Late Pleistocene Climate Research Articles

Phylogeography of the Euro-Siberian steppe plant Astragalus austriacus: Late Pleistocene climate fluctuations fuelled formation and expansion of two main lineages from a Pontic-Pannonian area of origin

The Euro-Siberian steppes have experienced large-scale range fluctuations due to the climatic changes of the Pleistocene that may have also fuelled reshuffling of past steppe vegetation. These species-rich steppe grasslands were much more widespread during glacials and contracted during interglacials, a dynamic which should also be reflected by the evolutionary history of their biota. Astragalus austriacus is a widespread steppe species with European-western Siberian distribution and an ideal model to study the florogenesis of the Euro-Siberian steppes. Here, we inferred the phylogeography of A. austriacus based on genotyping-by-sequencing (GBS) data from populations sampled from the western edge of the Pannonian region across the Pontic region to the western Siberian region. Additionally, we applied molecular dating using single gene sequence data (ycf1, matK and ITS). We outline an evolutionary scenario in which intraspecific diversification occurred in the eastern part of Europe during the later Pleistocene (0.48–0.24 Ma). From there, the species expanded both eastwards and westwards, likely during a cold period, which is reflected by two main lineages within A. austriacus that today occur in the Pannonian sensu lato and in the Pontic/south-western Siberian regions, respectively. Demographic modelling supported such a scenario and showed that population sizes were larger during the last cold stage and contracted postglacially. Within the Pannonian sensu lato region, strong substructure was detected, likely as a result of repeated disintegration of the continuous cold-stage steppes in Europe. Finally, our results are in line with evolutionary scenarios suggested for other steppe species such as Adonis vernalis.

Mitogenomics reveals extremely low genetic diversity in the endangered Jilin clawed salamander: Implications for its conservation.

The Jilin clawed salamander (Onychodactylus zhangyapingi) is an endemic, endangered, and level-two protected amphibian species of China. In the context of serious threats to amphibians worldwide, conservation studies of this endangered species are urgently needed. In this study, mitogenomic conservation genetics and species distribution modeling analyses were performed for O. zhangyapingi. Sixty-three samples were collected from nine different locations, and the complete mitochondrial genome was sequenced. Population genetic analyses revealed that O. zhangyapingi exhibits only one genetic structure with extremely low nucleotide diversity. Late Pleistocene climate cooling may have led to a reduction in effective population size and extremely low mitogenomic nucleotide diversity in this salamander, and the subsequent temperature increase (~20 kya to present) provided the opportunity for rapid population growth. The continuous highly suitable region for O. zhangyapingi is only approximately 3000 km2 on the southeastern boundary of Jilin Province, China. Fortunately, there are three large forested national nature reserves within the distribution of O. zhangyapingi that can effectively protect endangered species. Our findings suggest that O. zhangyapingi is a vulnerable species with a narrow distribution and extremely low genetic diversity, and we should pay more attention to the conservation management of this species.

Deep mitochondrial phylogeographical pattern: cryptic population structure within an ecological niche in the near-threatened Himalayan vulture (Gyps himalayensis)

Abstract The Himalayan vulture (Gyps himalayensis) has higher environmental specificity than other species in the same genus, and its population has declined due to diclofenac exposure and shortage of carcasses as a food source. Previous analysis of mitochondrial (mt) DNA cytochrome b (Cyt b) sequences reported no distinct geographical population structure in the Himalayan vulture. Contradictory results were obtained in the present study, which investigated the population structure of 14 Himalayan vultures that migrated to Thailand during winter. Using samples obtained between 2010 and 2021, as well as limited GenBank samples, the study found that the Cyt b locus was incapable of distinguishing population structure. This dataset contrasted with the mtDNA control region (CR) and Cyt b + CR dataset, which divided them into two groups, as explained by the Middle–Late Pleistocene climate change scenario. The species split into populations from the central, western, and northern regions of its distribution range within the highland vulture ecological niche. This study reviews the different methods used as compared with previous proposals for defining guidelines for the conservation of this near-threatened scavenging species.

Elevated Southern Hemisphere moisture availability during glacial periods.

Late Pleistocene ice-age climates are routinely characterized as having imposed moisture stress on low- to mid-latitude ecosystems1-5. This idea is largely based on fossil pollen evidence for widespread, low-biomass glacial vegetation, interpreted as indicating climatic dryness6. However, woody plant growth is inhibited under low atmospheric CO2(refs. 7,8), so understanding glacial environments requires the development of new palaeoclimate indicators that are independent of vegetation9. Here we show that, contrary to expectations, during the past 350 kyr, peaks in southern Australian climatic moisture availability were largely confined to glacial periods, including the Last Glacial Maximum, whereas warm interglacials were relatively dry. By measuring the timing of speleothem growth in the Southern Hemisphere subtropics, which today has a predominantly negative annual moisture balance, we developed a record of climatic moisture availability that is independent of vegetation and extends through multiple glacial-interglacial cycles. Our results demonstrate that a cool-moist response is consistent across the austral subtropics and, in part, may result from reduced evaporation under cool glacial temperatures. Insofar as cold glacial environments in the Southern Hemisphere subtropics have been portrayed as uniformly arid3,10,11, our findings suggest that their characterization as evolutionary or physiological obstacles to movement and expansion of animal, plant and, potentially, human populations10 should be reconsidered.

Timing and extent of glaciation since the Last Glacial Maximum in the upper Kalguty basin, Russian Altai Mountains

ABSTRACTThe mountains systems of Central Asia are primary targets to study late Pleistocene climate evolution given their location at the crossroads of several atmospheric circulation systems. The timing of glacier extent during this period remains understudied, especially in the Altai Mountains. Here, we have reconstructed glacier extent during three main Late Pleistocene stadials in the upper Kalguty basin (south‐eastern Russian Altai) based on field‐based geomorphic analysis. Additionally, surface exposure dating with 10Be and 26Al at a key site was used to infer a minimum‐limiting age for the outermost well‐preserved Pleistocene frontal moraine system and to date the inception of glacier withdrawal. According to our data, around 20.6 ± 1.8 ka Kalguty Glacier was still 200 m thick at the key site, 10 km upstream of the outermost moraine, and the site was totally deglaciated shortly after 20.4 ± 0.4 ka. These results point to a rapid retreat of this low‐gradient valley glacier after its probably MIS 2 maximum which was prior to 21 ka and probably prior to 22.5 ka. Two other glacier stages have been identified upvalley, characterized by a depression of the equilibrium‐line altitude of 420 and 314 m with respect to the Little Ice Age, thus corresponding to Lateglacial advances. Our glacier reconstruction further provides a geomorphological and geochronological background to put into context archaeological findings in this area.

Review: Biogeographic and environmental history of Fagus and beech‐dominant forest in Japan

AbstractThere is a rich beech fossil record in Japan dating from the Paleogene to the Holocene, which allows for the continuous tracing of the evolutionary history of the genus and allows us to understand the environmental background that facilitated the genus to obtain a dominant state in present‐day forests. In addition to the temperate climate, the oceanic climate was an important factor in controlling beech distribution and dominance in the forests in Japan. With the cooling climate, beech species began expanding their distribution in the Northern Hemisphere in the middle Eocene and appeared in Japan in the late middle Eocene. Beech species became dominant in forests in Japan during the Miocene along with the development of the oceanic climate by the opening of the Sea of Japan and with the strengthening of the monsoon. Fagus crenata appeared until the Late Pliocene and became dominant in forests in central Japan in the late Early Pleistocene coinciding with the onsetting inflow of the Tsushima Warm Current to the Sea of Japan in interglacial stages. During the full‐glacial stages since the late Middle Pleistocene, the cold and dry climate caused by the strong winter monsoon limited the distribution of beeches into refugia at humid places, including the inland. During the deglaciation since ca 19 ka, the beech population began to grow and its distribution expanded, controlled by the development of the Tsushima Warm Current, as well as latitudinal and altitudinal temperature clines.

Spatial differentiation of background matching strategies along a Late Pleistocene range expansion route

Late Pleistocene climate changes have deeply impacted the range dynamics of temperate species. While the genetic legacy of these dynamics has been widely investigated, little is known about their phenotypic consequences. Anti-predatory strategies offer intriguing opportunities to study phenotypic evolution in response to dispersal dynamics since the ability to avoid predation can be pivotal for populations colonising new environments. Here we investigated the spatial differentiation of background colour matching strategies along a Late Pleistocene range expansion route of a temperate species, the Tyrrhenian tree frog Hyla sarda. Using common-garden experiments, we tested whether individuals from the source area (Sardinia) and individuals from the newly founded area (Corsica) differ in two components of the camouflage strategy: colour change abilities and background choice behaviour. We found a remarkable spatial structure in both colour change abilities and background choice behaviour, across the expansion range. Tree frogs from the source area displayed higher colour change abilities and a more pronounced preference for a greener background, with respect to tree frogs from the newly colonised area. Our results support the intriguing hypothesis that Late Pleistocene biogeographic history might be an overlooked major player in shaping current spatial patterns of phenotypic traits variation across animal populations.

Subglacial precipitates record Antarctic ice sheet response to late Pleistocene millennial climate cycles

Ice cores and offshore sedimentary records demonstrate enhanced ice loss along Antarctic coastal margins during millennial-scale warm intervals within the last glacial termination. However, the distal location and short temporal coverage of these records leads to uncertainty in both the spatial footprint of ice loss, and whether millennial-scale ice response occurs outside of glacial terminations. Here we present a >100kyr archive of periodic transitions in subglacial precipitate mineralogy that are synchronous with Late Pleistocene millennial-scale climate cycles. Geochemical and geochronologic data provide evidence for opal formation during cold periods via cryoconcentration of subglacial brine, and calcite formation during warm periods through the addition of subglacial meltwater originating from the ice sheet interior. These freeze-flush cycles represent cyclic changes in subglacial hydrologic-connectivity driven by ice sheet velocity fluctuations. Our findings imply that oscillating Southern Ocean temperatures drive a dynamic response in the Antarctic ice sheet on millennial timescales, regardless of the background climate state.

An astronomically calibrated 40Ar/39Ar age for the North Atlantic Z2 Ash: Implications for the Greenland ice core timescale

Timescales based on counted annual ice layers underpin the interpretation of late Quaternary rapid climatic oscillations recorded in the Greenland ice cores and their correlation to tropical and Antarctic climate archives. An inherent problem in the annual counted ice layer dating method is the large accumulated age uncertainties for the older part of the Greenland ice core timescale due to so called uncertain annual ice layers. Annual ice layers become thinner with depth due to increased compaction. Thus, the occurrence of uncertain annual layers becomes more frequent, such that by a depth of ∼2150 m (43 ka) in the NGRIP ice core the accumulated uncertainty on the age is > 2%. Radio-isotopic age determination of interbedded volcanic ash layers can provide independent verification of the Greenland counted annual ice layer ages along with the possibility of improved precision for the older part of this important timescale. Here we report an astronomically calibrated Ar40/Ar39 age of 56.14 ± 0.44 ka (2σ) for the widespread North Atlantic Z2 ash forming Icelandic Thórsmörk peralkaline rhyolitic eruption. The Z2 ash is found at a depth of 2359.45 m in the NGRIP ice core and has an annual layer counted age of 55.38 ± 2.37 ka (2σ, b2k). Our radio-isotopic age for the Z2 eruption is > 5 times more precise than the one based on counted annual ice layers and when referenced relative to b2k indicates that the oldest part of the GICC05 timescale is systematically too young by approximately 740 years. We use our Z2 eruption age to calculate refined astronomically calibrated ages for Greenland Interstadials (GI) 11 to 17 which results in reducing the age uncertainties on the majority of these events from the millennial to the centennial level. Our refined ages for GI 11–17 generally show good agreement with the NALPS U–Th stalagmite record that covers this same interval and together these high-precision radio-isotopic timescales provide firmer constraints for testing for synchronicity, or leads and lags between different geographical parts of the late Pleistocene climate system.

Contemporary genetic structure of Xantus's Hummingbird (Basilinna xantusii) in the Baja California peninsula

Genetic structure and phylogeographic patterns of natural populations are of great importance in assessing the conservation status of species. These population properties can be estimated using molecular markers of either mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) to understand the historical, ecological and dispersal patterns that influence genetic exchange within and between populations. Basilinna xantusii is a sexually dimorphic hummingbird endemic to the Baja California Peninsula (BCP). It comprises three ancestral mitochondrial lineages linked to vicariant events, late Pleistocene climate changes and the geographical distribution of oases. This study aimed to determine and understand the current population genetic structure of this hummingbird. The genotypes of 16 microsatellite loci from 100 individuals collected across the geographical range of this species were compared with mtDNA sequences previously published. Cluster analyses identified five populations, two with almost no genetic admixture in the northern part of the BCP and three others with varying levels of admixed ancestry across the BCP. In San José de Magdalena, at the northernmost end of the range of Xantus's Hummingbird, 40% of individuals collected belong to one genetic cluster and the remaining 60% to another, both genetic clusters showing very little admixed ancestry. We hypothesize that, despite being in sympatry, these individuals do not interbreed, unlike the other populations where individuals showed ancestry coefficients of the other genetic groups. The philopatric behaviour of males and the long‐range dispersal capacity of females probably determine the observed genetic differentiation pattern. The mito‐nuclear discordance detected could be due to the molecular markers used and to female‐biased dispersal. Gene flow is asymmetric in this species, being greater from north to south than vice versa, which is probably related to differences in the seasonality of precipitation across the BCP and to urbanization of the oases.

Effects of Late Pleistocene Climatic Fluctuations on the Phylogeographic and Demographic History of Japanese Scad (Decapterus maruadsi)

The Late Pleistocene-Holocene climate fluctuations have greatly influenced the phylogeographic structure and historical dynamics of many marine organisms in the western Pacific marginal seas. Here, we investigated the impact of Pleistocene glacial-interglacial cycles on the phylogeographic structure and demographic dynamics of Decapterus maruadsi, an economically important fish along the coast of the East China Sea (ECS) and northern South China Sea (NSCS). We obtained 430 concatenated sequences (Cyt b + control region, 1548–1554 bp) of D. maruadsi, including 246 newly sampled from the ECS and 184 previously determined from the NSCS. Genetic structure and phylogenetic analysis demonstrated a lack of significant population structure among 16 populations. Moreover, there was no significant differentiation among populations from Chinese coastal waters and northern Vietnam. Neutrality tests, unimodal mismatch distributions, Bayesian skyline plots, and the star-like haplotype networks all indicated a recent demographic expansion for D. maruadsi population during the Late Pleistocene-Holocene, explaining the low genetic diversity in D. maruadsi along the southeast coast of China. Notably, phylogenetic analyses and net genetic distances based on Cyt b jointly confirmed that 57 Cyt b haplotypes identified as D. maruadsi from the previously defined Sundaland-Rosario-Ranong clade actually represented D. russelli. These results not only reveal the complex effects of Pleistocene-Holocene climate fluctuations on the phylogeographic structure and demographic history of D. maruadsi but also provide useful genetic information for the management of genetic resources.

Revisiting Late Pleistocene Loess–Paleosol Sequences in the Azov Sea Region of Russia: Chronostratigraphy and Paleoenvironmental Record

Loess-paleosol sequences are the most intensively studied terrestrial archives used for the reconstruction of Late Pleistocene environmental and climatic changes in the Azov Sea region, southwest Russia. Here we present a refined chronostratigraphy and a multiproxy record of Late Pleistocene environmental dynamics of the most complete and representative loess–paleosol sequences (Beglitsa and Chumbur-Kosa sections) from the Azov Sea region. We propose a new chronostratigraphy following the Chinese and Danubean loess stratigraphic models that refines the subdivision of the Last Interglacial paleosol (S1) complex in two Azov Sea sites, resolve the uncertainty of the stratigraphic position of the weakly developed paleosol (L1SSm) in Beglitsa section, and allow for direct correlation of the Azov Sea sections with those in the Danube Basin and the Chinese Loess Plateau. More importantly, it may serve as a basis for better constraining local and regional chronostratigraphic correlations, and facilitate the interpretation of climatic connections and possible forcing mechanisms responsible for the climatic trends in the region. In addition, a general succession of environmental dynamics is reconstructed from these two vital sections, which is broadly consistent with other loess records in the Dnieper Lowland and Lower Danube Basin, demonstrating similar climatic trends at Glacial–Interglacial time scales. Furthermore, our results have important implications for the chronostratigraphic representativeness of Beglitsa as a key regional loess section and for the reconstruction of the temporal and spatial evolution of Late Pleistocene climate in the Azov Sea region.

Hydroclimatic variability of opposing Late Pleistocene climates in the Levant revealed by deep Dead Sea sediments

Abstract. Annual and decadal-scale hydroclimatic variability describes key characteristics that are embedded into climate in situ and is of prime importance in subtropical regions. The study of hydroclimatic variability is therefore crucial to understand its manifestation and implications for climate derivatives such as hydrological phenomena and water availability. However, the study of this variability from modern records is limited due to their relatively short span, whereas model simulations relying on modern dynamics could misrepresent some of its aspects. Here we study annual to decadal hydroclimatic variability in the Levant using two sedimentary sections covering ∼ 700 years each, from the depocenter of the Dead Sea, which has been continuously recording environmental conditions since the Pleistocene. We focus on two series of annually deposited laminated intervals (i.e., varves) that represent two episodes of opposing mean climates, deposited during MIS2 lake-level rise and fall at ∼ 27 and 18 ka, respectively. These two series comprise alternations of authigenic aragonite that precipitated during summer and flood-borne detrital laminae deposited by winter floods. Within this record, aragonite laminae form a proxy of annual inflow and the extent of epilimnion dilution, whereas detrital laminae are comprised of sub-laminae deposited by individual flooding events. The two series depict distinct characteristics with increased mean and variance of annual inflow and flood frequency during “wetter”, with respect to the relatively “dryer”, conditions, reflected by opposite lake-level changes. In addition, decades of intense flood frequency (clusters) are identified, reflecting the in situ impact of shifting centennial-scale climate regimes, which are particularly pronounced during wetter conditions. The combined application of multiple time series analyses suggests that the studied episodes are characterized by weak and non-significant cyclical components of sub-decadal frequencies. The interpretation of these observations using modern synoptic-scale hydroclimatology suggests that Pleistocene climate changes resulted in shifts in the dominance of the key synoptic systems that govern rainfall, annual inflow and flood frequency in the eastern Mediterranean Sea over centennial timescales.

Late Pleistocene Climate and Dust Source From the Mobarakabad Loess–Paleosol Sequence, Northern Foothills of the Alborz Mountains, Northern Iran

Paleoclimatic investigation of loess-paleosol sequences from northern Iran is important for understanding past changes in a region highly sensitive to shifts in precipitation, and along potential routes of past human migration. Here, we present carbon and oxygen isotopic compositions of bulk carbonate (δ13Cbc and δ18Obc, respectively) coupled with particle size distributions of samples from the Mobarakabad section, northern Iran, to study past wind dynamics and hydroclimate. We also present new initial clay-sized Hf-Nd isotope results from key horizons in order to assess general dust sources. Variations of δ13Cbc and δ18Obc values of modern soils compared to paleosols allow reconstruction of late Pleistocene–Holocene climate change in the area. Our results show severe drought during a major eolian deposition phase (EDP) after 34 ka. The thickness and PSD of the C horizon of unit 5 suggest significant shifts in loess sources and depositional environments during this EDP after 34 ka. Indeed, based on our new clay-sized Hf-Nd data, we hypothesize that the loess unit 5 might originate from the young crustal source of the Alborz and Kopet Dagh mountains. In general, the PSD of C horizons in the section is bimodal in the silt fraction and the very small, very fine clay fraction, with a mode at c. 1 μm in the modern soil and paleosols possibly produced by weathering and pedogenic processes. There also appears to be a good correlation between δ13Cbc and δ18Obc values, differentiating phases of loess accumulation and paleosol formation and hence providing quantitative data for reconstructing paleoclimatic conditions in the study area.

Impact of Late Pleistocene climate variability on paleo-erosion rates in the western Himalaya

It has been proposed that at short timescales of 102–105 yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained. To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya. We compare past and present 10Be-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data. Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene. We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 ± 13°) erode at lower rates of 0.1–0.4 mm/yr compared to steeper (>40°) crestal regions of the Dhauladhar Range that erode at 0.8−1.3 mm/yr. In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed. Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas.

Parallel genomic responses to historical climate change and high elevation in East Asian songbirds

Parallel evolution can be expected among closely related taxa exposed to similar selective pressures. However, parallelism is typically stronger at the phenotypic level, while genetic solutions to achieve these phenotypic similarities may differ. For polygenic traits, the availability of standing genetic variation (i.e., heterozygosity) may influence such genetic nonparallelism. Here, we examine the extent to which high-elevation adaptation is parallel-and whether the level of parallelism is affected by heterozygosity-by analyzing genomes of 19 Paridae species distributed across East Asia with a dramatic east-west elevation gradient. We find that western highlands endemic parids have consistently lower levels of heterozygosity-likely the result of late-Pleistocene demographic contraction-than do parids found exclusively in eastern lowlands, which remained unglaciated during the late Pleistocene. Three widespread species (east to west) have high levels of heterozygosity similar to that observed in eastern species, although their western populations are less variable than eastern ones. Comparing genomic responses to extreme environments of the Qinghai-Tibet Plateau, we find that the most differentiated genomic regions between each high-elevation taxon and its low-elevation relative are significantly enriched for genes potentially related to the oxygen transport cascade and/or thermogenesis. Despite no parallelism at particular genes, high similarity in gene function is found among comparisons. Furthermore, parallelism is not higher in more heterozygous widespread parids than in highland endemics. Thus, in East Asian parids, parallel functional response to extreme elevation appears to rely on different genes, with differences in heterozygosity having no effect on the degree of genetic parallelism.

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‰).

Spatiotemporal Rates of Tectonic Deformation and Landscape Evolution above a Laterally Propagating Thrust Fault: Wheeler Ridge Anticline, California, USA

AbstractThe Wheeler Ridge anticline, located in the southern San Joaquin Valley of California, USA, is a well-studied and classic example of a laterally growing fault propagation fold. New high-resolution lidar elevation data combined with nine infrared stimulated luminescence (IRSL) ages of discrete geomorphic surfaces that are bounded by prominent transverse wind and river gaps allow for investigation of tectonic topography through time. Luminescence ages from four of the six surfaces yield depositional ages that range from 32 ka to 153 ka, which are broadly consistent with a previously published soil chronosequence. Our graphical modeling indicates an average surface uplift rate of ~2.1 mm/yr and an average along-strike fold propagation rate of ~20 mm/yr. However, our probabilistic modelling and topographic analysis suggest a rate decrease of both uplift and lateral propagation toward the fault tip from ~2.4 to 0.7 mm/yr and from ~49 to 14 mm/yr, respectively. Rate decreases are not progressive but rather occur in punctuated deformational intervals across previously documented structural barriers (tear faults) resulting in a fold that is characterized by discrete segments that exhibit a systematic deformational decrease toward the east. The punctuated tectonic growth of Wheeler Ridge has also locally controlled the topographic evolution of the anticline by effecting the formational timing and position of at least seven wind and river gaps that result from multiple north-flowing antecedent streams that traverse the growing structure. We quantify the timing of wind and river gap formation, based on IRSL results and inferred incision rates, and present a model for the spatiotemporal evolution of transverse drainages and the topographic development of Wheeler Ridge. Our chronology of gap formation broadly correlates with regional Late Pleistocene dry climate intervals suggesting that both tectonics and climate were integral to the geomorphic development of the Wheeler Ridge anticline.

Neanderthal palaeoecology in the late Middle Palaeolithic of western Iberia: a stable isotope analysis of ungulate teeth from Lapa do Picareiro (Portugal)

ABSTRACTAdaptation to Late Pleistocene climate change is an oft‐cited potential contributor to Neanderthal disappearance in Eurasia. Accordingly, research on Neanderthal behaviour – including subsistence strategies, mobility, lithic technology, raw material procurement and demography – often focuses on linking changes observable in the archaeological record to specific phases of climate and environmental change. However, these correspondences are often tenuous because palaeoclimatic and archaeological records are rarely available on the same scale. In Iberia, a critical location for understanding the demise of Neanderthals, some research indicates that Neanderthal populations were unable to recover from environmental degradations known as Heinrich Events, while other studies suggest that enclaves of Neanderthal populations survived for several millennia longer in refugial zones. Here, we present a palaeoenvironmental reconstruction study using analysis of δ13C and δ18O of herbivore tooth enamel recovered from two Mousterian deposits at Lapa do Picareiro, a site located in Portuguese Estremadura. We then use these data, combined with other site‐based palaeoenvironmental indicators, to assess whether central Portugal acted as a refugium during periods of unfavourable climate, and to test whether Neanderthals in Portuguese Estremadura reorganised their mobility strategies after severe climate episodes.

A palaeovegetation and diatom record of tropical montane forest fire, vegetation and hydroseral changes on Mount Kenya from 27,000–16,500 cal yr BP

Fire is an important ecological disturbance in moist tropical forests influencing vegetation composition and structure. Contemporary and historical records of forest fires in mountain forests of Kenya are limited to the past decades and have a strong anthropogenic influence for ignition patterns and fire suppression activities. Palaeoenvironmental geoarchives provide the temporal depth to investigate long-term (multidecadal-to-millennial) changes in fire activity. Here we use a sediment record from the Rumuiku wetland, located in a volcanic crater on the eastern flank of Mount Kenya that was radiocarbon dated and analysed for diatom, pollen and charcoal subfossils to produce a highly resolved time series of local hydroclimatic change, vegetation, and fire; respectively. This study focuses on the time during and following the global Last Glacial Maximum, a time of rapid warming and changing regional hydroclimate with relatively stable atmospheric CO2 and not yet intensive anthropogenic modification of ecosystems. Charcoal and pollen data support associated changes in vegetation-fire centred around 21,500 cal yr BP when Afromontane forests with predominant abundances of Juniperus, Podocarpus and other montane forest trees changed to Hagenia-dominated forests that are relatively more open and adapted to burn more frequently but with less intense fires.These transitions in ecosystem composition, distribution and structure support the important role of fire in driving and maintaining forest composition in the watershed and contributing to the spatial complexity of forests around the mountain. These changes in composition, structure and biomass occurred during a time of rapid Late Pleistocene climate warming, regional hydroclimatic drying, and slowly rising atmospheric CO2 from 27,000 to 16,500 cal yr BP, during and following the conditions of the global Last Glacial Maximum. Temperature, hydroclimate and atmospheric CO2 are well-known drivers of montane vegetation change in the tropics and the role of fire is shown here to be a contributing driver to the spatial heterogeneity of forest patches at long time scales. Vegetation modelling at spatial scales relevant to land management and conservation should include retrospective evidence of the range of drivers of ecological disturbance regimes.