Southernmost South America Research Articles

First Middle Devonian Bivalves from Argentina, New Records from the Punta Negra Formation and Insights on Middle Paleozoic Faunas from the Precordillera Basin

Abstract. Middle Devonian bivalves from Argentina are reported for the first time, based on records of the Precordilleran Punta Negra Formation (Emsian—Frasnian?), San Juan Province. This finding is the youngest Devonian record of bivalves from southernmost South America. The impoverished bivalve association in the Punta Negra Formation includes five shallow infaunal deposit feeders, i.e. Nuculites argentinum Sanchez, Anthracoleda (Pseudoleda) minuta Sanchez, Praenucula sp., Deceptrix sp. and Praectenodonta sp. The distribution of the Silurian—Devonian bivalves from Precordillera shows a decreasing diversity trend during this interval, due to potential biases in sampling and paleoecology and thus suggesting that this trend might be apparent. Early and Middle Devonian bivalves from Precordillera show a strong cosmopolitan paleobiogeographic signature, in contrast with other geographically related basins showing endemic (Malvinokaffric Realm) signals during the Devonian. Contrarily, an endemic composition i...

Maritime Hunter-Gatherers in the Chonos Archipelago (43°50’–46°50’ S), Western Patagonian Channels

ABSTRACTThis article presents the current advances in archeological research on the Western Patagonian Channels, specifically the Chonos Archipelago (43°50’–46°50’ S). Based on a large spatial scale, we aim to contribute to the discussion of the dispersion and characteristics of the occupation of the Pacific coast of southernmost South America. Results show that all of the contexts recorded do not exceed 3600 cal BP. Site formation processes that may have acted in the preservation of the archeological record of this area led us to question if this region was among the last to be settled (as suggested by current chronological data), or if the dynamic tectonic activity that permanently transforms this coast is playing a major role in concealing earlier evidence, thereby introducing a significant research bias.

Physiological responses to temperature in Merizodus soledadinus (Col., Carabidae), a subpolar carabid beetle invading sub-Antarctic islands

Recent human activities and rising air temperature have increased the vulnerability of sub-Antarctic islands to alien species. At the Kerguelen Islands, the predaceous ground beetle Merizodus soledadinus is the only invasive insect originating from the southern cold temperate area (native from Patagonia, Tierra del Fuego and Falkland Islands). This austral origin raises the question of the limits of its physiological tolerance and capability to withstand (1) global change and (2) warmer climates of archipelagos where its accidental transportation could be facilitated from the Kerguelen Islands (namely Amsterdam and Saint Paul). Using gas chromatography/mass spectrometry metabolomics, we compared metabotypes of adults exposed to different temperatures (0, 4, 8, 12, 16, 20 °C). All individuals survived after 2 weeks regardless of the temperature they were exposed to. The physiological changes observed were consistent with increased metabolic rate at increased temperatures, without extreme metabotypes that are characteristic of acute stress. First cues of sublethal stress were observed after prolonged exposure to 20 °C, a warm regime unrealistic for such duration in sub-Antarctic Islands. Overall, M. soledadinus’ thermal tolerance exceeded temperatures currently experienced in nature, suggesting that climate warming may boost its invasion by eliciting its activity and broadening habitat suitability in both invaded and still pristine islands. This thermal tolerance may allow survival aboard ships and development in sub-Antarctic islands with conditions warmer than the Kerguelen Islands, such as Amsterdam and St Paul. Stringent biosecurity measures are thus needed to prevent transfer from Kerguelen to these islands. The native range of this predaceous beetle limited to the Falkland Islands and southernmost South America may be partly constrained by factors other than temperature, such as desiccation, predation or competition.

Geomorphology and weathering characteristics of erratic boulder trains on Tierra del Fuego, southernmost South America: Implications for dating of glacial deposits

Erratic boulder trains (EBTs) are a useful glacial geomorphological feature because they reveal former ice flow trajectories and can be targeted for cosmogenic nuclide exposure dating. However, understanding how they are transported and deposited is important because this has implications for palaeoglaciological reconstructions and the pre-exposure and/or erosion of the boulders. In this study, we review previous work on EBTs, which indicates that they may form subglacially or supraglacially but that large angular boulders transported long distances generally reflect supraglacial transport. We then report detailed observations of EBTs from Tierra del Fuego, southernmost South America, where their characteristics provide a useful framework for the interpretation of previously published cosmogenic nuclide exposure dates. We present the first comprehensive map of the EBTs and analyse their spatial distribution, size, and physical appearance. Results suggest that they were produced by one or more supraglacial rock avalanches in the Cordillera Darwin and were then transported supraglacially for 100s of kilometres before being deposited. Rock surface weathering analysis shows no significant difference in the weathering characteristics of a sequence of EBTs, previously hypothesized to be of significantly different age (i.e., different glacial cycles). We interpret this to indicate that the EBTs are much closer in age than previous work has implied. This emphasises the importance of understanding EBT formation when using them for cosmogenic nuclide exposure dating.

Lamniform shark teeth from the late cretaceous of southernmost South America (Santa Cruz province, Argentina).

Here we report multiple lamniform shark teeth recovered from fluvial sediments in the (Campanian-Maastrichtian) Cerro Fortaleza Formation, Santa Cruz Province, Argentina. This small tooth assemblage is compared to various lamniform sharks possessing similar dental morphologies, including Archaeolamna, Cretalamna, Dwardius, Dallasiella, and Cretodus. Although the teeth share numerous morphological features with the genus Archaeolamna, including a developed neck that maintains a relatively consistent width along the base of the crown, the small sample size and incomplete nature of these specimens precludes definitive taxonomic assignment. Regardless, the discovery of selachian teeth unique from those previously described for the region broadens the known diversity of Late Cretaceous South American sharks. Additionally, the discovery of the teeth in fluvial sandstone may indicate a euryhaline paleobiology in the lamniform taxon or taxa represented by this tooth assemblage.

Structure and tectonic evolution of the Fuegian Andes (southernmost South America) in the framework of the Scotia Arc development

The major structural and tectonic features of the Fuegian Andes provide an outstanding onshore geological framework that aids in the understanding of the tectonic evolution of the Scotia Arc, mainly known from offshore studies. The orogenic history of the Fuegian Andes (Late Cretaceous–Miocene) is thus compared and integrated with the tectonic history of the Scotia Sea. Late Cretaceous–Paleocene structures in the Fuegian Andes suggest a N-directed contraction consistent with an oroclinal bending of the southernmost South America–Antarctic Peninsula continental bridge. This N-directed contraction in the Fuegian Andes continued during the spreading of the West Scotia Ridge, between 40–50 and 10Ma ago. The onset of major strike-slip faulting in Tierra del Fuego is considered here to be not older than the late Miocene, consistent with the recent history of the North Scotia Ridge; thus forming part of a tectonic regime superposed to the prior contraction in the Fuegian Andes.

Parmelioid lichens (Parmeliaceae) in southernmost South America

The parmelioid lichens is a speciose group in the Parmeliaceae family, and the biodiversity of this group is still far from completely understood in many regions of the world. One such region is southernmost South America, viz. the parts of Chile and Argentina south of 49 and 46° S, respectively, and the Falkland Islands. Based on examination of 366 herbarium samples and a study of relevant literature, 51 species of parmelioid lichens are here accepted for southernmost South America, whereas 12 species reported from the area during the last decades have been rejected. Xanthoparmelia austrosorediata and X. tehuelchorum are described as new to science here. In addition, six species are reported as new to southernmost South America, three of which are new to Chile, whereas an additional five species are new to the Chilean region of Magallanes. The apothecia of Flavoparmelia gerlachei and Xanthoparmelia subplittii are described for the first time here. Xanthoparmelia is the largest genus in the area with 21 species, two still undescribed, followed by Hypotrachyna with 11 and Parmelia with five. The lichenologically least explored part of the area is the Patagonian steppe and adjacent areas. Half of the total number of species, including all Xanthoparmelia species, is concentrated to these arid areas, and the majority of these are species which are endemic to South America. Hypotrachyna species are characteristic of the humid evergreen forest zone along the coast, and most of these species have wide pantropical or subcosmopolitan distribution ranges and few records from the present study area. The strongest focus of the present study is the National Park Torres del Paine in Magallanes, and a total of 35 parmelioid species are reported from this area here. Several of these have had their only known localities in southernmost South America destroyed by the 2011/2012 forest fire. Exploration history, frequency, distribution and evolutionary patterns are also discussed for single species or groups of species.

Observed crustal uplift near the Southern Patagonian Icefield constrains improved viscoelastic Earth models

Thirty‒one GPS geodetic measurements of crustal uplift in southernmost South America determined extraordinarily high trend rates (> 35 mm/yr) in the north‒central part of the Southern Patagonian Icefield. These trends have a coherent pattern, motivating a refined viscoelastic glacial isostatic adjustment model to explain the observations. Two end‒member models provide good fits: both require a lithospheric thickness of 36.5 ± 5.3 km. However, one end‒member has a mantle viscosity near η =1.6 ×1018 Pa s and an ice collapse rate from the Little Ice Age (LIA) maximum comparable to a lowest recent estimate of 1995–2012 ice loss at about −11 Gt/yr. In contrast, the other end‒member has much larger viscosity: η = 8.0 ×1018 Pa s, half the post–LIA collapse rate, and a steadily rising loss rate in the twentieth century after AD 1943, reaching −25.9 Gt/yr during 1995–2012.

Integrated reconstruction of Holocene millennial-scale environmental changes in Tierra del Fuego, southernmost South America

This study presents new paleoenvironmental data obtained from sedimentary cores from Lago Fagnano, an elongated lake located at 54°S in southernmost South America. Data from palynomorphs (pollen, spores and algae) and associated palynofacies as well as from diatom taxa retrieved from these cores compared with other regional proxies contribute to evaluate the similarities and differences in the climate patterns based on different proxies from southernmost Patagonia. The pollen analysis reveals that a grass steppe environment existed during the early Holocene (11,300–~8000calaBP) followed by a major vegetation change characterized by development of forest-steppe ecotone communities between ~8000 and ~6500calaBP, under more humid conditions. Between ~6500 and ~4000calaBP, expansion and colonization by Nothofagus forests reflect an increase in effective moisture levels, while openness in the forest communities characterizes the region after ~1100calaBP. The palynological organic matter combined with the algal content reflects hydrological changes occurring in the lake and its nutrient status, probably in close relation with past climate oscillations. All these past ecological changes are closely related to oscillations in precipitation and temperature as a response to the variations in the latitudinal position and/or strength of the Southern Westerlies wind belt during the Holocene.

Selknamella: a new agglutinated foraminiferal genus from the early Eocene southern high latitudes

A new, unusual agglutinated foraminifera, Selknamella basketi n. gen., n. sp. is described from the Fuegian lower Eocene, Magallanes Basin, southernmost South America. It has a morphology and paleohabitat similar to those of the subfamily Remaneicinae Loeblich and Tappan 1964, particularly to the Holocene genera Bruneica Brönnimann, Keij and Zaninetti 1983, and Remaneica Rhumbler 1938: It has a low trochospirally coiled to patelliform small test; the first two or three embryonic chambers are globular and undivided; following chambers are semilunate-shaped from spiral view and mushroom-shaped from umbilical view, and subdivided by radial secondary septula. Selknamella n. gen. differs from all the organically-cemented Remaneicinae by the perforate rigid wall, completely calcareous in the initial chambers to very finely agglutinated in the last whorls. The new genus is the only case of calcareous cemented agglutinated foraminifera in the Cretaceous and Cenozoic of the Magallanes Basin, and is restricted to the early Eocene, coincident with the warmest time in the high southern latitudes.

Spatial patterns in Late Holocene lithic projectile point technology of Tierra del Fuego (southern South America): assessing size and shape changes

This paper focuses on the application of geometric morphometrics to the study of the lithic record in southern South America. We review the regional background, discuss methodological issues and summarize research advances. Here a geometric morphometric approach is applied to the case study of Late Holocene stemmed lithic projectile points from Grande Island of Tierra del Fuego (southernmost South America). Our aim is to assess size and shape changes in a broad spatial scale. Projectile point morphometric variations are used to discuss spatial scales of interaction and differentiation among past human populations across the island. Finally, several hypotheses are introduced to explain the patterns observed.

Holocene coastal environments and processes in subantarctic/temperate cold Tierra del Fuego, Argentina-Chile

Abstract Holocene coastal environments in the Tierra del Fuego archipelago, southernmost South America, evolved in a temperate cold climate characterized by strong and persistent mid-latitude westerly winds, and under stable to falling relative sea-level. Southern and western coasts are rocky, microtidal and generally devoid of Holocene accretionary coastal landforms. They are young, having originated from flooding by the early Holocene. Northern and eastern coasts are lined by receding cliffs that supply abundant sediment to macro/mesotidal embayments lodging extensive accretionary coastal landforms. Spit growth on the Atlantic shore played a major part in modifying the development of other landforms by barring the shoreline from wave attack. Sediment was mainly supplied from Pleistocene glacial deposits exposed at eroding headlands and, more locally, obtained by cannibalization and from elevated Pleistocene beaches. In places, westerly winds combined with Atlantic swell to foster spit growth under high-energy wave power on both bay and ocean flanks – a unique occurrence. In addition, the westerlies caused widespread deflation on supratidal marshes and delivered fine-grained sediment inland and to the sea. Recent acceleration of glacio-eustatic rise is gradually changing the coastal zone to a condition of relative sea-level rise. The generally high and steep coastlines will not be greatly affected. A few gently-dipping lowlands might be flooded and biodiversity will be negatively affected.

Cenozoic contractional tectonics in the Fuegian Andes, southernmost South America: a model for the transference of orogenic shortening to the foreland

The Fuegian thrust-fold belt has been subjected to significant shortening during the Cenozoic. Although contemporaneous shortening and uplift was also recognized in the Fuegian Andes central belt (hinterland), previous studies stated that most of that deformation developed out-of-sequence with the thrust-fold belt and hence did not contribute to its shortening. Therefore, no suitable geometric and kinematic model has been proposed for the mechanism that links deformation in both domains. Here we address the style and timing of the younger (Late Cretaceous-Paleogene) structures of the central belt and the structural evolution of the thrust-fold belt, based on published and own data. We reinterpret the style of the central belt structures, proposing a new model in which basement thrusting in the central belt caused all the shortening in the foreland cover. We postulate that the basement was involved in a regional-scale duplex whose roof thrust was the decollement of the thin-skinned thrust-fold belt. Therefore, the total slip transferred through the roof thrust accounted for the shortening in the cover rocks. The basement duplex incorporated the underthrust crust from the footwall of the orogenic wedge through forward propagation, in sequence with the thrust-fold belt, from the Late Cretaceous to the Miocene.

The peopling of the Fuego-Patagonian fjords by littoral hunter–gatherers after the mid-Holocene H1 eruption of Hudson Volcano

Early Holocene (>8500 cal BP) littoral sites are well documented along the Pacific coast of Chile north of 32°S, but they do not occur south of this latitude. It has been proposed that canoe Indians of Fuego-Patagonia, the earliest evidence for which is mid-Holocene (Punta Santa Ana; 7440 cal BP), adapted themselves to the sea from terrestrial hunter–gatherer populations already living since >13,000 cal BP in southernmost South America south of 52°S. This adaption may have taken place first in the area around Seno Otway, near the earliest maritime cultural sites, where transit to and from the interior pampas was relatively easy and forest providing trees for canoes existed. Seno Otway is also the proposed source for green obsidian, a distinctive lithic material found in many of the oldest maritime sites, including Túnel 1 and Imiwaia 1 along the Canal Beagle >300 km to the southeast. This green obsidian was previously exploited and transported long distances by terrestrial hunter–gatherers, as evidenced by its presence in the Period III (9500–7400 cal BP) levels of Pali Aike and Fell's Cave located >200 km east of Seno Otway. However, this obsidian does not occur in Period IV (after 7400 cal BP), when it and other obsidian types from distant sources are absent among the lithic tools found in these two sites. This hiatus in the long distant terrestrial transport of obsidian in southernmost Patagonia has been attributed to the catastrophic environmental effects of the H1 eruption of Hudson volcano (46°S) at ∼7750 cal BP. This eruption, which was more than five time larger than the 1991 eruption of the same volcano, covered much of Tierra del Fuego with up to >20 cm of tephra, and the Seno Otway area with at least >4 cm of tephra. As well as interrupting long distance terrestrial transport of obsidian over all of southernmost Patagonia, it may have devastated for an extended time period the flora and fauna supporting the local terrestrial hunter–gatherers in this area, particularly in Tierra del Fuego, which was already isolated by the opening of the Strait of Magellan at ∼9240 cal BP. Here it may have actually extinguished this culture completely. However, it was unlikely to have affected marine species. We propose that this volcanic eruption was a significant trigger to the development of the maritime population from the older terrestrial hunter–gatherers.

Diatom assemblage changes in lacustrine sediments from Isla de los Estados, southernmost South America, in response to shifts in the southwesterly wind belt during the last deglaciation

Isla de los Estados (54A degrees 45'S, 63A degrees 10'aEuro"64A degrees 46'W) lies east of the main island of Tierra del Fuego and is the southeastern-most point in Argentina. Because of its geographic position near the latitudes of the Southern Hemisphere Westerlies and the strong influence of the Antarctic Circumpolar Current (ACC), the area is suitable for paleoecological and paleoclimate research. The island is not far north of the Subantarctic Front, which limits the northern boundary of the ACC. Paleoenvironmental study in this geographic location can shed light on past changes in atmospheric and marine circulation patterns. Diatom analysis of the lower part of a sediment sequence from Laguna Cascada (54A degrees 45' 51.3''S, 64A degrees 20' 20.07''W) enabled inference of changing lake conditions between 16 and 11.1 cal ka BP. Between 16 and 14.4 cal ka BP fragilarioid diatom species, often a pioneer group, dominated the record. Their presence shows seasonally open-water conditions from the onset of sedimentation. In zone II (14.4-12.8 cal ka BP), the dominance of planktonic/tychoplanktonic Aulacoseira spp. might represent longer ice-free periods and windier conditions, which would have kept this heavy species suspended in the water column. This period corresponds to the Antarctic Cold Reversal, when the Southern Hemisphere Westerlies were possibly centered on the latitudes of Tierra del Fuego, resulting in windy and wet conditions. Zone III (12.8-11.1 cal ka BP) is dominated by benthic diatom taxa that are mainly associated with peat and wetland vegetation. This suggests that climate conditions had become milder and less windy, favoring aquatic productivity and terrestrial vegetation development. This change in environmental conditions may have been a consequence of the southward movement of the Southern Hemisphere Westerlies at the start of the Antarctic Holocene thermal optimum.

HLA genetic profile of Mapuche (Araucanian) Amerindians from Chile

Amerindian Mapuche (Araucanians) are now living in Chile and Argentina at both sides of Andean Mountains. They are anthropologically and genetically different from southernmost South America Patagonian Amerindians. Most of the HLA alleles found in our Mapuche sample are frequent or very frequent in North and South America Amerindians: (1) Class I: A*02:01, A*03:01, A*68:01, B*39:09, B*51:01, (2) Class II: DRB1*03:01, DRB1*04:03, DRB1*07:01, DRB1*08:02, DRB1*14:02, DRB1*16:02. One of the nine most frequent extended haplotypes seems to be from European origin, suggesting the existence of a degree of admixture with Europeans in our Mapuche sample. It has been calculated of about 11 % admixture. Three of the extended haplotypes are also found in other Amerindians and five of them are newly found in Mapuche Amerindians: A*68:01-B*39:09-DRB1*08:02-DQB1*04:02; A*68:01-B*51:01-DRB1*04:03-DQB1*03:02; A*29:01-B*08:01-DRB1*03:01-DQB1*02:01; A*02:01-B*15:01-DRB1*04:03-DQB1*03:02; A*33:01-B*14:02-DRB1*07:01-DQB1*03:03. The medical importance of calculating HLA profile is discussed on the diagnostic (HLA and disease) and therapeutical bases of HLA pharmacogenomics and on the construction of a virtual transplantation HLA list profile. Also, anthropological conclusions are drawn.

Petrological vestiges of the Late Jurassic-Early Cretaceous transition from rift to back-arc basin in southernmost Chile: New age and geochemical data from the Capitán Aracena, Carlos III, and Tortuga ophiolitic complexes

The ophiolitic remnants of the Upper Mesozoic Rocas Verdes basin in southernmost South America were studied from the perspectives of petrography, chemistry of minerals, bulk-rock geochemistry, and U-Pb geochronology. The study aimed to unravel the tectonic, magmatic, and metamorphic evolution of a suprasubduction rift zone that underwent a transition to a back-arc basin. The rifting phase and bimodal magmatism within the Rocas Verdes basin started prior to or during the Late Jurassic, as indicated by a gabbro in contact with pillow basalts that dated at 154 Ma. In the Late Jurassic Capitán Aracena and Carlos III complexes, tholeiitic basalts are geochemically comparable to enriched mid-oceanic ridge basalts. Back-arc basin development continued for 35 myr until the Early Cretaceous, as suggested by the ages of detrital zircons in cherty layers within pillow basalts and metamorphic titanite that crystallized during seafloor metamorphism near the spreading/magmatic axis. In the Early Cretaceous Tortuga Complex, tholeiitic basalts are comparable to normal mid-oceanic ridge basalts. Non-deformative metamorphism converted the primary mineralogy of the ophiolites to low- to intermediate-grade metamorphic assemblages formed during ocean-floor type alteration in a suprasubduction setting. Fossilized bacteria, preserved as rounded aggregates of titanite microcrystals, were identified in the pillow basalts up to the Early Cretaceous. The Rocas Verdes basin closed during the Andean orogeny, which started during the Late Cretaceous, and ophiolites were tectonically juxtaposed and thrust over the sedimentary infill of the quasi-oceanic basin in which they developed. The tectonic emplacement of the ophiolitic complexes was complete before the latest Cretaceous, as indicated by crystallization ages of granites intruded into the ophiolitic complexes.

Extensive recession of Cordillera Darwin glaciers in southernmost South America during Heinrich Stadial 1

The geographic expression and phasing of events during the last termination are important for isolating mechanisms that caused Earth to emerge from the last ice age. Heinrich Stadial 1 (HS1; 14,600–18,000 yr BP) is a key because of the central role that its far-field effects had on the last termination in the Southern Hemisphere. Here, we present new data from Cordillera Darwin that show rapid glacier recession in southern South America during HS1. This retreat was coeval with ice recession elsewhere in South America and New Zealand, with increased upwelling in the Southern Ocean, with warming of SSTs offshore of Chile, and with a rise in atmospheric CO2. Together, these data indicate a coherent and rapid response to the effects of HS1 in the middle and high latitudes of the Southern Hemisphere.

Late Quaternary environmental changes in southernmost South America reflected in marine calcareous macro-and-microfossils

Late Quaternary environmental changes, especially sea-level fluctuations and glacial advances and retreats, affected the distribution of the benthic marine fauna which inhabited the Beagle Channel in southernmost South America. To evaluate these changes, calcareous macro-and-microfossils obtained from Holocene marine sediments along a sector of the western side of the Beagle Channel have been used for a multi-proxy approach. In total, 119 species were recovered: 65 mollusks (24 bivalves, 35 gastropods and 6 chitons), 33 foraminifera and 21 ostracods. Other preserved calcareous groups, which appeared in minor proportions, were brachiopods and cirripeds. The calcareous fossil assemblages from the early Holocene represent an ecosystem transition which started with vacant niches first occupied by opportunistic species, and/or eurytopic taxa. These were then replaced by more diverse fauna assemblages, associated with the proliferation of habitats which occurred under truly marine conditions during the Mid Holocene. When Holocene calcareous fauna is compared with its Pleistocene counterparts from the same region, some differences in the proportion of taxonomic groups and taxa composition are noted. These partly follow the heterogeneity of habitats in the Beagle Channel and water masses of different origin which have either greater or less influence throughout the Late Quaternary, but they can also be interpreted in association with environmental changes after the Last Glacial Maximum. In conclusion, the data provide insights into both spatial and temporal changes, and show evidence of a gradual transformation from a brackish to a marine environment caused by the Holocene sea transgression. It also documents Late Quaternary faunistic changes associated with topographic and oceanographic local conditions in this microbasin.

An examination of possible relationships between paleoenvironmental conditions during the Pleistocene–Holocene transition and human occupation of southern Patagonia (Argentina) east of the Andes, between 46° and 52° S

Spatial and temporal variations in evidence for human occupation of Argentinian south Patagonia closely resemble changes in past vegetation reconstructed from pollen records. The Antarctic Cold Reversal was cold and dry in the Deseado Massif and there is little evidence of humans at this time. In contrast, the Younger Dryas interval was warmer and slightly wetter and this was when humans moved into the Deseado area. Increasing temperatures during the early Holocene brought higher precipitation to much of Patagonia east of the Andes except the northern Deseado Massif, explaining the increase in evidence of human occupation in western areas and the decrease in evidence in the massif. Spatial and temporal variations in the frequency of radiocarbon dates indicating human presence, show that in southern Patagonia humans were not only influenced by the major climate shifts of the Pleistocene–Holocene transition but possibly also by distinct short-term changes lasting only a few to several centuries that are apparent in the high-resolution Antarctic Byrd ice core. Water availability may have had the greatest influence on human use of the landscape rather than temperature. However, as temperature is crucial in controlling the latitude of the core of the Southern Westerly Winds, associated with reduced precipitation over most of eastern Patagonia, it is difficult to separate water from temperature in examining impacts on the first humans in southernmost South America.