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2014 | Buch

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Climatic and Environmental History of Isla de los Estados, Argentina

verfasst von: Juan Federico Ponce, Marilén Fernández

Verlag: Springer Netherlands

Buchreihe : SpringerBriefs in Earth System Sciences

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This book is the result of ten years’ of scientific research carried out by the authors on Isla de los Estados. The research includes their doctoral thesis and many published scientific papers related to the island.

The book is divided into two principal parts. The first part covers different social and natural aspects of this remote island and includes chapters on the scientific and historical background, physiography with topographical and hydrographical descriptions, climate and oceanographic circulation, vegetation and geology (including stratigraphy, structural geology and geological history).

The second part comprises a reconstruction of the paleoenvironmental, paleoclimatic and paleogeographic history of the island from the Last Glacial Maximum to the present, correlating with other paleoecological records from the southern part of Isla Grande de Tierra del Fuego and Patagonia. This second part also includes a geomorphological chapter with a characterization of the principal erosive glacial landforms on Isla de los Estados constructed by means of morphometric analysis, inventories, maps, paleogeographic and glacial models, and a paleoecological chapter evaluating the palaeoenvironment and palaeoclimatic conditions that prevailed during the Late Pleistocene-Holocene times based on pollen and diatom analysis from three 14C-dated peat bogs and lakes. Finally, the book concludes with a review of the island’s archaeology and the relationship between the palaeoenvironmental history and human occupation of this island.

Inhaltsverzeichnis

Frontmatter

Chapter 1. History, Previous Works and Physiography

Abstract

Isla de los Estados (Staaten Island) is located at the southernmost end of South America, forming part of the argentina province of Tierra del Fuego, Antarctica and South Atlantic Islands. The island, due to its geographical location, conforms a unique and sensitive area for Quaternary palaeoecological and palaeoclimatic studies giving information on the atmospheric and environmental conditions from cold-temperate high latitudes in the Southern Hemisphere. It is located at a distance of ca. 30 km southeast from Península Mitre, Isla Grande de Tierra del Fuego (Main Island of Tierra del Fuego) and has a surface area of 496 km². It is the southeastern end of the Andes range above present sea level. The topography is characteristic of terrain repeatedly glaciated during the Quaternary. At the eastern area of the island the topography is less rugged than at its central and western areas.Isla de los Estados was discovered in the year 1616. Currently, and continuously since 1977, a contingent of the Argentine Navy has been stationed in Puerto Parry. These people represent the entire population of the island together with the post on Observatorio Island (Año Nuevo Island).

Juan Federico Ponce, Marilén Fernández

Chapter 2. Climate

Abstract

The climate of Isla de los Estados is strongly influence by the centre of the sub-polar low pressure which develops around the Antarctic Circle. The current climate of Isla de los Estados is cold and humid and corresponds to general classification of Oceanic Insular Cold Climate. Summer has a mean temperature of 8.3 °C, with mean daily extremes of 16.2 and 3 °C. Winter mean temperature is 3.3 °C, with mean daily extremes of 7.4 and −4 °C. Though no reliable records are yet available, rainfall is estimated to be in the range of 2,000 mm/year, but actual precipitation may be highly variable across the island, particularly in altitude. Prevailing winds are from the southwest and the northwest and they are active throughout the year. Isla de los Estados is washed by the western branch of the Malvinas/Falkland current, an arm of the Antarctic Circumpolar Current that brings cold Sub-Antarctic waters.

Juan Federico Ponce, Marilén Fernández

Chapter 3. Vegetation

Abstract

In the island, seven vegetation types related to altitude and terrain forms are recognized. The more protected and lower mountain slopes and valleys show the development of Nothofagus betuloides and Drimys winteri forest characteristics of the true Subantarctic Evergreen Forest. In those sites constantly exposed to continuously strong wind conditions, the main vegetation is the Magellanic Moorland Formation, a mosaic of interfingered and superimposed subunits that may cover a rather small area forming blanket-like patches. The Scrub Formation occurs on mountain slopes exposed to the prevailing southwesterly and westerly winds where trees of Nothofagus antarctica and shrubs grow low and tortuous. Above approximately 450 m the so-called Alpine Formation occurs with sparse vegetation cover, and often includes dwarfed forms of Nothofagus antarctica and Empetrum rubrum. Soil conditions also influence the vegetation that characterizes the island. For example, the cold and damp climate favors peat development mainly at low and intermediate elevations. However, in spite of the constant soil humidity, the topography influences drainage patterns and this is reflected by the composition of the vegetation. Littoral and Maritime Tussock Formations develop along the stony and rocky coastal areas, small peats and soils above the high tide line and in rock crevices at the intertidal zone.

Juan Federico Ponce, Marilén Fernández

Chapter 4. Geology

Abstract

The oldest geological unit is the Lemaire Formation which is a stratified volcanic complex active during the upper Jurassic. This formation is composed by tuffs and acidic lavas interlayered with tuffite, tuffaceous sandstones, silty claystones, black mudstones and fine conglomerates. Above this formation is developed the Beauvoir Formation, formed by mudstones, siltstones, greywackes, massive quartzose sandstones and limestones. This formation represent a process of marine sedimentation would have taken place during the first half of the Cretaceous period. Post-Cretaceous sedimentary rocks are arranged horizontally to sub-horizontally over the folded strata of the Beauvoir Formation via an angular unconformity. The deposits of the Late Cenozoic are composed of till accumulations of Pleistocene age and Holocene silts, clays, sands, and gravels. The principal structure of the island is the folding of both formations (Lemaire and Beauvoir) in a large syncline, the axis of which describes a large S oriented generally east–west. The age of the folding is assigned to the middle part of the Cretaceous.

Juan Federico Ponce, Marilén Fernández

Chapter 5. Glacial Geomorphology

Abstract

Based on a geomorphological analysis, a timeless glacial model of the island is presented, that is, a model that could be applied to any of the Pleistocene glaciations of the region. This model is basically oriented towards the formation of large valley glaciers, fed by cirque glaciers and small, local ice caps. Several of these glaciers excavated their troughs following the orientation of tectonic alignments, such as faults and folds and also, stratigraphic, intra-formational boundaries. In the southern sector of the island, the glaciers became in contact with the ocean quite soon, ending in an ablation process of the “calving” type, that is, the formation of icebergs. The glaciers of the northern coast, instead, were flowing nested in deep valleys until they reached the extensive plain located north of their mountain sources, a plain that had been covered by the sea during the interglacial periods, as it happens today. There, these ice bodies ended as piedmont glaciers, in an ablation process by simple melting of their terminal portions.

Juan Federico Ponce, Marilén Fernández

Chapter 6. Paleogeography

Abstract

In this chapter, we reconstruct the paleogeographic evolution of the Isla de los Estados for the period spanning the Last Glacial Maximum (LGM, ca. 24 cal. ka B.P.) to the present using the global sea-level rise curve proposed by Fleming et al. (1998) for this period and the Global Mapper 10 program. During the LMG, the Isla de los Estados was connected to the rest of the continent as the Isla Grande de Tierra del Fuego similarly did so. The northern coastline of the present Isla de los Estados, during this time, was found at around 100 km away from a straight line of its current position. The paleogeographic model has allowed to estimate the time of the opening of the Le Maire Strait, with the subsequent separation of Isla de los Estados and Isla Grande de Tierra del Fuego. This event would have taken place approximately at around 15 cal. ka B.P., when sea level rose above −85 m. Around 11,000 cal. years B.P., the small group of the Año Nuevo islands began to separate from the rest of Isla de los Estados, thus forming the archipelago with a configuration similar to the current arrangement.

Juan Federico Ponce, Marilén Fernández

Chapter 7. Palinology

Abstract

A vegetation reconstruction was made in western Isla de los Estados using palynological analysis for the last 13,000 cal year BP. The pollen data indicates initial treeless herbaceous and paludal vegetation with scarce Empetrum/Ericaceae type heaths and scrubs as a result of plan invasion and short-term succession vegetal communities spreading over the shoreline areas under locally more humid conditions. The vegetation between 10,300 and 8300 cal year BP included dwarf shrub heaths, scrubs, cushion plants and grasses with scattered trees, under warmer and drier climate conditions than today. After 8300 cal year BP, more humid conditions allowed the expansion of an open Nothofagus forest associated with dwarf shrub heath communities. It was followed at 6700 cal year BP by a gradual closed forest development in association with Drimys winteri and shrub and herb vegetation indicative of Subantarctic Evergreen Forest-Magellanic Moorland vegetational transition. After 5500 cal year BP, the rate of evergreen beech forest greatly increased with the development of almost pure Subantarctic Evergreen Forest communities. These vegetational changes accompanied a modification of the climate toward colder and wetter conditions. After 2700 cal year BP, the closed forest was replaced by an open Nothofagus forest indicative of warmer and drier conditions.

Juan Federico Ponce, Marilén Fernández

Chapter 8. Diatom Analysis

Abstract

In this chapter we present the diatom analysis results from glaciolacustrine and lacustrine sedimentary sequences (Laguna Cascada, 54° 45′51″ S, 64° 20′20.7″ W and Lago Galvarne Bog, 54° 44′16″S, 64° 19′37.9″W). The deeper part of Laguna Cascada core was radiocarbon dated in 13.285 ± 80 ¹⁴C B.P. (15.949–15.545 cal. years B.P.). Diatom analysis has showed the existence of significant climate and paleoenvironmental fluctuations around the end of the Late Glacial and beginning of the early Holocene. The deglacial period was dominated by fragilarioids species. However, diatom assemblages had changed during the Holocene due to different climate trends. Diatom analyses from Lago Galvarne Bog were carried out only in the section corresponding to the middle Holocene marine transgression. The base of the core was dated at 13,515 ¹⁴C B.P. (16,260 cal. years B.P.). Between 8,000 and 7,400 cal. years B.P., the dominance of marine diatoms together with species of brackish waters has suggested a strong marine influence within the basin. Between 7,400 and 3,700 cal. years B.P., a coastal environment would have been developed at Lago Galvarne, or perhaps even a fjord-type environment, as suggested by the high frequency of brackish diatoms together with fresh waters.

Juan Federico Ponce, Marilén Fernández

Chapter 9. Reconstruction of Paleoenvironmental Conditions During Late Glacial and Holocene Times in Isla de los Estados and Their Correlation with the Beagle Channel and Southern Patagonia

Abstract

Late Glacial-Holocene environmental conditions were interpreted in Isla de los Estados from palynological and diatomological analysis and linked also with geoquimical studies. The deglaciation started after 16,000 cal. years B.P. followed by a rapid glacial retreat under gradually warmer conditions, with alternation of drier and wetter periods until ca. 12,800 cal. years B.P. Between ca. 12,600 and 10,300 cal. years B.P. the plant communities indicated moderately cold to mild and arid climatic conditions. During the Early Holocene the expansion of Nothofagus forests is interpreted as a signal of increasing temperature and precipitation in spite of the humidity levels being then lower than today. Around 8,000–6,000 cal. years B.P. the marine diatom assemblages and geoquimical analysis indicates the Middle Holocene marine transgression. An abrupt rise of arboreal taxa occurred between ca. 8,300 and 5,500 cal. yr BP related to increased effective precipitation that culminated with the establishment and persistence of closed-canopy forest communities of Sub-Antarctic Evergreen Forest. The diatoms assemblages suggest wetter conditions, and a greater development of aquatic vegetation from ca. 4,800 cal. years B.P. From ca. 2,700 cal. years B.P. an important vegetation change in the area can be seen, probably as a consequence of warmer and drier conditions.

Juan Federico Ponce, Marilén Fernández

Chapter 10. Archaeology

Abstract

The present chapter explores the palaeoenvironmental situation of Isla de los Estados and its relationship with the archaeological record left behind by ancient canoeing people. Was there an environmental barrier to limit the accessibility to the outer edge groups of islands as, for example, Isla de los Estados or Bayly Island (located near Cape Horn)? The palaeoenvironmental information could be used as an explanation for the absence of cultural remains and also for the scarce archaeological sites. The paleoenvironmental conditions inferred from different proxy analysis demonstrate that the Middle Holocene was a windy period, with also higher precipitation rates and variable temperature. The strong wind drifts or the westerlies might have dominated the climatic scenario of the period; hence the navigation conditions would have been almost risky or even impossible. During the late Holocene, milder conditions might have favored seasonal travelling to the outer islands of the Fuegian Archipelago, though no definitive or permanent settlements have been found yet.

Juan Federico Ponce, Marilén Fernández

Titel: Climatic and Environmental History of Isla de los Estados, Argentina
verfasst von: Juan Federico Ponce
Marilén Fernández
Verlag: Springer Netherlands
Electronic ISBN: 978-94-007-4363-2
Print ISBN: 978-94-007-4362-5
DOI: https://doi.org/10.1007/978-94-007-4363-2