Austral Andes Research Articles

Multisequal aeolian deposition during the Holocene in southwestern Patagonia (51°S) was modulated by southern westerly wind intensity and vegetation type

We studied a multisequal soil succession (MSS) just south of Torres del Paine National Park (51°S), at the present-day core of the Southern Westerly Winds (SWW). The Río Serrano Section comprises paleosol horizons with associated intervening loess and sandy loess beds formed during the Holocene. Our record suggests strong and stable aeolian activity between ∼9.3–7.2 ka followed by a decline with centennial-scale variations until ∼5 ka. A strengthening commenced at ∼5 ka and culminated in a maximum between ∼2.2–0.5 ka with millennial-scale variations. Subsequent weakening of aeolian activity between ∼0.5 and 0 ka was coeval with the deposition of a ∼40 cm-thick paleosol, after which aeolian activity increased abruptly and reached an unprecedented maximum starting in the mid-20th century. The inferred wind intensity variations from our data bear partial agreement with competing hypotheses of SWW evolution, which postulate minimum SWW influence in SW Patagonia during the early Holocene and maximum influence during the Late Holocene, or vice versa. When analyzed through the lens of vegetation physiognomy/distribution and associated hydrological balance inferences from neighboring sites, our results suggest a primary control by precipitation and wind speeds associated to SWW strength at regional scale, modulated by the position of the forest/steppe ecotone east of the austral Andes. Human activities during the mid-20th century (deforestation, fire-regime shifts, livestock grazing, land use changes) caused an unprecedented increase in aeolian activity through decreased vegetation cover that increased sediment availability for aeolian transport, marking a striking difference with the magnitude of natural processes before the Anthropocene. Our results highlight the importance of climate change and natural/human-driven changes in vegetation cover for deciphering wind intensity histories, particularly in the transition from humid to semiarid environments along the eastern slope of the southern Patagonian Andes.

Didymium pseudonivicola: A new myxomycete from the austral Andes emerges from broad-scale morphological and molecular analyses of D. nivicola collections

ABSTRACT A new nivicolous myxomycete is described as a result of a comprehensive study of Didymium nivicola collections from the entire range of its occurrence. Statistical analysis of 12 morphological characters, phylogenetic analyses of nuc 18S rDNA and elongation factor 1-alpha gene (EF1A), and a delimitation method (automatic barcode gap diversity) have been applied to corroborate the identity of the new species. A preliminary morphological analysis of D. nivicola revealed high variability of South American populations where four types of spore ornamentation were noted. However, results of molecular study and statistical analysis of morphological characters did not support recognition of these four forms but the distinction of two morphotypes. Consequently, two species have been recognized: D. nivicola and the newly proposed D. pseudonivicola. The new species can be distinguished from D. nivicola by distinctly larger and mostly plasmodiocarpic sporophores, which are scattered to gregarious, paler spores, and by the paler, more delicate and more elastic capillitium. Spore ornamentation of D. pseudonivicola is uniform and can be described as distinctly spiny (pilate under scanning electron microscope [SEM]), whereas those of D. nivicola is more variable, where spines (pilae under SEM) are delicate, distinct, or conspicuous. Additionally, whereas D. nivicola is a species distributed worldwide, D. pseudonivicola occurs only in the austral Andes of Argentina and Chile.

Range-wide Phylogeography of a Nivicolous Protist Didymium nivicola Meyl. (Myxomycetes, Amoebozoa): Striking Contrasts Between the Northern and the Southern Hemisphere

Soil protists play a crucial role in terrestrial ecosystems and often show immense taxonomic diversity. However, for many groups, distribution patterns remain largely unknown. We investigated range-wide intraspecific diversity of a specialized airborne protist (Didymium nivicola Meyl.) that occupies a narrow ecological niche associated with long-lasting snow cover. We sampled 122 collections covering all areas where the species was recorded worldwide. We obtained 105 and 41 sequences of small ribosomal subunit rDNA (SSU) and elongation factor 1-alpha (EF1A), respectively. While the species is very diverse in the austral Andes, Southern Hemisphere (SH; 17 SSU ribotypes and 12 EF1A genotypes identified), its populations are genetically uniform across three continents of the Northern Hemisphere (NH; single ribotype, single genotype). Our results indicate the austral Andes as a possible diversification centre for D. nivicola where populations seem to reproduce sexually. Two main parts of the range display highly contrasting genetic patterns, thus biogeographical history and dynamics. Current distribution of D. nivicola in the NH is likely a result of a dispersal event from the SH and subsequent long-distance dispersal (LDD) that might be associated with a shift to asexual mode of reproduction.

A tree-ring δ18O series from southernmost Fuego-Patagonia is recording flavors of the Antarctic Oscillation

A 154 year-long, tree-ring based stable oxygen isotope time series (δ 18 O TRC ) of the evergreen southern beech ( Nothofagus betuloides ) was established for the southernmost part of Patagonia. The trees grew on the terminal moraine system of the Schiaparelli Glacier (54.4°S) within the windward and hyper-humid zone of the Austral Andes. The annually resolved δ 18 O TRC record spans the common period 1861–2015 and is based on the analysis of five individually analyzed tree individuals showing a significant mean interseries correlation ( r = 0.69). To date, this time series represents the worldwide southernmost chronology of tree-ring δ 18 O TRC . Variations of the δ 18 O TRC values are significantly correlated with hydroclimatic conditions, as derived from ERA-Interim reanalysis gridded data. Negative relationships between the δ 18 O TRC -series and relative humidity (r Oct-Feb = −0.62, p < 0.0001) or the amount of precipitation (r Jan-Feb = −0.52, p < 0.0001) can be observed for the austral spring and summer seasons. In contrast, a drier environment will increase the δ 18 O TRC as revealed by a positive influence of evaporation (r Sep-Feb = 0.44, p < 0.01), sea level pressure (r Oct-Feb = 0.56, p < 0.0001) or maximum temperature (r Oct-Feb = 0.43, p < 0.01). Spatial correlation maps indicate a strong supra-regional influence of climate variables on the chronology. The annular pressure seesaw, termed as Antarctic Oscillation (AAO), mostly influences climate variability within the Southern Hemisphere and is positively correlated with the δ 18 O TRC -chronology (r JF = 0.61, p < 0.0001). Since our chronology, as well as a neighboring δ 18 O TRC -chronology from the Perito Moreno Glacier (50°S), are showing a high correspondence in their sensitivities to climate variabilities and towards the AAO, we merged both time series into a mean chronology. This new regional mean δ 18 O TRC -chronology is highly sensitive to variations of the AAO ( r = 0.79, p < 0.0001)) and is tested for the suitability to reconstruct the AAO for the last 150 years. The reconstructed time series of the AAO reveals an increasing trend towards more positive index values, which is associated with an amplification in the amount of precipitation and wind speed in southernmost South America. • Southernmost existing tree-ring cellulose (δ 18 O TRC ) time series from the hyper-humid Austral Andes, Tierra del Fuego. • Highly significant hydroclimate imprints on δ 18 O TRC of the evergreen southern beech ( Nothofagus betuloides ). • Strong fingerprints of the Antarctic Oscillation (AAO) are reflected in δ 18 O TRC from Southern Patagonia. • Annual reconstruction of the Antarctic Oscillation based on tree-ring δ 18 O TRC since 1860.

Nivicolous Trichiales from the austral Andes: unexpected diversity including two new species

ABSTRACT Nivicolous myxomycetes are a group of amoebozoan protists dependent on long-lasting snow cover worldwide. Recent fine-scale analysis of species diversity from the austral Andes revealed high intraspecific variability of most taxa, suggesting independent evolutionary processes and significant differences in species compositions between the Northern (NH) and Southern (SH) Hemispheres. The present study is the second part of this analysis based on representatives of Trichiales. A total of 173 South American collections were studied based on morphological and molecular data, and 15 taxa have been identified. Two of them, Hemitrichia crassifila and Perichaena patagonica, are proposed as new species confirmed by a phylogeny of Trichiales. However, their affinity to the genera in which they are proposed are not confirmed due to polyphyletic character of all genera of Trichiales. Four species, Dianema subretisporum, Trichia contorta var. karstenii, T. nivicola, and T. sordida, are reported for the first time from the Southern Hemisphere. One species, T. alpina, is new for Argentina. Additionally, we provide the first record of Perichaena megaspora from Chile. Specimen frequency and species diversity of Trichiales found at nivicolous localities in the austral Andes are unexpectedly high, exceeding those of Stemonitidales, the most numerous group in the Northern Hemisphere, where Trichiales play a marginal role. By contrast, Trichiales appear the main component of nivicolous assemblages in the Andes. Results of the present work, together with the earlier analysis of Stemonitidales, indicate that the Andes constitute an exceptionally important evolutionary hot spot for nivicolous myxomycetes characterized by an outstanding species diversity.

Las dinámicas familiares en torno al videojuego social Fortnite

In 2017 the company Epic Games created the videogame Fortnite. This game has become the cross-platform survival and open experience with the greatest penetration worldwide. The rapid increase of use has spread alarm voices among parents and the media have echoed these concerns criticizing the game for being responsible for most afflictions suffered by children and adolescents. 178 The study is based on an understanding of the game as a key element in personal and social development. Therefore, this project aims to explore and describe the specific interactions emerging as a result of the penetration of Fortnite into family life, seeking to extend our understanding of the phenomenon and the potential effects that it may produce in the family dynamics. The research also seeks to categorize the dynamics generated, emphasizing more specifically on implications for parents in terms of educative mediation. Concerning the methodology, this is a qualitative exploratory case study, in which observations and in-depth interviews are the main sources of data collection. According to the analysis of the first interviews and observations, it is possible to provisionally hypothesize that, unlike simplistic views spread through mass media of Fortnite as a new dangerous addictive platform for young people, the diverse contexts and realities that configure each family make this type of linear interpretations highly problematic. Most technological devices affect the interaction and relational dynamics already installed in families. Throughout the last forty years, television and offline video games have been playing a significant role in shaping the family relationships. Online environments today increase such influence. The complex interrelations generated in blended social ecosystems, such as 'what is' or 'what is not' permitted, the mechanism of videogame banning or use as a form of punishment or reward, the myths, and ignorance on the part of adults concerning the ‘virtual’ socialization of youth and the relevance of this practice among young people, are some of the contributions that can be drawn from this investigation. This presentation exposes the collaborative work conducted by researchers of Universidad Austral (Argentina) and Universidad de los Andes (Chile), which has gained the first place in the award provided by the Network of Latin American University Institutes of Family (REDIFAM).

Seismic stratigraphy and glacial cycles in the inland passages of the Magallanes Region of Chile, southernmost South America

We present results of a marine geophysical survey that imaged submarine sedimentary and geomorphic features of the main inland channels of the Magallanes Region of Chile, in southernmost South America. This region holds a remarkable terrestrial and marine record of glacial variations in the closest landmass to Antarctica. We report evidence for grounded ice along the main channels associated with two ice lobes that flowed from Cordillera Darwin, part of the Austral Andes, into Central Estrecho de Magallanes and Seno Almirantazgo. Multibeam data show drumlins and glacial lineations in Whiteside Channel the northern continuation of Seno Almirantazgo, and iceberg plough marks in Central Estrecho de Magallanes. Multichannel seismic data show a complex array of seismic facies, interpreted as representing two main types of sedimentary units: glacimarine sediments, corresponding to glacial periods, and pelagic sediments, corresponding to interglacial periods. We find that there are two interglacial-glacial cycles represented in this marine sedimentary record. Chronologically: 1) the youngest glacial unit corresponds to the last regional glaciation (~31–18ka); 2) these passageways deglaciated with the retreat from regional glacial limit ‘D’ (~17–18ka), and 3) there is no marine sedimentary or morphological evidence that the Magallanes glaciers readvanced into the main passageways during the Antarctic Cold Reversal (~14–13ka). These findings suggest that final deglaciation of southernmost South America was driven by the atmospheric and ocean warming that started ~18ka as recorded in Antarctic ice core records and sea surface temperature proxies offshore the Magallanes Region.

Nivicolous Stemonitales from the Austral Andes: analysis of morphological variability, distribution and phenology as a first step toward testing the large-scale coherence of species and biogeographical properties

Nivicolous myxomycetes occur at the edge of spring-melting snow in mountainous areas. They are mostly considered cosmopolitan species morphologically and ecologically uniform across their entire distribution ranges. Thus, long-distance dispersal has been suggested to be the main mechanism shaping their ranges and geographical variability patterns. To test this hypothesis we conducted the first detailed analysis of morphological variability, occurrence frequency and phenology of nivicolous myxomycetes collected in the hitherto unexplored Austral Andes of South America (southern hemisphere = SH) in the comparative context of data from the northern hemisphere (NH). We used Stemonitales, the most representative and numerous taxonomic order in nivicolous myxomycetes, as a model. A total of 131 South American collections represented 13 species or morphotypes. One of them, Lamproderma andinum, is new to science and described here. Several others, L. aeneum, L. album, L. pulveratum, “Meriderma aff. aggregatum ad. int.”, M. carestiae and “M. spinulosporum ad. int.”, were previously unknown from the SH. Lamproderma ovoideum is reported for the first time from South America and Collaria nigricapillitia is new for Argentina. The fine-scale morphological analysis of all species from the study area and reference NH material demonstrated a high intraspecific variability in most of them. This suggests isolation and independent evolutionary processes among remote populations. On the other hand, the uniform morphology of a few species indicates that long-distance dispersal is also an effective mechanism, although not as universal as usually assumed, in some nivicolous myxomycetes. Analysis of nivicolous species assemblages also showed significant differences among major geographic regions in that the Stemonitales were significantly less common in the SH than in the NH. Furthermore, the occurrence of nivicolous species in summer and autumn, out of the typical phenological season, is recognized as a possible distinctive phenomenon for the SH populations.

Lightning in Western Patagonia

AbstractOn the basis of 8 years (2005–2012) of stroke data from the World Wide Lightning Location Network we describe the spatial distribution and temporal variability of lightning activity over Western Patagonia. This region extends from ~40°S to 55°S along the west coast of South America, is limited to the east by the austral Andes, and features a hyper‐humid, maritime climate. Stroke density exhibits a sharp maximum along the coast of southern Chile. Although precipitation there is largely produced by cold nimbostratus, days with more than one stroke occur up to a third of the time somewhere along the coastal strip. Disperse strokes are also observed off southern Chile. In contrast, strokes are virtually nonexistent over the austral Andes—where precipitation is maximum—and farther east over the dry lowlands of Argentina. Atmospheric reanalysis and satellite imagery are used to characterize the synoptic environment of lightning‐producing storms, exemplified by a case study and generalized by a compositing analysis. Lightning activity tends to occur when Western Patagonia is immersed in a pool of cold air behind a front that has reached the coast at ~40°S. Under these circumstances, midlevel cooling occurs before and is more prominent than near‐surface cooling, leading to a weakly unstable postfrontal condition. Forced uplift of the strong westerlies impinging on the coastal mountains can trigger convection and produces significant lightning activity in this zone. Farther offshore, large‐scale ascent near the cyclone's center may lift near‐surface air parcels, fostering shallow convection and dispersing lightning activity.

Hafnium isotope evidence for slab melt contributions in the Central Mexican Volcanic Belt and implications for slab melting in hot and cold slab arcs

This study presents evidence that Quaternary frontal arc calc-alkaline lavas from Central Mexican Volcanic Belt (CMVB) contain contributions from partial melts of the subducting garnet-bearing eclogitic oceanic crust and sediment, based on chemical and Hf–Nd isotope data. The CMVB includes both calc-alkaline lavas with arc-type trace element patterns such as aqueous fluid mobile element enrichments and high field strength element depletions; and “high-Nb” alkaline lavas with trace element patterns similar to ocean island basalts. The two types of lavas are closely related geographically and temporally. Distinct from the high-Nb lavas, the calc-alkaline lavas show trends toward higher 176Hf/177Hf and 143Nd/144Nd ratios coupled with lower Lu/Hf. The high Hf–Nd isotope ratios fingerprint contributions of subducted basaltic ocean crust, while the correlation with low Lu/Hf indicates melting in the presence of residual garnet, which reflects conversion of the subducted oceanic crust to eclogite. Isotopic and chemical mass balance considerations indicate that the slab melts are ~80% basaltic oceanic crust and ~20% subducted sediment. The calc-alkaline lavas have higher SiO2 at a given Mg# compared to the high-Nb alkaline lavas, also reflecting melt contributions from the subducted slab.A survey of global arc lavas shows that calc-alkaline lavas with low Lu/Hf ratios, reflecting melting in the presence of residual garnet and preferential mobilization of Hf over Lu from the subducted slab, are generally associated with hot slab conditions. These include arcs where young (<30Ma old) ocean crust is subducted (e.g. Mexican Volcanic Belt, Cascades, Austral Andes, Luzon, Setouchi), where slab tearing occurred and hot asthenospheric mantle could upwell through the slab window (e.g., western Aleutians, Sunda, southern Scotia), and where oblique or slow subduction leads to higher slab temperatures (e.g. Lesser Antilles, western Aleutians). In some of these hot slab arcs, where low Lu/Hf ratios are coupled with high Nd–Hf isotope ratios, slab melt contributions are dominated by partial melts from the subducted oceanic basalt (e.g., Mexican Volcanic Belt, Aleutians and Cascades). In other hot slab arcs, low Lu/Hf ratios are coupled with low Nd–Hf isotope ratios, reflecting slab contributions dominated by sediment melts (e.g. Setouchi, Lesser Antilles, Luzon, Sunda, and southern Scotia). Arcs associated with colder subducted oceanic crust (e.g. Izu–Bonin–Marianas, Tonga–Kermadec, central and northern Scotia) erupt lavas with high Lu/Hf along with high Hf–Nd isotope ratios, similar to mid-ocean ridge basalts, thus they lack the signature of residual garnet as well as significant slab melt input.

Large-Scale Control on the Patagonian Climate

Abstract Patagonia, located in southern South America, is a vast and remote region holding a rich variety of past environmental records but a small number of meteorological stations. Precipitation over this region is mostly produced by disturbances embedded in the westerly flow and is strongly modified by the austral Andes. Uplift on the windward side leads to hyperhumid conditions along the Pacific coast and the western slope of the Andes; in contrast, downslope subsidence dries the eastern plains leading to arid, highly evaporative conditions. The authors investigate the dependence of Patagonia’s local climate (precipitation and near-surface air temperature) year-to-year variability on large-scale circulation anomalies using results from a 30-yr-long high-resolution numerical simulation. Variations of the low-level zonal wind account for a large fraction of the rainfall variability at synoptic and interannual time scales. Zonal wind also controls the amplitude of the air temperature annual cycle by changing the intensity of the seasonally varying temperature advection. The main modes of year-to-year variability of the zonal flow over southern South America are also investigated. Year round there is a dipole between mid- and high latitudes. The node separating wind anomalies of opposite sign migrates through the seasons, leading to a dipole over Patagonia during austral summer and a monopole during winter. Reanalysis data also suggests that westerly flow has mostly decreased over north-central Patagonia during the last four decades, causing a drying trend to the west of the Andes, but a modest increase is exhibited over the southern tip of the continent.

Volcanic hotspots of the central and southern Andes as seen from space by ASTER and MODVOLC between the years 2000 and 2010

Abstract We examine 150 volcanoes and geothermal areas in the central, southern and austral Andes for thermal anomalies between the years 2000 and 2010 from two different spaceborne sensors: (1) those automatically detected by the MODVOLC algorithm from MODIS; and (2) manually identified hotspots in night-time images from ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer). Based on previous work, we expected to find eight volcanoes displaying thermal anomalies (Ubinas, Villarrica, Copahue, Láscar, Llaima, Chaitén, Lonquimay and Chiliques). We document 35 volcanic areas with pixel-integrated temperatures of 4 up to more than 100 K above background in at least two images, and another 16 areas that have questionable hotspots with either smaller anomalies or a hotspot identified in only one image. Most of the thermal anomalies are related to known activity (i.e. lava and pyroclastic flows, growing lava domes, fumaroles, and lakes) while others are of unknown origin or reflect activity at volcanoes that were not thought to have surface activity. A handful of volcanoes exhibit temporal variations in the magnitude and location of their temperature anomalies that can be related to both documented and undocumented pulses of activity. Our survey reveals that low-amplitude volcanic hotspots detectable from space are more common than expected, based on lower spatial resolution data, and that these features could be more widely used to monitor changes in the activity of remote volcanoes. We find no evidence from ASTER or MODVOLC that the thermal anomalies were affected by six earthquakes with M w above 7 in our study area from 2000 to 2010, although the observations may not have been optimal to detect such anomalies. Supplementary material: Supplementary tables of data and figures for the volcanoes studied are available at http://www.geolsoc.org.uk/SUP18581 .

Crustal and upper mantle structure of southernmost South America inferred from regional waveform inversion

We determine the crustal and upper mantle structure of southern South America by inverting regional seismograms recorded by the Seismic Experiment in Patagonia and Antarctica. We present a waveform inversion method that utilizes a niching genetic algorithm. The niching genetic algorithm differs from the traditional genetic algorithm in that the inversion is performed in multiple subpopulations, thus generating a broader search of the model space and enabling us to examine alternative local error minima. The vertical and transverse waveforms were used, extending from the P arrival to the surface waves, and the inversion was performed at either 0.005–0.06 Hz (larger events) or 0.02–0.06 Hz (smaller events). The inversion included anisotropy by solving for separate SV and SH structures in the upper mantle. Results indicate that crustal thickness varies from 26 to 36 km with thicker values toward the northeast, suggesting that there is little crustal thickening beneath the austral Andes. The average upper mantle velocities are similar to the preliminary reference Earth model (PREM) except that the southernmost region shows velocities of 5% slower than PREM. The upper mantle has up to 5% polarization anisotropy between the Moho and 120 km depth. The strongest anisotropy is localized in a lithospheric lid shallower than 65 km depth, which overlies a pronounced low‐velocity zone. This shallow limit to anisotropy is consistent with the relatively small shear wave splitting values found in this region. These results suggest that the anisotropy is limited to lithospheric depths and may imply the absence of a strong mantle flow pattern in the asthenosphere.

Biogeographic delimitation of the Subantarctic subregion and its provinces

The Subantarctic subregion, which belongs to the Andean region of the Austral kingdom, comprises the austral Andes from 37 ° south latitude to Cabo de Hornos, the archipelago of southern Chile and Argentina, and the Malvinas, South Georgia, and Juan Fernandez islands. The Subantarctic subregion comprises six provinces: Maule (southern Chile and Argentina, between 34-37 ° south latitude), Valdivian (southern Chile and Argentina, south of the Maule province, reaching 47 ° south latitude), Magellanic forest (southern Chile from 47 ° south latitude to Cabo de Hornos, and southern Argentina in small portions of western Santa Cruz and Tierra del Fuego), Magellanic moorland (southern Chile and Argentina, limited by the Magellanic forest province to the east), Malvinas islands (Argentinean archipelago of the Malvinas or Falkland islands and South Georgia island, situated in the south Atlantic ocean, about 550 km from Tierra del Fuego), and Juan Fernandez islands (Chilean islands of Masatierra or Robinson Crusoe, Masafuera or Alejandro Selkirk, and Santa Clara, situated in the Pacific ocean, 600 km west of Valparaiso, at 33° south latitude).