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Paleoenvironmental studies provide both climate and habitat scenarios for Archeology. The archaeological background of the Argentine Patagonian forest environments is still not well-known. However, thanks to the undertaken palaeoenvironmental studies some processes are now much better understood. This paper focus on the forest history of Rio Manso valley during the last 13,000 years, with special reference to the dynamics of humid forest structure and composition, depicted from pollen and charcoal analyses. Subsequently, the archaeological records are considered to investigate the human occupation of the valley. Our evidences showed that during Late-Glacial and Early Holocene a highly diverse humid Nothofagus forest was frequently disturbed by high severity fires. The change to a closed forest with a reduced understory began at ca. 10,600 cal yr BP under less severity fires. The expansion of Austrocedrus chilensis with the establishment of the mixed forest under a regime of more frequent fires occurred at ca. 3500 cal yr BP. Scrubland expanded favored by frequent and high severity fires dramatically changing the landscape appearance by ca. 750 cal yr BP. Although archaeological data indicate human presence in the valley since ca. 8200 cal yr BP it is not until Late Holocene that a clear occupation is detected. Groups of hunter-gatherers with high mobility started a more intense use of the forest at ca.1700 cal yr BP. Throughout the Holocene the forest appears to be sensitive to fire perturbations, making it difficult to discern between climatic or anthropic causes. Therefore, the influence of native people in the vegetation dynamic of the Rio Manso valley is still under debate. Clear evidence of human impact is observed later on, when European colonization started at the end of 19th century.

Accumulated pollen sequences are used to infer temporal changes in vegetation composition. Pollen transport and dispersal by winds introduce large biases in the interpretation of pollen records. In order to calibrate the models used to infer past species distributions, human activities or climate, contemporary time series of pollen records are assessed and modelled. The Gaussian plume model assumes that pollen transport takes place in a neutral atmosphere and pollen contribution is even from all directions (isotropy). In this study, we analyse these assumptions with airborne pollen measurements of Weinmannia trichosperma, a forest tree which grows mainly on the western slopes of the Andes, along with other characteristic species of the steppe which develops in eastern Patagonia. Instead of the Gaussian plume mixing model that is usually employed in the theory of pollen analysis, we apply a full 3D Lagrangian dispersion model, which allows calculation of potential source distributions (footprint) from modelled backward trajectories of airborne pollen observations. Results show that neutral atmospheric conditions are properly assumed for the region. The footprint calculated from the modelled trajectories of a five-year record is consistent with the location of pollen sources but the footprint shape showed that pollen contribution is uneven due to the influence of transient weather systems. Fil: Perez, Claudio Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina Fil: Gassmann, María Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Tonti, Natalia Edith. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina Fil: Pisso, Ignacio. Norwegian Institute for Air Research; Noruega

La ecología de incendios es una actividad interdisciplinaria concerniente al estudio de los procesos naturales que involucran fuego en los ecosistemas y su interacción con los componentes bióticos y abióticos. Numerosos estudios orientados al conocimiento de la evolución de los ecosistemas naturales y humanos bajo la influencia recurrente del fuego atraviesan el trabajo interdisciplinario en el marco de la Ecología y de las Ciencias de la Tierra. El efecto de los incendios naturales y antrópicos en la evolución del paisaje, su impacto en las comunidades de bosque y la respuesta de los ecosistemas a los incendios son temas de debate y deben ser evaluados en diferentes escalas, tanto temporales como espaciales. En este trabajo se presentan algunos ejemplos que ponen en evidencia en qué medida la metodología aplicada al estudio de la producción, dispersión y depositación del carbón vegetal sedimentario o charcoal en cuencas lacustres y humedales contribuye a dar respuestas a estos interrogantes, se realiza una actualización bibliográfica y se describen algunos ejemplos de los estudios a escala de siglos a milenios, realizados hasta el momento en el sur de América del Sur. Fire ecology is an interdisciplinary activity concerning the study of natural processes that involve fire interactions with biotic and abiotic components of the ecosystems. Numerous studies focused on the knowledge of the evolution of natural and human ecosystems under the recurrent influence of fire need the interdisciplinary work between Ecology and Earth Sciences. The effect of natural and anthropogenic fires on the evolution of the landscape, its impact on forest communities and the response of ecosystems to fires are topics for debate and should be evaluated at both temporal and spatial scales. In this paper we present some examples that show the extent to which the methodology applied to the study of the production, dispersion and deposition of sedimentary charcoal in lake basins and wetlands contributes to give answers to these debates. We also present some updated references and describe examples of these paleoecological studies focused at centuries to millennia scales in southern South America. Fil: Sottile, Gonzalo David. 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 Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Giache, Yamila Soledad. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina

Patagonian vegetation has dramatically changed in composition and distribution over the last 23,000 years. Although the vegetation history has been inferred from individual pollen records, the regional patterns and drivers of vegetation development are poorly understood. High resolution pollen and charcoal data from eleven sites located along the eastern flanks of the Patagonian Andes (41–43°S) were examined to reconstruct the Lateglacial and Holocene vegetation and fire history of steppe/forest ecotone and separate the relative influence of climatic versus non-climatic factors in shaping the patterns of ecological change. Pollen data indicate that, as the Lateglacial climate became progressively wetter, the initial steppe vegetation was replaced by open forest of Nothofagus in the Lateglacial and early Holocene periods, and by closed forest in the late Holocene. Fire activity was lowest during the Lateglacial/early-Holocene transition and gradually increased through the Holocene. Prior to ca 5000 cal yr BP, the conifer Austrocedrus chilensis possibly persisted in isolated populations along the eastern boundary of its modern distribution. Cooler/more humid conditions after ca 5000 cal yr BP allowed the development of the modern mixed Nothofagus–Austrocedrus forest. The paleoenvironmental record points to the sensitivity of the forest/steppe ecotone in the past, not only to climate but also to complex environmental feedbacks that amplified the effects of climate change. Fil: Iglesias, Virginia. State University of Montana; Estados Unidos Fil: Whitlock, Cathy. State University of Montana; Estados Unidos Fil: Markgraf, Vera. State University of Colorado Boulder; Estados Unidos. University of Arizona; Estados Unidos Fil: Bianchi, Maria Martha. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

The vast diversity of present vegetation and environments that occur throughout South America (12°N to 56°S) is the result of diverse processes that have been operating and interacting at different spatial and temporal scales. Global factors, such as the concentration of CO2 in the atmosphere, may have been significant for high altitude vegetation during times of lower abundance, while lower sea levels of glacial stages potentially opened areas of continental shelf for colonisation during a substantial portion of the Quaternary. Latitudinal variation in orbital forcing has operated on a regional scale. The pace of climate change in the tropics is dominated by precessional oscillations of c. 20 kyr, while the high latitudes of the south are dominated by obliquity oscillations of c. 40 kyr. In particular, seasonal insolation changes forced by precessional oscillations must have had important consequences for the distribution limits of species, with potentially different effects depending on the latitude. The availability of taxa, altitude and human impact, among other events, have locally influenced the environments. Disentangling the different forcing factors of environmental change that operate on different timescales, and understanding the underlying mechanisms leads to considerable challenges for palaeoecologists. The papers in this Special Issue present a selection of palaeoecological studies throughout South America on vegetation changes and other aspects of the environment, providing a window on the possible complexity of the nature of transitions and timings that are potentially available.

Patagonian vegetation has dramatically changed in composition and distribution over the last 16,000. yr. Although patterns of vegetation change are relatively clear, our understanding of the processes that produce them is limited. High-resolution pollen and charcoal records from two lakes located at lat 41°S provide new information on the postglacial history of vegetation and fire activity at the forest-steppe ecotone, and help clarify the relative importance of local and regional drivers of late-Holocene ecological change. Our results suggest that late-glacial parkland was colonized by shrubs at ca. 11,200. cal. yr BP and this vegetation persisted until 4900. cal. yr BP, when increased humidity allowed for the establishment of Nothofagus forest. The late Holocene is characterized by oscillations in forest dominance largely driven by changes in humidity, possibly associated with the onset or strengthening of ENSO. In the last 4900. yr, humid periods (4900-3800 and 2850-1350. cal. yr BP) have promoted Nothofagus forest, whereas drier times (3800-2850 and 1350-450. cal. yr BP) have favored Austrocedrus expansion. At intermediate moisture levels, however, the lower forest supported both taxa, and fire became an important control of community composition, with severe, infrequent fires facilitating Nothofagus regeneration and high fire frequency and intensity supporting Austrocedrus. © 2012. Fil: Iglesias, Virginia. State University of Montana; Estados Unidos Fil: Whitlock, Cathy. State University of Montana; Estados Unidos Fil: Bianchi, Maria Martha. Universidad Nacional del Comahue. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales.; Argentina Fil: Villarosa, Gustavo. Universidad Nacional del Comahue. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales.; Argentina Fil: Outes, Ana Valeria. Universidad Nacional del Comahue. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Patagónico de Estudios de Humanidades y Ciencias Sociales.; Argentina

Ecosystem fire regimes are a consequence of interactions among fuels and climate. The reconstruction of past fire regimes is of great importance for studying past climate changes and controls. The aim of this study is to compare two charcoal and pollen records from the Nothofagus forest-grass steppe ecotone (50°S) and the grass steppe (49°S). We compare fire regime responses to local vegetation changes, and inferred variation on climate conditions between 49° and 52°S during the Holocene. Cerro Frías and La Tercera charcoal records seem to be sensitive to centennial and millennial timescales of vegetation and climate variability inferred for southern Patagonia. During the Pleistocene–Holocene transition and during the middle Holocene, forest patchiness provided fuel vertical and horizontal continuity favoring fire activity. In contrast, in steppe environments high cover of shrubs favored grass patchiness, impeding fire spread. Higher pollen richness and variability through time seem to be related to higher vegetation patchiness. Past fire regime variability at the eastern side of the Andes has been closely related to westerly moisture influence between 52° and 48°S. Southern latitudes have been influenced by polar air mass intrusions to the continent during the last 5000 cal. yr BP.

Recent airborne pollen records data from Northern Patagonia (San Carlos de Bariloche, Argentina, Lat. 41.1435° S, Long. 71.375° W, 800 m elevation) suggest that pollen transport takes place from the west to the east slope of the Andes. However, the atmospheric characteristics responsible of this transport have not yet been studied. The aim of this paper is to assess potential source areas and to describe the involved atmospheric mechanisms of the trans-Andean pollen transport. Methodology relies on the analysis of backward trajectories of air masses calculated with the HYSPLIT 4.9 regional model for particular days where airborne pollen of Weinmannia trichosperma Cav. was detected east of the Andes. This pollen type was selected because it is found regularly at localities in eastern Patagonia beyond its present-day distribution. Weinmannia's substantial presence during early Holocene times would also benefit from better knowledge of its transport mechanisms. Correspondence between atmospheric trajectories and the position of sources was checked using GIS maps. Mode T, Principal Component Analysis (PCA) with Varimax rotation was used to identify the main spatial structure of geopotential height anomalies producing the calculated trajectories. Eighty-eight cases showed that the calculated directions of trajectories trended from the Northwest to Southwest passing over the Chilean region of W. trichosperma distribution. PCs results showed two patterns of negative anomalies over southern Patagonia. The prevailing circulation pattern which drives airborne transport is the presence of a trough located south of 37 to 40° S with its axis over western Patagonia. The synoptic situations for two cases highly correlated with principal component scores were described.

Freshwater mussels of the genus Diplodon (Unionida) are common inhabitants of lakes and rivers in South America, and have slow growth and long life spans. We established the annual periodicity of incremental shell growth in Diplodon chilensis patagonicus (d'Orbigny, 1835) and calculated growth rates at different ages, using internal ring counting supported by dyeing methods and δ 18 O isotope analyses, in two Patagonian populations (Lago Steffen and its effluent Rio Manso Inferior, Argentina). Longevities of ca. 90 years (Lago Steffen) significantly extend the life spans reported in the past. Growth rates for old individuals (>30 years) from both lake and river populations average 0.16 mm per year along the axis of minimal growth. We evaluated the seasonal periodicity of minor and trace elements (Mn, Mg, Sr, Ba, Na, S) in situ by Laser Ablation ICP-MS and Electron Probe Microanalyser analyses. Line-scans in a valve from Lago Steffen show that Mn, Sr and Ba are preferentially accumulated during the summer, while higher concentrations of Mg are found in the winter bands. Metal/Ca ratios may serve as long-term archives of environmental variables, e.g. metal concentrations in water, water temperature and primary productivity. Diplodon chilensis patagonicus valves exhibit excellent characteristics to construct an accurate chronological archive with time windows of up to around a century, resolving the environmental signal annually and even seasonally.

Ecotone areas are the most dynamic areas of the world where small changes in some condition produce rapid and abrupt responses such as shifts in the distribution of dominant species and associated community's patches. Studying southwestern Santa Cruz forest-steppe ecotone is an ideal landscape to explore potential feedbacks of grazing and fire on vegetation diversity because of the juxtaposition of fire-resistant forests dominated by obligate seedlers with fire-sprouting shrublands and the prevalence of wild cattle since the early XX century. In this study, we analyzed how climate (precipitation, temperature and water balance), stand characteristics (basal area, quantity of cohorts and exotic species cover) and disturbances (fire and grazing) affect native species diversity, Plant Functional Types (PFTs) diversity and PFTs response in the forest-steppe ecotone of southern Patagonia. The study was conducted on 124 plots located on the eastern slope of the Andes (between 48°50' and 50°50'S) including forest-steppe ecotone sites between 1000 and 400. mm of annual precipitation. Native species and PFTs diversity indices modeling were carried out by generalized least squares and generalized lineal models. Stand characteristics, disturbance type and climate variables were used as factors over native species and PFTs diversity variables. An ordination and a Spearman rank correlation analysis were achieved between scores of the two first axes with total basal area, exotic species cover, mean annual temperature, annual precipitation, and water balance in order to explore PFTs responses to biotic or abiotic ecological conditions. The relationship between native species and PFTs richness (number of PFTs per plot) was modeled in order to evaluate the redundancy degree of PFTs under different disturbance types by fitting nonlinear power models to both richness measurements for each disturbance type. Fire impact over forest-steppe ecotone communities is one of the most important top down factor driving major increases on PFTs redundancy and heliophilous plants species abundance. At stand level, multicohort fire-disturbed stands support the highest native species diversity. Thus, mimicking this natural pattern on silvicultural practices could safeguard higher understory native species diversity than managing policies creating homogeneous conditions. Even if closed forest communities present lower native species diversity values than open canopy communities, they sustain different PFTs that present high conservation values for forest fauna. Grazing pressure represents a threatening agent diminishing native forest-steppe biodiversity. The coexistence of different stands at different development stages in the same landscape ensures the seed bank pools of shade tolerant and heliophilous species. Fil: Sottile, Gonzalo David. 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. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología y Palinología; Argentina Fil: Meretta, Pablo Ezequiel. 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: Tonello, Marcela Sandra. 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. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología y Palinología; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina Fil: Mancini, Maria Virginia. 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. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Laboratorio de Paleoecología y Palinología; Argentina

The Southern Hemisphere Westerly Winds (SWW) constitute an important zonal circulation system that dominates the dynamics of Southern Hemisphere mid-latitude climate. Little is known about climatic changes in the Southern South America in comparison to the Northern Hemisphere due to the low density of proxy records, and adequate chronology and sampling resolution to address environmental changes of the last 2000 years. Since 2009, new pollen and charcoal records from bog and lakes in northern and southern Patagonia at the east side of the Andes have been published with an adequate calibration of pollen assemblages related to modern vegetation and ecological behaviour. In this work we improve the chronological control of some eastern Andean previously published sequences and integrate pollen and charcoal dataset available east of the Andes to interpret possible environmental and SWW variability at centennial time scales. Through the analysis of modern and past hydric balance dynamics we compare these scenarios with other western Andean SWW sensitive proxy records for the last 2000 years. Due to the distinct precipitation regimes that exist between Northern (40–45° S) and Southern Patagonia (48–52° S) pollen sites locations, shifts on latitudinal and strength of the SWW results in large changes on hydric availability on forest and steppe communities. Therefore, we can interpret fossil pollen dataset as changes on paleohydric balance at every single site by the construction of paleohydric indices and comparison to charcoal records during the last 2000 cal yrs BP. Our composite pollen-based Northern and Southern Patagonia indices can be interpreted as changes in latitudinal variation and intensity of the SWW respectively. Dataset integration suggest poleward SWW between 2000 and 750 cal yrs BP and northward-weaker SWW during the Little Ice Age (750–200 cal yrs BP). These SWW variations are synchronous to Patagonian fire activity major shifts. We found an in phase fire regime (in terms of timing of biomass burning) between northern Patagonia Monte shrubland and Southern Patagonia steppe environments. Conversely, there is an antiphase fire regime between Northern and Southern Patagonia forest and forest-steppe ecotone environments. SWW variability may be associated to ENSO variability especially during the last millennia. For the last 200 cal yrs BP we can concluded that the SWW belt were more intense and poleward than the previous interval. Our composite pollen-based SWW indices show the potential of pollen dataset integration to improve the understanding of paleohydric variability especially for the last 2000 millennial in Patagonia.

Airborne pollen in San Carlos de Bariloche was sampled from September to March 2001–2004 with a Hirst-type volumetric spore trap placed at a height of 15 m in a city extending from the humid forests, through the mesic forests, to the steppe. The total amount of pollen recorded varied widely from year to year. The pollen index was 4,395 in the sampling period 2001/2002; 9,055 in 2002/2003 and 2,756 in 2003/2004. The main pollen period extended from October to January. In October, pollen concentration was the highest. Sixty-six pollen types were identified. Cupressaceae and Nothofagus were the major contributors. Betula, Prunus, Pinus and Populus, the most abundant ornamental taxa in the city, also contributed to the pollen record. Pollen of Maytenus and Lomatia was representative of the mesic forest, while pollen in the lower layers of the humid forest was present in trace amounts. Cupressaceae, Nothofagus and Betula prevailed during spring (September–December), and Plantago, Rumex and Poaceae during summer (December–March). The association of daily pollen concentration and meteorological variables, temperature (mean, maximum, minimum), dew point, rainfall and wind speed, was significant. Correlations showed to be negative, with the exception of that to wind speed. The total sum of fungi spores increased from 1,771 in 2001/2002; through 8,441 in 2002/2003 to 13,782 in 2003/2004. Relative concentration rose to 29%, 48% and 84% of the total number of pollen and fungal spores recorded during each sampling period.

210Pb, 137Cs and 14C dated sediments of two late Holocene landslide lakes in the Provincial Park Lagunas de Yala (Laguna Rodeo, Laguna Comedero, 24°06′S, 65°30′W, 2100 m asl, northwestern Argentina) reveal a high-resolution multi-proxy data set of climate change and human impact for the past ca. 2000 years. Comparison of the lake sediment data set for the 20th century (sediment mass accumulation rates MARs, pollen spectra, nutrient and charcoal fluxes) with independent dendroecological data from the catchment (fire scars, tree growth) and long regional precipitation series (from 1934 onwards) show that (1) the lake sediment data set is internally highly consistent and compares well with independent data sets, (2) the chronology of the sediment is reliable, (3) large fires (1940s, 1983/1984-1989) as documented in the local fire scar frequency are recorded in the charcoal flux to the lake sediments and coincide with low wet-season precipitation rates (e.g., 1940s, 1983/1984) and/or high interannual precipitation variability (late 1940s), and (4) the regional increase in precipitation after 1970 is recorded in an increase in the MARs (L. Rodeo from 100 to 390 mg cm-2 yr-1) and in an increase in fern spores reflecting wet vegetation. The most significant change in MARs and nutrient fluxes (Corg and P) of the past 2000 years is observed with the transition from the Inca Empire to the Spanish Conquest around 1600 AD. Compared with the pre-17th century conditions, MARs increased by a factor of ca. 5 to >8 (to 800 +130, -280 mg cm-2 yr-1), PO4 fluxes increased by a factor of 7, and Corg fluxes by a factor of 10.5 for the time between 1640 and 1930 AD. 17th to 19th century MARs and nutrient fluxes also exceed 20th century values. Excess Pb deposition as indicated by a significant increase in Pb/Zr and Pb/Rb ratios in the sediments after the 1950s coincides with a rapid expansion of the regional mining industry. Excess Pb is interpreted as atmospheric deposition and direct human impact due to Pb smelting. © 2006 Elsevier Ltd and INQUA. Fil: Lupo, Liliana Concepcio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Jujuy; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Comahue; Argentina Fil: Aráoz, Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Investigaciones Ecológicas de las Yungas; Argentina Fil: Grau, Hector Ricardo. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Laboratorio de Investigaciones Ecológicas de las Yungas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lucas, Christoph. University of Bern; Suiza Fil: Kern, Raoul. University of Bern; Suiza Fil: Camacho, María. Universidad Nacional de Jujuy; Argentina Fil: Tanner, Willi. University of Bern; Suiza Fil: Grosjean, Martin. University of Bern; Suiza

The history of the low-elevation forest and forest-steppe ecotone on the east side of the Andes is revealed in pollen and charcoal records obtained from mid-latitude lakes. Prior to 15,000 cal yr BP, the vegetation was characterized by steppe vegetation with isolated stands of Nothofagus. The climate was generally dry, and the sparse vegetation apparently lacked sufficient fuels to burn extensively. After 15,000 cal yr BP, a mixture of Nothofagus forest and shrubland/steppe developed. Fire activity increased between 13,250 and 11,400 cal yr BP, contemporaneous with a regionally defined cold dry period (Huelmo/Mascardi Cold Reversal). The early-Holocene period was characterized by an open Nothofagus forest/shrubland mosaic, and fire frequency was high in dry sites and low in wet sites; the data suggest a sharp decrease in moisture eastward from the Andes. A shift to a surface-fire regime occurred at 7500 cal yr BP at the wet site and at 4400 cal yr BP at the dry site, preceding the expansion of Austrocedrus by 1000–1500 yr. The spread of Austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late Holocene. The change to a surface-fire regime is consistent with increased interannual climate variability and the onset or strengthening of ENSO. The present-day mixed forest dominated by Nothofagus and Austrocedrus was established in the last few millennia.

Late Pleistocene palaeolakes on the eastern side of Andes (glacial lakes) and in the Patagonian Steppe (pluvial lakes) along 41°S latitude were studied. Natural dams (glaciers, moraines) that maintained a high water level in glacial palaeolakes were melted or cut by erosion during Late Pleistocene climate amelioration. With the retreat of the glaciers from the Andean valleys during prominent regional deglaciation, outflow from the eastern side of Andes to the Pacific Ocean was formed about 13.2 ka BP. As a result, the water level in glacial palaeolakes fell rapidly in stages. These changes were often preceded by volcanic-tectonic activity, which is suggested to be the “touch of butterfly” releasing mass balance adjustment in the changing landscape. The lacustrine tephra stratigraphic pattern from the Andes, comprising more than 50 horizons since the last glaciation, is presented. The correlation of palaeoenvironmental changes between the Andes and the Patagonian Steppe is suggested on the basis of two dacite marker horizons. The deglaciation event that led to development of the new hydrological system in the Andean palaeolakeland formed several large but short-lived palaeolakes in closed basins in the Patagonian Steppe probably due to melting of local ice and permafrost accumulated during glaciation on the surrounding mountains and elevated plains.

Several high-resolution continental records have been reported recently in sites in South America, but the extent to which climatic variations were synchronous between the northern and southern hemispheres during the Late-glacial–Holocene transition, and the causes of the climatic changes, remain open questions. Previous investigations indicated that, east of the Andes, the middle and high latitudes of South America warmed uniformly and rapidly from 13 000 14C yr BP, with no indication of subsequent climate fluctuations, equivalent, for example, to the Younger Dryas cooling. Here we present a multiproxy continuous record, radiocarbon dated by accelerated mass spectroscopy, from proglacial Lake Mascardi in Argentina. The results show that unstable climatic conditions, comparable to those described from records obtained in the Northern Hemisphere, dominated the Late-glacial–Holocene transition in Argentina at this latitude. Furthermore, a significant advance of the Tronador ice-cap, which feeds Lake Mascardi, occurred during the Younger Dryas Chronozone. This instability suggests a step-wise climatic history reflecting a global, rather than regional, forcing mechanism. The Lake Mascardi record, therefore, provides strong support for the hypothesis that ocean–atmosphere interaction, rather than global ocean circulation alone, governed interhemispheric climate teleconnections during the last deglaciation. © 1997 John Wiley & Sons, Ltd.

We analyzed the behavior of interstitial telomeric sequences (ITSs) in the progeny of Chinese Hamster Ovary (CHO) cells exposed to the radiomimetic compound bleomycin (BLM) in order to determine if ITSs play some role in the long-term clastogenic effect of this antibiotic. To this end, CHO cells were treated with a single concentration of BLM (2.5 μg/ml), and the frequency of unstable chromosomal aberrations was determined at several times after treatment (18. h, and 6, 15 and 34/36 days) by using PNA-FISH with a pan-telomeric probe [(TTAGGG). n repeats]. Cytogenetic analysis revealed a higher frequency of aberrations at 18. h and 6 days after treatment in BLM-exposed cultures vs. untreated cultures, although the yield of BLM-induced aberrations decreased on average five times 6 days after treatment compared with the one induced 18. h after treatment. Moreover, no significant differences in the frequency of aberrations were observed between untreated and BLM-exposed cells at 15 or 34/36 days after treatment. These data indicate that, in terms of unstable aberrations, the in vitro clastogenic effect of BLM on CHO cells persists for at least 6 days but less than 15 days after exposure. In addition, we found that BLM induces ITSs instability, cytogenetically detectable as acentric fragments (18. h after treatment) or additional (new) FISH signals (6 days after treatment). We propose that the delayed effect of BLM on ITSs mainly results from breakage of heterochromatic ITSs blocks and further insertion of these sequences at the sites of monochromatid breaks occurring at G2 phase of the cell cycle, since most of the additional FISH signals were present as single dots and located at interstitial sites of the involved chromosomes. © 2011 Elsevier B.V. Fil: Vidal Bravo, Malena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Multidisciplinario de Biología Celular. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Multidisciplinario de Biología Celular. Universidad Nacional de La Plata. Instituto Multidisciplinario de Biología Celular; Argentina Fil: Bianchi, Maria Martha. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Multidisciplinario de Biología Celular. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Multidisciplinario de Biología Celular. Universidad Nacional de La Plata. Instituto Multidisciplinario de Biología Celular; Argentina Fil: Bolzan, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Multidisciplinario de Biología Celular. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Multidisciplinario de Biología Celular. Universidad Nacional de La Plata. Instituto Multidisciplinario de Biología Celular; Argentina

Gracias a su potencial como registro ambiental, las valvas del molusco Diplodon han despertado recientemente el interes de la comunidad cientifca. En este trabajo, por medio de microscopia electronica de barrido (SEM) y espectroscopia Raman se investigo la microestructura y el polimorfsmo en valvas recientes de Diplodon chilensis patagonicus. Se encontro que la valva es completamente aragonitica y que la capa nacarada “externa" es la region mas favorable para realizar mediciones de isotopos estables o elementos traza. Los analisis de microscopia confocal y SEM realizados demostraron que un incremento anual esta compuesto de dos bandas: una de color claro, depositada durante los meses frios y una de color oscuro, depositada durante los meses calidos. Ambas bandas estan formadas por nacar, compuesto de plaquetas poligonales de aproximadamente 5-7 µm de diametro y 0.6-2 µm de espesor. Las plaquetas se encuentran ubicadas con el eje “c” del cristal (grupo cristalino: ortorrombico) paralelo a la superfcie de la valva y estan unidas entre si por medio de material organico inter-cristalino, traslucido a los electrones. El nacar depositado sobre la marca anual de crecimiento muestra plaquetas de espesores mas delgados, coincidiendo con la hipotesis de un crecimiento desacelerado asociado a la epoca de reproduccion. Como consecuencia, en esta zona la proporcion de material organico es mayor que la de CaCO,, y explica la formacion de una linea azul mas nitida, cuando la muestra es tenida con Alcian blue.

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