The last glacial-Holocene transition in southern Chile

Tabula rasa in the Patagonian Channels? The phylogeography of Oreobolus obtusangulus (Cyperaceae)

The extent of the Pleistocene glaciations in the Patagonian Channel region (southwesternmost South America) and their impact on the vegetation there are largely unknown. Whether the regional flora was wiped out completely (tabula rasa) or survived in ice-free pockets (in situ survival) is still an open question. The molecular imprint of either scenario should still be visible in extant populations. Therefore, DNA sequence data of Oreobolus obtusangulus Gaudich. (Cyperaceae) were analysed. This species is an abundant constituent of Patagonian cushion peat bogs, one of the Patagonian Channel region's major vegetation types. Three hundred and eighty-four individuals from 48 populations were sequenced for two chloroplast (ycf3-psaA and trnQ^UUG -psbK intergenic spacers) and 14 nuclear loci containing simple sequence repeats (SSRs; microsatellites). Phylogenetic reconstructions and the geographic distribution of genetic diversity revealed that the species was split into three main lineages whose general distributions comprise three separate major regions, that is, south-central Chile, Fuego-Patagonia and the East Patagonian Andes, which probably constitute glacial refugia. Postglacial migration fronts formed a suture zone with high levels of genetic diversity in the Northwest Patagonian Andes, where remnants of a supposedly ancestral lineage were also found to be locally restricted to a single population (Huinay). The heavily glaciated Patagonian Channels were likely recolonized from the northwest, and partly from the south. Although the westernmost Patagonian Channel population (Estero Bachem) harboured private SSR alleles (singletons) and showed slightly elevated genetic diversity, it remained unclear whether this population actually survived in situ. This study helps fill a major gap in reconstructing the Pleistocene vegetation history of West and Andean Patagonia.

Comparison of modern pollen distribution between the northern and southern parts of the South China Sea

The authors conducted a palynological analysis based on different number of air pollen samples for the northern and southern parts of the South China Sea, respectively, in order to give a reference to reconstruct the paleoclimate of the area. (1) Fifteen air pollen samples were collected from the northern part of the South China Sea from August to September 2011, and 13 air pollen samples were collected from the southern part of the South China Sea in December 2011. The pollen types were more abundant in the north than in the south. The total pollen number and concentration in the north was 10 times more than that in the south, which may be because of the sampling season. Airborne pollen types and concentrations have a close relationship with wind direction and distance from the sampling point to the continent. (2) Seventy-four samples were collected from surface sediments in the northern part of the South China Sea in the autumn. Thirty-three samples were collected from surface sediments in the southern part of the South China Sea in the winter. Pollen concentrations in the north were nearly 10 times higher than that in the south. This is because trilete spores are transported by rivers from Hainan Island to the sea and also by the summer monsoon-forced marine current. (3) Ten air pollen samples and 10 surface sediments samples were selected for comparison. The pollen and spores in the air were mainly herbaceous and woody pollen, excluding fern spores, having seasonal pollen characteristics. Pollen in the surface sediments were mainly trilete, Pinus, and herbaceous, and may also show a combination of annual pollen characteristics.

Metabolic and molecular characterization of bacterial community associated to Patagonian Chilean oligotrophic-lakes of quaternary glacial origin

The Patagonian Lakes have particular environmental conditions with or without intermittent disturbances. The study of the microorganisms present in aquatic ecosystems has increased notably because they can be used as micro-scale bioindicators of, among others, anthropogenic pollution and climatic change. The aim of the work was to compare the composition of the bacterial communities associated with sediments of three Patagonian Lakes with different geomorphologic patterns and disturbances. The lake sediments were characterized by molecular techniques, physiology profiles and physico-chemical analyses. The metabolic and physiological profiles of the microbial community demonstrated that non-impacted Tranquilo Lake is statistically different to impacted Bertrand and Plomo Lakes. Similar results were detected by DGGE profiles. FISH results demonstrated that betaproteobacteria showed the highest count in the Tranquilo Lake while gammaproteobacteria showed the highest counts in the Bertrand and Plomo Lakes, indicating that their sediments are highly dystrophic. The results demonstrate differences in the metabolic activity and structural and functional composition of bacterial communities of the studied lakes, which have different geomorphological patterns due to disturbances such as volcanic activity and the climatic change.

Constraints on the development of agriculture

The development of agriculture was limited by external constraints, mainly climate, before the Holocene and mainly by social institutions after that. Population size and growth was important but ultimately did not determine where and why agriculture evolved.

Population genetic structure of long-tailed pygmy rice rats (Oligoryzomys longicaudatus) from Argentina and Chile based on the mitochondrial control region

The rodent Oligoryzomys longicaudatus (Bennett, 1832) (Rodentia, Cricetidae) inhabits southern forests of Argentina and Chile, a region severely affected by glaciations during the Pleistocene–Holocene periods. We evaluate here the diversity of the mitochondrial control region to characterize the genetic structure of this species from forests and bushy areas of seven populations from Argentina and four populations from Chile. Statistical analyses showed shallow haplotype trees and mismatch distributions compatible with recent range expansions. The presence of “private” haplotypes indicates that current levels of gene flow among populations of each country would be low to moderate. Significant differences in haplotype frequencies were detected between eastern and western populations, indicating that the Andes mountains would be an effective geographic barrier for gene flow despite the existing valleys that could act as corridors for dispersion. A single clade containing all the haplotypes was recovered in the phylogenetic trees, suggesting postglacial dispersion from a single refugium during the Last Glacial Maximum. The higher effective size and levels of polymorphism in populations from Chile suggest that the refugium was located in this country. The asymmetric gene flow from Chile to Argentina may reflect a recent colonization of the eastern populations.

The late Pleistocene colonization of South America: an interdisciplinary perspective

In this article, we briefly review scenarios for the first peopling of the New World, including the Clovis First/Single Origin, Tripartite, and Dual Migration models. We then discuss bioanthropological, molecular genetic, archaeological and biogeographic evidence for the peopling of the continent. To conclude, we draw on different lines of evidence to make inferences concerning the timing, direction, and type of early human dispersion in South America.

Antarctic Timing of Surface Water Changes off Chile and Patagonian Ice Sheet Response

Marine sediments from the Chilean continental margin are used to infer millennial-scale changes in southeast Pacific surface ocean water properties and Patagonian ice sheet extent since the last glacial period. Our data show a clear "Antarctic" timing of sea surface temperature changes, which appear systematically linked to meridional displacements in sea ice, westerly winds, and the circumpolar current system. Proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore, but reveal a variable glacier-response time of up to approximately 1000 years, which may explain some of the current discrepancies among terrestrial records in southern South America.

Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event

During the Younger Dryas event, about 12,000 years ago, the Northern Hemisphere cooled by between 2 and 10 degrees C (refs 1, 2) whereas East Antarctica experienced warming. But the spatial signature of the event in the southern mid-latitudes and tropics is less well known, as records are sparse and inconclusive. Here we present high-resolution analyses of skeletal Sr/Ca and 18O/16O ratios for a giant fossil Diploastrea heliopora coral that was preserved in growth position on the raised reef terraces of Espiritu Santo Island, Vanuatu, in the southwestern tropical Pacific Ocean. Our data indicate that sea surface temperatures in Vanuatu were on average 4.5 +/- 1.3 degrees C cooler during the Younger Dryas event than today, with a significant interdecadal modulation. The amplified annual cycle of sea surface temperatures, relative to today, indicates that cooling was caused by the compression of tropical waters towards the Equator. The positive correlation in our record between the oxygen isotope ratios of sea water and sea surface temperatures suggests that the South Pacific convergence zone, which brings 18O-depleted precipitation to the area today, was not active during the Younger Dryas period.

Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile

Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.

The Younger Dryas: Cold, Cold Everywhere?

The transition from the last ice age to the current warm period was interupted by a ~1000-year return to glacial conditions. Most of the evidence for this Younger Dryas (YD) event comes from in and around the North Atlantic, and the geographical extent of the event remains uncertain. In his Perspective, Rodbell reviews the evidence for and against a YD event in the Southern Hemisphere and highlights the study by Bennett et al., who have found no evidence for a YD event in four lake records from southern Chile.