Mid-late Holocene lake levels and trophic states of a shallow lake from the southern Pampa plain, Argentina

Changes in trophic status of the shallow Lake La Brava (southeastern Pampa plain of Argentina) are evaluated based on geochemical, biological and sedimentological data. Based on a conceptual framework, we propose that the lake level defines the water column mixing conditions, affecting internal lake processes and determining the transparency of lake water. The shift between alternative states is reconstructed for the last ~4800 years. Four main lake stages have been recognized, although short term shifts characterize all stages. A turbid phytoplankton-dominated state prevailed between ~4700-4500 cal yr before present (BP). Drier conditions and low lake levels pushed the lake to a clear state until 2000 cal yr BP. Afterwards the lake switched back to a turbid state, and these conditions persisted until ~200 cal yr BP. In the last 200 years, the lake switched back and forth between clear and turbid states. The latter represents the modern conditions of the lake since ~1950 AD. These shifts can be attributed mainly to climatic drivers.We thank to Dr Juan Manuel Lirio and Lic Mario Núñez (Instituto Antártico Argentino) for field support. Nora Irene Maidana (Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina) help with diatom identification. Financial support was provided by PIP-CONICET 1265/08, PIP-CONICET 2142001100 100014, UBACyT 20020110100153 and CICYT project EROMED (CGL2011-25486). We thank the editor and two anonymous reviewers for their constructive comments, which helped us to improve the manuscript. This is the IDEAN contribution number R-112.Peer Reviewe

Vehicle-derived emissions and pollution on the road autovia 2 investigated by rock-magnetic parameters: A case study from Argentina

35 Pag., 7 Fig., 1 Tabl. The definitive version is available at: www.springerlink.comIn this work, we carried out a preliminary study of traffic-derived pollutants from primary sources (vehicles), and on roads (paved area), road borders and surroundings areas. The study is focussed on the identification, distribution and concentration of pollutants and magnetic carriers. Magnetic parameters and their analyses suggest that the magnetic signal of vehicle-derived emissions is controlled by a magnetite-like phase. Magnetic grain size estimations reveal the presence of fine particles (0.1–5 μm) that can be inhaled and therefore are dangerous to human health. Magnetic susceptibility results (about 175 × 10−5 SI) show a higher magnetic concentration — magnetic enhancement — in the central area of the tollbooth line that is related to higher traffic. In addition, magnetic susceptibility was computed on several roadside soils along a length of 120 km and used to generate a 2-D contour map, which shows higher magnetic values (100–200 10−5 SI) near the edge of the road. The observed distribution of magnetic values indicates that magnetic particles emitted by vehicles are accumulated and mainly concentrated within a distance of several meters (1–2 m) from the edge of the road. In consequence, the magnetic susceptibility parameter seems to be a suitable indicator of traffic-related pollution. Non-magnetic studies show an enrichment of some trace elements, such as Ba, Cr, Cu, Zn and Pb, that are associated with traffic pollution. Furthermore, statistical correlations between the content of toxic trace metals and magnetic variables support the use of magnetic parameters as potential proxies for traffic-related pollution in this study area.D. Marié was supported by two Fellowships (2005-2006, 2008) from the Comisión de Investigaciones Científicas de la Pcia. de Buenos Aires (CICPBA) and the Inter U program. Financial support was also received from a PICT-2005 of the ANPCYT, project No. 38050.Peer reviewe

Magnetic studies and scanning electron microscopy — X-ray energy dispersive spectroscopy analyses of road sediments, soils and vehicle-derived emissions

27 Pag., 2 Tabl., 6 Fig. The definitive version is available at: http://www.springerlink.com/content/0039-3169/Human health and environmental problems related to particulate matter emission from vehicles has become a topic of research interest in recent years. These airborne particles can not only be directly inhaled, but are also present as suspended and deposited particles on paved areas and roadside soils. Here we report on magnetic studies, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and chemical analyses of vehicle-derived particles collected from both primary sources and as deposited particles on roads and soils. Preliminary results, recently published by the authors, have revealed that the magnetic signal of such particles is controlled by a magnetite-like phase with magnetic grain size ranging between 0.1 µm and 5 µm. An enrichment of some trace elements: Ba, Cr, Cu, Zn and Pb was also found. In this study we focus on SEM and EDS complementary studies of magnetic extracts. SEM observations showed small individual particles or spherulites, small aggregates in the form of chains or clusters, large aggregates of spherules, flake-like bodies, fibre-like particles, sheet-like particles, irregular debris and large particle agglomerates, i.e. a wide variety of shapes. Grain size distribution is also in agreement with magnetic grain size estimations. Additionally the following elements: C, O, Na, Mg, Al, Si, S, K, Ca, V, Ba, Ti, Cr, Mn, Fe, Cu, Zn and Pb were detected by EDS analysis.The authors would like to thank the CONICET, UNCPBA and UNMdP. Financial support was also received from a PICT-2005 of the ANPCYT, project No. 38050 and by the CICYT project MEDEROCAR (CGL2008-0831).Peer reviewe

A high-resolution palaeoclimate record for the last 4800 years from lake la Brava, SE pampas plains, Argentina

19 Pags.- 1 Tabl.- 6 Figs. Geofísica Internacional by Instituto de Geofísica is licensed under a Creative Commons Reconocimiento-NoComercial-SinObraDerivada 3.0 Unported License.[ES] Los cambios climáticos son reflejados en las variaciones de diferentes parámetros. Las secuencias sedimentarias de lagos son buena fuente de esta información debido a que proveen grabaciones continuas y detalladas de cambios paleoclimáticos. Para determinar los cambios en el clima al SE de la llanura Pampeana, se presentan estudios de magnetismo de rocas realizados en un testigo colectado del fondo de la Laguna La Brava (Argentina). También se midieron contenidos totales de sulfuro, carbón orgánico e inorgánico (TS, TOC y TIC), elementos alcalinos, metales pesados y livianos, y cambios en las comunidades de vegetación. Se realizaron cinco determinaciones de edades radiocarbónicas y se calcularon las edades calibradas. La tasa promedio de acumulación de sedimento es 1.3 mm/año y la secuencia representa los últimos 4800 años en edades calibradas (cal. BP). El objetivo principal fue reconstruir el balance hidrológico de la laguna, cambios erosionales y de contribución de sedimento dentro del área de aporte, y explorar la medida en que pueden estar relacionados con cambios climáticos y/o actividades humanas. Los resultados de este trabajo y estudios previos sugieren cambios periódicos de condiciones frías a cálidas y húmedas. La relación entre plantas sumergidas y emergentes es consistente con el comportamiento de susceptibilidad magnética κ . Los cambios en TOC sugieren un ambiente húmedo durante períodos de mejoramiento magnético. Se identificaron eventos de desbordes y bajos niveles de la laguna. Para los últimos 50 cal. BP, cambios en la contribución de sedimento y procesos deposicionales fueron causados por impacto humano, en particular por el uso de recursos naturales.[EN] Climatic changes are reflected in variations of different parameters. Sequences of lake sediments are good sources of this information because they provide continuous and detailed records of palaeoclimatic changes. In order to determine the changes in climate in SE Pampas plain,in this paper we present a series of rock magnetic studies performed on a bottom core collected from Lake La Brava (Argentina). In order to establish lake level variations, we also measure total sulphur, organic and inorganic carbon (TS, TOC and TIC) content,alkaline elements, light and heavy metals and changes in vegetation communities. Five radiocarbon age determinations were made from samples of organic-rich clay and calibrated ages were calculated. The averaged sediment accumulation rate is 1.3 mm/yr and the sequence represents a temporal extent of about 4800 calibrated years before the present (cal. BP). The main aim was to reconstruct the hydrological balance of the lake, the changes in erosional strength and sediment supply within the catchment area since the Middle Holocene, and to explore the extent to which these may be linked to changes in climate and/or human activities. The results of this work and previous studies suggest periodic changes from cooler to warmer and humid conditions. Relationships between submerged and emergent plants are consistent with the behaviour of magnetic susceptibility. TOC changes suggest wet environment during magnetic enhancement. Floods and lower lake level events were identified in detail. Changes in sediment contribution and depositional processes for the last 50 cal. BP are caused by human impact, particularly by the use of natural resources.The authors wish to thank UNCPBA, IAA and CONICET. They are also grateful for funds provided by the CICYT project MEDEROCAR (CGL2008-0831), PIP-CONICET 1265/08 and the project PICT-O nº 13-11502.Peer reviewe

High-resolution paleomagnetic records from Laguna Potrok Aike (Patagonia, Argentina) for the last 16,000 years

Holocene and Late-glacial records documenting variations in direction and intensity of the geomagnetic field during the last 16,000 cal. BP are presented for Southern Patagonia. This continuous high-resolution terrestrial record from Laguna Potrok Aike (51°58`S, 70°23`W) was recovered within the SALSA (South Argentinean Lake Sediment Archives and modeling) project. Mineral magnetic measurements indicate that pseudo single-domain magnetite is the major carrier of the remanence allowing the reliable definition of stable natural remanent magnetization inclinations and declinations from alternating field demagnetization and principal component analysis. Paleomagnetic secular variation records reveal many of the familiar features of declination and inclination that have previously been recorded in other records from South Argentina but conspicuous centennial-scale differences are also observed. The results illustrate the potential of PSV records for dating sedimentary sequences in southern South America