Pleistocene-Holocene Transition Research Articles

Optimal Linear Estimation (OLE) Modeling Supports Early Holocene (9000–8000 RCYBP) Copper Tool Production in North America

The discovery and development of metal as a tool medium is a topic of global interest. A fundamental research goal involves establishing the timing of human experimentation with naturally occurring copper ore, which is commonly associated with sedentary, agrarian-based societies. However, in North America, there is well-documented millennia-scale exploitation of copper as tool media by small, seasonally mobile hunter-gatherer groups in the western Great Lakes. Archaeologists have suggested that Late Paleoindian groups may have begun using copper as a tool medium almost immediately after they entered the Lake Superior basin. However, only a few radiocarbon dates support such early use of copper. Here, we use optimal linear estimation modeling to infer the origin date for copper tool production in North America. Our results show that the invention of copper as a tool media likely occurred shortly after the first pioneering populations encountered copper ore during the Pleistocene-Holocene transition. The origin dates modeled here (ca. 8100 RCYBP) reveal several important features about the behavior of pioneering hunter-gatherer populations. Moreover, our results suggest that this phenomenon represents the earliest known use of metal for utilitarian copper tool production.

Marmot hunting during the Upper Palaeolithic: The specialized exploitation at Grotte di Pradis (Italian pre-Alps)

In the last few years several studies have reassessed the attraction and the role of small game in the subsistence economy of hunter-gatherers across Europe and the Mediterranean region since the Middle Paleolithic. The exploitation of small mammals intensified during the Pleistocene-Holocene transition, when some unusual faunal assemblages were recorded in the Alpine arch and the Prealpine belt. In this region marmot became a relevant resource during the Late Glacial, albeit the relative foraging systems were mostly focused on the exploitation of medium and large size herbivores. In this report we present zooarchaeological data from Grotte di Pradis (northeastern Italy) which displays a faunal assemblage composed of at least 637 marmot individuals, representing about the 99% of the total remains. Taphonomic evidence suggests a standardized processing of marmot carcasses finalized to the deferred consumption and utilization of different resources. The intensive exploitation together with the acquisition through repetitive hunting events and the ecological and ethological factors proper of this animal, substantially affected its definition of prey type and its ranking in terms of energy return balance. Hence, in this particular context marmot might be regarded as a high-ranked resource, seasonally exploited within a well-established logistical mobility system which reflects a repetitive regional phenomenon peculiar of the alpine area throughout the Late Glacial.

14,000-year Carbon Accumulation Dynamics in a Siberian Lake Reveal Catchment and Lake Productivity Changes

A multi-proxy paleolimnological analysis of a sediment core sequence from Lake Malaya Chabyda in Central Yakutia (Eastern Siberia, Russia) was conducted to investigate changes in lake processes, including lake development, sediment and organic carbon accumulation, and changes in primary productivity, within the context of Late Pleistocene and Holocene climate change. Age-depth modeling with 14C indicates that the maximum age of the sediment core is ∼14 cal kBP. Three distinct sedimentary units were identified within the sediment core. Sedimentological and biogeochemical properties in the deepest section of the core (663–584 cm; 14.1–12.3 cal kBP) suggests a lake environment mostly influenced by terrestrial vegetation, where organic carbon accumulation might have been relatively low (average ∼100 g OC m−2 a−1), although much higher than the global modern average. The middle section of the core (584–376 cm; 12.3–9.0 cal kBP) is characterized by higher primary productivity in the lake, much higher sedimentation, and a remarkable increase in OC delivery (average ∼300 g OC m−2 a−1). Conditions in the upper section of the core (<376 cm; < 9.0 cal kBP) suggest high primary productivity in the lake and high OC accumulation rates (average ∼200 g OC m−2 a−1), with stable environmental conditions. The transition from organic-poor and mostly terrestrial vegetation inputs (TOC/TNatomic ratios ∼20) to conditions dominated by aquatic primary productivity (TOC/TNatomic ratios <15) occurs at around 12.3 cal kBP. This resulted in an increase in the sedimentation rate of OC within the lake, illustrated by higher sedimentation rates and very high total OC concentrations (>30%) measured in the upper section of the core. Compact lake morphology and high sedimentation rates likely resulted in this lake acting as a significant OC sink since the Pleistocene-Holocene transition. Sediment accumulation rates declined after ∼8 cal k BP, however total OC concentrations were still notably high. TOC/TNatomic and isotopic data (δ13C) confirm the transition from terrestrial-influenced to aquatic-dominated conditions during the Early Holocene. Since the mid-Holocene, there was likely higher photosynthetic uptake of CO2 by algae, as suggested by heavier (isotopically enriched) δ13C values (>−25‰).

Plant use and vegetation trends in Algeria from Late Glacial to Middle Holocene: Charcoal and seeds from Gueldaman GLD 1 cave (Babors d'Akbou)

Vegetation dynamics during the Pleistocene–Holocene transition and the beginning of farming are major topics for palaeoenvironmental sciences, especially interesting in ecologically sensitive areas, such as in North Africa. However, there are still important geographic and chronological gaps of environmental information in this region. Archaeobotanical record from Gueldaman GLD 1 deals with these issues, as it presents the longest archaeobotanical sequence available nowadays for Algeria, which includes these moments of major changes in landscapes. This topic has been approached from an interdisciplinary point of view, focused on the analysis of various types of plant remains that result in the reconstruction of both environment and use of plant resources. Results reveal the existence of a postglacial phase of plant colonization with Cupressaceae formations, which are gradually integrating some elements of sclerophyllous vegetation, such as several species of Pistacia, well documented both in charcoal and seed records. Neolithic levels show a shift in vegetation composition, as Olea europaea dominates the spectra, accompanied by strawberry tree and evergreen Quercus, among others. The presence of Olea in earlier chronologies has resulted from intrusions from the Neolithic levels: a set of radiocarbon dates has made it possible to evidence this process and detect the extent of the intrusions, which are inherent to cave records.

The rank abundance distribution of large-bodied vertebrates from Natural Trap Cave, Wyoming

Natural Trap Cave (NTC) is a well-known fossil locality located in Wyoming that contains a discontinuous record of sediments from the early Sangamonian (∼150 ka) to the present and produces a diverse vertebrate assemblage from 2-9 and 23–47 cal ka BP. This study examines changes in the rank abundance distribution (RAD) of NTC's large-bodied (>8 kg) vertebrates, to assess the stability of the local ecosystem surrounding the cave across the Late Pleistocene-Holocene transition. RADs were generated based on 2208 skeletal elements from four stratigraphic units, collected by Gilbert and Martin from 1974 to 1979. All bones included in this study had: a north-west grid coordinate, a known depth below the sediment surface, were over 20% complete and taxonomically diagnostic. Isotaphonomy was assessed using multinomial regressions of %MAU against multiple taphonomic variables: size, shape, degree of abrasion and weathering, fracture type, percent complete, original bulk density, and surface area to volume ratio. Changes in RADs were analyzed using rank abundance curves (RACs), Wilcoxon Rank Sums test, and kurtosis. RADs were also fit to a suite of standard ecological models (i.e., geometric, log-series, zero-sum multinomial, & log-normal) using maximum likelihood and the Akaike Information Criterion corrected for small sample size (AICc). The four faunal assemblages show little variation in taphonomic biasing, so any changes in the RADs reflects changes in the ecosystem. The four RACs showed little change in their shape or faunal composition and are dominated by a few abundant taxa, representing an ecosystem that experienced perturbations (i.e., a concave RAC and a kurtosis value > 3). The Wilcoxon Rank Sums test found no statistical difference among the RADs from the lower three stratigraphic units. This means that the abundance structure of the large-bodied vertebrates did not change prior to (35.8–25.3 cal ka BP) or during the Last Glacial Maximum (25.3–17.2 cal ka BP) and the local ecosystem surrounding NTC never approached equilibrium. The uppermost stratigraphic unit represented a mixed Late Pleistocene and Early Holocene assemblage, so changes in ecosystem structure from the Last Glacial Maximum to the Holocene (10.5 cal ka BP – present) cannot be evaluated. Unfortunately, the ecological models used in this study provide little insight into the maturity or processes influencing the formation of the local ecosystem surrounding NTC because only three models produced a ΔAICc value between 4.4 and 6.7.

Re-evaluating Pleistocene–Holocene occupation of cave sites in north-west Thailand: new radiocarbon and luminescence dating

Established chronologies indicate a long-term ‘Hoabinhian’ hunter-gatherer occupation of Mainland Southeast Asia during the Terminal Pleistocene to Mid-Holocene (45 000–3000 years ago). Here, the authors re-examine the ‘Hoabinhian’ sequence from north-west Thailand using new radiocarbon and luminescence data from Spirit Cave, Steep Cliff Cave and Banyan Valley Cave. The results indicate that hunter-gatherers exploited this ecologically diverse region throughout the Terminal Pleistocene and the Pleistocene–Holocene transition, and into the period during which agricultural lifeways emerged in the Holocene. Hunter-gatherers did not abandon this highland region of Thailand during periods of environmental and socioeconomic change.

Aquatic ecosystem responses to environmental and climatic changes in NE China since the last deglaciation (∼17, 500 cal yr BP) tracked by diatom assemblages from Lake Moon

The scarcity of research in NE China on lake ecosystem responses to large-scale climate oscillations since the last deglaciation limits our abilities for informing conservation practices and policies in the context of recent global warming. Here, a high-resolution, sedimentary diatom record covering the past ∼17,500 years was retrieved from Lake Moon, a small, hydrologically closed crater lake in the remote central part of the Great Khingan Mountain Range in NE China. We compare diatom changes with geochemical data from the same core, and with regional palynological and dust deposition records, to better understand the influences of long-term environmental and climatic variability on aquatic ecosystems in this climatically sensitive region. Several abrupt and pronounced shifts in dominance among diatom taxa corresponded to marked fluctuations in the climate regime since the last deglaciation. During the close of the Last Glacial Period, a series of short-lived diatom shifts that were indicative of an increase in nutrients, signaled the transition from the cold period of the Heinrich event 1 (∼17,500–∼14,700 cal yr BP) to the warmer Bølling - Allerød interstadial period (∼14,700–∼12,900 cal yr BP). The onset of the cold Younger Dryas period was marked by a brief rise to dominance of benthic taxa (∼12,900–∼11,800 cal yr BP), followed by a pronounced lake ecosystem shift to a new trophic state at the Pleistocene-Holocene transition (∼11,800–∼9900 cal yr BP), evidenced by an abrupt rise to dominance of several eutrophic diatom indicators (e.g. Cyclostephanos dubius, Aulacoseira ambigua and Stephanodiscus parvus). This nearly complete compositional turnover was indicative of an increase in phosphorus supply to the lake with the onset of a warmer and moister climate and an increased frequency of strong dust storms. During the mid-Holocene (∼6000 cal yr BP), a striking increase in the relative abundance of Discostella pseudostelligera and Asterionella formosa, at the expense of previously dominant eutrophic indicators, signified another lake ecosystem change from well-mixed, turbid and phosphorus-rich conditions to a lower nutrient state with longer open-water periods and increased thermal stability. The turnover to oligotrophic diatom taxa was likely in response to variations in seasonal temperature, precipitation and dust deposition. The diatom shifts of Lake Moon during the past ∼17,500 years were directly or indirectly mediated by climate change that affected thermal stratification, productivity, lake level and trophic state. Our results indicate that climate change had an overarching control on aquatic ecosystem changes in the mountain regions of NE China since the last deglaciation.

OSL-dating of the Pleistocene-Holocene climatic transition in loess from China, Europe and North America, and evidence for accretionary pedogenesis

Loess deposits intercalated by paleosols are detailed terrestrial archives of Quaternary climate variability providing information on the global dust cycle and landscape dynamics. Their paleoclimatic significance is often explored by quantifying their mineral magnetic properties due to their sensitivity to local/regional hydroclimate variability. Detailed chronological assessment of such regional proxy records around the climatic transitions allow a better understanding of how regional records react to major global climatic transitions such as the Pleistocene-Holocene climatic transition. Logs of high-resolution magnetic susceptibility and its frequency dependence were used as paleoclimatic proxies to define the environmental transition from the last glacial loess to the current interglacial soil as reflected in nine loess-paleosol sequences across the northern hemisphere, from the Chinese Loess Plateau, the southeastern European loess belt and the central Great Plains, USA. The onset of increase in magnetic susceptibility above typical loess values was used to assess the onset of, and developments during, the Pleistocene-Holocene climatic transition. High-resolution luminescence dating was applied on multiple grain-sizes (4–11 μm, 63–90 μm, 90–125 μm) of quartz extracts from the same sample in order to investigate the timing of Pleistocene-Holocene climatic transition in the investigated sites. The magnetic susceptibility signal shows a smooth and gradual increase for the majority of the sites from the typical low loess values to the interglacial ones. The initiation of this increase, interpreted as recording the initiation of the Pleistocene-Holocene climatic transition at each site, was dated to 14–17.5 ka or even earlier. Our chronological results highlight the need of combining paleoclimatic proxies (magnetic susceptibility) with absolute dating when investigating the Pleistocene-Holocene climatic transition as reflected by the evolution of this proxy in order to avoid chronostratigraphic misinterpretations in loess-paleosol records caused by simple pattern correlation. The detailed luminescence chronologies evidence the continuity of eolian mineral dust accumulation regardless of glacial or interglacial global climatic regimes. Coupled with magnetic susceptibility records this indicates that dust sedimentation and pedogenesis act simultaneously and result in a non-negligible accretional component in the formation of Holocene soils in loess regions across the Northern Hemisphere. The luminescence ages allowed the modeling of accumulation rates for the Holocene soil which are similar for European, Chinese and U.S.A. loess sites investigated and vary from 2 cm ka −1 to 9 cm ka −1 . While accretional pedogenesis has often been implicitly or explicitly assumed in paleoclimatic interpretation of loess-paleosol sequences, especially in the Chinese Loess Plateau, our luminescence data add direct evidence for ongoing sedimentation as interglacial soils formed. • High-resolution magnetic susceptibility record as paleoclimate proxy. • High-resolution luminescence dating applied on multiple quartz fractions. • Initiation of magnetic susceptibility enhancement dated prior to ~11.7 ka. • Continuous dust accumulation during Pleistocene-Holocene transition and in Holocene. • Accretional Holocene soils in European, Chinese Loess Plateau and US loess sites.

Stratigraphy And Paleolithic Landscapes of the Beganchik Site at the Kama-Volga Confluence

The Beganchik locality is a stratigraphic sequence of loessic deposits, pedogenic horizons and Paleolithic occupations located at the Kama-Volga confluence. The sequence is exposed on a bluff formed on the west side of an erosional remnant between the Kuybyshev Reservoir and the former channel of the Aktay River. Although the site is known for its Terminal Paleolithic-Mesolithic occupations of the Pleistocene-Holocene transition, evidence of older occupations and remains of fauna has been identified. Our research team identified evidence of human presence associated with a pedogenic horizon of MIS 3 age. Two AMS radiocarbon ages from a hearth produced ages around 47 000 years BP. Pollen and phytoliths from two soils horizons, including the one associated with the hearths indicate a steppe environment coincident with the formation of correlative soils elsewhere in the Russian Plain.

Upper Pleistocene–Holocene in the continental slope of the Cará Basin: an integrated analysis based on planktic foraminifera, sedimentological and geochemical aspects

This research addresses paleoclimatic variations using sedimentological, geochemical, and planktic foraminifera. The study was carried out in a survey core (ANP 1011) collected on the continental slope of the Icaraí Sub-basin (Ceará Basin), on the coast of the Municipality of Itapipoca, CE, Brazil. Particle size analysis, CaCO3 content, Ti/Ca and Fe/Ca ratios, and the analysis of foraminifera associations for biostratigraphic purposes were performed. Based on the relative abundance of planktic foraminifera, with indicators of warm and cold water throughout the studied cores, two biozones (Y: Upper Pleistocene and Z: Holocene), and two subzones (Z2 and Z1) were recognized. The data of sedimentological markers obtained confirmed the occurrence of more wet phases in northeastern Brazil during the early stages of the Holocene. The Ti/Ca and Fe/Ca ratios, as well as the geochemical and micropaleontological proxies, indicated a farther north displacement of the Intertropical Convergence Zone (ITCZ) in the Pleistocene–Holocene transition. This may have caused greater precipitation in the Northeastern region of Brazil, effectuating the entry of a high volume of terrestrial sediments directly into the ocean basin. Keywords: Quaternary biostratigraphy, marine sedimentation, ITCZ mobility, paleoclimate.

A Paleo-Lake and wetland paleoecology associated with human use of the distal Old River Bed Delta at the Pleistocene-Holocene transition in the Bonneville Basin, Utah, USA

AbstractMollusk and ostracode assemblages from the distal Old River Bed delta (ORBD) contribute to our understanding of the Lake Bonneville basin Pleistocene-Holocene transition (PHT) wetland and human presence on the ORBD (ca. 13,000–7500 cal yr BP). Located on U.S. Air Force-managed lands of the Great Salt Lake Desert (GSLD) in western Utah, USA, the area provided 30 samples from 12 localities. The biological assemblages and the potential water sources using87Sr/86Sr analyses showed wetland expansion and contraction across the PHT, including the Younger-Dryas Chronozone (YDC). The record reflects cold, freshwater conditions, which is uncharacteristic of the Great Salt Lake Desert, after recession of Lake Bonneville.Lymnaea stagnalis jugularis,Cytherissa lacustris, and possiblyCandonasp. cf.C.adunca, an endemic and extinct species only reported from Lake Bonneville, suggest cold-water environments. Between 13,000–12,400 cal yr BP, a shallow lake formed, referred to as the Old River Bed delta lake, fed by Lake Gunnison, as shown by87Sr/86Sr ratios of 0.71024–0.71063 in mollusk fossils collected at the ORBD, characteristic of the Sevier basin. These findings add paleoenvironmental context to the long-term use of the ORBD by humans in constantly changing wetland habitats between 13,000–9500 cal yr BP.

Herpetofaunal diversity changes with climate: evidence from the Quaternary of McEachern’s Deathtrap Cave, southeastern Australia

ABSTRACT The Quaternary Period is characterized by dramatic global climatic changes. Quaternary fossil deposits, which can offer excellent stratigraphic resolution, provide a unique opportunity to understand how fauna respond to past environmental change. Here, we test if the herpetofauna of McEachern’s Deathtrap Cave, a late Pleistocene to Holocene pitfall trap deposit from Victoria, Australia, shows climate-related shifts in taxonomic relative abundance through time. During the last 14,000 years, southeastern Australia experienced pronounced periods of aridity, while temperatures remained relatively stable. We show that the stratigraphic layers of this deposit are characterized by different relative abundances of reptile subfamilies, and that changes in subfamily abundance between layers correlate with known shifts to aridity, based on the percentage of C4 grasses present in the region. We further identify 13 lizard morphotypes from the fossil deposit and compare this diversity with the present-day lizard fauna. Our analyses indicate that gradual changes in community structure, which are typically observed in southeastern Australian vertebrate communities during the Pleistocene–Holocene transition, can partly be explained by changing aridity. These findings represent an important contribution to understanding Quaternary community change in Australia, particularly because evidence of faunal succession of reptile and amphibian communities in Victoria is lacking. Our results further demonstrate the utility of the Australian herpetofaunal fossil record for detecting community responses to past climate change on relatively shallow timescales and at higher levels of taxonomic identification.

Heat Treatment and Changes in Siliceous Rock Quality in the Southern End of the Deseado Massif (Patagonia, Argentina)

ABSTRACT The use of high-quality rocks and heat-treatment by hunter-gatherers during the initial exploration of America has been emphasized by different authors. Here we present the case of the Southern End of the Deseado Massif (Patagonia, Argentina), where human occupations have been dated from the Pleistocene-Holocene transition until historical times. An intense survey of lithic resources has shown the presence of primary and secondary sources of high quality siliceous rocks, most of them of hydrothermal origin. These siliceous rocks have a highly localized occurrence. In most cases, their quality does not match the one found at the archaeological record, which encompasses caches of artifacts, logistic and multiple activity sites. We present the results of heat treatment experiments on samples from local primary sources. Results obtained are compared with the artifacts found, in order to evaluate the potential utilization of the sources and the presence of heat treatment in the archaeological record.

Holocene settlement, stratigraphy and chronology at the site of Uruguai 1-sector 1, Foz do Chapecó archaeological area, South Brazil

Uruguai 1 is a recently discovered site in the Foz do Chapecó Archaeological Area, which contains an exceptional archaeological record, documenting the expansion of Homo sapiens in southern Brazil, within the Rio de la Plata basin. The aim of this paper is to present the results of field investigations within sector 1 of the site, providing a detailed description of the entire stratigraphic sequence that spans the Pleistocene-Holocene transition to the present day. The site comprises a variety of archaeological evidence including six archaeological levels (palaeosurfaces), evidenced by lithic tools, charcoal horizons, combustion features, small faunal remains and, for the youngest one, ceramic fragments. The overlapping of six archaeological levels in an open-air stratigraphic context is unprecedented in inland of southern Brazil and provides evidence for a long-term human presence in the area, which is of great archaeological importance in the southern part of South America..

Landscape evolution and unusual geomorphological-pedological-chronological relations in an alluvial plain associated with early Amerindian settlement in southeastern Brazil

This article deals with geomorphological, sedimentary, paleopedological, chronological (OSL and 14C) and archaeological records within a segment of the Jacaré-Guaçu River alluvial plain in southeast Brazil, aiming to evaluate climatic, hydrological and landscape transformations over the past 115 ka. The results show alternations between humid and drier climates that contribute to different drainage conditions, accounting for seven paleosurfaces and five paleosols amid sandy and gravel deposits along Late Pleistocene and Holocene. Micromorphological and OSL data characterize a humid and warm phase in the Eemian associated to the formation of a paleosol under good drainage conditions, followed between 111 ka and the end of Pleistocene by sandy deposition intercalated with the genesis of two new soils and by a sedimentary discontinuity. The lithics artifacts records of Amerindian settlements since the Pleistocene–Holocene transition contributed to the demarcation of paleosurfaces that formed concurrently with landscape and river level changes, and the density of human activities was found to vary simultaneously with environmental transformations in the area. A phase of ephemeral torrential channels under a drier climate, and predominance of grassland vegetation in the Pleistocene end (~12.4 ka) was followed by the set up of perennial meandering channels of dimensions four times greater than that of the current Jacaré-Guaçu river, formed under increase of forestal associations and rise in water table, with aggradation of up 7 m, sandy deposition and formation of two new soils in the Early Holocene; from Middle Holocene, the fluvial system experienced incision (<8.5 m), avulsion (<600 m), decrease of channel size and uneven erosion of the deposits and paleosols previous formed in the area. Such changes in the landscape contributed to the establishment of lower terraces with older (115–111 ka) deposits and paleosols linked to good drainage conditions and higher terraces with newer (12.4–8.0 ka) deposits and paleosols linked to poor drainage conditions. This pattern of connections between terrace levels, soil types and ages of deposits is different from that previously registered in the alluvial plains of southeast Brazil.

Onthophagus pilauco sp. nov. (Coleoptera, Scarabaeidae): evidence of beetle extinction in the Pleistocene-Holocene transition in Chilean Northern Patagonia.

The South American Pleistocene–Holocene transition has been characterized by drastic climatic and diversity changes. These rapid changes induced one of the largest and most recent extinctions in the megafauna at the continental scale. However, examples of the extinction of small animals (e.g., insects) are scarce, and the underlying causes of the extinction have been little studied. In this work, a new extinct dung beetle species is described from a late Pleistocene sequence (~15.2 k cal yr BP) at the paleoarcheological site Pilauco, Chilean Northern Patagonia. Based on morphological characters, this fossil is considered to belong to the genus Onthophagus Latreille, 1802 and named Onthophagus pilaucosp. nov. We carried out a comprehensive revision of related groups, and we analyzed the possible mechanism of diversification and extinction of this new species. We hypothesize that Onthophagus pilaucosp. nov. diversified as a member of the osculatii species-complex following migration processes related to the Great American Biotic Interchange (~3 Ma). The extinction of O. pilaucosp. nov. may be related to massive defaunation and climatic changes recorded in the Plesitocene-Holocene transition (12.8 k cal yr BP). This finding is the first record of this genus in Chile, and provides new evidence to support the collateral-extinction hypothesis related to the defaunation.

Procurement, Reduction, and Use of Lithic Technology from ca. 9500–11,800 Years Ago at Niidhaayh Na’, Central Alaska

ABSTRACT The middle Tanana Valley near Fairbanks, Alaska has been the subject of nearly a century of archaeological research focused on the earliest inhabitants of the region. Recent research at Niidhaayh Na’ (XBD-110) provides new information about human behavior and technological organization at the Pleistocene-Holocene transition. This multicomponent site is located on the Delta moraine and overlooks Delta Creek (Niidhaayh Na’). The results of the first seasons of full-scale excavation research at the site, begun in 2017, reveal two lithic workshops dating to ca. 11,800 and 9500 calendar years ago, associated with core fragments, tools, debitage, and intact faunal remains. Future research at the site will advance archaeological understandings of human adaptive decision-making during the late glacial period in central Alaska, with implications for our understanding of the first Americans and human behavior more generally.

Late Quaternary evolution of a lowland anastomosing river system: Geological-topographic inheritance, non-uniformity and implications for biodiversity and management

Lowland multiple-channel rivers are characterised by floodplain-corridor heterogeneity, high ecological and heritage value, and can be in quasi-stable states. This holistic study of a surviving temperate zone example (Culm, UK) uses geomorphological mapping, 14C, direct sediment dating (OSL, fallout radionuclides), and palaeoecology. This reveals the evolution of a channel-floodplain system from an initial braided state in the Late Pleistocene to its late Holocene anastomosing state. After the Pleistocene-Holocene transition the reduced channel system incised into its braid-plain, only able to rework gravels locally due to reduced competence in relation to inherited bounding sediment calibre. This resulted in the creation of terrace islands, palaeochannels, and a stable anastomosing pattern dominated by channel junctions, bifurcations and palaeochannel intersections. Survey, coring and excavation reveal a persistence of mid-channel bars and riffles at channel junctions, and where channels crossed palaeochannel fills. In common with most other European lowland rivers this system evolves in the later Holocene due to both climate and catchment changes with a major hydrological critical transition in the mid-Holocene (c. 5300 BP). However, in the case of the Culm, the increase in fine sediment supply often seen in lowland catchments in the Middle-Late Holocene, occurred later, and was insufficient to convert the system to a single medium-low sinuosity channel-floodplain. This allowed the persistence of high heterogeneity and biodiversity (including the persistence of riffle beetles) as part of multiple-scales of non-uniformity. Indeed the pool-riffle persistence is an example of this system’s non-uniformity, being due, at least in part, to the effects of previous channel history. This paper reveals why this river survived in a multichannel state, and by implication, why others did not. These results are being used in the bespoke eco-heritage management of the Culm, but could also inform the restoration of other former multi-channel lowland temperate river systems worldwide.

Contrasting dynamical responses of sympatric caribou and muskoxen to winter weather and earlier spring green-up in the Arctic

Alteration of local biodiversity by climate change may be especially impactful in the Arctic, where species richness is characteristically low and environmental conditions are changing rapidly. Two species of arctic large herbivores that survived rapid warming during the Pleistocene-Holocene transition, caribou and muskoxen, again face accelerated warming and changes in vegetation seasonality under contemporary climate change. While numerous studies have investigated the roles of weather and primary productivity in population dynamics of these species, opportunities for investigation of their dynamics in sympatric populations have been limited. We analyzed the population dynamics and offspring production of sympatric caribou and muskoxen at a study site in West Greenland over an 18-year period (2002–2019) during which the timing of spring green-up has advanced rapidly. In caribou, population growth rate and calf production were greater following warm winters but lower in years with earlier spring green-up. While calf production was highly variable, caribou abundance declined over the course of the study. In contrast, muskox population growth and calf production both increased following earlier springs. Moreover, muskox abundance increased over the course of the study, despite a negative association between their rate of increase and winter temperature, perhaps indicating that winter weather was less important than spring green-up timing in their dynamics. Hence, sympatric populations of these two herbivores displayed opposing demographic responses to winter weather and spring plant phenology at this shared location. These results emphasize the complexity of predicting large herbivore responses to climate change, and highlight the potential for impacts to species richness of large herbivore communities as the Arctic continues to warm.

Genomic Variation and Recent Population Histories of Spotted (Strix occidentalis) and Barred (Strix varia) Owls.

Spotted owls (SOs, Strix occidentalis) are a flagship species inhabiting old-growth forests in western North America. In recent decades, their populations have declined due to ongoing reductions in suitable habitat caused by logging, wildfires, and competition with the congeneric barred owl (BO, Strix varia). The northern spotted owl (S. o. caurina) has been listed as “threatened” under the Endangered Species Act since 1990. Here, we use an updated SO genome assembly along with 51 high-coverage whole-genome sequences to examine population structure, hybridization, and recent changes in population size in SO and BO. We found that potential hybrids identified from intermediate plumage morphology were a mixture of pure BO, F1 hybrids, and F1 × BO backcrosses. Also, although SO underwent a population bottleneck around the time of the Pleistocene–Holocene transition, their population sizes rebounded and show no evidence of any historical (i.e., 100–10,000 years ago) population decline. This suggests that the current decrease in SO abundance is due to events in the past century. Finally, we estimate that western and eastern BOs have been genetically separated for thousands of years, instead of the previously assumed recent (i.e., <150 years) divergence. Although this result is surprising, it is unclear where the ancestors of western BO lived after the separation. In particular, although BO may have colonized western North America much earlier than the first recorded observations, it is also possible that the estimated divergence time reflects unsampled BO population structure within central or eastern North America.