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  • 2020-2024  (22)
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  • 1
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    Neotectonics of the Sea of Galilee (northeast Israel): implication for geodynamics and seismicity along the Dead Sea Fault system (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: The Sea of Galilee in northeast Israel is a freshwater lake filling a morphological depression along the Dead Sea Fault. It is located in a tectonically complex area, where a N-S main fault system intersects secondary fault patterns non-univocally interpreted by previous reconstructions. A set of multiscale geophysical, geochemical and seismological data, reprocessed or newly collected, was analysed to unravel the interplay between shallow tectonic deformations and geodynamic processes. The result is a neotectonic map highlighting major seismogenic faults in a key region at the boundary between the Africa/Sinai and Arabian plates. Most active seismogenic displacement occurs along NNW-SSE oriented transtensional faults. This results in a left-lateral bifurcation of the Dead Sea Fault forming a rhomb-shaped depression we named the Capharnaum Trough, located off-track relative to the alleged principal deformation zone. Low-magnitude (ML = 3–4) epicentres accurately located during a recent seismic sequence are aligned along this feature, whose activity, depth and regional importance is supported by geophysical and geochemical evidence. This case study, involving a multiscale/multidisciplinary approach, may serve as a reference for similar geodynamic settings in the world, where unravelling geometric and kinematic complexities is challenging but fundamental for reliable earthquake hazard assessments.
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  • 2
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    Geochemical characterization of deep-sea sediments on the Azores Plateau – From diagenesis to hydrothermal activity (2020)
    Elsevier
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    Publication Date: 2023-02-08
    Description: Highlights • Overview on geochemical composition of pore water and solid phase of sediments on the Azores Plateau. • Evidence for deep marine hydrothermal activity on the Azores Plateau. • Pore water data suggest ongoing anaerobic oxidation of methane and carbonate recrystallization. The Azores Plateau is an active magmatic region in the Central North Atlantic Ocean. In this study, we present a comprehensive data set of major element compositions and 87Sr/86Sr ratios of pore waters from surface sediments (0–9 mbsf) of the Azores Plateau. Based on distinct geochemical signatures we can separate normal marine from hydrothermally affected sediments. Normal marine sediments can further be differentiated by their ash content. Pore waters of ash rich gravity cores (GCs) do not show any deviations from seawater values except of a minor increase in Sr. In contrast, ash poor GCs generally show a trend for decreasing Ca with increasing depth, accompanied by a minor SO4 decrease and a more pronounced Sr increase. We suggest that these deviations are caused by processes such as anaerobic oxidation of methane and carbonate recrystallization. At four additional sample locations we observed a decrease in Mg and SO4 accompanied by a Ca increase in the pore waters, a pattern typical for hydrothermal fluids. The existence of hydrothermal systems in this region are corroborated by multi-channel seismic data, suggesting that sill or dyke intrusions are present in the subsurface close to the core locations. Overall, our observations offer preliminary indications for the existence of submarine hydrothermal systems on the Azores Plateau away from the Mid- Atlantic Ridge.
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  • 3
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    The Guaymas Basin Subseafloor Sedimentary Archaeome Reflects Complex Environmental Histories (2020)
    Elsevier
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    Publication Date: 2023-02-08
    Description: Highlights • Archaeal community composition reflects locally specific environmental challenges • Biogeochemical properties do not predict archaeal community structure • Environmental history controls subseafloor archaeal populations Summary We explore archaeal distributions in sedimentary subseafloor habitats of Guaymas Basin and the adjacent Sonora Margin, located in the Gulf of California, México. Sampling locations include (1) control sediments without hydrothermal or seep influence, (2) Sonora Margin sediments underlying oxygen minimum zone water, (3) compacted, highly reduced sediments from a pressure ridge with numerous seeps at the base of the Sonora Margin, and (4) sediments impacted by hydrothermal circulation at the off-axis Ringvent site. Generally, archaeal communities largely comprise Bathyarchaeal lineages, members of the Hadesarchaea, MBG-D, TMEG, and ANME-1 groups. Variations in archaeal community composition reflect locally specific environmental challenges. Background sediments are divided into surface and subsurface niches. Overall, the environmental setting and history of a particular site, not isolated biogeochemical properties out of context, control the subseafloor archaeal communities in Guaymas Basin and Sonora Margin sediments.
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  • 4
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    Impact of ambient conditions on the Si isotope fractionation in marine pore fluids during early diagenesis (2020)
    Copernicus Publications (EGU)
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    Publication Date: 2023-02-08
    Description: Benthic fluxes of dissolved silica (Si) from sediments into the water column are driven by the dissolution of biogenic silica (bSiO2) and terrigenous Si minerals and modulated by the precipitation of authigenic Si phases. Each of these processes has a specific effect on the isotopic composition of silica dissolved in sediment pore waters such that the determination of pore water δ30Si values can help to decipher the complex Si cycle in surface sediments. In this study, the δ30Si signatures of pore fluids and bSiO2 in the Guaymas Basin (Gulf of California) were analyzed, which is characterized by high bSiO2 accumulation and hydrothermal activity. The δ30Si signatures were investigated in the deep basin, in the vicinity of a hydrothermal vent field, and at an anoxic site located within the pronounced oxygen minimum zone (OMZ). The pore fluid δ30Sipf signatures differ significantly depending on the ambient conditions. Within the basin, δ30Sipf is essentially uniform averaging +1.2 ± 0.1 ‰ (1SD). Pore fluid δ30Sipf values from within the OMZ are significantly lower (0.0 ± 0.5 ‰, 1SD), while pore fluids close to the hydrothermal vent field are higher (+2.0 ± 0.2 ‰, 1SD). Reactive transport modelling results show that the δ30Sipf is mainly controlled by silica dissolution (bSiO2 and terrigenous phases) and Si precipitation (authigenic aluminosilicates). Precipitation processes cause a shift to high pore fluid δ30Sipf signatures, most pronounced at the hydrothermal site. Within the OMZ however, additional dissolution of isotopically depleted Si minerals (e.g. clays) facilitated by high mass accumulation rates of terrigenous material (MARterr) is required to promote the low δ30Sipf signatures while precipitation of authigenic aluminosilicates seems to be hampered by high water / rock ratios. Guaymas OMZ δ30Sipf values are markedly different from those of the Peruvian OMZ, the only other marine setting where Si isotopes have been investigated to constrain early diagenetic processes. These differences highlight the fact that δ30Sipf signals in OMZs worldwide are not alike and each setting can result in a range of δ30Sipf values as a function of the environmental conditions. We conclude that the benthic silica cycle is more complex than previously thought and that additional Si isotope studies are needed to decipher the controls on Si turnover in marine sediment and the role of sediments in the marine silica cycle.
    Type: Article , PeerReviewed
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  • 5
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    3-D Dynamics of a natural gas hydrate system in the western Black Sea (2023)
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    Publication Date: 2023-11-30
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
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    Thermal state of the Guaymas Basin derived from gas hydrate bottom simulating reflections and heat flow measurements (2022)
    AGU (American Geophysical Union) | Wiley
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    Publication Date: 2024-02-07
    Description: Seafloor heat flow provides information about the thermal evolution of the lithosphere, the magnitude and timing of volcanic activity, and hydrothermal circulation patterns. In the central Gulf of California, the Guaymas Basin is part of a young marginal spreading rift system that experiences high sedimentation (1–5 km/Myr) and widespread magmatic intrusions in the axial troughs and the off-axis regions. Heat flow variations record magmatic and sedimentary processes affecting the thermal evolution of the basin. Here, we present new seismic evidence of a widespread bottom-simulating reflection (BSR) in the northwestern Guaymas Basin. Using the BSR depths and thermal conductivity measurements, we determine geothermal gradient and surface heat flow variations. The BSR-derived heat flow values are less than the conductive lithospheric heat flow predictions for mid-oceanic ridges. They suggest that high sedimentation (0.3–1 km/Myr) suppresses the lithospheric heat flow. In the central and southeastern regions of the basin, the BSR-derived geothermal gradient increases as the intruded magmatic units reach shallower subsurface depths. Thermal modeling shows that recent (〈5000 years) igneous intrusions (〈500 m below the seafloor) and associated fluid flow elevate the surface heat flow up to five times. BSR-derived geothermal gradients correlate little with the depth of the shallowest magmatic emplacements to the north, where the intrusions have already cooled for some time, and the associated hydrothermal activity is about to shut down. Key Points - A regional bottom-simulating reflection (BSR) in the Guaymas Basin indicates a widespread occurrence of gas hydrates - The BSR derived thermal gradients show wavy patterns farther away from the spreading centre, indicating strong lateral heat flow variations - High sedimentation suppresses heat flow, while recent magmatic intrusion and fluid advection increase heat flow
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 7
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    Offshore freshened groundwater in continental margins (2021)
    AGU (American Geophysical Union) | Wiley
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    Publication Date: 2024-02-07
    Description: First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyse it to establish the general characteristics and controlling factors. We also assess methods used to map and characterise OFG, identify major knowledge gaps and propose strategies to address them. OFG has a global volume of 1 million km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea‐level lowstands. Key factors influencing OFG distribution are topography‐driven flow, salinisation via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection, electromagnetic surveys and mathematical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three‐dimensional hydrological models. We show that such advances, combined with site‐specific modelling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub‐seafloor geomicrobiology.
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  • 8
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    Interactions between temperature and energy supply drive microbial communities in hydrothermal sediment (2021)
    Nature Research
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    Publication Date: 2024-02-07
    Description: Temperature and bioavailable energy control the distribution of life on Earth, and interact with each other due to the dependency of biological energy requirements on temperature. Here we analyze how temperature-energy interactions structure sediment microbial communities in two hydrothermally active areas of Guaymas Basin. Sites from one area experience advective input of thermogenically produced electron donors by seepage from deeper layers, whereas sites from the other area are diffusion-dominated and electron donor-depleted. In both locations, Archaea dominate at temperatures 〉45 °C and Bacteria at temperatures 〈10 °C. Yet, at the phylum level and below, there are clear differences. Hot seep sites have high proportions of typical hydrothermal vent and hot spring taxa. By contrast, high-temperature sites without seepage harbor mainly novel taxa belonging to phyla that are widespread in cold subseafloor sediment. Our results suggest that in hydrothermal sediments temperature determines domain-level dominance, whereas temperature-energy interactions structure microbial communities at the phylum-level and below.
    Type: Article , PeerReviewed
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  • 9
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    Recycling and burial of biogenic silica in an open margin oxygen minimum zone (2021)
    AGU (American Geophysical Union) | Wiley
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    Publication Date: 2024-02-07
    Description: An extensive data set of biogenic silica (BSi) fluxes is presented for the Peruvian oxygen minimum zone (OMZ) at 11ºS and 12ºS. Each transect extends from the shelf to the upper slope (∼1000 m) and dissects the permanently anoxic waters between ∼200 – 500m water depth. BSi burial (2100 mmol m‐2 yr‐1) and recycling fluxes (3300 mmol m‐2 yr‐1) were highest on the shelf with mean preservation efficiencies (34±15%) that exceed the global mean of 10 – 20%. BSi preservation was highest on the inner shelf (up to 56%), decreasing to 7% and 12% under anoxic waters and below the OMZ, respectively. The data suggest that the main control on BSi preservation is the rate at which reactive BSi is transported away from undersaturated surface sediments by burial and bioturbation to the underlying saturated sediment layers where BSi dissolution is thermodynamically and/or kinetically inhibited. BSi burial across the entire Peruvian margin between 3ºS to 15ºS and down to 1000m water depth is estimated to be 0.1 – 0.2 Tmol yr‐1; equivalent to 2 – 7% of total burial on continental margins. Existing global data permit a simple relationship between BSi rain rate to the seafloor and the accumulation of unaltered BSi, giving the possibility to reconstruct rain rates and primary production from the sediment archive in addition to benthic Si turnover in global models.
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  • 10
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    Oceanic strike-slip faults represent active fluid conduits in the abyssal sub-seafloor (2022)
    GSA (Geological Society of America)
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    Publication Date: 2024-02-07
    Description: We present pore-fluid geochemistry and heat-flow data along the SWIM1 fault in the Horseshoe Abyssal Plain (northeastern Atlantic Ocean). The SWIM1 fault is part of the transcurrent plate boundary between Africa and Eurasia and cuts through as much as 5-km-thick sediments overlying 〉140 Ma oceanic lithosphere. In a number of places, restraining segments (as long as 15 km) of the SWIM1 fault generate anticlines (positive flower structures) that protrude as ~100-m-high hills above the abyssal plain. Heat flow and gradients of dissolved constituents in pore water are enhanced at these seafloor highs. Transport-reaction modeling confirms that slow advection of deep-seated fluids, depleted in Mg and enriched in Sr and CH4, can explain the observations. The geochemical signature is similar to the one observed at deep-sea mud volcanoes located eastward on the SWIM1 fault. The upward-migrating fluids have interacted with carbonate rocks at maximum 5 km depth, which represent the oldest sedimentary unit on top of the basement. We argue that deep-rooted fluids can generally be mobilized and transported upward along flower structures that formed in restraining-bend segments of long strike-slip faults. Such tectonic settings represent largely unrecognized corridors for mass exchange between lithosphere and ocean.
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