Late Pleistocene and early Holocene ecological response of Lake El Trébol (Patagonia, Argentina) to environmental changes (original) (raw)
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Palaeogeography, Palaeoclimatology, Palaeoecology, 2009
Laguna Las Vizcachas is a cirque lake located at the margin of an extra-Andean volcanic plateau in southern Patagonia, Argentina, within the area of steppe and semi-desert east of the Andes. The number of paleoenvironmental records is still limited in this region. Sediments of this lake were studied in order to obtain multi-proxy information about the paleoenvironmental history of this site for the 'Medieval Climate Anomaly' and the 'Little Ice Age' chronozones. In combination with results from other sites across southern Patagonia, our data enhance the understanding of spatial patterns of past hydrological changes and contribute to distinguishing between the signals of temperature and precipitation. As Laguna Las Vizcachas is situated at 1100 m a.s.l. in a cool 'mountain climate', the lake system is more sensitive to changes of temperature and winter ice cover than other sites from lower elevations in this region. Our interpretation of the multi-proxy dataset is based on signals of clastic sediment input, lake productivity, organic matter sources and preservation, dilution effects and early diagenetic overprint. The record reveals a period of enhanced fluvial runoff resulting from higher precipitation from the 12th until the end of the 14th century as inferred from high concentrations of Ti, Ca, and from magnetic susceptibility. This may coincide with higher wind intensities as suggested by higher proportions of epiphytic diatoms which point to an enhanced lateral transport from their littoral habitat towards the coring position at the center of the lake. In comparison with other records from southern Patagonia, the results from Laguna Las Vizcachas suggest opposite precipitation regimes between the western and eastern parts of Patagonia during that time which corresponds partly to the 'Medieval Climate Anomaly' chronozone. However, this proposal is compromised by the chronological uncertainties of the different records under consideration. The diatom record of Laguna Las Vizcachas indicates temperature changes: highest proportions of benthic diatoms point to coldest conditions from the mid-15th until the mid-17th century, followed by relatively warm conditions until the mid-18th century as suggested by a decrease of benthic taxa and a conspicuous rise of the planktonic/non-planktonic diatom ratio that can be used as an indicator for the length or presence/absence of winter ice cover.
Palaeogeography Palaeoclimatology Palaeoecology, 2005
Marked environmental changes in the southern Patagonian steppe during the last 1100 years are detected by a multi-proxy study of radiocarbon-dated sediment cores from the crater lake Laguna Azul (52805VS, 69835VW). A prominent shift in carbon isotope records occurred between AD 1670 and AD 1890 induced by a change to cooler climate conditions with a concurrent lake level rise. A second perturbation of the lake ecosystem started with a fire event around AD 1830. The fire event triggered increased soil erosion initiating a change of the diatom assemblages. This shift in diatom assemblages may have been enhanced by shrinkage of littoral habitats and higher nutrient supply in the course of permanent European settlement at the end of the 19th century. The introduction of neophytes by European sheep farmers is confirmed by the permanent occurrence of Rumex pollen in the sediment record since the beginning of the 20th century. D
The Holocene
South American paleoreconstructions are of global interest because it is the only landmass extending from the tropics to the southern high latitudes and intersecting the entire southern westerly wind belt. In this context, endorheic environments, as Lake Cari-Laufquen Grande (LCLG; 41º35’S, 69º25’W) are excellent sites for paleoenvironmental studies, since they react rapidly to changes in the precipitation/evaporation ratio. In this study, the limnological conditions prevailing during the last 3000 years have been inferred based on a multiproxy analysis of the sedimentary sequence of LCLG (water depth 4 m, core length 505 cm). Today, this is one of the few lakes in Northern Patagonia, providing a unique paleoclimatic and paleoecological lacustrine record. The ostracod assemblages, along with sedimentological, petrophysical and geochemical data, show hydrological changes in Cari-Lauquen Grande basin during the studied period. Our results indicate the continuous presence of a saline t...
Quaternary
Patagonian shrub and ecotonal communities were sensitive to past environmental changes and thus may also be affected by future ones. Therefore, their paleoecological study constitutes a valuable tool to understand the way in which these plant communities respond to the forcings responsible for environmental variability. The aim of this paper is to reconstruct the vegetation dynamics of the Pueyrredón Lake area (47°25′55′′ S; 72°0.7′7′′ W) for the last 3000 cal yr BP and to contextualize these changes in a regional paleoclimatic framework. The results indicate that at the beginning of the 2900 cal yr BP, the vegetation in the northwest of Santa Cruz, Argentinian Patagonia, was represented by a grass-shrub steppe associated with forest–shrub steppe ecotonal elements. This information correlates with the larger-scale environmental inferences described for the period, which indicate an increase in moisture availability due to the weakening of the westerly winds. A marked change to arid ...
Physics of The Earth and Planetary Interiors
Paleomagnetic studies carried out on six cores from the bottom sediments from lake El Trébol, South Argentina are described.Measurements of directions declination and inclination (D and I) and intensity of natural remanent magnetisation (NRM), magnetic susceptibility at low and high frequency (specific, X and volumetric, k), isothermal remanent magnetisation (IRM), saturation isothermal remanent magnetisation (SIRM), back field and anhysteric remanent magnetisation (ARM) were carried out. Stability of the NRM was investigated by alternating-field demagnetisation.Rock magnetic studies suggest that the main carriers of magnetisation are ferrimagnetic minerals, predominantly pseudo single domain magnetite.Records of NRM and k show a good correlation with the sedimentological description, and also with those of shorter cores previously studied.The tephra layers were identified from the lithologic profiles and also from the magnetic susceptibility logs. Due to their different chronologic...
Journal of Paleolimnology, 2005
The volcanogenic lake Laguna Potrok Aike, Santa Cruz, Argentina, reveals an unprecedented continuous high resolution climatic record for the steppe regions of southern Patagonia. With the applied multi-proxy approach rapid climatic changes before the turn of the first millennium were detected followed by medieval droughts which are intersected by moist and/or cold periods of varying durations and intensities. The 'total inorganic carbon' content was identified as a sensitive lake level indicator. This proxy suggests that during the late Middle Ages (ca. AD 1230-1410) the lake level was rather low representing a signal of the 'Medieval Climate Anomaly' in southeastern Patagonia. At the beginning of the 'Little Ice Age' the lake level rose considerably staying on a high level during the whole period. Subsequently, the lake level lowered again in the course of the 20th century.
Recent environmental changes inferred from sediments in a shallow lake of the Argentinian pampas
Journal of Paleolimnology, 2018
The Pampas are fertile lowland plains that extend across east-central Argentina and are renowned for their agricultural importance. The low geomorphologic relief of the region accounts for the occurrence of numerous shallow lakes whose sediments constitute paleoenvironmental archives of the outcomes of natural processes and human activities in the Pampas. We identified the main forcing factors behind hydrological shifts during the past ca. 200 years in La Barrancosa, a shallow lake located in the southeastern Pampas. The data provide a historical context to better understand environmental changes in the area during the twentieth century. Variations in biological (ostracods, chironomids and pigments), geochemical and sedimentological variables were interpreted in terms of lake level and trophic state changes. The low diversity of biological assemblages and the autoecology of the ostracod and chironomid taxa suggest that during parts of the record assigned to the nineteenth century, near the end of the Little Ice Age, La Barrancosa was a shallow, ephemeral, subsaline wetland, indicating drier-than-present conditions. Thereafter, a hiatus from ca. AD 1860-1940 is attributed to denudation processes during the Pampas Dust Bowl drought of the 1930s. The onset of wetter
Holocene, 2003
Multiproxy palaeoenvironmental and palaeolimnological analyses of two Holocene-age sediment cores from the margin of Lago Cardiel, a 76 m deep, closed-basin lake in southern Patagonia (latitude 49°S), provide information on lake-level changes that can be related to regional palaeoclimate scenarios. Sedimentologic (magnetic susceptibility, organic and inorganic carbon content) and environmental indicators (pollen, diatoms, ostracodes and stable isotopes on ostracodes) show lake levels markedly higher than today during the early Holocene, following a rapid lake-level rise after a desiccation phase prior to 11000 BP. After about 6000 BP, lake levels were generally lower, but underwent repeated uctuations. These inferred changes support the previously proposed view that the southern westerly stormtracks were focused (zonal) north of latitude 50°S during the early Holocene, allowing for Antarctic cold fronts to bring easterly moisture to southern Patagonia, whereas during the late Holocene the stormtracks shifted seasonally, with an overall more meridional behaviour, resulting in less and more variable moisture at these latitudes.