Mineral magnetic record of paleoclimate variation in loess and paleosol from the Buenos Aires formation (Buenos Aires, Argentina)

Environmental magnetic techniques were applied to a loess–paleosol sequence of the Chacopampean plain (Buenos Aires, Argentina). Mineral magnetic carriers and their grain size were identified in order to detect magnetic mineral fluctuations associated with climatic changes. Multidomain magnetite of detrital origin dominates the record. In paleosols, a high coercivity fraction was identified. Horizons with no visual evidence of pedogenesis, but showing magnetic behavior analogous to that of paleosols were observed and are thought to represent environmental conditions similar to those prevailing during paleosol formation.The results suggest that the magnetic signal yielded by paleosols in these South American loess deposits is different from that in the Chinese loess. This may be due to differences in parent materials, diagenetic processes and/or differences in paleoclimatic conditions in both regions.     

Sea breeze in Mallorca. A numerical study

Summary The Spanish island of Mallorca is located almost in the centre of the western Mediterranean. Very often from April to October, and almost every day during the summer, the sea breeze circulation develops. The shape and the topography of the island determine that the main characteristic feature of the sea breeze is the existence of a convergence line in the centre of the island. In this paper we describe the sea breeze circulation. A very simple non-eulerian numerical model allows us to simulate the evolution of the circulation during 24 hours.With 10 Figures     

A Case of Convection Development over the Western Mediterranean Sea: A Study through Numerical Simulations

Summary  A convective case producing heavy precipitation in the western Mediterranean region, characterized by pronounced upper level forcing and main rainfall over the sea, is studied. On the day of the event (September 28^th, 1994), more than 140 mm of precipitation were recorded in coastal lands of eastern Spain, and 180 mm were estimated over the sea with radar data. Synoptically, the case appears to combine warm and moist easterly advection at low levels, typically observed in torrential rainfall events of the region, with a less common strong upper level dynamical forcing. A set of mesoscale numerical simulations using the Hirlam model is performed to investigate the mechanisms responsible for the convection development, and to assess the influence of the orography on the rainfall field. Model output diagnosis indicates that in addition to the lower level forcing, a two-jets interaction is decisive for the triggering and driving of the convection during the event. Moreover, a non-topographic simulation reveals a relatively weak influence of the orography on this event when compared with other similar heavy precipitation cases in eastern Spain. Previous studies have shown an orographic influence of more than 90% on the rainfall whereas in this case about 50% of the precipitation over the area is attributed to the orographic forcing. The study is extended with an analysis of the individual effects of the Atlas and Iberian Peninsula, by means of a factor separation technique. It is shown that the Atlas range induces a redistribution of the precipitation over the Mediterranean, whereas local enhancements can be attributed to the Iberian topography. Received March 2, 1999     

Recent trends in temperature and precipitation over the Balearic Islands (Spain)

Changes in climatic parameters are often given in terms of global averages even though large regional variability is generally observed. The study of regional tendencies provides not only supplementary conclusions to more large-scale oriented results but is also of particular interest to local policy-makers and resource managers to have detailed information regarding sensible and influential climatic parameters. In this study, changes in precipitation for the Balearic Islands (Spain) have been analyzed using data from 18 rain gauges with complete daily time series during the period 1951–2006 and two additional sites where only monthly totals were available. Tendencies for maximum and minimum 2-m temperatures have also been derived using data from three thermometric stations with daily time series for the period 1976–2006. The thermometric stations are located at the head of the runways in the airports of the three major islands of the archipelago, where urbanization has arguably not had a relevant impact on the registered values. The annual mean temperature in the mid-troposphere and lower stratosphere has also been analyzed using the Balearics radiosonde data for the period 1981–2006. Results show there is a negative tendency for annual precipitation (163 mm per century) with 85% significance on the sign of the trend. An abrupt decrease in mean yearly precipitation of 65 mm is objectively detected in the time series around 1980. Additionally, the analysis shows that light and heavy daily precipitation (up to 4 mm and above 64 mm, respectively) increase their contribution to the total annual, while the share from moderate-heavy precipitations (16–32 mm) is decreasing. Regarding the thermometric records, minimum temperatures increased at a rate of 5.8°C per century during the 31 years and maximum temperatures also increased at a rate of 5.0°C per century, both having a level of statistical significance for the sign of the linear trend above 99%. Temperatures in the mid-troposphere decreased at a rate of ??5.4°C per century while a tendency of ??7.8°C per century is found in the lower stratosphere. The level of statistical significance for the sign of both the tropospheric and stratospheric linear trends is above 98% despite the great inter-annual variability of both series.     

Global environmental effects versus galaxy interactions

We explore properties of close galaxy pairs and merging systems selected from the Sloan Digital Sky Survey Data Release 4 in different environments with the aim to assess the relative importance of the role of interactions over global environmental processes. For this purpose, we perform a comparative study of galaxies with and without close companions as a function of local density and host halo mass, carefully removing sources of possible biases. We find that at low- and high-local-density environments, colours and concentration indices of close galaxy pairs are very similar to those of isolated galaxies. At intermediate densities, we detect significant differences, indicating that close pairs could have experienced a more rapid transition on to the red sequence than isolated galaxies. The presence of a correlation between concentration index and colours indicates that the physical mechanism responsible for the colour transformation also operates in the transformation of the luminous matter distribution. At fixed local densities, we find a dependence of the red galaxy fraction on dark matter halo mass for galaxies with or without a close companion. This suggests the action of host halo mass related effects. Regardless of dark matter halo mass, we show that the percentage of red galaxies in close pairs and in the control sample are comparable at low- and high-local-density environments. However, at intermediate local densities, the gap in the red fraction between close pairs and the control galaxies increases from ∼10 per cent in low-mass haloes up to ∼50 per cent in the most massive ones. Interestingly, we also detect that 50 per cent of merging systems populate the intermediate local environments, with a large fraction of them being extremely red and bulge dominated. Our findings suggest that in intermediate-density environments galaxies are efficiently pre-processed by close encounters and mergers before entering higher local density regions.     

A neutron activation technique for the analysis for fluorine in fluorspar samples

This article explains the results of the feasibility study about using neutron activation technique via Deferred gamma rays, to analyze the fluorine content in a sample from a fluorspar concentration plant. The theoretical responses of 12 items, constituting the samples have been analyzed. 468 reactions have been obtained from the study with the database EXFOR of these elements with neutrons from an Americium Beryllium source of 1 Ci activity.The radioactive decay of 29 products, anticipated from such an activation, has also been analyzed. From these results, a prototype for neutron activation has been designed. The different criteria of the measurement procedure to enable the activation of the fluorspar samples and to record their spectra with minimal interference from the source have been adjusted. A mathematical model of the activation response has been created and validated. The activation method to determine the fluorine content in fluorspar samples proved to be scientifically and technically feasible and verified by the results obtained.     

Characterization of a loess–paleosols section including a new record of the last interglacial stage in Pampean plain,Argentina

A new record of the Marine Isotopic Stage 5, the last Interglacial Stage before present is presented in this paper. Sedimentological, micromorphological, trace elements analyses (Rb–Sr) and magnetic polarity determination were performed on Buenos Aires and Ensenada Formation (Late Cenozoic) deposits in the southern Chaco-Pampean Basin (Argentina). This work aims to unravel paleoclimatic and paleoenvironmental information from the analyzed data.The studied deposits encompass a complex and cyclic 8 m-thick sedimentary-pedogenetic sequence formed by loessic sediments and paleosols with volcano-pyroclastic provenance.Four tabular units, with net base and top, were defined from erosion surfaces.An OSL age >126 kyr was obtained from the upper middle part of unit B, which suggests that this unit as well as unit C, could have developed during the latest interglacial stage, equivalent to MIS 5.The occurrence of calcretes indicates periods of little clastic supply and seasonal arid or semiarid climate while iron oxides, smectites and illite-bearing pedogenetic calcretes point to annual rain rates between 100 and 500 mm. No calcretes of any origin occur in present soils of the same zone. According to our proposed interpretation of the available data, climate during MIS 5 was drier than today. The drier conditions may have been related to lower temperatures during summer.     

Water level as the main driver of the alternation between a free-floating plant and a phytoplankton dominated state: a long-term study in a floodplain lake

This 10-year field data study explores the relevance of water level fluctuations in driving the shift from a free-floating plant (FFP) to a phytoplankton dominated state in a shallow floodplain lake from the Lower Paraná River. The multi-year natural flood pulse pattern in the Lower Paraná River drove the ecosystem regime from a FFP-dominant state during very high waters (1998–1999) to absolute phytoplankton prevalence with blooms of nitrogen fixing Cyanobacteria during extreme low waters (2008–2009). Satellite images support the observed changes over the decade and show the decrease of the surface lake area covered by FFP as well as the modification of the spectral firm in open waters, which documents the significant increases in phytoplankton chlorophyll a concentrations. We discuss the possibility that, despite a slow eutrophication in these highly vegetated systems, water level changes and not nutrients account for the shift from a floating macrophyte community to phytoplankton dominance. Cyclic shifts may occur in response to the seasonal floodpulse, but more strongly, as indicated by our results, in association to the extreme drought and flood events related to the El Niño Southern Oscillation, which is linked to discharge anomalies in the Paraná River.     

Interaction between seabed morphology and water masses around the seamounts on the Motril Marginal Plateau (Alboran Sea, Western Mediterranean)

The seabed morphology in the vicinity of the seamounts on the Motril Marginal Plateau (northern Alboran Sea) was investigated using high-resolution (sparker) and very high-resolution (TOPAS) seismic reflection profiles and multibeam bathymetry. The aim of the study was to determine the recent geological processes, and in particular those that control the contourite depositional system associated with the intermediate and deep Mediterranean water masses. Six groups of morphological features were identified: structural features (seamount tops, tectonic depressions), fluid escape-related features (pockmarks), mass-movement features (gullies, slides), bottom-current features (moats, scour marks, terraces, elongated and separated drifts, plastered drifts, confined drifts, sheeted drifts), mixed features (ridges) and biogenic features (including evidence of (dead) cold water corals such as Lophelia pertusa and Madrepora oculata). The main processes controlling the formation of these features are recent tectonic activity and the interaction of Mediterranean water masses with the seafloor topography. Seamounts act as topographic barriers that affect the pathway and velocity of the deep Mediterranean water masses, which are divided into strands that interact with the surrounding seafloor. The influence of the intermediate Mediterranean water mass, by contrast, is restricted mainly to the tops of the seamounts. Sediment instability and fluid-escape processes play a minor role, their occurrence being probably related to seismicity.     

Heavy metal chemical fractionation and immobilization in lightweight aggregates produced from mining and industrial waste

The fractionation of five heavy metals in a washing aggregate sludge, a sewage sludge, a clay-rich sediment, the mixtures of these materials and the lightweight aggregates manufactured with them has been determined by applying the optimized European Community Bureau of Reference sequential extraction procedure in order to evaluate the effects of the heating process on the extraction of these elements. Additionally, preparation of eluates by aggregate leaching has been performed in accordance with the UNE-EN-H44-3 standard. The availability of all the studied heavy metals has been reduced by the thermal treatment, since most of the heavy metals have become part of the undigested material in the lightweight aggregates. Nickel has been the heavy metal that has presented the highest concentration in the eluates obtained after completion of the single extraction procedure in the lightweight aggregates. The studied lightweight aggregates may be used in lightweight concrete manufacturing from the standpoint of heavy metal leaching.