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We describe five new araphid diatom species belonging to the genus Pseudostaurosira. These new taxa were found in modern and fossil material collected from five southern Patagonian waterbodies (49–...

Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1191435 3110180 Millennium Science Initiative of the Ministry of Economy, Development and Tourism

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.

We examine the response of Nothofagus forests to climate change and disturbance regimes over the last 3200 years near Coyhaique (45°S), central–east Chilean Patagonia, using fine-resolution pollen and charcoal records from lake sediment cores. Closed-canopy deciduous Nothofagus forests have dominated the region with little variation until the arrival of Chilean–European settlers, suggesting a predominance of cool-temperate and wet conditions. Within this state we identify centennial-scale episodes of forest fragmentation, increase in littoral macrophytes and volcanic/paleofire disturbance between 2700 and 3000 cal a BP, 2200 and 2500 cal a BP and over the last ∼250 years, which we interpret as intervals with negative hydrologic balance. Natural variability caused little impact on the physiognomy and composition of the vegetation in pre-European time, in contrast to the accelerated shift that started during the late 19th century associated with deforestation, homogenization and synchronization of ecosystem changes at the landscape level, and spread of exotic plant species brought by Chilean and European settlers during a warm/dry interval. The resilience of deciduous Nothofagus forests to natural disturbance regimes and climate change was exceeded by large-scale human disturbance since the late 19th century by fire, timber exploitation and livestock grazing. These disturbances caused an ecosystem shift towards artificial meadows and scrublands with frequent high-magnitude fires.

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

The deep-time dynamics of coupled socio-ecological systems at different spatial scales is viewed as a key framework to understand trends and mechanisms that have led to the Anthropocene. By integrating archeological and paleoenvironmental records, we test the hypothesis that Chilean societies progressively escalated their capacity to shape national biophysical systems as socio-cultural complexity and pressures on natural resources increased over the last three millennia. We demonstrate that Pre-Columbian societies intentionally transformed Chile’s northern and central regions by continuously adjusting socio-cultural practices and/or incorporating technologies that guaranteed resource access and social wealth. The fact that past human activities led to cumulative impacts on diverse biophysical processes, not only contradicts the notion of pristine pre-Industrial Revolution landscapes, but suggests that the Anthropocene derives from long-term processes that have operated uninterruptedly since Pre-Columbian times. Moreover, our synthesis suggests that most of present-day symptoms that describe the Anthropocene are rooted in pre-Columbian processes that scaled up in intensity over the last 3000 years, accelerating after the Spanish colonization and, more intensely, in recent decades. The most striking trend is the observed coevolution between the intensity of metallurgy and heavy-metal anthropogenic emissions. This entails that the Anthropocene cannot be viewed as a universal imprint of human actions that has arisen as an exclusive consequence of modern industrial societies. In the Chilean case, this phenomenon is intrinsically tied to historically and geographically diverse configurations in society-environment feedback relationships. Taken collectively with other case studies, the patterns revealed here could contribute to the discussion about how the Anthropocene is defined globally, in terms of chronology, stratigraphic markers and attributes. Furthermore, this deep-time narrative can potentially become a science-based instrument to shape better-informed discourses about the socio-environmental history in Chile. More importantly, however, this research provides crucial “baselines” to delineate safe operating spaces for future socio-ecological systems.

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.

Climate and disturbance regimes play key roles in shaping the structure, composition and functioning of terrestrial ecosystems. Despite this importance, very few stratigraphic studies in the temperate rainforests from northwestern Patagonia have explored this relationship in detail along a time continuum through the entire Holocene. Here we present a high-resolution fossil pollen and charcoal record from Lago Fonk (median resolution: 20 years), a small closed-basin lake in the lowlands of the Chilean Lake District (41°S), where wildfires and explosive volcanism have intermittently taken place during the Holocene, along with pronounced human-induced disturbance in post-colonial time. Our results show persistence of temperate rainforest throughout the Holocene, with changes in the composition and structure of Valdivian rainforests (VRF) at millennial timescales. We detect centennial-scale alternations in dominance between the VRF tree Eucryphia/Caldcluvia and generalist trees found in VRF and North Patagonian rainforests after ∼6.5 cal ka BP. Intervals dominated by VRF coincide with enhanced fire occurrence signaling negative hydroclimate anomalies with a mean duration of ∼150 years, which alternate with positive hydroclimate anomalies lasting ∼312 years on average. Our results suggest that the magnitude and rapidity of vegetation changes detected at 10.2–9.9, 4.0–3.0, ∼1.0, and ∼0.7 cal ka BP were amplified by disturbance regimes, and led to the establishment and maintenance of Eucryphia/Caldcluvia-dominated forests in the Longitudinal Valley of the Chilean Lake District. On several occasions the higher incidence of fire disturbance during warm/dry climate intervals coincided with episodes of heightened explosive volcanic activity from multiple eruptive centers within the Southern Andean Volcanic Zone.

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.

We examine hydroclimate changes at centennial/millennial timescales since 16,000 yr BP in northwestern Patagonia based on the pollen and charcoal record from Lago El Salto, a small closed-basin lake located in the Chilean Lake District (41°38′48.02″S, 73° 5′48.42″W). We observe cold/wet conditions between 14,500–16,000 yr BP, followed by further cooling with increased precipitation until 13,000 yr BP, enhanced precipitation seasonality and/or variability between 11,600–13,000 yr BP, and an extended warm-and-dry interval between 7600 and 11,300 yr BP with peak paleofire activity. Colder-and-wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr BP, followed by alternating cold/wet and centennial-scale warm/dry phases starting at 5300 yr BP with three conspicuous megadroughts since 2500 yr BP. The most recent megadrought occurred during the Medieval Climate Anomaly. We identify a cold reversal that spans the Antarctic Cold Reversal (ACR) and the Younger Dryas (YD) chrons with stronger-than-present westerly influence during the former and enhanced variability during the latter. These results extend the northern limit of strong cooling and increase in precipitation during the ACR and the southern limit of influence of strong hydrologic variations during the YD in terrestrial environments, suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes. An extended warm southern westerly wind (SWW)-minimum interval is evident between 7600 and 11,300 yr BP, followed by a rapid shift to cool-moist conditions between 5300 and 7600 yr BP brought by a mid-Holocene SWW maximum. Since then we observe centennial-scale hydroclimate variability, which has driven biodiversity and fire-regime shifts of evergreen temperate rainforests.

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.

Glacier behaviour during the mid-Holocene (MH, 6000 years BP) in the Southern Hemisphere provides observational data to constrain our understanding of the origin and propagation of palaeoclimate signals. In this study we examine the climatic forcing of glacier response in the MH by evaluating modelled glacier equilibrium line altitudes (ELAs) and climatic conditions during the MH compared with pre-industrial time (PI, year 1750). We focus on the middle latitudes of the Southern Hemisphere, specifically Patagonia and the South Island of New Zealand. Climate conditions for the MH were obtained from PMIP2 model simulations, which in turn were used to force a simple glacier mass balance model to simulate changes in ELA. In Patagonia, the models simulate colder conditions during the MH in austral summer (−0.2 °C), autumn (−0.5 °C), and winter (−0.4), and warmer temperatures (0.2 °C) during spring. In the Southern Alps the models show colder MH conditions in autumn (−0.7 °C) and winter (−0.4 °C), warmer conditions in spring (0.3 °C), and no significant change in summer temperature. Precipitation does not show significant changes but exhibits a seasonal shift, with less precipitation from April to September and more precipitation from October to April during the MH in both regions. The mass balance model simulates a climatic ELA that is 15–33 m lower during the MH compared with PI conditions. We suggest that the main causes of this difference are driven mainly by colder temperatures associated with the MH simulation. Differences in temperature have a dual effect on glacier mass balance: (i) less energy is available for ablation during summer and early autumn and (ii) lower temperatures cause more precipitation to fall as snow rather than rain in late autumn and winter, resulting in more accumulation and higher surface albedo. For these reasons, we postulate that the modelled ELA changes, although small, may help to explain larger glacier extents observed by 6000 years BP in South America and New Zealand.

The degree to which vegetation and site type have influenced fire regimes through the Holocene has not been investigated in detail in the temperate ecosystems of southern Patagonia. Here we present a first attempt using a paired-basin approach to study the evolution of fire regimes in sectors dominated by humid Nothofagus forests and the xeric Patagonian steppe in the Magallanes region of Chilean Patagonia (51°S). We analyzed sediment cores from two small lakes and a bog located within the same climate zone on opposite sides of the forest-steppe ecotone, ~28 km apart. The position of this biological boundary east of the Andes is controlled by the strength and position of the southern westerly winds, which constitute the sole source of precipitation throughout western Patagonia. Our results indicate that fires have occurred in the study region repeated times over the last ~13,000 years at bi- and tridecadal timescales. Sectors currently dominated by Patagonian steppe feature high frequency and low magnitude of local fires, and vice versa in humid forests. Climate-driven expansion of Nothofagus scrubland/woodland into steppe environments over the last ~4,200 years increased the magnitude and lowered the frequency of fire events, culminating with peak Nothofagus abundance, fire magnitude and frequency during the last millennium. We also detect divergences between lake-based vs. bog-based paleofire histories among paired sites located within the Patagonian steppe, ~12 km apart, which we attribute to local burning of the bog at times of lowered water table. This divergence suggests to us that bog-based vegetation and fire histories exacerbate a local, azonal, signal blurring extra-local or regional regimes, thus accounting for some discrepancies in the Quaternary paleovegetation/paleoclimate literature of southern Patagonia. Fil: Moreno, Patricio I.. Universidad de Chile; 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 Fil: Villa Martínez, Rodrigo P.. Universidad de Magallanes; Chile Fil: Francois, Jean P.. Universidad de Playa Ancha; Chile

The Southern Westerly Winds (SWW) are the surface expression of geostrophic winds that encircle the southern mid-latitudes. In conjunction with the Southern Ocean, they establish a coupled system that not only controls climate in the southern third of the world, but is also closely connected to the position of the Intertropical Convergence Zone and CO2 degassing from the deep ocean. Paradoxically, little is known about their behavior since the last ice age and relationships with mid-latitude glacier history and tropical climate variability. Here we present a lake sediment record from Chilean Patagonia (51°S) that reveals fluctuations of the low-level SWW at mid-latitudes, including strong westerlies during the Antarctic Cold Reversal, anomalously low intensity during the early Holocene, which was unfavorable for glacier growth, and strong SWW since ∼7.5 ka. We detect nine positive Southern Annular Mode-like events at centennial timescale since ∼5.8 ka that alternate with cold/wet intervals favorable for glacier expansions (Neoglaciations) in southern Patagonia. The correspondence of key features of mid-latitude atmospheric circulation with shifts in tropical climate since ∼10 ka suggests that coherent climatic shifts in these regions have driven climate change in vast sectors of the Southern Hemisphere at centennial and millennial timescales. Fil: Moreno, P.I.. Universidad de Chile; 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 Fil: Villa-Martínez, R.. Universidad de Magallanes; Chile Fil: Dunbar, R.B.. University of Stanford; Estados Unidos Fil: Mucciarone, D.A.. University of Stanford; Estados Unidos Fil: Kaplan, M.R.. Columbia University; Estados Unidos Fil: Garreaud, R.D.. Universidad de Chile; Chile Fil: Rojas, M.. Universidad de Chile; Chile Fil: Moy, C.M.. University of Otago; Nueva Zelanda Fil: De Pol-Holz, R.. Universidad de Magallanes; Chile Fil: Lambert, F.. Pontificia Universidad Católica de Chile; Chile

We describe the stratigraphy, age, constituent geochemistry and phenocryst thermobarometry of a closely spaced Holocene tephra couplet from Volcan Melimoyu (VMm), located in the Northern Patagonian Andes. The lower tephra unit (La Junta Tephra, Mm-1) is distinctly banded comprising a dominant lower layer of rhyodacitic (∼70% SiO2) pumiceous ash and lapilli (Mm-1p) that abruptly transitions to a subordinate upper scoriaceous layer (Mm-1s) of basaltic andesite composition (∼53% SiO2). This bimodality within Mm-1 contrasts significantly with the closely overlying Santa Ana Tephra (Mm-2) that has a homogeneous trachyte-dacite (∼63% SiO2) composition and is intermediate between the two magmatic end members of Mm-1. We propose a genetic affiliation between Mm-1 and Mm-2, and that the latter event likely represents a hybridised-remnant of those discrete magmas involved in the earlier Mm-1 eruption. To test this hypothesis we applied whole rock elemental mixing and fractional crystallisation model to reproduce the composition and crystallinity of Mm-2. Results indicate that Mm-2 can be reproduced by mixing ∼70% Mm-1p with ∼30% Mm-1s, with subsequent ∼13% fractional crystallisation of plagioclase, and minor amphibole, orthopyroxene, magnetite and biotite. Equilibrium P-T conditions calculated from Mm-1p phenocrysts point towards magma residency at moderately shallow depths (200–290 MPa, ∼7–10-km depth, 850–1000 °C), whereas Mm-1s phenocrysts indicate higher overall P-T conditions (240–480 MPa, ∼8.5–17-km depth, 1080–1150 °C). P-T conditions determined for Mm-2 (∼290 MPa, ∼10-km depth, 930–1000 °C) are similar to those of Mm-1p. There is no physical and/or geochemical evidence of mafic magma involvement in the Mm-2 eruption. Similar compositionally bimodal tephra are known from other Northern Patagonian Andean centres (i.e. Playas Blanca-Negra Tephra, Antillanca; Lepue Tephra, Michimahuida; Ho and H3 eruptions of Hudson) suggests that the intrusion of mafic magma into more silicic magma bodies is a common occurrence throughout this Andean sector. These widely dispersed, compositionally bimodal tephra not only provide key insights into pre-eruptive magmatic conditions and triggering processes, but can also be readily identified geochemically, and thereby be more fully utilised within future hazard- and paleoenvironmental-related studies.

We present a 16 000-year vegetation and climate reconstruction from pollen and plant macrofossil records obtained at a small alpine lake in South Island, New Zealand (41°S). The expansion of lowland forest taxa suggests a lifting of the altitudinal forest limits because of a warming pulse between 13 and 10k cal a BP and between 7 and 6k cal a BP, while their decline relative to upland forest taxa indicates cooling phases between 10 and 7k cal a BP and over the last 3000 years. The modern treeline was first established locally by 9.7k cal a BP. Forest persisted at the site until 3k cal a BP then disappeared from the record. Close correspondence between the temperature trends inferred from the pollen and macrofossil records and proxies from Antarctica and the Southern Ocean suggests a strong teleconnection between New Zealand and the Southern Hemisphere high-latitudes between 15 and 6k cal a BP. We note that the breakdown of this coupling, a cooling trend in Adelaide Tarn and the local disappearance of beech forest after 3k cal a BP occur during a period of increased frequency of El Nino events, suggesting an enhanced teleconnection with the low-latitudes during the late Holocene.

South America lost around 52 genera of mammals during a worldwide event known as the Late Quaternary Extinction episode. More than 80% of South American mammals weighing > 44 kg succumbed. Analysis of the megafaunal extinction chronology in relation to human arrival and major climate changes have revealed slightly different extinction patterns in different eco-regions of the continent, highlighting the importance of detailed regional analysis in order to understand how the possible drivers of extinction operated. Here we present an analysis of the megafaunal extinction in the Ultima Esperanza (UE) area of southwestern Patagonia, Chile. We have compiled a comprehensive chronology of megafaunal extinctions and earliest human occupation between 18–7 cal ka BP, based on radiocarbon dates from published literature. We calculated confidence intervals using the GRIWM method to estimate the times of human arrival and megafaunal local extinctions, and then compared these events to the timing of major climate and vegetation changes, fire frequency increase, and the Reclus volcanic eruption. Our results suggest that a combination of human impacts and climate–vegetation change drove megafaunal extinctions in the UE area, with the balance of factors being taxon specific; the volcanic eruption does not seem to have exacerbated extinctions. Competition between humans and mega-carnivores seems to be the most plausible cause for the extinction of the mega-carnivores. Coexistence of humans with extinct horses, extinct camels, and mylodonts for several thousand years rules out a scenario of blitzkrieg overkill of megafauna by humans. The transition of vegetation from cold grasslands to Nothofagus forests corresponds with the disappearance of Hippidion saldiasi and Lama cf. owenii. The later full establishment of Nothofagus forests and an increasing fire frequency coincided with the disappearance of mylodonts. A climate-driven reduction of open environments plausibly reduced herbivore's populations making them susceptible to local extinction.

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.

Diatoms can access mineral iron from dust if it is reduced, and reduced particulate iron is common in glacial dust sources., Little is known about the bioavailability of iron (Fe) in natural dusts and the impact of dust mineralogy on Fe utilization by photosynthetic organisms. Variation in the supply of bioavailable Fe to the ocean has the potential to influence the global carbon cycle by modulating primary production in the Southern Ocean. Much of the dust deposited across the Southern Ocean is sourced from South America, particularly Patagonia, where the waxing and waning of past and present glaciers generate fresh glaciogenic material that contrasts with aged and chemically weathered nonglaciogenic sediments. We show that these two potential sources of modern-day dust are mineralogically distinct, where glaciogenic dust sources contain mostly Fe(II)-rich primary silicate minerals, and nearby nonglaciogenic dust sources contain mostly Fe(III)-rich oxyhydroxide and Fe(III) silicate weathering products. In laboratory culture experiments, Phaeodactylum tricornutum, a well-studied coastal model diatom, grows more rapidly, and with higher photosynthetic efficiency, with input of glaciogenic particulates compared to that of nonglaciogenic particulates due to these differences in Fe mineralogy. Monod nutrient accessibility models fit to our data suggest that particulate Fe(II) content, rather than abiotic solubility, controls the Fe bioavailability in our Fe fertilization experiments. Thus, it is possible for this diatom to access particulate Fe in dusts by another mechanism besides uptake of unchelated Fe (Fe′) dissolved from particles into the bulk solution. If this capability is widespread in the Southern Ocean, then dusts deposited to the Southern Ocean in cold glacial periods are likely more bioavailable than those deposited in warm interglacial periods.

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

We present a detailed record from Lago Pichilafquen to unravel the vegetation, climate and disturbance history of the lowlands of northwestern Patagonia (40 °S) since 14,500 cal yr BP. The presence of 30 tephras throughout the record attest for the proximity of the site to active volcanic centres and allows assessment of the role of volcanic disturbance on past vegetation and fire regime shifts. We interpret alternations in dominance between North Patagonian and Valdivian rainforests driven by changes in temperature and precipitation of westerly origin at multi-millennial and millennial timescales. These trends were punctuated by centennial-scale changes, most of which were coeval with or immediately followed the deposition of tephras and/or paleofires. We identify departures of the local vegetation from the regional trend between 2400 and 7100 cal yr BP, which we interpret as a response of rainforest vegetation and local fire regimes to the disturbance effect of tephra deposition near Lago Pichilafquen. We also find that volcanic disturbance promoted consistent increases in Eucryphia/Caldcluvia within 30 years and paleofires between 60 and 120 years following tephra deposition. Comparisons with palynological records having similar span, time resolution and age control suggest that regional climate has played a central role on the establishment, composition and maintenance of temperate rainforests. This influence is overprinted by disturbance regimes at the local and landscape level, driving divergences and heterogeneity especially at times of relatively weak climatic forcing.

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

Two Holocene tephras encountered in outcrops, cores and trenches in bogs, and lake cores in the area around Cochrane, southern Chile, are identified (based on their age, tephra glass color and morphology, mineralogy, and both bulk and glass chemistry) as H1 derived from Hudson volcano, and MEN1 derived from Mentolat volcano. New AMS radiocarbon ages indicate systematic differences between those determined in lake cores (MEN1=7,689 and H1=8,440 cal yrs BP) and surface deposits (MEN1=7,471 and H1=7,891 cal yrs BP), with the lake cores being somewhat older. H1 tephra layers range from 8 to 18 cm thick, suggesting that both the area of the 10 cm isopach and the volume of this eruption were larger than previously suggested, but not greatly, and that the direction of maximum dispersion was more to the south. MEN1 tephra layers range from 1-4 cm in thickness, indicating that this was probably a reasonably large (>5 km3) eruption. Some of the lake cores also contain thin layers (

We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes.

Comparative phylogeography describes the patterns of evolutionary divergence and whether or not they are congruent, in co-distributed populations of different taxa. If the populations of these taxa have been co-distributed for a prolonged time, and if the times between processes of perturbation or vicariance have been more or less stable, it is expected that patterns of divergence will be congruent in closely related species, for example because of similar biological and demographic characteristics.Liolaemus pictusandL. cyanogasterare widely co-distributed lizard species in southern Chile, occurring in a region with a complex topology. We analyzed the phylogeographic structure of the two lizard species usingCytochromebDNA sequences to estimate their genetic structure in response to historical events. Our results suggest an evolutionary pattern of genetic diversity for each species that is consistent with the geomorphological history of the region, suggesting a complex phylogeographic history inLiolaemusspecies. Also, the high levels of divergence among haplotypes in several populations suggest the possibility that their origin might predate the middle Pleistocene in both species. Finally, our results are consistent with our hypothesis that two species have responded to historical events in parallel, where historical process have been sufficient to influence their phylogeographical structure (0.80 congruency between topologies).

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.

Newly described outerops, excavations and sediment cores from the region of Última Esperanza, Magallanes, contain tephra derived from the large late-glacial explosive Rl eruption of the Reclús 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 Rl 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 wave-cut terraces, and also caves, such as the Cueva de Milodón, 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 Península Antonio Varas west of Seno Ultima Esperanza, to-150 m a.s.l. aroundLago Sofía, anddownto-125 m a.s.l. along their easternmost margin. The presence of thick deposits of Rl tephra in some of the caves around Lago Sofía 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 oceupied these caves. The depositional environment of Rl 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 BF) 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 Península 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 Rl 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 Obstrucción. The final stage of lake drainage, from the lower terrace level (20-30 m a.s.l.) oceurred at 10.3 cal kyrs BP.En este trabajo reportamos hallazgos de tefras derivadas de la gran explosión volcánica tardiglacial Rl del volcán Reclús situado en la Zona Volcánica Austral Andina, a partir de nuevos afloramientos, excavaciones y testigos sedimentarios de lagos y pantanos, obtenidos en la región de Ultima Esperanza, Magallanes. Nuevas fechas asociadas a estos depósitos permiten refrnar su edad a 14,9 ka cal AP (12.670±240 14C años AP) y su volumen a >5 km³. Además, la ubicación geográfica y estratigráfica de Rl permite acotar la evolución del lago proglacial represado por hielo que se desarrolló al este de la cordillera al intervalo temporal entre el término del Ultimo Máximo Glacial y el Holoceno. Este lago proglacial generó terrazas y cuevas, producto de la acción del oleaje, como la Cueva de Mlodón, a lo largo de la terraza más alta y conspicua. La altitud actual de estas terrazas depende de la cantidad total de rebote isostático posglacial, el cual se desconoce. Debido a las variaciones en el rebote isostático posglacial, las terrazas lacustres más altas y prominentes disminuyen en altitud de oeste a este, desde -170 m s.n.m. en la Península Antonio Varas, al oeste del Seno Ultima Esperanza, a 150 m s.n.m. alrededor del lago Sofía y descienden hasta -125 m s.n.m. a lo largo de su margen más oriental. La presencia de grandes depósitos de la tefra Rl en algunas de las cuevas alrededor del lago Sofía indican que el lago proglacial ya había descendido, con respecto a su nivel más alto, antes de la erupción de Rl y de hecho incluso antes de 16,1 ka cal AP (13.560±180 14C años AP) que es cuando los mamíferos terrestres ocuparon por primera vez estas cuevas. El ambiente deposicional de Rl, en el registro sedimentario del pantano Dumestre, sugiere incluso que el nivel del lago era inferior a 80 m s.n.m. durante el momento de esta erupción. Probablemente el lago proglacial original habría drenado a este nivel a través de sectores de baja altitud ubicados entre fiordo Obstrucción y seno Skyring, siguiendo hacia el seno Otway para desembocar en el Océano Pacífico, una vez que el canal Jerónimo ya estaba libre de hielo antes de la erupción de Rl. Otro grupo de testigos, del sitio Eberhard, indican que el lago persistió a >70 m s.n.m. hasta 12,8 ka cal AP (10.695±14C años AP). Sin embargo, a 14,2 ka cal AP (12.125±14C años AP), la pelvis de Mylodon de un sitio cercano, ubicado a 7 m s.n.m., sugiere que el lago podría haberse vaciado temporalmente durante este período. Este último dato, combinado con la ausencia de terrazas prominentes entre las más altas (170-125 m s.n.m.) y las más bajas (a solo 30 m s.n.m. en la Península Antonio Varas y 20 m s.n.m. a lo largo de la costa norte y sur de Puerto Natales), sugiere cambios abruptos en el nivel del lago proglacial después de la erupción de Rl. Probablemente el mecanismo que ocasionó estos cambios en Ultima Esperanza fue la ruptura catastrófica y el subsecuente resellamiento del dique de hielo que bloqueaba el Paso Kirke, el único paso al Océano Pacífico bajo el nivel del mar al norte del fiordo Obstrucción. El drenaje final del lago, desde la terraza inferior (20-30 m s.n.m.), ocurrió a los 10,3 ka cal AP.