Juan Federico Ponce

Climatic and Environmental History of Isla de los Estados, Argentina

This book is the result of 10 years of scientific research carried out by the authors on Isla de los Estados. The research includes their doctoral theses and many published scientific papers related to the island. Isla de los Estados (Staten Island) is located at the southernmost end of South America, forming part of the Argentine province of Tierra del Fuego, Antarctica and South Atlantic Islands. It is included within the Argentine continental shelf by which it is connected to the Islas Malvinas/Falklands and the Isla Grande de Tierra del Fuego. It is separated from the latter by the Le Maire Strait, which is only 30 km wide. It is located at a distance of ca. 30 km southeast from Peninsula Mitre, Isla Grande de Tierra del Fuego (Main Island of Tierra del Fuego) and has a surface area of 496 km2. The island, due to its geographical location, conforms a unique and sensitive area for Quaternary paleoecological and paleoclimatic studies, providing information on the atmospheric and environmental conditions from cold-temperate high latitudes in the Southern Hemisphere. This book can be divided into two principal parts. The first part (chapters 1 to 4) contains 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 (chapters 5 to 10) comprises a reconstruction of the paleoenvironmental, paleoclimatic, and paleogeographic history of the island from the Last Glacial Maximum to 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 (Chapter 5) with a characterization of the principal erosive glacial landforms in Isla de los Estados constructed by means of morphometric analysis, inventories, maps, paleogeographic, and glacial models. 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. In Chapter 6, they 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 present using the global sea-level rise curve proposed by Fleming et al. for this period and the Global Mapper 10 program. A vegetation reconstruction (Chapter 7) was made in western Isla de los Estados using palynological analysis for the last 13,000 cal year BP. In Chapter 8 they present the diatom analysis results from glaciolacustrine and lacustrine sedimentary sequences. And in Chapter 9 they evaluated the paleoenvironment and paleoclimatic conditions that prevailed during the Late Pleistocene-Holocene times based on pollen and diatom analysis from three 14C-dated peat bogs and lakes. Finally (Chapter 10), the book concludes with a review of the island’s archaeology and the relationship between the paleoenvironmental history and human occupation of this island.This chapter explores the paleoenvironmental situation of Isla de los Estados and its relationship with the archaeological record left behind by ancient canoeing people. One of the aims of this chapter was to analyze why there is no evidence of human occupation at Isla de los Estados during the Middle Holocene, and to discuss if this could be related to certain paleoenvironmental conditions prevailing in this area and the adjacent seas. The low number of tools or artifacts found in these sites is linked with feeding activities such as the catch of fish and terrestrial animals. Currently, and continuously since 1977, a contingent of the Argentine Navy has been stationed in Puerto Parry. This post is occupied by four people. Isla de los Estados is without doubt one of the most isolated and uninhabited places in the Argentine territory. All information provided in this book is well documented and clearly expressed. It is easy and enjoyable to read. Photographs and graphics are of excellent quality and representative of the data provided.

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.

Paleogeographic Evolution of the Atlantic Coast of South America During Marine Isotope Stage 3 (MIS 3)

The preparation of a digital model showing the rising and lowering of relative sea level, by means of using the Global Mapper 10 program, allowed an approximate reconstruction of the paleogeographic evolution of the Atlantic coast of South America during the Marine Isotopic Stage 3 (MIS 3). To elaborate this digital model, the curve of global sea level variations as proposed by Lambeckand Chappell (2001), for the last glacial cycle, was taken into consideration. The model shows the development of an extensive coastal plain, which extended almost continuously from Staten Island (Isla de los Estados; southeastern end of Argentina) until the Panama isthmus. The surface of this coastal plain varied from a maximum expansion of around 1,182,000 km2, when sea level achieved its minimum level of approximately −80 m below present sea level (b.p.s.l.) within the Marine Isotope Stage 3 , in between 40,000 and 30.000 cal. years B.P., and a minimum area of approximately 954,000 km2, when sea level was at its highest position of −60 m b.p.s.l. (in between 57,000 and 63,000 cal. years B.P.). These figures represent an overall surface variation in the order of only 20 % between both extreme paleogeographic configurations, proving that the coastal plain was a permanent, stable feature of the landscape of eastern South America, not only during the Late Pleistocene glacial stages MIS 4 and MIS 2, but even also during MIS 3. Its average width varied between 76 ± 73 km and 61 ± 71 km, showing significant latitudinal variations. Thus, South America increased its total surface by 6.6 and 5.3 % during MIS 3. This coastal plain had its maximum extent at the latitude of the eastern Argentina province of Buenos Aires (between approximately 35° and 40° South latitude), when the Rio de la Plata estuary did not exist. Its minimum amplitude occurred in central Brazil and in front of the Caribbean coast of Venezuela and Colombia. The information provided by the present model sustains the importance of the Atlantic coastal plain of South America as a distinctive feature of the South American landscape and proves its paleogeographic continuity even during the warmest periods of Marine Isotope Stage 3. These facts suggest that the coastal plain, most of it submerged today, has been a major element of the landscape during most of the Quaternary.

Palaeogeographic changes drove prehistoric fishing practices in the Cambaceres Bay (Tierra del Fuego, Argentina) during the middle and late Holocene

Fishing intensification is evidenced in the archaeological record of the Beagle Channel region (Tierra del Fuego, Argentina) during the late Holocene by significant diachronic increases in both the representation of coastal taxa and the diversity of pelagic fish species taken. Faunal evidence from the Imiwaia I site, however, shows a different pattern in temporal variation in the exploitation of coastal fish in contrast to that of the regional trend. By comparing data from palaeogeography and archaeoichthyology, we have been able to evaluate how changes in Holocene coastal geomorphology near the Imiwaia I site influenced hunter–gatherer subsistence. The results show that the abundance and taxonomic diversity recorded in ichthyofaunal assemblages at the Imiwaia I site coincide with the environmental expectations arising from palaeogeographic reconstructions of the Cambaceres Bay during the middle and late Holocene.

The Heinrich and Dansgaard–Oeschger Climatic Events During Marine Isotopic Stage 3

The Marine Isotope Stage 3 (MIS 3) was an interstadial stage, a relatively warm climatic period which developed roughly between 60 and 50 and 30 cal. ka B.P. Several very cold periods, known as Heinrich (H) events, developed during MIS 3 as a result of partial collapse of the North American ice sheet margins, with formation of huge amounts of icebergs which, after melting in more temperate latitudes, would have inundated the North Atlantic Ocean with low salinity waters which would have impeded the penetration of the Gulf Stream into the North Atlantic Ocean. Several paleoclimatic moments with relatively warmer conditions, known as the Dansgaard–Oeschger (D-O) events, took place in-between the Heinrich (H) events, throughout MIS 3. These H and D-O cycles would have been very short in geological terms (perhaps even only around 1 kiloyears (kyr) each in some cases) and quite intense, with mean annual temperatures, for instance in the area of Beringia (the land bridge between Siberia and North America) ca. 5–8 °C higher than those active at the Last Glacial Maximum (LGM; ca. 24 cal. ka B.P.) and perhaps close to those occurring in past interglacial periods, respectively. Even though climate was warmer than during the LGM, total melting of the continental ice sheets did not take place; thus, global sea level was perhaps lower than today during the entire MIS 3. It was low enough to allow the persistence of Beringia, without any interruptions throughout the whole of MIS 3. The aim of this paper is to present basic paleoclimatic and paleogeographic information about MIS 3, which may be useful to understand the nature and evolution of the South American terrestrial and marine ecosystems later on during the LGM.

Astroblemes-Wrong (Structures that Resemble Astroblemes but They Are Not)

A bowl-shaped depression has been dismissed as of impact origin because it is undoubtedly a glacial cirque. Its diameter is 1 km and its depth, 200 m. The geology is composed of rhyolites and rhyodacites of the Lemaire Formation (Jurassic).

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

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.

History, Previous Works and Physiography

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 Peninsula 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 (Ano Nuevo Island).