+A 5680-year tree-ring temperature record for southern South America

It is widely documented that the Earth’s surface temperatures have increased in recent decades. However, temperature increment patterns are not uniform around the globe, showing different or even contrasting trends. Here we present a mean maximum summer temperature record, based on tree-ring widths, over the past 5682 years (3672BC e 2009AD) for southern South America (SSA), covering from mid-Holocene to the present. This is the longest such record for the Southern Hemisphere (SH), and expands available annual proxy climate records for this region in more than 2060 years. Our record explains 49% of the temperature variation, and documents two major warm periods between 3140 e2800BC and 70BC e 150AD, which coincide with the lack of evidence of glacier advances in SSA. Recent decades in the reconstruction (1959e2009) show a warming trend that is not exceptional in the context of the last five millennia. The long-term relationship between our temperature reconstruction and a reconstructed total solar irradiance record, with coinciding cycles at 293, 372, 432e434, 512 and 746 years, indicate a persistent influence of solar forcing on centennial climate variability in SSA. At interannual to interdecadal scales, reconstructed temperature is mainly related to the internal climate variability of the Pacific Ocean, including El Nino Southern Oscillation (ENSO) and longer oscillations. Our ~ study reveals the need to characterize regional-scale climate variability and its drivers, which in the context of global-scale processes such as anthropogenic warming, interact to modulate local climate affecting humans and ecosystems.Fil: Lara, Antonio. Center for Climate and Resilience Research; Chile. Universidad Austral de Chile; Chile. Fundación Centro de los Bosques Nativos; ChileFil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Urrutia Jalabert, Rocío. Center for Climate and Resilience Research; Chile. Instituto Forestal; Chile. Universidad Austral de Chile; ChileFil: González Reyes, Álvaro. Center for Climate and Resilience Research; Chile. Universidad Austral de Chile; Chile. Universidad Mayor; ChileFil: Aravena, Juan Carlos. Universidad de Magallanes; ChileFil: Luckman, Brian Henry. Western University; CanadáFil: Cuq, Emilio. Universidad Austral de Chile; ChileFil: Rodríguez, Carmen Gloria. Universidad Austral de Chile; ChileFil: Wolodarsky Franke, Alexia. Cooperativa Calahuala; Chil

Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century

South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia–New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisture transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions

Tree-ring growth patterns and temperature reconstruction from Nothofagus pumilio (Fagaceae) forests at the upper tree line of southern Chilean Patagonia Patrones de crecimiento arbóreo y reconstrucción de la temperatura en bosques de Nothofagus pumilio (Fagaceae) en el límite arbóreo superior de la Patagonia austral de Chile

Nothofagus pumilio (Poepp. et Endl. Krasser) is a deciduous species that dominates the upper tree line of the Chilean and Argentinean Andes between 35º 36' and 55º 31' S. In this study we describe the development of 21 tree-ring width chronologies of N. pumilio across its southernmost range of distribution (51-55º S) in Chile, and analyze the relationship between N. pumilio tree-growth and climate. Ten of the tree-ring chronologies in our study, show an increasing trend and/or above average tree-ring growth since ca. 1960 to 1996, which coincides with the increase in temperatures shown by instrumental records from southern Patagonia. Another dominant pattern in tree-growth is a remarkable ca. 7-year cycle present in three of the study sites from Isla Navarino, the southernmost of our study areas (ca. 55º S). These two dominant tree-growth patterns, represent the main modes of variation of the N. pumilio tree-ring records in the southern Chilean Patagonia, accounting for 14 and 28 % of its total variance, respectively. Based on the positive correlation between tree growth and temperature in several of the study sites analyzed in this work, we developed a reconstruction of the Punta Arenas minimum annual temperatures from the seven tree-ring records with the highest correlation with temperature, covering the 1829-1996 period. The reconstruction shows that during most of the 19th century, minimum annual temperatures remained below-average and increased to values fluctuating around the mean during the 1900-1960 period, followed by a clear trend with above-average values after 1963Nothofagus pumilio (Poepp. et Endl. Krasser) es una especie caducifolia que domina el límite arbóreo superior de los Andes de Chile y Argentina entre los 35º 36' y 55º 31' S. En este trabajo describimos el desarrollo de 21 cronologías de ancho de anillos de N. pumilio para su rango más austral de distribución (51-55º S) en Chile, así como el análisis de su relación con el clima. Diez de las cronologías de ancho de anillos estudiadas muestran una tendencia al incremento y/o crecimiento sobre el promedio a partir de aproximadamente 1960 hasta 1996, lo cual coincide con un incremento sostenido en las temperaturas mostrado por los registros instrumentales de la Patagonia austral. Otra característica particular del crecimiento de los árboles es un notable ciclo de cerca de 7 años presente en tres de los sitios de estudio en la Isla Navarino, el área de estudio más austral estudiada por nosotros (55º S). Estos dos patrones de crecimiento, representan los principales modos de variación de los registros de anillos de crecimiento de N. pumilio en la Patagonia austral de Chile, y explican respectivamente el 14 y 28 % de la varianza total. Sobre la base de la correlación positiva que se verifica entre el crecimiento arbóreo y la temperatura en varios de los sitios de estudio analizados en este trabajo, reconstruimos las variaciones de las temperaturas mínimas anuales de Punta Arenas para el período 1829-1996. La reconstrucción muestra que durante la mayor parte del siglo 19 las temperaturas mínimas anuales permanecieron por debajo del promedio, aumentando a valores que fluctuaron en torno a la media durante el período 1900-1960, seguido por una clara tendencia sobre la media para el período posterior a 196

Tree-ring growth patterns and temperature reconstruction from Nothofagus pumilio (Fagaceae) forests at the upper tree line of southern Chilean Patagonia

Nothofagus pumilio (Poepp. et Endl. Krasser) is a deciduous species that dominates the upper tree line of the Chilean and Argentinean Andes between 35° 36' and 55° 31' S. In this study we describe the development of 21 tree-ring width chronologies of N. pumilio across its southernmost range of distribution (51-55° S) in Chile, and analyze the relationship between N. pumilio tree-growth and climate. Ten of the tree-ring chronologies in our study, show an increasing trend and/or above average tree-ring growth since ca. 1960 to 1996, which coincides with the increase in temperatures shown by instrumental records from southern Patagonia. Another dominant pattern in tree-growth is a remarkable ca. 7-year cycle present in three of the study sites from Isla Navarino, the southernmost of our study areas (ca. 55° S). These two dominant tree-growth patterns, represent the main modes of variation of the N. pumilio tree-ring records in the southern Chilean Patagonia, accounting for 14 and 28 % o

El Nino-Southern Oscillation signal in the world's highest-elevation tree-ring chronologies from the Altiplano, Central Andes

El Niño-Southern Oscillation (ENSO) is the largest source of inter-annual variability operating in the earth's climate system with enormous ecological, social, and economic impacts. As the instrumental record of ENSO variability is limited to the past 150 yr, the search for proxies sensitive to ENSO has become a priority task in recent years. It is vital to expand the sparse network of annually resolved and exactly dated ENSO-sensitive proxies to entirely capture the spatial variability of the ENSO coupled ocean-atmospheric phenomenon. Several tree-ring records have been used to reconstruct past ENSO variability, however, none of them are from tropical South America. The Polylepis tarapacana woodlands form the world's highest elevation treeline. Trees grow on the Altiplano plateau between 4000–5200 m elevation (16°–23° S). The climate variability in this climatically transitional tropical–subtropical region is strongly modulated by ENSO. Two chronologies of P. tarapacana along the Western Cordillera in the tropical central Andes were analyzed to determine the strength of the ENSO signal present in these tree-ring records. The growth of P. tarapacana has a strong common signal amongst trees in a single site and between sites across the Altiplano. Ring formation is induced by climatic conditions during the previous and current growing season (December–February), at the time of the strongest ENSO influences on the Peruvian Coast. Tree growth variations show opposite relationships with climate between consecutive growing seasons. During the current growing season, ring-width variations show positive and negative relationships with temperature and precipitation, respectively. Both tree-ring chronologies are significantly correlated with austral spring–summer (August–February) SST in the Niño3.4 region and show oscillatory modes within the classical ENSO bandwidth. Our results support the idea that P. tarapacana chronologies from the south-central tropical Andes provide high-resolution records extremely sensitive to ENSO in the tropical Pacific, and represent an important component to be considered in future multiproxy ENSO reconstructions

Unusual Southern Hemisphere tree growth patterns induced by changes in the Southern Annular Mode

Recent changes in the summer climate of the Southern Hemisphere extra-tropics are primarily related to the dominance of the positive phase of the Southern Annular Mode. This shift in the behaviour of the Southern Annular Mode—essentially a measure of the pressure gradient between Southern Hemisphere mid and high latitudes—has been predominantly induced by polar stratospheric ozone depletion. The concomitant southward expansion of the dry subtropical belts could have consequences for forest growth. Here, we use tree-ring records from over 3,000 trees in South America, Tasmania and New Zealand to identify dominant patterns of tree growth in recent centuries. We show that the foremost patterns of growth between 1950 and 2000 differed significantly from those in the previous 250 years. Specifically, growth was higher than the long-term average in the subalpine forests of Tasmania and New Zealand, but lower in the dry-mesic forests of Patagonia. We further demonstrate that variations in the Southern Annular Mode can explain 12–48% of the tree growth anomalies in the latter half of the twentieth century. Tree-ring-based reconstructions of summer Southern Annular Mode indices suggest that the high frequency of the positive phase since the 1950s is unprecedented in the past 600 years. We propose that changes in the Southern Annular Mode have significantly altered tree growth patterns in the Southern Hemisphere