Sediment penetration depths of epi- and infaunal ostracods from Lake Geneva (Switzerland)

Many (palaeo-)environmental parameters can be deduced from ecological and chemical analyses of ostracods. However, the specific ecology of each taxon has a great impact on its reaction to changing environmental conditions. As a consequence, each taxon records these changes differently. The mean penetration depth (MPD) and relative individual abundances have been documented along sediment depth profiles for the dominant sub-littoral to profundal species of ostracods in western Lake Geneva, Switzerland, and this data can be used to estimate their preferential habitat in terms of sediment depths. Isocypris beauchampi, Limnocytherina sanctipatricii, Cypria ophtalmica forma lacustris at 13-m water depths, Limnocythere inopinata, and a winter generation of Herpetocypris reptans have the shallowest habitat preferences at the study sites (MPDs of 0.45, 0.48, 0.49, 0.60, and 0.81cm, respectively). These results suggest that these populations may be regarded as being preferentially epifaunal forms. Populations of Cytherissa lacustris (MPDs of 0.61, 0.73, and 0.82cm at 13-, 33-, and 70-m water depths, respectively), Cypria ophtalmica forma lacustris at 70m (MPD=0.96cm), Fabaeformiscandona caudata (MPD=0.99cm), and a summer generation of Herpetocypris reptans (MPD=1.03cm) were identified as being infaunal. Candona neglecta is the species that was found the deepest in the sediment of Lake Geneva, with MPDs of 0.65, 1.22, and 1.30cm at 13-, 33-, and 70-m water depths, respectively. Information on the sediment texture and oxygen concentrations inferred from the analyses of sediment pore water suggest that the oxygen content of the sediment pore water is not the only dominant parameter controlling the differences in ostracod sediment penetration depths observed among the different sites, but that they might also be influenced by the sediment ‘softness,' which itself depends on grain size, water content, and the abundance of organic matter in sedimen

Vegetation history of the Río Manso Superior catchment area, Northern Patagonia (Argentina), since the last deglaciation

In Northern Patagonia, the long-term vegetation-climate relationships that gave shape to southern South American forests have been the subject of extensive investigations in the Andean regions of Argentina and Chile for about a century. The Río Manso Superior originates in one of the tongues of the Cerro Tronador Glacier, near the international border, discharging into the Pacific Ocean after feeding present Lago Mascardi and flowing east to west on a mountain landscape. Ongoing pollen studies in this watershed provide us with a modern analogue to better understand the vegetation history of the region. A pollen record from a 15 m long sediment core retrieved from Lago Mascardi (41°08°S, 71°34°W) contains continuous evidence of vegetation changes in the Río Manso watershed extending back to the last deglaciation. High Andean steppe vegetation with forest patches, and extended waterlogged areas gave place to a forest, probably deciduous, during the Lateglacial-Holocene transition. A forest diversification took place during the climate amelioration that encompassed the deglaciation whilst the vegetation became more open before the onset of the Huelmo-Mascardi cold reversal. A mixed Nothofagus-Austrocedrus forest expanded during the middle Holocene. This forest became denser under the higher climate variability registered in the region during the late Holocene as shown by independent published data. Statistical analyses of modern pollen samples along an altitudinal transect from low Nothofagus forest and shrubland to high Andean semi-desert support this interpretation. Pollen results are discussed in the context of paleoenvironmental reconstructions at a regional scale.Fil: Bianchi, Maria Martha. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ariztegui, Daniel. Universidad de Ginebra; Suiz

Precipitation linked to Atlantic moisture transport: clues to interpret Patagonian palaeoclimate

Westerlies are the main climatic feature in the mid-latitudes of the Southern Hemisphere (SH), driving the amount and distribution of precipitation. Patagonia is a vast region in South America’s mid-latitudes, which encompasses 2 sub regions with highly distinct precipitation features. These two regions include wet Western Patagonia extending from the Pacific coast to the Andean highs (i.e. maximum elevations), and dry Eastern Patagonia situated leeward of the Andes in the Argentine steppe plains. Patagonia is influenced by strong mid-latitude westerlies throughout the year. Westerlies have been considered the unique driver of climate both in Western and Eastern Pata gonia. This research is focused on the Lago Cardiel catchment area in central Eastern Patagonia. A significant link between precipitation in that region and local zonal moisture transport from the Atlantic was established. A fraction of intense precipitation was related to strong local westward moisture transport, partly as a consequence of slow-moving weather systems crossing over Patagonia. As long as a dipolar pattern of long-term precipitation anomaly was observed between dry central Western/Southern Patagonia and wet central Eastern Patagonia, it could be interpreted as due to enhanced synoptic easterly moisture flux from the Atlantic. Thus, the westerlies rule was broken at least under blocking-like flows, which induced moist easterlies. The relatively wet 1940s exemplified this phenomenon. Such a conceptual framework can be applied to palaeoclimatic proxy record reconstructions as well as to general circulation model (GCM) outcomes for the late and mid-Holocene.Facultad de Ciencias Astronómicas y Geofísica

Echo-g outputs of the 1000hpa zonal wind and temperature fields over southern South America for the last millennium

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.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.Fil: Maenza, Reinaldo Agustín. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Compagnucci, Rosa Hilda. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ariztegui, Daniel. Universidad de Ginebra; Suiz

Origin of the tsunami of may 1960 in the Lake Nahuel Huapi, Patagonia: application of the high-resolution bathymetric and seism ic techniques

El tsunami ocurrido en el lago Nahuel Haupi, Patagonia Argentina, el 22 de Mayo de 1960, constituye el primer ejemplo de tsunami en lagos continentales en Argentina. La batimetría de detalle obtenida con sonar batimétrico por medición de fase (SBMF) y dos perfiles sísmicos de alta resolución junto con tres testigos sedimentarios cortos del lago permitieron vincular al tsunami con el gran movimiento sísmico conocido como el terremoto de Valdivia, el sismo más fuerte registrado instrumen- talmente a escala global (Mw 9,5). El impacto de las ondas sísmicas provocó la movilización de grandes volúmenes de sedi- mentos lacustres del sustrato, especialmente por debajo de los 70-80 m de profundidad de agua. El fallo fue probablemente inducido por la presencia de una superficie de baja coherencia (tefra?) que funcionó como plano de deslizamiento posibilitan- do la remoción de sedimentos y conformando una megaturbidita en la parte más profunda. La movilización de estos mate- riales provocó el desplazamiento de un gran volumen de agua, originando el tsunami que golpeó las costas de Bariloche y des- truyó el muelle de la ciudad.The tsunami recorded in the Lake Nahuel Huapi, Patagonia Argentina, on May 22, 1960 is the first example of a tsu- nami in a continental lake in Argentina. High-resolution bathymetry (SBMF), 2 high-resolution seismic profiles together with three short sedimentary cores allowed linking this tsunami to the 1960 earthquake of Valdivia, the strongest (Mw 9.5) ever ins- trumentally recorded earthquake. The impact of the seismic waves produced huge mass-failure below 70-80 m water depth. The failure was probably induced by the presence of a non-cohesive surface (tephra layer?) that acted as a sliding surface, and the mo- bilized material evolved into a mega turbidite in the deep basin. A large volume of water was displaced by the mobilization of these sediments producing a tsunami that hit the coasts of Bariloche and destroyed the harbor of the city.Fil: Villarosa, Gustavo. 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: Outes, Ana Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Gomez, Eduardo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Chapron, Emmanuel. Universidad de Orleans; FranciaFil: Ariztegui, Daniel. Universidad de Ginebra; Suiz

Establishing Sampling Procedures in Lake Cores for Subsurface Biosphere Studies: Assessing In Situ Microbial Activity

Sub-recent sediments in modern lakes are ideal to study early diagenetic processes with a combination of physical, chemical, and biological approaches. Current developments in the rapidly evolving field of geomicrobiology have allowed determining the role of microbes in these processes (Nealson and Stahl, 1997; Frankel and Bazylinski, 2003). Their distribution and diversity in marine sediments have been studied for some years (Parkes et al., 1994; D’Hondt et al., 2004; Teske, 2005). Comparable studies in the lacustrine realm, however, are quite scarce and mainly focused on the water column (Humayoun et al., 2003) and/or very shallow sediments(Spring et al., 2000; Zhao et al., 2007). Thus, there is a need to determine the presence of living microbes in older lacustrine sediments, their growth, and metabolic paths, as well as their phylogenies that seem to differ from already known isolates.During the PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Project) ICDP (International Continental Scientific Drilling Program) drilling, more than 500 meters of sedimentary cores were retrieved from this crater lake (Zolitschka et al., 2009). A 100-m-long core was dedicated to a detailed geomicrobiological study and sampled in order to fill the gap of knowledge in the lacustrine subsurface biosphere. Here we report a complete in situ sampling procedure that aims to recover aseptic samples as well as determining active in situ biological activity. Preliminary results demonstrate that these procedures provide a very useful semi-quantitative index which immediately reveals whether there are biologically active zones within the sediments

Magnetic investigations of framboidal greigite formation: a record of anthropogenic environmental changes in eutrophic

Abstract: Magnetic minerals found in sediments can either be transported to the basin from the catchment area or can be authigenically formed in the sediments. SEM studies, x-ray diffraction spectra and magnetic mineralogical analyses performed on magnetic extracts from freeze-dried sediments of Lake St Moritz, Switzerland, undoubtedly identified the presence of greigite

Evolving controls on mineralization in Patagonian microbial mats as inferred by water chemistry, microscopy and DNA signatures

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 viceversa, which can be undistinguishable in fossilized microbialites.Fil: Eymard, Inès. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Alvarez, Maria del Pilar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; ArgentinaFil: Bilmes, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; ArgentinaFil: Vasconcelos, Crisogono. ETH, Geologisches Institut; Suiza. CGA-SGB/CPRM; BrasilFil: Thomas, Camille. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Ariztegui, Daniel. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; Suiz

Paleoenvironmental conditions define current sustainability of microbial populations in Laguna Potrok Aike sediments, Argentina

Rainfall and geology of the catchment exert a dominant control on the trophic state of endorheic basins. River inflows and runoff provide nutrients, influencing primary productivity in the water column. Through time, paleoenvironmental conditions are recorded as variations within the sedimentary organic fraction. Thereafter, microbial populations settle and develop within sediments and lead to degradation processes as long as they remain active. However, their presence is generally not considered in Quaternary studies. The present study is based on the sedimentary record of the maar lake of Laguna Potrok Aike, southern Patagonia. We investigate the relationship between paleoenvironmental conditions and colonization of the corresponding sediments by microbes. Microbiological and geochemical analyses were combined to determine factors allowing microbes to sustain their activity over time. The study of Holocene sediments, containing dense and active microbial communities, provided means to evaluate the potential of microbial communities as agents of early diagenesis. We show that phosphorus released during organic matter degradation is essential for microbial growth. In highly colonized sediments, microbial communities appear capable of recycling the excreted ammonium, thus accounting for nitrogen fractionation toward high values in bulk sediment. Microbial activity in Laguna Potrok Aike still persists in 30ka old sediments. Thus, we proposed that future lacustrine studies should include some microbial indicators to assess their impact in diagenetic processes

Precipitation linked to Atlantic moisture transport: clues to interpret Patagonian palaeoclimate

Westerlies are the main climatic feature in the mid-latitudes of the Southern Hemisphere (SH), driving the amount and distribution of precipitation. Patagonia is a vast region in South America’s mid-latitudes, which encompasses 2 sub regions with highly distinct precipitation features. These two regions include wet Western Patagonia extending from the Pacific coast to the Andean highs (i.e. maximum elevations), and dry Eastern Patagonia situated leeward of the Andes in the Argentine steppe plains. Patagonia is influenced by strong mid-latitude westerlies throughout the year. Westerlies have been considered the unique driver of climate both in Western and Eastern Pata gonia. This research is focused on the Lago Cardiel catchment area in central Eastern Patagonia. A significant link between precipitation in that region and local zonal moisture transport from the Atlantic was established. A fraction of intense precipitation was related to strong local westward moisture transport, partly as a consequence of slow-moving weather systems crossing over Patagonia. As long as a dipolar pattern of long-term precipitation anomaly was observed between dry central Western/Southern Patagonia and wet central Eastern Patagonia, it could be interpreted as due to enhanced synoptic easterly moisture flux from the Atlantic. Thus, the westerlies rule was broken at least under blocking-like flows, which induced moist easterlies. The relatively wet 1940s exemplified this phenomenon. Such a conceptual framework can be applied to palaeoclimatic proxy record reconstructions as well as to general circulation model (GCM) outcomes for the late and mid-Holocene.Facultad de Ciencias Astronómicas y Geofísica