Extraterrestrial microspherules from Bajada del Diablo,Chubut, Argentina

The Quaternary infilling of a circular structure located in Bajada del Diablo, Chubut Province, Argentina has been proposed as a crater strewn field in previous studies. Here we report the finding of about 65 microspherules collected in a trench excavated in the center of the structure. The majority of hand-picked specimens are single, but some of them exhibit compound forms. The single specimens are spherical with a mean size of 137 μm, whereas the more complex samples show peduncles and drop shapes. Dendritic crystal growth is recognized in the internal structure of some broken microspherules. Preliminary chemical composition from the surface and center of microspherules was determined by energy dispersive spectrometry employing EDS. Quantitative EMPA and XRD analysis indicate that the microspherules are mainly composed of Fe and O with magnetite, Fe0 with subordinate wüstite. Following consideration of possible anthropogenic and volcanic origins, these spherulites are ascribed to an extraterrestrial input. An accumulation rate of 47 microspherules per m²/yr is estimated for the studied sediments. This value is two orders of magnitude higher than the reference flux for cosmic dust estimated for the last 1 Ma in the Transantarctic Mountains. The microspherules might have been generated as a byproduct of asteroid entry in the atmosphere.     

Nocturnal Surface-Layer Characteristics at the Bottom of a Valley

Nighttime data collected at the bottom of a valley locatedin southern Brazil are studied. The analyzed quantities includemomentum and sensible heat fluxes, turbulence statistics andintermittency factors, and their relationship to the stability parameter.The proper interval for averaging and flux calculations is foundto be 20 min, based on the comparison of the fluxes and therandom error associated in their determination. Each data seriesis classified as calm or windy, according to the mean windspeed. A much better dependency of the variables in terms of thestability parameter is found under windy conditions. Analysis ofthe wind direction and topographic scales indicates that distortioneffects under calm conditions affect the flow, while the flow is inlocal equilibrium for windy conditions. In this case, the sensible heatflux shows a minimum for a value of z/L=0.08, while the momentumflux and the normalized scales of the wind components andtemperature decrease monotonically as the stability increases. Anintermittency factor is proposed and shown to be larger (moreintermittency) for more stable conditions.     

Intermittency and the Exchange of Scalars in the Nocturnal Surface Layer

The determination of nocturnal surface fluxes in low wind conditions is a major problem for micrometeorological studies. The eddy correlation technique, extensively used in field measurements, becomes inappropriate if not enough turbulent activity exists. At the same time, the phenomenon of turbulence intermittency is responsible for the existence of localized events of short duration within which a large fraction of the total nighttime scalar exchange occurs. The scalar flux within a certain intermittent event varies considerably depending on the window used for the flux calculation. In many cases, events with very different time durations occur in the same night, and therefore, the proper determination of the surface flux would require averaging within data windows of different sizes for each event. In this work, the surface exchanges of temperature, moisture and carbon dioxide are analysed at a micrometeorological tower at southern Brazil. Intermittent turbulence is a common occurrence at the location. The analysis shows that the fluxes vary with turbulence intensity and the estimation technique. A variable-window size method for flux estimation is suggested and shown to cause an increase in the magnitude of the nocturnal surface fluxes     

Turbulent carbon exchange in very stable conditions

Turbulent fluxes obtained using the conventional eddy covariance approach result in erratic results with large time fluctuations in extremely stable conditions. This can limit efforts to estimate components of the nocturnal energy budget and respiratory CO₂ fluxes. Well-organized fluxes that show a clear dependence on turbulent intensity were obtained when multiresolution decomposition was used to estimate turbulent exchanges. CO₂, heat and water vapour fluxes were observed at a site in the eastern Amazon basin that had been cleared for agricultural purposes. Temporal scales of the carbon transfer were determined and shown to be similar to those of latent heat, but as much as three times larger than those of sensible heat. CO₂ eddy diffusivities at the temporal scales on which most of the vertical CO₂ exchange occurs are shown to be 50 times larger than the eddy diffusivity for heat. A process associated with the vertical scale of the scalar accumulation layer is suggested to explain these different scales and turbulent diffusivities of carbon and sensible heat transfer. For an appreciable range of turbulence intensities, the observed vertical turbulent carbon exchange is insufficient to account for the locally respired CO₂ estimated independently. Evidence that shallow drainage currents may account for this is given.     

Using Empirical Mode Decomposition to Filter Out Non-turbulent Contributions to Air–Sea Fluxes

A methodology based on Empirical mode decomposition (EMD) was used to filter out non-turbulent motions from measurements of atmospheric turbulence over the sea, aimed at reducing their contribution to eddy-covariance (EC) estimates of turbulent fluxes. The proposed methodology has two main objectives: (1) to provide more robust estimates of the fluxes of momentum, heat and CO\(_2\); and (2) to reduce the number of flux intervals rejected due to non-stationarity criteria when using traditional EC data processing techniques. The method was applied to measurements from a 28-day cruise (HALOCAST 2010) in the Eastern Pacific region. Empirical mode decomposition was applied to 4-h long time series data and used to determine the cospectral gap time scale, \(T_\mathrm{{gap}}\). Intrinsic modes of oscillation with characteristic periods longer than the gap scale due to non-turbulent motions were assumed and filtered out. Turbulent fluxes were then calculated for sub-intervals of length \(T_\mathrm{{gap}}\) from the filtered 4-h time series. In the HALOCAST data, the gap scale was successfully identified in 89% of the 4-h periods and had a mean of 37 s. The EMD approach resulted in the rejection of 11% of the flux intervals, which was much less than the 68% rejected when using standard filtering methods based on data non-stationarity. For momentum and sensible heat fluxes, the averaged difference in flux magnitude between the traditional and EMD approaches was small (3 and 1%, respectively). For the CO\(_2\) flux, the magnitude of EMD flux estimates was on average 16% less than fluxes estimated from linear detrended 10-min time series. These results provide evidence that the EMD method can be used to reduce the effects of non-turbulent correlations from flux estimates.     

Evaluation of the seismic risk of the unreinforced masonry building stock in Antioquia,Colombia

This work focuses on the exploitation of very high-resolution (VHR) satellite imagery coupled with multi-criteria analysis (MCA) to produce flood hazard maps. The methodology was tested over a portion of the Yialias river watershed basin (Nicosia, Cyprus). The MCA methodology was performed selecting five flood-conditioning factors: slope, distance to channels, drainage texture, geology and land cover. Among MCA methods, the analytic hierarchy process technique was chosen to derive the weight of each criterion in the computation of the flood hazard index (FHI). The required information layers were obtained by processing a VHR GeoEye-1 image and a digital elevation model. The satellite image was classified using an object-based technique to extract land use/cover data, while GIS geoprocessing of the DEM provided slope, stream network and drainage texture data. Using the FHI, the study area was finally classified into seven hazard categories ranging from very low to very high in order to generate an easily readable map. The hazard seems to be severe, in particular, in some urban areas, where extensive anthropogenic interventions can be observed. This work confirms the benefits of using remote sensing data coupled with MCA approach to provide fast and cost-effective information concerning the hazard assessment, especially when reliable data are not available.     

Review of the current distribution of southern elephant seals in the eastern South Pacific

The eastern South Pacific southern elephant seal population was extinguished by extensive hunting and the current presence of this species in this area is not well understood. We reviewed existing records from the 1900s to 2014 in the eastern South Pacific, as well as tagged seals and movement records in order to assess the potential immigration source of these individuals. A total of 409 confirmed sightings were compiled, ranging from the southern tip of South America (Cape Horn Archipelago) as far north as Ecuador, including some oceanic island groups. The evidence shows also that recolonisation of its former Pacific distribution has started, with slow population growth in three incipient pupping sites in southern Chile (south of 51°S). Although the source of all of the individuals in the growing colonies is unknown, evidence from tags and satellite tagging indicates that some seals come from subpopulations on the Peninsula Valdes and the Falkland/Malvinas Islands, although mtDNA analysis showed, preliminarily, a greater genetic relationship only with the Falkland/Malvinas Islands rookery.     

Construction of an evolutionary deglaciation model for the Irish midlands based on the integration of morphostratigraphic and geophysical data analyses

Alternative, established models for the deglaciation of the midlands of Ireland are tested against an interpretation of a suite of deglacial sediments covering an area of 600 km² in the east central midland area. Interpretation of the sediments is based on geomorphological mapping, lithostratigraphic characterization of exposures and geotechnical data supported by electrical resistivity tomography (ERT) and ground penetrating radar (GPR). GPR depicted small‐scale sedimentological and deformational structures within low‐conductivity soft sediments, such as cross‐bedding, planar bedding, channel‐like features and faulting planes, and revealed the internal architecture of eskers, glaciodeltas, subaqueous fans and raised bogs. ERT data permitted the detection of depth to bedrock and the lithological characterization of unconsolidated sediments. The ten sites presented were surveyed by traditional mapping methods and/or geophysical techniques. This allowed the construction of a local model of the deglaciation of the area which recognized five main stages. An ice sheet covering most of Ireland withdrew as a single body as far as the midlands. At this stage, two main directions of ice retreat are identified from the spatial distribution of meltwater/overflow channels, esker and morainic ridges, and ice‐marginal glaciolacustrine deposits. A pattern of deglacial sedimentation into an expanding ice‐marginal glacial lake is depicted. The glacial lake was dammed to the west by two ice dome fronts, one decaying to the north‐west and another to the south‐west, and by the Shannon Basin watershed to the east. Glacial lake outlets identified along the watershed and the altitude of the topset/foreset interface zone depicted in glaciodeltaic deposits allowed the identification of three lake water levels. The highest level is at 87–89 m Ordnance Datum (OD), the second lake level at 84 m OD and the third at 78 m OD. Copyright © 2012 John Wiley & Sons, Ltd.     

Bajada del Diablo impact crater-strewn field: The largest crater field in the Southern Hemisphere

Recent remote sensing analyses and field studies have shown that Bajada del Diablo, in Argentina, is a new crater-strewn field. Bajada del Diablo is located in a remote area of Chubut Province, Patagonia. This amazing strewn field contains more than 100 almost circular, crater-type structures with diameters ranging from 100 to 500 m in width and 30 to 50 m in depth. It is composed of three separated impact crater fields, which formed simultaneously. The impact was upon a Miocene basaltic plateau and Pliocene–Early Pleistocene pediments. The original crater field (60 km²) was later eroded by Late Pleistocene fluvial processes; thus, three major, separate areas were defined. Due to the erosional processes that have affected the area, it is difficult to determine yet if the crater field has a classic elliptical distribution. Crater structures are similar in target rocks, although showing different response and morphology in relation to rock type. They are simple rings, bowl-shaped with raised rimrock. Basaltic boulders have been deposited as a ring-shaped pile and the ejecta are found toward the NE flanks. The craters present a hummocky bottom, with dry ponds and lakes in the center, but they do not show raised central peaks. The rocks within the craters have strong and stable magnetic signature. No meteorite fragments or other diagnostic landmarks have been found yet. The craters have been partially filled in by debris flows from the rim and windblown sands in recent times. The origin of these crater fields may be related to multiple fragmentation of one asteroid that broke up before impact, perhaps traveling across the space as a rubble pile. Alternatively, multiple collisions of comet fragments could explain the formation of these crater fields. Based on field geological and geomorphological data, the age of this event is estimated to be bracketed between Early Pleistocene and Late Pleistocene (i.e., 0.78–0.13 Ma ago).