Synchronisation of sedimentary records using tephra : a postglacial tephrochronological model for the Chilean Lake District

Well-characterised tephra horizons deposited in various sedimentary environments provide a means of synchronising sedimentary archives. The use of tephra as a chronological tool is however still widely underutilised in southern Chile and Argentina. In this study we develop a postglacial tephrochronological model for the Chilean Lake District (ca. 38 to 42 degrees S) by integrating terrestrial and lacustrine records. Tephra deposits preserved in lake sediments record discrete events even if they do not correspond to primary fallout. By combining terrestrial with lacustrine records we obtain the most complete tephrostratigraphic record for the area to date. We present glass geochemical and chronological data for key marker horizons that may be used to synchronise sedimentary archives used for palaeoenvironmental, palaeoclimatological and palaeoseismological purposes. Most volcanoes in the studied segment of the Southern Volcanic Zone, between Llaima and Calbuco, have produced at least one regional marker deposit resulting from a large explosive eruption (magnitude >= 4), some of which now have a significantly improved age estimate (e.g., the 10.5 ka Llaima Pumice eruption from Llaima volcano). Others, including several units from Puyehue-Cordon Caulle, are newly described here. We also find tephra related to the Cha1 eruption from Chaiten volcano in lake sediments up to 400 km north from source. Several clear marker horizons are now identified that should help refine age model reconstructions for various sedimentary archives. Our chronological model suggests three distinct phases of eruptive activity impacting the area, with an early-to-mid-Holocene period of relative quiescence. Extending our tephrochronological framework further south into Patagonia will allow a more detailed evaluation of the controls on the occurrence and magnitude of explosive eruptions throughout the postglacial

From the Holocene to the Anthropocene: a historical framework for land cover change in southwestern South America in the past 15,000 years.

a b s t r a c t The main forest transitions that took place in south-central Chile from the end of the last glaciation to the present are reviewed here with the aim of identifying the main climatic and socio-economic drivers of land cover change. The first great transition, driven primarily by global warming, is the postglacial expansion of forests, with human populations from about 15,000 cal. yr. BP, restricted to coastlines and river basins and localized impact of forest fire. Charcoal evidence of fire increased in south-central Chile and in global records from about 12,000 to 6000 cal. yr. BP, which could be attributed at least partly to people. The subsequent expansion of agriculture led to much clearing of forests and the spread of weeds and other indicators of open habitats. The Spanish colonial period in America may have been followed by a transient expansion of forest cover into abandoned land, as indigenous population declined rapidly due to disease and slaughter. The 18th and 19th centuries brought about extensive loss of forests due to the massive impact of lumber extraction for mining operations both in central Chile and in western North America. Two centuries of intensive deforestation, coupled to grazing by cattle and extremely variable rainfall had long-lasting effects on forest cover in south-central Chile, which persist until today. The transition from a preindustrial to an industrial society brought about the "golden age" of timber harvest, assisted by mobile sawmills and railway transportation since the late 1800s. These advances led to the exhaustion of native commercial timber by the late 20th century in south-central Chile. In North America, harvestable stands were exhausted in New England and the Midwest around 1920. Settlement of the independent territories in the late 1800s and early 1900s implied vast burning and clearing of land and mounting soil erosion. Industrial forestry, based on government-subsidized massive plantations of short-rotation exotic trees, developed in the late 20th century, in connection with postindustrial displacement of exploitative activities from developed to third-world nations. In the last two decades, economic globalization and free trade promoted the expansion of new crops and further decline of woodlands, despite modest increases in forest cover. These patterns are repeated in many Latin American countries. To prevent further depletion of native forest resources and to provide an insurance against climate change, in the 21st century developing nations should aim at: (1) relocating subsidies from fiber farms to restoring diverse forest cover, (2) promoting ecosystem management of diverse forest and crops within landscapes, and (3) fostering diverse cultural relationships between people and their land

Understanding climate change impacts on biome and plant distributions in the Andes: Challenges and opportunities

Aim: Climate change is expected to impact mountain biodiversity by shifting species ranges and the biomes they shape. The extent and regional variation in these impacts are still poorly understood, particularly in the highly biodiverse Andes. Regional syntheses of climate change impacts on vegetation are pivotal to identify and guide research priorities. Here we review current data, knowledge and uncertainties in past, present and future climate change impacts on vegetation in the Andes. Location: Andes. Taxon: Plants. Methods: We (i) conducted a literature review on Andean vegetation responses to past and contemporary climatic change, (ii) analysed future climate projections for different elevations and slope orientations at 19 Andean locations using an ensemble of model outputs from the Coupled Model Intercomparison Project 5, and (iii) calculated changes in the suitable climate envelope area of Andean biomes and compared these results to studies that used species distribution models. Results: Future climatic changes (2040–2070) are projected to be stronger at high-elevation areas in the tropical Andes (up to 4°C under RCP 8.5), while in the temperate Andes temperature increases are projected to be up to 2°C. Under this worst-case scenario, temperate deciduous forests and the grasslands/steppes from the Central and Southern Andes are predicted to show the greatest losses of suitable climatic space (30% and 17%–23%, respectively). The high vulnerability of these biomes contrasts with the low attention from researchers modelling Andean species distributions. Critical knowledge gaps include a lack of an Andean wide plant checklist, insufficient density of weather stations at high-elevation areas, a lack of high-resolution climatologies that accommodates the Andes' complex topography and climatic processes, insufficient data to model demographic and ecological processes, and low use of palaeo data for distribution modelling. Main conclusions: Climate change is likely to profoundly affect the extent and composition of Andean biomes. Temperate Andean biomes in particular are susceptible to substantial area contractions. There are, however, considerable challenges and uncertainties in modelling species and biome responses and a pressing need for a region-wide approach to address knowledge gaps and improve understanding and monitoring of climate change impacts in these globally important biomes.publishedVersio

Comparison of lake and land tephra records from the 2015 eruption of Calbuco volcano, Chile

Tephra layers in lake sediment cores are regularly used for tephrostratigraphy as isochronous features for dating and recording eruption frequencies. However, their value for determining volcanic eruption size and style may be complicated by processes occurring in the lake that modify the thickness and grain size distributions of the deposit. To assess the reliability of data from lake cores, we compare tephra deposited on land during the 2015 eruption of Calbuco volcano in Chile to records in sediment cores from three lakes of different sizes that are known to have received primary fall deposits. In general, the thickness and granulometry of the deposit in lake cores and nearby terrestrial sections are very similar. As anticipated, however, cores sampled close to (here, within 300 m of) fluvial inflows were affected by sediment deposition from the lake’s catchment; they differed from primary deposits not only in their greater thickness and organic content but a

Multiproxy evidence for leaf-browsing and closed habitats in extinct proboscideans (Mammalia, Proboscidea) from Central Chile

Proboscideans are so-called ecosystem engineers and are considered key players in hypotheses about Late Pleistocene megafaunal extinctions. However, knowledge about the autoecology and chronology of the proboscideans in South America is still open to debate and raises controversial views. Here, we used a range of multiproxy approaches and new radiocarbon datings to study the autoecology of Chilean gomphotheres, the only group of proboscideans to reach South America during the Great American Biotic Interchange (∼3.1 to 2.7 million years before present). As part of this study, we analyzed stable isotopes, dental microwear, and dental calculus microfossils on gomphothere molars from 30 Late Pleistocene sites (31° to 42°S). These proxies provided different scales of temporal resolution, which were then combined to assess the dietary and habitat patterns of these proboscideans. The multiproxy study suggests that most foraging took place in relatively closed environments. In Central Chile, there is a positive correlation between lower δ13C values and an increasing consumption of arboreal/scrub elements. Analyses of dental microwear and calculus microfossils have verified these leaf-browsing feeding habits. From a comparative perspective, the dietary pattern of South American gomphotheres appears to be constrained more by resource availability than by the potential dietary range of the individual taxa. This multiproxy study is aimed at increasing knowledge of the life history of gomphotheres and thus follows an issue considered one of the greatest challenges for paleontology in South America, recently pointed out by the need to thoroughly understand the role of ecological engineers before making predictions about the consequences of ecosystem defaunation

Understanding climate change impacts on biome and plant distributions in the Andes: Challenges and opportunities

Aim: Climate change is expected to impact mountain biodiversity by shifting species ranges and the biomes they shape. The extent and regional variation in these impacts are still poorly understood, particularly in the highly biodiverse Andes. Regional syntheses of climate change impacts on vegetation are pivotal to identify and guide research priorities. Here we review current data, knowledge and uncertainties in past, present and future climate change impacts on vegetation in the Andes. Location: Andes. Taxon: Plants. Methods: We (i) conducted a literature review on Andean vegetation responses to past and contemporary climatic change, (ii) analysed future climate projections for different elevations and slope orientations at 19 Andean locations using an ensemble of model outputs from the Coupled Model Intercomparison Project 5, and (iii) calculated changes in the suitable climate envelope area of Andean biomes and compared these results to studies that used species distribution models. Results: Future climatic changes (2040–2070) are projected to be stronger at high-elevation areas in the tropical Andes (up to 4°C under RCP 8.5), while in the temperate Andes temperature increases are projected to be up to 2°C. Under this worst-case scenario, temperate deciduous forests and the grasslands/steppes from the Central and Southern Andes are predicted to show the greatest losses of suitable climatic space (30% and 17%–23%, respectively). The high vulnerability of these biomes contrasts with the low attention from researchers modelling Andean species distributions. Critical knowledge gaps include a lack of an Andean wide plant checklist, insufficient density of weather stations at high-elevation areas, a lack of high-resolution climatologies that accommodates the Andes' complex topography and climatic processes, insufficient data to model demographic and ecological processes, and low use of palaeo data for distribution modelling. Main conclusions: Climate change is likely to profoundly affect the extent and composition of Andean biomes. Temperate Andean biomes in particular are susceptible to substantial area contractions. There are, however, considerable challenges and uncertainties in modelling species and biome responses and a pressing need for a region-wide approach to address knowledge gaps and improve understanding and monitoring of climate change impacts in these globally important biomes

Multiproxy Approach to Reconstruct the Fire History of <i>Araucaria araucana</i> Forests in the Nahuelbuta Coastal Range, Chile

Multiproxy reconstructions of fire regimes in forest ecosystems can provide a clearer understanding of past fire activity and circumvent some limitations of single proxy reconstructions. While inferring fire history from scars in trees is the most precise method to reconstruct temporal fire patterns, this method is limited in Araucaria araucana forests by rot after fire injuries, successive fires that destroy the evidence and the prohibition of sample extraction from living Araucaria trees. In this context, dendrochemical studies in Araucaria trees and charcoal analysis from sediment cores can complement and extend the time perspective of the fire history in the relictual Araucaria-Nothofagus forests of the coastal range. We used dendrochemical, fire scar and charcoal records from the Nahuelbuta Coastal Range (37.8° S; 73° W) spanning the last 1000 years to reconstruct the fire history. The results indicate that periods with higher fire activity occurred between 1400 and 1650 AD. Long-term changes in the fire regime are related to increased climate variability over the last 1000 years, and especially with the arrival of settlers to the area after 1860 CE. The most severe fire events in the Nothofagus and Araucaria forests occurred when suitable fire-prone conditions were superimposed with high human densities