Polycyclic aromatic hydrocarbons and amino acids in meteorites and ice samples from LaPaz Icefield,Antarctica

Abstract— –We have analyzed ice samples and meteorites from the LaPaz region of Antarctica to investigate the composition of polycyclic aromatic hydrocarbons (PAHs) and amino acids with the goal to understand whether or not there is a compositional relationship between the two reservoirs. Four LL5 ordinary chondrites (OCs) and one CK carbonaceous chondrite were collected as part of the 2003/2004 ANSMET season. Ice samples collected from directly underneath the meteorites were extracted. In addition, exhaust particles from the snowmobiles used during the expedition were collected to investigate possible contributions from this source. The meteorite samples, the particulate matter and solid‐state extracts of the ice samples and the exhaust filters were subjected to two‐step laser mass spectrometry (L2MS) to investigate the PAH composition. For amino acids analysis, the meteorites were extracted with water and acid hydrolyzed, and the extracts were analyzed with offline OPA/NAC derivatization combined with liquid chromatography with UV fluorescence detection and time of flight mass spectrometry (LC‐FD/ToF‐MS). PAHs in the particulate matter of the ice were found to be qualitatively similar to the meteorite samples, indicating that micron‐sized grains of the meteorite may be embedded in the ice samples. The concentration levels of dissolved PAHs in all the ice samples were found to be below the detection limit of the L2MS. The PAH composition of the snowmobile exhaust is significantly different to the one in particulate matter, making it an unlikely source of contamination for Antarctic meteorites. The amino acids glycine, β‐alanine and γ‐amino‐n‐butyric acid that were detected at concentrations of 3 to 19 parts per billion (ppb) are probably indigenous to the Antarctic meteorites. Some of the LaPaz ice samples were also found to contain amino acids at concentration levels of 1 to 33 parts per trillion (ppt), in particular α‐aminoisobutyric acid (AIB), an abundant non‐protein amino acid of extraterrestrial origin found in some carbonaceous chondrites. We hypothesize that this amino acid could have been extracted from Antarctic micrometeorites and the particulate matter of the meteorites during the concentration procedure of the ice samples.     

Caldera subsidence in extensional tectonics

A 45-km-long regional dike was emplaced over a period of 2 weeks in August 2014 at the boundary between the East and North Volcanic Zones in Iceland. This is the first regional dike emplacement in Iceland monitored with modern geophysical networks, the importance of which relates to regional dikes feeding most of the large fissure (e.g., Eldgja 934 and Laki 1783) and lava shield (e.g. early Holocene Skjaldbreidur and Trölladyngja) eruptions. During this time, the dike generated some 17,000 earthquakes, more than produced in Iceland as a whole over a normal year. The dike initiated close to the Bardarbunga Volcano but gradually extended to the northeast until it crossed the boundary between the East Volcanic Zone (EVZ) and the North Volcanic Zone (NVZ). We infer that the strike of the dike changes abruptly at a point, from about N45°E (coinciding with the trend of the EVZ) to N15°E (coinciding with the trend of the NVZ). This change in strike occurs at latitude 64.7°, exactly the same latitude at which about 10 Ma dikes in East Iceland change strike in a similar way. This suggests that the change in the regional stress field from the southern to the northern part of Iceland has been maintained at this latitude for 10 million years. Analytical and numerical models indicate that the dike-induced stress field results in stress concentration around faults and particularly shallow magma chambers and calderas in its vicinity, such as Tungnafellsjökull, Kverkfjöll, and Askja. In particular, the dike has induced high compressive, shear, and tensile stresses at the location of the Bardarbunga shallow chamber and (caldera) ring-fault where numerous earthquakes occurred during the dike emplacement, many of which have exceeded M5 (the largest M5.7). The first segment of the dike induced high tensile stresses in the nearby part of the Bardarbunga magma chamber/ring-fault resulting in radially outward injection of a dike from the chamber at a high angle to the strike of the regional dike. The location of maximum stress at Bardarbunga fluctuates along the chamber/ring-fault boundary in harmony with dike size and/or pressure changes and encourages ring-dike formation and associated magma flow within the chamber. Caldera collapse and/or eruption in some of these volcanoes is possible, most likely in Bardarbunga, but depends largely on the future development of the regional dike.     

Downsizing of supermassive black holes from the SDSS quasar survey – II. Extension to z∼ 4

Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for which the C  iv line is observed, we use an analysis scheme to derive the z -dependence of the maximum mass of active black holes, which overcomes the problems related to the Malmquist bias. The same procedure is applied to the low-redshift sample of SDSS quasars for which Hβ measurements are available. Combining with the results from the previously studied Mg  ii sample, we find that the maximum mass of the quasar population increases as  (1 + z )^1.64±0.04  in the redshift range  0.1 z 4  , which includes the epoch of maximum quasar activity.     

Tectonics,sea-level changes and palaeoenvironments in the early Pleistocene of Rome (Italy)

The historical site of the Monte Mario lower Pleistocene succession (Rome, Italy) is an important marker of the Pliocene/Pleistocene boundary. Recently, the Monte Mario site was excavated and restudied. A spectacular angular unconformity characterizes the contact between the Monte Vaticano and the Monte Mario formations, which marks the Pliocene/Pleistocene boundary. Biostratigraphical analyses carried out on ostracod, foraminifer, and calcareous nannofossil assemblages indicate an Early Pliocene age (topmost Zanclean, 3.81–3.70 Ma) for the underlying Monte Vaticano Formation, whereas the Monte Mario Formation has been dated as early Pleistocene (Santernian, 1.66–1.59 Ma). Palaeomagnetic analyses point to C2Ar and C1r2r polarity chrons for the Monte Vaticano and the Monte Mario formations, respectively. The Monte Mario Formation consists of two obliquity-forced depositional sequences (MM1 and MM2) characterized by transgressive systems tracts of littoral marine environments at depths, respectively, of 40–80 m and 15–20 m. The data obtained from foraminifer and ostracod assemblages allow us to reconstruct early Pleistocene relative sea-level changes near Rome. At the Plio/Pleistocene transition, a relative sea-level drop of at least 260 m occurred, as a result of both tectonic uplift of the central Tyrrhenian margin and glacio-eustatic changes linked to early Pleistocene glaciation (Marine Isotope Stage 58).     

Salinity Variability and Water Exchange in Interconnected Estuaries

A high-resolution coastal ocean model is used to investigate salinity variability and water exchange in a complex coastal system off the southern U.S. characterized by three adjacent sounds that are interconnected by a network of channels, creeks, and intertidal areas. Model results are generally highly correlated with observations from the Georgia Coastal Ecosystem Long Term Ecological Research (GCE-LTER) program, revealing a high degree of salinity variability at the Altamaha River and Doboy Sound, decreasing sharply toward Sapelo Sound. A Lagrangian particle tracking method is used to investigate local residence time and connectivity in the system. Local residence time is highly variable, increasing with distance from the Altamaha River and decreasing with river flow, revealing that discharge plays a dominant role on transport processes and estuary-shelf exchange. The Altamaha River and Doboy Sound are connected to each other in all seasons, with exchange occurring both via coastal and estuarine pathways. While particles released at the Altamaha and Doboy rarely reach Sapelo Sound, particles released at Sapelo Sound and the creeks surrounding its main channel can reach the entire estuarine system.     

Using a maximum simplicity paleoclimate model to simulate millennial variability during the last four glacial periods

Many studies have documented the existence of millennial-scale variability in the Earth system during the last glacial period. An increasing number of studies document the occurrence of similar millennial variability during glacial periods previous to the last one. Here we use the simplest possible thermal-bipolar seesaw model to consider this variability for the last four glacial periods. We invert this model and use the high-pass filtered Vostok stable isotope records to make a first, tentative, attempt to estimate high-latitude N. Hemisphere temperature variability over the last four glacial periods, beyond the reach of Greenland ice-core records. The model result is compared against the Vostok methane record, which shows rapid variations in parallel to Greenland temperature records during the last glacial period. A further comparison is carried out against the planktonic oxygen isotope of north Atlantic core ODP 980. There is agreement between the records on the existence of similar millennial-scale variability during the last three glacial periods with very similar characteristics to the variability during the last glacial cycle.     

Continuous in situ measurements of volcanic gases with a diode-laser-based spectrometer: CO<Subscript>2</Subscript> and H<Subscript>2</Subscript>O concentration and soil degassing at Vulcano (Aeolian islands: Italy)

We report on a continuous-measurement campaign carried out in Vulcano (Aeolian islands, Sicily), devoted to the simultaneous monitoring of CO₂ and H₂O concentrations. The measurements were performed with an absorption spectrometer based on a semiconductor laser source emitting around a 2-μm wavelength. The emitted radiation was selectively absorbed by two molecular ro-vibrational transitions specific of the investigated species. Data for CO₂ and H₂O concentrations, and CO₂ soil diffusive flux using an accumulation chamber configuration, were collected at several interesting sampling points on the island (Porto Levante beach- PLB, Fossa Grande Crater – FOG- and Valley of Palizzi, PAL). CO₂/H₂O values, measured on the ground, are very similar (around 0.019 (± 0.006)) and comparable to the previous discrete detected values of 0.213 (Fumarole F5-La Fossa crater rim) and 0.012 (Fumarole VFS – Baia Levante beach) obtaid during the 1977–1993 heating phase of the crater fumaroles.     

Wetland Plant Diversity in a Coastal Nature Reserve in Italy: Relationships with Salinization and Eutrophication and Implications for Nature Conservation

Wetlands are important centers of biodiversity. Coastal wetlands are subject to anthropogenic threats that can lead to biodiversity loss and consequent negative effects on nature conservation. We investigated relationships between wetland vegetation and habitat conditions in a coastal Nature Reserve in Northern Italy that has undergone seawater intrusion and eutrophication for several decades. The wetland vegetation in the Nature Reserve consisted of nine communities of hygrophytic and helophytic vegetation and five communities of waterplant vegetation. The hygrophytic and helophytic communities were arranged according to a salinity gradient, from salt-free habitats to strongly saline habitats. The saline habitats had high nutrient levels, due to the influx of nitrate-rich saltwater from an adjacent lagoon. The waterplant communities were all typical of freshwater habitats. Water-table depth and concentration of dissolved nutrients in the water were the main factors structuring waterplant vegetation. The main driver of future changes in the wetland vegetation of the Nature Reserve is the ongoing increase in salinity levels which may enhance expansion of halophilic species and communities, thus outcompeting locally rare freshwater species. If nutrient, especially nitrate, load further increases in the next future, this may exert negative effects on wetland species and communities preferring nutrient-poor habitats.     

Shear and dilatational wave velocities for unsaturated soils

The primary objective of this study is for presenting some simple-to-use expressions relating the shear and dilatational wave velocities (V_S and V_P) to some physical and constitutive parameters of unsaturated soils. To this purpose, a simplified formulation is developed using the theory of linear poroelasticity in conjunction with some constitutive parameters widely used in geotechnical engineering. The derived expressions are of practical interest in view of the fact that they could be employed for evaluating the involved soil parameters from V_S and V_P measurements by in-situ or laboratory geophysical tests.