Search

High-mountain lake records in semiarid foreland settings, such as the central Andes of North-western Argentina, are highly restricted and often deprived of well-preserved microstratigraphic information to analyze palaeoenvironmental changes and their causes, particularly for periods prior to the Last Glacial Maximum. Laguna La Salada Grande (23°S/65°W, 4063 metres above sea-level) is a closed shallow lake located at Cordillera Oriental, North-western Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of palaeoenvironmental changes since the Late Pleistocene. In order to understand the depositional dynamics of this mountain lacustrine system at different timescales, limnogeological multiproxy analyses together with a radiocarbon and 210Pb-based chronology were applied on massive and laminated sediments from La Salada Grande. Laminated deposits were further analyzed using novel sub-centimetric mineralogical, textural and geochemical automated methods (including a combination of micro-X-ray fluorescence and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®). Thick laminated microfacies at the beginning of the sequence record a deep and organic matter productive palaeolake prior to ca 34 ka (1 ka = 1000 years before 1950), that changed into a highly fluctuating shallower-palaeolake with frequent detrital influxes after ca 34 ka. Microstratigraphy of the coarser-grained detrital laminae between 31 ka and 25 ka reveals irregular and probably sub-centennial high-energy discharge events, pointing to convective atmospheric activity as the main trigger. After ca 21 ka the lake evolved to deeper water-level conditions resulting in fine-grained deposits with limited delivery of coarse-grained sediments, followed by an abrupt lake level drop and incision. The multi-millennial palaeoenvironmental reconstruction of La Salada Grande, and its correlation with other palaeoclimate records, shows a close link between the lacustrine depositional processes and palaeoclimate changes associated with the South American summer monsoon dynamics. This multifocal research in such an understudied environment provides key knowledge about lacustrine functioning and discharge events−climate interactions of mountain lakes of semi-arid climates., Sedimentology, 69 (6), ISSN:0037-0746, ISSN:1365-3091

The replacement of native dry forests by commercial (exotic) tree plantations could generate changes in rainfall partitioning, which further affects the water cycle. In this study, we determined (i) the rainfall partitioning into interception, throughfall and stemflow, (ii) the role of rainfall event size on rainfall partitioning, (iii) the pH of water channelized as throughfall and stemflow, and (iv) the runoff in Lithraea molleoides (a native species) and Pinus elliottii (an exotic species) stands in the dry Chaco mountain forests, central Argentina. On average, interception, throughfall and stemflow accounted for 19.3%, 79.5% and 1.2% of the gross rainfall in L. molleoides stand, and 32.6%, 66.7% and 0.7% of the gross rainfall in P. elliottii stand, respectively. Amounts of interception, throughfall and stemflow presented positive linear relationships with the increment of rainfall event size for both tree species (P

Reservoirs hold a detailed record of the changes in the input of sediments and nutrients over decades to centuries. Paleolimnological multi-proxy analysis makes it possible to reconstruct baseline conditions to infer early evidence of environmental change. Our study aims to reconstruct historical human impacts derived from urban development on the San Roque reservoir (Cordoba, Argentina) related to the centennial dynamics of sedimentary and eutrophication processes. A paleolimnological record, dated by 210Pb and 137Cs, made it possible to identify two stages during the environmental evolution of the San Roque reservoir. Physical processes, such as fluvial discharge and water level variation, dominantly ruled stage 1 (Unit C) during the initial infilling of the reservoir. Nutrient load and eutrophication processes controlled stage 2 (Units B and A). Stage 1 (77-55 cm; AD 1921 to 1965) occurred before and after the second dam was built and while the level of water increased by ≈ + 8 m; it displayed a high variation in mean grain size and maximum values of magnetic susceptibility. Stage 2 (AD 1965–2017) records a new reservoir base level and the maintenance of high water levels and comparatively more stable conditions. Regarding the eutrophication process throughout stage 2, three sub-stages were defined: a) Sub-stage I (AD 1965–1985) is a period of incipient eutrophication; b) Sub-stage II (AD 1985–2005) is an interval of increase of eutrophication as shown by the increase in several organic proxies related to the abundance of phytoplankton. Echinenone, zeaxanthin and myxoxanthophyll indicate that cyanobacteria increased concentration by three-to four-fold in comparison with the previous sub-stage. c) Sub-stage III (AD 2005–2017) shows the transition to a hypereutrophic state. Diatomea (fuco and diato), dinophyceae (diadino), chlorophyta (lut) and cryptophyta (allo) groups show a comparatively higher contribution. Our results mostly highlight that during the last century the main drivers of changes in the environmental state of the San Roque reservoir were trophic, fluvial and hydrometeorological. These results might provide tools for anticipating future scenarios for water management plans under increasing anthropic pressure.

Uruguayan Southern lagoons exhibit high Holocene resolution paleoenvironmental-paleoclimatic records for inferring long-term regional changes. The multiproxy analysis of three sediment cores enabled the recognition of Holocene climatic variability from the paleolimnological record of the Peña lagoon over the last 2,458 cal. years BP. Four main stages were identified throughout the record. The first stage (2,458–1,500 cal. years BP) was characterized as a shallow meso-eutrophic system with high abundances of aerophilic benthic species, epiphytic taxa and planktonic taxa. The second stage (1,415–390 cal. years BP) showed a noticeable change in the diatom assemblage dominated by the fresh-brackish benthic species Staurosira construens, but also presented fluctuations in the abundance of Aulacoseira ambigua and Aulacoseira granulata, which indicate the occurrence of temperate to cold and semiarid climatic conditions including intervals of high rainfall. The core chronology allowed us to ascribe this stage to the Little Ice Age (LIA). The third stage, post 390 cal. years BP, showed the highest proportion of freshwater planktonic species throughout the entire core, thus indicating the development of an eutrophic system under relatively warm and wet conditions, which were assigned to the Current Warm Period. After ca. 1,962 AD, a sharp increase in the abundance of epiphytic species highlights the onset of the fourth stage, which was characterized by littoral expansion and, consequently, the proliferation of associated macrophytes due to anthropogenic impacts. Las lagunas costeras del sudeste uruguayo son sistemas naturales que exhiben registros paleoclimaticos y paleoambientales de alta resolución temporal para analizar la variabilidad ambiental holocena. El análisis “multiproxy” de tres testigos sedimentarios permitió identificar la variabilidad climática Holocena en la laguna Peña durante los últimos 2.458 años. Se identificaron cuatro estadios, el más antiguo (2.458 a 1.500 años cal. AP), caracterizando un sistema somero meso-eutrófico, con abundancias relativas altas de especies bentónicas aerófílas, especies epifíticas y especies planctónicas. La segunda fase (1.415–390 años cal. AP) se identifica por alto contenido de la especie bentónica dulce acuícola-salobre Staurosira construens y fluctuaciones de la abundancia de Aulacoseira ambigua and Aulacoseira granulata, infiriendo condiciones climáticas templadas-frías y semiáridas con intervalos de precipitación. La cronología sedimentaria permite relacionar esta fase con la Pequeña Edad de Hielo. La tercera fase (posterior a 390 años cal. AP) presenta la mayor proporción de especies dulceacuícolas planctónicas, indicando el desarrollo de un sistema eutrófico bajo condiciones cálidas y húmedas, asociadas al Periodo Cálido Actual (PCA). Posterior a los ca. 1.962 AD, el aumento de especies epifíticas infiere un sistema léntico con proliferación de macrófitas y una zona litoral ampliamente desarrollada, debido al impacto antrópico. Fil: Cuña Rodriguez, Carolina Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: del Puerto, Laura. Universidad de la República; Uruguay Fil: Inda, Hugo. Universidad de la República; Uruguay Fil: Garcia Rodriguez, Felipe. Universidad de la República; Uruguay. Universidade Federal do Rio Grande do Sul; Brasil

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 δ13Ccarbonatos 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 δ18Ocarb fueron más positivos (promedio = -2.76 y máximo = 4.86 ‰) sugiriendo 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 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 (LOI550 and LOI1000) 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 δ18Ocarb 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 δ13Ccarb were relatively more positive (-4.50‰), and δ18Ocarb 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. Fil: Zanor, Gabriela Ana. Universidad de Guanajuato; México. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Ariztegui, Daniel. Universidad de Ginebra; Suiza Fil: Vennemann, Torsten. Universite de Lausanne; Suiza Fil: Martínez Jaime, Oscar A.. Universidad de Guanajuato; México Fil: Puy Alquiza, María Jesús. Universidad de Guanajuato; México

Geochemical, sedimentological, historical and instrumental information from Melincué Lake (33° 43?S /61°28? W) was analyzed in order to reconstruct main hydro-climatic changes along the Pampean region, considering the end of theLittle Ice Age (LIA) and the Current Warm Period (CWP) climatic phases. Elemental X-ray fluorescence determinations were performed on a dated short core extracted from the deepest part of the lake. Chemical (Ca, Sr, Al, K, Si, Ti and Fe) variation was analyzed along with physical (magnetic susceptibility, dry bulk density and medium particle size) and mineralogical proxies, as well as carbon and nitrogen contents (organic and inorganic carbon and organic nitrogen). Multicomponent statistical analyses allowed the identification of the main environmental processes ruling sedimentation, which included carbonate precipitation, detrital input and primary productivity. Homogeneous, carbonate-rich, detrital-rich and organic matter-poor deposits reflect very shallow and ephemeral lake conditions during the last years of the LIA period. Very low sedimentation rates and the presence of discontinuities in the sedimentary record pointed to episodes of extensive lake shrinkages and probable lake-floor subaerial exposures. Bedded and laminated organic-rich muds accumulated in perennial lake conditions after ca. AD 1880 reveal an important environmental change concurrent with the onset of the Current Warm Period. The contrast of sediment composition and lithological characteristics with the instrumental record of the CWP allowed us to consider the development of a shallow saline-lake system, enhanced detrital input and carbonate precipitation during dry periods. In turn, higher lake levels, and thus more diluted lake-waters during wetter periods, resulted in enhanced organic lake productivity and lower carbonate precipitation. The comparison of the paleolimnological reconstruction from Melincué Lake to different hydrological and paleoclimatic records (i.e. limnimetric measurements and ocean temperature changes) suggests that the moisture variation registered between the LIA and the CWP was consistent with (and likely forced by) large-scale climatic oscillations. The present study provides new evidences to evaluate the climate and environmental changes in central Argentina related to the dynamics of the South American Monsoon systemduring the last five centuries. Fil: Guerra, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Cordoba, Francisco Elizalde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Jujuy. Universidad Nacional de Jujuy. Centro de Investigaciones y Transferencia de Jujuy; Argentina Fil: Tachikawa, Kazuyo. Centre National de la Recherche Scientifique; Francia. Aix-Marseille Université; Francia Fil: Rostek, Frauke. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia Fil: Garcia, Marta. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia Fil: Bard, Edouard. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia Fil: Sylvestre, Florence. Aix-Marseille Université; Francia. Centre National de la Recherche Scientifique; Francia

Organic matter accumulation and preservation in aquatic systems can be linked to variations in organic matter sources as well as primary productivity. These changes can be used to determine contemporaneous environmental variations in the catchment area. The source, quality and distribution of lacustrine organic matter (LOM) have been determined in a sedimentary core covering the last ~1,500 years from Laguna Mar Chiquita, a saline lake in central Argentina. Petrophysical, sedimentological and geochemical data along with results of high-resolution pigment analyses provide a unique dataset that allow characterization of both source and type of LOM. Climatically triggered changes in the Laguna Mar Chiquita catchment led to changes in the water salinity and lake trophic state that in turn influenced primary productivity and thus organic matter accumulation. Distinctive high lake water levels and associated low salinity characterize the Medieval Climatic Anomaly (MCA) as well as the last quarter of the twentieth century and beginning of the twentyfirst century. Conversely, extremely low lake levels with resulting high salinity correspond with the Little Ice Age (LIA). High-resolution sedimentary pigment analyses in these two end–members (i.e., LIA and MCA) do not indicate major changes in the structure of phototrophic communities signifying that the biota survives a large range of salinity and temperature. High lake stands (low salinity) correspond with increased primary productivity as shown by high pigment concentrations along with a decrease in authigenic carbonates and evaporites. These high lake level intervals have been previously linked to a warmer and more humid climate. Conversely, low lake levels (hyper saline waters) correlate with decreasing lake productivity and precipitation of both authigenic carbonates and evaporites. These sediments correspond to cooler intervals with a negative moisture balance. The relative similarity between LOM indicated by the pigment stratigraphy for both intervals show no clear evidence of a linkage between human impact and lake productivity. Hence, Laguna Mar Chiquita has been naturally productive even prior to agriculture expansion by the end of the twentieth century.

Major ion and stable isotopic compositions of a saline lake linked to the SW margin of Laguna Mar Chiquita, Argentina (30°55′ S, 62°51′ W) were studied. The groundwater inflow into the Laguna del Plata was quantified for the first time using a stable isotope mass balance. Shallow groundwater inflow is expected in the Laguna Mar Chiquita system since it represents the terminal water body of the catchment. Lake waters are alkaline and exhibit total dissolved solids contents >30 g L−1. The cationic relative abundance is Na+ ≫ Mg2+ > Ca2+ > K+, whereas that of major anions is Cl− ≫ SO42− > HCO3− + CO32−, which are mainly present as free aqueous ions. PHREEQC simulations indicate that lake waters are oversaturated in Ca2+ and Mg2+ carbonates (calcite, huntite, aragonite, dolomite, magnesite), which are expected to be the first minerals to precipitate due to evaporation processes. The main tributary of the lake (Suquia River) and the phreatic aquifer exhibit δ18O and δ2H values consistent with the isotopic signature of rainfall, whereas lake waters define an evaporation line (δ2H (‰) = 5.4 δ18O (‰) + 1.8). The confined aquifer shows a more depleted isotopic composition, reflecting an allochthonous recharge from the mountain ranges (Sierras Pampeanas). The δ18O mass balance indicates a groundwater inflow of ~4.7 m year−1 to the lake, confirming the hydrological conceptual model for the catchment. However, the groundwater contributions do not affect the chemical composition of lake waters, which mainly results from the evaporation processes as shown by the Spencer diagram.

We report here the results of detailed 210Pb analysis from two lake sediment cores collected from Lagunas Encadenadas del Oeste (LEO), located in the southern Argentinean Pampas (37°S, 62°W). Non-exponential and non-monotonic 210Pbuns depth-profiles in the sedimentary record of these shallow lacustrine systems indicate the interaction of complex processes behind radionuclide fluxes and lake sedimentation. The chronologies and sediment accumulation rates (SAR) for the lake sediment sequences were modeled using different 210Pb-based mathematical models. Since modeled 210Pb ages must be validated against independent stratigraphic markers of known age, two chrono-stratigraphic markers were selected to control the upper and lowermost parts of the 210Pb dated sediments. The younger stratigraphic marker of AD 1980 ± 2 corresponds to an uppermost organic carbon-rich mud accumulated by 1977–78 matching the most noticeable lake highstand occurred during the 20th century, registered on instrumental and paleolimnological records across the Pampean Plains. The oldest stratigraphic marker corresponds to AD 1878 ± 10 matching with a high lake productivity and wet phase related to anomalously intense rainfall and flooding events in southeastern South America for AD 1877–1878. When comparing the resulting ages to the stratigraphic markers, our results show that CRS-model (constant rate of supply) performs better than the other models. Thus, these independent chronostratigraphic markers used along the sedimentary records were critical to validate 210Pb-derived ages and therefore to select the most appropriate model to establish the chronological framework of the recent sediments of the LEO system. The CRS-model appears to be an adequate technique for deriving ages and SAR in the LEO sedimentary record and other Pampean lacustrine systems under strong hydrological variability. Fil: Cordoba, Francisco Elizalde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Jujuy. Universidad Nacional de Jujuy. Centro de Investigaciones y Transferencia de Jujuy; Argentina Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Guerra, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Mulsow, Sandor. Universidad Austral de Chile; Chile Fil: Sylvestre, Florence. Centre National de la Recherche Scientifique; Francia Fil: Zárate, Marcelo Arístides. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; Argentina

Water availability is fundamental to societies and ecosystems, but our understanding of variations 55 in hydroclimate (includingextreme events, flooding, and decadal periods of drought) is limited because of a paucity of modern instrumental observationsthat are distributed unevenly across the globe and only span parts of the 20th and 21st centuries. Such data coverage isinsufficient for characterizing hydroclimate and its associated dynamics because of its multidecadal-to-centennial variability andhighly regionalized spatial signature. High-resolution (seasonal to decadal) hydroclimatic proxies that span all or parts of the60 Common Era (CE) and paleoclimate model simulations are therefore important tools for augmenting our understanding ofhydroclimate variability. In particular, the comparison of the two sources of information is critical for addressing theuncertainties and limitations of both, while enriching each of their interpretations. We review the principal proxy data availablefor hydroclimatic reconstructions over the CE and highlight contemporary understanding of how these proxies are interpreted ashydroclimate indicators. We also review the available last-millennium simulations from fully-coupled climate models and65 discuss several outstanding challenges associated with simulating hydroclimate variability and change over the CE. A specificreview of simulated hydroclimatic changes forced by volcanic events is provided, as well as a discussion of expectedimprovements in estimated forcings, models and their implementation in the future. Our review of hydroclimatic proxies andlast-millennium model simulations is used as the basis for articulating a variety of considerations and best practices for how toperform proxy-model comparisons of CE hydroclimate. This discussion provides a framework for how best to evaluate70 hydroclimate variability and its associated dynamics using these comparisons, as well as how they can better informinterpretations of both proxy data and model simulations. We subsequently explore means of using proxy-model comparisonsto better constrain and characterize future hydroclimate risks. This is explored specifically in the context of several examplesthat demonstrate how proxy-model comparisons can be used to quantitatively constrain future hydroclimatic risks as estimatedfrom climate model projections. Fil: Smerdon, Jason E.. Columbia University; Estados Unidos Fil: Luterbacher, Jürg. University Of Giessen; Alemania Fil: Phipps, Steven J.. University of Tasmania; Australia Fil: Anchukaitis, Kevin J.. University of Arizona; Estados Unidos Fil: Ault, Toby. Cornell University; Estados Unidos Fil: Coats, Sloan. State University of Colorado at Boulder; Estados Unidos Fil: Cobb, Kim M.. Instituto Tecnológico de Georgia; Estados Unidos Fil: Cook, Benjamin I.. Nasa Goddard Institute For Space Studies; Estados Unidos Fil: Colose, Chris. Nasa Goddard Institute For Space Studies; Estados Unidos Fil: Felis, Thomas. Universitat Bremen; Alemania Fil: Gallant, Ailie. Monash University; Australia Fil: Jungclaus, Johann H.. Max-Planck-Institute for Meteorology; Alemania Fil: Konecky, Bronwen. State University of Colorado at Boulder; Estados Unidos Fil: LeGrande, Allegra. NASA Goddard Institute for Space Studie; Estados Unidos Fil: Lewis, Sophie. The Australian National University; Australia Fil: Lopatka, Alex S.. University of Maryland; Estados Unidos Fil: Man, Wenmin. Chinese Academy of Sciences; República de China Fil: Mankin, Justin S.. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos. NASA Goddard Institute for Space Studies; Estados Unidos Fil: Maxwell, Justin T.. Indiana University; Estados Unidos Fil: Otto-Bliesner, Bette L.. National Center for Atmospheric Research; Estados Unidos Fil: Partin, Judson W.. University of Texas at Austin; Estados Unidos Fil: Singh, Deepti. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Stevenson, Samantha. National Center for Atmospheric Research; Estados Unidos Fil: Tierney, Jessica E.. Arizona State University; Estados Unidos Fil: Zanchettin, Davide. Ca’ Foscari University of Venice; Italia Fil: Zhang, Huan. Justus Liebig University; Alemania Fil: Atwood, Alyssa R.. Georgia Institute of Technology; Estados Unidos. Brown University; Estados Unidos Fil: Andreu Hayles, Laia. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Baek, Seung H.. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Buckley, Brendan. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Cook, Edward. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: D'Arrigo, Rosanne. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Dee, Sylvia G.. Brown University; Estados Unidos Fil: Griffiths, Michael L.. William Paterson University; Estados Unidos Fil: Kulkarni, Charuta. City University of New York; Estados Unidos Fil: Kushnir, Yochanan. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Lehner, Flavio. National Center for Atmospheric Research; Estados Unidos Fil: Leland, Caroline. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Linderholm, Hans W.. University of Gothenburg; Suecia Fil: Okazaki, Atsushi. University of Tokyo; Japón Fil: Palmer, Jonathan. University of New South Wales; Australia Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Raible, Christoph C.. University of Bern; Suiza Fil: Rao, Mukund P.. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Scheff, Jacob. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Schmidt, Gavin A.. NASA Goddard Institute for Space Studie; Estados Unidos Fil: Seager, Richard. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Widmann, Martin. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Park Williams, A.. Lamont-Doherty Earth Observatory of Columbia University; Estados Unidos Fil: Xoplaki, Elena. Justus Liebig University; Alemania

Laguna Mar Chiquita (Central Argentina) is a highly variable saline lake particularly suitable for palaeolimnological studies. The most recent (20th century) and past (several 1000s of years) regional hydrological balance variability in southeastern South America has produced dramatic lake level fluctuation, making Laguna Mar Chiquita a sensitive climatic indicator. These fluctuations in the hydrological cycle additionally control the chemistry and biology of the water column and a variety of sedimentary processes, which are distinctively recorded in the composition of the sedimentary organic matter (OM). Lipid extracts, after fractionation, were analysed using gas chromatography/mass spectrometry (GC/MS) and gas chromatography/flame ionization detection (GC/FID). The n -alkanes range from n -C 15 to n -C 35 , with total hydrocarbon concentration in the range 8.49–133 μg g −1 , and carbon preference index (CPI) values for n -C 15–35 between 0.55 and 1.19. C/N values are in the range 4.6–12.5, indicative of mainly algal, bacterial and non-vascular plant origins. The δ 13 C values of individual n -alkanes in the C 15–33 range vary between –22.4‰ and –34.1‰, suggesting a mixed OM input, i.e., C 3 and C 4 plants, and lacustrine algae. The presence of C 27 , C 28 and C 29 sterols (C 27 dominant) and their diagenetic products reflects a major algal contribution. Evaluation of all the data together points to a mainly lacustrine algal input to the OM. Samples for which a high lake level occurred showed a clear predominance in water column production of OM. On the other hand, samples for which an increase in vascular plant (C 3 and C 4 ) input occurred are in accord with a low lake level. The data, combined with sedimentology, geochemical and isotopic information allow the development of a robust model for reconstructing past lake level fluctuation. Furthermore, the results are useful for interpreting similar saline lacustrine records on wider geographical and temporal scales.

During the 1970s, Laguna Mar Chiquita (Argentina) experienced a dramatic hydroclimatic anomaly, with a substantial rise in its level. Precipitations are the dominant driving factor in lake level fluctuations. The present study investigates the potential role of remote forcing through global sea surface temperature (SST) fields in modulating recent hydroclimatic variability in Southeastern South America and especially over the Laguna Mar Chiquita region. Daily precipitation and temperature are extracted from a multi-member LMDz atmospheric general circulation model (AGCM) ensemble of simulations forced by HadISST1 observed time-varying global SST and sea-ice boundary conditions from 1950 to 2005. The various members of the ensemble are only different in their atmospheric initial conditions. Statistical downscaling (SD) is used to adjust precipitation and temperature from LMDz ensemble mean at the station scale over the basin. A coupled basin-lake hydrological model (cpHM) is then using the LMDz-downscaled (LMDz-SD) climate variables as input to simulate the lake behavior. The results indicate that the long-term lake level trend is fairly well depicted by the LMDz-SD-cpHM simulations. The 1970s level rise and high-level conditions are generally well captured in timing and in magnitude when SST-forced AGCM-SD variables are used to drive the cpHM. As the LMDz simulations are forced solely with the observed sea surface conditions, the global SST seems to have an influence on the lake level variations of Laguna Mar Chiquita. As well, this study shows that the AGCM-SD-cpHM model chain is a useful approach for evaluating long-term lake level fluctuations in response to the projected climate changes. Fil: Troin, Magali. Université du Québec a Montreal; Canadá. Aix-Marseille Université; Francia Fil: Vrac, Mathieu. Centre D'etudes de Saclay; Francia Fil: Khodri, Myriam. Sorbonne Université; Francia Fil: Caya, Daniel. Université du Québec a Montreal; Canadá Fil: Vallet Coulomb, Christine. Aix-Marseille Université; Francia Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Sylvestre, Florence. Aix-Marseille Université; Francia

We explore the reliability of large-scale climate variables, namely precipitation and temperature, as inputs for a basin-lake hydrological model in central Argentina. We used data from two regions in NCEP/NCAR reanalyses and three regions from LMDZ model simulations forced with observed sea surface temperature (HadISST) for the last 50 years. Reanalyses data cover part of the geographical area of the Sali-Dulce Basin (region A) and a zone at lower latitudes (region B). The LMDZ selected regions represent the geographical area of the Sali-Dulce Basin (box A), and two areas outside of the basin at lower latitudes (boxes B and C). A statistical downscaling method is used to connect the large-scale climate variables inferred from LMDZ and the reanalyses, with the hydrological Soil Water Assessment Tool (SWAT) model in order to simulate the Rio Sali-Dulce discharge during 1950–2005. The SWAT simulations are then used to force the water balance of Laguna Mar Chiquita, which experienced an abrupt level rise in the 1970's attributed to the increase in Rio Sali-Dulce discharge. Despite that the lowstand in the 1970's is not well reproduced in either simulation, the key hydrological cycles in the lake level are accurately captured. Even though satisfying results are obtained with the SWAT simulations using downscaled reanalyses, the lake level are more realistically simulated with the SWAT simulations using downscaled LMDZ data in boxes B and C, showing a strong climate influence from the tropics on lake level fluctuations. Our results highlight the ability of downscaled climatic data to reproduce regional climate features. Laguna Mar Chiquita can therefore be considered as an integrator of large-scale climate changes since the forcing scenarios giving best results are those relying on global climate simulations forced with observed sea surface temperature. This climate-basin-lake model is a promising approach for understanding and simulating long-term lake level variations.

Laguna Mar Chiquita, a closed, shallow, hypersaline lake in central Argentina (∼30–31°S, 62–63°W), is a sensitive marker of high- and low-frequency changes in regional hydrology and, therefore, of climatic changes at middle latitudes in southeastern South America. Its drainage basin and neighboring areas, including the Sierras Pampeanas de Cordoba, and Sierra del Aconquija (27–33°S, 62–66°W), are under the influence of diverse climate drivers that determine a complex behavior in rainfall and runoff dynamics. Statistical (Mann–Kendall and seasonal Kendall trend tests) and spectral analyses (Fourier and wavelet transform) of the available data show that: (a) there is significant evidence that rainfall has increased in the region since the 2nd half of the 20th century; (b) concurrently, runoff has also increased, particularly in the northern tributaries (north of 31°S) of Mar Chiquita; (c) northern rainfall and discharge records mostly exhibit an apparent near-decadal (also near-bidecadal in runoff) climatic signature; and d) the ENSO influence on rainfall appears faint but discernible in the southern (south of ∼31°S) portion.

Laguna Mar Chiquita, a highly variable closed saline lake located in the Pampean plains of cetral Argentina, is presently the largest saline lake in South America ("-6000km2). The availability of hitorical, instrumental lake-level and salinity data for the past 100 years allows for the calibration of the isotopic archive recorded in the lake sediments. Prolonged intervals with either negative or positive hydrlogical balances have severely modified lakewater levels, salinity and primary productivity, and have also controlled the isotopic composition of both the authigenic carbonate (&8Ooarb and f133Ccarb) and sedimetary organic matter (6"C0,,). Extensive evaporation during lowstand stages results in an enrichment of 180 and 13C in the lake waters, and is recorded in the sediments as the most positive &8O8arb and 613C carb compositions (0.0%o and-1.9Yoo, respectively). Conversely, more negative 6f'8Ocarb and 813Ccarb values (-1.8%o and-3.8Yoo, respectively) are the result of increasing freshwater input into the lake system. The fi3Com values are related to the isotopic composition of the dissolved inorganic carbon pool and the cabonate equilibrium of the lake water. Relatively low 613COm values correspond with high lake levels, low salinity, low alkalinity and high lake productivity. High salinity during lowstands diminishes the amount of primary production and the 613Com value is correspondingly high. The calibrated isotopic model was extrapolated to reconstruct precipitation-evaporation variability from the end of the‘Little Ice Age’ (c. AD 1770) to the present. Low water levels predominated until the last quarter of the twentieth century, when a positive hydrological balance without equivalent in the previous history of Laguna Mar Chiquita became dominant.

Laguna Mar Chiquita, a highly variable closed saline lake located in the Pampean plains of central Argentina, is presently the largest saline lake in South America ( 6000 km 2 ). Recent variations in its hydrological budget have produced dry and wet intervals that resulted in distinctive lake level fluctuations. Results of a multiproxy study of a set of sedimentary cores indicate that the system has clearly recorded these hydrological variations from the end of the Little Ice Age ( AD 1770) to the present. Sedimentological and geochemical data combined with a robust chronology based on 2 1 0 Pb profiles and historical data provide the framework for a sedimentary model of a lacustrine basin with highly variable water depth and salinity. Lake level drops and concurrent increases in salinity promoted the development of gypsum-calcite-halite layers and a marked decrease in primary productivity. The deposits of these dry stages are evaporite-bearing sediments with a low organic matter content. Conversely, highstands are recorded as diatomaceous organic matter-rich muds. Average bulk sediment accumulation rose from 0.22 g cm - 2 year - 1 in lowstands to 0.32 g cm - 2 year - 1 during highstands. These results show that Laguna Mar Chiquita is a good sensor of high- and low-frequency changes in the recent hydrological budget and, therefore, document climatic changes at middle latitudes in south-eastern South America. Dry conditions were mostly dominant until the last quarter of the twentieth century, when a humid interval without precedent during the last 240 years of the lake's recorded history started. Thus, it is an ideal system to model sedimentary and geochemical response to environmental changes in a saline lacustrine basin.

A new approach explaining the main forcing factor of Hirnantian glaciation is proposed herein. It follows the models associating occurrences of continental glaciations with periods of low atmospheric CO2 levels. The accumulation of great volumes of carbonates during pre-Hirnantian late Ordovician, in regions where these deposits were previously absent, is suggested as a major sink of atmospheric CO2. This would have caused an important lowering of the average temperature in the early Hirnantian, after CO2 values had attained a certain threshold. This process was maintained by other positive feedbacks, such as the short-term carbonate weathering CO2 sink. An increase of the direct flux of CO2 from the atmosphere to the oceans by means of dissolution would have been driven by the enhancement of carbonate deposition. The great inundation of the low latitude Laurentia craton during Cincinnatian times and the establishment of a temperate-water carbonate sedimentation on the North Gondwana margin during pre-Hirnantian Ashgill allowed the burying of more than 840 × 1015 kg (1.9 × 1019 mol) of dissolved CO2. This mass is equivalent to nearly 350 times the present values of atmospheric CO2. This is important enough to have greatly altered the equilibrium between the CO2 dissolved in the oceans and the partial pressure of CO2 in the air, eventually causing an important reduction of the latter. The new model also offers a simple explanation for the end of the glaciation after a short time-span. Glacioeustatic lowering of the sea level, concomitant with the glaciation, would have stopped the extra-sedimentation of carbonate due to the retreat of the oceans from the platforms, closing this CO2 sink. Pre-glacial CO2 levels would then recover, due to volcanic and metamorphic CO2 outgassing. After subsequent melting of the ice cap, oceanic circulation did not recover pre-Hirnantian Ashgill strength, resulting in a strong stratification of ocean waters and precluding the recovery of an extensive carbonate deposition. The well-known positive shift in the δ13C at the base of the Hirnantian is assumed to have been caused by weathering and dissolution of carbonates, relatively enriched in 13C, during the glacioeustatic regression and exposure of the platforms.

The main carrying phases of mercury (Hg) were analyzed in a 120 cm sediment core taken at the Laguna del Plata (LP), a small lake connected to the main water body of Laguna Mar Chiquita (LMC) during highstands. LMC is considered to be one of the largest saline lakes in the world representing a sensitive climatic indicator due to its frequent lake level variations at millennial and interdecadal scale like the last ones that started early in the 1970s and after 2004. Total particulate Hg (Hg TP ) concentrations vary between ∼13 and ∼131 μg kg −1 indicating a system with low pollution. Selective extractions with ascorbate, HCl and H 2 O 2 were performed in the sediments and they revealed that Hg is associated mainly to reactive sulphides in the base of the core, while in the middle and upper part the organic matter seems to be the main Hg-bearing phase. The highest and most important peak was found in sediments accumulated between 1991 and 1995. More than a punctual source of pollution, this peak is likely related to two eruptive events occurred in the Andean Cordillera in this period: the eruption of Hudson volcano in southern Patagonia that occurred in 1991 and the one of the Lascar volcano in northern Chile that occurred in 1993. In both cases, the respective ash plumes were documented to have reached the Laguna del Plata region.

Laguna del Plata (Cordoba, Argentina) is a small saline lake connectedto Laguna Mar Chiquita. Its level fluctuations have changed notably throughthe centuries with both high level (HLP) and low level (LLP) periods. Theradionuclides 226 Ra and 210 Pb were analyzed in a core to determine datesand sedimentation rates. The elements As, Ba, Br, Co, Cr, Cs, Fe, Hf, Na,Rb, Sb, Sc, Se, Ta, Th, U, Zn, Zr and rare earth Ce, Eu, La, Lu, Nd, Sm, Tband Yb were determined by instrumental neutron activation analysis. Statisticalanalysis of elemental concentrations (cluster analysis) reflects the associationof the samples along the core according to the provenance of the sedimentsand if they had been deposited during HLP or LLP.

Metamorphic rocks, granitic rocks, and sediments from the Eastern Sierras Pampanas, Argentina, were analyzed for major and trace element concentrations, including rare earth elements (REE). Parental rocks exhibit distinctive REE normalized diagram patterns and elemental ratios, and some elemental ratios reveal significant differences between rock sources. For example, ratios such as Th/Sc, Cr/Th, and La/Cr have a mean value of 0.7, 8.4 and 0.4 in metamorphic rocks, whereas granitic rocks exhibit means of 1.4, 0.7 and 4.9, respectively. These ratios are also useful in linking detrital materials with the corresponding parental rocks. Metamorphic sources yield sediments with lower Th/Sc and La/Cr, and higher Cr/Th ratios than sediments derived from granitic sources. REE and other elements are enriched in the silt-size fraction, whereas they are diluted by quartz in the sand-size fraction. The size of the Eu/Eu* anomaly can be used as a stratigraphical correlation tool in the sedimentary record: Cretaceous rocks show a mean value of 0.9±0.1, whereas Tertiary rocks have a mean value of 2.9±0.3. The Eu anomaly in Quaternary and modern sediments ranges from 0.5 to 0.8.

The 1970s abrupt lake level rise of Laguna Mar Chiquita in central Argentina was shown to be driven by an increase in the Rio Sali-Dulce discharge outflowing from the northern part of the lake catchment. This regional hydrological change was consistent with the 20th century hydroclimatic trends observed in southeastern South America. However, little is known about the impacts of climate or land cover changes on this regional hydrological change causing the sharp lake level rise. To address this question, the present study aims to provide an integrated basin-lake model. We used the physically-based SWAT model in order to simulate streamflow in the Sali-Dulce Basin. The ability of SWAT to simulate non-stationary hydrological conditions was evaluated by a cross-calibration exercise. Based on observed daily meteorological data over 1973-2004, two successive 9-year periods referred to as wet (P1976-1985=1205mm/yr) and dry (P1986-1995=796mm/yr) periods were selected. The calibration yielded similar Nash-Sutcliffe efficiencies (NSE) at the monthly time scale for both periods (NSEwet=0.86; NSEdry=0.90) supporting the model's ability to adapt its structure to changing climatic situations. The simulation was extended in scarce data conditions over 1931-1972 and the simulation of monthly discharge values was acceptable (NSE=0.71). When precipitation in the model was increased until it reach the change observed in the 1970s (ΔP/P̄=22%), the resulting increase in streamflow was found to closely match the 1970s hydrological change (ΔQ/Q̄=45%). Sensitivity analyses revealed that the land cover changes had a minor impact on the 1970s hydrological changes in the Sali-Dulce Basin. Integrating the SWAT simulations within the lake model over 1973-2004 provided lake level variations similar to those obtained using observed discharge values. Over the longer period, going back to 1931, the main features of lake levels were still adequately reproduced, which suggests that this basin-lake model is a promising approach for simulating long-term lake level fluctuations in response to climate. Fil: Troin, Magali. Aix-Marseille Université; Francia Fil: Vallet-Coulomb, Christine. Aix-Marseille Université; Francia Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Sylvestre, Florence. Aix-Marseille Université; Francia

La Laguna Mar Chiquita, ubicada en la provincia de Cordoba, Argentina, es el mayor lago salino de America del Sur, con una superficie variable entre 2.000 y 6.000 km2. Durante las ultimas decadas 50 y 60 el lodo recogido directamente del fondo del lago se utilizaba ampliamente para la aplicacion topica sobre la piel y las sales precipitadas en la costa se utilizaban para banos domiciliarios. Posteriores incrementos del nivel de agua (decadas de los 70, 80, 90) disminuye la posibilidad de utilizar estos materiales. Sin embargo, durante la ultima decada la disminucion de los niveles de agua ha incrementado el potencial de reutilizacion de los lodos y depositos de sales de este lago. El objetivo de este estudio fue caracterizar la composicion de los lodos y sales obtenidas a partir de Laguna Mar Chiquita como materiales naturales con posibles usos terapeuticos. La salinidad del agua, de 28 a 360 g/l como minimo y maximo reportado, se ha alcanzado en los valores de las ultimas decadas, como bajo como 33 g / L, con contenidos de sal superiores a 70 g / L en la presente. Los iones disueltos predominantes son el cloruro y el sodio. El sulfato estaba presente en proporciones menores en el agua pero era el anion mas importante de las sales precipitadas. El pH era neutro o ligeramente alcalino. La composicion dominante del lodo, con posible aplicacion terapeutica, era una mezcla de ilita-predominante como filosilicatos, cuarzo, plagioclasa, feldespato, moscovita, calcita y halita. Las aguas y los lodos de la Laguna Mar Chiquita mostraron una importante similitud con los de la Lo Pagan en el Mar Menor, Murcia, Espana, lugar relacionado con el turismo que promueva ampliamente la utilizacion de los lodos con fines terapeuticos.

Salina de Ambargasta is a playa located at mid latitudes in central Argentina (29 °S–64 °W). Because of its hydrological behaviour, this playa complex can be subdivided into a closed system “ sensu-stricto ” and an “open-like system” due to the presence of a seasonal outflow. Geomorphological and sedimentological features enable the separation of the Ambargasta playa into well-defined western, eastern and northern zones, where aeolian processes, groundwater supply and surface inflow, respectively, define distinctive sedimentary environments and typical processes of deposition. The following depositional settings were recognized: (1) alluvial fan; (2) sandflat; (3) springs; (4) dunes and palaeo-dune field; (5) dry mudflat; (6) capillary mudflat; (7) ephemeral saline lake (includes saline mudflat and salt pan). The dry mudflat is present at the highest topographical zone, where the groundwater influence is less important and only intermittent ponds are present. In the capillary mudflat, evaporite sedimentation is limited to the development of efflorescence by evaporative pumping. The ephemeral saline lake, placed in the lowermost topographical region, alternates cycles of lake expansion and contraction responding to inter-annual hydrological variability as well as to seasonal variability. Lake expansion takes place during early austral summer (December–March), while continuous evaporation of brine leads to the growth of halite crystals during late summer. Sodium chloride-type brines result from both chemical fractionation as evaporation increases and salt dissolution. The isotopic compositions of surficial and underground waters (δ 18 O and δ 2 H) indicate that lake waters become isotopically enriched during summer when evaporation plays a significant role in the playa complex.

Although paleolimnological studies in the Argentinean and Uruguayan Pampas are relatively incipient, they have already provided critical information on the regional response of aquatic systems to climate variability. The combined results of these research initiatives highlight the key role Figure 2: Conceptual paleolimnological model displaying the relationship between trophic development of Uruguayan lakes (purple line), climate change in the region (black line) and Holocene sea-level curves (colored lines) observed in Uruguayan lakes. Temperature and humidity curves were reconstructed from opal phytolith data (Bracco et al., 2005; Inda et al., 2006; del Puerto et al., 2006; 2008; 2009). Sea level curves reconstructed from stratigraphical and topographical data. 117 PAGES news ? Vol 17 ? No 3 ? October 2009 Science Highlights: Paleolimnology of the subtropical region of South America (i.e., the transition between the tropics and the extra tropics) in deciphering the forcing factors of past changes in atmospheric circulation. Both Argentinean and Uruguayan Holocene paleolimnological records indicate similar paleoclimatic trends, i.e. dominant dry conditions were observed during cold phases, whereas wet conditions prevailed during warm climatic phases. To our knowledge, this is the first attempt to integrate paleoclimatic data for the whole Pampean region. In addition, our results underscore the need to reinforce paleoclimate research at mid-latitudes in South America, in an attempt to fully appreciate natural climate variability beyond the instrumental record, as well as to design new strategies for the sustainable development of ecosystems and natural resources. Fil: Garcia Rodriguez, Felipe. Universidad de la República; Uruguay Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: del Puerto, Laura. Universidad de la República; Uruguay Fil: Inda, Hugo. Universidad de la República; Uruguay Fil: Stutz, Silvina Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Bracco, Roberto. Universidad de la República; Uruguay Fil: Panario, Daniel. Universidad de la República; Uruguay Fil: Cordoba, Francisco Elizalde. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Sylvestre, Florence. Aix-Marseille University; Francia Fil: Ariztegui, Daniel. Universidad de Ginebra; Suiza

In contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess (41°22 20 S, 71°44 0W) located in the Nahuel Huapi National Park in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi-pristine lake which receives meltwaters from the Tronador ice cap. Chronology was based on 137Cs and 210Pb measurements of the upper sediments, and the inferred sedimentation rate of 23.2 mg cm-2 y-1 (0.15 cm y-1) was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility (MS) profiles. Results from the multiproxy analyses in the longest core (83 cm) identify three main phases of change. From the bottom up to 42 cm (ca. ad 1800), the sediment is composed of light-grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone (ad 1770-1850), pigment concentrations were very low. From 42 cm to ca. 25 cm (ad 1800-1940), the sedimentary record is composed of alternating black and dark organic-matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm (ca. ad 1940) showing a strong increase in organic matter content, algal nutrients and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. Fil: Guilizzoni, Piero. Consiglio Nazionale delle Ricerche; Italia Fil: Massaferro, Julieta. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentina Fil: Lami, Andrea. Consiglio Nazionale delle Ricerche; Italia Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Ribeiro Guevara, Sergio. Comisión Nacional de Energía Atómica; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Formica, Stella Maris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Daga, Romina Betiana. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear; Argentina Fil: Rizzo, Andrea Paula. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Ingeniería Nuclear; Argentina. Consiglio Nazionale delle Ricerche; Italia Fil: Gerli, Stefano. Consiglio Nazionale delle Ricerche; Italia

New limnogeological results (Laguna Mar Chiquita, 30°S) at the middle latitudes in the subtropical Pampean plains of Southern South America are used to establish comparisons with records spanning Late Glacial times and the Holocene covering the Northern Andean Patagonia and the Extra Andean Southern Patagonia. Historical and archaeological data were also used to enlarge existing environmental reconstructions in the central plains of Southern South America. Two groups of climate records – at both sides of the Arid Diagonal- can be distinguished according to their hydrological response during dominant warm or cold climatic phases. The first group includes records from the Pampean region and allows to reconstruct the past activity of the South America Monsoonal System. The second group includes archives of the Patagonian climate, as well as the Salinas del Bebedero, and provides a record of past changes in the strength and latitudinal position of the Southern Westerlies.

Geoscientific data combined with historical documents on past natural hazard events and on the disasters that followed are essential to improve mitigation plans. It is only with this method that the full scale of potential rapid changes that are not covered by the instrumental record can be obtained. Therefore, the collection of these past data and their integration into planning should become one of the priorities of the Hyogo Framework of Actions. This paper analyses the following five case studies: global warming impact on the indigenous populations at high latitudes of Canada, hurricane impact on the southern coast of the USA as experienced in New Orleans, rapid level rise in several lakes of the Argentinian Pampas with emphasis on Laguna Mar Chiquita, the rapid sea level rise of the Caspian Sea as seen from Iran and the tsunami risk in a large Alpine lake of Northern Italy, Lake Como. In each area, the main natural hazard is part of a potential series of hazards that, if combined, could lead to a shift from disaster to catastrophe. The most successful cases of transfer of information between geoscientists and end-users are when the hazards and subsequent disasters are visible or when the messengers bearing the information are trusted by the local communities.

The (210)Pb dating method was first introduced by Goldberg (1963), and since then has been applied to study sediment from lakes, estuaries and coastal marine environments. Hundreds of studies around the world have used (210)Pb as a geochronological tool in aquatic ecosystems. However little attention has been paid to the potential of this naturally occurring isotope as an environmental tracer of ecological events. Here we report three instances in which (210)Pb profiles measured on undisturbed sediment cores from lakes, rivers and fjords show us the potential of (210)Pb profile as a tracer of natural and anthropogenic processes. The methodology used here is a suite of techniques combining biogeochemistry (micro-electrodes), paleomagnetism (susceptibility), sediment characteristics (LOI) and visualization (SPI and X-ray) applied to the interpretation of (210)Pb profiles. We measured (210)Pb profiles on sediments from a river, Cruces River (Chile), which recorded a clear shift in the water chemistry caused by a pulp mill effluent to the river. Here metal mobilization and remobilization of the tracer may be the cause of the observed profile. We also measured (210)Pb profiles in sediment from two fjords of Southern Chile (Pillan and Reñihue), the sudden deposition change of fresh (210)Pb with depth observed could very well be the result of bioturbation but it occurred in a seafloor area deprived of bioturbators. In this case, (210)Pb recorded the onset of aquaculture activities (fish farming) that took place two decades ago. Finally, (210)Pb profiles measured in two lakes in the "pampa Argentina": Epecuen and Venado showed a particular shape with depth. These profiles apparently registered a sudden depositional event with recent (210)Pb material, probably related to strong shifts in precipitation and drought cycles in that part of the world. These three examples show that (210)Pb profiles provide valuable information not only on geochronology, but also related to natural and anthropogenic short term processes, as shown here, but these are not always reported and well understood.

Using instrumental neutron activation analysis, the vertical distribution of La, Ce, Nd, Sm, Eu, Tb, Yb and Lu was determined in 3 well dated sedimentary cores collected from Laguna Mar Chiquita, Argentina. Validation of the methodology was done using the Soil 7 (IAEA) reference material. The REE contents vary according to core location and lithological units, depending on the proportion of fluvial terrigenous components in the lake sediments. Lithologies with higher proportion of terrigenous components show higher REE concentrations, suggesting that the dominant REE carrier phase might be a detrital mineral. There is a consistent value of about 1.2 for (La/Yb)N and (LREE/HREE)N ratios for all sediments at the three sites, indicating a slight LREE enrichment in relation to the average shale NASC. Ce/Ce* values are close to 1.0, meaning that Ce behaves similarly to other light REE's.