Pleistocene-Holocene Transition Research Articles

Understanding Paleoclimate Through Southern California’s Packrat Middens

Documenting how ecosystems responded to climate change in the past can inform models for the future relevant to conservation decision-making. Packrat middens, or giant nests consisting of gathered plant material made by rodents of the genus Neotoma, represent one of the best data sources for understanding how plant communities change over time. These nests can be preserved for thousands of years, spanning episodes of glacial-interglacial variation, such as the Pleistocene-Holocene transition, or more recent fluctuations, such as the Little Ice Age and Medieval Warm Period. We used the USGS-NOAA paleoclimate open-access database to develop spatiotemporal reconstructions of plant species in Southern California, incorporating more than 242 individual middens with a total of 193 available radiocarbon dates spanning around 44,493 years cal BP. As a result, 374 plant species were identified within the SoCal middens, with Joshua Tree (Yucca brevifolia), Joint Pine (Ephedra species), and California Juniper (Juniperus californica) being the most abundant. We then applied these data to reconstruct past vegetation communities and contextualize a recently discovered asphaltic midden recovered from the La Brea Tar Pits (Los Angeles, California). The La Brea midden represents both the oldest and most coastal midden in our dataset in California and contains vegetation spanning Marine Isotope Stages 2-3. Ultimately, this research allows us to paint a picture of changing vegetation over time as a baseline for palaeoecological food web studies and can be compared with present day packrat nests found in this urban biodiversity hotspot. These data will be curated through the Conservation Paleobiology Network’s urban vegetation working group (based in Los Angeles, California) and made available for use by conservation and management projects throughout the region. With this information, CPN can implement habitat restoration projects in SoCal.

Drainage integration of small endorheic basins at the Pleistocene-Holocene transition: An example from southern Italy

The drainage integration of three Late Pleistocene intramontane basins located in the southern Italian Apennines was reconstructed by integrating information derived from geomorphic, structural, and stratigraphic analyses. The Santaloja (SLJ), Lago (LG), and Pantani (PN) basins are located in the axial zone of the Apennines fold-and-thrust belt where they mainly comprise Mesozoic to Cenozoic deep-sea water siliceous and calcareous rocks. The Quaternary development of these intramontane basins draining the Basento River catchment provides an example of drainage evolution within collisional mountain belts and its tectonic and climatic controlling mechanisms. Tectonically, sets of NW-SE- and NE-SW-trending faults formed a large trough with ensuing river valley development configured to synclinal folds. The ongoing interplay of these active and passive tectonic controls lead to compartmentalisation into three endorheic basins. Uncalibrated radiocarbon dating of peat layers from boreholes reveals that lacustrine facies conditions prevailed during the Late Pleistocene, spanning 34,785 to 41,325 ka during Marine Isotope Stage 3. Morphometric analysis suggests that these endorheic lacustrine basins subsequently became integrated via overspill from 13.25 kyr calBC onwards linked to Late Pleistocene climatic changes creating the Basento River. Within the axial zone of the southern Apennines, tectonically driven headwards erosion is commonly attributed to lengthening of major rivers like the Basento River. However, this study demonstrates a more complex interplay between tectonics and climate change for intramontane basin development and its drainage evolution.

Glacial Influence Affects Modularity in Bacterial Community Structure in Three Deep Andean North-Patagonian Lakes.

We analyze the bacteria community composition and the ecological processes structuring these communities in three deep lakes that receive meltwater from the glaciers of Mount Tronador (North-Patagonia, Argentina). Lakes differ in their glacial connectivity and in their turbidity due to glacial particles. Lake Ventisquero Negro is a recently formed proglacial lake and it is still in contact with the glacier. Lakes Mascardi and Frías lost their glacial connectivity during the Pleistocene-Holocene transition. Total dissolved solid concentration has a significant contribution to the environmental gradient determining the segregation of the three lakes. The newly formed lake Ventisquero Negro conformed a particular bacterial community that seemed to be more related to the microorganisms coming from glacier melting than to the other lakes of the basin. The net relatedness index (NRI) showed that the bacterial community of lake Ventisquero Negro is determined by environmental filtering, while in the other lakes, species interaction would be a more important driver. The co-occurrence network analysis showed an increase in modularity and in the number of modules when comparing Lake Ventisquero Negro with the two large glacier-fed lakes suggesting an increase in heterogeneity. At the same time, the presence of modules with phototrophic bacteria (Cyanobium strains) in lakes Frías and Mascardi would reflect the increase of this functional photosynthetic association. Overall, our results showed that the reduction in ice masses in Patagonia will affect downstream large deep Piedmont lakes losing the glacial influence in their bacterial communities.

Holocene vertebrate fauna in Fergana Valley, Kyrgyzstan, based on fossils from the Obishir-5 rock shelter

Central Asia is a region that, owing to its geographical position, has always been at the intersection of cultures. In the Fergana Valley, located in the very heart of Central Asia, the Late Pleistocene–Early Holocene is characterized by the expansion and intensification of human settlements. This cultural event has previously been linked to global climate changes that took place during the Pleistocene–Holocene transition. In order to reconstruct local climatic conditions in the area during this period, it is worth studying the fossil vertebrate faunas from late Quaternary sites in the Fergana Valley. The Obishir-5 rock shelter, dating to the Late Pleistocene–Early Holocene period, discovered in the middle of the 20th century, is a key archeological site in the valley. To date no thorough zooarcheological research has been done on the excavated faunal remains. Here we present the results of the first faunal analysis of the small vertebrates found at this site. We studied the taxonomic composition of remains, which was then used to make paleoenvironmental reconstructions. In total, we identified 13 small mammal species and three bird species. In addition, the assemblage contained one amphibian and two reptile taxa. The faunal composition suggests that during the final Pleistocene and Early Holocene the study area enjoyed a stable climate with vegetation dominated by open biotopes (alpine meadows, steppes, semi-deserts). Its location makes the Fergana Valley an example of a geographically isolated area for a terrestrial fauna which can exist for a long time without being influenced by biotic factors from neighbouring territories.

Paleoenvironmental significance of Benthic Foraminifera and Ostracoda from the late Quaternary of the Ceará Basin, Brazilian Equatorial Margin

Benthic foraminifera, ostracods and pteropods are reliable paleoenvironmental indicators in Quaternary deposits. However, in the Ceará Basin, on the Brazilian Equatorial Margin, these microfossils are poorly studied. This paper investigates environmental changes during the Pleistocene–Holocene transition in the Icaraí subbasin based on micropaleontological analysis of the core ANP 1011. Seventy-four taxa of benthic foraminifera, represented predominantly by Globocassidulina, Uvigerina, Pyrgo and Melonis, have been identified. The ostracod assemblages are composed mainly by the families Macrocyprididae, Cytheruridae, Trachyleberididae, Pontocyprididae and Krithidae, of which the genus Krithe was the most abundant. The composition of the ostracod assemblages identified in this study area differs somewhat from other regions of the Brazilian Margin. The assemblages of foraminifera and ostracod characterize a typical bathyal paleoenvironment. The occurrence of pteropods and dominance of epifaunal foraminifera taxa, mainly Pyrgo sp. and Miliolinella sp. in the lower portion of the core (Pleistocene), indicates higher phytodetritus input and oxygen concentration. A conspicuous environmental change was observed in the upper portion of the core, which corresponds to the Holocene, where the increase of infaunal foraminifera (e.g., Uvigerina, Globocassidulina and Melonis) suggests reduction in the organic matter input and, probably, increased bacterial density and depletion in dissolved oxygen in the sediment.

Prehistoric frontier or frontier of prehistorians: what about litho-spaces during the Pleistocene-Holocene transition in central France?

Abstract. The aim of this paper is about discussing to the homogeneity and relationship of the Belloisian tradition with the more southern Laborian. In this regard, we choose central France, the reputed southern margin of Belloisian, to be the geographical framework of this study. It is punctuated by key sites belonging to the Pleistocene-Holocene transition: Muides-sur-Loire, Champ-Chalatras and Cuze de Sainte-Anastasie. What we are questioning in this article are the networks relationships between the Belloisian and the Laborian traditions through the study of lithic industry. This research area is on the fringes of the major dynamic’s university programs too and involves research traditions that differ regionally. We therefore also question the notion of “prehistoric” or “prehistorian” boundaries through a petro-techno-typological analysis of lithic series. In this case study, the techno-economic data shows a frequentation of common outcrops and economic management of the silicites for the three sites. This complex network of relationships between groups shows the porosity between the prehistorian designation. The identification of laborian “know-how” from silicites in the south of the Paris Basin and the circulation of large laminar supports corroborate this fact. So finally, these results lead us to propose the hypothesis of an interweaving of a Belloisian technical sub-system with a Laborian tradition, now well defined.

Geomorphologic evidence of jökulhlaups along the Hvítá River, southwestern Iceland

Glacial outburst floods (jökulhlaups) have been a significant driver of landscape evolution, environmental change, and geohazards throughout the Quaternary. Iceland experiences more frequent jökulhlaups than nearly anywhere else on Earth, though most research focuses on subglacial volcanogenic floods that drain across outwash plains. Abundant geomorphologic evidence exists for largescale jökulhlaups that drained along the modern-day course of the Hvítá River in southwestern Iceland during early Holocene deglaciation, originating from ice-dammed Glacial Lake Kjölur; yet only one previous publication has investigated these events. This study uses a combination of field mapping and remote sensing to identify new jökulhlaup geomorphologic evidence along the Hvítá River, including erosional landforms such as scoured bedrock, anastomosing channel networks, cataracts, and canyons, and depositional features such as boulder bars and channel infill. We synthesize new findings with previously reported work to: 1) present an updated geomorphologic map of Hvítá jökulhlaup evidence; 2) reconstruct flood drainage routes, landscape impact, hydrology, and relative chronology; and 3) hypothesize scenarios of ice margin position and glacial lake evolution. Interpreting flood landform assemblages reveals a more extensive geomorphologic record than previously reported, with a complex drainage pattern along four separate routes from two potentially different sources. Reconstructed peak flow discharges span four orders of magnitude from 10² to 10$^5$ m³/s. Geomorphologic and paleohydraulic results introduce four hypothesized drainage scenarios, though absolute geochronology is necessary to determine whether multiple floods drained along each route. The Hvítá jökulhlaups yield insight into the timing and dynamics of the final phase of Icelandic Ice Sheet decay, advancing understanding of Iceland’s Pleistocene–Holocene transition, demonstrating the importance of high magnitude, low frequency floods in landscape evolution, and serving as an analogue to ice and meltwater response to past, present, and future climate warming in glaciated regions worldwide.

Preservation of Mammalian Teeth and Bones Influences Identification of Terminal Pleistocene to Middle Holocene Hunter-Gatherer Subsistence at Ban Rai Rockshelter, Northwest Thailand

Ban Rai Rockshelter in northwest Thailand, dating to the Terminal Pleistocene and Middle Holocene, includes evidence for hunter-gatherer exploitation of mammals, birds, reptiles, fish, and arthropods. Abundant faunal remains, identified throughout site deposits, include macaques (Macaca sp.) and Sambar deer (Rusa unicolor), but these identifications are influenced by an assemblage largely comprised of preserved tooth elements and fragmented bone. Area 3 at Ban Rai has the largest abundance and diversity of faunal remains recovered and identified in this study. Here, we examine the zooarchaeological assemblage from Ban Rai Rockshelter, to understand long-term hunter-gatherer subsistence change, influenced by site preservation, during and after the Pleistocene–Holocene transition. Our results support the presence of the exploitation of arboreal taxa during the Early and Middle Holocene in northwest Thailand.

Small mammal taphonomy and palaeoecological Holocene interpretations in the Andean piedmont (southern Mendoza province, Argentina)

ABSTRACT Salamanca cave (southern Mendoza province) is in the Andean piedmont, a transitional area in which small mammal communities may have been affected by climatic pulses. The site yields three archaeological components covering from the early to the late-Holocene with a mid-Holocene occupational and sedimentological hiatus. Taphonomic analyses of the small mammal assemblages indicate that barn owls (Tyto furcata) were the main accumulation agent, ensuring accurate palaeoecological inferences. Taxonomic composition of the site shows the dominance of Eligmodontia sp. followed by Thylamys pallidior, Phyllotis cf. P. vaccarum-pehuenche and Ctenomys sp., all of them indicative of shrubland and bare ground habitats. Palaeoclimatic inferences indicate a trend to warmer temperatures from the lower to the upper component with a slight increase in humidity in the middle component. This humid pulse is also supported by post-depositional taphonomic processes. The taxonomic structure and abundance of small mammals do not show deep changes amongst the three archaeological components, following the general trend observed in other archaeological sites from the Pampean region, southern Mendoza province and the arid and semi-arid zones of north Patagonia, in which changes in the taxonomic composition of small mammal communities are almost absent since Pleistocene–Holocene transition to late Holocene.

Relict permafrost preserves megafauna, insects, pollen, soils and pore-ice isotopes of the mammoth steppe and its collapse in central Yukon

In eastern Beringia (unglaciated Alaska and western Yukon), the Pleistocene-Holocene transition was characterised by rapid changes in plant, insect and mammal communities as the mammoth steppe ecosystem was replaced, first by shrub tundra and later boreal forest. These changes indicate a transition from well drained terrain with deep active layers to wetter, cooler soils, to which steppe-tundra vegetation was poorly adapted. The nature and precise timing of these events is not well resolved, particularly in central Yukon where regional climate may have been strongly affected by the retreating Cordilleran-Laurentide ice sheet complex. Resolving this uncertainty is not only important for understanding past ecosystems, but also provides a long-term perspective for contemporary environmental change and shrub expansion that affects large areas of northern high-latitudes today. Here, we report chronology (41 radiocarbon dates), stratigraphy, pore-ice δ2H/δ18O measurements, pollen data, megafauna remains and fossil insect assemblages from a permafrost-preserved loessal sequence in central Yukon, named Lucky Lady. The site spans the interval from ca. 17,000 to 8000 cal yr BP (calibrated years before C.E. 1950) and records the Pleistocene-Holocene transition in exceptional resolution. Full glacial environments (ca. 16,500 cal yr BP) supported elements of steppe-tundra vegetation and an insect fauna dominated by Connatichela artemisiae - an endemic weevil indicating warm soil temperatures. The collapse of the mammoth steppe ecosystem began with slowing of loess accumulation and development of paleosol ca. 13,480 cal yr BP. At this time, C. artemisiae remains become infrequent and Artemisia pollen decline to be replaced by Cyperaceae (ca. 13,220), before mesic, shrub taxa (likely dwarf Betula and Salix) becomes dominant ca. 13,210 cal yr BP. The establishment of shrub tundra is associated with rapid changes in δ2H/δ18O measurements, suggesting that ecological turnover coincided with a shift in atmospheric conditions and moisture availability. Finally, boreal vegetation communities became established ca. 10,680 cal yr BP. The replacement of steppe-tundra vegetation in central Yukon lagged other areas of eastern Beringia by as much as 1000 years and coincided with rapid deglaciation during the Bølling–Allerød time-period (14,600–12,900 cal yr BP). Turnover in insect and vegetation communities took place in ca. 40 years as shrub tundra became dominant. This rapid turnover has parallels with contemporary Arctic greening and re-emphasises the sensitivity of high-latitude environments to climate change.

Armes de chasse dans l’Épipaléolithique du Caucase du Nord

The article is devoted to the traceological study of points and geometric microliths that are characteristic of the Epipaleolithic sites of the northwestern Caucasus and the Elbrus region. The regularities between the type of stone tools and their functional use are analyzed. Composite hunting weapons were effectively used in hunting a variety of ungulate herd animals. The composition of faunal assemblages largely depended of climatic and landscape conditions of the sites in different periods of the Late Glacial period: from the Oldest Dryas to the Pleistocene–Holocene transition. The proximity of lithic industries within a vast region in the North Caucasus, similar shapes of projectiles and lithic inserts into composite hunting weapons could be associated with active human movements, which are confirmed by the transportation of obsidian from the Elbrus region to the northwestern Caucasus and the transportation of high-quality flint from the west to the Elbrus region in the north-central Caucasus.

Blue Turns to Gray: Paleogenomic Insights into the Evolutionary History and Extinction of the Blue Antelope (Hippotragus leucophaeus).

The blue antelope (Hippotragus leucophaeus) is the only large African mammal species to have become extinct in historical times, yet no nuclear genomic information is available for this species. A recent study showed that many alleged blue antelope museum specimens are either roan (Hippotragus equinus) or sable (Hippotragus niger) antelopes, further reducing the possibilities for obtaining genomic information for this extinct species. While the blue antelope has a rich fossil record from South Africa, climatic conditions in the region are generally unfavorable to the preservation of ancient DNA. Nevertheless, we recovered two blue antelope draft genomes, one at 3.4× mean coverage from a historical specimen (∼200 years old) and one at 2.1× mean coverage from a fossil specimen dating to 9,800-9,300 cal years BP, making it currently the oldest paleogenome from Africa. Phylogenomic analyses show that blue and sable antelope are sister species, confirming previous mitogenomic results, and demonstrate ancient gene flow from roan into blue antelope. We show that blue antelope genomic diversity was much lower than in roan and sable antelope, indicative of a low population size since at least the early Holocene. This supports observations from the fossil record documenting major decreases in the abundance of blue antelope after the Pleistocene-Holocene transition. Finally, the persistence of this species throughout the Holocene despite low population size suggests that colonial-era human impact was likely the decisive factor in the blue antelope's extinction.

The velocity of postglacial migration of fire-adapted boreal tree species in eastern North America

The Earth's climate has been warming rapidly since the beginning of the industrial era, forcing terrestrial organisms to adapt. Migration constitutes one of the most effective processes for surviving and thriving, although the speed at which tree species migrate as a function of climate change is unknown. One way to predict latitudinal movement of trees under the climate of the twenty-first century is to examine past migration since the Last Glacial Maximum. In this study, radiocarbon-dated macrofossils were used to calculate the velocity of past migration of jack pine (Pinus banksiana) and black spruce (Picea mariana), two important fire-adapted conifers of the North American boreal forest. Jack pine migrated at a mean rate of 19 km per century (km-cent) from unglaciated sites in the central and southeastern United States to the northern limit of the species in subarctic Canada. However, the velocity increased between unglaciated and early deglaciated sites in southern Quebec and slowed from early to mid-Holocene in central and eastern Quebec. Migration was at its lowest speed in late-Holocene times, when it stopped about 3,000 y ago. Compared with jack pine, black spruce migrated at a faster mean rate of 25 km-cent from the ice border at the last interstadial (Bølling/Allerød) to the species tree limit. The modern range of both species was nearly occupied about 6,000 y ago. The factors modulating the changing velocity of jack pine migration were closely associated with the warm-dry climate of the late Pleistocene-Holocene transition and the more humid climate of the mid- and late-Holocene.

Climate and Vegetation Change, Hillslope Soil Erosion, and the Complex Nature of Late Quaternary Environmental Transitions, Eastern Mojave Desert, USA

In what are now the warm deserts of the American Southwest, direct effects of changing climate on plant distributions are typically viewed as the principal driver of vegetation changes that followed the late Pleistocene–Holocene transition (LPH). However, at a semi-arid site in the eastern Mojave Desert, the transition to modern, shrub-dominated desert scrub on xeric, south-aspect hillslopes occurred only after the erosion of relatively thick soils toward the end of the mid-Holocene. Soils with well-developed Bt horizons began to form in the late Pleistocene on both north- and south-aspect hillslopes through the entrapment and accumulation of aeolian sediments in coarse colluvium. Those soils are capable of absorbing and retaining substantial moisture and support relatively dense stands of perennial C4 grasses that have diffuse, fibrous root systems. The age of alluvial deposits on the basin floor indicates a surge in sediment production through the erosion of some of those hillslope soils toward the end of the mid-Holocene. However, that erosion was largely limited to the more xeric, more sparsely vegetated, south-aspect hillslopes. The soils formed on mesic north-aspect hillslopes remain largely non-eroded to the present day, demonstrating the central role of vegetation in modulating erosion and sediment supply. The loss of soils from south-aspect hillslopes fundamentally changed the capacity of those environments to absorb and store moisture, and altered the depth and temporal durations of plant-available moisture. Those hydrological changes drove a loss of perennial C4 grasses and a transition to dominance by xerophytic plants—shrubs with deeper taproots capable of extracting moisture stored within bedrock joints and fractures, and shallow-rooted succulent plants that store moisture internally. Following the LPH, vegetation change at the site apparently occurred in two distinct phases separated in time: (1) initial vegetation changes driven directly by increasing climatic aridity and (2) subsequent changes linked to the later episode of soil erosion. Although climate shifts ultimately generate vegetation changes, the proximate mechanisms to which plants directly respond can lag far behind climatic transitions and involve complex relationships of vegetation, soils, and changing soil hydrologic conditions.

Do genetically informed distribution models improve range predictions in past climates? A case study with balsam poplar

Species distribution models (SDMs) are one of the most widely used approaches to predict changes in habitat suitability in response to climate change. However, as typically implemented, SDMs treat species as genetically uniform throughout their ranges and thereby ignore potentially important genetic differences between populations. While numerous studies have used SDMs to model genetically based subgroupings within species, the ability of such models to be transferred to new times has rarely been evaluated. Here, we used standard and genetically informed distribution models (gSDMs) to predict the future and past range of balsam poplar (Populus balsamifera L.). We then assessed model transferability of standard SDMs and gSDMs using balsam poplar fossil pollen and macrofossil occurrences. In general, standard and gSDMs performed similarly through time, with both predicting a northward expanding range from refugia as glaciers receded over the past 22 ky BP and declining suitable area in future climates. Both standard and gSDMs showed moderate abilities to distinguish balsam poplar fossils from pseudo-absences but tended to predict lower suitability at fossil sites during the Pleistocene-Holocene transition. Although gSDMs applied to balsam poplar did not prove more transferable than standard SDMs, they provided numerous unique insights, such as the change in suitable area of genetic clusters through time and potential refugial locations. We argue more research is needed to determine which species may benefit most from the gSDM approach and to test gSDMs with temporally or spatially independent occurrences, as is often recommended for standard SDMs.

Spatiotemporal influences of climate and humans on muskox range dynamics over multiple millennia.

Processes leading to range contractions and population declines of Arctic megafauna during the late Pleistocene and early Holocene are uncertain, with intense debate on the roles of human hunting, climatic change, and their synergy. Obstacles to a resolution have included an overreliance on correlative rather than process-explicit approaches for inferring drivers of distributional and demographic change. Here, we disentangle the ecological mechanisms and threats that were integral in the decline and extinction of the muskox (Ovibos moschatus) in Eurasia and in its expansion in North America using process-explicit macroecological models. The approach integrates modern and fossil occurrence records, ancient DNA, spatiotemporal reconstructions of past climatic change, species-specific population ecology, and the growth and spread of anatomically modern humans. We show that accurately reconstructing inferences of past demographic changes for muskox over the last 21,000 years require high dispersal abilities, large maximum densities, and a small Allee effect. Analyses of validated process-explicit projections indicate that climatic change was the primary driver of muskox distribution shifts and demographic changes across its previously extensive (circumpolar) range, with populations responding negatively to rapid warming events. Regional analyses show that the range collapse and extinction of the muskox in Europe (~13,000 years ago) was likely caused by humans operating in synergy with climatic warming. In Canada and Greenland, climatic change and human activities probably combined to drive recent population sizes. The impact of past climatic change on the range and extinction dynamics of muskox during the Pleistocene-Holocene transition signals a vulnerability of this species to future increased warming. By better establishing the ecological processes that shaped the distribution of the muskox through space and time, we show that process-explicit macroecological models have important applications for the future conservation and management of this iconic species in a warming Arctic.

Mainland-coastal interactions in East Borneo: Inter-site comparison and Bayesian chronological models of two Late Pleistocene–Holocene sequences (Liang Abu and Kimanis rock shelters)

In recent decades, East Borneo has become an increasingly important archaeological “hot-spot” in Island Southeast Asia as a result of early dates for rock art ca. 38,000 BP and the greater number of excavated sites that support a much longer period of human occupation. However, the chronology of settlement and adaptation to environmental changes during the Pleistocene–Holocene transition is still poorly known. Here we report on an excavation at the Liang Abu rock shelter which has contexts dating from the Late Pleistocene (12,660 ± 58 uncal. BP) to the present day, indicating a terminus ante quem (TAQ) for human occupation at 23,790 BP. We present the results of an attempt to systematically integrate and compare data from Liang Abu and Kimanis, a geographically close site with a previously published sequence. Particular attention is paid to post-depositional issues in tropical settings and to data compatibility, reuse, and reproducibility, relying on open-source software for data processing (R scripts) and Bayesian chronological modeling. Two Bayesian models are built and compared using the ChronoModel software, which can handle outliers and uncertainty (e.g., freshwater reservoir effect). This first inter-site comparison for Borneo results in a new chronology of human settlement and mainland–coastal interactions in East Borneo and paves the way for future regional synthesis.

Ecological niche modeling and diachronic change in Paleoindian land use in the northwestern Great Basin, USA

The Great Basin underwent considerable environmental change during the Pleistocene-Holocene transition, such as lower precipitation, increased temperatures, and the diminishment of lakes and wetlands. Archaeologists have long hypothesized that people responded by altering their settlement-subsistence strategies. Models outlining these responses feature predictions that generally fall into two categories: (1) people should have spent more time in remaining productive patches and expanded their diet breadth; and (2) people should have added new habitats to their settlement-subsistence regimes. These responses are not mutually exclusive, and both may have occurred, but they have been difficult to evaluate using empirical data because the region’s archaeological record is predominantly comprised of open-air lithic scatters that lack food remains. Through ecological niche modeling, we test the hypothesis that early Holocene groups added new habitats. We develop two models—one for the Younger Dryas and one for the early Holocene—using recorded Paleoindian sites in Humboldt County, Nevada and a set of environmental variables. Our results show that Younger Dryas sites mostly occur around lowland and upland lakes and within ecotones, while early Holocene sites mostly occur around valley bottoms, riparian corridors, and upland springs. They demonstrate that people added new habitats, presumably in response to disappearing wetlands. This shift may be best explained using the patch choice model.

Paleoenvironmental dynamics in central‐eastern Brazil during the last 23 000 years: tropical peatland record in the Cerrado biome

AbstractThe Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central‐eastern Brazil. A multi‐proxy approach was used that involved palynological analysis, stable isotopes (δ13C, δ15N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub‐humid climatic conditions seem to have been established in the mid‐/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc.

Environmental Changes on Kunashir Island (Kuril Archipelago) during the Middle and Late Holocene

Sea level rise during the Pleistocene-Holocene transition period caused the formation of lagoon lakes along the western and eastern coasts of the Kuril Islands. These lakes include Lake Serebryanoye, located in the northern part of the South Kuril Isthmus near the Pacific coast of Kunashir Island (44°03'21" N; 145°49'46" E). The total thickness of sediments in the lake was 367 cm. They are characterized by diatom flora (334 species), representing various ecological groups: freshwater, brackish water, marine, marsh, lacustrine, rheophilic, planktonic, benthic. The analysis of diatoms made it possible to distinguish two complexes. As shown by radiocarbon dating, in the Middle Holocene (100.5-367 cm interval) the sediments corresponded to the lagoon stage, which changed in the Late Holocene (100.5-0 cm interval) to the freshwater lake stage. Palynological analysis showed a successive change of biocenoses, reflecting the development in the Middle Holocene of birch-broadleaved forests with the participation of Pinus koraiensis, Picea sp. The most abrupt change in biocenoses is observed at the boundary of the Middle and Late Holocene. This change of biocenoses is expressed by the dominance of conifers in the vegetation cover, represented by various species of Picea, Pinus, Abies, Larix. It also shows the relative cooling of the climate in the Late Holocene.