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Strike-Slip Versus Extensional Tectonics at the Oceanographer Transform Fault, Mid-Atlantic Ridge at 35°N
No full textOceanic transform faults and their fracture zones are among the most striking features of ocean basins. Plate tectonics describes them as strike-slip zones connecting mid-ocean ridge segments. Still, no generally accepted theory exists for the lateral strain partitioning resulting in the deep and wide transform valleys and extensively tectonized inside corners. Here, we present results from multibeam bathymetry and a micro-seismicity survey from the slow-slipping Oceanographer transform on the Mid-Atlantic Ridge near 35°N. Swath-mapping echosounder data reveal a segmented transform fault. Away from the ridge-transform intersections (RTI) and in the eastern half of the transform valley, micro-earthquakes recorded on ocean-bottom-seismometers focus along the observed fault strands. Approaching the RTI, however, many micro-earthquakes cut across the inside corner, while the active faults step toward the inside corner, paralleling the trend of the transform valley. Focal mechanisms point to extension in the inside corner region, while strike-slip deformation is only recorded at distances larger than 15 km and away from the RTIs. These observations support a scenario in which deformation beneath a right-angular ridge-transform boundary at the seafloor develops into an oblique shear zone at depth, causing crustal thinning and consequently forming transform valleys. Away from RTIs, seismicity is focused on a narrow and segmented strike-slip fault as predicted by plate tectonics. Oceanic transform faults are consequently not only strike-slip but are also shaped by extensional processes, arguing for a revision of the concept of conservative plate boundaries to account for their morphology, segmentation, and significant lateral differences in seismic behavior.
Key Points
The Oceanographer transform is morphologically and seismically segmented, outlining systematic changes of stress patterns
At distances >15 km from the ridge-transform intersections, the transform fault is a narrow zone of deformation, with strike-slip faulting
Near ridge-transform intersections, deformation is distributed and cross-cuts the inside corner, issuing normal faulting and nurturing a wide valle
Numerical flow analysis for hull shape optimization of an autonomous underwater vehicle
No full textIn this study, the nose geometry of AUV Poseidon, developed by the GEOMAR Helmholtz Centre for Ocean Research Kiel, was improved to increase the operating time of the vehicle. Starting with a spherical nose shape, various elliptical geometry variants were analysed and compared. Numerical flow simulations (FV-RANS, k-ω SST turbulence model, gamma theta transition model) and results from model tests with scaled AUV models were compared. To analyse the characteristics of the flow and to analyse the transition from laminar to turbulent flow, the local friction coefficient was evaluated. Different turbulent transport quantities (u+, k+, turbulent eddy viscosity) are visualized and discussed. The analysis reveals a more uniform flow behaviour and a reduction of the resistance in the range of 32% due to the improved nose geometry and the fairing of the sensors. The tail section was not subject to modification
"Es wird immer schlimmer werden"
No full textKlimaforscher Mojib Latif wundert sich, dass der Klimaschutz nicht oben auf der Tagesordnung steh
Connectivity and Adaptation Patterns of the Deep-Sea Ground-Forming Sponge Geodia hentscheli Across Its Entire Distribution
No full textGeodia hentscheli, a species forming sponge grounds in the North Atlantic and Arctic Oceans, is a common deep-sea organism, that plays a fundamental role in forming biogenic habitats. However, there is little information about gene flow and adaptation patterns of this species, which is crucial to develop effective management/conservation plans under current global change scenarios. Here, we generated ddRADseq data from 110 specimens of G. hentscheli, together with microbial profiling, transcriptomics, and metatranscriptomics for a selection of specimens to investigate their genetic diversity, molecular connectivity, and local adaptations. Sampling covered the species' entire distribution within a wide bathymetric range. We obtained 1,115 neutral SNPs and identified long-distance genetic connectivity among regions separated 1,000s of km, but strong genetic structure segregating populations by depth at ca. 1,300 m, in line with our microbial analyses. Coalescent analyses inferred the split of these depth-related genetic entities similar to 10 KYA, coincident with the last postglacial maximum. Analyses of SNPs under selection, combined with transcriptomic and metatranscriptomic data highlight the presence of several sponge genes and microbial metabolic pathways involved in adaptation to depth, including heat shock proteins and fatty acids, among others. The physiological plasticity of the sponge and its microbiome as a function of depth suggest the existence of a host-microbiome metabolic compensation for G. hentscheli. This study provides a multiscale paradigmatic example of the depth-differentiation hypothesis, a phenomenon mainly caused by changes in environmental conditions at different depths, mainly related to the presence of water masses with different characteristics that drive local adaptations
3D reservoir quality estimation of the Lower Volpriehausen Unit in the Eastern German North Sea: A statistic and stochastic modelling approach
No full textHighlights:
• 3D model to assess reservoir quality of sandstones on West Schleswig Block.
• Lower Volpriehausen sandstones show variable thickness and porosity distributions.
• Distribution maps of reservoir quality aid future storage site evaluations.
• Results aid dynamic models to evaluate CO2 storage in the Germany North Sea.
Carbon dioxide (CO2) storage in deeply buried sandstones can contribute to the mitigation of greenhouse gas emissions, particularly from hard-to-abate industrial sectors. Triassic sandstones of the Middle Buntsandstein Subgroup on the West Schleswig Block offer favourable conditions to act as potential storage reservoir. While previous studies focused on regional assessments of trap structures and static capacity estimations, this is the first assessment of the extent and quality of the reservoir itself. We have created a 3D model of the West Schleswig Block to assess the reservoir quality and spatial distribution of the basal sandstones of the Volpriehausen Formation, the primary reservoir of the Middle Buntsandstein Subgroup in this region, at top depths between 2121 m (P10) and 2854 m (P90). To this end, we have developed parameter models for shale content, effective porosity, and permeability to obtain regional trend maps. Our results show that the Lower Volpriehausen Unit exhibit good lateral continuity, with a median thickness of 43 m (ranging from 25 m to 85 m) and a mean porosity of 21 % (12 % - 28 %, P10-P90). Locally, low porosities are primarily caused by high shale content and diagenetic cementation. These findings indicate variable reservoir quality for formerly mapped reservoir structures on the West Schleswig Block, which has to be considered in future carbon storage exploration efforts. Our study can facilitate future developments in the screening and evaluation of potential storage sites in the German North Sea and presents a valuable resource for local CO2 storage capacity models
Transient modeling for ocean redox conditions during the mid-cretaceous Oceanic Anoxic Event 2
No full textHighlights
• Increased nutrient input and phosphate recycling are essential in OAE2 anoxia.
• Enhanced ventilation during the cool interval contributes to the reoxygenation.
• A modest P weathering flux increase is sufficient to trigger widespread OAE2 anoxia.
Reconstructions of the mid-Cretaceous Oceanic Anoxic Event 2 (OAE2) indicate that the ocean redox state was temporally and spatially heterogeneous. Its evolution is considered to be induced by the variation of atmospheric carbon dioxide concentrations (pCO2) due to the activities of large igneous provinces (LIPs) and associated changes in global meridional overturning circulation, nutrient input, and phosphorus recycling. However, their respective roles on the OAE2 are still under debate. Here, we conduct transient numerical simulations using an intermediate-complexity Earth system model with reconstructed pCO2 values. In our simulations, bottom anoxia occurred in the equatorial Atlantic Ocean and the Tethyan rim before OAE2. This changed only slightly with varying pCO2. In contrast, increasing nutrient concentrations due to increased continental weathering can lead to a marked increase in anoxic areas, which is further expanded by enhanced phosphorus recycling in the low-oxygen marine area. The North Atlantic, low-latitude South Atlantic, Southeast Pacific, and Western Tethys oceans are most prone to developing bottom water anoxia. The modeled anoxic areas exhibit distinctly different spatio-temporal patterns during OAE2 with varying weathering intensities. Comparison of the simulation results with newly assembled geological records suggests that anoxic bottom water only accounted for ∼20–40% of the global bottom area and that the continental phosphorus weathering intensity was increased by ∼40–60% compared to the pre-OAE2 level
Charting the course to cleaner shipping routes: emission inventory for Baltic Sea shipping and green fuel potential
No full textThis study presents a high-resolution shipping emission inventory for the Baltic Sea, assessing the environmental impacts of four fuel-based scenarios under a projected threefold increase in gross tonnage by 2050. The study evaluates how regulatory changes and alternative fuels, such as hydrogen and ammonia, can reduce emissions and advance sustainability in shipping. The study uses a bottom-up approach, combining activity data, fuel data, and emission factors to estimate tank-to-wake emissions. Comparative analysis indicates improved emissions prediction across all pollutants. While use of liquefied natural gas (LNG) and scrubber-equipped ships reduce sulphur oxides (SOx) emissions, they incur notable environmental trade-offs. By 2050, significant reductions in particulate matter (99%) and carbon dioxide are projected, while SOx emissions are expected to approach zero using hydrogen, ammonia, and methanol fuels. These reductions are helped by the decline in traditional fuels and technological progress. The current transition to cleaner marine fuels is insufficient to meet the IMO’s 2030 and 2050 carbon reduction targets. While tank-to-wake contributes significantly toward emissions reduction, a broader focus on the well-to-wake approach is also critical for achieving net-zero emissions by 2050. Policy efforts should accelerate the adoption of green fuels and address challenges such as methane slip from LNG-powered ships
Connecting Tibetan Plateau Snow Change With Arctic Sea‐Ice
No full textDocumenting changes in the Arctic sea‐ice variability are essential for understanding the spring sea‐ice predictability barrier. While Tibetan Plateau snow cover (TPSC) has been linked to Arctic sea‐ice variability, the spatiotemporal stability of this relationship remains unclear. In this study, combing satellite observations and snow experiments, we identified a shift in connections between TPSC and Barents‐Kara Seas sea‐ice around 1990. Before 1990, a positive dipole TPSC pattern (eastern enhanced/western reduced snow cover) induces Arctic anticyclonic anomalies through a circumglobal wave train. These anomalies facilitate polar vortex splitting, enhancing moisture transport and solar radiation over the northern Kara Sea, which accelerates sea‐ice reduction. Conversely, post‐1990, a positive monopole TPSC pattern (positive snow anomalies on the entire Tibetan Plateau) strengthens the polar vortex, suppressing Barents Sea (BS) moisture and solar radiation, thereby promoting sea‐ice growth. This regime shifts underscore TPSC's capacity to modulate Arctic sea‐ice dynamics through polar vortex system.
Plain Language Summary
Investigating the causes and driving mechanisms behind year‐to‐year variations in Arctic sea‐ice is important for understanding its spring prediction barrier. This study reveals how shifting snow patterns on the Tibetan Plateau (TP), Earth's Third Pole, drive Arctic sea‐ice fluctuations. Before 1990, positive phase of out‐phase TP snow distribution (heavier snow in the Plateau's east and lighter snow in the west) favors Arctic anticyclonic circulation anomalies (wind pattern). Such wind distribution weakens the polar vortex, a key circulation system, and promoting warm, moist air into the northern Kara Sea. This combination melts sea‐ice rapidly. After 1990, positive phase of TP snow cover (unform snow gains across the Tibetan) strengthens the polar vortex, blocking warm and air inflow to the Barents Sea and allowing ice growth. These findings show how Tibetan snow changes “steer” Arctic sea‐ice conditions through atmospheric waves and energy shifts, offering mechanistic insights to seasonal sea‐ice predictability.
Key Points
The Tibetan Plateau snow cover (TPSC)‐Arctic sea‐ice linkage has experienced a regime shift around 1990
TPSC‐driven Arctic circulation anomalies regulate the TPSC‐sea‐ice connection through modulating polar vortex dynamics
TPSC phase transitions modulate Arctic sea‐ice melt and growth via affecting moisture and solar radiation anomalie
How To: OSIS Device and O2A Registry
No full textAssigning a Device in OSIS is implemented via the O2A-Registry, the meta database for research devices, hosted by AWI. This instruction is a step by step guide on how to register a new device in O2A-registry and how to link the device to the OSIS catalogue
Tropical climate variability and coral reefs-a past to future perspective on current rates of change at ultra-high resolution
No full textClimate change, in particular the rise in tropical sea surface temperatures, is the greatest threat to coral reef ecosystems today and causes climatic extremes affecting
the livelihood of tropical societies. Assessing how future warming will change coral reef ecosystems and tropical climate variability is therefore of extreme urgency. Ultra-high resolution (monthly, weekly) coral geochemistry provides a tool to understand the temporal response of corals and coral reefs to ongoing climate and environmental change, to reconstruct past tropical climate and environmental variability, and to use these data in conjunction with advanced statistical methods, earth system modelling and observed ecosystem responses for improved projections of future changes in tropical climate and coral reef ecosystems. The recently established Priority Programme “Tropical Climate Variability and Coral Reefs - A Past
to Future Perspective on Current Rates of Change at Ultra-High Resolution” (SPP 2299, https://www.spp2299.tropicalclimatecorals.de/) of the German Research Foundation (DFG) aims to enhance our current understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world, by quantifying climatic and environmental changes during both the ongoing warming and past warm periods on timescales relevant for society. The programme aims to provide an ultra–high resolution past to future perspective on current
rates of change to project how tropical marine climate variability and coral reef ecosystems will change in a warming world. Information on the organizational structure and research topics of this collaborative programme, which involves ten universities and five research centres from
all over Germany, will be provided