New records of late Holocene tephras from Lake Futalaufquen (42.8°S), northern Patagonia

In regions with limited knowledge of the historical volcanic record, like remote areas in the Andean Southern Volcanic Zone, the definition of reliable age-depth models for lake sequences represents a valuable tool for tephra layers dating. In Lake Futalaufquen (42.8°S), Northern Patagonia, a short sedimentary sequence was extracted after the AD 2008 Chaitén eruption with the purpose to analyze the records of volcanic eruptions at these poorly studied latitudes. The sequence was dated by 210Pb, 137Cs, and 14C techniques. Five tephras were identified for the last 1600 years, restricted to the last 5 centuries. Sedimentology, morphology, and geochemical properties allowed the characterization of the tephras and their correlation with tephras recently identified proximal to the sources, mainly from Chaitén and Huequi volcanoes, and Michinmahuida accessory cones, representing the first distal records reported of these tephras. Furthermore, tephras modeled ages obtained by the sequence age-depth model shrink the ages for the volcanic events, like a potential cycle of activity from Michinmauida accessory cones during AD 1530 ± 55, one eruption from Huequi volcano at AD 1695 ± 50, and a possible recent eruption from Chaitén at AD 1775 ± 40. Additionally, the work contributes to improve the regional volcanic records knowledge, basic for volcanic hazard assessment.Fil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Ribeiro, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Arribere, Maria Angelica. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Trace element distribution and pollution status of surface sediments in lakes impacted by volcanic activity

Purpose: The main objective of the study was to assess the environmental quality status of the sediments of eleven Patagonian lakes regarding the concentrations of five trace elements, evaluating the influence of volcanic activity and water and sediment parameters on element concentration and distribution. Materials and methods: Surface sediment samples from 11 lakes were collected at different depths for granulometric analysis, organic matter (OM) contents, and determination of As, Br, Cr, Hg, Ni, and Zn concentrations. Physicochemical variables of the water column were also measured. The quality of the sediments and the potential ecological risks were assessed by comparing the concentrations of elements with local and global geochemical background values and with consensus-based sediment quality guidelines and through the calculation of environmental quality indices (enrichment factor and index of geo-accumulation). Results and discussion: A higher proportion of sand with a lower %OM characterized the surface sediments in lakes close to the volcanic complex (PCCVC), while a higher proportion of silt–clay with a higher %OM was found in sediments from lakes furthest from the PCCVC, consistent with the expected gradient of volcanic ash size deposited in the lakes. The presence of volcanic ashes in sediments seems to dilute trace element concentrations of samples, having sediment samples from lakes near the PCCVC lower concentrations of Br, Cr, and Ni than the furthest lakes. Environmental quality indices indicated minimal to moderate enrichment/contamination in sediments from deep lakes near the PCCVC and significant to high enrichment/contamination in sediments from lakes far from the volcano and in the shallower lakes. The concentrations of As, Cr, and Ni in six of the 11 sampled lakes are at levels considered harmful for sediment-dwelling organisms according to north hemisphere guidelines. Conclusions: Despite being in a protected area, the sediments of some Patagonian lakes have concentrations of potentially toxic elements at levels that may cause pollution and be of risk to the aquatic biota, with the volcanic ashes acting to dilute this effect.Fil: Apestegui, Aranza. Universidad Nacional de Río Negro; ArgentinaFil: Juncos, Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Daga, Romina Betiana. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Barriga, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Rizzo, Andrea Paula. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Ribeiro, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentin

Tephras emitted during the initial hydromagmatic phase (July 2012) of the 2012-2016 eruptive cycle of the Copahue volcano (Andes del Sur)

El volcán Copahue presenta un registro de erupciones históricas de limitada intensidad cuyo carácter ha sido analizado principalmente a partir de los eventos de las últimas décadas. Hacia fines del año 2011 comenzaron a observarse cambios significativos en diversos parámetros asociados a la actividad del volcán hasta que, luego de doce años de quietud, en julio de 2012 comenzó un nuevo ciclo eruptivo. En este trabajo se presenta la caracterización de los productos piroclásticos emitidos durante el evento del día 19 de julio de 2012, el cual tuvo una dispersión limitada, pero resulta de importancia para la definición del carácter de la fase inicial del ciclo eruptivo. Una alta proporción de litoclastos y la presencia de vitroclastos juveniles primarios, los cuales son estudiados en detalle, permiten caracterizar el mecanismo eruptivo, consistente con una erupción hidromagmática. La particularidad de la tefra generada está dada por la presencia de azufre piroclástico. Si bien este tipo de partículas ha sido identificado en erupciones previas, su presencia resulta de importancia ya que refleja la existencia de azufre fundido por debajo del lago de cráter. La participación de este material precipitado permitiría inferir la influencia del mismo en el mecanismo eruptivo.Copahue volcano has a record of historical eruptions of low intensity which have mainly been characterized from the events ob-served in last decades. Significant changes in several parameters associated with the volcano activity were observed since the end of 2011. After 12 years of quiescence, on July 2012, the volcano started a new eruptive period. In this work, the characterization of the pyroclastic products emitted on 19th July 2012 is presented. Although the limited dispersion of the event, its study is central in the definition of the character of the initial phase of the eruptive cycle. A high proportion of lithics and the presence of juvenile first-cycled vitroclasts studied in detail allow us to characterize the eruptive mechanism, consistent with a phreatomagmatic erup-tion. A distinctive feature of the tephra is the presence of pyroclastic sulfur. Although these kinds of particles have been identified in previous eruptions, its presence is crucial revealing the existence of molten sulfur under the crater lake. The participation of this precipitated material allow us to infer its influence in the eruptive mechanism.Fil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Caselli, Alberto Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Ribeiro Guevara, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Agusto, Mariano Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. Grupo de Estudio y Seguimiento de Volcanes Activos; Argentin

Characterization of tephras dispersed by the recent eruptions of volcanoes Calbuco (1961), Chaitén (2008) and Cordón Caulle Complex (1960 and 2011), in Northern Patagonia

Pyroclastic materials dispersed in recent volcanic eruptions in Northern Patagonia were analysed in order to characterize the volcanic provenance by the geochemical fingerprint. The volcanic products studied were dispersed by eruptions of volcanoes Calbuco in 1961, Chaitén in 2008, and Cordón Caulle Volcanic Complex (CCVC) in 1960 and 2011. The geochemical characterization was based on the determination of 35 major and trace elements by Instrumental Neutron Activation Analysis, including geochemical tracer such as Rare Earth Elements (REE). The study of the pyroclastic products also included the morphological analysis by petrographic and scanning electron microscopy, and the mineralogical characterization by X-ray diffraction.Geochemical tracers determined in the glass fraction of the dispersed pyroclastic materials allowed a clear discrimination of the three volcanoes that gave origin to the tephras, the three of them with different evolution degree. Tephras from 1960 and 2011 CCVC eruptions showed the same geochemical signature. The geochemical parameters providing the differential characterization are the normalized REE and multi-element patterns, the Eu anomaly, the heavy to light and medium to light REE normalized ratios, and the Cs, Sc, Rb, Ta and Th concentrations. The bulk glassy fraction showed the same composition for each volcanic eruption in samples collected even in distant sites (from 100 to 220km in Chaitén, 2008, and from 80 to 650km in CCVC 2011), attesting to be the most reliable material for correlation purposes.According to the mineralogy, cristobalite was found in volcano Chaitén tephra as an indicator of such origin. Arsenic, an element of environmental interest, exhibited concentrations ranging from 6 to 16μgg-1, with the highest values corresponding to Puyehue-Cordón Caulle and Chaitén products.Fil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Ribeiro Guevara, Sergio. Comision Nacional de Energia Atomica. Gerencia D/area de Energia Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Analisis Por Activación Neutronica; ArgentinaFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Arribere, Maria Angelica. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

Variations in anthropogenic silver in a large Patagonian lake correlate with global shifts in photographic processing technology

At the beginning of the 21st century, digital imaging technology replaced the traditional silver-halide film photography which had implications in Ag contamination. Lake Nahuel Huapi is a popular Patagonia tourist destination impacted by municipal silver (Ag) contamination from photographic processing facilities since 1990's. Silver concentrations in a dated sediment core from the lake bottom showed a 10-fold increase above background levels in the second half of the 20th century, then a decrease. This trend corresponds well with published annual global photography industry demand for Ag, which clearly shows the evolution and replacement of the traditional silver-halide film photography by digital imaging technology. There were significant decreases in Ag concentrations in sediments, mussels and fish across the lake between 1998 and 2011. Lower trophic organisms had variable whole-body Ag concentrations, from 0.2–2.6 μg g−1dry weight (DW) in plankton to 0.02–3.1 μg g−1DW in benthic macroinvertebrates. Hepatic Ag concentrations in crayfish, mussels and predatory fish were significantly elevated relative to muscle which often have Ag concentrations below the detection limit (0.01–0.05 μg g−1DW). Trophodynamic analyses using δ15N and whole-body invertebrate and muscle Ag concentrations indicated food web biodilution trends. High sedimentation rates in conjunction with the reduction of silver waste products discharged to the lake, as a result of the change to digital image processing technologies, are resulting in unplanned but welcome remediation of the Ag contamination in Lake Nahuel Huapi.Fil: Juncos, Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Campbell, Linda. Saint Mary's University; CanadáFil: Arcagni, Marina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Rizzo, Andrea Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Arribere, Maria Angelica. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; ArgentinaFil: Ribeiro Guevara, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutróica; Argentin

Bromine as indicator of source of lacustrine sedimentary organic matter in paleolimnological studies

Bromine (Br) to organic matter (OM) concentration ratio is studied in lake sediment sequences to provide information on environmental changes modifying OM production. The sequences studied were extracted from shallow lakes Morenito, El Trébol, Escondido, and Portezuelo; and deep lakes Futalaufquen, Moreno, and Traful (North Patagonia Andean range). Lake Morenito, a former Lake Moreno bay until its closure in AD 1960, showed a decrease in Br:OM ratios from 1.38 to 0.74 after lake closure, associated with an increase of primary autochthonous productivity attributable to the development of submerged and emerging macrophytes. Sedimentary sequences from Lakes Escondido, Portezuelo, and El Trébol (with large participation of macrophytes in primary productivity), and from Lakes Moreno, Futalaufquen, and Traful (with little development of littoral macrophytes), showed Br:OM ratios consistent with the Lake Morenito pattern. Consistently, the morphometric parameters mean depth and shoreline development correlate with Br:OM ratios. Therefore, Br:OM ratios can be associated with the composition of primary autochthonous productivity, with values of about 0.7 associated to significant macrophyte contributions, and higher values associated with more pelagic contributions. Accordingly, Br:OM variations along a sedimentary sequence can be associated with modifications on the composition of the primary autochthonous productivity of the water body, providing information on environmental changes.Fil: Ribeiro Guevara, Sergio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Rizzo, Andrea Paula. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Daga, Romina Betiana. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Williams Velázquez, Natalia Noemi. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Villa, Stefania. Universidad Nacional de Río Negro; Argentin

A reinterpretation of pyroclastic density current deposits at Copahue volcano, Andean Southern Volcanic Zone, Argentina-Chile

Pyroclastic density currents (PDCs) are one of the most dangerous volcanic phenomena. The correct interpretation and mapping of PDC deposits in the volcano record is important to establish the eruptive style and play a fundamental role in hazard assessment and risk management. The Copahue volcano is an active intermediate volcano of the Southern Volcanic Zone of the Andes (Argentina-Chile) that presents fragmentary evidence of explosive activity during its evolution, with unusual minor PDC deposits. The recorded historic eruptions were mainly phreatomagmatic due to the presence of a crater lake. In this study, four key deposits previously interpreted as PDC products corresponding to different stages of the Copahue volcano evolution (Pleistocene, Holocene, and Historic times) are analyzed and this origin is discussed: (i) A Pleistocene reddish succession located in the northeast flank of the volcano formed by stretched bombs in a coherent lava is interpreted as clastogenic lavas; (ii) a series of proximal bedded volcaniclastics deposits of Pleistocene age are interpreted as redeposition of hyaloclastic fragments from syn-eruptive subglacial meltwater flows associated with subglacial eruptions; (iii) a distal Holocene deposit located ~12 km east of the active crater consist mainly in fine-sized clasts forming aggregates is reinterpreted as a sedimentary (lacustrine) deposit with volcaniclastic input; and, (iv) a historic whitish-grey clastic deposit located on the eastern flank is considered a product of a mixed avalanche generated during the 1992–1995 activity. Consequently, the PDC occurrence during the Copahue volcano evolution is less than previously thought. Large PDCs are unlikely in the future and their influence area would be reduced near the active crater as observed in recent eruptions. Flows triggered by the melting of snow/ice during volcanic activity and sudden drainage of the crater lake appear to be a more likely potential hazard that should be considered during risk assessment.Fil: Báez, Alejandro David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Caselli, Alberto Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear. Laboratorio de Análisis por Activación Neutrónica; ArgentinaFil: Sommer, Carlos Augusto. Universidade Federal do Rio Grande do Sul; Brasi

Historical records of mercury in southern latitudes over 1600 years: Lake Futalaufquen, Northern Patagonia

Mercury is released to the environment from natural and anthropogenic sources, and through atmospheric transport is distributed globally. Lake Futalaufquen (42.8°S) is an oligotrophic lake located in Los Alerces National Park (Northern Patagonia), providing a remote and unpolluted study system. A lacustrine sedimentary sequence revealed 1600 years of Hg deposition, identifying natural baselines and marked peaks not correlated with long-range atmospheric transport. Organic matter and catchment erosion were discarded as Hg drivers. Natural background, pre-1300 CE Hg concentrations, ranged between 27 and 47 ng g-1 (accumulation rates from 8 to 15 μg m-2 y-1). From 1300 CE on, the Hg background profile did not follow the generally increasing Hg pattern observed in both Southern and Northern Hemisphere since pre-industrial times. It was not until the last century that a 1.6-fold increase is observed in the Hg accumulation rate, considered among the lowest increments in southern South America. Noteworthy local/regional sources of Hg for this area, along with global transport, are forest fires and volcanic activity. Between approx. 1340 and 1510 CE, sharp increase in Hg concentration and accumulation rate (up to 204 ng g-1 and 51 μg m-2 y-1, respectively) were clearly associated with extended fire episodes. Furthermore, high Hg peaks during the last 300 years were associated with volcanic eruptions in northernmost Patagonia together with fairly irregular fire episodes, caused by anthropogenic burning by settling population in the Andes.Fil: Daga, Romina Betiana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Ribeiro, Sergio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Pavlin, Majda. Jožef Stefan Institute; EsloveniaFil: Rizzo, Andrea Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Lojen, Sonja. Jožef Stefan Institute; Eslovenia. University of Nova Gorica; EsloveniaFil: Vreca, Polona. Jožef Stefan Institute; EsloveniaFil: Horvat, Milena. Jožef Stefan Institute; EsloveniaFil: Arribere, Maria Angelica. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentin

The 2012 Eruption

This contribution is a detailed description of the precursory activity and theeruptive events that took place during July and December 2012 at Copahue volcano, based on field observations and geophysical and geochemical monitoring. After the Mw 8.8 Chilean earthquake on February 27th 2010, several signals of anomalous behavior were detected at Copahue, revealing the instability of the volcanic system. Starting from July 2012 a phreatic activity occurred with emission of a low amount of material mainly constituted by rocks from the volcanic conduit and sediments from the bottom of the crater lake. Seismic activity and degassing continued until December 22nd when the eruption started with an opening phreatic event that rapidly evolved to a phreatomagmatic, and finally a magmatic eruption.Fil: Caselli, Alberto Tomás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Agusto, Mariano Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Velez, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Forte, Pablo Brian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Bengoa, Cintia Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Daga, Romina Betiana. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Albite, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin

Reconstruction of the hydrologic history of a shallow Patagonian steppe lake during the past 700 yr, using chemical, geologic, and biological proxies

The limnological conditions during the past 700 yr were reconstructed based on multiproxy analysis of a short sedimentary sequence from El Toro Lake (~40°S, 70°W). Mineralogical and geochemical features, as well as ostracods and chironomids, record hydrologic changes in the El Toro Lake basin. The ostracod Limnocythere rionegroensis var. 1, a reliable indicator of high salinity, and Eucypris fontana, a euryhaline species with preferences for moderate-salinity waters, are studied as paleolimnological proxies. The chironomid fauna indicates less saline conditions in the mid-twentieth century. These salinity changes are interpreted in terms of negative-positive hydrologic balance. High lake level and low salinity between AD 1500 and 1700 match with the wetter and colder climate during the second pulse of the Little Ice Age in northern Patagonia. High-salinity conditions occurred during the late nineteenth century, corresponding to the driest period during the past 400 yr in northeastern Patagonia. An increase in the precipitation around the middle of the twentieth century, in contrast to the records from the Chilean side of the mountains, correlates with a positive phase of the Southern Annular Mode. This is associated, in turn, with a strengthening, poleward shift of the midlatitude westerlies, possibly enhancing easterly moist air flows into central-north Patagonia.Fil: Coviaga, Corina Anabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Rizzo, Andrea Paula. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Perez, Alejandra Patricia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Daga, Romina Betiana. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Cusminsky, Gabriela Catalina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Ribeiro Guevara, Sergio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin