Biología

In Buenos Aires coasts, sedimentary processes were particularly active during the Quaternary owing to eustatic fluctuations in sea level. As a result, during the late Quaternary transgressions, marine and marginal marine sediments were deposited in the coastal plain. In order to interpret these Holocene littoral sequences, we analyzed the distribution, diversity, species composition and taphonomic features of total benthic foraminifera assemblages from modern littoral settings, from the top of the dune to the lower shoreface, in two close but geomorphologically different transects located in the Atlantic coast of Northern Buenos Aires Province (Argentina, South America). Total benthic foraminiferal assemblages from subtidal and supratidal environments are distinguishable in terms of composition, diversity and taphonomic features. In upper shoreface, foreshore, backshore and foredune environments, assemblages are clearly dominated by three species: Buccella peruviana, Ammonia beccarii and Elphidium discoidale (the BAE group). This feature is the result of taphonomic processes that favor the selective preservation of such species. The study of taphonomic modifications of shells in modern assemblages allows a better discrimination between subenvironments than the analysis of taxonomic composition. Although Holocene assemblages have no strict counterparts between total modern assemblages, taxonomic composition and taphonomic modification of shells allow us to infer that the Holocene sequence was deposited between the upper shoreface and the backshore.

Los cambios climáticos son reflejados en las variaciones de diferentes parámetros. Las secuencias sedimentarias de lagos son buena fuente de esta información debido a que proveen grabaciones continuas y detalladas de cambios paleoclimáticos. Para determinar los cambios en el clima al SE de la llanura Pampeana, se presentan estudios de magnetismo de rocas realizados en un testigo colectado del fondo de la Laguna La Brava (Argentina). También se midieron contenidos totales de sulfuro, carbón orgánico e inorgánico (TS, TOC y TIC), elementos alcalinos, metales pesados y livianos, y cambios en las comunidades de vegetación. Se realizaron cinco determinaciones de edades radiocarbónicas y se calcularon las edades calibradas. La tasa promedio de acumulación de sedimento es 1.3 mm/año y la secuencia representa los últimos 4800 años en edades calibradas (cal. BP). El objetivo principal fue reconstruir el balance

Paleoenvironmental record of the Marine Isotope Stage 2 in the South-bonaerensian outer continental shelf, Argentina: a new contribution to the regional evolution A core obtained at 100 m water depth in the outer shelf of southeastern Buenos Aires is described. It contains a sedimentary sequence in transgressive facies that records for the first time in the region the evolution of barriers-coastal lagoon environments during the last part of Marine Isotope Stage 2 with an age ca. 15 ka cal AP.

RESUMEN El océano Atlántico Sur es clave en la distribución de masas de agua profunda hacia otros océanos. Dado el papel que juega la circulación termohalina en el clima, el reconocimiento de variaciones en su distribución durante los ciclos glaciales/intergla-ciales reviste gran interés. Los foraminíferos bentónicos son utilizados como herramientas de reconstrucción paleoceanográ-fica, y la existencia de especies asociadas a masas de agua fue utilizada para definir cambios en la circulación oceánica profun-da. Sin embargo, la relación entre foraminíferos bentónicos y masas de agua es controversial. Con el objetivo de determinar si las asociaciones de foraminíferos bentónicos reflejan la distribución de las masas de agua profunda durante un evento glacial del Pleistoceno Medio, se analizó un testigo ubicado en el límite entre dos masas de agua profunda: la North Atlantic Deep Water y la Circumpolar Deep Water. En las asociaciones se hallaron especies consideradas indicadoras de amba...

Se describe la evolución paleoambiental de la plataforma exterior del sureste bonaerense durante la última parte del Estadio Isotópico 2, a partir del estudio de un testigo a 100 m de profundidad cuya secuencia sedimentaria transgresiva grada desde facies fluvio-estuarinas a facies de barreras-lagunas costeras de edad ca. 15 ka cal AP.A core obtained at 100 m water depth in the outer shelf of southeastern Buenos Aires is described. It contains a sedimentary sequence in transgressive facies that records for the first time in the region the evolution of barriers-coastal lagoon environments during the last part of Marine Isotope Stage 2 with an age ca. 15 ka cal AP.Fil: Violante, Roberto Antonio. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; ArgentinaFil: Laprida, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; ArgentinaFil: Bressan, Graciela Susan...

Different precipitation regimes across Patagonia generate an environmental gradient that is expected to reflect upon the solute composition and concentration of lake water through the ensuing differences in water balance. In turn, this hydrochemical gradient could influence the occurrence and distribution of ostracods in the area. A cluster analysis on hydrochemical data of 36 Southern Patagonian waterbodies shows that low salinity, bicarbonatedominated waters characterize Andean and ecotonal lakes, located in the wetter part of the precipitation gradient, while their steppe counterparts, which receive a much lower precipitation input, are more saline, enriched in all major anions and sodiumdominated. Kruskal-Wallis tests followed by Mann-Whitney pairwise comparisons show statistically significant differences in the ostracod species each water type hosts, with L. patagonica, E. cecryphalium, P. smaragdina and P. incae being found in the more dilute waters characteristic of Andean and ecotonal lakes and Limnocythere rionegroensis in the mesohaline, evaporatively evolved waters typical of steppe lakes. Other species studied do not appear to have such distinct distributions, having been found throughout the range of conditions studied. These findings promote the use of the aforementioned ostracods as semi-quantitative paleohydrological indicators, which could improve paleoclimatic reconstructions in Patagonia.

Lacustrine ooids and pseudomorphs after ikaite Multiple dating Bioproxies XRF-scanning Lake-level changes Southern hemisphere westerly winds Hydrological changes that occurred during the last 4700 years have been reconstructed using multi-proxy analyses of sediment cores from the volcanic crater lake of Laguna Cháltel (50°S, 71°W). The chronology is based on AMS 14 C age modeling constrained by paleomagnetic secular variations. Chemical and physical properties of the lake water together with results of lake-water surface-temperature monitoring, as well as sediment characteristics reveal conspicuous features archived as different sedimentary carbonate phases and morphologies which are attributed to lake-level changes. Sedimentological, geochemical and biological proxies together suggest the development from an initial playa lake-phase towards a system with progressively rising lake level. In detail, proxies indicate the existence of an ephemeral lake since 4700 cal BP until a glauberite-bearing carbonate crust formed around 4040 cal BP which probably is associated to the globally recognized 4.2 ka event. This crust is interpreted as a desiccation event terminating the ephemeral lake phase. Following this desiccation a shift towards conditions with a positive hydrological balance of Laguna Cháltel occurs, which leads to the development of a saline lake with ooid formation between 4040 and 3200 cal BP. Further lake-level increase with initially high minerogenic input until 2700 cal BP resulted in a lake freshening which allowed the preservation of diatoms. Sigmoidal and star shaped carbonate crystals occurred until 1720 cal BP indicating a syn-or post-depositional formation of ikaite. Anoxic conditions and increased deposition of clay and sand through fluvial and eolian input are interpreted as a further lakelevel rise and/or a prolonged winter ice cover culminating during the Little Ice Age. The highest lake level was probably reached at that time and since then dropped to its present day height. Previous studies have shown that the southern hemisphere westerly winds (SWW) exert an oppositional control on hydrological regimes at the eastern and the western sides of the Patagonian Andes. At Laguna Cháltel SWW forcing is changing evaporation rates by varying wind intensities, air temperatures and lake ice coverages as well as by precipitation rates (easterly vs. westerly sources of moisture). Our data suggests that the lake-level history of Laguna Cháltel reflects changes in the SWW during the last 4.7 ka on the eastern side of the Andes. However, the elevated location of Laguna Cháltel on an 800 m high plateau at the leeward side of the Andes potentially leads to a local overprint of the SWW influence on the hydrological balance.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The main goal of this contribution is to summarize our current knowledge on paleolimnological research in Argentina using bioproxies, particularly ostracods (Crustacea) and chironomids (Diptera). Additionally, we present our perspective on the strengths and weaknesses of the major approaches to reconstruct past climate from these biological proxies. Ostracod and chironomid assemblages are powerful tools in Paleolimnology. These arthropods live in continental waters where they can reflect climate and environmental changes because of their high sensitivity to variations in the physical and chemical parameters controlling aquatic systems. Based on their modern ecological requirements it is possible to apply numerical, multivariate, and qualitative techniques to reconstruct some key parameters of late Quaternary environments. For the past 20 years, the use of modern and fossil ostracods and chironomids has increased significantly allowing the development of robust and unbiased high-reso...

Se realiza una síntesis de los cambios paleohidrológicos en Antofagasta de la Sierra para generar un modelo de evolución paleoambiental que considera la heterogeneidad ambiental y permite evaluar su utilidad en relación con el análisis de las ocupaciones humanas desde el Holoceno medio. Las investigaciones previas en sistemas fluviales y lacustres (que incluyen relevamientos geomorfológicos y diversos análisis sedimentológicos, edafológicos, de diatomeas y ostrácodos) permitieron inferir que durante los últimos 7200 años cal AP existió disponibilidad de recursos hídricos aunque de variada magnitud y distribución espacio-temporal, que generaron condiciones locales favorables para la ocupación humana en espacios específicos. Entre ca. 7200-3500 años cal AP, predominaron condiciones áridas con una distribución de los recursos hídricos de forma mosaico en escala intra- e intercuencal. Entre ca. 3500-1600 años cal AP, se evidencian condiciones relativamente más húmedas con mayor desarrol...

Fossil (Late Pleistocene) assemblages of cold-water corals (Scleractinia) were collected in the northern sector of the Argentine continental margin. After discussing its characteristics and setting it is considered that they were controlled by the influence of the high-energy interface between water-masses at the base of the Antarctic Intermediate Water on a hard substrate at the head of Mar del Plata canyon.

The Cenozoic rocks of Argentina contain a rich, exceptionally well preserved and remarkable diverse marine and continental invertebrate fauna. The main goal of the present synthesis consists in revealing the continuous progress of the scientific research performed during the last 50 years dealing with these assemblages. Initial studies of microfaunas were carried out between the 50? and 60? and since then the interest for forams and ostracods experimented a marked increase among workers. Analysis on these faunas not only improved the knowledge of their taxonomic composition, provided a proper frame for biostratigraphic works for accurating age assignments of Argentinean Cenozoic strata, but also became a new source of data to be used in paleoenvironmental interpretations. Although known since the middle part of the XIX century, during the last five decades, macroinvertebrates have been matter of a renewed interest by paleontologists. Being the most abundant, the Tertiary marine shal...

The southern tip of South America, commonly referred to as Patagonia, is a key area to understand Southern Hemisphere Westerlies (SHW) dynamics and orographic isotope effects in precipitation. However, only few studies have addressed these topics. We evaluated the stable isotope ( 2 H,  18 O) compositions of precipitation, lentic waters, and lotic waters in that area to characterize and understand isotope fractionation processes associated with orographic rainout, moisture recycling and moisture sources. Observational data were interpreted with the help of backward trajectory modelling of moisture sources using reanalysis climate data. While the Pacific serves as the exclusive moisture source for sites upwind of the Andes and on the immediate downwind area of the Andes, recycled moisture from the continent seems to be the main humidity source at the Patagonian Atlantic coast. In contrast, the Pampean Atlantic coast north of Patagonia obtains moisture from the Atlantic Ocean. In the core zone of the SHW at a latitude of 50° S, a depletion in the heavy isotopes of 10 ‰ and 85 ‰, for  18 O and  2 H, respectively, occurs due to orographic rainout corresponding to a drying ratio of 0.45.

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

In the Patagonian region (∼37-56 • S) E of the Andes, the salinity and solute composition of lakes is strongly related to their location along the marked W-E decreasing precipitation gradient that is one of the main climatic features of the area. A calibration function (n = 34) based on 12 ostracod species (Ostracoda, Crustacea) was developed by WA-PLS to quantitatively reconstruct electrical conductivity (EC) values as a salinity proxy. The selected one component model had a r 2 = 0.74 and RMSEP and maximum bias equal to 16% and 31% of the sampled range, respectively, comparable to other published ostracod-based calibration functions. This model was applied to the ostracod record of the closed lake Laguna Cháltel (49 • 58 S, 71 • 07 W), comprising seven species and dominated by two species of the genus Limnocythere. In order to evaluate the calibration function's robustness, the obtained EC values were compared with qualitative lake level and salinity variations inferred through a multiproxy hydrological reconstruction of the lake. Both reconstructions show good overall agreement, with reconstructed EC values in the oligo-mesohaline range (average: 11 060 ± 680 S/cm) between 4570 and 3190 cal BP, corresponding to the ephemeral and shallow lake phases, and a marked decrease in EC concurrent with a lake level rise, reaching an average EC of 1140 ± 90 S/cm during the deep lake phase (1720 cal BP to present). The variability in the reconstructed EC values for the ephemeral lake phase showed some inconsistency with the expected trend, which was attributed to time-averaging effects; for its part, the pace of the decrease in EC during the medium-depth phase (3190-1720 cal BP) differed from the expected, which could be due to autigenic effects (redissolution of salts) at the onset of this phase. This comparison not only lends support to the adequacy of the calibration function, but also suggests that its application in the context of a multiproxy study can greatly contribute to distinguish between autigenic and climatic-related controls of paleosalinity in closed lakes, allowing performing more accurate paleoenvironmental inferences on the basis of paleohydrological reconstructions.

Fil: Grana, Lorena Giselle. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro de Investigaciones y Transferencia de Catamarca. Universidad Nacional de Catamarca. Centro de Investigaciones y Transferencia de Catamarca; Argentina