidal) forming in a relatively tranquil depositional setting and deeper water. The maturity of the detrital mineral fraction generally increases from crust to discoidal to spheroidal concretions. The Fe-rich concretions contain greater proportion of micas, clay minerals and K-feldspar to plagioclase, while the more Mn-containing concretions have proportionally high quartz contents. The detrital minerals likely act as nucleation sites promoting Fe precipitation and are redistributed diagenetically toward the interfaces dominated by Fe phases, which are slightly more tolerant to reductive dissolution than Mn phases. The preferential reductive dissolution of Mn phases results in thick Fe-rich growth layers and relative enrichment of the detrital mineral fraction. Stable Pb isotope data show distinct regional signatures, indicating that the composition of concretions is affected by bedrock erosion in the catchment area. Our findings highlight contrasts in mineral phases, geochemistry, formation environments, and diagenetic evolution across sites in Fe-rich crust concretions compared to more Mn containing discoidal and spheroidal concretions. These insights are relevant to ferromanganese concretions in shelf areas worldwide, and their potential use in paleoenvironmental reconstructions and resource exploration
Constraining Solid Dynamics, Interface Rheology, and Slab Hydration in the Hikurangi Subduction Zone Using 3‐Dimensional Fully Dynamic Models
No full textSimulating present‐day solid Earth deformation and volatile cycling requires integrating diverse geophysical data sets and advanced numerical techniques to model complex multiphysics processes at high resolutions. Subduction zone modeling is particularly challenging due to the large geographic extent, localized deformation zones, and the strong feedbacks between reactive fluid transport and solid deformation. Here, we develop new workflows for simulating 3‐dimensional thermal‐mechanical subduction and patterns of volatile dehydration at convergent margins, adaptable to include reactive fluid transport. We apply these workflows to the Hikurangi margin, where recent geophysical investigations have offered unprecedented insight into the structure and processes coupling fluid transport and solid deformation across broad spatiotemporal scales. Geophysical data sets constraining the downgoing and overriding plate structure are collated with the Geodynamic World Builder, which provides the initial conditions for forward simulations using the open‐source geodynamic modeling software code ASPECT. We systematically examine how plate interface rheology and hydration of the downgoing plate and upper mantle influence Pacific–Australian convergence and seismic anisotropy. Models prescribing a plate boundary viscosity of Pa s best reproduce observed plate velocities, and changing the configuration of the Pacific–Australia plate boundary directly influences the modeled plate motions. Models considering hydrated olivine fabrics best reproduce observations of seismic anisotropy. Predicted patterns of slab dehydration and mantle melting correlate well with observations of seismic attenuation and arc volcanism. These results suggest that hydration‐related rheological heterogeneity and related fluid weakening may strongly influence slab dynamics. Future investigations integrating coupled fluid transport and global mantle flow will provide insight into the feedbacks between subduction dynamics, fluid pathways, and arc volcanism.
Plain Language Summary
Subduction zones are tectonic plate boundaries where an oceanic plate sinks beneath another oceanic or a continental plate, which generates abundant large‐magnitude earthquakes and surface volcanism. Understanding the underlying processes responsible for these geohazards, drivers of large‐scale plate motions, and long‐term chemical cycling remain frontier areas of research. Here, we use 3‐dimensional geodynamic modeling to investigate these processes at the Hikurangi subduction zone offshore New Zealand, which is unique due to the presence of the Hikurangi plateau, voluminous surface volcanism in the Taupo region, and geophysical observations constraining fluid movement through the system. Our simulations demonstrate that the strength of the interface between the subducting and overriding plates strongly controls the subducting plate speed, and also suggest large‐scale patterns of mantle flow from far‐field regions may impact observed plate motions. Predictions of seismic anisotropy and fluid release from the downgoing plate are consistent with observations that highlight the presence of fluids transported downward in the subducting plate, and then later released beneath the Taupo region. Future work can build on these findings by adding coupled fluid flow and its effects on the strength of solid rock.
Key Points
We construct a high resolution, buoyancy driven, fully dynamic visco‐plastic 3‐dimensional model of subduction at the Hikurangi margin
Hydrated olivine fabrics improve the fit to observed seismic anisotropy within the slab beneath the North Island of New Zealand
Slab devolatilization predictions show strong agreement with observations of seismic attenuatio
Massive Sulfide Deposition at the 13°30’N Oceanic Core Complex: Lessons Learned From Coupled Hydro‐Thermo‐Mechanical Modeling
No full textYoung oceanic lithosphere created at mid‐ocean spreading centers is subject to complex magmatic, tectonic and hydrothermal processes, especially in regions of widespread detachment faulting. This study focuses on the oceanic core complex (OCC) at the Mid Atlantic Ridge at 13°30’N. The OCC hosts the active Semenov‐2 vent field and four inactive fields, including the exceptionally large Semenov‐4 sulfide deposit (10 Mt), which is located near the emergence of a detachment fault. To study the relationship between tectonic detachment faulting and fluid circulation we couple models for mechanical deformation and hydrothermal fluid flow. Our aim is to identify the role of the detachment in controlling location and size of sulfide deposition. First, we develop a baseline model for the tectono‐magmatic evolution of the OCC using a data‐based sequence for magnitude and position of axial magmatic diking. The resulting history of tectonic deformation provides a dynamic framework for modeling hydrothermal flow through porous rock, incorporating regions of active faulting and seafloor topography evolution. We then examine the impact of various fault zone permeability structures and heat sources on hydrothermal sulfide deposition. Our results show that a combination of a topographic influence, anisotropic permeability along the fault zone, transient shallow heat sources and plume interactions can efficiently reorganize the hydrothermal system. Increasing horizontal distance between heat source and vent field, however, significantly reduces hydrothermal plume stability. Modeled mass flow rates suggest that vent fields like Semenov‐4 and TAG result from the focusing of fluid flow across the entire along‐axis extent of the detachment structure.
Plain Language Summary
Mid‐ocean ridges are boundaries where tectonic plates move apart and new seafloor forms. In these regions, the Earth's outer layer is thinner, allowing heat from the mantle to drive hydrothermal circulation. Hot fluids travel through the porous rock, where they dissolve minerals, which then settle on the seafloor as ore deposits when the fluids are released into the ocean and cool. These deposits have both scientific and economic importance. At slow‐spreading ridges, large and long‐lived tectonic faults called detachment faults are common, and many massive ore deposits form near them. This study explores how these faults form and how they influence hydrothermal fluid flow and ore deposition using computer models. We first model the tectonic and magmatic history of a specific detachment fault at 13°30’N at the slow‐spreading Mid‐Atlantic Ridge. Then, we examine the channeling of fluids along the detachment fault, the influence of different heat sources, and the impact of seafloor topography. Our results suggest that a combination of these factors is needed to focus fluid flow over the large area controlled by the detachment (about 10 km by 10 km) to create the massive ore deposits observed in nature.
Key Points
We model the tectono‐magmatic evolution of the 13°30’N OCC as well as hydrothermal circulation and sulfide deposition
Combined effects of topography, fault permeability, transient shallow heat sources and hydrothermal plume interactions control fluid flow
Modeled 2‐D fluid mass flow rates indicate strong 3‐D hydrothermal flow focusing across an OC
A series of fine-scale resolving coupled climate simulations
No full textOceanic fine-scale flows with horizontal extends of 1 - 100 km have been shown to be relevant for the ocean energy balance and cascade, for the restratification of the upper ocean, and for the vertical exchange between the oceans interior and the sea-surface and associated transports of heat and dissolved gases. Recent fine-scale resolving coupled ocean-atmosphere simulations show that submesoscale oceanic fronts affect the maritime weather in the whole atmosphere above, but were affordable only for integration lengths of single years. Here, we present a model development plan for a series of coupled climate simulations that we are running within the ERC synergy project "The impacts of ocean fine-scale whirls on climate and ecosystems" (WHIRLS). We couple the ocean-model NEMO 4.2.2 to the atmospheric model OpenIFS with the coupler OASIS. We start at 1/4 degree oceanic resolution (eORCA025) and about 31 km atmospheric resolution and gradually increase the horizontal resolution to 1/100 degree oceanic resolution and a kilometer-scale atmospheric resolution. For the ocean, we use AGRIF for a 1/20 degree grid-refinement that extends over the South Atlantic, the western Indian ocean, and the adjacent Southern ocean including the Antarctic shelf, as well as a secondary grid-refinement down to 1/100 degree for the core Agulhas region. Fine-scale resolving experiments with and without the 1/20 degree nest will be integrated for climatic time-scales of more than 70 years. Finally, additional parallel sensitivity experiments including the coupling to only the global parent grid or the use of absolute, partial, and relative winds are planned
Testing the reliability of global surface temperature reconstructions of the Last Glacial Cycle with pseudo-proxy experiments
No full textReconstructions of past variations in the global mean surface temperature (GMST) are used to characterise the Earth system response to perturbations and to validate Earth system simulations. Beyond the instrumental period, reconstructions rely on local proxy temperature records and algorithms aggregating these records. Here, we propose to establish standards for evaluating the performance of such reconstruction algorithms. Our framework relies on pseudo-proxy experiments (PPEs). That is, we test the ability of an algorithm to reconstruct a simulated GMST, using artificially generated proxy data created from the same simulation. We apply the framework to an adapted version of the GMST reconstruction algorithm used in Snyder (2016) and the metadata of the synthesis of marine proxy records for the temperature of the last 130 kyr from Jonkers et al. (2020). We use an ensemble of four transient simulations of the Last Glacial Cycle (LGC) or the last 25 kyr for the pseudo-proxy experiments.
Given the dataset and the algorithm, we find that the reconstruction is reliable for timescales longer than 4 kyr during the last 25 kyr. However, beyond 40 kyr BP, age uncertainty limits the reconstruction reliability to timescales longer than 15 kyr. For the long timescales, uncertainty on temperature anomalies is caused by a factor that re-scales near-global-mean sea surface temperatures to GMST, the proxy measurements, the specific set of record locations, and potential seasonal biases. Increasing the number of records significantly reduces all sources of uncertainty but the scaling. We also show that a trade-off exists between the inclusion of many records, which reduces the uncertainty on long timescales, and of only records with low age uncertainty, high accumulation rate, and high resolution, which improves the reconstruction of the short timescales.
Finally, the method and the quantitative results presented here can serve as a basis for future evaluations of reconstructions. We also suggest future avenues to improve reconstruction algorithms and discuss the key limitations arising from the proxy data properties
A holistic assessment framework for marine carbon dioxide removal options
No full textMarine Carbon Dioxide Removal (mCDR) options could potentially play an important role in future CDR policy portfolios. They include, for example, ocean alkalinity enhancement, blue carbon projects such as mangrove cultivation, as well as sub-seabed storage of captured atmospheric CO2. We present a novel assessment framework designed for mCDR options. The framework provides important conceptual advancements to existing frameworks currently used to assess climate options: It clearly distinguishes between and allows for the assessment of both the feasibility and desirability of mCDR options, it makes explicit the evaluative standards upon which the assessment is based and it separates the descriptive listing of information from the evaluation of said information. The assessment framework aims to advance the debate on what role mCDR can and should play in responding to the climate crisis by providing a tool for both policymakers and stakeholders to assess mCDR options in a transparent and comprehensive way
Performance prediction for Stommel’s perpetual salt fountain in the context of artificial ocean upwelling
No full textDue to the typical temperature and salinity structure in wide parts of the global oceans, a self-sustaining, convective up or downflow within a vertical pipe can be established. This concept was introduced by Stommel et al. (1956) as the perpetual salt fountain. Recently, Stommel Upwelling Pipe (SUP) systems are gaining new interest as possible enabling technology for large-scale implementations of artificial upwelling of nutrient-rich deep ocean water to the ocean surface. This process is currently actively researched as part of several marine Carbon Dioxide Removal (CDR) approaches. Despite multiple studies conducted over the past decades, no method has yet been proposed to reliably predict performance and thus enable quantification of the potential of Stommel Upwelling Pipe (SUP) systems for artificial upwelling. In the present work, two performance prediction methods for SUP systems are introduced, one method based on the Reynolds-Averaged Navier–Stokes (RANS) equations and a one-dimensional method based on pipe flow equations. This twofold approach overcomes the limitations of previous studies and enables reliable performance estimation for a wide range of SUP setups. Both numerical methods are described in the present work, and their predictive capabilities are proven through rigorous verification, validation, and model intercomparison. The respective model assumptions are critically reviewed. Our results reveal key aspects of SUP performance and provide the basis for a reliable evaluation of the potential of SUP systems for artificial upwelling.
Highlights:
• Self-sustaining convection in vertical ocean pipes can drive artificial upwelling.
• We introduce two new performance prediction methods for Stommel Upwelling Pipes.
• Reliability is achieved through verification, validation, and model intercomparison.
• We present new results for different device concepts and ocean conditions.
• Our results reveal key aspects of Stommel Upwelling Pipe performance