Ana María Borromei

Paleovegetational and paleoclimatic changes during the Late Quaternary in southwestern Buenos Aires Province and Southern Tierra del Fuego (Argentina)

Pollen analysis from a sedimentary section in the valley of the Sauce Grande River (southwestern Buenos Aires Province) and a peat core from the Andorra Valley (southern Tierra del Fuego) provides evidence for the apparent large‐scale synchroneity of major past vegetational changes and inferred climatic trends during the late Pleistocene and Holocene in this region. Climate before 10,000 years B.P. was relatively cold and dry, both in southwestern Buenos Aires Province and in southern Tierra del Fuego. A climatic amelioration to wanner and wetter conditions during the late Pleistocene and early Holocene is recorded in both regions. Late Holocene climates show greater variability and they suggest the onset of modern environmental conditions as represented by cool and wet conditions in southern Tierra del Fuego, and by arid to semi‐arid conditions in southwestern Buenos Aires Province.

Late and Postglacial Paleoenvironments of Tierra del Fuego: Terrestrial and Marine Palynological Evidence

Publisher Summary This chapter discusses the late and postglacial paleoenvironments of Tierra del Fuego. Paleovegetational communities and paleoenvironments of the Late Pleistocene and Holocene in southern Tierra del Fuego are interpreted from pollen assemblages, microplankton and palynofacies in radiocarbon-dated peat bogs, glaciolacustrine sediments, and marine deposits. The available evidence of the pollen sequences from the interior Fuegian valleys close to the Beagle Channel area, such as Valle de Andorra, Valle Carbajal and the Route 3 exposure site, allows a comparison with the pollen record from the Beagle Channel peat bog sections to confirm and refine the previously established Late Pleistocene and Holocene paleoecology and chronostratigraphy. The pollen sequence from the Puerto Harberton site is taken as a proxy record at the Beagle Channel area because of its time extension and detailed studies developed there in the past two decades. The palynological analysis based on pollen and spores have been intensively developed in Tierra del Fuego to reconstruct Quaternary environments. However, little attention has been paid to the study of marine microplankton, mainly dinoflagellate.

Pollen and fungal remains as environmental indicators in surface sediments of Isla Grande de Tierra del Fuego, southernmost Patagonia

Palynological studies have been performed in order to increase knowledge of relations between present vegetation and fungal biota. The analysis of modern analogues will help to improve the palaeoenvironmental reconstructions of fossil sequences from Isla Grande de Tierra del Fuego. A total of 24 fungal taxa have been found, described and illustrated. Surface samples were collected from the different vegetation communities developed on the island: steppe, Nothofagus forest-steppe ecotone and Nothofagus forest. The steppe is characterised by a predominance of Poaceae pollen accompanied by Nothofagus pollen (up to 30%) and spores of Glomus sp. In the forest-steppe ecotone, Nothofagus pollen frequencies rise up to 50% along with dwarf shrub heath communities and Gaeumannomyces species. In the forest unit, the percentage values of Nothofagus pollen surpass 50%. Among the fungal remains, fructifications of Microthyriaceae and dematiaceous spores such as Alternaria sp., Dictyosporium sp. and Sporidesmium sp. are present in forest samples and may be related to damp environments. Ascospores of the coprophilous Sordaria-type and Sporormiella-type appear to be common and are probably associated with livestock grazing. Fungal remains are very scarce in some of the samples obtained in mire environments. The ecological requirements of some of the fungi identified allowed inferences about the local conditions of the sampled site. This study demonstrates the palaeoenvironmental indicator value of fungal components and encourages further investigation of surface samples considering local habitat features to obtain a better understanding of local environmental conditions in the past.

Palynofacies analysis of surface sediments from the Beagle Channel and its application as modern analogues for Holocene records of Tierra del Fuego, Argentina

Palynofacies analysis of surface sediments from the Beagle Channel, Tierra del Fuego, Argentina, was carried out to establish modern analogues for comparison with other Holocene marine records in southern Isla Grande de Tierra del Fuego. Our results show the dominance of highly degraded translucent phytoclasts, associated with amorphous organic matter (AOM) and palynomorphs, while opaque phytoclasts are poorly represented. The organic constituents indicate the proximity of the continental source area to marine environments, with distances and/or times of relatively short transport. The predominance of translucent phytoclasts associated with pyrite suggests reducing conditions, probably associated with marginal-marine environments. Among the terrestrial palynomorph group, the predominance of Nothofagus pollen reveals the presence of forests along the channel. The high terrestrial organic matter input to the depositional area are consistent with a marginal-marine environment. The aquatic palynomorphs, mainly dinoflagellate cysts show assemblages characterised by low species diversity and low concentration values. The dominance of Peridiniales over Gonyaulacales suggests inner neritic environments. Comparison with two fossil sections of Mid-Late Holocene age (Albufera Lanushuaia and Río Ovando) shows similar distribution of the total palynological matter.

Inferencias paleoecológicas a partir del análisis de microfósiles fúngicos en una turbera pleistoceno-holocena de Tierra del Fuego, Argentina

Palaeoecological inferences from the analysis of fungal microfossils of a mire in Tierra del Fuego, Argentina. this paper presents the fungal remains recovered from the fossil peat sequence at La correntina mire (S 54° 33 W 67°), located in the central part of Isla Grande de tierra del Fuego, Argentina. newly recognised fungal microfossils have distinctive morphological features that allow their systematic classification. representatives of Glomeromycota (1), Ascomycota (7), mitosporic fungi (4) and three types of spores without taxonomic rank are identified and described. this study represents a contribution to the knowledge of the fossil fungal remains and provides data about their ecological implications.

Quaternary Climate Changes in Southernmost South America Inferred from Lacustrine Sediments Preserved in Volcanic Maars

As part of the Southern Hemisphere Paleo- and Neoclimates Project (UNESCO IGCP- 341), sediments deposited in three small basins of volcanic maars which outcrop in the southern Santa Cruz extra-Andean volcanic belt at 52° S latitude were cored up to 59 meters depth. Undisturbed samples were obtained from six coring sites. A preliminary palynological study of sediments from the Magallanes Maar (one sample/meter) seems to indicate several pulses of higher and lower relative humidity. Radiocarbon analyses indicate an Upper Pleistocene age for these sediments.s

POSTGLACIAL VEGETATION AND CLIMATE CHANGES INFERRED FROM A PEAT POLLEN RECORD IN THE RÍO PIPO VALLEY, SOUTHERN TIERRA DEL FUEGO

Abstract. The pollen analysis from Canadon del Toro peat bog (54° 49’ 36” S; 68° 27’ 36” W), located in an interior valley of the Fuegian Andes, provides information about vegetation and climate changes during the last 13,500 years. The results indicate the postglacial development of steppe-like vegetation under drier and colder conditions than today, followed by the expansion of Nothofagus into the valley after 10,350 cal. yr BP. At this time, the predominance of a forest-steppe ecotone suggests warm conditions and an increase in moisture availability. By about 6,700 cal. yr BP, the closed-canopy Nothofagus forest spread under cold and wet conditions. The mire environment also reflects the increasing trend of effective moisture changing from an initial minerotrophic Cyperaceae fen to an ombrotrophic Sphagnum bog development. KEY WORDS. Vegetation and climate history. Lateglacial-Holocene. Interior valleys. Tierra del Fuego. Resumen. CAMBIOS DE LA VEGETACION Y CLIMA POSTGLACIAL INFERIDOS A PARTIR DE UN REGISTRO POLINICO DE UNA TURBERA EN EL VALLE DEL RIO PIPO, SUR DE TIERRA DEL FUEGO. El analisis polinico de la turbera Canadon del Toro (54° 49’ 36” S; 68° 27’ 36” W), ubicada en un valle interior de los Andes Fueguinos, brindo informacion sobre los cambios de vegetacion y clima durante los ultimos 13.500 anos. Los resultados indicaron el desarrollo postglacial de una vegetacion de estepa bajo condiciones mas secas y frias que las actuales, seguidas por la expansion de Nothofagus en el valle con posterioridad a los 10.350 anos cal. AP. Durante este periodo, la predominancia del ecotono bosque-estepa sugiere condiciones mas calidas y un incremento en la disponibilidad de humedad. Alrededor de los 6.700 anos cal. AP, el bosque cerrado de Nothofagus se expande bajo condiciones frias y humedas. El ambiente de la turbera tambien refleja el paulatino incremento de humedad efectiva cambiando desde una turbera minerotrofica de Cyperaceae a una ombrotrofica de Sphagnum. PALABRAS CLAVE. Historia de la vegetacion y el clima. Tardiglacial-Holoceno. Valles interiores. Tierra del Fuego.

Vegetation and Climate in Southern South America during Marine Isotope Stage 3 (MIS 3): an Overview of Existing Terrestrial Pollen Records

Data from terrestrial pollen records in the Chilean sector show that Marine Oxygen Isotope Stage 3 (MIS 3) was characterized by the Heinrich (stadials)/Dansgaard–Oeschger (interstadials) oscillations. At central Chile (32–38° S) an open beech/podocarp woodland was apparently established during the last ice age under cold and humid climates, where nowadays grows a semiarid, broad sclerophyllous vegetation, while episodes of aridity with rise of temperature were indicated by expansion of chenopods–amaranths. At the Southern Lake District and northern Isla Grande de Chiloe (40°–42° 30′ S), the stadial events were characterized by higher amounts of grasses indicative of the Subantarctic Parkland vegetation. This vegetation implied summer temperatures of ~6 °C (~8 °C below present). The interstadials were represented by expansion of the Valdivian-North Patagonian Evergreen Forest-Subantarctic Evergreen Forest implying summer temperatures of ~12 °C. In the Argentine sector, the steppe environmental conditions prevailed. Interstadial conditions are pointed out at 39° S, in NW Patagonia. Meanwhile, in southern Patagonia at 51°–52° S, and Tierra del Fuego at 54° S, the climatic conditions during MIS 3 are interpreted as colder and drier than today.