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Seafloor anomalies along mid-ocean ridges with exceptionally thick and compositionally distinct basaltic crust, for example, at Iceland, suggest that the underlying mantle is hotter and chemically different from the adjacent subridge mantle. Here we present hafnium and neodymium isotope ratios of peridotites from the Charlie Gibbs Transform Zone, which is located at the southern end of the Reykjanes Ridge south-west of Iceland. These peridotites are strongly depleted in incompatible elements with extremely high hafnium isotope ratios, suggesting that they had already melted to a large extent before being incorporated into the plume, at least 1 billion years ago, and thereby also became less dense. We argue that seismic velocity anomalies, geodynamic models and geochemical affinities of ridge basalts connect the peridotites from the Charlie Gibbs Transform Zone to the ‘Iceland plume’. The thermochemical buoyancy of the moderately hot Iceland plume, but also that of other plumes worldwide, may therefore be strongly influenced by composition. Variable peridotite depletion along the rising Iceland plume could also cause the transient, density-driven pulses in plume flux, which have formed the V-shaped Reykjanes Ridge south of Iceland. Overall, expansion of a ridge-centred plume along adjacent ridges and melting of heterogeneous plume material explains the topographic swell, the seismic anomaly and the formation of V-shaped ridges, as well as the regional distribution of basalts with Icelandic affinity. The upwelling mantle beneath Iceland underwent melt depletion at least 1 billion years ago and is therefore compositionally buoyant, according to a study of neodymium and hafnium isotope ratios in peridotites from the Charlie Gibbs Transform Zone.

Eastern Sicily is characterised by fast tectonic uplift, intricate GPS-derived velocity fields, and significant seismic activity. Mount Etna, the largest subaerial active volcano in Europe, dominates the landscape, influencing the development of large-scale instability processes on the facing continental margin. South of Etna, the Malta Escarpment discloses crustal thinning, with active tectonics, extensional faults, and half grabens. Indications of active tectonics extend to northern sectors, suggesting a lithospheric tear and interaction with the Calabria-Peloritani uplift. This area has been affected by historical seismicity, with the 1693 earthquake triggering tsunami waves up to 15m high. Offshore seismic events, including the one in 1908, induced slope failures and turbidity currents on the Ionian abyssal plain, witnessed by several breaks in submarine cables. The continental margins of this region are generally characterized by narrow shelves and tectonically-controlled steep slopes, which are susceptible to different mass-wasting processes.

— This article presents results of the structural and morphological analysis of the fracture zones that are part of Doldrums Megatransform System (DMS), located in the northern part of the Equatorial Atlantic (6.5°–9° N) that include Vernadskiy and Bogdanov transform faults and the Doldrums and Pushcharovskiy megatransforms. Bathymetric map, based on the multibeam echo sounding data, collected during the 45th cruise of the R/V Akademik Nikolaj Strakhov was used for this analysis. It was established that large-scale variations in the width of fracture zone valleys are determined by the distribution of stresses perpendicular to the fracture zone. In the areas with compressive stresses, the fracture zone valleys are narrower and the extension areas are wider. The difference in geodynamic settings within the DMS is due to the difference in spreading directions, which change from 89° to 93° when moving from south to north. The depth of fracture zone valleys consistently increases from the periphery of the DMS (Bogdanov and Doldrums faults) to the center (Pushcharovskiy fracture zone) in accordance with a decrease in the upper mantle temperature. In each fracture zone, the valley depth decreases from the rift- fracture zone intersections towards the center of the active part to a certain background depth. It is assumed that this phenomenon is the result of the uplift of the valley bottom, which occurred due to the decompaction of the lithosphere, caused by the serpentinization of ultramafic rocks. The violation of the revealed variations in the width and depth of fracture zone valley patterns occurs as a result of various ridges and uplifts formation in the fracture zone. In the axial zones of the active parts of the fracture zone valleys median ridges are widespread, extending parallel to the fracture zone and representing serpentinite diapirs squeezed out above the bottom surface. Transverse ridges that were formed 10‒11 million years ago as a result of the lithospheric plate edge flexural bending under extensional conditions are now located in the western passive parts on the southern sides of the of Doldrums and Pushcharovskiy fracture zone valleys. The transverse ridge on the northern side of the Vernadskiy fracture zone, which includes Mount Peyve, was formed between 3.65‒2.4 Ma. Due to the frequent jumps of the spreading axis in this region, it was divided into three segments. There are interfracture zone ridges in megatransforms, which in the active part consist of two fracture zone valleys. The times of their formation were in the Pushcharovskiy megatransform, 30‒32 million years ago and in the Doldrums megatransform, about 4 million years ago. Due to the curvilinearity of the outlines and under the pressure of moving lithospheric plates, the interfracture zone ridges experience longitudinal (along the fault) compressive and tensile stresses, which are compensated by vertical uplifts of their separate blocks and the formation of depressions, pull apart depressions, and spreading centers (the latter are only in Pushcharovskiy megatransform). The structure-forming processes that determine the patterns and morphology of the fracture zones as a part of the DMS are related in their origin to the spreading and transform geodynamic systems.

Hydrothermal alteration may weaken volcanic rocks, causing the gravitational instability of portions of active volcanoes with potentially hazardous collapses. Here we show high‐resolution multibeam, magnetic and gravity surveys of the Marsili seamount, the largest active volcano of Europe located in the southern Tyrrhenian back‐arc basin. These surveys reveal zones with exceptionally low densities and with vanishing magnetizations, due probably to the comminution of basalts during hyaloclastic submarine eruptions and to their post‐eruptive hydrothermal alteration. The location of these regions correlates with morphological data showing the occurrence of past collapses. Similar evidence has been obtained from pre‐existing data at Vavilov Seamount, another older volcanic system in the Tyrrhenian back‐arc basin. Here a large volume of at least 50 km3 may have collapsed in a single event from its 40 km long western flank. Given the similarities between these volcanoes, a large collapse event may also be expected at Marsili.

A hyperspectral reflectance database was acquired for Baltic Sea submerged aquatic vegetation (SAV) and bare substrates by using Ramses (TriOS GmbH, Germany) radiometers capturing spectral data within the visible (VIS) and near-infrared (NIR) spectral ranges. The target samples included the most dominant and characteristic SAV species in the Baltic Sea, as well as several bare substrate types and beach cast communities. Target samples were measured within the 350–900 nm wavelength range under sunlight conditions without the water column influence. That is, samples were taken out of the water. Such a library is expected to provide insight into the spectral properties of various SAV species and substrates occurring in the coastal waters of the temperate geographic regions, facilitating the development of algorithms for differentiating and mapping various SAV communities. Additionally, measured reflectance spectra can be used as spectral end-members in physical models and classification algorithms for coastal vegetation mapping and quantification. The data are openly available in the PANGAEA online repository at https://doi.org/10.1594/PANGAEA.971518 (Vahtmäe et al., 2024).

An intercomparison of radiance and irradiance ocean color radiometers (the second laboratory comparison exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: (1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; (2) indoor, laboratory intercomparison using stable radiance and irradiance sources in a controlled environment; (3) outdoor, field intercomparison of natural radiation sources over a natural water surface. The aim of the experiment was to provide a link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the third phase of LCE-2: The results of the field experiment. The calibration of radiometers and laboratory comparison experiment are presented in a related paper of the same journal issue. Compared to the laboratory comparison, the field intercomparison has demonstrated substantially larger variability between freshly calibrated sensors, because the targets and environmental conditions during radiometric calibration were different, both spectrally and spatially. Major differences were found for radiance sensors measuring a sunlit water target at viewing zenith angle of 139° because of the different fields of view. Major differences were found for irradiance sensors because of imperfect cosine response of diffusers. Variability between individual radiometers did depend significantly also on the type of the sensor and on the specific measurement target. Uniform SI traceable radiometric calibration ensuring fairly good consistency for indoor, laboratory measurements is insufficient for outdoor, field measurements, mainly due to the different angular variability of illumination. More stringent specifications and individual testing of radiometers for all relevant systematic effects (temperature, nonlinearity, spectral stray light, etc.) are needed to reduce biases between instruments and better quantify measurement uncertainties.

An intercomparison of radiance and irradiance ocean color radiometers (The Second Laboratory Comparison Exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: 1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; 2) Indoor intercomparison using stable radiance and irradiance sources in controlled environment; and 3) Outdoor intercomparison of natural radiation sources over terrestrial water surface. The aim of the experiment was to provide one link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the activities and results of the first two phases of LCE-2: the SI-traceable radiometric calibration and indoor intercomparison, the results of outdoor experiment are presented in a related paper of the same journal issue. The indoor experiment of the LCE-2 has proven that uniform calibration just before the use of radiometers is highly effective. Distinct radiometers from different manufacturers operated by different scientists can yield quite close radiance and irradiance results (standard deviation s < 1%) under defined conditions. This holds when measuring stable lamp-based targets under stationary laboratory conditions with all the radiometers uniformly calibrated against the same standards just prior to the experiment. In addition, some unification of measurement and data processing must be settled. Uncertainty of radiance and irradiance measurement under these conditions largely consists of the sensor’s calibration uncertainty and of the spread of results obtained by individual sensors measuring the same object.

In the present study, the variable surface glycoprotein (VSG) gene of Trypanosoma evansi was cloned and expressed in Pichia pastoris (X-33). The diagnostic potential of recombinant VSG (rVSG) in ELISA has been determined using 1818 field sera samples collected from different species across different states of India. The developed test was compared with the standard reference test such as, CATT/T. evansi; moreover, the new assay was also compared in ELISA using VSG RoTat 1.2 antigen. The diagnostic sensitivity and specificity of recombinant protein were found to be 95.4% and 93.8% respectively, with Cohen's kappa value of 0.86. The epidemiological study revealed varied prevalence of surra in different species and across different geographical regions of India. Cattle experienced higher prevalence of surra with 42.2% seropositivity from eastern region of India, whereas camel showed 19.9% seropositivity from Rajasthan. Hence, the present study is useful as an effective tool in sero-diagnosis as well as surveillance.

The Ionian Sea in southern Italy is at the center of active interaction and convergence between the Eurasian and African–Adriatic plates in the Mediterranean. This area is seismically active with instrumentally and/or historically recorded Mw>7.0 earthquakes, and it is affected by recently discovered long strike-slip faults across the active Calabrian accretionary wedge. Many mud volcanoes occur on top of the wedge. A recently discovered one (called the Bortoluzzi Mud Volcano or BMV) was surveyed during the Seismofaults 2017 cruise (May 2017). High-resolution bathymetric backscatter surveys, seismic reflection profiles, geochemical and earthquake data, and a gravity core are used here to geologically, geochemically, and geophysically characterize this structure. The BMV is a circular feature ≃22 m high and ≃1100 m in diameter with steep slopes (up to a dip of 22∘). It sits atop the Calabrian accretionary wedge and a system of flower-like oblique-slip faults that are probably seismically active as demonstrated by earthquake hypocentral and focal data. Geochemistry of water samples from the seawater column on top of the BMV shows a significant contamination of the bottom waters from saline (evaporite-type) CH4-dominated crustal-derived fluids similar to the fluids collected from a mud volcano located on the Calabria mainland over the same accretionary wedge. These results attest to the occurrence of open crustal pathways for fluids through the BMV down to at least the Messinian evaporites at about −3000 m. This evidence is also substantiated by helium isotope ratios and by comparison and contrast with different geochemical data from three seawater columns located over other active faults in the Ionian Sea area. One conclusion is that the BMV may be useful for tracking the seismic cycle of active faults through geochemical monitoring. Due to the widespread diffusion of mud volcanoes in seismically active settings, this study contributes to indicating a future path for the use of mud volcanoes in the monitoring and mitigation of natural hazards.

The St. Paul F.Z. is a large structural domain made up of multiple transform faults interrupted by several Intra-Transform Ridge (ITR) spreading segments. Two regions were studied in details by submersible: (1) The ITR short (<20 km in length) segment near 0° 37'N-25° 27'W and 1° N-27° 42'W and (2) The St. Peter and St. Paul's Rocks (SPPR) massif located at 29° 25'W (¡3700 m depth). (1) The short ITR segments consist of a magma starved rift valley with recent volcanic activities at 4700 m depth. A geological profile made along the rift valley wall showed localized volcanics (basalts and dykes) which are believed to overlay and intrude the ultramafics. The geological setting and the high ultramafic/volcanic ratio suggest an extremely low magmatic supply and crustal-mantle uplift during lithospheric stretching and denudation. (2) The St. Peter and St. Paul's Rocks (SPPR) massif consists of a sigmoidal ridge within the active transform zone. The SPPR is divided into two different geological domains called the North and the South Ridges. The North Ridge consists of strongly tectonized fault scarps composed of banded and mylonitized peridotite, sporadic gabbros (3900-2500 m) and metabasalts (2700-1700 m). The South Ridge is less tectonized with undeformed, serpentinized spinel lherzolite (2000-1400 m) and basalts. Extensional motion and denudation accompanied by diapirism affected the South Ridge within a transform domain. Instead, the North Ridge was formed during an important strike-slip and faulting motion resulting in the uplifted portion of the St. Paul F.Z. transverse ridge. There is a regional compositional variation of the volcanics where E-MORBs and alkali basalts are produced on the SPPR massif and are comparable to the adjacent northern segments of the Mid-Atlantic Ridge. On the other hand, N and T- MORBs collected from the eastern part of the St. Paul F.Z. (25° 27'W IRT) are similar to the volcanics from the southern segments of the MAR. The peridotites exposed in these provinces (SPPR and ITR) are similar in their REE and trace element distribution. Different degrees (3-15%) of partial melting of a mixed composite mantle consisting of spinel and amphibole bearing lherzolite veined with 5-40% clinopyroxenite gave rise to the observed MORBs and alkali basalts.[PUBLICATION ABSTRACT]