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Alpine glaciers are sensitive indicators of changes in climate, and their ubiquity in mountainous regions make them valuable proxies for terrestrial climate reconstructions worldwide. However, the timing and extent of glacier change across the South American mid-latitudes through the Holocene are still poorly constrained relative to their counterparts in the Northern Hemisphere. Here we report a new 10Be surface exposure-based chronology of moraines recording a series of progressively less-extensive glacier advances of Glaciar Torre (Argentina, 49.3°S/73.0°W) since the Last Glacial Maximum, with expansions culminating at 17,600 ± 900, 13,500 ± 500, 9700 ± 400, 6900 ± 200, 6100 ± 300, 4500 ± 200, and 530 ± 60 yr BP. The declining magnitude of Holocene glacier expansions parallels a gradual rise in local summer insolation intensity during the Holocene, while individual advances occurred during inferred negative Southern Annular Mode (SAM)-like states at centennial to millennial timescales. These observations suggest that (i) summer insolation intensity modulated antiphased trends in glacier extent in the polar hemispheres during the Holocene, and that (ii) centennial-scale ‘SAM-like’ temperature and precipitation anomalies paced glacier fluctuations throughout Patagonia. Given the persistence of the inferred ’SAM-like’ anomalies throughout the Holocene, the modern measured trend towards positive SAM index conditions could mark the onset of a fundamental shift in the climate of the Southern Hemisphere midlatitudes that warrants consideration in projections of future climate.

The history and dynamics of deciduous Nothofagus forests along the eastern slopes of the central Patagonian Andes (44°-49°S) remain insufficiently studied and understood, particularly at timescales ranging from centuries to millennia. Available fossil pollen records point to time-transgressive responses of the arboreal vegetation to climatic changes during the Last Glacial Termination (T1) and early Holocene, and spatial heterogeneity since then along north-south, east-west, and elevation transects. The degree to which these results represent biogeographic and climatic trends, varying environmental gradients, or site-specific phenomena has not been assessed in detail. Here we present a fossil pollen and macroscopic charcoal record from Lago Churrasco (45°41′S, 71°49′W), a small closed-basin lake located in the deciduous Nothofagus forest zone of the central-east Andes of Chilean Patagonia. Our results suggest that Nothofagus trees colonized newly deglaciated terrains at ∼16,000 cal yr BP and formed scrublands/woodlands several millennia earlier than reported by previous studies east of the Andes. This suggests expansion and local densification of tree populations sourced from the eastern margin of the Patagonian Ice Sheet during the Last Glacial Maximum, with the additional implication that temperature and precipitation conditions favorable for tree survival and reproduction developed early during T1. We posit that the amount of moisture delivered by the Southern Westerly Winds was not a limiting factor for arboreal expansion during T1 in this sector of the central Patagonian Andes. Closed-canopy Nothofagus forests established at ∼10,000 cal yr BP and have remained essentially invariant despite climate change and natural disturbance regimes. This resilience was challenged and exceeded by human disturbance during the 20th century through the use of fire, leading to deforestation and spread of invasive exotic species in an extraordinarily rapid event. Our record suggests a permanent influence of the Southern Westerly Winds over the last 10,000 years, with relatively modest variations at centennial and millennial timescales. Fil: Moreno, P. I.. Universidad de Chile; Chile Fil: Simi, E.. Universidad de Chile; Chile Fil: Villa Martínez, R. P.. Universidad de Magallanes; Chile Fil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

This paper reviews current understanding of deglaciation in North, Central and South America from the Last Glacial Maximum to the beginning of the Holocene. Together with paleoclimatic and paleoceanographic data, we compare and contrast the pace of deglaciation and the response of glaciers to major climate events. During the Global Last Glacial Maximum (GLGM, 26.5-19 ka), average temperatures decreased 4° to 8°C in the Americas, but precipitation varied strongly throughout this large region. Many glaciers in North and Central America achieved their maximum extent during the GLGM, whereas others advanced even farther during the subsequent Heinrich Stadial 1 (HS-1). Glaciers in the Andes also expanded during the GLGM, but that advance was not the largest, except on Tierra del Fuego. HS-1 (17.5-14.6 ka) was a time of general glacier thickening and advance throughout most of North and Central America, and in the tropical Andes; however, glaciers in the temperate and subpolar Andes thinned and retreated during this period. During the Bølling-Allerød interstadial (B-A, 14.6-12.9 ka), glaciers retreated throughout North and Central America and, in some cases, completely disappeared. Many glaciers advanced during the Antarctic Cold Reversal (ACR, 14.6-12.9 ka) in the tropical Andes and Patagonia. There were small advances of glaciers in North America, Central America and in northern South America (Venezuela) during the Younger Dryas (12.9-11.7 ka), but glaciers in central and southern South America retreated during this period, except on the Altiplano where advances were driven by an increase in precipitation. Taken together, we suggest that there was a climate compensation effect, or ‘seesaw’, between the hemispheres, which affected not only marine currents and atmospheric circulation, but also the behavior of glaciers. This seesaw is consistent with the opposing behavior of many glaciers in the Northern and Southern Hemispheres.

We present a high-resolution precisely dated terrestrial paleovegetation/paleoclimate record from Lago Pichilaguna, northwestern Patagonia (40°–44°S), which spans continuously from the Last Glacial Maximum (LGM) to the present. We find abundant and continuous presence of arboreal pollen (chiefly Nothofagus) during the LGM, accompanied by other trees, shrubs, and alpine herbs. These results suggest Subantarctic parkland and/or scattered woodlands under a cold and hyperhumid climate during the LGM (∼25,000–17,800 cal. yr BP) with expansion of Nothofagus under relatively warm interstadial conditions between 25,000 and 19,200 cal. yr BP. This was followed by cooling and a precipitation increase between 19,200 and 17,800 cal. yr BP, which was contemporaneous with the youngest LGM advance of Andean glaciers in the region and maximum influence of the Southern Westerly Wind (SWW). The Last Glacial Termination (T1) started at 17,800 cal. yr BP and featured the spread of thermophilous trees and ferns characteristic of North Patagonian rainforests, along with lake level lowering. These results suggest a warm pulse and southward shift of the SWW, concurrent with a rapid collapse of Andean glacier lobes. Subsequent changes led to the establishment of closed-canopy rainforests under peak interstadial warmth between ∼16,000 and 15,000 cal. yr BP. We detect a shift to cold/wet conditions during the Antarctic Cold Reversal (14,800–12,700 cal. yr BP) and a precipitation decline during Younger Dryas time, followed by maximum temperature, relatively lower lake level and minimum SWW influence between 11,300 and 7700 cal. yr BP. Precipitation then rose punctuated by centennial-scale variations since 6200 cal. yr BP. Chilean-European deforestation and spread of invasive exotic species started at ∼350 cal. yr BP aided by fire. We conclude that temperate rainforests have persisted with little interruption since T1, with major changes in floristic composition driven by climate change and fires. Rainforest composition and heterogeneity declined in response to Chilean/European disturbance during the 1600s and intensified since the 1800s. These events constitute the fastest/largest-magnitude vegetation changes of the last ∼25,000 years.

South Westland, New Zealand, and southern Chile, are two narrow continental corridors effectively confined between the Pacific Ocean in the west and high mountain ranges in the east which impart significant influence over regional climate, vegetation and soils. In both these southern mid-latitude regions, evidence for extensive and repeated glaciations during cold phases of the Quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants. In South Westland, these variably aged glacial landforms are mantled by layered (multisequal) soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment. These cover-bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial/warm and glacial/cold climate during the Quaternary. In this study, we recognise multisequal soils overlying glacial landforms in southern continental Chile but, unlike the spodic (podzolic) soil sequences of South Westland, these are of dominantly volcanigenic (andic) provenance and are very similar to multisequal soils of andic provenance that predominate in, and adjacent to, areas of rhyolitic to andesitic volcanism in North Island, New Zealand. Here we develop a soil-stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental Chile. Based on proxy data from southern Chile, we propose that persistent vegetation cover and high precipitation on the western side of the Andes, during colder-than-present episodes tended to suppress the widespread production of glacially-derived loessial materials despite the pervasive occurrence of glacial and glacio-fluvial deposits that have frequently inundated large tracts of this landscape during the Quaternary. Given the lack of loess cover-beds that have traditionally assisted in the relative dating of glacial episodes prior to the Late Quaternary, surface exposure dating techniques could provide another chronological alternative to address this issue. However, there have been two main obstacles to successfully apply this dating technique in Patagonia. First, minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion, although dating outwash plains is more robust. Second, on the wet western side adjacent to the Andes, persistent vegetation cover during both glacial and post-glacial times, as well as widespread inundation by volcanic mass-flows, appear preventive. We make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted Andean-sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified. As already demonstrated by New Zealand studies, multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the Quaternary. On this basis, similar sequences in northwest Patagonia provide a relatively untapped archive to enable Quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed.

Iniciativa Cientifica Milenio NC120066 FONDECYT 11121280 1160488 1151469 CONICYT USA 2013-0035 NSF-BCS 1263474 Fulbright

The anatomy of the Last Glacial Termination (T1) in the southern mid-latitudes, and its relationship with changes in the Southern Westerly Winds (SWW), offers empirical constraints for understanding the mechanisms involved in the transition from the Last Glacial Maximum into the current interglacial. Northwestern Patagonia (40°-44°S) is a sensitive region for monitoring past changes in the SWW, the Patagonian Ice Sheet, terrestrial ecosystems, and fire regimes through T1. Here we present results from Lago Fonk (∼40°S) to examine the structure of T1 based on the palynological, macroscopic charcoal, elemental, and isotopic composition of organic lake sediments. We observe an instantaneous establishment of Nothofagus-dominated forests at the onset of T1, followed by a diversification and densification trend that culminated with the establishment of thermophilous, Myrtaceae-dominated North Patagonian rainforests between ∼15.6–14.7 cal ka BP. The expansion of the conifer Podocarpus nubigena marks a shift to cool-temperate and hyperhumid conditions, coeval with high lake levels and enhanced algal productivity between ∼14.7–11.9 cal ka BP. Stand-replacing fires, driven by enhanced seasonality or high-frequency rainfall variability, started at ∼12.4 cal ka BP and catalyzed the rapid spread of Weinmannia trichosperma. Subsequent warming and a decline in precipitation at ∼11.4 cal ka BP led to intense fire activity, lake-level lowering, and establishment of the Valdivian rainforest trees Eucryphia/Caldcluvia. Our results suggest a coherent linkage between changes documented in the amphi south Pacific region and Antarctic ice cores during T1. This implies a zonal and hemispheric response to changes in the position/intensity of the SWW that emphasizes their central role as a key driver of the hemispheric and global climate evolution through T1.

Resolving the history of vegetation, fire, and glaciation on the eastern slope of the central Patagonian Andes (44°-49°S) since the Last Glacial Termination (T1) has proved difficult. This is due to the steep environmental gradients, vegetation heterogeneity, and scarcity of dated glacial deposits and geomorphic features. Unsurprisingly, published records show important heterogeneities which limit our understanding of the timing and magnitude of climate and vegetation changes, and their driving mechanisms since T1. In this paper, we describe sediment cores from small closed-basin lakes located in the deciduous Nothofagus forest zone near Coyhaique, Chile. Our results indicate that the Coyhaique glacier lobe abandoned its final Last Glacial Maximum position just before ~17.9 cal kyr BP and underwent a step-wise recession that included a halt/readvance that culminated at ~16.8 cal kyr BP, contemporaneous with the formation of an ice-dammed proglacial lake in the Coyhaique/Balmaceda sector. This glacial lake stood at its highest level between ~17.9–17.2 cal kyr BP ( 650 m.a.s.l.), lowered between ~17.2–16.2 cal kyr BP ( 570 m.a.s.l.), and disappeared thereafter. Herbs and shrubs, currently dominant in high Andean and Patagonian steppe environments, colonized the ice-free terrains distal to the glacier margins and proglacial lakes under cold and dry conditions. This was followed by a steady increase in Nothofagus between ~16.6–14.8 cal kyr BP that led to the establishment of forests starting at ~14.8 cal kyr BP. The Holocene started with a sudden increase in Nothofagus and disappearance of conifers in the context of increase fire activity between ~11.7–9.4 cal kyr BP. Closed-canopy Nothofagus forests persisted virtually unaltered from ~9.4 cal kyr BP to the present day, despite frequent explosive volcanism and millennial-scale variations in fire regimes, attesting to their extraordinary postglacial resilience which contrasts with their behavior during T1. Recent large-scale deforestation by fire, livestock grazing, and the spread of non-native invasive plant species drove the fastest and largest-magnitude shifts seen during the last ~16,500 years.

We describe the stratigraphy, age and correlation of a prominent tephra marker, named Lepue Tephra, extensively distributed in north-western Patagonia. Lepue Tephra is well dated at c. 11 000 cal a BP from numerous lake and soil cover-bed sequences and its recognition is useful for assessing the rate and timing of deglaciation as well as associated environmental changes in this region during the last glacial termination and early Holocene. Lepue Tephra has attributes typical of a complex and compositionally zoned phreatomagmatic eruptive. While the initial rhyolitic phase can be readily distinguished from multiple eruptive products sourced from the adjacent Volcan Chaiten, the main erupted end member is of basaltic–andesitic bulk composition − similar to younger tephras sourced from Holocene monogenetic cones adjacent to the Volcan Michimahuida massif (tMim). Lepue Tephra can be correlated to an equivalent-aged pyroclastic flow deposit (Amarillo Ignimbrite) prominently distributed in the south-eastern sector of tMim. The source vent for these co-eruptive events is obscured by an extensive ice field and is currently unknown. The widespread radially symmetrical distribution of Lepue Tephra centred on tMim cannot be attributed solely to volcanological considerations. Reduced Southern Hemisphere westerly wind influence interpreted from climate proxies at the time of eruption are also implicated.

Southern South America is the only continental landmass that intersects the core of the Southern Westerly Winds (SWW), and thus is important for studying their role as a driver/conduit for the initiation/propagation of climate signals since the last glaciation. Their interaction with the Southern Ocean (SO) affects global climate through its influence on high-latitude upwelling and biological productivity, deep-water convection sites and, consequently, ventilation of CO2 from the deep ocean. Variations in the SWW-SO coupled system have been postulated as fundamental drivers of climate change during glacial terminations and the current interglacial. Hence, deciphering the evolution of the SWW from sensitive locations in the southern middle latitudes is essential for understanding important climatic transitions during and since the Last Glacial Termination (T1). Terrestrial records from the central Patagonian Andes (CPA) (44°-49°S), however, show heterogeneities in the timing, rates, and direction of climate change during T1, impeding detailed assessment of its drivers at regional, hemispheric, and global scales. Here we present new data on glacier, vegetation, and fire-regime changes in the Coyhaique sector (45°34′S) of CPA to improve our understanding on the timing and structure of the T1, including the behavior of the SWW. Our results indicate glacial recession from the youngest Last Glacial Maximum moraines just before ∼17.9 ka and development of an ice-dammed proglacial lake during the early stages of T1. Drainage of the ice-dammed lake, triggered by renewed glacial recession, was near-synchronous with the onset of a gradual multi-millennial trend toward arboreal dominance that started at ∼16 ka east and west of the Andes at that latitude. We detect increased influence of the SWW at ∼45°S starting at ∼16.6 ka, relative to the first millennium of T1, that led to positive anomalies in precipitation between ∼16–14.4 and ∼12.8–11.5 ka, followed by negative anomalies between ∼11.5–9 ka. The synchronous spread of arboreal vegetation east and west of the CPA divide during T1, despite the trans-Andean precipitation contrasts, suggests an upward shift in the temperature-controlled Andean tree line, underscoring the role of deglacial warming as the critical driver for afforestation at regional scale. Fil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Moreno, P. I.. Universidad de Chile; Chile Fil: Miranda, C. G.. Universidad de Chile; Chile Fil: Villa Martínez, R. P.. Universidad de Magallanes; Chile

Robust glacial chronologies are needed to address the fundamental questions of when and why Ice Age climates begin and end. Well-preserved glacial deposits left by large ice sheet lobes adjacent to Estrecho de Magallanes (53°S; Chile) in southernmost South America provide a unique opportunity to reconstruct the timing and fine structure of the last two major glaciations, as well as the last termination. We present a new precise 10Be surface exposure dataset of 34 moraine boulders directly tied to a recently published, high resolution glacial geomorphic map of the deposits left by the Magallanes lobe. We find that the southern section of the Patagonian Ice Sheet was more extensive during Marine Isotope Stage 4 (MIS 4) than during MIS 2, representing the first direct dating of the MIS 4 glacier culmination in South America. Similar to the MIS 2 glacial maxima, within MIS 4 there were multiple advances that we date (n = 6 samples) to between 67.5 ± 2.1 and 62.1 ± 2.0 ka. A similarly timed MIS 4 advance was identified in New Zealand, indicating that this is a hemisphere-wide glacier-climate signal, which is further corroborated by South Atlantic and Pacific temperature proxy records. Inboard of the MIS 4 moraine complex, we date a sequence of geomorphically distinct MIS 2 moraines that represent separate major periods of glacial stability. The MIS 2 maximum extent occurred by 27.4 ± 0.8 ka (n = 4; arithmetic mean, with the standard error of the mean and 3% propagated production rate error) and was followed by at least four more full glacial culminations at 25.7 ± 0.8 (n = 3), 23.9 ± 0.8 (n = 5), 19.1 ± 0.7 (n = 3), and 18.1 ± 0.6 ka (n = 3), which represent periods when the glacier was in equilibrium with the climate for long enough to form major moraines. About 18 km inboard, this sequence is followed by smaller-scale recessional moraine crests, deposited on drumlinized terrain rather than a moraine drift, that we date to 18.0 ± 0.8 ka, indicating the glacier was in net retreat at this time. Tentative results from a 2D ice sheet model suggest that the Magallanes lobe may have reached mapped inner and outer MIS 2 moraines from a climate with approximately 4.5 °C and 5.5 °C cooler summers, respectively, assuming ∼25% less annual precipitation, relative to modern climate. We hypothesize that during the last glacial cycle, shifts in the subtropical and subantarctic fronts, and related ocean-atmosphere patterns, explain MIS 4 to 2 glacial behavior in the southern mid-latitudes.

We present results from Lago Negro, a small closed-basin lake adjacent to Lago Rosselot, to examine the vegetation and environmental history of an insufficiently studied sector of Chiloe Continental (41°30′-44°S) in northwestern Patagonia. Lake sediment cores from Lago Negro reveal 27 tephra deposited since ∼12.7 ka, including two prominent rhyodacite tephra marker beds erupted from Volcan Melimoyu, and a stratified basal clastic unit we attribute to meltwater discharge from an ice tongue that originated from Monte Queulat and covered Lago Rosselot during its expanded position, presumably Antarctic Cold Reversal in age. The pollen record shows closed-canopy North Patagonian rainforests since ∼12.7 ka, with variations in species composition and structure that suggest dynamic responses of the vegetation to past environmental changes. Vegetation responses to climate in the Lago Negro record were modulated, sometimes interrupted, by high magnitude and frequent disturbance regimes, most notably during maxima in explosive volcanic activity (∼9.5–7.2 ka and ∼3.6–1.6 ka) and heightened fire activity. Since Lago Negro is the southernmost palynological site so far investigated in the region and is located within a volcanically active sector, it provides a valuable perspective for assessing past vegetation responses along environmental gradients since the last glaciation. When compared with other sites throughout northwestern Patagonia, our record reveals a distinct north-to-south gradient in temperature and precipitation, with peak temperature and rainfall seasonality in the north, and a west-to-east gradient in disturbance regimes, with maximum frequency and magnitude of explosive volcanic events in the east. These gradients have modulated the response of rainforest vegetation to climate forcing at regional scale since ∼12.7 ka. We identify negligible differences in timing for the majority of key vegetation signals during the initial phase of the Lago Negro record, and propose that plant colonization and expansion along the ∼360 km long corridor through the Pacific slope of the northwestern Patagonian Andes was a rapid process during the Last Glacial Termination.

An important coupled ocean-atmospheric system in the mid- and high latitudes involves the Southern Westerly Winds (SWW) and the Southern Ocean (SO), which controls climate in the southernmost third of the world, deep water formation, and ventilation of CO2 from the deep ocean. Most studies have examined its role as a driver of atmospheric CO2 concentrations during glacial terminations, but very few have investigated its influence during the Holocene, i.e. the current interglacial. A fundamental problem, however, is resolving whether the SWW strength increased or declined during the early Holocene (∼11.5–7.5 ka, ka = 1000 cal yr BP) in sectors adjacent to the Drake Passage. Here we assess past changes in SWW influence over the last ∼17,000 years using terrestrial paleoclimate records from southwestern Patagonia (∼52°S). We detect a zonally symmetric Early Holocene Westerly Minimum which diminished wind stress and upwelling on the SO, contributing to a contemporary decline in atmospheric CO2 concentrations and enrichment in the stable carbon isotope ratio of atmospheric CO2 (δ13Catm). Our mid-latitude data also indicate a shift to strong SWW influence at ∼7.5 ka which correlates with a sustained increase in atmospheric CO2 and halt in the δ13Catm rise, suggesting enhancement of high-latitude ocean ventilation by an invigorated SWW-SO coupled system.

Pleistocene glaciations produced significant increases in continental ice cover in polar and mid-latitude temperate areas, sea-level declines and shifts and reshuffling of biomes, all of which promote either isolation, coalescence or fragmentation in the distribution of land biota. If populations of several taxa have been co-distributed for a prolonged time, and if the periods between perturbation or vicariance processes have been more or less stable, it is expected that divergence patterns of closely related and ecologically similar species will be congruent because of their similar biological and demographic characteristics. Based on this premise, we analysed the phylogeographic structure (cytochrome b) of Liolaemus pictus and Batrachyla leptopus, two widely co-distributed lizard and frog species, respectively, in the Chiloe Archipelago of southern Chile, to decipher their genetic structure in response to a common climatic and environmental history. Haplotype network analysis and Bayesian inference suggest an evolutionary pattern of genetic diversity for the two species that is consistent with the Quaternary glacial history of southern Chile, and suggests a complex phylogeographic history in the Liolaemus and Batrachyla species. High-divergence levels among haplotypes in some island populations of the archipelago also suggest genetic connectivity between putative refuges from Chiloe Island and the mainland along the exposed continental shelf during sea level minima associated with the most recent Quaternary glaciations. Our results are consistent with our hypothesis that two species have responded to parallel historical events in which the historical process during the last glacial maximum (approximately 41°S) has been sufficient to influence their phylogeographic structure.

By virtue of its location in the southern mid-latitudes, northwestern Patagonia (40°-44°S) offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance. Of particular importance is deciphering the evolution of the Southern Westerly Winds (SWW) considering their influence at continental, zonal, hemispheric, and global scale. Here I present a multi-decadal record from Lago Proschle, a small closed-basin lake located on the Pacific slope of northwestern Patagonia, to examine the timing and structure of vegetation, fire, and climate change along a continuum since the onset of the Last Glacial Termination (T1). The record shows rapid glacier recession during T1, reaching the western Andean foothills in ∼400 years or less. Nothofagus-dominated forests established between ∼17.4–17 ka, followed by closed-canopy North Patagonian Rain Forests (NPRF) with shade-tolerant thermophilous trees between ∼16.3–15.4 ka. These changes suggest an abrupt warming trend and an increase in precipitation at ∼16.3 ka, associated with a northward shift of the SWW. Subsequent increases in cold-tolerant hygrophilous trees between ∼15.4–12.8 ka imply a shift to cold, more humid conditions during the Antarctic Cold Reversal, suggesting stronger SWW influence. This was followed by stand-replacing fires brought by a sudden decline in summer precipitation at ∼12.8 ka, associated with a millennial-scale southward shift of the SWW which was contemporaneous with the onset of the Younger Dryas. Dominance of thermophilous, summer-drought tolerant Valdivian rainforest trees and high fire activity ensued between ∼10.3–7.8 ka, suggesting peak warmth and overall decline in annual precipitation associated with weakening of the SWW during the early Holocene. A multi-millennial cooling and wetting trend started at ∼7.8 ka, brought by stronger SWW influence, followed by recurrent, centennial-scale variations in temperature and precipitation starting at ∼6.4 ka. Deforestation, fire, and spread of non-native herbs by Chilean/European settlers began during the late 18th century. Abrupt vegetation changes in the Lago Proschle record were driven by rapid climate changes over the last 17,400 years amplified, in some instances, by fire disturbance.

We examine the timing and magnitude of the last glacial maximum (LGM) and the last glacial termination (LGT) in northwestern Patagonia, situated in the middle latitudes of South America. Our data indicate that the main phase of the LGT began with abrupt warm pulses at 17,800 and 17,100 cal yrs BP, accompanied by rapid establishment of evergreen temperate rainforests and extensive deglaciation of the Andes within 1000 years. This response shows that South American middle-latitude temperatures had approached average interglacial values by 16,800 cal yrs BP. The temperature rise in northwestern Patagonia coincides with the beginning of major warming and glacier recession in the Southern Alps of New Zealand at southern mid-latitudes on the opposite side of the Pacific Ocean. From this correspondence, the warming that began at 17,800 cal yrs BP appears to have been widespread in middle latitudes of the Southern Hemisphere, accounting for at least 75% of the total temperature recovery from the LGM to the Holocene. Moreover, this warming pulse is coeval with the first half of the Heinrich Stadial 1 (HS1) in the North Atlantic region. HS1 featured a decline of North Atlantic meridional overturning circulation, a southward shift of the westerly wind belt in both hemispheres and of the Intertropical Convergence Zone, as well as a weakening of the Asian monsoon. Along with the initiating trigger, identifying the mechanisms whereby these opposing climate signals in the two polar hemispheres interacted —whether through an oceanic or an atmospheric bipolar seesaw, or both— lies at the heart of understanding the LGT.

Concern is growing that global climate change will have widespread impact on the world’s terrestrial ecosystems, but future impacts are imperfectly constrained by ecosystem models and direct observations. All available data, including records of past ecological change, need to be utilized to assess the range of potential future outcomes. Here we show that pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was of comparable magnitude to climatic change projected to occur in the next 100 to 150 years under high-emission scenarios. We used data from 596 published paleoecological records to examine compositional and structural changes in global terrestrial vegetation since the last glacial period, and to project the magnitude of ecosystem transformations under different emission scenarios in the future. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change, and suggest that without major reductions in greenhouse-gas emissions to the atmosphere (i.e., in line with those targeted in the 2015 Paris Agreement), most terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

The 2008 eruption of Volcán Chaitén (VCha) in northwestern Patagonia was the first explosive rhyolitic eruption to have occurred within a century and provided an unprecedented scientific opportunity to examine all facets of the eruption ranging from magma rheology/ascent rates to ash-fall effects on biota and infrastructure. Up to very recently it was thought that the latest eruption prior to the 2008 event occurred c. 9750 cal. a BP. Although a number of researchers have recognised additional eruptive products, but their stratigraphy, age, and geochemical attributes have not been systematically described and/or recorded. In this study, we provide a detailed examination of andic cover-beds and tephra-bearing lake sequences located both proximally and distally to VCha, which record a series of hitherto unknown rhyolitic eruptive products and place all previous observations firmly within a coherent stratigraphic framework. Through major- and trace-element glass shard geochemistry we are able to confidently verify eruptive source. A total of 20 discrete tephra beds are recognised, with at least 10 having widespread areal distributions and/or depositional imprints broadly comparable to, or greater than, the 2008-tephra event. This record indicates that VCha has been continuously but intermittently active as far back as the end of the Last Glacial Maximum (c. 18,000 cal a BP) with two dominant, genetically related magma types and an intermediary ‘mixed’ type. Before this the eruptive record has been largely obscured and/or erased by widespread Andean piedmont glaciation. However, based on the tempo of VCha activity over the last c. 18,000 years, older VCha eruptives can be anticipated to occur as well as future hazardous explosive events. The new eruptive inventory will ultimately be useful for correlating equivalent-aged sequences and refining long-term eruptive tempo as well as corresponding temporal changes in magmatic evolution. Fil: Alloway, Brent V.. The University of Auckland; Nueva Zelanda. University Of Wollongong; Australia Fil: Pearce, Nick J.G.. Aberystwyth University; Reino Unido Fil: Moreno, Patricio I.. Universidad de Chile; Chile Fil: Villarosa, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina Fil: Jara, Ignacio. Victoria University Of Wellington; Nueva Zelanda Fil: De Pol-Holz, Ricardo. Universidad de Magallanes; Chile Fil: Outes, Valeria. Universidad de Chile; Chile

The development of quantitative temperature reconstructions in regions of paleoclimate interest is an important step for providing reliable temperature estimates in that region. Fossil chironomid assemblages have been studied in Patagonia showing great promise for reconstructing paleotemperatures; however there is still a lack of robust temperature inference models in that area. To contribute to the understanding of climate change, a transfer function using chironomids preserved in 46 lakes in Chile and Argentina was developed. The best performing model to infer the mean air temperature of the warmest month was a 3-component WA-PLS model with a coefficient of correlation (r 2 jack ) of 0.56, a root mean square error of prediction (RMSEP) of 1.69 °C and a maximum bias of 2.07 °C. This model was applied to the chironomids preserved in the sediment of the Huelmo mire (41°31′ S, 73°00′ W), in the lake district of northwestern Patagonia. The reconstruction showed several cold spells (one at 13,200 to 13,000 cal yr BP and a cooling trend between 12,600 and 11,500 cal yr BP) associated with the Younger Dryas and/or Huelmo–Mascardi Cold Reversal (HMCR). Our findings support climate models proposing fast acting inter-hemispheric coupling mechanisms including the recently proposed bipolar atmospheric and/or bipolar ocean teleconnections rather than a bipolar see-saw model.

Paleoecological studies from the northern Patagonian Andes (40–44°S) have identified past changes in vegetation, fire regimes and paleoclimate since the last glaciation, including variations in strength and position of the Southern Westerly Winds (SWW). The extent to which records west and east of the Andes provide a congruent paleoclimatic history, however, has not been explored in detail in the literature. Physical and biological contrasts are evident between these regions today and are to be expected in paleoclimate reconstructions. In this context, we present pollen and charcoal records from sediment cores collected in Lago Espejo, a small closed-basin lake located in the core sector of the northern Patagonian Andes that spans uninterrupted the last ∼15,400 years. Following glacier withdrawal, the vegetation surrounding Lago Espejo features scattered Nothofagus woodlands, including relatively thermophilous rainforest trees between ∼15,400 and 14,400 cal yr BP. The disappearance of these trees and an abrupt rise in Nothofagus at ∼14,400 cal yr BP mark the establishment of closed-canopy forests during the Antarctic Cold Reversal, followed by increases in the cold-tolerant hygrophilous conifer Podocarpus nubigena during the Younger Dryas (∼12,700–11,500 cal yr BP). The Holocene vegetation consists of Nothofagus-dominated forests with modest variation in composition and structure until the present, attesting to the resilience of these forest communities to climate change and natural disturbance regimes. Rapid deforestation, anthropogenic fires and the establishment of artificial meadows with exotic herbs introduced by Europeans at ∼150 cal yr BP, triggered a rapid, large-magnitude landscape transformation unprecedented in the last 14,000 years. The timing and structure of vegetation changes revealed by the Lago Espejo record suggest that changes in the SWW were the main driver of vegetation and fire regimes in the Andes of northern Patagonia over the last 15,400 years. Comparison between multiple reconstructions from northern Patagonia reveals overall coherent vegetation and fire regime changes in the western and Andean sectors, and a spatially variable and more divergent behaviour in sites located further east. This spatial patter is akin to the present-day correlation between precipitation and SWW in this region.

Few studies have examined in detail the sequence of events during the last glacial termination (T1) in the core sector of the Patagonian Ice Sheet (PIS), the largest ice mass in the Southern Hemisphere outside of Antarctica. Here we report results from Lago Edita (47°8′ S, 72°25′ W, 570 m a.s.l.), a small closed-basin lake located in a valley overridden by eastward-flowing Andean glaciers during the Last Glacial Maximum (LGM). The Lago Edita record shows glaciolacustrine sedimentation until 19 400 yr BP, followed by organic sedimentation in a closed-basin lake and a mosaic of cold-resistant hygrophilous conifers and rainforest trees, along with alpine herbs between 19 400 and 11 000 yr BP. Our data suggest that the PIS retreated at least ∼ 90 km from its LGM limit between ∼ 21 000 and 19 400 yr BP and that scattered, low-density populations of cold-resistant hygrophilous conifers, rainforest trees, high-Andean and steppe herbs thrived east of the Andes during the LGM and T1, implying high precipitation levels and southern westerly wind (SWW) influence at 47° S. The conifer Podocarpus nubigena increased between 14 500 and 13 000 yr BP, suggesting even stronger SWW influence during the Antarctic Cold Reversal, after which it declined and persisted until 11 000 yr BP. Large increases in arboreal pollen at ∼ 13 000 and ∼ 11 000 yr BP led to the establishment of forests near Lago Edita between 10 000 and 9000 yr BP, suggesting a rise in the regional tree line along the eastern Andean slopes driven by warming pulses at ∼ 13 000 and ∼ 11 000 yr BP and a subsequent decline in SWW influence at ∼ 11 000 yr BP. We propose that the PIS imposed a regional cooling signal along its eastern, downwind margin through T1 that lasted until the separation of the northern and southern Patagonian ice fields along the Andes during the Younger Dryas period. We posit that the withdrawal of glacial and associated glaciolacustrine environments through T1 provided a route for the dispersal of hygrophilous trees and herbs from the eastern flank of the central Patagonian Andes, contributing to the afforestation of the western Andean slopes and pacific coasts of central Patagonia during T1. Fil: Henríquez, William I.. Victoria University Of Wellington; Nueva Zelanda Fil: Villa-Martinez, Rodrigo. Gaia-antártica Universidad de Magallanes; Chile Fil: Vilanova, Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina Fil: De Pol-Holz, Ricardo. Gaia-antártica Universidad de Magallanes; Chile Fil: Moreno, Patricio. Instituto de Ecología y Biodiversidad, Departamento de; Chile

The Chilotan Archipelago and surrounding areas of north-western Patagonia (41°-43°S, 72°-74°W) offer a unique opportunity to study the interplay between the recent genetic and paleoenvironmental evolution on temperate rainforest environments. Previous studies in this region have postulated that land biota persisted west of the Patagonian ice sheet, in ice-free low-elevation regions of the mainland, and the north-western portion of Isla Grande de Chiloe during Quaternary ice ages. In this study, we analysed the phylogeographical structure (Cyto- chrome b) of the iguanid lizard Liolaemus pictus to estimate their genetic structure in response to glacial-interglacial cycles and colonization routes. We found that populations from the mainland and Isla Grande de Chiloe do not share haplotypes and, thus, are divergent haplogroups. This divergence might reflect an ancient isolation, much older than the last glaciation. Moreover, the existence of four divergent haplogroups among L. pictus populations in the mainland suggests the persistence of multiple isolated populations during the last glaciation. Our results also indicate that the colonization of small islands occurred from several source sites, located both in the mainland and in Isla Grande de Chiloe, after the Last Glacial Maximum.

Glacial geologic studies in the Southern Hemisphere (SH) mid-latitudes (40–54°S) indicate renewed glacial activity in southern South America (Patagonia) and New Zealand’s (NZ) South Island starting at ∼7 kyr, the so-called neoglaciation. Available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric CO2 and CH4 concentrations, lower-than-present but increasing summer insolation and seasonality contrasts. In this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete Paleoclimate Modelling Inter-comparison Project (PMIP2) database of simulations at 6 kyr for the SH. We observe that the amplitude of the annual insolation cycle in the SH did not change significantly at 6 kyr compared to the pre-industrial values, the largest difference occurring in autumn (MAM, negative anomalies) and spring (SON, positive anomalies). The simulated changes in temperatures over the SH respond to the insolation changes, with a 1–2 month delay over the oceans. This results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions, except over Patagonia and NZ, that show a slight increase. In contrast, large-scale circulation features, such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle, as a direct response to the increased/decreased insolation during the transitional seasons SON/MAM. In the annual mean, there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1–3° over the entire SH, which results in a small increase of wind speed over the South Pacific and Atlantic Oceans north of ∼50°S and a widespread decline south of 50°S. PMIP2 simulations for 6 kyr, indicate that in the annual mean, the SH mid-latitudes were colder, wetter and with stronger winds north of about 50°S. These conditions are consistent with the observed neoglacial advances in the region, as well as with terrestrial paleoclimate records from Patagonia that indicate cooling and a multi-millennial rising trend in Southern Westerly Wind intensity starting at ∼7.8 kyr.

We present chironomid and pollen records from the Huelmo site (∼41°30′S), NW Patagonia, to examine in detail the timing and structure of climate changes during the Last Glacial Termination in the southern mid-latitudes. The chironomid record has the highest temporal and taxonomic resolution for this critical interval, and constitutes the first account of midge faunas at the culmination of the Last Glacial Maximum (LGM) for the region. The chironomid record suggests cold and wet conditions during the LGM, followed by deglacial warming between 17.6 and 16.8 cal kyr BP. Relatively warm conditions prevailed between ∼15–14 cal kyr BP, followed by a reversal in trend with cooling pulses at ∼14 and 13.5 cal kyr BP, and warming at the beginning of the Holocene. Cool-temperate conditions prevailed during the Huelmo Mascardi Cold Reversal (HMCR) which, according to chironomid data, exhibits a wet phase (13.5–12.8 cal kyr BP) followed by a conspicuous drier phase (12.8–11.5 cal kyr BP). The chironomid and pollen records from the Huelmo site indicate step-wise deglacial warming beginning at 17.6 cal kyr BP, in agreement with other paleoclimate records from NW Patagonia and isotopic signals from Antarctic ice cores. Peak warmth during the Last Glacial Termination was achieved by ∼14.5 cal kyr BP, followed by a cooling trend that commenced during the Antarctic Cold Reversal, which later intensified and persisted during the HMCR (13.5–11.5 cal kyr BP). We observe a shift toward drier conditions at ∼12.8 cal kyr BP superimposed upon the HMCR, coeval with intense fire activity and vegetation disturbance during Younger Dryas time.

Correlations among and identification of the source volcanoes for over 60 Late Glacial and Holocene tephras preserved in eight lacustrine sediment cores taken from small lakes near Coyhaique, Chile (46 degrees S), were made based on the stratigraphic position of the tephra in the cores, lithostratigraphic data (tephra layer thickness and grain size), and tephra petrochemistry (glass color and morphology, phenocryst phases, and bulk-tephra trace element contents determined by ICP-MS). The cores preserve a record of explosive eruptions, since similar to 17,800 calibrated years before present (cal years BP), of the volcanoes of the southernmost Andean Southern Volcanic Zone (SSVZ). The suggested source volcanoes for 55 of these tephras include Hudson (32 events), Mentolat (10 events), and either Maca or Cay or some of the many minor monogenetic eruptive centers (MECs; 13 events) in the area. Only four of these eruptions had been previously identified in tephra outcrops in the region, indicating the value of lake cores for identifying smaller eruptions in tephrochronologic studies. The tephra records preserved in these lake cores, combined with those in marine cores, which extend these records back to 20,000 cal years BP, prior to the Last Glacial Maximum, suggest that no significant temporal change in the frequency of explosive eruptions was associated with deglaciation. Over this time period, Hudson volcano, one of the largest and longest lived volcanoes in the Southern Andes, has had >55 eruptions (four of them were very large) and has produced >45 km(3) of pyroclastic material, making it also one of the most active volcanoes in the SVZ in terms of both frequency and volume of explosive eruptions.

A pollen record from the Huelmo site (ca. 41°30′S) shows that vegetation and climate changed at millennial time-scales during the last glacial to Holocene transition in the mid-latitude region of western South America. The record shows that a Nothofagus parkland dominated the landscape between 16 400 and 14 600 14C yr BP, along with Magellanic Moorland and cupressaceous conifers. Evergreen North Patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14C yr BP, following a prominent rise in Nothofagus at 14 600 14C yr BP. Highly diverse, closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14C yr BP, followed by the expansion of cold-resistant podocarps and Nothofagus at ca. 12 500 and 11 500 14C yr BP. Local disturbance by fire favoured the expansion of shade-intolerant opportunistic taxa between 10 900 and 10 200 14C yr BP. Subsequent warming pulses at 10 200 and 9100 14C yr BP led to the expansion of thermophilous, summer-drought resistant Valdivian rainforest trees until 6900 14C yr BP. Our results suggest that cold and hyperhumid conditions characterised the final phase of the Last Glacial Maximum (LGM), between 16 400 and 14 600 14C yr BP. The last ice age Termination commenced with a prominent warming event that led to a rapid expansion of North Patagonian trees and the abrupt withdrawal of Andean ice lobes from their LGM positon at ca. 147 000 14C yr BP. Hyperhumid conditions prevailed between 16 400 and 13 000 14C yr BP, what we term the ‘extreme glacial mode’ of westerly activity. This condition was brought about by a northward shift and/or intensification of the southern westerlies. The warmest/driest conditions of the last glacial–interglacial transition occurred between 9100 and 6900 14C yr BP. During this period, the westerlies shifted to an ‘extreme interglacial mode’ of activity, via a poleward migration of stormtracks. Our results indicate that a highly variable climatic interval lasting 5500 14C years separate the opposite extremes of vegetation and climate during the last glacial-interglacial cycle, i.e. the end of the LGM and the onset of the early Holocene warm and dry period. Copyright © 2003 John Wiley & Sons, Ltd.

Lakes formed in the Aysen region of southern Chile after the retreat of mountain glaciers, established by ~17,900 calendar years before present (cal years BP) or earlier, contain numerous late-glacial and Holocene tephra layers derived from >70 eruptions of the volcanoes in the region, including Hudson, the southernmost in the Andean Southern Volcanic Zone (SVZ). Sediment cores from seven of these lakes contain an unusually thick late-glacial age tephra layer, which based on its distribution and bulk trace-element composition was derived from a large explosive eruption of Hudson volcano between 17,300 and 17,440 cal years BP and is termed Ho. In 13 cores from six of these lakes, each located ~100 km generally northeast of Hudson, the Ho tephra layer ranges between 50 and 88 cm in thickness, and contains pumice grains up to 2 cm in maximum diameter. Comparison with three previously documented large explosive Holocene Hudson eruptions (H1 at 7,750 cal years BP, H2 at 3,920 cal years BP, and H3 in 1991 AD) suggests that Ho was larger, with an estimated tephra volume of >20 km3, the largest post-glacial eruption documented for any volcano in the southern Andes and most likely responsible for the formation of the Hudson caldera. In total, Hudson has erupted ≥45 km3 of pyroclastic material in the last ~17,500 years, making it the most productive volcano in the southern Andes in terms of the total volume erupted since the beginning of deglaciation in the region. Chemical stratification is not seen in the waterlain Ho tephra, but these deposits are bi-modal, consisting of a much greater proportion of dark glassy basaltic-trachyandesite dense fragments and pumice, with glasses which range between 55 and 59 wt.% SiO2, along with volumetrically less-significant lighter-colored trachydacite pumice, with glass of 66 wt.% SiO2. In contrast, H1 products are trachyandesitic in composition, H2 ones are more felsic than H1, being composed essentially of trachydacite, and although H3 1991 AD again produced tephra of bi-modal compositions, it erupted a much smaller proportion of mafic compared to felsic material than did Ho. Thus, the repetitive large explosive eruptions of Hudson volcano have evolved to progressively less-mafic overall compositions from late-glacial to historic times, and their volumes have decreased. Sr-isotopic composition of bulk samples of the most mafic dense glass and most felsic pumice components of the Ho tephra, as well as samples from other Hudson eruptions, which overall range from 51 to 66 wt.% SiO2, with 525 to 227 ppm Sr, are all similar (0.70444 ± 0.00007), indicating that crystal-liquid fractionation rather than crustal assimilation was the main process responsible for these chemical variations.

We present a detailed record from Lago Lepue to examine vegetation, climate and fire-regime changes since the Last Glacial Maximum (LGM) in central-east Isla Grande de Chiloe (43°S), northwestern Patagonia. Precipitation in this region correlates with the intensity of the southern westerly winds (SWW), allowing reconstruction of past SWW behavior through precipitation-sensitive sensors. Recession from the LGM glacier margins exposed the central-east sector of Isla Grande de Chiloe by 17,800 cal yr BP, followed by the immediate colonization of pioneer cold-resistant herbs/shrubs and rapid establishment of closed-canopy Nothofagus forests by 17,000 cal yr BP. Broad-leaved temperate rainforests have persisted since then with compositional changes driven by changes in temperature, hydrologic balance and disturbance regimes. We detect low lake levels and enhanced fire activity between 800–2000, 4000–4300, ∼8000–11,000 and 16,100–17,800 cal yr BP, implying southward shifts and/or weaker SWW flow that alternated with cold, humid phases with muted fire activity. Covariation in paleoclimate trends revealed by the Lago Lepue record with tropical and Antarctic records since the LGM, suggests that the SWW have been a highly dynamic component of the climate system capable of linking climate changes from low- and high-southern latitudes during the Last Glacial termination and the current interglacial.

Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes1,2,3,4 and New Zealand5,6,7,8 for the period of transition from glacial to interglacial conditions—about 14.6–10 kyr before present, as determined by radiocarbon dating—show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41° S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (bp), followed by cooling events at about 12.2 and 11.4 14C kyr bp, and then by a warming at about 9.8 14C kyr bp. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region9, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

We report pollen, spore, and charcoal records from Lago Augusta (47°05′S, 72°23′W, 440 m a.s.l.), a small closed-basin lake located near the modern forest-steppe ecotone east of the Andes in Central Patagonia, Chile. The record shows local ice-free conditions through the last glacial termination in the Rio Chacabuco Valley and flooding by an ice-dammed lake. Once this proglacial lake ceased to inundate areas above 450 m a.s.l., the valley was colonized by herbs, shrubs and evergreen rainforest taxa between 15,600 and 16,000 cal yr BP, indicating an open landscape under cold/wet conditions. Millennial-scale fluctuations in the hygrophilous conifer Fitzroya / Pilgerodendron suggest precipitation variations within a cool/wet climate between 11,800 and 13,400 cal yr BP, followed by the establishment of dense Nothofagus forests between 9800 and 11,800 cal yr BP and declines in hygrophilous and cold-resistant trees, herbs and shrubs. This interval coincided with peak fire activity and laminated carbonate deposition. Nothofagus forests have persisted with little variation since 9800 cal yr BP, except for a sudden decline associated with a rapid increase in Rumex cf. acetosella , an exotic weed introduced by Europeans. Our results and interpretations are best explained by changes in the strength/position of the southern westerly winds at millennial and multi-millennial timescales since the last glaciation. Contrary to previous interpretations, we propose increased precipitation of westerly origin in the Andean sector of central-east Patagonia between 11,800 and 16,000 cal yr BP followed by a decline between 9800 and 11,800 cal yr BP and an increase thereafter. These trends are coherent with variations of the southern westerly winds identified in other terrestrial mid-latitude records, suggesting zonally symmetric changes in atmospheric circulation since the last glaciation.

Much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid- latitudes, in particular the southwestern Patagonian region (50 � e55 � S). Its location adjacent to the Drake Passage and near the southern margin of the southern westerly winds (SWW) allows examining the postulated links between the Southern OceaneSWW coupled system and atmospheric CO2 variations through the last glacial termination. Results from two sites located in the Ultima Esperanza area (52

Newly described outcrops, excavations and sediment cores from the region of Ultima Esperanza, Magallanes, contain tephra derived from the large late-glacial explosive R1 eruption of the Reclus volcano in the Andean Austral Volcanic Zone. New radiocarbon dates associated to these deposits refine previous estimates of the age, to 14.9 cal kyrs BP (12,670±240 14C yrs BP), and volume, to >5 km3, of this tephra. The geographic and stratigraphic distribution of R1 also place constraints on the evolution of the ice-dammed proglacial lake that existed east of the cordillera in this area between the termination of the Last Glacial Maximum (LGM) and the Holocene. This proglacial lake generated wavecut terraces, and also caves, such as the Cueva de Milodon, along the highest prominent terrace. The current elevation of these terraces depends on the total amount of post-glacial isostatic rebound, which is unknown. Due to differential rebound, the highest prominent lake terraces decrease in height from west-to-east, from ~170 m a.s.l. on Peninsula Antonio Varas west of Seno Ultima Esperanza, to ~150 m a.s.l. around Lago Sofia, and down to ~125 m a.s.l. along their easternmost margin. The presence of thick deposits of R1 tephra in some of the caves around Lago Sofia implies that the proglacial lake had already dropped below its highest level prior to the time of this eruption, and, in fact, even earlier, prior to 16.1 cal kyrs BP (13,560±180 14C yrs BP), when land mammals first occupied these caves. The depositional environment of R1 in a core from Dumestre bog suggests that the lake level was in fact 70 m a.s.l. until 12.8 cal kyrs BP (10,695±40 14C yrs BP). However, a 14.2 cal kyrs BP (12,125±85 14C yrs BP) Mylodon pelvis from a nearby site, located at only ~7 m a.s.l., suggests that the lake could have emptied, for at least a brief period, to this low level at this time. This latter datum, combined with the lack of any prominent terraces between the highest ones (170-125 m a.s.l.) and much lower ones (at only 30 m a.s.l. on Peninsula Antonio Varas and 20 m a.s.l. along the coast north and south of Puerto Natales), suggests abrupt changes in the lake level after the R1 eruption. The likely mechanism for producing these changes in Ultima Esperanza was the catastrophic failure and subsequent re-sealing of an ice dam in Paso Kirke, the only below sea-level pathway west to the Pacific north of Fjordo Obstruccion. The final stage of lake drainage, from the lower terrace level (20-30 m a.s.l.) occurred at 10.3 cal kyrs BP.

We present a new record from the Ultima Esperanza region (51°25’-52°25'S), southwestern Patagonia, to unravel the timing and structure of glacial fluctuations during the Last Glacial Termination (T1). This sector of southern South America represents the only windward-facing continental landmass in the Southern Hemisphere that intersects the core of the Southern Westerly Wind belt. Geomorphic, stratigraphic and geochronological evidence indicate the following stages during and since the Last Glacial Maximum (LGM): (i) deposition of prominent moraine complexes during at least two advances dated between ~ 39 and > 17.5 ka; (ii) development of an ice-dammed proglacial lake (glacial lake Puerto Consuelo) accompanying ice recession; (iii) active deposition of moraine complexes at intermediate positions followed by recession at ≥ 15.2 ka; (iv) lake level drop and subsequent stabilization between 15.2-12.8 ka; (v) a glacial readvance in glacial lake Puerto Consuelo between 14.8-12.8 ka; (vi) ice recession, stabilization, and lake level lowering between 12.8-10.3 ka; and (vii) glacial withdrawal and disappearance of glacial lake Puerto Consuelo prior to 10.3 ka. By comparing our results with the chronologies from neighboring regions we explore whether there was a consistent temporal/geographic pattern of glacial fluctuations during the LGM and T1, and examine their implications at regional, hemispheric, and global scales. The correspondence of these variations with key paleoclimate events recorded in the Southern and the Northern Hemispheres suggest a common forcing that, most likely, propagated through the atmosphere. Regional heterogeneities at millennial timescales probably reflect the influence of processes related to deep ocean circulation, and changes in the position/intensity of the Antarctic Polar Front and Southern Westerly Winds.

Resolving the timing, direction, and magnitude of paleoclimate changes in the southern midlatitudes is a prerequisite for determining the mechanisms underlying abrupt and widespread climate changes between the hemispheres during the Last Glacial-Interglacial transition (LGIT). This issue is still debated, with previous studies producing apparently discordant fi ndings. Here we show evidence for a glacial readvance and a cold episode between ca. 14.8 and 12.6 ka in southwestern Patagonia (50°S), contemporaneous with the Antarctic cold reversal. This was followed by ice recession under cold but relatively milder conditions until ca. 11.5 ka, when paleovegetation records indicate the onset of warm interglacial conditions. These fi ndings differ from those reported in northern Patagonia (~40°S), where deteriorating conditions before 13.5 ka were followed by the coldest part of the LGIT that lasted until ca. 11.5 ka. We interpret the apparent blend of Greenlandic and Antarctic cold phases as evidence for their co-occurrence in the southern middle latitudes in Patagonia, and hypothesize that the position of the Antarctic Polar Front modulated the strength of these cold events in regions to the north or south of it.

NSF ATM-0212450 Royal Society of London NERC Comer Science and Educational Fellowship Fondecyt 1070991 1050416 CEQUA Institute of Ecology and Biodiversity P02-051 PFB-23 L-DEO 7158 Weeks Postdoctoral Fellowship

Variability of atmospheric 14C content often complicates radiocarbon-based chronologies; however, specific features such as periods of constant 14C age or steep changes in radiocarbon ages can be useful stratigraphic markers. The Younger Dryas event in the Northern Hemisphere is one of those periods, showing conspicuous 14C wiggles. Although the origin of those variations is not fully understood, we can make practical use of them and determine: (i) whether the Younger Dryas was global in extent; if so, (ii) were the initial cooling and the final warming synchronous worldwide; and (iii) what are the implications of these similarities/differences? Here we report high-resolution AMS 14C chronologies from the mid-latitudes of South America that pinpoint a cool episode between 11,400 and 10,20014C yr B.P. The onset of the final cool episode of the Late Glacial in the southern mid-latitudes, i.e., the Huelmo/Mascardi Cold Reversal, preceded the onset of the Younger Dryas cold event by ∼550 calendar years. Both events ended during a radiocarbon-age plateau at ∼10,20014C yr B.P. Thus, the Huelmo/Mascardi Cold Reversal encompasses the Younger Dryas, as well as a couple of short-term cool/warm oscillations that immediately preceded its onset in the North Atlantic region.

A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and/=33,500 carbon-14 years before present ((14)C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000(14)C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720(14)C yr B.P., and at the beginning of the Younger Dryas at 11,050 (14)C yr B. P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges.