Southern Patagonia Research Articles

Jurassic Osmundaceous Landscapes in Patagonia: Exploring the Concept of Ecological Stasis in the Deseado Massif, Argentina

Herein, we report the presence of a plant paleocommunity, dominated by ferns of the family Osmundaceae, structurally preserved from the only known Mesozoic, fossiliferous geothermal deposits, from the La Matilde Formation (Middle-Upper Jurassic) in the Deseado Massif of Southern Patagonia, Argentina. A total of 13 siliceous chert blocks sampled in an area of approximately 250 m2, preserving a monotypic assemblage dominated by Osmundaceae embedded within its original swampy substrate, are documented. Additional Osmundaceae and fewer ferns and conifers are present in the stratigraphically continuous, adjacent chert levels. This association is comparable to those dominated by Osmundaceae in modern swampy settings, such as in high-altitude lagoons in the Paraná Forest in Northeastern Argentina. In addition, a diverse community of mutualistic, parasitic, and saprotrophic microorganisms associated with the ferns and conifers in the assemblage is present. These compositional, paleoenvironmental, and trophic characteristics of the Jurassic Osmundaceae suggest a possible case of ecological stasis, where Osmundaceae-dominated plant communities apparently persisted in swamps of comparable structures, functions, and physical characteristics for over 150 million years. This suggests that Osmundaceae formed similar communities in compatible settings in the Jurassic, becoming preserved in analogous configurations.

Development of an early warning system to reduce the impact of floods related to glacial lake outburst floods (SAGAZ)

Abstract. The retreat of glaciers has led to increasing in natural hazards due, for example, by emptying of lakes dammed by unconsolidated glacial deposits (moraines) or ice, which are susceptible to catastrophic erosion, generating rapid floods, phenomena known as “Glacial Lake Outburst Floods” (GLOFs). Current systems that warn of the occurrence of a GLOF are activated when the emptying begins, which leaves little time to act, so they should be considered early alarm systems. The challenge is to predict the onset of the flood allowing the generation of an early warning system. To address this problem, SAGAZ ultimately aims to develop a system capable of identifying periods of increased GLOF risk using a predictive model fed by weather forecasts and monitoring station data. This system identifies a period of higher risk, which allows informing authorities several days in advance. This paper presents the results of the first phase of SAGAZ implementation, which aimed to (1) develop and validate a prototype monitoring station and deploy a network of stations on glacial lakes across southern Patagonia, (2) collect the necessary data for the development, training and validation of predictive models and (3) begin the implementation and testing of the predictive model. As a result, a network of 10 monitoring stations was installed in the Aysén and Magallanes regions of Chile and 1 in the Province of Santa Cruz in Argentina, of which 6 are currently operational and transmitting data in real time. The rest went off due to power failures and icebergs damaging sensors. The measures we have taken to avoid station’s failures are described, as well as some characteristics of the implemented prototype, the installed networks and the data obtained so far.

Temporal Estimation of Snow Line Altitude in Glaciers of the Southern Patagonian Icefield Using Google Earth Engine

Abstract. The study analyzes the variability over time of the Snow Line Altitude (SLA) and its correspondence with the Equilibrium Line Altitude (ELA) in four glaciers of the Southern Patagonian Icefield (SPI): Perito Moreno, Upsala, Viedma and De los Tres. Using Google Earth Engine and Landsat satellite imagery, an automated algorithm based on the Otsu image segmentation method was developed to analyze the 1985–2023 time series to obtain the Snow Cover Ratio (SCR) and subsequently estimate the SLA using the ALOS World 3D DSM. The study employed the near infrared (NIR) and shortwave infrared (SWIR) bands of Landsat images, with the SCR and subsequently the SLA determined using only the NIR band, as well as a band ratio between the NIR/SWIR bands. The results indicated that the Viedma glacier showed a statistically significant positive trend in SLA elevation, while the other three glaciers showed a stationary behavior with high variability. The SLA calculated using the NIR/SWIR bands tended to be higher compared to the NIR band calculation, especially for the Viedma and Upsala glaciers. Comparisons with previous studies (De Angelis, 2014; Popovnin et al., 1999) and recent glaciological measurements from the Inventario Nacional de Glaciares (2015–2022) showed that the SLA derived from the NIR bands aligned more closely with the aforementioned works.

Ice flow line maps of three large freshwater calving glaciers in the Southern Patagonian Icefield

Abstract. The Southern Patagonian Icefield is experiencing rapid retreat and thinning in its calving glaciers. To better understand the dynamics of these changes, we generated ice flow line maps for the Viedma, Upsala, and Pio XI glaciers during 2017–2018. An evenly spaced streamline placement algorithm, integrating topographic and flow curvature criteria, was employed to calculate over 2,700 streamlines per glacier at a 50-meter resolution. The algorithm's performance was assessed by comparing the generated flow lines with manually digitized reference lines, resulting in a mean error, standard deviation, and root mean square error of 57.35, 33.62, and 66.46 meters, respectively. The resulting maps reveal detailed flow structures, highlighting flow lines from accumulation to ablation zones, increased velocities in central areas, tributary flows merging with main channels, and regions of flow convergence and divergence. Additionally, the glaciers' 3D lengths were estimated by identifying the longest ice flow lines, with Pio XI measuring 62.27 km, Viedma 54.49 km, and Upsala 51.24 km. We consider that the methodology used, along with the generated maps, provides excellent visual and analytical tools for identifying glacier areas, lengths, and shapes, defining ice origins and glacier catchment boundaries, and analysing zones of flow convergence and divergence—parameters that are critically important for understanding the dynamics, geometry, and evolution of glaciers in this region.

Changes in guanaco distribution from Late Holocene to present times in Northwest Patagonia: connecting archaeological, ethnohistoric and current data

Context The guanaco (Lama guanicoe) is one of the four species of South American camels, and is the largest native mammal inhabiting arid and semi-arid environments in South America. Although the guanaco was abundant and widely distributed in the past, currently its density and distribution range are substantially reduced, inhabiting mainly Southern Patagonia in small isolated groups. The decline in guanaco populations is most likely related to the Anthropocene defaunation process that is affecting large mammals in developing countries worldwide, but the extent and causes of these changes are not well understood. Aims To explore both the changes in the distribution of guanaco populations in Northwest Patagonia and the environmental and anthropic factors that shaped the distribution patterns, by employing a long-term perspective spanning from the end of the Late Holocene to present times (i.e. the last 2500 years). Methods We combine archaeological information, ethnohistorical records and current observations and apply Species Distribution Models using bioclimatic and anthropic factors as explanatory variables. Key results Guanaco spatial distribution in Northwest Patagonia changed significantly throughout time. This change consisted in the displacement of the species towards the east of the region and its disappearance from northwest Neuquén and southwest Mendoza in the last 30 years. In particular, the high-density urban settlements and roads, and secondly, competition with ovicaprine livestock (goats and sheep) for forage are the main factors explaining the change in guanaco distribution. Conclusions Guanaco and human populations co-existed in the same areas during the Late Holocene and historic times (16th to 19th centuries), but during the 20th century the modern anthropic impact generated a spatial dissociation between both species, pushing guanaco populations to drier and more unproductive areas that were previously peripheral in its distribution. Implications As with many other large mammal species in developing countries, Northwest Patagonia guanaco populations are undergoing significant changes in their range due to modern anthropic activities. Considering that these events are directly related to population declines and extirpations, together with the striking low density recorded for Northwest Patagonia guanaco populations, urgent management actions are needed to mitigate current human impacts.

Zooplankton community in coastal waters of the Southern Patagonian Shelf during early autumn: diversity and distribution pattern linked to regional water circulation

Zooplankton community in coastal waters of the Southern Patagonian Shelf during early autumn: diversity and distribution pattern linked to regional water circulation

Multiple late Holocene glacier advances on the sub-Antarctic Kerguelen (49°S) islands: Evidence from a 1200 yr sediment core from a glacial threshold basin

Southern Ocean (SO) climate is rapidly changing because of global warming and regional climate feedback loops like shifts of the Southern Hemisphere (SH) westerly winds (SHW) and related Southern Annular Mode (SAM). Over the past decades, the former has been persistently positive, shifting the latter southwards: the ensuing changes in temperature and precipitation are linked to the rapid retreat of mid-latitude mountain glaciers. Beyond the short instrumental period, the long-term impact of this coupled SHW-SAM system on regional glaciers remains poorly constrained. To help close this gap, we reconstruct glacier advances from an outlet glacier on the sub-Antarctic Kerguelen (49°S, 69°E), an archipelago that is strategically located in an under-investigated region of the SHW core belt. Based on alternations between relatively organic and minerogenic mud detected using a multiproxy approach on a 1200-year-long sediment record from a glacial threshold basin, we document glacier advances between 1150 and 850, 820–620, 500–250 and 160–90 cal yr BP. Coincident glacier advances in adjacent regions like sub-Antarctic South Georgia and southern Patagonia, suggest that SO glaciers responded symmetrically to climate forcings during the past 1200 years. We attribute this synchronicity to shifting SAM-like conditions and associated temperature changes. We suggest that cold and negative SAM-like conditions, favourable for glacier growth on the Kerguelen and other SO land masses, dominated during much of this period. Furthermore, the findings presented here support the growing consensus for a two-phased regional expression of the Little Ice Age (LIA).

Detrital zircon provenance links between outcrop and subsurface, Rocas Verdes and Magallanes-Austral Basins, Patagonia

Analyzing how provenance signatures of tectonically complex ancient sedimentary basins vary between the outcrop and the subsurface provides a more complete sediment provenance history. The 500+-km-long outcrop belt of the Rocas Verdes and the Magallanes-Austral Basins in southern Patagonia and its subsurface to the east allow us to constrain relationships between longitudinal and transverse sediment sources feeding the basin. New detrital zircon U-Pb ages (n = 2558) from nine subsurface core samples from the Springhill, Piedra Clavada, and La Anita Formations along a 140 km E-W seismic reflection transect (50°S, 71.5°W–69.5°W) reveal the provenance of the basin’s eastern subsurface extent and the influence that tectonic activity can have on sediment capture. Detrital zircon ages (n = 1068) were also collected from four outcrop Springhill Formation samples 140 km NW from the transect near Lago San Martín. Maximum depositional ages (MDAs) from the Springhill Formation cores range from 159 to 157 Ma, which are older than correlative outcrop ages of 151–148 Ma. MDAs from the Piedra Clavada and La Anita Formations range from 93.7 to 91.5 Ma and from 79.3 to 78.3 Ma, respectively, and overlap in age or are slightly younger than outcrop ages. The unimodal Late Jurassic age distribution from the Springhill Formation suggests that it almost exclusively was sourced by recycling of the underlying El Quemado Complex. Early–Middle Jurassic ages in the Early Cretaceous Piedra Clavada Formation samples suggest the basin was either sourcing from the North Patagonian Massif to the N-NE and from the Deseado Massif to the NE or recycling exhumed volcaniclastic sequences in the northern margin of the basin. By the Late Cretaceous, the basin fill was more locally sourced, as suggested by the muted abundance of Early–Middle Jurassic ages in La Anita Formation samples and a second mode of Late Jurassic–Early Cretaceous ages locally derived from recycling of the exhumed El Quemado Complex from the Patagonian fold-and-thrust belt. We suggest that the latitudinal and local transverse drainages that sourced the Magallanes-Austral Basin outcrop belt also fed the eastern, subsurface extent of the basin. Results of this work highlight the importance of using several types of provenance methods and a three-dimensional approach to study the erosional history of sedimentary basins.

Retention Levels and Years-After-Harvesting Influence over Soil Microbial Activity and Biomass in Southern Patagonian Forests

Variable retention harvesting (VRH) was designed for timber purposes and biodiversity conservation in natural forests. This system was globally tested, but few studies are related to soil microbial components. The objective was to evaluate different retention types (aggregated and dispersed retention) considering different years-after-harvesting (6, 9, 16 YAH) on soil microbial community attributes compared with unmanaged primary forests (PF) in Nothofagus pumilio forests of Tierra del Fuego (Argentina). This study also evaluated the influence of climate, soil, and understory vegetation. Results showed that aggregated retention increased microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and soil basal respiration (SBR) compared to dispersed retention, but with similar values than PF. However, harvested areas decreased MBC/MBN values compared with PF. The results showed an overall decrease in microbial biomass and activity in 9 YAH stands, with a positive recovery at 16 YAH. Soil pH, mean annual temperature, and understory vegetation cover showed a positive relationship with MBC, MBN, and SBR. The recovery after 16 YAH reached to different microbial communities. Therefore, the maintenance of retention components in managed stands for longer periods is needed. The results highlight some advantages of VRH as a tool for conservation of forest-dwelling soil microorganisms, including microbial biomass and activity.

Endscrapers Variability and Differential Use of Landscapes During the Late Holocene in Central-Western Santa Cruz, Patagonia

ABSTRACT In the last 2500 years BP the environment of Southern Patagonia was affected by significant climatic changes. In this scenario, in the central-western portion of Santa Cruz province (Patagonia, Argentina), hunter-gatherer populations made a complementary use of the different ecological areas (highlands and lowlands). Differences in artefactual assemblages have been recorded in these areas. Within this context, we analyze variability in the most frequent lithic artifact from the region: endscrapers. We assess morphology and compare results between different sectors from highlands and lowlands. The question is whether the morphology of endscrapers also differs between ecological areas. Quantitative (length, width and thickness) and qualitative variables (raw material and blank type) were measured on 514 endscrapers. Results show that there are no statistical differences between highlands and lowlands. Variability in dimensions is only detected for some raw materials. Indeed, standardization in the morphology of this type of tool is proposed for the period under study.

Glacier Fragmentation on the Southern Patagonian Icefield: A Comprehensive Analysis of the Upsala Glacier

Glacier Fragmentation on the Southern Patagonian Icefield: A Comprehensive Analysis of the Upsala Glacier

Magnetotelluric image of the Patagonian slab window: Constraints on upper mantle physical properties and sources of intraplate magmatism

The Patagonian slab window (PSW) is a region of the Southamerican subduction zone where the absence of subducted slabs is interpreted, due to the subduction of the Chile Mid-Ocean Ridge at the Chile Triple Junction. Here we report the results of a long-period magnetotelluric (MT) study conducted in two 300 km-long trench-parallel transects crossing the northern boundary of the PSW in the proximal backarc. We modeled the MT data using 3-D inversion, obtaining an electrical resistivity model of the continental crust and upper mantle up to a depth of ∼150 km. Our model shows a heterogeneous resistivity structure in the uppermost mantle, dominated by resistivities >300 Ωm below the array of sites even within the PSW, and some low-resistivity zones (LRZs, <10 Ωm) mainly at the edge of the array. Using petrophysical models, we estimated the mantle temperature, water content, melt fraction, and viscosity based on obtained resistivity values and a preexistent model of P-wave velocity (Vp) at 50 km and 100 km depth. These estimates suggest that the uppermost mantle within the PSW region is heterogeneous and dominated by high-viscosity blocks, compatible with the continental mantle lithosphere or even subducted slabs. Based on relatively hot and low-viscosity zones estimated in the periphery of LRZs, we interpret the presence of asthenospheric mantle in areas where LRZs coincide with relatively low Vp. According to this interpretation, asthenospheric upwelling in the study area at depths ≤150 km would be localized rather than ubiquitous over the interpreted extent for the PSW. Such localized asthenosphere upwelling processes in the past could explain the scattered distribution of Neogene basaltic lavas in the southern Patagonia backarc. The continental crust exhibits LRZs in the upper and lower crust. Remarkably, ensembles of LRZs at different crustal depths within the presumable area of the PSW were found below the General Carrera Lake, and towards the North Patagonian Icefield, likely indicating the presence of hidden intraplate magmatic and/or hydrothermal systems.

Precipitation drives western Patagonian glacier variability and may curb future ice mass loss.

Two-thirds of all glaciers worldwide are projected to disappear by 2100 CE. Large uncertainties however remain in maritime settings, where some glaciers have recently gained mass in response to increased snowfall. One of these regions is southern Patagonia, where increased precipitation since the 1980s seems to have attenuated glacier retreat. Whether this exceptional behavior will continue in a warmer future is unclear. Here, we use a numerical ice-flow model constrained by paleoglaciological data to simulate how climate variability influenced the evolution of three maritime outlet glaciers of the Southern Patagonian Icefield during the last 6000 years. Our experiments suggest that precipitation drove 67% of the centennial-scale fluctuations in the volume of the modeled glaciers. When applied to the temperature projected by 2100 CE, our simulations show that precipitation needs to increase by 10-50% to maintain present-day glacier volumes, depending on the climate scenario (SSP1-2.6 to SSP5-8.5). This implies that if greenhouse-gas emission cuts fail, these glaciers will enter a warmer regime unseen over the last 6000 years, where precipitation cannot offset glacier mass loss. Conversely, if emissions are curtailed, increased precipitation could halt mass loss of some of Patagonia's largest glaciers, and potentially of other maritime glaciers worldwide.

Similar sources but distinct δ13C signatures in adjacent low-temperature travertines from Laguna Amarga (Southern Patagonian Andes)

This study examined the waters and carbonates from two cold spring travertines (ca. 13 °C) located on the sun-exposed (north-facing travertine) and sun-shaded (south-facing travertine) margins of Laguna Amarga, an alkaline lake from the semiarid region of the eastern Patagonian Andes (51°S).The travertines are composed of calcite + low-Mg calcite ± aragonite. Both exhibit similar sedimentological transitions along their longitudinal profiles. In the proximal zones, biologically-influenced carbonates form in wetland-like environments. Spherulitic calcite precipitates in association with extracellular polymeric substances in microbial biofilms containing cyanobacteria-like molds at the vent of the south-facing travertine, while aragonite spherulite formation at the north-facing travertine vent also involves sulfate-reducing bacteria, as indicated by their close association with framboidal pyrite. Downstream, in the intermediate and distal zones, crystalline dendrites predominantly precipitate due to increased turbulence-induced CO2 degassing.Both travertines share a similar range of carbonate 87Sr/86Sr composition (0.70720–0.70740) and isotopic signatures of the spring waters, including δ2H (ca. −110 ‰ VSMOW), δ18Owater (ca. −14 ‰ VSMOW) and δ13C-DIC (ca. −5 ‰ VPDB), suggesting common sources and processes influencing fluid composition. This points to the dissolution of carbonates from mudstone-rich marine units of the Lower Cretaceous (δ13C ca. −1 ‰ VPDB) and Upper Cretaceous (δ13C ca. −10 ‰ VPDB) during shallow subsurface circulation of meteoric waters through the bedrock. The carbon isotopic composition of the deposits resembles those of endogenic travertines (δ13Ctrav −1.2 to 5.3 ‰ VPDB), with the highest δ13Ctrav values associated with carbonates from the vents. However, the involvement of deep CO2 sources is unclear and epigenic processes capable of producing the observed 13C enrichments are discussed.Despite their common sources, similar sedimentological features and δ18Otrav compositional range (−12.4 to −10.1 ‰ VPDB), the δ13Ctrav values are lower in the south-facing travertine (−1.2 to 1.9 ‰ VPDB) compared to the north-facing travertine (1.8 to 5.3 ‰ VPDB). This disparity is inferred to result from variations in local environmental conditions due to different levels of insolation, which favored the incorporation of soil-derived CO2 in the south-facing travertine and likely increased photosynthetic productivity in the north-facing travertine, thereby shifting their δ13Ctrav signatures to lower and higher values, respectively. These relationships highlight the sensitivity of low-temperature spring carbonates to subtle environmental changes at basin scales.

Do Streptomyces sp. Help Mycorrhization in Raspberry?

Actinobacteria may help the mycorrhizal symbiosis by producing various bioactive metabolites. Mycorrhizae, in turn, are very important since they increase the absorption of nutrients, promoting the growth of their host plant and making inoculation with arbuscular mycorrhizae fungi (AM) a common practice applied in agriculture and forestry. The cultivation of Rubus idaeus (raspberry) is widespread in Patagonia, Argentina; however, the potential benefits of using actinobacteria-mycorrhizal inoculums to enhance crop growth and yield remain unexplored. The objective of this work was to study the interaction between actinobacteria (Streptomyces, Actinomycetota) and AM in raspberry plants. We performed an experiment applying 4 treatments to raspberry plants growing in two substrates, sterile soil and natural (non-sterile) soil. The treatments consisted in a control (without inoculation) and three inoculations treatments (AM, Streptomyces SH9 strain, and AM + Streptomyces). After 3months of inoculation, mycorrhization parameters (%) and plant growth were recorded. When comparing both substrates, the mycorrhization parameters were higher in natural soil than in sterile soil. The co-inoculation with AM + Streptomyces SH9 showed the highest mycorrhization. Both factors (treatment x substrate) interacted showing that in sterile soil the treatments with the highest effect on mycorrhization parameters were AM and the co-inoculation, while in natural soil all inoculations improved mycorrhization parameters, being highest with the co-inoculation. These results show that Streptomyces SH9 strain helps the mycorrhizal symbiosis in raspberry, being the first report about the effect of a native rhizospheric actinobacterium on an economically important species, promising potential for environmentally friendly improvements in raspberry crops within the temperate Southern Patagonian region.

Magellanic ecological identity: comparison between groups from different cultural and regional backgrounds / Identidad ecológica magallánica: comparación entre grupos de orígenes culturales y territoriales diferentes

This study investigates the relationship between ecological identity and various social and pro-environmental variables among the inhabitants of Southern Patagonia, comparing groups with internal (Chilote) and external (Croatian) migratory ancestry. A total of 212 individuals participated, selected based on their self-categorization as Magellanic, identifying as descendants of Croatian ( n = 71), Chilote ( n = 66) or other origin ( n = 75). We used a non-experimental cross-sectional correlational design to measure regional identity, pro-environmental attitudes, ecological behaviour, essentialism and regionalism. Findings point to differences in ecological variables between the groups compared. Magellanic participants with Chilote ancestry show a stronger relationship between ecology and identity than those with Croatian ancestry. The findings are discussed in terms of the impact of indigenous cultures on the current relationship of Magellanic inhabitants with their natural environment and the importance attributed to territoriality.

Ectomycorrhizal fungi and the nitrogen economy of Nothofagus in southern Patagonia.

Subantarctic Nothofagus forests are the southernmost forests in the world, with negligible atmospheric nitrogen (N) deposition. Most paradigms about the role of ectomycorrhizal (ECM) fungi in N cycling and plant N uptake at high latitudes have been tested in boreal coniferous forests, while in the southern hemisphere, ECM hosts are primarily angiosperms. Using ITS1 meta-barcoding, we characterized ECM and saprotrophic fungal communities in evergreen and deciduous Nothofagus forests forming monodominant and mixed stands in the archipelago of Tierra del Fuego (Chile and Argentina). We assessed the N economy of Nothofagus by correlating host species with fungal relative abundances, edaphic variables, net N mineralization, microbial biomass N and the activity of eight extracellular soil enzymes activities. The N economy of deciduous N. pumilio forests was strikingly similar to boreal coniferous forests, with the lowest inorganic N availability and net N mineralization, in correlation to higher relative abundances of ECM fungi with enzymatic capacity for organic N mobilization (genus Cortinarius). In contrast, the N economy of evergreen N. betuloides forests was predominantly inorganic and correlated with ECM lineages from the family Clavulinaceae, in acidic soils with poor drainage. Grassy understory vegetation in deciduous N. antarctica forests likely promoted saprotrophic fungi (i.e., genus Mortierella) in correlation with higher activities of carbon-degrading enzymes. Differences between Nothofagus hosts did not persist in mixed forests, illustrating the range of soil fertility of these ECM angiosperms and the underlying effects of soil and climate on Nothofagus distribution and N cycling in southern Patagonia.

Another Traveler Design In Southern Patagonia: Long Edges (Knives and Side-Scrapers) Manufactured on Bifacial Blanks

ABSTRACT New information is presented on the particular design of side-scrapers and knives, referred to as long-edge artifact on biface (LEAB), and its spatial and temporal distribution in southern Patagonia is explored. The analysis considers morphological and technological characteristics, the presence of four specific attributes (overshot, platform, end thinning, and domes), and functional information at a microscopic level. A total of 101 lithics originating from academic investigations, private collections, and environmental impact assessments from different locations around the Santa Cruz province (Patagonia, Argentina) are studied. The distribution of LEAB reaches different sectors of steppe and mountain forest areas from at least 7000 years BP and into the late Holocene. In addition, LEAB manufacture among inland hunting-gathering populations and between them and maritime hunter-gatherers is recorded. These results support the transmission of information about LEAB design circulation across Southern Patagonia.

Evidence for a floristically diverse rainforest on the Falkland archipelago in the remote South Atlantic during the mid- to late Cenozoic

Abstract We report the discovery of an ancient forest bed near Stanley, on the Falkland Islands, the second such ancient deposit identified on the South Atlantic island archipelago that is today marked by the absence of native tree species. Fossil pollen, spores and wood fragments preserved in this buried deposit at Tussac House show that the source vegetation was characterized by a floristically diverse rainforest dominated by Nothofagus-Podocarpaceae communities, similar to cool temperate Nothofagus forests/woodlands and Magellanic evergreen Nothofagus rainforests. The age limit of the deposit is inferred from the stratigraphic distribution of fossil pollen species transported by wind, birds or ocean currents from southern Patagonia, as well as similar vegetation types observed across the broader region. The deposit is suggested to be between Late Oligocene and Early Miocene, making it slightly older than the previously analysed Neogene West Point Island forest bed (200 km west of Tussac House). The combined evidence adds to our current knowledge of the role of climate change and transoceanic dispersal of plant propagules in shaping high-latitude ecosystems in the Southern Hemisphere during the late Palaeogene and Neogene.

Late Quaternary glacial maxima in southern Patagonia: insights from the Lago Argentino glacier lobe

Abstract. Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Evidence from the southern mid-latitudes indicates that local glacial maxima preceded the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital forcings. To shed light on these processes, we investigated the glacial landforms shaped and deposited by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet, in southern Argentina. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We report that the Lago Argentino glacier lobe reached more extensive limits prior to the global LGM, advancing during the middle to late Pleistocene between 243–132 ka and during Marine Isotope Stage 3 (MIS 3), culminating at 44.5 ± 8.0 and at 36.6 ± 1.0 ka. Our results indicate that the most extensive advance of the last glacial cycle occurred during MIS 3, and we hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a latitudinal migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in modulating ice mass changes in the southern mid-latitudes.