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  • 1
    Publication Date: 2022-10-25
    Description: The seismic receiver function (RF) technique is widely used as an economic method to image earth's deep interior in a large number of seismic experiments. P-wave receiver functions (RFs) constrain crustal thickness and average Vp/Vs in the crust by analysis of the Ps phase and multiples (reflected/converted waves) from the Moho. Regional studies often show significant differences between the Moho depth constrained by RF and by reflection/refraction methods. We compare the results from RF and controlled source seismology for the Baikal Rift Zone by calculating 1480 synthetic RFs for a seismic refraction/reflection velocity model and processing them with two common RF techniques [H–κ and Common Conversion Point (CCP) stacking]. We compare the resulting synthetic RF structure with the velocity model, a density model (derived from gravity and the velocity model), and with observed RFs. Our results demonstrate that the use of different frequency filters, the presence of complex phases from sediments and gradual changes in the properties of crustal layers can lead to erroneous interpretation of RFs and incorrect geological interpretations. We suggest that the interpretation of RFs should be combined with other geophysical methods, in particular in complex tectonic regions and that the long-wavelength Bouguer gravity anomaly signal may provide effective calibration for the determination of the correct Moho depth from RF results. We propose and validate a new automated, efficient method for this calibration.
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  • 2
    Publication Date: 2022-11-02
    Description: The investigation of innovative macroalgal cultivation is important and needed to optimize farming operations, increase biomass production, reduce the impact on the ecosystem, and lower system and operational costs. However, most macroalgal farming systems (MFSs) are stationary, which need to occupy a substantial coastal area, require extensive investment in farm infrastructure, and cost high fertilizer and anchoring expenses. This study aims to model, analyze, and support a novel binary species free-floating longline macroalgal cultivation concept. The expected outcomes could provide a basis for the design and application of the novel MFS to improve biomass production, decrease costs, and reduce the impact on the local ecosystem. In this paper, Saccharina latissima and Nereocystis luetkeana were modeled and validated, and coupled with longline to simulate the binary species MFS free float in various growth periods and associated locations along the US west coast. The numerical predictions indicated the possibility of failure on the longline and breakage at the kelp holdfasts is low. However, the large forces due to an instantaneous change in dynamic loads caused by loss of hydrostatic buoyancy when the longline stretches out of the water would damage the kelps. Buoy-longline contact interactions could damage the buoy, resulting in the loss of the system by sinking. Furthermore, the kelp-longline and kelp-kelp entanglements could potentially cause kelp damage.
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  • 3
    Publication Date: 2022-11-23
    Description: The economics of biodiversity is gaining traction and with it the economic valuation of ecosystem services (ESS). Most current developments neglect microbial diversity, although microbial communities provide ecosystem services of great importance. Here we argue that microbial biodiversity (hereafter microbiodiversity) translates into considerable economic value which is usually not explicitly included in quantitative valuation of ecological functions to date. This omission may result in inaccurate values, potentially entailing substantial economic losses, both in private and in public decision-making, due to external effects that arise as microbiodiversity is horizontally and vertically transferred between hosts and natural environments. Microbiodiversity, an important part of biodiversity in general, occupies an irreplaceable position as a natural resource in ecosystems, because of option values derived from the evolutionary potential of microbes, especially if host-associated, and also because of their additional insurance value within changing environments. We illustrate our arguments with specific examples (microbiomes associated with humans, soil, and corals), all of which are jeopardized through anthropogenic pressure. We conclude that the consideration of microbiodiversity in economic valuation will help to find essential assets and guide decision-makers to conserve and protect the economic value of highly diverse microbial communities for future generations.
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  • 4
    Publication Date: 2022-11-23
    Description: Stable barium (Ba) isotopes are emerging as tracers for the recycling of crustal material into the mantle. Small but significant Ba isotope variations have been found in global MORB (δ138/134Ba values of −0.04‰ to 0.15‰), but the processes causing these Ba isotope variations remain poorly understood. In addition, uncertainties still exist in the estimate of the Ba isotope composition of the depleted upper mantle. Here, we present a systematic study of Ba isotopes for well-characterized MORB glass samples from the South Mid-Atlantic Ridge (SMAR) between 5 and 11°S, which span a wide range of radiogenic isotope ratios and trace element contents. Our results show that the northernmost segment A0 basalts with highly depleted radiogenic isotope compositions have δ138/134Ba values ranging from −0.02 to 0.05‰. In comparison, the δ138/134Ba values of the isotopically enriched basalts from the A1-A4 segments vary from 0.02 to 0.11‰. Thus, while small, the enriched components involved can be observed to modify the Ba isotope composition of the mantle source beneath A1-A4 segments. Combining our new measurements with literature data, this study places new constraints on the Ba isotope composition of the depleted upper mantle, as well as the origin of Ba isotope heterogeneity in MORB. The Ba isotope composition of the depleted upper mantle in the absence of recycled components is estimated to have a δ138/134Ba value of 0.03 to 0.05‰, which can be adopted as the baseline for using Ba isotope ratios as a tracer of mass transfer processes between the crust and mantle. In comparison, global MORB have δ138/134Ba values ranging from −0.04‰ to 0.15‰. No global correlation is observed between Ba isotope ratios and geochemical parameters that record mantle enrichment, indicating that the Ba isotope variations in MORB cannot be simply ascribed to the addition of some single component, such as sediment. Models for melting and mixing between recycled materials and depleted mantle suggest that the variable Ba isotope compositions of the enriched MORB require a contribution from recycled altered oceanic crust and crustal sedimentary materials. Therefore, these recycled components both play important roles in the chemical budget of the convecting upper mantle, especially for incompatible elements such as Ba.
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  • 5
    Publication Date: 2022-11-25
    Description: This literature review presents major environmental indicators and their optimum variation ranges for the prevalence of Vibrio parahaemolyticus in the marine environment by critically reviewing and statistically analyzing more than one hundred studies from countries around the world. Results of this review indicated that the prevalence of Vibrio parahaemolyticus in the marine environment is primarily responsive to favorable environmental conditions that are described with environmental indicators. The importance of environmental indicators to the prevalence of Vibrio parahaemolyticus can be ranked from the highest to lowest as Sea Surface Temperature (SST), salinity, pH, chlorophyll a, and turbidity, respectively. It was also found in this study that each environmental indicator has an optimum variation range favoring the prevalence of Vibrio parahaemolyticus. Specifically, the SST range of 25.67 ± 2 °C, salinity range of 27.87 ± 3 ppt, and pH range of 7.96 ± 0.1 were found to be the optimum conditions for the prevalence of Vibrio parahaemolyticus. High vibrio concentrations were also observed in water samples with the chlorophyll a range of 16–25 μg/L. The findings provide new insights into the importance of environmental indicators and their optimum ranges, explaining not only the existence of both positive and negative associations reported in the literature but also the dynamic associations between the Vibrio presence and its environmental drivers.
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  • 6
    Publication Date: 2022-12-07
    Description: The United Nations is dedicated to bringing countries together to solve international problems and to shape a better future. One of the greatest challenges facing society today is meeting the population’s basic needs, while protecting the environment, hence the UN Sustainable Development Goals — 17 goals to overcome current and future sustainability challenges. We incorporate the 17 goals into a simplified global socio-ecological model to analyze what actions are necessary to promote a desirable future. We find that the current population size and resource use are not sustainable with any one goal or combination of goals. In the sustainable scenarios described here the global population decreases, while maintaining higher consumption levels. We estimate that sustainability hinges on maintaining an equivalence between natural and agricultural land areas and the human population — approximately 1ha of land per person is necessary to promote human well-being and environmental sustainability. Furthermore, we find that long-term sustainability hinges on changes within the next 50 years and goals that solely target environmental degradation or consumption are too slow to drive sustainability. Social progress is occurring much faster than environmental progress, therefore actions that target shifts in power dynamics, inequality, development and education in lower income countries should be prioritized to maintain ecosystem services and promote well-being. The goals that incorporate a combination of socio-ecological policies (SDGs 3,6,8,9,10,11) promote well-being and sustainability.
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  • 7
    Publication Date: 2022-12-12
    Description: Although parasitism is one of the most common species interactions in nature, the role of parasites in their hosts' thermal tolerance is often neglected. This study examined the ability of the trematode Podocotyle atomon to modulate the feeding and stress response of Gammarus locusta towards temperature. To accomplish this, infected and uninfected females and males of Gammarus locusta were exposed to temperatures (2, 6, 10, 14, 18, 22, 26, 30 °C) for six days. Shredding (change in food biomass) and defecation rates (as complementary measure to shredding rate) were measured as proxies for feeding activity. Lipid and glycogen concentrations (energy reserves), catalase (oxidative stress indicator), and phenoloxidase (an immunological response in invertebrates) were additionally measured. Gammarid survival was optimal at 10 °C as estimated by the linear model and was unaffected by trematode infection. Both temperature and sex influenced the direction of infection effect on phenoloxidase. Infected females presented lower phenoloxidase activity than uninfected females at 14 and 18 °C, while males remained unaffected by infection. Catalase activity increased at warmer temperatures for infected males and uninfected females. Higher activity of this enzyme at colder temperatures occurred only for infected females. Infection decreased lipid content in gammarids by 14 %. Infected males had significantly less glycogen than uninfected, while infected females showed the opposite trend. The largest infection effects were observed for catalase and phenoloxidase activity. An exacerbation of catalase activity in infected males at warmer temperatures might indicate (in the long-term) unsustainable, overwhelming, and perhaps lethal conditions in a warming sea. A decrease in phenoloxidase activity in infected females at warmer temperatures might indicate a reduction in the potential for fighting opportunistic infections. Results highlight the relevance of parasites and host sex in organismal homeostasis and provide useful insights into the organismal stability of a widespread amphipod in a warming sea.
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  • 8
    Publication Date: 2022-12-12
    Description: Microplastics are substrates for microbial activity and can influence biomass production. This has potentially important implications in the sea-surface microlayer, the marine boundary layer that controls gas exchange with the atmosphere and where biologically produced organic compounds can accumulate. In the present study, we used six large scale mesocosms to simulate future ocean scenarios of high plastic concentration. Each mesocosm was filled with 3 m3 of seawater from the oligotrophic Sea of Crete, in the Eastern Mediterranean Sea. A known amount of standard polystyrene microbeads of 30 μm diameter was added to three replicate mesocosms, while maintaining the remaining three as plastic-free controls. Over the course of a 12-day experiment, we explored microbial organic matter dynamics in the sea-surface microlayer in the presence and absence of microplastic contamination of the underlying water. Our study shows that microplastics increased both biomass production and enrichment of carbohydrate-like and proteinaceous marine gel compounds in the sea-surface microlayer. Importantly, this resulted in a ∼3 % reduction in the concentration of dissolved CO2 in the underlying water. This reduction was associated to both direct and indirect impacts of microplastic pollution on the uptake of CO2 within the marine carbon cycle, by modifying the biogenic composition of the sea's boundary layer with the atmosphere.
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  • 9
    Publication Date: 2022-12-13
    Description: Knowledge of temporal patterns of past explosive eruptions is necessary to understand possible future eruptive behavior. However, volcanic records based on geological reconstructions remain incomplete. This inference is true not only for remote and sparsely populated areas like the Aleutian or Kurile-Kamchatka arcs, but also for Europe, where past large explosive events are continuously recognized in the geological record. Here we report the first age and geochemical data on the violent middle to late Pleistocene explosive eruptions from the Elbrus volcanic center (Greater Caucasus), which towers over the densely populated regions in southern Russia and Georgia. We attribute six disparate ash deposits found in the terrestrial and marine sediments along the SE European margin to the Elbrus volcanic center based on major and trace element compositions of individual shards of volcanic glass and radiogenic Sr-Nd-Pb isotope compositions of bulk tephra. We suggest that these deposits represent products of five different eruptions that were dispersed over distances of more than 150–560 km from their source. Three of four eruptions are dated at 522 ± 36, 258 ± 13, and 84.6 ± 7.4 ka by a combined zircon U–Th–Pb and (U–Th)/He approach. One sample revealed an overdispersed spectrum of single crystal (U–Th)/He dates with an average of 176 ± 40 ka. Zircon characteristics and statistical deconvolution of the geochronology data suggest that this sample contains zircon crystals from two different eruptions tentatively dated at 156.5 ± 7.7 ka and 222.8 ± 13 ka. These eruption ages represent the first recognition of a suite of large pumiceous eruptions from the Elbrus volcanic center postdating the previously known explosive activity, documented by ∼800 ka old welded tuffs. These data also provide the first geochemical and geochronological characterization of both proximal and distal Elbrus tephra glasses and contribute to the global tephra database, permitting the identification of Elbrus tephras in distal terrestrial and marine paleoenvironmental archives and hence their use as paleoclimate and archaeological markers. We consider the significance of the identified tephras for paleoenvironmental research and show their potential for tephrochronological studies in the East European Plain and adjacent areas.
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  • 10
    Publication Date: 2022-12-15
    Description: Highlights • Role of salt leaching in seafloor stability is assessed via experiments and models. • Undrained cohesive strength of clayey silt subjected to leaching decreased by 50%. • Failure occurs when flushed layer is 〉3.5 m thick and slope gradient is 〉3°. Abstract Offshore freshened groundwater (OFG) has been documented in many continental margins worldwide. OFG systems are dynamic, expanding and contracting with falling and rise sea-levels. OFG has long been thought to be an important geomorphic agent in continental margins, either via active discharge at the seafloor, which can erode depressions, or the generation of excess pore pressure, which can deform sediments and cause slope failure. It has also been proposed that OFG flow can drive the loss of sediment shear strength via salt leaching, when seawater in pores is replaced by freshwater. Here, we measure changes in the geotechnical properties of seafloor clayey silt due to salt leaching using flushing experiments, and assess the implications of these changes on the stability of siliciclastic continental margins with 2D limit equilibrium modelling. We document a ~ 50% decrease in undrained cohesive strength of seafloor sediment after flushing, as well as a decrease in its shear strength, bulk density, and moisture content, which is similar to that reported for subaerial quick clays undergoing salt leaching. When applied to a theoretical submarine domain 300 m wide by 100 m high, we estimate that salt leaching can trigger slope failure when the thickness of the flushed layer is 〉3.5 m or when the slope gradient is 〉3°. Such conditions are primarily satisfied on the continental slope or the shallow seafloor close to the shoreline. Salt leaching by OFG flow merits consideration as a potential mechanism destablising submarine sedimentary slopes.
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  • 11
    Publication Date: 2022-12-19
    Description: Highlights • The hydrothermal fluids were sampled from a neovolcanic ridge within a non-transform offset. • Serpentinization has been involved on the pathway of hydrothermal circulation • The fluids are strongly affected by phase separation with extremely high Cl content in brine phase • A hybrid model of hydrothermal circulation controlled by tectonic and magmatic activities simultaneously was proposed. The Daxi Vent Field (DVF) is located on a neovolcanic ridge within a non-transform offset at water depths of ∼3500 m, on the Carlsberg Ridge, northwest Indian Ocean. In 2017, we investigated this site using the submersible Jiaolong and collected two fluid samples from orifices of chimneys named “Buddha's Hands” and “A1”, about 37 m apart. Their in-situ measured temperatures are 273 °C and 272 °C, respectively. The Buddha's Hands fluid is highly Cl-enriched (928 mM), while the A1 fluid is Cl-depleted (303 mM). This indicates that they have undergone phase separation. The segregated phases must have remixed during the ascent because the vapor and brine phases sampled cannot be produced by the same phase separation history without other processes. Olivine-rich and/or ultramafic mantle rocks must have been involved during the hydrothermal circulation as evidenced by high dissolved H2 (7.07 mM) and methane (0.884 mM) concentrations, a depletion in B relative to seawater, high Ca and low K, and large positive Eu anomalies. The Fe content in Buddha's Hands fluid is extremely high (11,900 μM) as a result of phase separation, while the Cu concentrations in both fluids are relatively low due to entrainment of seawater which results in precipitation of Cu-rich sulfides in the subseafloor. The concentrations of Zn, Ag, Ga, Sn, Sb, and Cd in A1 vent fluid are significantly elevated due to generation of acidity and remobilization of these elements as Cu-rich sulfides are deposited. The subseafloor processes and associated geochemistry of hydrothermal fluids at the DVF are distinct from other mid-ocean ridge hydrothermal systems due to the specific geologic setting. Hence a hybrid model of hydrothermal circulation is proposed. This study broadens our understanding of the hydrothermal processes occurring in areas of NTO setting and provides more information on mass fluxes discharging from hydrothermal systems and the formation of sulfide deposits.
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  • 12
    Publication Date: 2022-12-19
    Description: We interpret the crustal and upper mantle structure along ∼2500 km long seismic profiles in the northeastern part of the Sino-Korean Craton (SKC). The seismic data with high signal-to-noise ratio were acquired with a nuclear explosion in North Korea as source. Seismic sections show several phases including Moho reflections (PmP) and their surface multiple (PmPPmP), upper mantle refractions (P), primary reflections (PxP, PL, P410), exceptionally strong multiple reflections from the Moho (PmPPxP), and upper mantle scattering phases, which we model by ray-tracing and synthetic seismograms for a 1-D fine-scale velocity model. The observations require a thin crust (30 km) with a very low average crustal velocity (ca. 6.15 km/s) and exceptionally strong velocity contrast at the Moho discontinuity, which can be explained by a thin Moho transition zone (〈 5 km thick) with strong horizontal anisotropy. We speculate that this anisotropy was induced by lower crustal flow during delamination dripping. An intra-lithospheric discontinuity (ILD) at ∼75 km depth with positive velocity contrast is probably caused by the phase transformation from spinel to garnet. Delayed first arrivals followed by a long wave train of scattered phases of up to 4 s duration are observed in the 800–1300 km offset range, which are modelled by continuous stochastic velocity fluctuations in a low-velocity zone (LVZ) below the Mid-Lithospheric Discontinuity (MLD) between 120 and 190 km depth. The average velocity of this LVZ is about 8.05 km/s, which is much lower than the IASP91 standard model. This LVZ is most likely caused by rocks which are either partially molten or close to the solidus, which explains both low velocity and the heterogeneous structure.
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  • 13
    Publication Date: 2022-12-22
    Description: This chapter aims at introducing the reader to general concepts about the main forcings of the Mediterranean Sea, in terms of exchanges through the Strait of Gibraltar, and air-sea exchanges of heat, freshwater, and momentum. These forcings are also responsible for the peculiar characteristics of Mediterranean water masses. Therefore, the chapter continues with giving a general explanation on water mass analysis, and then it describes the properties and vertical and horizontal distributions of the main Mediterranean water masses. To conclude, the reader is introduced to the use of other (biogeochemical, and chemical) tracers of water masses, with a focus on the Mediterranean Sea.
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  • 14
    Publication Date: 2023-01-03
    Description: Food web research provides essential insights into ecosystem functioning, but practical applications in ecosystem-based management are hampered by a current lack of knowledge synthesis. To address this gap, we provide the first systematic review of ecological studies applying stable isotope analysis, a pivotal method in food web research, in the heavily anthropogenically impacted Baltic Sea macro-region. We identified a thriving research field, with 164 publications advancing a broad range of fundamental and applied research topics, but also found structural shortcomings limiting ecosystem-level understanding. We argue that enhanced collaboration and integration, including the systematic submission of Baltic Sea primary datasets to stable isotope databases, would help to overcome many of the current shortcomings, unify the scattered knowledge base, and promote future food web research and science-based resource management. The effort undertaken here demonstrates the value of macro-regional synthesis, in enhancing access to existing data and supporting strategic planning of research agendas.
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  • 15
    Publication Date: 2023-01-03
    Description: Aim: Invasive alien species are a growing problem worldwide due to their ecological, economic and human health impacts. The “killer shrimp” Dikerogammarus villosus is a notorious invasive alien amphipod from the Ponto-Caspian region that has invaded many fresh and brackish waters across Europe. Understandings of large-scale population dynamics of highly impactful invaders such as D. villosus are lacking, inhibiting predictions of impact and efficient timing of management strategies. Hence, our aim was to assess trends and dynamics of D. villosus as well as its impacts in freshwater rivers and streams. Location: Europe. Methods: We analysed 96 European time series between 1994 and 2019 and identified trends in the relative abundance (i.e. dominance %) of D. villosus in invaded time series, as well as a set of site-specific characteristics to identify drivers and determinants of population changes and invasion dynamics using meta-regression modelling. We also looked at the spread over space and time to estimate the invasion speed (km/year) of D. villosus in Europe. We investigated the impact of D. villosus abundance on recipient community metrics (i.e. abundance, taxa richness, temporal turnover, Shannon diversity and Pielou evenness) using generalized linear models. Results: Population trends varied across the time series. Nevertheless, community dominance of D. villosus increased over time across all time series. The frequency of occurrences (used as a proxy for invader spread) was well described by a Pareto distribution, whereby we estimated a lag phase (i.e. the time between introduction and spatial expansion) of approximately 28 years, followed by a gradual increase before new occurrences declined rapidly in the long term. D. villosus population change was associated with decreased taxa richness, community turnover and Shannon diversity. Main Conclusion: Our results show that D. villosus is well-established in European waters and its abundance significantly alters ecological communities. However, the multidecadal lag phase prior to observed spatial expansion suggests that initial introductions by D. villosus are cryptic, thus signalling the need for more effective early detection methods.
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  • 16
    Publication Date: 2023-01-02
    Description: Highlights • Plinian eruptions linked to rheologically different mingling andesite magmas. • Magma decompression regimes producing variable degassing/crystallization kinetics. • Least explosive eruptions at slowest decompression, ascent and strain rates. • Plinian phases at rapid/intermittent magma decompression, ascent and strain rates. Abstract Estimating the kinetics of andesite magma vesiculation and crystallization inside volcanic plumbing systems is key for unraveling andesite Plinian eruption dynamics. The conduit kinetics provide the necessary input data for estimating the magma flow rates driving magma ascent and the fragmentation mechanisms controlling shifts in eruption explosivity and style. This information is crucial for increasing knowledge on expected hazards and for developing realistic eruption scenarios. In this work, we estimate conduit magma vesiculation and crystallization kinetics during the 3300 cal BP Upper Inglewood Plinian eruptive episode of Mount Taranaki, New Zealand. This episode comprised (i) low-intensity, conduit-opening phases of dome-collapse PDCs; (ii) pre-climactic, highly explosive phases of diverse PDCs, of up to violent 18-km-runout lateral blasts; (iii) climactic phases of steady 22-km-high Plinian eruption columns; and (iv) waning phases of column-collapse PDCs. By employing synchrotron microtomography, combined with mineral/glass chemistry and electron-microscopy, we quantified 3D vesicle and crystal size and shape distributions in juvenile pyroclasts over time, and corresponding number densities ranging from 1.1 × 105 to 2.5 × 106 mm−3 for vesicles, and from 8.0 × 104 to 5.1 × 106 mm−3 for crystals. Our results indicate that tapping of chemically alike yet rheologically contrasting magmas over a multi-phase andesite eruptive episode is linked to: (a) mafic magma recharge and differentiation in multiple storage reservoirs at distinct crustal levels, (b) stepwise to rapid magma decompression while mingling, producing variable pre- and syn-eruptive degassing and crystallization, and (c) syn-eruptive changes in melt viscosity, strain rate, localized shear deformation, and conduit geometry. The earliest and least explosive eruptive phases (≈ 2 × 106 kg s−1) were produced at the slowest rates of magma decompression (0.3–0.6 MPa s−1), ascent (0.01–0.02 m s−1) and strain (〈 0.002 s−1), driven by volatile diffusion and exsolution. All subsequent pre-climactic and Plinian phases (4 × 107–1 × 108 kg s−1) were produced at either rapid or intermittent rates of magma decompression (2.0–6.0 MPa s−1), ascent (0.06–0.2 m s−1) and strain (〉 0.003–0.010 s−1), powered by combined magma volatile supersaturation and delayed disequilibrium degassing, decompression-induced microlite crystallization and rapid heterogeneous vesiculation kinetics, shear deformation and magma mingling. These processes enabled complex fragmentation mechanisms of the rheologically most homogeneous magmas.
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  • 17
    Publication Date: 2023-01-02
    Description: The present worldwide study of 31 off-shore back-arc basins and subbasins (BABs) identifies their principal characteristics based on a broad spectrum of geophysical and subduction-related parameters. This synthesis is next used to identify trends in evolution of the back-arc basins for improving our understanding of subduction systems in general. The analysis, based on the present plate configuration, demonstrates that geophysical characteristics and fate of the back-arc basins are essentially controlled by the nature of the overriding plate, which controls lithosphere thermo-compositional structure and rheology. The plate nature governs the length of the extensional zone in back-arc settings along the trench, the efficiency of lithosphere stretching, BAB crustal structure, its buoyancy and bathymetry. Subduction dip angle apparently controls the location of slab melting zone and the efficiency of slab roll-back with feedback link to other parameters. By tectonic nature of the overriding plate (the downgoing plate is always oceanic) the back-arc basins are split into active BABs formed by ocean-ocean, arc-ocean, and continent-ocean convergence, and extinct back-arc basins. By geophysical characteristics, BABs formed on continental plates are subdivided into active BABs with and without seafloor spreading, and extinct BABs are subdivided to Pacific, possibly formed on oceanic plates, and non-Pacific with reworked continental or arc fragments. Six types of BABs are distinctly different. Extension of the overriding oceanic plate above a steeply dipping old oceanic plate, preferentially subducting nearly westwards, forms large deep back-arc basins with a thin oceanic-type crust. In contrast, BABs on the overriding continental or arc plates form at small opening rates and often by shallow subduction of younger oceanic plates with random subduction orientation; these BABs have small size, shallow bathymetry, and hyperextended or transitional ~20 km thick arc- or continental-type crust typical of passive margins. The presence of a 2–5 km thick high-Vp lowermost crustal layer, characteristic of BABs in all settings, indicates the importance of magmatic underplating in their crustal growth. Conditions required for the initiation of a back-arc basin and transition from stretching to seafloor opening depend on the nature of the overriding plate. BABs formed on oceanic plates always evolve to seafloor spreading. BABs formed on continental or arc plates require a long spreading duration with large (〉8 cm/y) opening rates and crustal thinning factor 2.8–5.0 to progress from crustal extension to seafloor spreading; such transition does not happen in back-arc basins formed behind a shallow subduction (〈45o) of a young (〈40 My) oceanic plate. The nature of the overriding plate also determines the fate of back-arc basins after termination of lithosphere extension: extinct Pacific back-arc basins with oceanic-type crust evolve towards deep old “normal” oceans, while shallow non-Pacific BABs with low heat flow and thick crust are likely to preserve their continental or arc affinity. BABs do not follow oceanic cooling plate model predictions. Distinctly different geophysical signatures for spreading at mid-ocean ridges and for back-arc seafloor spreading are caused by a principally different nature of their dynamics.
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  • 18
    Publication Date: 2023-01-04
    Description: The acclimative response of phytoplankton, which adjusts their nutrient and pigment content in response to changes in ambient light, nutrient levels, and temperature, is an important determinant of observed chlorophyll distributions and biogeochemistry. Acclimative models typically capture this response and its impact on the C : nutrient : Chl ratios of phytoplankton by explicitly resolving the dynamics of these constituents of phytoplankton biomass. The instantaneous acclimation (IA) approach only requires resolving the dynamics of a single tracer and calculates the elemental composition assuming instantaneous local equilibrium. IA can capture the acclimative response without substantial loss of accuracy in both 0D box models and spatially explicit 1D models. A major drawback of IA so far has been its inability to maintain mass balance for the elements with unresolved dynamics. Here we extend the IA model to capture both C and N cycles in a 0D setup, which requires analytical derivation of additional flux terms to account for the temporal changes in cellular N quota, Q. We present extensive tests of this model, with regard to the conservation of total C an N and its behavior in comparison to an otherwise equivalent, fully explicit dynamic acclimation (DA) variant under idealized conditions with variable light and temperature. We also demonstrate a modular implementation of this model in the Framework for Aquatic Biogeochemical Modelling (FABM), which facilitates modeling competition between an arbitrary number of different acclimative phytoplankton types. In a 0D setup, we did not find evidence for computational advantages of the IA approach over the DA variant. In a spatially explicit setup, performance gains may be possible but would require modifying the physical-flux calculations to account for spatial differences in Q between model grid cells.
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  • 19
    Publication Date: 2023-01-09
    Description: Highlights: • The fate of PS microbeads in an exposure experiment was assessed over 50 h. • Targeted and realized MP concentrations can differ largely in controlled laboratory experiments. • Clearance rates of mussels were significantly decreased in the presence of MP. • Reduction of clearance rates was more pronounced in mussels that had recently spawned. Abstract: The fate of microplastic particles (MP) in exposure experiments is mostly unclear. We measured the recovery of polystyrene (PS) microbeads, which were applied in various concentrations from 0.07 to 47.47 beads/ml, from the different compartments of an experimental system with mussels (Mytilus spp.). At the end of the experiment, we detected a significant loss of MP indicating that the mussels were exposed to less particles than intended. If such a discrepancy remains un-recognized by the experimenter, observed effects are related to an inaccurate particle concentration. Additionally, we observed reduced clearance rates of the mussels in the presence of MP and the effect size increased with increasing particle concentration. This effect was more pronounced in mussels that had recently spawned than in mussels that still had mature gonads. This is a hint that effects of MP may depend on the reproductive status of an organism.
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  • 20
    Publication Date: 2023-01-09
    Description: Algen, Zooplankton und Fische gehören zu den Schlüsselakteuren der biologischen Kohlenstoffpumpe, mithilfe derer der Ozean der Atmosphäre auf natürliche Weise Kohlendioxid entnimmt und den enthaltenen Kohlenstoff in großen Wassertiefen einlagert. Damit dieser Mechanismus jedoch optimal funktioniert, braucht es Nährstoffe, die vielerorts fehlen, zumindest im lichtdurchfluteten Oberflächenwasser. Durch das Heraufpumpen nährstoffreichen Tiefenwassers könnte der Mensch diesen Nährstoffmangel beheben. Ob ein solcher künstlicher Auftrieb aber tatsächlich klimawirksam wäre, welche Risiken er mit sich brächte und ob er technisch und rechtlich im großen Stil umgesetzt werden könnte, ist bislang ungewiss. Die Forschungsmission CDRmare liefert Antworten.
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  • 21
    Publication Date: 2023-01-09
    Description: Squid play a major role in the Southern Ocean food web. However, their age and growth remain poorly studied. Here, using upper and lower beaks of Moroteuthopsis longimana collected from the diet of Dissostichus mawsoni from Pacific and Atlantic sectors of the Southern Ocean, we studied: (1) Feasibility of using beaks collected from predators’ stomachs to study the age of Southern Ocean oceanic squid; and (2) Age estimation and growth patterns of M. longimana. The rostrum sagittal section (RSS) of both beaks had micro-increments, with the lower beak being the best to observe and count a readable sequence of increments to estimate the age. Assuming a daily deposition of increments, our results suggest that M. longimana can live up to 820 days and may hatch throughout the year. Studied individuals presented a consistent growth rate from hatching to death but with, at least, one period of faster growth. A novel pattern of regular cycles, composed of 7–10 lighter increments followed by a darker one, was found in the medium-anterior region of the RSS. Differences were found in the growth rate and size reached at the same age between individuals from the Pacific and Atlantic sectors, which might be related with different environmental conditions between both capture sites. This study shows that lower beaks from predators’ stomachs can be used to study the age of Southern Ocean squids and that M. longimana hatches in all seasons, being available year round to predators that feed of this species.
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  • 22
    Publication Date: 2023-01-10
    Description: The topographic fabric of the rift valley floor has been analyzed using the multibeam echosounder data obtained by the autonomous underwater vehicle (AUV) Abyss at two locations over a short segment of the slow-spreading Central Indian Ridge between 10°18′ and 10°57′S. The region is influenced by hydrothermal venting in the near vicinity. Two AUV dives D51 and D52 were performed over this segment at two locations that are 30 km apart and covered 5 km2 and 8 km2 seafloor area, respectively. The dive D51 covered the off-axis part of the rift valley floor in the middle part of the segment, and the dive D52 is located near to the non-transform discontinuity that covered the terminal part of an oceanic core complex (OCC). High-resolution seafloor topography as revealed by the AUV-mounted multibeam echosounder system brought out several micro-bathymetric fabric features such as a lava lake, a cratered volcano, an OCC, and the foot wall volcanic complex at the distal part of the OCC. The valley floor imaged in the D51 is marked by a lava flow encompassing an area of 1 km2 and a volcano in the NE corner. The volcano has a diameter of about 800 m with an elevation of about 200 m from the adjacent seafloor, and the partially mapped volcano crater has a relief of about 60 m. A prominent linear fissure running parallel to the ridge axis has been identified; this feature joins with the volcano. Analysis of AUV-mounted CTD data indicated three distinct temperature spikes ranging 0.009 to 0.013 °C in the region of dive D51. The observed temperature spikes appear to be related to the linear fissure on the seafloor and probably represent leaky venting of fluids from the fissure. With respect to the dive D52, the foot wall volcanic features associated with the OCC are prominent. The volcanic seafloor feature covered an area of 3.45 km2 and is conspicuous with rugged topographic fabric at the base of the OCC. These inferences and the morphotectonics of the rift valley floor as revealed by the AUV data suggest moderate hydrothermal venting in this segment of the slow-spreading Central Indian Ridge.
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  • 23
    Publication Date: 2023-01-12
    Description: Elevated dimethyl sulfide (DMS) concentrations in the sea surface microlayer (SML) have been previously related to DMS air–sea flux anomalies in the southwestern Pacific. To further address this, DMS, its precursor dimethylsulfoniopropionate (DMSP), and ancillary variables were sampled in the SML and also subsurface water at 0.5 m depth (SSW) in different water masses east of New Zealand. Despite high phytoplankton biomass at some stations, the SML chlorophyll a enrichment factor (EF) was low (〈 1.06), and DMSP was enriched at one station with DMSP EF ranging from 0.81 to 1.25. DMS in the SML was determined using a novel gas-permeable tube technique which measured consistently higher concentrations than with the traditional glass plate technique; however, significant DMS enrichment was present at only one station, with the EF ranging from 0.40 to 1.22. SML DMSP and DMS were influenced by phytoplankton community composition, with correlations with dinoflagellate and Gymnodinium biomass, respectively. DMSP and DMS concentrations were also correlated between the SML and SSW, with the difference in ratio attributable to greater DMS loss to the atmosphere from the SML. In the absence of significant enrichment, DMS in the SML did not influence DMS emissions, with the calculated air–sea DMS flux of 2.28 to 11.0 µmol m−2 d−1 consistent with climatological estimates for the region. These results confirm previous regional observations that DMS is associated with dinoflagellate abundance but indicate that additional factors are required to support significant enrichment in the SML.
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  • 24
  • 25
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    GEOMAR Helmholtz Zentrum für Ozeanforschung Kiel
    Publication Date: 2023-01-16
    Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 15. - 21. Januar 2023 „MOSES Eddy Study IV“
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  • 26
    Publication Date: 2023-01-17
    Description: The Carpathian-Pannonian Region (CPR) hosted some of the largest silicic volcanic eruptions in Europe during the Early and Middle Miocene, contemporaneously with major lithospheric thinning of the Pannonian Basin. This was recorded as an ignimbrite flare-up event from approximately 18.1–14.4 Ma. To gain in-depth perspectives on the eruption chronology, tephrostratigraphy, and petrogenesis at the onset of CPR silicic volcanism, we applied a multi-proxy approach to Lower Miocene rhyolitic ignimbrites and pyroclastic fall deposits from the northern CPR to the Dinaride Lake System. High-precision zircon U-Pb geochronology distinguished two Lower Miocene groups of volcaniclastic rocks at ∼ 18.1 Ma and ∼ 17.3 Ma. Based on combined tephrostratigraphic signatures we propose that the ∼ 18.1 Ma Kalnik and ∼ 17.3 Ma Eger eruptions produced widespread (intermediate to) large caldera-forming massive rhyolitic ignimbrites, deposited across northern and southwestern regions of the CPR. Due to easterly winds that carried volcanic ash hundreds of kilometers to the southwest, Eger eruption products also reached distal intra-montane Dinaride lacustrine basins, recorded as pyroclastic fall deposits. Heterogeneous major and trace elemental compositions of ∼ 18.1 Ma volcanic glass shards suggest that the Kalnik eruption was sourced from complex silicic magmatic systems, with simultaneous tapping of two discrete melt bodies during the eruption. The homogeneous geochemical composition of ∼ 17.3 Ma glasses is distinct from the older glasses. Integrated zircon and bulk glass Nd-Hf isotope compositions have a positive correlation, defining a regional mantle array, and are more radiogenic in the younger phase of volcanism. The recorded systematic isotopic change, moving from older more crustal signatures to younger more juvenile compositions, imply that during the period of lithospheric thinning of the Pannonian Basin the region underwent more complex variations in the interaction between metasomatized lithospheric mantle-derived magmas and various crustal components than previously recognized.
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  • 27
    Publication Date: 2023-01-18
    Description: Bacterial populations face the constant threat of viral predation exerted by bacteriophages (‘phages’). In response, bacteria have evolved a wide range of defense mechanisms against phage challenges. Yet the vast majority of antiphage defense systems described until now are mediated by proteins or RNA complexes acting at the single-cell level. Here, we review small molecule-based defense strategies against phage infection, with a focus on the antiphage molecules described recently. Importantly, inhibition of phage infection by excreted small molecules has the potential to protect entire bacterial communities, highlighting the ecological significance of these antiphage strategies. Considering the immense repertoire of bacterial metabolites, we envision that the list of antiphage small molecules will be further expanded in the future.
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  • 28
    Publication Date: 2023-01-19
    Description: Here, we outline how to identify hydrogenase enzymes from metagenomic fosmid libraries through an activity-based screening approach. A metagenomic fosmid library is constructed in E. coli and the fosmids are transferred into a hydrogenase deletion mutant of Shewanella oneidensis MR-1 (ΔhyaB) via triparental mating. If a fosmid clone exhibits hydrogen-uptake activity, S. oneidensis’ phenotype is restored and hydrogenase activity is indicated by a color change of the medium from yellow to colorless. The screen enables screening of 48 metagenomic fosmid clones in parallel.
    Type: Book chapter , NonPeerReviewed , info:eu-repo/semantics/bookPart
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  • 29
    Publication Date: 2023-01-19
    Description: Defining a precise timeline for past eruptions from explosive volcanoes in continental arcs is imperative to forecast future hazards and mitigate volcanic disasters in these often densely populated regions. However, establishing reliable ages for Quaternary eruptions in the Central American Volcanic Arc has been challenging due to the common lack or alteration of suitable K-rich phases for 40Ar/39Ar geochronology, but also from their position in time beyond the reach of 14C dating. This especially holds for the active Amatitlán caldera in Guatemala, from which at least six explosive silicic eruptions have produced tephra blanketing neighboring regions that are today inhabited by millions of people. Zircon, a common datable accessory mineral in Amatitlán caldera magmas, is used here to retrieve eruption ages by applying the novel zircon double-dating method (ZDD) that integrates 238U–230Th disequilibrium dating and (U–Th)/He thermochronology. This approach yielded the first-ever radioisotopic ages of 24 ± 3 ka and 48 ± 6 ka (1σ), respectively, of two of Amatitlán caldera's most recent eruptions (J-tephra and E-tephra). Remarkably, both zircon crystallization and ZDD eruption ages for the older and voluminous T-tephra and L-tephra units significantly post-date existing plagioclase 40Ar/39Ar dates by ca. 26 and 70 kyr, respectively. The ZDD eruption age for T-tephra is 93 ± 4 ka, whereas zircon crystallization ages for L-tephra yield a maximum model eruption age of ca. 124 ka. The strong eruption age divergence between ZDD and plagioclase 40Ar/39Ar dating argues for the presence of inherited or xenocrystic plagioclase in Amatitlán caldera eruptive products. Statistical analysis based on the updated eruptive history suggests a recurrence interval of ca. 17 kyr, which is significantly shorter than previously estimated. The new age data, thus, suggest a more frequent eruptive activity of Amatitlán caldera than formerly thought and underscores the necessity to better understand the current underlying magmatic system and to constrain its past eruptive history more precisely.
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  • 30
    Publication Date: 2023-01-19
    Description: Highlights • Study of wetland sediment in the easternmost Asian monsoon affected region. • Sediment on the Konsen Plateau has continuously deposited since ∼4.0 ka. • C/N and C/S ratios suggest environmental changes during the late Holocene. Abstract Wetland soils are among the largest carbon reservoirs in terrestrial ecosystems and are vulnerable to climate change. Here we elucidate the developmental history of a wetland soil located on the Konsen Plateau in Hokkaido, Japan, during the Holocene. Through radiocarbon dating of sediment samples, we revealed that continuous sedimentation persisted over the past 4000 years. This onset of peat sedimentation was simultaneous with those reported in other wetlands in eastern Hokkaido. We hypothesized that cooling associated with the end of climatic optimal may have contributed to peat preservation. Elemental analyses also confirmed the formation of a stable wetland condition during the late Holocene. The C/N ratios were approximately 15–25 throughout the core, indicating that the organic materials in the sediments were steadily derived from terrestrial plants. The C/S ratios of the core varied between 43 and 97, suggesting that the sediments are free from marine influences. Our results provided continuous and stable record of wetland sedimentary environment in eastern Hokkaido over the past 4000 years.
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  • 31
    Publication Date: 2023-01-19
    Description: Geological histories of volcanic ocean islands can be revealed by the sediments shed by them. Hence there is an interest in studying cores of volcaniclastic sediments that are particularly preserved in the many flat-floored basins lying close to the Azores islands. We analyse four gravity cores collected around the central group of the islands. Three sedimentary facies (F1-F2a, F2b) are recognized based on visual core logging, particle morphometric and geochemical analyses. F1 is clay-rich hemipelagite comprising homogeneous mud with mottled structures from bioturbation. F2a and F2b are both clay-poor volcaniclastic deposits, which are carbonate-rich and carbonate-poor, respectively. More biogenic carbonate in F2a reflects the incorporation of unconsolidated calcareous material from island shelves or bioturbation. Within F2a and F2b we identify deposits emplaced by pyroclastic fallout, primary or secondary turbidity currents by combining multiple information from lithological composition, sedimentary structures, chemical composition of volcanic glass shards and morphometric characteristics of volcanic particles. Primary volcaniclastic sediments were found in all four cores, echoing activity known to have occurred up to historical times on the adjacent islands. These preliminary results suggest that greater details of geological events could be inferred for other volcanic islands by adopting a similar approach to core analysis.
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  • 32
    Publication Date: 2023-01-19
    Description: Climate change and plastics pollution are dual threats to marine environments. Here we use biogeochemical and microplastic modelling to show that even if there is complete removal of microplastics and cessation of deposition in the oceans in 2022, regional recovery from microplastic-induced remineralization and water column deoxygenation could take hundreds of years for coastal upwelling zones, the North Pacific and Southern Ocean. Surface stratification and reduced sea ice cover further impede regional recovery, highlighting the importance of aggressive mitigation of plastic pollution.
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  • 33
    Publication Date: 2023-01-19
    Description: Offshore freshened groundwater (OFG) is groundwater with a salinity below that of seawater that is stored in sub-seafloor sediments and rocks. OFG has been proposed as an alternative solution to relieve water scarcity in coastal regions and to enhance oil recovery. Although OFG has been documented in most continental margins, we still have a poor understanding of the extent and flow characteristics of OFG systems, and their evolution through time. In view of the general absence of appropriate field data, paleohydrogeological models have been used. The majority of these models are based on 2D approaches, and they rarely consider the future evolution of OFG systems, especially in response to predicted climate change. Here we utilize recently acquired geological, geophysical and hydrogeological data from onshore and offshore the Maltese Islands, and employ 2D and 3D numerical models, to: (i) reconstruct the evolution of the onshore-offshore groundwater system during the last 188 ka, (ii) predict the evolution of the OFG system in response to climate-related changes. We show that the mechanisms emplacing OFG include a combination of active meteoric recharge at present as well as at sea-level lowstands. The Maltese onshore-offshore groundwater system is relatively dynamic, with 23% of groundwater being preserved in the last 18 ka. The control of geology is expressed by the more prevalent distribution of OFG north of the Great Fault, which is associated to the occurrence of low permeability units, and the asymmetry of the groundwater lens during the 18 ka lowstand. A 30% decrease in recharge predicted in the coming 100 years will diminish OFG extent by 38%, whereas sea-level rise will play a negligible role. At present the estimated volume of OFG is 1 km 3 , which could potentially provide an alternative supply of potable water to the Maltese Islands for 75 years. Exploitation of OFG with minimal salinization of onshore groundwater bodies would require locating pumping wells close to the coast.
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  • 34
    Publication Date: 2023-01-19
    Description: Tropical peat swamps are essential ecosystems, which provide numerous services, and also serve as a rich source of dissolved organic carbon (DOC), hydrogen ions and trace elements to peat draining rivers. However, not much is known about trace element export from tropical peat swamps. We investigated trace element dynamics in rivers and estuaries draining tropical peat swamps on Borneo, and examined the influence of estuarine processes as well as dissolved organic carbon (DOC) on the distribution and concentration of trace elements. Our results indicate acidic conditions (pH = 3.3) and high DOC concentration (3500 µmol L −1 ) at salinities〈1. We observed an initial release of trace elements at low salinity (0.05〈S〈 0.5), followed by scavenging to particles at intermediate salinities (0.5〈S〈10) due to an increasing ionic strength and pH. Peak concentrations (µmol kg −1 ) of Al (24.9), Si (96.2), Mn (4.9), Cu (0.035) and Ni (0.047) were observed during the dry season (July), and Fe concentrations (43.2) were highest during the wet season (December). We used the NICA-Donnan model to investigate the combined impact of DOC and pH on the formation of solid iron hydroxide (Fe(OH) 3 (s)). The Maludam river was predicted to be supersaturated for Fe hydroxides and the results affirmed our model prediction. The output showed Fe and Cu had a strong affinity for DOC and to a lesser extent Al and Ni in the conditions prevailing at the study sites. Statistical analyses also indicated strong correlation between Cu and Ni (r 2 = 0.97, 0.94 and 0.82) in Maludam, Sebuyau and Belait rivers and estuaries, respectively. The results obtained in this study are comparable to values published for southeast Asia and other continents for pristine peat draining rivers.
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  • 35
    Publication Date: 2023-01-19
    Description: The main goal of the study is to establish the spatial and temporal distribution of pyroclastic material from large explosive eruptions of the volcanoes of Kamchatka, the Kuril, and Aleutian Islands to create a generalized tephrochronological model and reveal patterns of explosive activity in this region. This paper presents new data on the composition of volcanic ash (tephra) found in the Pleistocene deposits of the northwestern Pacific from the eastern slope of the Detroit Rise (northwestern part of the Imperial Ridge), 450–550 km east of the Kamchatka Peninsula. Eleven layers and lenses of tephra aged from 28 to 245 ka, which were previously unknown, were studied in the core Lv63-4-2. Their stratigraphic position and age were determined based on age models developed in this study. Based on the geochemical composition of volcanic glass (determined using an electron microprobe), seven layers were correlated with tephra from several cores in the northwestern Pacific and the Bering Sea. The obtained results supplement the information on large explosive eruptions of volcanoes in the region and their periods of activity. They also allow the development of a generalized tephrochronological model of Quaternary deposits, which is necessary for stratigraphic correlation, and of paleooceanological and paleogeographic reconstructions.
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  • 36
    Publication Date: 2023-01-19
    Description: This review focuses on the recognition of volcanic ash occurrences in marine sediment cores and on using their appearance and properties to deduce their origin. Widespread marine tephra layers are important marker horizons for both volcanological as well as general geological investigations. We describe ash detection by visual inspection and logging of sediment cores. Ash layer structure and texture, particle morphologies and lithological compositions of primary volcanic deposits are summarized and processes modifying them are discussed, both natural processes acting on and in the seafloor, i.e. erosion and bioturbation, and anthropogenic modifications during drilling/coring and core preparation. We discuss primary emplacement processes of marine fall and flow tephra deposits derived from either subaerial or submarine sources in order to identify distinguishing properties. We also elaborate on processes generating secondary, resedimented volcaniclastic layers such as submarine landslides and shelf erosion as well as fluvial input and ice-rafting, and how they can be distinguished from primary volcaniclastic deposits, which is essential in tephrostratigraphy. Finally, methods of tephra correlation between cores and on-land deposits/volcanoes are illustrated because they allow us to extend the 1D information from single cores to 3D distribution and facies changes of tephras and to bridge the land–sea gap.
    Type: Book chapter , NonPeerReviewed , info:eu-repo/semantics/bookPart
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  • 37
    Publication Date: 2023-01-20
    Description: Ocean ecosystems are at the forefront of the climate and biodiversity crises, yet we lack a unified approach to assess their state and inform sustainable policies. This blueprint is designed around research capabilities and cross-sectoral partnerships. We highlight priorities including integrating basin-scale observation, modelling and genomic approaches to understand Atlantic oceanography and ecosystem connectivity; improving ecosystem mapping; identifying potential tipping points in deep and open ocean ecosystems; understanding compound impacts of multiple stressors including warming, acidification and deoxygenation; enhancing spatial and temporal management and protection. We argue that these goals are best achieved through partnerships with policy-makers and community stakeholders, and promoting research groups from the South Atlantic through investment and engagement. Given the high costs of such research (€800k to €1.7M per expedition and €30–40M for a basin-scale programme), international cooperation and funding are integral to supporting science-led policies to conserve ocean ecosystems that transcend jurisdictional borders.
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  • 38
    Publication Date: 2023-01-25
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  • 39
    Publication Date: 2023-01-25
    Description: As an important external forcing, the effect of the 11-yr solar cycle on the tropical Pacific decadal variability is an interesting question. Here, we systematically investigate the phase-locking of the atmosphere and ocean covariations to the solar cycle in the tropical Pacific and propose a new mechanism to explain these decadal covariations. In both observation/reanalysis datasets and a solar cycle forced sensitivity experiment (named the SOL experiment), the ocean heat content anomalies (OHCa; 300 m) resemble a La Niña–like pattern in the solar cycle ascending phase, and the Walker circulation shifts westward. In the declining phase, the opposite is true. The accumulative solar irradiation directly contributes to this coherent decadal variability via changing the warm water volume and the solar-related heat is redistributed by the ocean dynamic processes. During the 11-yr solar cycle, the Pacific Walker circulation anomalies maintain the OHCa in the western equatorial Pacific and work as negative feedback for the eastern Pacific to help the OHCa phase transition. In addition, oceanic meridional heat transport via the subtropical cells and the propagation of off-equatorial Rossby waves also provide a lagged negative feedback to the OHCa phase transition according to the 11-yr solar cycle. The decadal coupled responses of the tropical Pacific climate system are 2 years more lag in the SOL experiment than in the observation/reanalysis. Significance Statement Here, we propose a new mechanism that the heating effect of the accumulative solar irradiation during the 11-yr solar cycle can be “integrated” into the tropical Pacific OHC and then provide a bottom-up effect on the atmosphere at decadal time scales. The strongly coupled processes in this region amplify the decadal phase-locking of the covariations to the 11-yr solar cycle. Our study demonstrates the role of the 11-yr solar cycle in the tropical Pacific decadal variability and provides a new explanation for the “bottom-up” mechanism of the solar cycle forcing. Our results update the understanding of the tropical Pacific decadal variability and may help to improve climate predictions at decadal time scales.
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  • 40
    Publication Date: 2023-01-25
    Description: This chapter gives an overview of the general biogeochemistry in the Mediterranean Sea explaining the particularities of the main biogeochemical variables and the physical, biological, and geochemical processes driving their distribution in the main basins of this marginal sea. Each subsection focuses on one essential variable, starting from dissolved oxygen and following inorganic nutrients, dissolved organic carbon and the CO2 system. A brief overview on the utility of those biogeochemical variables to identify water masses is also given. The chapter concludes with a summary of the projections and threats on biogeochemistry in the Mediterranean Sea under different future climate change scenarios.
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  • 41
    Publication Date: 2023-01-25
    Description: Alteration of volcanogenic aluminosilicates (VAs) in marine sediments is recognized as critical in regulating geochemical cycles and sustaining the oceanic deep biosphere, but rates of VA alteration and its associated authigenic mineral formation are not commonly reported. Here we present results on analyses of sediments and pore water recovered from the upper 150 mbsf of four sites drilled on the northern Hikurangi margin during IODP Expeditions 372 and 375. Petrographic analyses show that volcanogenic materials (glass shards, feldspar, volcanic lithoclasts) constitute important components (15–45 wt%) of the hemipelagic mud, and reveal ongoing glass alteration with accompanying authigenic phase formation. A reaction-transport model constrained by pore water Sr, 87Sr/86Sr, Ca, Mg, and Si was applied to simulate VA diagenetic reactions. Our model results yield VA alteration rates of 0.047–0.64 mmol Sr m−2 yr−1, with substantially higher values at Sites U1517 and U1520 that experienced rapid sediment emplacement. In addition, our simulations show that 〉99% of the dissolved Si generated by VA alteration is fixed in silica cement and authigenic clay, and that ∼50% of Ca incorporated in the authigenic carbonate is supplied by VA alteration. First-order estimates suggest that, in addition to authigenic carbonate precipitation, authigenic clay formation may represent an important sink for dissolved Mg. This study quantitatively examines the linkage between VA alteration and formation of authigenic phases, highlights its role in subsurface geochemical cycles, and indicates that slope instability may play an important role in promoting VA diagenesis.
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  • 42
    Publication Date: 2023-01-25
    Description: Climate change is expected to produce major effects across marine life, and cephalopods seem to benefit from these effects. Of these animals, squids exhibit the greatest levels of biomass and of a substantial importance for human consumption. To test the hypothesis that effects of climate change are beneficial for commercial squid, we used species distribution models on climate scenarios for the period between 2000 and 2014, as well as the years 2050 and 2100 (RCP [representative concentration pathway] 2.6, 4.5, 6.0, and 8.5; CMIP5). Our results suggest that consequences of climate change scenarios are species specific. In the North Pacific and Northwest Atlantic, habitat suitability may increase (from + 0.83% [Doryteuthis pealeii] to + 8.77% increase [Illex illecebrosus]), while the habitat of other species is predicted to decrease (from − 1.03% [Doryteuthis opalescens] to -15.04% decrease [Loligo reynaudii]). Increases in habitat suitability occurred mostly at higher latitudes, while suitable habitat decrease was predicted for the tropical regions. Stronger changes were attained with the harsher emission scenarios. In the future, as a result of warming of the Arctic, squid habitat may increase along both coasts of North America. In the Southern Hemisphere, squids may lose habitat with no poleward habitat alternatives to move into. Contrary to our hypothesis, commercial squid do not stand to benefit from climate change. Since these squid are an important food source for marine megafauna and humans, it is imperative that climate change biogeographic impacts are considered for a sustainable management of this important group of molluscs.
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  • 43
    Publication Date: 2023-01-25
    Description: Highlights: • First eddy–mean flow interaction analysis in the Deep Western Boundary Current between 5°S and 16°S. • Eddy kinetic energy is mainly generated via barotropic instability. • Enhanced upstream mean flow induces intensification in the downstream eddy field. Abstract: Thirty-six years output of a 1/10° eddy-resolving Ocean General Circulation Model are used to analyze the energetics of eddy–mean flow interactions in the Deep Western Boundary Current (DWBC) region of the tropical South Atlantic between 5°S and 16°S. The DWBC flow has a coherent structure between 5°S and 8°S but breaks up into a train of eddies downstream of a region of strong bathymetric curvature at 8°S. In the train of eddies area, the seasonal cycle of eddy kinetic energy (EKE) exhibits poleward phase propagation from May to September. The connection between the seasonal cycle of mean kinetic energy and EKE indicates an intensification of the downstream eddy field associated with enhanced upstream mean flow. The magnitudes of the baroclinic conversion and vertical eddy density flux terms are small in the DWBC core layer depth but somewhat elevated 500 m above and below the core. Eddy processes, including eddy generation and propagation, are accompanied by high EKE and large barotropic conversion. While in the global ocean baroclinic conversion is thought to dominate the energy transfer to EKE, our results suggest that barotropic energy conversion is the primary source of EKE and modulates its variability in the DWBC region of the deeper ocean.
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  • 44
    Publication Date: 2023-01-25
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 45
    Publication Date: 2023-01-25
    Description: Europe has experienced a substantial increase in non-indigenous crayfish species (NICS) since the mid-20th century due to their extensive use in fisheries, aquaculture and, more recently, pet trade. Despite relatively long invasion histories of some NICS and negative impacts on biodiversity and ecosystem functioning, large spatio-temporal analyses of their occurrences are lacking. Here, we used a large freshwater macroinvertebrate database to evaluate what information on NICS can be obtained from widely applied biomonitoring approaches and how usable such data is for descriptions of trends in identified NICS species. We found 160 time-series containing NICS between 1983 and 2019, to infer temporal patterns and environmental drivers of species and region-specific trends. Using a combination of meta-regression and generalized linear models, we found no significant temporal trend for the abundance of any species (Procambarus clarkii, Pacifastacus leniusculus or Faxonius limosus) at the European scale, but identified species-specific predictors of abundances. While analysis of the spatial range expansion of NICS was positive (i.e. increasing spread) in England and negative (significant retreat) in northern Spain, no trend was detected in Hungary and the Dutch-German-Luxembourg region. The average invasion velocity varied among countries, ranging from 30 km/year in England to 90 km/year in Hungary. The average invasion velocity gradually decreased over time in the long term, with declines being fastest in the Dutch-German-Luxembourg region, and much slower in England. Considering that NICS pose a substantial threat to aquatic biodiversity across Europe, our study highlights the utility and importance of collecting high resolution (i.e. annual) biomonitoring data using a sampling protocol that is able to estimate crayfish abundance, enabling a more profound understanding of NICS impacts on biodiversity.
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  • 46
    Publication Date: 2023-01-25
    Description: We use output from a freely-running NEMO model simulation for the equatorial Pacific to investigate the utility of linearly removing the local influence of vertical displacements of the thermocline from variations in sea surface height. We show that the resulting time series of residual sea surface height, denoted ηnlti, measures variations in near-surface heat content that are independent of the local vertical displacement of the thermocline and can arise from horizontal advection, surface heat flux and diapycnal mixing processes. We find that the variance of ηnlti and its correlation with sea surface temperature, are focused on the Niño4 region. Furthermore, ηnlti averaged over the Niño4 region is highly correlated with indices of Central Pacific El Niño Southern Oscillation (CP ENSO), and its variance in 21 year running windows shows a strong upward trend over the past 50 years, corresponding to the emergence of CP ENSO following the 1976/77 climate shift. We show that ηnlti can be estimated from observations, using satellite altimeter data and a linear multi-mode model. The time series of ηnlti, especially when estimated using the linear model, show pronounced westward propagation in the western equatorial Pacific, arguing an important role for zonal advective feedback in the dynamics of CP ENSO, in particular for cold events. We also present evidence that the role of the thermocline displacement in influencing sea surface height increased strongly after 2000 in the eastern part of the Niño4 region, at a time when CP ENSO was particularly active. Finally, the diagnostic is easy to compute and can be easily applied to mooring data or couple climate models.
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  • 47
    Publication Date: 2023-01-25
    Description: Abstract Mesopelagic fishes are an important element of marine food webs, a huge, still mostly untapped food resource, and great contributors to the biological carbon pump, whose future under climate change scenarios are unknown. The shrinking of commercial fishes within decades has been an alarming observation, but its causes remain contended. Here, we investigate the effect of warming climate on mesopelagic fish size in the eastern Mediterranean Sea during a glacial–interglacial–glacial transition of the Middle Pleistocene (marine isotope stages 20–18; 814–712 Kyr B.P.), which included a 4 °C increase of global seawater temperature. Our results based on fossil otoliths show that the median size of lanternfishes, one of the most abundant groups of mesopelagic fishes in fossil and modern assemblages, declined by ~35% with climate warming at the community level. However, individual mesopelagic species showed different and often opposing trends in size across the studied time interval, suggesting that climate warming in the interglacial resulted in an ecological shift toward increased relative abundance of smaller-sized mesopelagic fishes due to geographic and/or bathymetric distribution range shifts, and the size-dependent effects of warming.
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  • 48
    Publication Date: 2023-01-25
    Description: Future change in sea surface temperature may influence climate via various air-sea feedbacks and pathways. In this study, we investigate the influence of surface seawater biogeochemical composition on the temperature dependence of sea spray number emission fluxes. Dependence of sea spray fluxes was investigated in different water masses (i.e. subantarctic, subtropical and frontal bloom) with contrasting biogeochemical properties across a temperature range from ambient (13–18 °C) to 2 °C, using seawater circulating in a plunging jet sea spray generator. We observed sea spray total concentration to increase significantly at temperatures below 8 °C, with an average 4-fold increase at 2 °C relative to initial concentration at ambient temperatures. This temperature dependence was more pronounced for smaller size sea spray particles (i.e. nucleation and Aitken modes). Moreover, temperature dependence varied with water mass type and so biogeochemical properties. While the sea spray flux at moderate temperatures (8–11 °C) was highest in frontal bloom waters, the effect of low temperature on the sea spray flux was highest with subtropical seawaters. The temperature dependence of sea spray flux was also inversely proportional to the seawater cell abundance of the cyanobacterium Synechococcus, which facilitated parameterization of temperature dependence of sea spray emission fluxes as a function of Synechococcus for future implementation in modelling exercises.
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  • 49
    Publication Date: 2023-01-25
    Description: Global warming may alter the dynamics of infectious diseases by affecting important steps in the transmission of pathogens and parasites. In trematode parasites, the emergence of cercarial stages from their hosts is temperature-dependent, being highest around a thermal optimum. If environmental temperatures exceed this optimum as a consequence of global warming, this may affect cercarial transmission. However, our knowledge of cercarial emergence patterns of species from high temperature environments is currently very limited. Here, we investigated the effect of temperature on the emergence of two common trematode species from an abundant mud snail Pirenella cingulata in the Persian Gulf, the warmest sea on Earth. Infected snails were incubated in the laboratory at 6 temperatures from 10 to 40°C for 3 days. We found an optimal temperature for cercarial emergence of 32.0°C and 33.5°C for Acanthotrema tridactyla and Cyathocotylidae gen. sp., respectively, which are the warmest recorded thermal optima for any aquatic trematode species. Emergence of both species dropped at 40°C, suggesting upper thermal limits to emergence. Overall, Persian Gulf trematodes may be among the most heat-tolerant marine trematode species, indicating a potential for dispersing to regions that will continue to warm in the future.
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  • 50
    Publication Date: 2023-01-25
    Description: Since the inception of the international South Atlantic Meridional Overturning Circulation initiative in the 21st century, substantial advances have been made in observing and understanding the Southern Hemisphere component of the Atlantic Meridional Overturning Circulation (AMOC). Here we synthesize insights gained into overturning flows, interocean exchanges, and water mass distributions and pathways in the South Atlantic. The overturning circulation in the South Atlantic uniquely carries heat equatorward and exports freshwater poleward and consists of two strong overturning cells. Density and pressure gradients, winds, eddies, boundary currents, and interocean exchanges create an energetic circulation in the subtropical and tropical South Atlantic Ocean. The relative importance of these drivers varies with the observed latitude and time scale. AMOC, interocean exchanges, and climate changes drive ocean warming at all depths, upper ocean salinification, and freshening in the deep and abyssal ocean in the South Atlantic. Long-term sustained observations are critical to detect and understand these changes and their impacts.
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  • 51
    Publication Date: 2023-01-25
    Description: The beginning of the Mid-Pleistocene Transition (MPT) ~920 ka BP marked the expansion of northern hemisphere ice shields and caused a significant climate change in NW Europe. The MPT ended with the establishment of the 100 kyr ice age cyclicity at ~640 ka BP, due to orbital eccentricity changes. Previous studies explained the northern hemisphere cooling by cooling of sea-surface temperatures, increased sea-ice cover and/or changes in the Atlantic Meridional Overturning Circulation (AMOC) strength. We here discuss very-high resolution parametric echosounder (Parasound) imagery and sediment core analytics from a plastered drift at the eastern Campeche Bank (southern Gulf of Mexico), which was deposited under the influence of the Loop Current (LC). The LC transports warm tropical waters from the Caribbean into the Gulf via the Yucatan Channel. It is a key component of the Gulf Stream system, driving the ocean heat, salinity, and moisture transport towards the N Atlantic. The joint interpretation of reflection patterns, age constraints from color-scanning, foraminiferal stable oxygen isotopes, Sr isotope ratios (87Sr/86Sr) and core-seismic integration led to consistent conclusions about changes in LC strength across the MPT, thereby modulating the deep base level and the deposition of the plastered drift. The development of offlapping or onlapping plastered drifts, or the transition between the two termination patterns is best explained by changes in the depth of the relative deep base level and interpreted by changes in the flow regime.Initially, the Middle Miocene to Pliocene closure of the Central American Seaway caused the onset and intensification of the LC and hence a deep base level fall. The sedimentary deposits from this phase have an offlapping prograding clinoform configuration, resembling a forced regression systems tract as is known from shelf areas. The deep base level fall caused sediment truncation above 500 m present day water depth. Below 500-550 m, the offlapping succession is overlain by sigmoidal and onlapping, transgressive systems tract like clinoforms. The transition from deep base level fall prior to the MPT to deep base level rise documents the weakening of the LC during the early MPT. After the MPT, the LC continued to weaken. The related reduction of heat transport from the Western Atlantic Warm Water Pool into the North Atlantic contributes to the further cooling of the northern hemisphere. Generally, the development of offlapping or onlapping plastered drifts or the transition between the two termination patterns can be explained by changes in the depth of the relative deep base level and interpreted by changes in the flow regime.
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  • 52
    Publication Date: 2023-01-26
    Description: Diatoms represent one of the most successful groups of marine phytoplankton and are major contributors to ocean biogeochemical cycling. They have colonized marine, freshwater and ice environments and inhabit all regions of the World’s oceans, from poles to tropics. Their success is underpinned by a remarkable ability to regulate their growth and metabolism during nutrient limitation and to respond rapidly when nutrients are available. This requires precise regulation of membrane transport and nutrient acquisition mechanisms, integration of nutrient sensing mechanisms and coordination of different transport pathways. This review outlines transport mechanisms involved in acquisition of key nutrients (N, C, P, Si, Fe) by marine diatoms, illustrating their complexity, sophistication and multiple levels of control.
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  • 53
    Publication Date: 2023-01-26
    Description: Since the 1980s, the Common Fisheries Policy (CFP) has shaped European fisheries. It has often been criticised for being too prescriptive and, above all, for failing to protect either fishermen or ecosystems. The last reform dates back to the early 2010 s and has led to a slight but slow improvement in the state of ecosystems. Given that the CFP is in the process of evaluation, a group of French fishery scientists set up an initiative to add to the debate on what should be retained, reinforced or added to a possible new reform. This initiative came 10 years after a previous manifesto that presented their vision for fisheries in Europe. Four major issues emerged from the current initiative: (1) a need for transparency and simplification in fisheries management, (2) a need for more consultation and dialogue between stakeholders, (3) the urgency of the situation in the Mediterranean Sea, and (4) the necessity of putting into practice all research developments for an ecosystem approach to fisheries. Compared to 10 years ago, the response of scientists shows that the focus is no longer on achieving the maximum sustainable yield, but rather on the following steps to protect ecosystems and fisheries. An ecosystem approach to fisheries remains indispensable for both ecosystems and fishing activities. To this end, scientists put forward numerous proposals to improve the CFP, acknowledging that the final solutions should emerge from consultation with stakeholders. Climate change, an issue raised much more than in the manifest, reinforces the need to act.
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  • 54
    Publication Date: 2023-01-26
    Description: In our previous study, a β-N-acetylhexosaminidase (HaHex74) from Haloferula sp. showing high human milk oligosaccharides (HMOs) synthesis ability was identified and characterized. In this study, HaHex74 was further engineered by directed evolution and site-saturation mutagenesis to improve its transglycosylation activity for HMOs synthesis. A mutant (mHaHex74) with improved transglycosylation activity (HaHex74-Asn401Ile/His394Leu) was obtained and characterized. mHaHex74 exhibited maximal activity at pH 5.5 and 35 °C, respectively, which were distinct from that of HaHex74 (pH 6.5 and 45 °C). Moreover, mHaHex74 showed the highest LNT2 conversion ratio of 28.2% from N,N’-diacetyl chitobiose (GlcNAc2), which is 2.2 folds higher than that of HaHex74. A three-enzyme cascade reaction for the synthesis of LNT2 and LNnT from chitin was performed in a 5–L reactor, and the contents of LNT2 and LNnT reached up to 15.0 g Lsingle bond1 and 4.9 g Lsingle bond1, respectively. Therefore, mHaHex74 maybe a good candidate for enzymatic synthesis of HMOs.
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  • 55
    Publication Date: 2023-01-26
    Description: Highlights • Zinc and copper isotope characterization of metalliferous sediments formed by brine pool deposition in the Atlantis II Deep. • Enrichments of light zinc and copper isotopes in sediments when compared to the hydrothermal inputs to the basin. • Isotopic data are consistent with metal sulfide precipitation and lesser adsorption of metals onto Si-Fe-OOH particles. • Increase of δ66Zn with increasing distance from hydrothermal metal release due to uptake of light isotopes by metal sulfides. • Zinc isotope patterns due to metal sulfide precipitation could be of interest in mineral exploration. Abstract This study provides a zinc and copper stable isotope characterization (δ66Zn, δ68Zn, and δ65Cu) of metalliferous seafloor sediments from the Atlantis II Deep, a hydrothermally influenced brine basin in the Red Sea. Samples collected from box cores that capture the entire stratigraphy in the Deep have δ66Zn and δ65Cu values of −0.31 to 0.34 ‰ (0.02 ‰ median) and − 1.81 to 1.02 ‰ (−0.34 ‰ median) relative to the JMC-Lyon and NIST SRM 976 standards, respectively. These results suggest enrichments of light stable isotopes in sediments compared to the hydrothermal inputs to the basin, which likely overlap the mantle-like isotopic signatures of basalts beneath the Deep. Such shifts to lower δ66Zn and δ65Cu values are consistent with widespread metal sulfide deposition from the brines because sulfide anions preferentially consume the light stable isotopes of zinc and copper. However, this interpretation contrasts with observations in the open ocean, where the fractionation of zinc and copper stable isotopes is strongly influenced by biological utilization and organic matter. Previous studies proposed that metal deposition in the Atlantis II Deep is also driven by adsorption onto iron oxides/hydroxides and their weakly crystalline (Si-)Fe-OOH precursor phases within the brines. However, because this process should accumulate heavy zinc and copper stable isotopes, its influence on isotopic fractionation is likely limited. Controls by metal sulfide precipitation are also indicated by spatial covariations between δ66Zn and concentrations of zinc and copper, that is, δ66Zn values increase whereas metal contents decrease with distance away from hydrothermal venting. Comparable trends are lacking for copper isotopes, perhaps because of additional influence by redox processes or, compared to zinc, a much stronger influence by adsorption onto (Si-)Fe-OOH phases, particularly in areas distal to hydrothermal venting where reduced sulfur could be scarce. Collectively, our results from the Atlantis II Deep indicate that zinc and copper stable isotopes could provide information about base and precious metals deposits from similar paleoenvironments. Firstly, zinc and copper stable isotopes shed light on metal sourcing and accumulation processes. Secondly, mineral precipitation in hydrothermally influenced brine pools produces zinc stable isotope patterns that, at least theoretically, could be of interest in mineral exploration at sub-basin and deposit scales.
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  • 56
    Publication Date: 2023-01-23
    Description: Equatorial Deep Jets (EDJ) are vertically alternating, stacked zonal currents that flow along the equator in all three ocean basins at intermediate depth. Their structure can be described quite well by the sum of high baroclinic mode equatorial Kelvin and Rossby waves. However, the EDJs' meridional width is larger by a factor of 1.5 than inviscid theory predicts for such waves. Here, we use a set of idealised model configurations representing the Atlantic Ocean to investigate the contributions of different processes to the enhanced EDJ width. Corroborated by the analysis of shipboard velocity sections, we show that instantaneous widening of the EDJ by irreversible mixing processes contributes more to their enhanced time mean width than averaging over meandering of the jets. Most of the widening due to meandering can be attributed to the strength of intraseasonal variability in the jets' depth range, suggesting that the jets are meridionally advected by intraseasonal waves. Only a weak connection to intraseasonal variability is found for the EDJs' instantaneous widening, corroborating and connecting earlier theories that any process dissipating the EDJs' momentum would broaden them, but that intraseasonal variability maintains, not dissipates, the EDJ.
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  • 57
    Publication Date: 2023-01-24
    Description: Invasive species can successfully and rapidly colonize new niches and expand ranges via founder effects and enhanced tolerance towards environmental stresses. However, the underpinning molecular mechanisms (i.e., gene expression changes) facilitating rapid adaptation to harsh environments are still poorly understood. The red seaweed Gracilaria vermiculophylla, which is native to the northwest Pacific but invaded North American and European coastal habitats over the last 100 years, provides an excellent model to examine whether enhanced tolerance at the level of gene expression contributed to its invasion success. We collected G. vermiculophylla from its native range in Japan and from two non-native regions along the Delmarva Peninsula (Eastern United States) and in Germany. Thalli were reared in a common garden for 4 months at which time we performed comparative transcriptome (mRNA) and microRNA (miRNA) sequencing. MRNA-expression profiling identified 59 genes that were differently expressed between native and non-native thalli. Of these genes, most were involved in metabolic pathways, including photosynthesis, abiotic stress, and biosynthesis of products and hormones in all four non-native sites. MiRNA-based target-gene correlation analysis in native/non-native pairs revealed that some target genes are positively or negatively regulated via epigenetic mechanisms. Importantly, these genes are mostly associated with metabolism and defence capability (e.g., metal transporter Nramp5, senescence-associated protein, cell wall-associated hydrolase, ycf68 protein and cytochrome P450-like TBP). Thus, our gene expression results indicate that resource reallocation to metabolic processes is most likely a predominant mechanism contributing to the range-wide persistence and adaptation of G. vermiculophylla in the invaded range. This study, therefore, provides molecular insight into the speed and nature of invasion-mediated rapid adaption.
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  • 58
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    GEOMAR Helmholtz Zentrum für Ozeanforschung Kiel
    Publication Date: 2023-01-24
    Description: FS MARIA S. MERIAN - MSM114, Las Palmas - Mindelo, 16. - 21. Januar 2023 „MOSES Eddy Study IV“
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  • 59
    Publication Date: 2023-01-24
    Description: The Ca isotope composition of calcite and aragonite can provide insights into their formation conditions. The accurate interpretation of the Ca isotope composition of natural samples, however, requires precise knowledge of the equilibrium Ca isotope fractionation between the solid and fluid phases. In this study, the three-isotope method with 42Ca, 43Ca and 44Ca has been used to estimate the equilibrium isotope fractionation of Ca between the CaCO3 minerals calcite and aragonite and the Ca2+ aquo ion. Reactive fluids were enriched with 43Ca and equilibrated with synthetic calcite and aragonite of natural Ca isotope distribution up to 3745 h at 25 °C. The isotopic composition of solids and fluids was measured using MC-ICP-MS and the estimated equilibrium fractionation for calcite-Ca2+(aq) and aragonite-Ca2+(aq) was Δ44/42Casolid-fluid=−0.02±0.13‰ and −0.80±0.10‰, respectively. Textural observations of the reacted solids suggest that isotope equilibration in aragonite experiments occurs via extensive Ostwald ripening, yielding large crystalline needles at the end of the experiments. In contrast, calcite did not exhibit an observable increase in size during the course of the experiments. Isotope exchange rates in the case of calcite are similar to those reported in previous studies and ∼4 orders of magnitude lower than the far-from-equilibrium calcite dissolution rate. Calcium isotope exchange rates for aragonite are more rapid than calcite driven by a greater extent of Ostwald ripening occurring via dissolution/precipitation reactions. The results of this study suggest that the Ca isotope compositions of calcite and aragonite crystals in chemical equilibrium, but isotope disequilibrium, with natural fluids could be significantly altered without overt evidence of diagenesis, especially in the case of calcite. The extent to which Ca isotope compositions are altered, however, would depend strongly on the environmental conditions, such as fluid:solid ratio and permeability of the solid facilitating fluid transport.
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  • 60
    Publication Date: 2023-01-27
    Description: Changes in the background climate are known to affect El Niño–Southern Oscillation (ENSO) by altering feedbacks that control ENSO’s characteristics. Here, the sensitivity of ENSO variability to the background climate is investigated by utilizing two Community Earth System Model, version 1 (CESM1), simulations in which the solar constant is altered by ±25 W m−2. The resulting stable warm and cold climate mean state simulations differ in terms of ENSO amplitude, frequency, diversity, asymmetry, and seasonality. In the warm run, ENSO reveals a larger amplitude and occurs at higher frequencies relative to the cold and control runs as well as observations. The warm run also features more eastern Pacific El Niños, an increased asymmetry, and a stronger seasonal phase locking. These changes are linked to changes in the mean state via the amplifying and damping feedbacks. In the warm run, a shallower mean thermocline results in a stronger subsurface–surface coupling, whereas the cold run reveals reduced ENSO variability due to a reduced Bjerknes feedback in accordance with a deeper mean thermocline and enhanced surface wind stress. A strong zonal advective and upwelling feedback further contribute to the large ENSO amplitude in the run with a warmer mean state. In the cold run, ENSO events are partly forced by anomalous shortwave radiation. However, in light of the large temperature contrast between the simulations of up to 6 K in the tropical Pacific, the relatively small changes in ENSO variability highlight the robustness of ENSO dynamics under vastly different climate mean states.
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  • 61
    Publication Date: 2023-01-27
    Description: Vouacapoua americana (Fabaceae) is an economically important tree in the Amazon region and used for its highly resistant heartwood as well as for medicinal purposes. Despite its frequent use, phytochemical investigations have been limited and rather focused on ecological properties than on its pharmacological potential. In this study, we investigated the phytochemistry and bioactivity of V. americana stem bark extract and its constituents to identify eventual lead structures for further drug development. Applying hydrodistillation and subsequent GC-MS analysis, we investigated the composition of the essential oil and identified the 15 most abundant components. Moreover, the diterpenoids deacetylchagresnone (1), cassa-13(14),15-dien-oic acid (2), isoneocaesalpin H (3), (+)-vouacapenic acid (4), and (+)-methyl vouacapenate (5) were isolated from the stem bark, with compounds 2 and 4 showing pronounced effects on Methicillin-resistant Staphylococcus aureus and Enterococcus faecium, respectively. During the structure elucidation of deacetylchagresnone (1), which was isolated from a natural source for the first time, we detected inconsistencies regarding the configuration of the cyclopropane ring. Thus, the structure was revised for both deacetylchagresnone (1) and the previously isolated chagresnone. Following our works on Copaifera reticulata and Vatairea guianensis, the results of this study further contribute to the knowledge of Amazonian medicinal plants.
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  • 62
    Publication Date: 2023-01-27
    Description: Limited constraints on the variability of the deep-water production in the Labrador Sea complicate reconstructions of the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Late Quaternary. Large volumes of detrital carbonates were repeatedly deposited in the Labrador Sea during the last 32 kyr, potentially affecting radiogenic Nd isotope signatures. To investigate this the Nd isotope compositions of deep and intermediate waters were extracted from the authigenic Fe-Mn oxyhydroxide fraction, foraminiferal coatings, the residual silicates and leachates of dolostone grains. We provide a first order estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. During the Last Glacial Maximum the Nd isotope signatures in the Labrador Sea would allow active water mass mixing with more radiogenic ɛNd values (-12.6 and -14) prevailing in its eastern part whereas less radiogenic values (ɛNd ∼ -18.4) were found on the western Labrador slope. The deposition of detrital carbonates during Heinrich stadials (2,1) was accompanied by negative detrital and authigenic Nd isotope excursions (ɛNd ∼ -31) that were likely controlled by dissolution of dolostone or dolostone associated mineral inclusions. This highly unradiogenic signal dominated the authigenic phases and individual water masses in the Labrador Sea, serving as potential source of highly unradiogenic Nd to the North Atlantic region, while exported southward. The Holocene authigenic ɛNd signatures of the coatings and leachates significantly differed from those of the detrital silicates, approaching modern bottom water mass signatures during the Late Holocene. Key Points - Estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea - Dissolution of detrital dolostones in the water column during Heinrich stadials at least partially controlled ɛNd signatures - During the LGM generally more radiogenic signatures possibly indicate active water mass advection and mixing in the Labrador Sea
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  • 63
    Publication Date: 2023-01-30
    Description: We calculate the depth to magnetic basement and the average crustal magnetic susceptibility, which is sensitive to the presence of iron-rich minerals, to interpret the present structure and the tecto-magmatic evolution in the Central Tethyan belt. Our results demonstrate exceptional variability of crustal magnetization with smooth, small-amplitude anomalies in the Gondwana realm and short-wavelength high-amplitude variations in the Laurentia realm. Poor correlation between known ophiolites and magnetization anomalies indicates that Tethyan ophiolites are relatively poorly magnetized, which we explain by demagnetization during recent magmatism. We analyze regional magnetic characteristics for mapping previously unknown oceanic fragments and mafic intrusions, hidden beneath sedimentary sequences or overprinted by tectono-magmatic events. By the style of crustal magnetization, we distinguish three types of basins and demonstrate that many small-size basins host large volumes of magmatic rocks within or below the sedimentary cover. We map the width of magmatic arcs to estimate paleo-subduction dip angle and find no systematic variation between the Neo-Tethys and Paleo-Tethys subduction systems, while the Pontides magmatic arc has shallow (∼15o) dip in the east and steep (∼50-55o) dip in the west. We recognize an unknown, buried 450 km-long magmatic arc along the western margin of the Kırşehir massif formed above steep (55o) subduction. We propose that lithosphere fragmentation associated with Neo-Tethys subduction systems may explain high-amplitude, high-gradient crustal magnetization in the Caucasus Large Igneous Province. Our results challenge conventional regional geological models, such as Neo-Tethyan subduction below the Greater Caucasus, and call for reevaluation of the regional paleotectonics. Key Points: Magnetic regionalization does not fully match regional geological models in the Central Tethyan Belt We identify previously unknown magmatic arcs and ocean relics Magnetization is weak in Gondwana and strong in Laurentia terranes: Kirsehir massif has Laurentia affinity
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  • 64
    Publication Date: 2023-01-30
    Description: Harmful marine bacteria, such as Vibrio or Aeromonas species, typically exist at low abundance in ocean environments but represent a reservoir from which epidemics can arise. Particularly, Vibrio strains and their associated infections are on the rise globally due to increasing sea surface temperature representing an emergent threat for human and animal health also being responsible for large economic losses in the aquaculture industry worldwide. New technological approaches are needed to improve strategies targeting these pathogens. This review discusses new approaches based on improved sampling strategies and novel analytical methods offering increased accuracy, high throughput, and informativeness to study and detect microbial pathogens in the marine environment. Detecting and characterizing ultra-low-abundance pathogenic strains can serve as a critical tool in risk management and outbreak prevention of diseases caused by emerging marine pathogens.
    Type: Article , PeerReviewed
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  • 65
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    GEOMAR Helmholtz Centre for Ocean Research Kiel
    Publication Date: 2023-01-30
    Description: (25.01. - 04.03.2023)
    Type: Report , NonPeerReviewed
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  • 66
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    Universität Hamburg
    Publication Date: 2023-01-30
    Description: Fahrtabschnitt 23.01. – 29.01.2023
    Type: Report , NonPeerReviewed
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  • 67
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    CDRmare Research Mission
    Publication Date: 2023-01-30
    Description: Algen, Zooplankton und Fische gehören zu den Schlüsselakteuren der biologischen Kohlenstoffpumpe, mithilfe derer der Ozean der Atmosphäre auf natürliche Weise Kohlendioxid entnimmt und den enthaltenen Kohlenstoff in großen Wassertiefen einlagert. Damit dieser Mechanismus jedoch optimal funktioniert, braucht es Nährstoffe, die vielerorts fehlen, zumindest im lichtdurchfluteten Oberflächenwasser. Durch das Heraufpumpen nährstoffreichen Tiefenwassers könnte der Mensch diesen Nährstoffmangel beheben. Ob ein solcher künstlicher Auftrieb aber tatsächlich klimawirksam wäre, welche Risiken er mit sich brächte und ob er technisch und rechtlich im großen Stil umgesetzt werden könnte, ist bislang ungewiss. Die Forschungsmission CDRmare liefert Antworten.
    Type: Report , NonPeerReviewed
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  • 68
    Publication Date: 2023-01-30
    Description: Despite low temperatures, poor nutrient levels and high pressure, microorganisms thrive in deep-sea environments of polar regions. The adaptability to such extreme environments renders deep-sea microorganisms an encouraging source of novel, bioactive secondary metabolites. In this study, we isolated 77 microorganisms collected by a remotely operated vehicle from the seafloor in the Fram Strait, Arctic Ocean (depth of 2454 m). Thirty-two bacteria and six fungal strains that represented the phylogenetic diversity of the isolates were cultured using an One-Strain-Many-Compounds (OSMAC) approach. The crude EtOAc extracts were tested for antimicrobial and anticancer activities. While antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecium was common for many isolates, only two bacteria displayed anticancer activity, and two fungi inhibited the pathogenic yeast Candida albicans. Due to bioactivity against C. albicans and rich chemical diversity based on molecular network-based untargeted metabolomics, Aspergillus versicolor PS108-62 was selected for an in-depth chemical investigation. A chemical work-up of the SPE-fractions of its dichloromethane subextract led to the isolation of a new PKS-NRPS hybrid macrolactone, versicolide A (1), a new quinazoline (−)-isoversicomide A (3), as well as three known compounds, burnettramic acid A (2), cyclopenol (4) and cyclopenin (5). Their structures were elucidated by a combination of HRMS, NMR, [α]D, FT-IR spectroscopy and computational approaches. Due to the low amounts obtained, only compounds 2 and 4 could be tested for bioactivity, with 2 inhibiting the growth of C. albicans (IC50 7.2 µg/mL). These findings highlight, on the one hand, the vast potential of the genus Aspergillus to produce novel chemistry, particularly from underexplored ecological niches such as the Arctic deep sea, and on the other, the importance of untargeted metabolomics for selection of marine extracts for downstream chemical investigations.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 69