ABSTRACT In recent years resulting investigations in living microbialites have provided significant data that have been critical to disentangle the role of the various biotic and abiotic processes contributing to their development. Despite these efforts separating the impact and magnitude of these processes remain a difficult task. At present the Maquinchao Basin in northeastern Patagonia, Argentina, contains both fossil and living microbialites. Thus, the region provides a unique opportunity to investigate the impact of intrinsic and extrinsic parameters in carbonate precipitation. Early investigations (Austral summer 2011) in living microbialites concluded that organomineralization was related to both photosynthetic activity in the more surficial layer (green), and sulfate-reduction in the lower part (beige). Field investigations in the same area four years later showed that the pounds previously containing abundant active mats had dried out, and in general revealed the absence of globular structured clusters of minerals in the microbial mats. Here we present microscale investigations using optical microscopy and SEM along with the 16SrRNA gene sequence diversity, and the physico-chemical parameters of the hosting waters. They were carried out in successive seasonal samplings in November 2015, April-May 2016, August 2016, February 2017, and March 2018. All microbialite samples show regular occurrences of sulfate reducing bacteria (SRB) along with filaments of unknown origin. Carbonates are observed associated with erect filaments in shallow and active running water locations whereas the mineral phase is located below organic matter film in comparatively deeper and calmer water areas. Additionally, seasonal changes in the physico-chemical properties of the hosting waters indicate that extrinsic parameters, especially evaporation, might play a more substantial role in the precipitation of these carbonates than previously proposed. The environmental differences between 2011 and 2015 in meteorological conditions, regional volcanic activity and associated deposits in the basin are analyzed. We concluded that they are likely responsible of the decrease of the mineralization processes, and particularly those associated with photosynthetic activity. These results call for caution when interpreting the degree of biological impact on the formation of microbialites in the geological record. Local extrinsic factors might have a changeable impact over time switching mineral precipitation from biotic to abiotic and vice-versa, which can be undistinguishable in fossilized microbialites.

Abstract Geometric morphometric methods are powerful tools to discriminate between closely related ostracods taxa as well as to study the relationship between their morphological variations, taxonomy and paleoecology. In this study, valve outline analysis allows the discrimination between the non-marine ostracod C. silvestrii and R. whatleyi juveniles, pointing out differences in the posterior valve area and surface ornamentation. Modern female specimens of C. silvestrii from 23 sites located in a spatial transect (41 to 51 °S) exhibited extensive morphological variability, on the basis of which three morphotypes (acuminated, transitional, subtruncated) were determined. Multivariate analyses showed that acuminated and transitional shapes are not arranged in groups but the subtruncated morphotype, previously described as E. cecryphalium, seems to be associated with low water conductivity (372 µS cm-1), dominant cold (5 ºC) and windy (8.6 m s-1) climatic conditions. The fossil cluster which included nine cores spanning the last 15.6 kyr, only covered acuminated and transitional shapes, which may indicate that these lineages might be older than the subtruncated morphotype. In addition, morphological differences between reproduction modes suggested that parthenogenetic females exhibit de posterior margin more acuminate than sexual females. These results set the ground for more precise ecological and paleoenvironmental studies in Patagonia.

Abstract In order to characterize Patagonian (Argentina) ecoregions using non-marine ostracods, their associations in 69 environments were assessed. Twenty eight taxa were recorded, including 12 endemic of the Neotropical region. Our results indicate that Patagonian ostracods are mainly influenced by electrical conductivity (EC), altitude, pH, and temperature; and shows a correlation with Argentinian ecoregions. Assemblage I is composed of sites located at high altitude in the Andean Patagonian forest ecoregion. Host waters have low temperature, EC and pH, and support as representative species Cypris pubera, Eucypris virens, Bradleystrandesia fuscata, Tonacypris lutaria and Amphicypris nobilis. Assemblage II, related to mid-altitude environments in the Patagonian Steppe ecoregion, thrived in waters with moderate to high EC, and alkaline pH values. Dominant species includes Limnocythere rionegroensis, L. patagonica, E. virgata, Riocypris whatleyi, Riocypris sarsi, Newnhamia patagonica, Kapcypridopsis megapodus, Ilyocypris ramirezi and Penthesinelula incae. Assemblage III inhabited environments within Monte and Espinal ecoregions, situated in the eastern part of the study area at low altitude, EC moderate and temperate waters, supporting Heterocypris hyalinus, Amphicypris argentinensis, Sarscypridopsis aculeata, Cypridopsis vidua, Herpetocypris intermedia and Chlamidotheca incisa. Our results indicates that Argentinian Patagonia hosts a diverse ostracod fauna and highlights their capacity as proxies in ecological and palaeoenvironmental studies.

Abstract Salina de Ambargasta is a playa system located at the subtropical region in South America (29°S), and influenced by the South American Monsoon System. The present work analyzed the isotopic records of δ13C and δ18O in carbonates throughout two sedimentary cores, previously dated by 14C AMS, in order to identify hydrological changes from ca. 45000 years cal. BP to the present. Additionally, the Pearson correlation coefficients were inspected among the stable isotopes, and also between each isotope and the Loss on Ignition (LOI and LOI ) values in the sediments. Following a dry phase at ca. 45000 years cal. BP, the most negative isotopic values of δ13Ccarb (average: -5.10‰) reflected a more humid period between ca. 39600 and 23600 years cal. BP (MIS 3) that favored water inflow into perennial carbonate and ephemeral sulfate lakes. Values of δ18O carb were more positive (average: 2.76 and maximum:4.86‰) suggesting periods influenced by high evaporation rates. From ca. 23600 years cal. BP to the present (MIS 2 and MIS 1), average compositions of δ13C carb were relatively more positive (-4.50‰), and δ Ocarb average values were comparatively more negative (-4.35‰), indicating less water input to the system and lower evaporation, respectively. From these records, the beginning of the Last Glacial Maximum (LGM) in Ambargasta is dated between ca. 25000 and 18000 years cal. BP in southern South America. In the sequence of the carbonate perennial lake, the existence of a hydrologically closed lacustrine system (ca. 39600 - 26700 years cal. BP) was revealed by a correlation between δ13Ccarb and δ18Ocarb (r = 0.62). Positive correlations between PPI550 and PPI1000 (carbonate lake; r = 0.88; ca. 39600 - 26,700 years cal. BP) and negative (sulfate lakes; average r = -0.81; ca. 39600 - 23600 years cal. BP) indicated high productivities associated with precipitation of evaporites during evaporative concentration stages (isotope positive excursions). This research allows inferring that between ca. 39600 - 23600 years cal. BP, a more humid and warmer stage occurred with respect to the period between ca. 23600 years cal. BP and the present in the Ambargasta region (central Argentina). This work documents important changes in the Precipitation/Evaporation ratio throughout the Late Pleistocene and Holocene, and provides vital information about time windows practically unexplored in southern South America. Taken together, these allow defining regional patterns of paleoclimatic variability during the Quaternary.

Resumen Salina de Ambargasta es un sistema playa ubicado en la región subtropical de Sudamérica (29 °S), influenciado por el Sistema Monzónico Sudamericano. Se analizó el registro isotópico de δ13C y δ18O en carbonatos a lo largo de dos núcleos sedimentarios fechados previamente por 14C AMS, a fin de identificar los cambios hidrológicos desde los ca. 45000 años cal. AP hasta la actualidad. Adicionalmente, se calcularon los coeficientes de correlación de Pearson entre los isótopos estables y entre cada isótopo con los valores de Pérdida por Ignición (PPI550 y PPI1000) en los sedimentos. Posterior a un intervalo seco documentado a los ca. 45000 años cal. AP, los valores de δ13C carbonatos más negativos (promedio = -5.10 ‰) evidenciaron un periodo más húmedo entre los ca. 39600 y 23600 años cal. AP (MIS 3), que contribuyó al desarrollo de lagunas perennes carbonatadas y efímeras sulfatadas. Por su parte, los valores de δ18O fueron más positivos periodos sujetos a altas tasas de evaporación. Desde los ca. 23600 años cal. AP al Presente (MIS 2 y MIS 1), los sedimentos presentaron composiciones promedio de δ13Ccarb relativamente más positivas (-4.50 ‰) y valores promedio de δ18Ocarb comparativamente más negativos (-4.35 ‰), reflejando un aporte menor de agua al sistema y una evaporación más baja, respectivamente. A partir de este registro se consideró el inicio del Último Máximo Glacial (UGM) en Ambargasta, definido en el sur de Sudamérica entre los ca. 25000 y 18000 años AP. En la secuencia de la laguna perenne carbonatada (ca. 39600 - 26700 años cal. AP) la existencia de un sistema lacustre hidrológicamente cerrado fue evidenciado por la correlación entre δ13Ccarb y δ18Ocarb (r = 0.62). Las correlaciones entre PPI550 y PPI1000 positivas (laguna carbonatada; r = 0.88; ca. 39600 - 26700 años cal. AP) y negativas (lagunas sulfatadas; r promedio = -0.81; ca. 39600 - 23600 años cal. AP) indicaron altas productividades asociadas a la precipitación de evaporitas durante etapas de concentración evaporítica (excursiones positivas en las relaciones isotópicas). Esta investigación permitió inferir que entre los ca. 39600 y 23600 años cal. AP existió una etapa más húmeda y cálida con respecto al periodo ca. 23600 años cal. AP-Presente en la región de Ambargasta (Argentina central). Este trabajo documentó cambios importantes en la relación Precipitación/Evaporación a lo largo del Pleistoceno tardío y Holoceno, y aportó información clave sobre ventanas de tiempo poco exploradas en el sureste de Sudamérica, que en conjunto permitirán definir patrones regionales de la variabilidad paleoclimática durante el Cuaternario.

Salina de Ambargasta is a playa system located at the middle latitude of Argentina (29°S; 64°W). Two sedimentary cores retrieved at the eastern border (AB-1) and the central area of the salina (AB-2) were studied using a multi-proxy approach, an actualistic sedimentary model and radiocarbon dates allowed reconstructing the paleohydrological history of the Salina de Ambargasta since the late Pleistocene. The paleoenvironmental reconstruction for the last ca. 45,000 years to the present suggests six main environmental stages: 1) between 44,700 and 39,600 cal. year BP, a dry period is represented by the development of a capillary mudflat; 2) between ca. 39,600 and 26,700 cal. year BP a more humid period is recorded by lacustrine facies with carbonate and sulfateprecipitation; 3) between ca. 26,700 and 23,600 cal. year BP occurs the most humid phase in Ambargasta, characterized by the sedimentation in an ephemeral sulfate lake, relatively deep, enriched with microbial mats and fringed by mudflats; 4) between 23,600 and 18,500 cal. year BP, a change to drier conditions with humid pulses is evidenced by the development of saline mudflats alternating with ephemeral lakes and associated with mudflats in the supralittoral areas; 5) between 18,500 and 8,600 cal. year BP a drier period is identified by the dominance of capillary and saline mudflats, and 6) since 8,600 cal. year BP to the present the most negative hydrological balance is recorded in the saline system, represented by an expansion of capillary mudflats The control of the hydrological balance in the Salina de Ambargasta is mostly associated with the variation of the South America Monsoon-like System. Thus, the record presented here allows us to provide new clues in order to decipherformerfluctuations of this important driver of the climatic system of South America since the late Pleistocene.

La Salina de Ambargasta es un sistema playa localizado a latitudes medias de Argentina (29°S; 64°W). El estudio de dos testigos sedimentarios, AB-1 (borde este de la salina) y AB-2 (área central), efectuado mediante un enfoque de multi-indicadores ambientales, la aplicación de un modelo sedimentario análogo y edades radiocarbónicas, permitió reconstruir la historia paleohidrológica de la salina de Ambargasta a partir del Pleistoceno tardío. La reconstrucción paleoambiental de los últimos ca. 45,000 años hasta el presente, indica seis estadios ambientales principales: 1) entre 44,700 y 39,600 años cal. AP, un intervalo seco está representado por el desarrollo de una planicie fangosa capilar; 2) entre 39,600 y 26,700 años cal. AP, un período más húmedo es registrado por facies lacustres con precipitación carbonática y sulfatada; 3) entre 26,700y 23,600 años cal. AP ocurre la fase más húmeda en Ambargasta, caracterizada por la sedimentación en una laguna efímera sulfatada, relativamente profunda, rica en tapices microbianos y marginada por planicies fangosas; 4) entre 23,600y 18,500 años cal. AP se presenta un cambio a condiciones más secas con pulsos húmedos intercalados, evidenciado por el desarrollo de planicies fangosas salinas que alternan con lagunas efímeras, y planicies fangosas capilares en las zonas supralitorales; 5) entre 18,500y 8,600 años cal. AP se identifica un intervalo más seco caracterizado por el dominio de planicies fangosas salinas y capilares, y 6) desde los 8,600 años cal. AP al presente se registra el balance hídrico más negativo en el sistema salino representado por una expansión de las planicies fangosas capilares. El control del balance hidrológico en la Salina de Ambargasta está vinculado con la variación del Sistema de tipo Monzónico Sudamericano, por lo cual la reconstrucción efectuada desde el Pleistoceno tardío permite aportar nuevas claves para comprender las fluctuaciones pasadas de este importante forzante del sistema climático de Sudamérica.

Important climatic variations have occurred during the last millennium. After the "Medieval Warming" period, a long period of cold conditions, called "Little Ice Age", took place, being followed by the current "Global Warming". Transient scenarios have been developed using the General Circulation Model ECHO-G to simulate the monthly anomalies for the period 1000-1990 AD. Firstly, the research analyses the ability of ECHO-G model to reproduce the temperature and zonal wind component at 1000hPa over southern South America in the period 1961-1990 to contrast the outputs with the NCEP/NCAR Reanalysis data. The difference of means and standard deviations has been tested for both temperature and zonal wind. In central-north Argentina, ECHO-G simulates higher temperatures than the NCEP/NCAR Reanalysis. However, the differences between model and reanalysis are smaller in the Patagonia region, especially close to the Cardiel Lake. Hence, extended simulations for the last millennium can be used to analyse paleoclimatic variations in such region. Although anomaly patterns between Maünder and Dalton solar Minimums are similar with respect to the 1960-1990 period, their amplitudes are higher for the Maünder Minimum. The alternating light and dark laminae (annual rythmites or varves) from the Cardiel Lake sediments in central Patagonia were previously interpreted as the result of regional wind intensity variations. In this work their thickness time series has been compared with the local zonal wind component and temperature time series at 1000hPa in the period 1000 AD and 1990 AD. A centered 80-years moving average has been applied to these time series to enhance the effect of the Gleissberg solar cycle and other lower frequency periodicities. The results show a reverse relationship between the zonal wind component and the thickness of the dark laminae. Such an inference is confirmed employing Coherence Wavelet Spectrum between the time series. The latter indicates that the thickness of the dark laminae can be used as a proxy for the strengthening of the zonal wind component over Patagonia.

Durante el último milenio han ocurrido importantes variaciones climáticas. Luego de la "Anomalía Climática Medieval" tuvo lugar un prolongado período de generalizadas condiciones frías llamado "Pequeña Edad de Hielo" seguido por el actual "Calentamiento Global". Con el Modelo de Circulación General ECHO-G se produjeron escenarios transientes que simulan las anomalías mensuales del período 1000 a 1990 AD. En este trabajo primeramente se analiza la capacidad del ECHO-G de reproducir los campos de temperatura y componente zonal del viento, ambos en el nivel de 1000hPa, en la región del cono sur de Sudamérica utilizando como referencia el re-análisis NCEP/NCAR para el período 1961-1990 testeando las diferencias de los valores medios y los desvíos estándar para la temperatura y la componente zonal del viento. En el centro norte del país el modelo ECHO-G simula temperaturas superiores a las del re-análisis NCEP-NCAR. Sin embargo, las diferencias entre el modelo y el re-análisis son menores en la Patagonia y particularmente despreciables en la región del Lago Cardiel. Por lo cual las simulaciones de los últimos 1000 años pueden ser utilizadas para analizar la variabilidad paleoclimática de esa región. Los patrones de anomalías para los Mínimos solares de Maünder y Dalton obtenidos con el ECHO-G respecto al período 1961-1990 resultan similares pero más intensos en el caso del Mínimo de Maünder. Las láminas alternantes claras y oscuras (ritmitas anuales o varves) de los testigos sedimentarios del Lago Cardiel en Patagonia central han sido previamente interpretadas como el resultado de la intensidad de los vientos regionales. En el trabajo además se comparara los espesores de dichas láminas con los valores de la componente zonal del viento y la temperatura en 1000hPa para el período comprendido entre los años 1000 a 1990 AD. Las series filtradas con promedios móviles de 80 años, que realzarían el efecto del ciclo de Gleissberg y otras periodicidades solares de menor frecuencia, sugieren relación inversa principalmente entre la componente zonal del viento y los espesores de las láminas oscuras. Esta inferencia es confirmada mediante los espectros de onditas de coherencia entre ambas series. Este primer resultado indicaría que la serie de espesores de láminas oscuras podría ser utilizada como "proxy" dato de la intensidad de la componente zonal del viento sobre la Patagonia.

Thetsunami recorded in the Lake Nahuel Huapi, Patagonia Argentina, on May 22, 1960is the first example of a tsunami in a continental lake in Argentina.High-resolution bathymetry (SBMF), 2 high-resolution seismic profiles togetherwith three short sedimentary cores allowed linking this tsunami to the 1960earthquake of Valdivia, the strongest (Mw 9.5) ever instrumentally recordedearthquake. The impact of the seismic waves produced huge mass-failure below70-80 m water depth. The failure was probably induced by the presence of anon-cohesive surface (tephra layer?) that acted as a sliding surface, and the mobilizedmaterial evolved into a mega turbidite in the deep basin. A large volume ofwater was displaced by the mobilization of these sediments producing a tsunamithat hit the coasts of Bariloche and destroyed the harbor of thecity.

El tsunami ocurrido en el lago Nahuel Haupi, PatagoniaArgentina, el 22 de Mayo de 1960, constituye el primer ejemplo de tsunami enlagos continentales en Argentina. La batimetría de detalle obtenida con sonarbatimétrico por medición de fase (SBMF) y dos perfiles sísmicos de altaresolución junto con tres testigos sedimentarios cortos del lago permitieronvincular al tsunami con el gran movimiento sísmico conocido como el terremotode Valdivia, el sismo más fuerte registrado instrumentalmente a escala global(Mw 9,5). El impacto de las ondas sísmicas provocó la movilización de grandesvolúmenes de sedimentos lacustres del sustrato, especialmente por debajo de los70-80 m de profundidad de agua. El fallo fue probablemente inducido por lapresencia de una superficie de baja coherencia (tefra?) que funcionó como planode deslizamiento posibilitando la remoción de sedimentos y conformando unamegaturbidita en la parte más profunda. La movilización de estos materialesprovocó el desplazamiento de un gran volumen de agua, originando el tsunami quegolpeó las costas de Bariloche y destruyó el muelle de la ciudad.