New Sediment Cores Reveal Environmental Changes Driven by Tectonic Processes at Ancient Helike,Greece

According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse‐grained littoral facies at the base to fine‐grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault‐slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan‐delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.     

Hydrographic and atmospheric analysis of an autumnal upwelling event in the Ria of Vigo (NW Iberian Peninsula)

An autumnal upwelling event was observed in the Ria of Vigo (NW Iberian Peninsula) on 15th November 2001. This event was analyzed by means of thermohaline variables measured at CTD stations located in the study area, satellite sea surface temperature and wind data provided by QuikSCAT. Salinity and temperature distributions revealed that the upwelled water mass was Eastern North Atlantic Central Water (ENACW), typically observed during summer upwelling events. However, previous to the upwelling event, the characteristic autumnal body of water was recorded on 31st October 2001. Subsequent sea surface temperature and upwelling index corroborated the presence of an autumnal upwelling event of approximately 15 days duration. The probability of upwelling-favorable winds (from 1999 to 2004) was lower during autumn–winter than during spring–summer, although they may occur at any time of the year. Probabilities of 45% were calculated for February and November, with the highest probability (65%) corresponding to July.     

Chicxulub impact ejecta from Albion Island, Belize

Impact ejecta from the Albion Formation are exposed in northern Belize. The ejecta come from the outer portion of the continuous ejecta blanket of the Chicxulub crater, which is located 360 km to the northwest. The basal unit of the Albion Formation is a 1-m-thick clay and dolomite spheroid bed composed of up to four discrete flows. The clay spheroids are altered impact glass, and the dolomite spheroids are accretionary lapilli. The upper unit is a 15-m-thick coarse diamictite bed containing altered glass, large accretionary blocks, striated, polished, and impacted cobbles, and rare shocked quartz. The abundance of accretionary clasts, evidence for atmospheric drag sorting, and the presence of multiple flows in the Albion Formation indicate that atmospheres play an important role in the formation of the outer portions of continuous ejecta blankets of large craters.     

Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites

Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn in the dehydroxylation process was investigated using X-ray diffraction (XRD) and the Rietveld refinement of XRD data together with scanning electron microscopy (SEM), differential thermogravimetric analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). In all cases, the formed hematites retained the acicular shape of the precursor goethite. The dehydroxylation temperature increased with the increase of the Mn content in the parent goethite. The cell parameters of both phases decreased with the thermal treatment, however the decrease in the goethite b-parameter was more pronounced. This fact could be attributed to the distortion in the goethite structure by the presence of manganese. The band shifts in the FT-IR spectra of the goethites with different Mn substitution were analysed. The intensities of the hydroxyl vibrations were indicative of the degree of dehydroxylation.The chemical reactivity of all the samples, before and after the thermal treatment, was also studied. The kinetic experiments were carried out at 40 °C in 4 mol dm^− 3 HCl. The acid dissolution of all Mn-goethites showed a congruent behavior indicative of a homogeneous distribution of Mn in the goethite crystals, this trend was not observed in the formed hematites presenting a high Mn content. The dissolution rate in goethites increased with the increase of Mn content, the opposite effect was observed in the corresponding hematites. The activation energy in both phases was also obtained and indicated that the Mn substitution produces an opposite effect on goethite- and hematite-phases. Different kinetic laws were applied in order to explain the dissolution behavior, but the modified first-order Kabai equation described the dissolution data best.     

A winter upwelling event in the Northern Galician Rias: Frequency and oceanographic implications

A winter shelf-water upwelling evidence (February 2008) is described by first time in the Northern Galician Rias (NW Iberian Peninsula). On February 20, after 9 consecutive days of upwelling favorable conditions, inside the O Barqueiro Ria was observed the presence of seawater below 10 m depth which replaced the less saline water previously observed in January. This situation was in agreement with the analyzed Ekman transport close to the northern Galician coast. Salinity and temperature distribution revealed that the upwelled water inside the rias corresponds to shelf bottom seawater which is not associated with Eastern North Atlantic Central Water or the Iberian Poleward Current. In addition, TS diagram indicated a higher influence of upwelling eastward (Viveiro–Barqueiro–Ortigueira). Nutrient salts' concentrations also suggested the presence of seawater from subsurface origin with a small variation with regard to the winter mixing in this marine area. Plankton showed the existence of spring conditions related to solar radiation increase associated to upwelling favorable winds. Some species also corroborated the intrusion of shelf-water inside the ria. Results from the analysis of Ekman transport data from 1967 to 2007 revealed that this event cannot be considered an isolated episode. In fact, the number of days per month under upwelling favorable conditions in winter (January–March) was not negligible (8–10 days) showing that upwelling events along the northern Galician coast are also possible during winter.     

Poleward intrusion in the northern Galician shelf

The evolution of a warm water mass related to the Iberian Poleward Current (IPC) was characterized along the northern Galician shelf in November 2008 by means of Sea Surface Temperature and wind data. It was observed that under upwelling favorable conditions water temperature decreased along the northern coast and a temperature break appeared between Cape Vilano and Cape Ortegal showing a relaxation of the poleward intrusion. The effect of the IPC was also analyzed inside the Northern Galician Rias taking into account the hydrographical and biogeochemical properties measured on November 18. Water driven by the IPC was observed close to the mouth of the rias, around Cape Estaca de Bares, causing a nutrient salts decrease. Inside the rias a slight biological activity was found near surface resulting from fluvial contributions.     

Radio observations of interplanetary magnetic field structures out of the ecliptic

New observations of the out-of-the ecliptic trajectories of type III solar radio bursts have been obtained from simultaneous direction finding measurements on two independent satellite experiments, IMP-6 with spin plane in the ecliptic, and RAE-2 with spin plane normal to the ecliptic. Burst exciter trajectories were observed which originated at the active region and then crossed the ecliptic plane at about 0.8 AU. We find a considerable large scale north-south component of the interplanetary magnetic field followed by the exciters. The apparent north-south and east-west angular source sizes observed by the two spacecraft are approximately equal, and range from 25° at 600 kHz to 110° at 80 kHz.     

Geostatistical Analysis of Inverse Problem Variables: Application to Seismic Tomography

In this article we present a geostatistical approach to the transmission tomographic inverse problem, which is based on consideration of the inverse problem variables (velocity and traveltime errors) as regionalized variables (R.V.). Their structural analysis provides us with a new method to study the geophysical anisotropy of the rock, an important source of a priori information in order to design the anisotropic corrections. The underlying idea is that the geophysical structure can be deduced from the spatial structure of the regionalized variables which result from solving the tomographic problem with an isotropic algorithm. Also, the application of the structural analysis technique to the anisotropic corrected velocity field allows us to characterize the reliability of these corrections (model quality analysis). Geostatistical formalism also provides us with different techniques (parametric and non-parametric) to estimate and even simulate the velocity in the areas where this field has been considered anomalous based on field studies and on geophysical and statistical criteria. The kriging acts as a low-pass smoothing filter for the anomalous model parameters (velocities), but is not a substitute for an adequate filtering of the outliers before the inversion. This methodology opens the possibility of considering the inverse problem variables as stochastic processes, an important feature in cases where the tomogram is to be used as a tool of assessment to quantify the rock heterogeneities.     

Base surge deposits in pleistocene volcanic ash near Rome

Volcanic base surge deposits, recorded from the Pacific volcanic belts, Iceland, and the Azores, are here reported for the first time from Italy. Dune forms produced by deposition from base surges occur in the products of phreatic eruptions of Vulsini, Vico, and Sabatini volcanoes north of Rome. The occurrence of cross bedding, drag and slump features, normal dunes, symmetric and asymmetric antidunes, and radial troughs can in some cases be related to individual volcanic craters. Antidune features are more common on crater rims than farther from the craters, and the antidunes appear to be favored by high particle velocities and high water contents in the eruption, and perhaps by density and cohesiveness of the underlying material.