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Fildes Peninsula, on King George Island, has been greatly influenced by recent rapid climate warming. Lakes are pervasive features of Fildes Peninsula landscapes, some of which are used as water sources for Antarctic stations. We studied seven Fildes Peninsula lakes to explore differences among lakes and between seasons in phytoplankton and bacterioplankton communities. We measured environmental variables, analysed pigments using high-performance liquid chromatography and examined bacterial DNA through high-throughput sequencing of the 16S rRNA gene. The main driver structuring microbial communities was the season (i.e. spring vs autumn). Chlorophyceae were the dominant phytoplankton group in all lakes and both seasons. Indicator bacteria for each season were identified, including Flavobacterium, Polaromonas and Oxalobacteraceae as indicators of spring conditions under thick ice, whereas Frankiales and Verrucomicrobia were indicator species of autumn following the ice-free summer. The indicator species for spring are generally observed in oligotrophic conditions, whereas many of the autumn indicators are commonly found in soils. There were lesser between-lake differences in microbial communities in autumn, at the end of the open-water period, than in spring at the end of the ice-covered period. This study will act as the basis for future assessments of changes in aquatic microbial communities.

Remobilization and deformation of surficial subaqueous slope sediments create turbidites and soft sediment deformation structures, which are common features in many depositional records. Palaeoseismic studies have used seismically‐induced turbidites and soft sediment deformation structures preserved in sedimentary sequences to reconstruct recurrence patterns and – in some cases – allow quantifying rupture location and magnitude of past earthquakes. However, current understanding of earthquake‐triggered remobilization and deformation lacks studies targeting where these processes take place, the subaqueous slope and involving direct comparison of sedimentary fingerprint with well‐documented historical earthquakes. This study investigates the sedimentary imprint of six megathrust earthquakes with varying rupture characteristics in 17 slope sediment cores from two Chilean lakes, Riñihue and Calafquén, and evaluates how it links to seismic intensity, peak ground acceleration, bracketed duration and slope angle. Centimetre‐scale stratigraphic gaps ranging from ca 1 to 20 cm – caused by remobilization of surficial slope sediment – were identified using high‐resolution multi‐proxy core correlation of slope to basin cores, and six types of soft sediment deformation structures ranging from ca 1 to 25 cm thickness using high‐resolution three‐dimensional X‐ray computed tomography data. Stratigraphic gaps occur on slope angles of ≥2.3°, whereas deformation already occurs from slope angle 0.2°. The thickness of both stratigraphic gaps and soft sediment deformation structures increases with slope angle, suggesting that increased gravitational shear stress promotes both surficial remobilization and deformation. Seismic shaking is the dominant trigger for surficial remobilization and deformation at the studied lakes. Total remobilization depth correlates best with bracketed duration and is highest in both lakes for the strongest earthquakes (M w ca 9.5). In lake Riñihue, soft sediment deformation structure thickness and type correlate best with peak ground acceleration providing the first field‐based evidence of progressive soft sediment deformation structure development with increasing peak ground acceleration for soft sediment deformation structures caused by Kelvin‐Helmholtz instability. The authors propose that long duration and low frequency content of seismic shaking favours surficial remobilization, whereas ground motion amplitude controls Kelvin‐Helmholtz instability‐related soft sediment deformation structure development.

In-situ soft sediment deformation structures (SSDS) are commonly used as paleoseismic indicators in marine and lacustrine sedimentary records. Earthquake-related shear can deform sediment in the shallow subsurface through Kelvin-Helmholtz instability. The SSDS related to Kelvin-Helmholtz instability have been used to quan-tify shaking strength of past earthquakes. However, the relative importance of i) lithology and physical proper-ties, ii) potential basal shear surfaces (e.g. clastic deposits), iii) slope angle, and iv) seismic shaking strength (e.g. peak ground acceleration) for deformation related to Kelvin-Helmholtz instability remains poorly studied. Lake Rinihue (south-central Chile) is chosen as a natural laboratory for disentangling the effect of the aforemen-tioned factors because i) the sediment composition of background sediment varies downcore and ii) volcanogenic clastic deposits are abundant within the sedimentary sequence. A previous study at lake Rinihue identified 25 SSDS intervals induced by historical earthquakes of varying rupture extent in 17 sediment cores taken at slope angles ranging from-0.2 degrees to-4.9 degrees (i.e. 16 slope sites and 1 basin site). Our study shows that defor-mation mostly occurs directly above volcanogenic deposits (i.e. 72 % of SSDS intervals), suggesting that volcanogenic deposits promote earthquake-induced deformation by strain softening, liquefaction or water film formation. Deformation thickness of SSDS increases with higher slope angles (i.e. strong positive correlation). Ad-ditionally, deformation thickness commonly corresponds to the stratigraphic depth of the youngest preceding volcanogenic deposit, but for steeper slope angles stratigraphically older volcanogenic deposits can function as basal shear surface. Therefore, we suggest that deformation thickness is primarily regulated by gravitational stress (i.e. slope angle) and secondarily by the stratigraphic depth of volcanogenic deposits. The earthquakes related to strongest shaking caused almost exclusively SSDS with highest deformation degrees (i.e. folds and intraclast breccia) as well as largest spatial extent of SSDS, resulting in highest numbers of related SSDS in the investigated cores. Thinner SSDS have higher deformation degrees at a given shaking strength, as seismically -induced shear energy acts more effectively on thinner deforming sequences. Therefore, we suggest that deforma-tion degree is primarily controlled by shaking strength and secondarily modulated by the thickness of the deforming sequences. We infer that deformation thickness is not a reliable indicator of paleoseismic shaking strength as this relies on many preconditioning factors independent of shaking strength. On the other hand, deformation degree can be a good proxy for shaking strength also in settings with varying lithotypes and intercalated clastic event deposits, provided multiple cores are studied to avoid under-or overestimation of paleoseismic shaking strength. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Subaqueous landslides are common features at active and passive ocean margins, in fjords and lakes. They can develop on very gentle slope gradients (

Earthquake-induced soft sediment deformation structures (SSDS) can be used to resolve earthquake recurrence rates, but also to provide more quantitative information on past earthquake shaking intensities. Thorough understanding of the interplay between i) different ground motion characteristics, ii) sediment properties, iii) slope morphology and iv) seismic site effects is paramount for full exploitation of the paleoseismological potential of subaqueous SSDS records. However, we lack comparative studies investigating different SSDS records related to well-documented earthquakes, varying sediment types and site morphologies.We investigated 17 slope and three basin sediment cores from two South-Central Chilean lakes: lakes Riñihue and Calafquén. Using X-ray computed tomography (CT) data, six different types of SSDS were observed: i) disturbed lamination, ii) folds, iii) intraclast breccia, iv) faults, v) load structures and vi) injection structures. We directly linked SSDS to five well-documented megathrust earthquakes using stratigraphic correlation of sediment sequences to well-dated basinal seismo-turbidite records.Sediment of both lakes consists of varve couplets of diatomaceous ooze and organic-rich terrestrial material intercalated with coarse-grained tephras and fine-grained lahar deposits. From the 49 SSDS intervals, 61% are assigned to one of the five megathrust earthquakes. Of the SSDS intervals not assigned to megathrust earthquakes, 68% are located directly above a tephra or lahar deposit. We suggest that dewatering of volcanic deposits could have weakened overlying sediment and facilitated deformation during later earthquakes.Slope gradient at coring sites range from 0.2-9.5° and 0.2-14.2° in lakes Riñihue and Calafquén, respectively. Deformation occurs from 0.2° and total deformation increases with slope angle in both lakes. Total deformation in lake Calafquén increases less with slope angle than in lake Riñihue. Our observations suggest seismically-induced shear stress alone can suffice to deform sediment, but even minor increases of gravitational downslope stress will ease deformation. Smaller increase of total deformation with slope angle for lake Calafquén could be explained by higher diatom content. Diatoms enhance shear strength through high particle interlocking and surface roughness. Therefore, we suggest that enhanced diatom content reduces sediment susceptibility to shear-induced deformation.We evaluate the effect of ground motion characteristics by correlating SSDS to peak ground acceleration (PGA) and bracketed duration (BD) of the causative strong megathrust earthquakes as derived from ground motion prediction equations. As first suggested for SSDS in the Dead Sea area, disturbed lamination develops to folds and finally intraclast breccia and is driven by earthquake-induced shear causing Kelvin-Helmholtz Instability (KHI). In lake Riñihue, SSDS type and count correlates best with PGA suggesting amplitude of ground acceleration as the main control of KHI-driven deformation.Future comparative analysis of lacustrine SSDS records in different geodynamic settings will put our findings in a broader perspective. Sediment types will be quantified by measuring characteristics like grain size, diatom and organic content, density, viscosity and Atterberg limits. Our study is the first to allow direct comparison of three different factors—sediment type, ground motion characteristics and slope morphology—with related earthquake-triggered SSDS, thereby advancing lacustrine paleoseismology towards a more quantitative interpretation of SSDS records.

Volcan Antuco (37°24′ S, 71°22′W; 2979 m asl) is the 13th ranked high threat volcano in Chile with 27 recorded historical eruptions, mostly (~96%) with volcanic explosivity indices (VEI) of ~1–2. An older eruptive record has been reconstructed from sections exposed on the western flank and is intimately related to a well-documented catastrophic sector collapse at ~7.2 cal ka BP. However, very little is known about Antuco's post-collapse eruptive history in other sectors, especially on the eastern flanks where prevalent westerly winds favor optimal eastward tephra transport and deposition. Our study reveals a more complete record of activity that has already been indicated from previous work with at least 23 tephra-forming explosive eruptions, most of them within the last c. 7.2 ka, including 4 events that have generated pyroclastic density currents that have widely inundated the lower eastern flanks. Tephra from these eruptive events are typically composed of scoria, free crystals and lithics, with occasional pumice. The composition of juvenile fragments varies between basalt and trachyandesite (50.2–62.2 wt% SiO2) and show phenocrysts of plagioclase, olivine and pyroxene. Our results show that most of the eruptions of Antuco (c. 79%) are Strombolian to violent Strombolian. These eruptions have an estimated longer repose times (c. 200 year) and are likely higher in magnitude than those registered during historical times. This study also shows that the composition, style and magnitude may change from one eruptive episode to the next. This eruptive variability seems in complete accord with recent findings from other centers in the Southern Volcanic Zone exhibiting similar temporal eruptive diversity and ultimately, has significant implications with respect to hazard assessment.

International audience; Paleoclimate studies in Patagonia show a high Holocene climate variability, strongly controlled by the intensity and latitudinal position of the Southern Westerly Winds. In this study, environmental and climate variability, and in particular winter precipitation, was reconstructed over the last centuries through sedimentological and geochemical analyses of a core from Lake Jeinimeni in North East Patagonia. Visual description, X-ray radiographies and thin section observations point to finely laminated sediments, made by fine sands and light brown clayey silts forming an annual deposition (varves) occasionally interrupted by two Hudson volcano-related tephras and 15 pluri-millimetre to pluri-centimetre coarser sandy to gravely layers. Varve counting confirmed by 210Pb and 137Cs indicates a detrital sequence of at least 750 yr. Based on a correlation with local meteorological data for the 1930–1988AD interval, varve thickness and statistical treatment of XRF geochemical data give information on transport pathway and sedimentary deposit conditions. The sandy laminae correspond to the deposition of high sedimentary load delivered by austral spring snowmelt whereas the clayey silt laminae result of particle settling in the water column during low hydrodynamical conditions. Thicker varves observed in dry conditions underline the importance of aeolian transport in sedimentary deposition. During locally dry and windy summer, the wind may erode and remobilise the sedimentary deposits along the lake margins. The sandy and gravely layers record massive erosional events due to proximal watershed perturbation driven by climatic or tectonic mechanisms. The clastic varves of Lake Jeinimeni document environmental decadal to multidecadal variability in East Patagonia over the last centuries. The more pronounced sediment transition around 1750 CE is consistent with the inception of the Little Ice Age-type event, in agreement with North Patagonian paleoclimate reconstructions derived from glacier advances, lacustrine varve thickness and tree-ring records.

We present an exceptionally long and continuous coastal lacustrine record of ∼5500 years from Lake Huelde on the west coast of Chiloe Island in south central Chile. The study area is located within the rupture zone of the giant 1960 CE Great Chilean Earthquake (MW 9.5). The subsequent earthquake-induced tsunami inundated Lake Huelde and deposited mud rip-up clasts, massive sand and a mud cap in the lake. Long sediment cores from 8 core sites within Lake Huelde reveal 16 additional sandy layers in the 5500 year long record. The sandy layers share sedimentological similarities with the deposit of the 1960 CE tsunami and other coastal lake tsunami deposits elsewhere. On the basis of general and site-specific criteria we interpret the sandy layers as tsunami deposits. Age-control is provided by four different methods, 1) 210Pb-dating, 2) the identification of the 137Cs-peak, 3) an infrared stimulated luminescence (IRSL) date and 4) 22 radiocarbon dates. The ages of each tsunami deposit are modelled using the Bayesian statistic tools of OxCal and Bacon. The record from Lake Huelde matches the 8 regionally known tsunami deposits from documented history and geological evidence from the last ∼2000 years without over- or underrepresentation. We extend the existing tsunami history by 9 tsunami deposits. We discuss the advantages and disadvantages of various sedimentary environments for tsunami deposition and preservation, e.g. we find that Lake Huelde is 2–3 times less sensitive to relative sea-level change in comparison to coastal marshes in the same region.

Turbidite records along ocean margins and in lake basins are increasingly used as paleoseismic proxies. However, the slope remobilization processes that formed the earthquake-related turbidity currents are poorly understood and, therefore, it is difficult to assess the consistency of turbidite paleoseismic records. We analyzed the sedimentary imprint of the giant AD 1960 (Mw 9.5) Chile earthquake in four South-Central Chilean lakes. Mass-transport deposits and turbidites were compared by interpreting reflection-seismic profiles, sedimentary facies, volume balances and proxies for turbidite composition (i.e. grain size, radionuclides, sediment color, organic matter). Sediment lightness was used as a proxy for organic matter content. Comparison of lightness of turbidites and the underlying sediments shows that earthquake-triggered turbidites in the four lakes result from remobilization of a thin veneer (on average about 5 cm) of slope sediments and do not result from disintegration of subaquatic landslides. Statistical analysis of 34 turbidites in a new 5200 year sedimentary record does not show any correlation between inter-event time and turbidite thickness (and thus volume). This means that inter-event slope recharging is not a dominant factor governing turbidite recurrence and that initiation of turbidity currents by remobilization of surficial sediments is different to slope failure related to subaquatic landslides. We conclude that surficial slope sediment remobilization forms a valid mechanism that explains why turbidite paleoseismic records can be of excellent continuity and high sensitivity. Moreover, based on correlations between seismic intensity, turbidite volume and stratigraphic remobilization depth, we propose that surficial slope sediment remobilization allows for turbidite records containing information about paleo-earthquake intensity.

Pore fluid pressure is a key parameter for subaquatic slope stability and has been put forward to explain the development of many submarine landslides especially when occurring on very gentle slopes or in areas with high sedimentation rate. Due to the sparse availability of in situ pore pressure data a profound understanding and quantification of excess pore pressure development and its influence on subaquatic landslide processes is still missing. In this study we use glacigenic Lake Villarrica (Chile) as a model basin in which we document in situ excess pore pressure focused fluid escape features and subaquatic slope failures at relatively shallow subsurface depth (< 10 m). A subaquatic slope was characterized in great detail by a dense network of high resolution seismic reflection profiles multibeam bathymetry and sediment cores. In situ undrained shear strength and formation pore fluid pressures were documented using free fall piezocone penetrometer (CPTU) and subsequent pore pressure dissipation tests. We show four independent lines of evidence for overpressure of variable magnitude within the sedimentary slopes: i) pockmarks and other fluid escape features on seismic profiles and bathymetric maps ii) estimation of ambient in situ pore pressure via CPTU dissipation tests iii) underconsolidation and downward decrease in in situ undrained shear strength within units of uniform lithology and iv) hydrofractured glacio lacustrine sediments. Locally overpressure reaches about 80–90 of the hydrostatic vertical effective stress. We hypothesize that glacier proximal sediments are strongly underconsolidated and overpressured due to rapid deposition and/or subglacial meltwater pumping. Postglacial consolidation of a thick glacier proximal unit leads to the upward expulsion of excess pore water. A permeability barrier is formed by the overlying glacio lacustrine clays and fine silts focusing these migrating fluids to topographic highs. There very high overpressure ratios facilitate the development of hydro fractures repeated fluid escape and pockmarks on the lake bottom. Overpressure may decrease slope stability in Lake Villarrica in different manners: by focused fluid escape weakening sediments by generating underconsolidated sequences of low undrained shear strength and by facilitating static failure. Based on high quality in situ data this study confirms that high overpressure ratios in shallow sediments may be a typical feature at formerly glaciated marine and lacustrine environments and highlights the major role of pore fluid overpressure for preconditioning subaquatic slopes to failure.

Even though Patagonia is ideally located to study climate of the southern mid-latitudes, many questions on the late Quaternary climate evolution remain unresolved. The timing of maximum glacier extent is still uncertain in vast areas, and the postglacial evolution of the Southern Westerly Wind Belt (SWWB) remains highly debated. Here, we study the sedimentary infill of a glacigenic lake (Lago Castor; 45.6°S, 71.8°W) located at the leeside of the Andes in Chilean Patagonia to i) reconstruct the deglacial evolution of the eastern flank of the Patagonian Ice Sheet (PIS), and ii) discuss postglacial changes in wind strength at a critical location where westerly wind records are critically lacking. A dense grid of high-resolution reflection-seismic data was used to reconstruct the large-scale infill history of the lake, and a radiocarbon dated sediment core penetrating all lacustrine seismic units, was retrieved. Results indicate that the deglaciation of the lake basin and its catchment occurred no later than ∼28 cal kyr BP (i.e. an early LGM), but possibly even already after MIS 4. Afterwards, the Lago Castor area was covered by a large proglacial lake that drained – possibly through an outburst flood – when the PIS outlet glaciers retreated to a critical location. Subsequently, very dry conditions caused the lake to desiccate, as evidenced by an unconformity visible on the seismic profiles and in the sediment core. This dry period likely resulted from the increased orographic effect of the PIS-covered Andes, accompanied by weaker westerlies. From ∼20 kyr BP onwards, the combination of a shrinking PIS and a southward shift of the SWWB resulted in increased precipitation, which caused the lake level to rise. After ∼17 cal kyr BP, lake sedimentation was more directly influenced by the southern westerlies, with the formation of sediment drifts resulting from strong bottom current during periods of intense westerly winds. Our results suggest a progressive increase in wind strength at 46°S from 11.2 to 4.5 cal kyr BP, which supports the hypothesis that the SWWB broadened during the early and middle Holocene.

In 1960 CE, Lake Cucao on Chiloe Island in south central Chile was inundated by the tsunami of the Great Chilean Earthquake (Mw 9.5). The area of what is now the lake basin has been submerged since the end of the rapid postglacial sea-level rise and has recorded tsunami inundations in its sediment record since then. This study reconstructs the tsunami history of Lake Cucao. Reflection-seismic profiles and side scan sonar data of the lake reveal a tidal delta with a crosscutting channel, which controls the sedimentary environment in the coast-facing part of Lake Cucao. The convergent pattern of seismic reflections near this channel indicates that tidal currents were active in the lake at least episodically since the formation of a major unconformity with strong reflection amplitude, which records the onset of lacustrine sedimentation. A radiocarbon date at the base of one of the 21 collected sediment cores dates this reflector to ~3800 years BP. Little net vertical displacement (≤2 m) in combination with an outlet river channel that can act as a pathway for sediment transport appears to have maintained the sensitivity of Lake Cucao to record tsunami inundation. The sedimentary record contains 15 clastic layers which are interpreted as tsunami deposits. The confidence level on the tsunami interpretation depends on five site-specific criteria, which are: (i) high magnetic susceptibility of the sediment indicating high clastic content, (ii) cross core correlation indicating widespread deposition, (iii) acoustic reflector correlation to the sedimentary record (also indicating widespread deposition), (iv) presence of mud clasts, and (v) age correlation to known paleotsunamis in the area. In this way, eight clastic layers are interpreted as tsunami deposits with a high confidence level, five with a medium confidence level and two with a relatively low confidence level. This study adds a long paleotsunami record on a coastline where extreme tsunamis occur frequently and where long (>2000 years) paleotsunami records are still sparse.

High-resolution records of calibrated proxy data for the past millennium are fundamental to place current changes into the context of pre-industrial natural forced and unforced variability. Although the need for regional spatially-explicit comprehensive reconstructions is widely recognized, the proxy data sources are still scarce, particularly for the Southern Hemisphere and especially for South America. We present a 600-year long warm season temperature record from varved sediments of Lago Plomo, a proglacial lake of the Northern Patagonian Ice field in Southern Chile (46°59′S, 72°52′W, 203 m a.s.l.). The thickness of the bright summer sediment layer relative to the dark winter layer (measured as total brightness; % reflectance 400–730 nm) is calibrated against warm season SONDJF temperature (1900–2009; r = 0.58, p (aut) = 0.056, RE = 0.52; CE = 0.15, RMSEP = 0.28 °C; five-year triangular filtered data). In Lago Plomo, warm summer temperatures lead to enhanced glacier melt and suspended sediment transport, which results in thicker light summer layers and to brighter sediments. Although Patagonia shows pronounced regional differences in decadal temperature trends and variability, the 600 years temperature reconstruction from Lago Plomo compares favourably with other regional/continental temperature records, but also emphasizes significant regional differences for which no data and information existed so far. These regional differences seem to be real as they are also reflected in modern climate data sets (1900–2010). The reconstruction shows pronounced subdecadal – multidecadal variability with cold phases during parts of the Little Ice Age (16th and 18th centuries) and in the beginning of the 20th century. The most prominent warm phase is the 19th century which is as warm as the second half of the 20th century. The exceptional summer warmth AD 1780–1810 is also found in other archives of Northern Patagonia and Central Chile. Our record shows the delayed 20th century warming in the Southern Hemisphere. The comparison between winter precipitation and summer temperature (inter-seasonal coupling) from Lago Plomo reveals alternating phases with parallel and contrasting decadal trends of winter precipitation and summer temperature (positive and negative running correlations R winter PP; summer TT ). This observation from the sediment proxy data is also confirmed by two sets of reanalysis data for the 20th century. Reanalysis data show that phases with negative correlations between winter precipitation and summer temperature (e.g., dry winters and warm summers) at Lago Plomo are characteristic for periods when circumpolar Westerly flow is displaced southward and enhanced around 60°S.

Temporal changes in the amounts of trace elements (As, Co, Cu, Mn, Ni, Pb, and Zn) and their correlations with temporal changes in charcoal abundance in age-dated sediments collected from Lake Thompson in Patagonia, Chile, attest to the substantial pyrogenic remobilization of contaminants that occurred in Patagonia during the mid-1900s. This remobilization was concurrent with the extensive slash and burn period in the region during that period. The changes in concentrations of Co, Cu, and Ni in relation to charcoal abundance in the lacustrine sediments over time were small compared to those of As, Mn, Pb, and Zn. However, the relatively low enrichment factors of all those trace elements, normalized to Fe, indicate that they were predominantly derived from local, natural sources impacted by fires rather than industrial sources. The primarily local source of Pb in the sediments was corroborated by the temporal consistency of its isotopic ratios (206Pb/207Pb:208Pb/206Pb), which were similar to previously reported values for natural lead in Central and Southern Chile. However, the pyrogenic remobilization of both natural and industrial trace elements by forest fires in Chile and elsewhere is expected to rise as a consequence of climate change, which is projected to increase both the frequency and intensity of forest fires on a global scale.

© 2015 International Association of Sedimentologists. Seismically induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent well documented great megathrust earthquakes provide an ideal opportunity to calibrate seismically induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 Mw 9·5 Valdivia and the 2010 Mw 8·8 Maule earthquakes in 17 lakes in South Central Chile (i.e. lakes Negra Lo Encañado Aculeo Vichuquén Laja Villarrica Calafquén Pullinque Pellaifa Panguipulli Neltume Riñihue Ranco Maihue Puyehue Rupanco and Llanquihue). A combination of image analysis magnetic susceptibility and grain size analysis allows identification of five types of seismically induced event deposits: (i) mass transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically induced event deposits were compared to local seismic intensities of the causative earthquakes eyewitness reports post earthquake observations and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin lacustrine turbidites type 1 are the most reliable type of seismically induced event deposits in quantitative palaeoseismology because they are almost exclusively triggered by earthquake shaking. Moreover they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity starting with no lacustrine turbidites type 1 at intensities between V1/2 and VI and reaching 100 when intensities are higher than VII1/2. Combining different types of seismically induced event deposits allows the reconstruction of the complete impact of an earthquake.

© 2015 Springer Verlag Berlin Heidelberg. Subaqueous slope failure mechanisms are still poorly understood partly because they are difficult to study due to the remote location of submarine landslides. Landslides in lakes are smaller in size and more readily accessible and therefore represent a good alternative to their marine counterparts. Lake Villarrica located in South Central Chile experienced significant slope failure and serves here as an exemplary study area for subaqueous landslide initiation mechanisms in tectonically active settings. Coring and CPTU testing were undertaken with the MARUM free fall CPTU deployed adjacent to the coring sites where all lithological units involved in the slope failure were sampled. Using geotechnical methods such as pseudo static factor of safety analysis and cyclic triaxial testing three types of soils (i.e. diatomaceous ooze volcanic ash and quick clay) were analyzed for their role in slope failure and earthquake shaking was identified as the primary trigger mechanism. The investigated landslide consisted of two distinct phases. During the first phase slope failure was initiated above a tephra layer. In the second phase retrogression led to the shoreward extension of the slide scarp along a second failure plane located in a stratigraphically deeper extremely sensitive lithology (i.e. quick clay). Results show that liquefaction of buried tephra layers was unlikely but such layers might still have contributed to a reduction in shear strength along the contact area with the neighboring sediment. Furthermore cyclic shaking induced pore pressure in diatomaceous ooze may be similar to that in granular soils. We generally infer that failure mechanisms observed in this study are equally important for landslide initiation in submarine settings as diatomaceous ooze intercalated with volcanic ash may be abundantly present along active continental margins.

Lake sediments contain valuable information about past volcanic and seismic events that have affected the lake catchment, and they provide unique records of the recurrence interval and magnitude of such events. This study uses a multilake and multiproxy analytical approach to obtain reliable and high-resolution records of past natural catastrophes from similar to 600-yr-old annually laminated (varved) lake sediment sequences extracted from two lakes, Villarrica and Calafquen, in the volcanically and seismically active Chilean Lake District. Using a combination of micro-X-ray fluorescence (mu XRF) scanning, microfacies analysis, grain-size analysis, color analysis, and magnetic-susceptibility measurements, we detect and characterize four different types of event deposits (lacustrine turbidites, tephra-fall layers, runoff cryptotephras, and lahar deposits) and produce a revised eruption record for Villarrica Volcano, which is unprecedented in its continuity and temporal resolution. Glass geochemistry and mineralogy also reveal deposits of eruptions from the more remote Carran-Los Venados volcanic complex, Quetrupillan Volcano, and the Huanquihue Group in the studied lake sediments. Time-series analysis shows 112 eruptions with a volcanic explosivity index (VEI) >= 2 from Villarrica Volcano in the last similar to 600 yr, of which at least 22 also produced lahars. This significantly expands our knowledge of the eruptive frequency of the volcano in this time window, compared to the previously known eruptive history from historical records. The last VEI >= 2 eruption of Villarrica Volcano occurred in 1991. Based on the last similar to 500 yr, for which we have a complete record from both lakes, we estimate the probability of the occurrence of future eruptions from Villarrica Volcano and statistically demonstrate that the probability of a 22 yr repose period (anno 2013) without VEI >= 2 eruptions is

On 21 April 2007, a Mw 6.2 earthquake struck Aysen fjord (Chilean Patagonia) and caused onshore and offshore mass movements which triggered tsunamis and density flows in the fjord. To better understand the facies successions in, and the intercalation of, the density-flow deposits, a study was made of the 2007 deposits in 22 short sediment cores taken in the inner Aysen fjord. By combining grain-size analysis with X-ray computed tomography scanning, it was possible to demonstrate that the encountered facies correspond to classical divisions of debrites and turbidites. The single-event deposits consist of a succession of several sub-deposits deposited under different flow directions and can be interpreted as stacked turbidites. Orientations of: (i) folds; (ii) imbricated mud clasts; iii) backsets and foresets of climbing ripples; and (iv) asymmetrical convolute lamination, were used to determine relative flow directions at the location of the cores. By assigning the basal flow of the stacked debrites and turbidites to the closest principal mass-flow, the absolute flow directions of the sub-deposits were determined which, in combination with multibeam basin-floor morphology, allowed reconstruction of the 2007 density-flow successions in Aysen fjord. Furthermore, alternating flow directions provide evidence for a seiche induced by the density flows. It was concluded that X-ray computed tomography scans provide crucial information for reconstructing palaeoflows and can be a useful tool in marine and lacustrine sedimentology and palaeoseismology. The multidirectionality of sub-deposits in turbidites is, next to differences in mineralogy, a new criterion to identify stacked turbidites. These multidirectional, stacked turbidites are an indication of simultaneous triggering of density flows and can therefore, in most cases, be attributed to earthquakes, ruling out other triggers, such as floods, storms or other sediment failures. This article is protected by copyright. All rights reserved.

The 2007 Mw 6.2 earthquake in Aysen fjord caused widespread basin-plain deformation and has had prehistorical predecessors. Both superficial and buried deformed basin-plain deposits are mapped using multibeam bathymetry and seismic-reflection (sparker) profiling. The seismic signature of the sediment was ground-truthed with short cores on key locations. Deformed basin-plain deposits induced by the 2007 earthquake can be divided in frontally emergent and confined deposits, with both a deep and shallow basal shear surface. All deformed basin-plain deposits with a deep basal shear surface are induced by the weight and impact of a slope-adjacent mass-flow wedge. The frontally emergent – most mobile – basin-plain deformation is triggered by mass flows originating from onshore mass movements (i.e. debris flows, rock slides and avalanches) propagating into the fjord. This basin-plain deformation results in vertical seafloor offsets of up to 20 m. Therefore it might be even more important for far-field tsunami propagation than the impact of the onshore mass movements on the sea surface. In the depressions created by the basin-plain deformation, megaturbidites occur, while more distally, sandy density-flow deposits cover the seafloor. The data also indicates that these density flows propagate slower than the basin-plain deformation. Based on correlations with the two main eruptions of the Hudson Volcano, we hypothesize that during the Holocene three to four similar events have struck the fjord. The small variability of the structural characteristics of the Liquine-Ofqui Fault Zone in the northern Patagonian fjordland and historical seismic swarms in this area make us conclude that similar hazards should be taken into account for most of the fjords in this region.

Due to its tectonic setting, the Andean Southern Volcanism Zone (SSVZ) is characterized by frequent volcanic activity. Chilean Patagonia lake sediments represent powerful archives of historical and past eruptions since the deglaciation. The lacustrine tephra record is investigated in 10 Holocene sedimentary cores collected in five lakes located along a 45–47° transect through Northern Chilean Patagonia. All the tephras identified by visual observation and strong magnetic susceptibility signal have been characterized for the major chemical composition of their glass shards by microprobe analyses, bulk mineralogical content by x-ray diffraction analyses and grain-size distribution by laser diffraction. Special care has been given to the chronostratigraphical framework in order to determine the age interval for each tephra layer and further to correlate the lacustrine records. The sedimentary age models are based on 210Pb data and calibrated radiocarbon dates measured on macroremains or reservoir effect-corrected bulk sediment. To present a more complete tephrochronological record, 28 microtephras have been confirmed by their mineralogical signature. Our lacustrine tephra record is compared with the Holocene eruptions registered in both surface deposits and continental, lacustrine and peat bog, environments. The different lacustrine eruption records are discussed according to their origin, age and location (distance from volcanoes, wind direction and dispersion of eruption produced). Our data confirm that Chilean Ande SSVZ tephras are mainly derived from historical and past Hudson eruptions. However, the peculiar low-K2O signature of the glass shards observed in one tephra layer from the Northernmost lake, Lake Thompson, confirms an influence from some other SSVZ volcanoes with low-abundance magma type, such as Maca and Cay. Our tephrochronological data compliment the database for volcanic activity in Chile bringing new information essential for the running discussion on the temporal distribution of eruptions over the Holocene.

Climate and environmental reconstructions from natural archives are important for the interpretation of current climatic change. Few quantitative high-resolution reconstructions exist for South America which is the only land mass extending from the tropics to the southern high latitudes at 56°S. We analyzed sediment cores from two adjacent lakes in Northern Chilean Patagonia, Lago Castor (45°36′S, 71°47′W) and Laguna Escondida (45°31′S, 71°49′W). Radiometric dating (210Pb, 137Cs, 14C-AMS) suggests that the cores reach back to c. 900 BC (Laguna Escondida) and c. 1900 BC (Lago Castor). Both lakes show similarities and reproducibility in sedimentation rate changes and tephra layer deposition. We found eight macroscopic tephras (0.2–5.5 cm thick) dated at 1950 BC, 1700 BC, at 300 BC, 50 BC, 90 AD, 160 AD, 400 AD and at 900 AD. These can be used as regional time-synchronous stratigraphic markers. The two thickest tephras represent known well-dated explosive eruptions of Hudson volcano around 1950 and 300 BC. Biogenic silica flux revealed in both lakes a climate signal and correlation with annual temperature reanalysis data (calibration 1900–2006 AD; Lago Castor r = 0.37; Laguna Escondida r = 0.42, seven years filtered data). We used a linear inverse regression plus scaling model for calibration and leave-one-out cross-validation (RMSEv = 0.56 °C) to reconstruct sub decadal-scale temperature variability for Laguna Escondida back to AD 400. The lower part of the core from Laguna Escondida prior to AD 400 and the core of Lago Castor are strongly influenced by primary and secondary tephras and, therefore, not used for the temperature reconstruction. The temperature reconstruction from Laguna Escondida shows cold conditions in the 5th century (relative to the 20th century mean), warmer temperatures from AD 600 to AD 1150 and colder temperatures from AD 1200 to AD 1450. From AD 1450 to AD 1700 our reconstruction shows a period with stronger variability and on average higher values than the 20th century mean. Until AD 1900 the temperature values decrease but stay slightly above the 20th century mean. Most of the centennial-scale features are reproduced in the few other natural climate archives in the region. The early onset of cool conditions from c. AD 1200 onward seems to be confirmed for this region.

Lago Puyehue is a glacigenic lake in the Chilean Lake District (40°S) with a complex deglaciation history. A detailed seismic–stratigraphic study of its sedimentary infill indicates a much earlier retreat of the glacier from the Lago Puyehue basin than the neighbouring glacier from the Lago Rupanco basin. Because of their close proximity, Rupanco meltwater streams played an important part in the depositional processes of Lago Puyehue. A timing discrepancy between the in-lake ages of a sediment core and the outer-lake ages of moraine deposits (re)opens the discussion on the timing of deglaciation in the Southern Hemisphere. Copyright © 2011 John Wiley & Sons, Ltd.

TanDEM-X digital elevation model (DEM) is a global DEM released by the German Aerospace Center (DLR) at outstanding resolution of 12 m. However, the procedure for its creation involves the combination of several DEMs from acquisitions spread between 2011 and 2014, which casts doubt on its value for precise glaciological change detection studies. In this work we present TanDEM-X DEM as a high-quality product ready for use in glaciological studies. We compare it to Aerial Laser Scanning (ALS)-based dataset from April 2013 (1 m), used as the ground-truth reference, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) V003 DEM and SRTM v3 DEM (both 30 m), serving as representations of past glacier states. We use a method of sub-pixel coregistration of DEMs by Nuth and Kääb (2011) to determine the geometric accuracy of the products. In addition, we propose a slope-aspect heatmap-based workflow to remove the errors resulting from radar shadowing over steep terrain. Elevation difference maps obtained by subtraction of DEMs are analyzed to obtain accuracy assessments and glacier mass balance reconstructions. The vertical accuracy (± standard deviation) of TanDEM-X DEM over non-glacierized area is very good at 0.02 ± 3.48 m. Nevertheless, steep areas introduce large errors and their filtering is required for reliable results. The 30 m version of TanDEM-X DEM performs worse than the finer product, but its accuracy, −0.08 ± 7.57 m, is better than that of SRTM and ASTER. The ASTER DEM contains errors, possibly resulting from imperfect DEM creation from stereopairs over uniform ice surface. Universidad Glacier has been losing mass at a rate of −0.44 ± 0.08 m of water equivalent per year between 2000 and 2013. This value is in general agreement with previously reported mass balance estimated with the glaciological method for 2012–2014.

We statistically reconstruct austral summer (winter) surface air temperature fields back to ad 900 (1706) using 22 (20) annually resolved predictors from natural and human archives from southern South America (SSA). This represents the first regional-scale climate field reconstruction for parts of the Southern Hemisphere at this high temporal resolution. We apply three different reconstruction techniques: multivariate principal component regression, composite plus scaling, and regularized expectation maximization. There is generally good agreement between the results of the three methods on interannual and decadal timescales. The field reconstructions allow us to describe differences and similarities in the temperature evolution of different sub-regions of SSA. The reconstructed SSA mean summer temperatures between 900 and 1350 are mostly above the 1901-1995 climatology. After 1350, we reconstruct a sharp transition to colder conditions, which last until approximately 1700. The summers in the eighteenth century are relatively warm with a subsequent cold relapse peaking around 1850. In the twentieth century, summer temperatures reach conditions similar to earlier warm periods. The winter temperatures in the eighteenth and nineteenth centuries were mostly below the twentieth century average. The uncertainties of our reconstructions are generally largest in the eastern lowlands of SSA, where the coverage with proxy data is poorest. Verifications with independent summer temperature proxies and instrumental measurements suggest that the interannual and multi-decadal variations of SSA temperatures are well captured by our reconstructions. This new dataset can be used for data/model comparison and data assimilation as well as for detection and attribution studies at sub-continental scales

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south-central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is situated in the urbanised area of the Biobio Region (36°S). The second lake, Lago Puyehue (40° S), is located 400 km to the southeast of LCSP and within an Andean national park. Our aim is to identify environmental impacts associated with increasing industrial activities and land degradation during the last 150 a. In LCSP, shifts in C/N atomic ratios, δ13C and δ15N from 1915–1937 to the late 1980s are attributed to successive land degradation episodes in the lake watershed. Based on a Pb isotopic mixing model, we estimate that up to 20% of lead in LCSP sediments is supplied from urban atmospheric pollution. By contrast, human impact in the watershed of Lago Puyehue is very limited. We observe no change in organic geochemistry during the last 150 a and lead contamination remains lower than 5%, even during the last decades. Although contamination levels are much higher in LCSP than in Lago Puyehue, a peak in anthropogenic Pb is recorded during the same period (1974–1976) at both sites. This maximum contamination level is consistent with increased industrial activity in the vicinity of Concepcion. Copyright © 2010 John Wiley & Sons, Ltd.

We present a pigment-based quantitative high-resolution (five years) austral summer DJF (December to February) temperature reconstruction for Central Chile back to AD 850. We used non-destructive in situ multichannel reflection spectrometry data from a short sediment core of Laguna Aculeo (33°50′S/70°54′W, 355 m a.s.l., central Chile). Calibration-in-time (period AD 1901—2000, cross-validated with split periods) revealed robust correlations between local DJF temperatures and total sedimentary chlorin (relative absorption band depth (RABD) centred in 660—670 nm RABD660;670: r=0.79, P660nm/670 nm: r=0.82, P

Prior to the collection of a series of sediment cores, a high- and very-high-resolution reflection seismic survey was carried out on Lago Puyehue, Lake District, South-Central Chile. The data reveal a complex bathymetry and basin structure, with three sub-basins separated by bathymetric ridges, bedrock islands and interconnected channels. The sedimentary infill reaches a thickness of >200 m. It can be sub-divided into five seismic-stratigraphic units, which are interpreted as: moraine, ice-contact or outwash deposits (Unit I), glacio-lacustrine sediments rapidly deposited in a proglacial or subglacial lake at the onset of deglaciation (Unit II), lacustrine fan deposits fed by sediment-laden meltwater streams in a proglacial lake (Unit III), distal deposits of fluvially derived sediment in an open, post-glacial lake (Unit IV) and authigenic lacustrine sediments, predominantly of biogenic origin, that accumulated in an open, post-glacial lake (Unit V). This facies succession is very similar to that observed in other glacial lakes, and minor differences are attributed to an overall higher depositional energy and higher terrigenous input caused by the strong seismic and volcanic activity in the region combined with heavy precipitation. A long sediment core (PU-II core) penetrates part of Unit V and its base is dated as 17,915 cal. yr. BP. Extrapolation of average sedimentation rates yields an age of ca. 24,750 cal. yr. BP for the base of Unit V, and of ca. 28,000 cal. yr. BP for the base of Unit IV or for the onset of open-water conditions. This is in contrast with previous glacial-history reconstructions based on terrestrial records, which date the complete deglaciation of the basin as ca. 14,600 cal. yr. BP. This discrepancy cannot be easily explained and highlights the need for more lacustrine records from this region.

Very high resolution reflection seismic profiling (3.5 kHz) revealed nine Holocene mass-wasting events in Lake Puyehue (South-Central Chile). These events are made up of numerous coeval mass-wasting deposits and some homogenites, which are radiocarbon-dated. The two youngest mass-wasting events could be attributed to the giant AD 1960 and AD 1575 Valdivia earthquakes. The most extensive event took place around 1660 cal yr BP. Evaluation of all possible slope failure processes led us to infer that giant earthquakes, roughly comparable to the AD 1960 Valdivia earthquake (Mw = 9.5), are the most likely trigger mechanisms of all mass-wasting events in Lake Puyehue. These occurred with a mean recurrence rate of 1000 yr although relatively aperiodically (ranging between 500 and 2000 yr). Quantitative comparison of mass-wasting events related to historically reported earthquakes (AD 1960 and AD 1575) showed significant differences although these earthquakes are assumed to have had a comparable strength. A lowered background sedimentation rate could be responsible for this variable earthquake recording, which highlights the importance of a thorough assessment of the depositional history before using lacustrine records for quantitative paleoseismic analysis.

Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past enviro nmental changes. In this study, we report changes i n diatoms, pollen, and chironomids assemblages after a tephra deposition in Lake Galletue (Chilean Andes). A sedi ment core obtained from Lake Galletue (40 m water depth) was sliced in 1 cm intervals and subsamples were t aken to analyze each proxy. 210 Pb and 137 Cs activities were measured to obtain the geochrono logy and mineralogical analyses were performed to determine the mineral co mposition of the tephra. Diatom species composition and productivity were modified when the lake received t he tephra; Aulacoseira granulata decreased and was later replaced by Cyclotella af. glomerata. After the tephra input, Aulacoseira granulata abundance increased to predisturbance levels and Cyclotella af. glomerata decreased. These changes seem to suggest a momentary increase in lake nutrient levels after the tephra deposition . Chironomid assemblages also decreased in head capsules just after the tephra deposition, but the most important change was the replacement of Ablabesmyia by Parakiefferiella, probably due to the sedimentological changes produced by the input of coarse tephra grains. Furthermore, unlike other studies, chironomid assem blages in Lake Galletue did not show a decrease dra stically in diversity within the tephra layer. The pollen an alysis indicated that, prior to the volcanic event, the vegetal community was dominated by Nothofagus sp., Araucaria araucaria, and Blechnum sp.-type. After the tephra deposition, the same taxa are dominant, indicating that the volcanic event seems not produce changes i n the vegetation. Nevertheless, within the tephra layer i t is possible to see an increase in Poaceae, which represent due to the percolation process - the effect of erup tion on the vegetation. According to our results, d iatoms were the most sensitive proxy for describing the changes produced by tephra deposition into the aquatic eco system and, despite the noticeable changes in its sediment ological properties; the lake seems to have a high resilience capacity, allowing it to return to pre-tephra input conditions.

Short-term climate changes in Southern Chile are investigated by a multi-proxy analysis of a 53-cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40°S). This core contains a 600-yr-long undisturbed record of paleo-precipitation changes. Two measurement methods for sediment density, organic matter and biogenic silica contents are compared and the most appropriate techniques are selected. Together with aluminium and titanium concentrations, grain size and geochemical properties of the organic matter, these proxies are used to demonstrate paleo-precipitation changes around 40°S. Increase of terrigenous particle supply between A.D. 1490 and A.D. 1700 suggests a humid period. Contemporaneously, δ13C data show increasing lake productivity, in response to the high nutrient supply. The A.D. 1700–1900 interval is characterized by a decreasing terrigenous supply and increasing δ13C values, interpreted as a drying period. The magnetic susceptibility signal, reflecting the terrigenous/biogenic ratio, demonstrates that similar variations occur in all the undisturbed sedimentary environments of Lago Puyehue. The A.D. 1490–1700 wet period is associated with the onset of the European Little Ice Age (LIA) and interpreted as its local signature. This work supports the fact that the LIA was a global event, not only restricted to the Northern Hemisphere.

Stable isotopes in mollusk shells have been widely used for hydrological balance reconstructions. However, their use is restricted to lakes that preserve the calcareous material of the shells. Lago Cisnes is located in Patagonia (47°S) and shows a continuous record of three species of mollusk during the past 5000 years. The isotopic records of δ18O in Pisidium sp., Lymnaea sp., and Biomphalaria sp. show discrepancies among them, which can be explained by the differential effect that evaporation has on the habitat where each species lives. Between 1800 and 500 cal. yr BP, the three species show similar isotopic variations, suggesting that climatic condition affecting in the same way the different microhabitats in the lake. Around 1700 cal. yr BP, an enrichment of 18O on mollusks shells indicates drier conditions that prevails until 1100 cal. yr BP. Later on, isotopic signal tends to decrease, suggesting a humid period between 750 and 500 cal. yr BP. Such humid conditions lasted until 170 cal. yr BP, which were evidenced only by Biomphalaria sp. and Pisidium sp. Climate variability during the late Holocene in Lago Cisnes is in agreement with marine records from northern Patagonia, which would suggest westerlies weakening during a northward migration after 1100 cal. yr BP and/or an important temperature control on the evaporation, where low temperatures could decrease the evaporation driven by the westerlies. Additional records in this area would be requested to clarify the westerlies effects on the east flank of the Andes.

Central Chile (32–35°S) lies at the northern border of strong Westerly influence and thus exhibits a steep precipitation gradient. Therefore, the palaeoclimatic archives in the region are suitable for detecting past moisture changes. The study of Laguna Aculeo (33°50'S, 70°54'W) presents a multiproxy Holocene lake record including sedimentology, geochemistry, mineralogy, pollen, diatoms, and radiocarbon dating (17 dates). Results indicate an arid early to mid-Holocene period (about 9500–5700 cal yr B.P.). After 5700 cal yr B.P. effective moisture increased progressively and around 3200 cal yr B.P., modern humid conditions were established. Numerous intercalated clastic layers reflect flood deposition during rainy winters. A fluvial unit was deposited shortly before 9000 cal yr B.P. Subsequently, flood events were absent until 5700 but have become frequent since 3200 cal yr B.P. The frequency of flood layers possibly points to weak or no El Niño activity during the early and mid-Holocene, with a subsequent increase during the late Holocene. During the early and mid-Holocene, the Westerlies were probably blocked and hence deflected southward by the subtropical high-pressure cell. Higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high-pressure cell with intensified Westerlies and possibly increased El Niño activity.

The multi-proxy study of lacustrine sediments from Laguna Aculeo (33°50′S) provides detailed information about moisture changes in the lowlands of Mediterranean Central Chile during the last 2000 years. The lake lies just at the northern border of the strong Westerlies influence with dry summers and humid winters. Geochemical, sedimentological and diatom analyses provide evidence for an arid period between cal 200 BC and AD 200 and a subsequent increase in moisture after cal AD 200. Abundant clastic layers in the core represent flood events. Periods with a higher frequency of flood events indicate an increased intensity of the Westerlies, more winter frontal system activity and possibly ENSO-related variability, probably comparable to modern conditions in Mediterranean Central Chile. Periods of high clastic input occur around cal AD 200–400, 500–700, especially around cal AD 1300–1700, and around AD 1850–1998. During the last 50 years, at least eight flood events were detected, correlating mainly with El Nino years. A very short drier period also occurred in the late 1960s. In recent decades, human impact has resulted in a eutrophication of the lake.

Two different methodologies were used for estimating the historical variations in soil losses for a lacustrine watershed in the Nahuelbuta Mountain Range (Laguna Chica de San Pedro, VIII Region). The first approach is based on the Universal Soil Loss Equation (USLE), while the second one focuses on an isotopic analysis ( 210Pb) of the lake sediments. In both cases, important temporal variations in sediment production were obtained. Values estimated with the USLE equation ranged from 0.45 to 1.00 t ha - 1 yr- 1 . Alternatively, values determined by isotopic analysis were between 0.10 and 1.16 t ha-1 yr- 1 . Comparing the results of both methodologies, similar tendencies can be observed for the years 1955-1981. However, some significant differences appeared both at the beginning and at the end of 1943-1955 and 1981-1994. This could be explained by the low resolution of USLE, since in this study it cannot distinguish the differential soil protection offered by native forest or exotic forestry.

High-resolution records of calibrated proxy data for the past 2000 yr are fundamental to place current changes into the context of pre-industrial natural forced and unforced variability. Although the need for regional spatially explicit comprehensive reconstructions is widely recognized, the proxy data sources are still scarce, particularly for the Southern Hemisphere and South America. We provide a 1500 yr long warm season temperature record from varved Lago Plomo, a proglacial lake of the Northern Patagonian Ice field in southern Chile (46°59' S, 72°52' W, 203 m). The thickness of the bright summer sediment layer relative to the dark winter layer (measured as total brightness; % reflectance 400–730 nm) is calibrated against warm season SONDJF temperature (1900–2009; r = 0.58, p(aut) = 0.056, RE = 0.52; CE = 0.15, RMSEP = 0.28 °C; five-year triangular filtered data). In Lago Plomo, warm summer temperatures lead to enhanced glacier melt and suspended sediment transport, which results in a thicker light summer layer and to brighter sediments (% total brightness). Although Patagonia shows pronounced regional differences in decadal temperature trends and variability, the 1500 yr temperature reconstruction from Lago Plomo compares favourably with other regional/continental temperature records but also emphasizes significant regional differences for which no data and information existed so far. The reconstruction shows pronounced sub-decadal–multi-decadal variability with cold phases in the 5th, 7th and 9th centuries, during parts of the Little Ice Age chronozone (16th and 18th centuries) and in the beginning of the 20th century. The most prominent warm phase is the 19th century which is as warm as the second half of the 20th century, emphasizing a delayed recent global warming in the Southern Hemisphere. The comparison between winter precipitation and summer temperature (inter-seasonal coupling) from Lago Plomo reveals alternating phases with parallel and contrasting decadal trends of winter precipitation and summer temperature and positive and negative running correlations(winterPP;summerTT). In the 20th century the trend of this correlation changes at 1920, 1945 and 1975 AD, and the phases with positive (negative) correlations inferred from the lake sediments are also found as a regional robust pattern in reanalysis data, and coincide with the changes of the instrumental PDO index. Enhanced circumpolar flow around 60° S is proposed for positive phases of PDO which leads to the reversed coupling and contrasting decadal trends of winter precipitation and summer temperature during PDO positive phases. Our reconstruction of the inter-seasonal coupling back to 1530 AD reproduces many features of existing PDO reconstructions from the Pacific suggesting that Lago Plomo provides a record for the regional expression of the PDO in Patagonia.

The combined influence of freshwater inputs and wind-driven upwelling may generate contrasting environmental conditions over small spatial scales in the coastal ocean. Over two consecutive years (mid-2006 through to mid-2008), we compared the springtime and wintertime composition, biomass, and primary production of the main phytoplankton groups at two coastal stations (RV and UW) near the Itata River mouth in the upwelling area off central Chile. Hydrographic and nutrient profiles showed distinct seasonal features: a relatively weak surface thermocline and weak river influence at both stations in spring, and in winter a stronger surface halocline at station RV, located closer to the river mouth. At both stations, primary production (24–8000 mg C m−2 d−1) and chlorophyll-a concentrations (5–20 mg Chl-a m−3) were highest in the spring, with a dominance of microphytoplankton (Chaetoceros spp., Thalassiosira spp.). Total primary production and chlorophyll-a in the winter corresponded mostly to smaller size fractions (pico- and nanoplankton), which dominated the phytoplankton community (>50%) in terms of carbon biomass at station RV. At this river-influenced station, small autotrophic and heterotrophic groups (

High-resolution climate reconstructions from a range of natural archives across the world are fundamental to place current climate change into perspective. Paleoclimate records for the Southern Hemisphere are scarce and only a few quantitative high-resolution reconstructions exist for the past millennium. We present a record of annually laminated sediments of Lago Plomo (46°59′S, 72°52′W,203 m a.s.l.) located east of the Northern Patagonian Ice Field (NPI). Radiometric dating (210Pb, 137Cs, 14C AMS) is consistent with counts of millimetre-scale laminae, confirming the annual nature of the laminae couplets with a light summer and a dark winter layer. The varves were analyzed for thickness, mass accumulation rate (MAR), scanning x-ray fluorescence (XRF) and scanning reflectance spectroscopy in the visible range (VIS-RS). MAR data were calibrated against austral winter (JJA) precipitation data (CRU TS 3.0) for the period ad 1930–2002 ( r = 0.67, p(aut) < 0.05). Using a linear inverse regression model we reconstructed winter precipitation for Lago Plomo back to ad 1530. The root mean squared error of prediction (RMSEP) is small (13.3 mm/month; 12% of the average precipitation) compared with the pronounced decadal and multidecadal variability, suggesting that most of the reconstructed variability is significant. Wetter phases (reference ad 1930–2002) were observed around ad 1600, ad 1630–1690 and ad 1780–1850, and a prolonged drier period ad 1690–1780 with a multidecadal minimum centered on ad 1770. The spatial correlation for South America suggests that the JJA precipitation record from Lago Plomo is representative for large areas in the southwest between c. 41°S and 51°S.

The offset between AMS radiocarbon ages obtained on bulk lake sediments and the true age of deposition was evaluated at four sites in Northern Chilean Patagonia. Our results show that the bulk radiocarbon ages are systematically older by 300 to 1100 years. In this region free of carbonate and carbonaceous rocks, we argue that this difference results from variable inputs of terrestrial organic carbon from the Holocene soils that cover the lake watersheds. For the four studied lakes, the age offset is clearly related to the fraction of terrestrial carbon preserved in the lake sediments, which was estimated using the N/C ratio of the bulk organic matter. We propose that N/C measurements can be used to significantly improve chronologies based on radiocarbon dating of bulk lake sediments.

A dense grid of very-high resolution seismic profiles on Lake Villarrica provides a quasi-3D view on intercalated lenses of low-amplitude reflections, which are connected by acoustic wipe-out patches and fractures to an underlying voluminous mass-wasting deposit. The lenses are interpreted as being created by earthquake-triggered liquefaction in this buried mass-wasting deposit and subsequent sediment fluidization and extrusion at the paleo-lake bottom. These sediment volcanoes are mapped in detail. They have a rather uniform circular geometry and show a linear relationship between apparent width and maximum thickness on a seismic section. The largest sediment volcanoes are up to 80 m wide and 1.9 m thick. Their slope angles designate a syn- to post-depositional sagging of most sediment volcanoes. Sediment volcano detection and mapping from nearby Lake Calafquen further strengthen the revealed geometrical relationships. Locally, some of the sediment/fluid escape structures extend to a higher position in the stratigraphy, which points to a polyphase escape process associated with multiple multi-century spaced strong earthquakes. Thickness and morphology of the source layer seem to exert a dominant control in the production of sediment/fluid extrusions. This study shows that reflection seismic profiling allowed recognizing 4 different seismic events in the studied stratigraphic interval, which are evidenced by mass-wasting deposits and/or fluidization features.

High-resolution and highly precise age models for recent lake sediments (last 100–150 years) are essential for quantitative paleoclimate research. These are particularly important for sedimentological and geochemical proxies, where transfer functions cannot be established and calibration must be based upon the relation of sedimentary records to instrumental data. High-precision dating for the calibration period is most critical as it determines directly the quality of the calibration statistics. Here, as an example, we compare radionuclide age models obtained on two high-elevation glacial lakes in the Central Chilean Andes (Laguna Negra: 33°38′S/70°08′W, 2,680 m a.s.l. and Laguna El Ocho: 34°02′S/70°19′W, 3,250 m a.s.l.). We show the different numerical models that produce accurate age-depth chronologies based on 210Pb profiles, and we explain how to obtain reduced age-error bars at the bottom part of the profiles, i.e., typically around the end of the 19th century. In order to constrain the age models, we propose a method with five steps: (i) sampling at irregularly-spaced intervals for 226Ra, 210Pb and 137Cs depending on the stratigraphy and microfacies, (ii) a systematic comparison of numerical models for the calculation of 210Pb-based age models: constant flux constant sedimentation (CFCS), constant initial concentration (CIC), constant rate of supply (CRS) and sediment isotope tomography (SIT), (iii) numerical constraining of the CRS and SIT models with the 137Cs chronomarker of AD 1964 and, (iv) step-wise cross-validation with independent diagnostic environmental stratigraphic markers of known age (e.g., volcanic ash layer, historical flood and earthquakes). In both examples, we also use airborne pollutants such as spheroidal carbonaceous particles (reflecting the history of fossil fuel emissions), excess atmospheric Cu deposition (reflecting the production history of a large local Cu mine), and turbidites related to historical earthquakes. Our results show that the SIT model constrained with the 137Cs AD 1964 peak performs best over the entire chronological profile (last 100–150 years) and yields the smallest standard deviations for the sediment ages. Such precision is critical for the calibration statistics, and ultimately, for the quality of the quantitative paleoclimate reconstruction. The systematic comparison of CRS and SIT models also helps to validate the robustness of the chronologies in different sections of the profile. Although surprisingly poorly known and under-explored in paleolimnological research, the SIT model has a great potential in paleoclimatological reconstructions based on lake sediments.

Galletue Lake (38° 41'S; 71° 17'W,IX Region-Chile) is located in an area that is highly influenced by eruptive activity of the Lonquimay and Llaima volcanoes. As a consequence, during the last century tephra was deposited into the lake. Sedimentary diatom assemblages were reconstructed in order to establish the tephra effect on their composition and productivity. This was done by taking a sediment core from Galletue Lake at 40m depth and sectioning it in 1 cm intervals. The core age was obtained with 210 Pb and 137 Cs activities and the mineral composition of the tephra was determined with mineralogical analyses. Furthermore, sedimentological analyses were performed and total organic matter was determined in the profile. The diatom assemblages were analysed using light and electronic microscopy. The results showed that the diatom stratigraphy can be separated in three zones recognizing the periods before and after tephra input. Aulacoseira granulata decreased during the tephra influx and was replaced by Cyclotella aff. glomerata. When the tephra disappeared from the sedimentary record, A. granulata returned to pre-volcanic event levels. At the same time, Cyclotella aff. glomerata decreased within the assemblages. Asterionella formosa and Urosolenia eriensis increased after the tephra input, with values surpassing earlier ones. These results indicate that, after the tephra input, the lake recovered its previous nutrient levels, which agrees with the organic matter content in the sedimentary matrix. Finally, the results reveal that the volcanic disturbance changed the structure and productivity of diatom assemblages in Galletue Lake.

This paper describes lake sediment spheroidal carbonaceous particle (SCP) profiles from Laguna Chica San Pedro, located in the Biobío Region, Chile (36 degrees 51' S, 73 degrees 05' W). The earliest presence of SCPs was found at 16 cm depth, corresponding to the 1915-1937 period, at the very onset of industrial activities in the study area. No SCPs were found at lower depths. SCP concentrations in Laguna Chica San Pedro lake sediments were directly related to local industrial activities. Moreover, no SCPs were found in Galletué lake (38 degrees 41' S, 71 degrees 17.5' W), a pristine high mountain water body used here as a reference site, suggesting that contribution from long distance atmospheric transport could be neglected, unlike published data from remote Northern Hemisphere lakes. These results are the first SCP sediment profiles from Chile, showing a direct relationship with fossil fuel consumption in the region. Cores were dated using the 210Pb technique.

Se analizan las asociaciones de restos sub-fosiles de quironomidos y los parametros sedimentologicos de un nucleo sedimentario del lago Galletue (38°41' S, 71°17' O). Es evidente en este nucleo la presencia de un estrato de sedimentos volcanicos (tefra) de una composicion distinta en el contenido deµmateria organica, en el tamano de particula y en la mineralogia, respecto de los sedimentos del lago. De acuerdo a la geocronologia isotopica (210Pb y 137Cs), los sedimentos de esta tefra podrian corresponder a la erupcion del volcan Llaima de 1956-1957. Por otra parte la depositacion de esta tefra tambien provoco un cambio en las asociaciones de quironomidos, siendo evidente el aumento de Parakiefferiella y la disminucion de Ablabesmyia dentro del estrato de tefra. Si bien nuestros resultados, al igual que estudios previos, registran un cambio en las asociaciones de quironomidos debido a la entrada de sedimentos volcanicos, un aspecto diferente es la presencia de capsulas cefalicas dentro de la tefra. Una posible explicacion a tal diferencia podria ser la percolacion de los restos de quironomidos por los espacios intersticiales de la tefra. La recuperacion en la abundancia de algunos taxa luego de la depositacion de la tefra, sugiere que el lago restableceria las condiciones existentes previo a la caida de la tefra