Past Climate Change Research Articles

Seasonality in cave dripwater and air properties – implications for speleothem palaeoclimatology, Nova Grgosova Cave (Croatia)

Due to the wealth of climate-sensitive properties, speleothems have been propelled into prominence as one of the most powerful continental archives of past climate changes. However, the multitude of processes that operate in the unsaturated karst zone and in the cave atmosphere can make palaeoclimate interpretations of the speleothem proxies challenging and site specific. Hence, to better understand the climate-proxy relationship, cave monitoring studies are usually undertaken. Here, we present the first results of an ongoing cave monitoring study in the Nova Grgosova Cave in Croatia covering an eighteen-month long monitoring period. The driving mechanisms for Mg/Ca and Sr/Ca variability in dripwater samples that feed ten stalagmites are discussed. The results reveal high variability in infiltration among the monitored sites as well as strong seasonal variability in cave air carbon dioxide (CO2) concentrations. A strong positive correlation between dripwater Mg/Ca and Sr/Ca suggests that prior calcite precipitation (PCP) is taking place at this site affecting the chemical composition of dripwater. Principal component analysis furthermore reveals that dripwater Mg/Ca and Sr/Ca are in strong negative correlation with cave air CO2 concentrations, while there is a weak correlation with dripwater quantity. Cave ventilation is a primary process leading to the PCP at the Nova Grgosova Cave. The seasonality revealed in this study suggests the possibility that the Mg/Ca and Sr/Ca ratio in the speleothems from this cave site can be used to aid seasonal reconstructions of past climate conditions in central Croatia and beyond.

Coastal fisheries adaptations to increasing climate change exposure in Japan

Abstract Climate change‐driven ocean warming is altering the geographic ranges of species, leading to a poleward shift of tropical species into temperate regions (tropicalisation). This threatens the native marine community assemblages by changing the availability of traditional marine resources, thus impacting the livelihood and well‐being of coastal fisheries. Fishers' individual responses are expected to transition from remaining to coping and from adapting to transforming as climate change exposure increases, yet empirical evidence is limited. The existing strong thermal gradient along the western coast of Shikoku (Japan), an area experiencing tropicalisation, provides a unique opportunity to analyse how regions facing different climate change exposure levels (North: low, Centre: medium and South: high) affect fishers' responses in relation to their adaptive capacity. Data from 92 face‐to‐face interviews with small‐scale fishers from 25 locations revealed that the largest proportion of coping and adaptive responses is in the Central region, while remaining responses predominated in the Northern and Southern regions. Results from a multinomial logistic model indicate that the exposure level is a good predictor for coping and adaptive responses but not for transformative ones. This possibly reflects the fact that these fishers might have exited coastal fisheries prior to our study as suggested by the strong fisher population decrease in the communities from the Southern region over the last three decades. This study provides novel empirical evidence on how climate change exposure influences fishers' responses to past and current climate change impacts, highlighting the intricate interplay between exposure level and individual adaptive capacity. Read the free Plain Language Summary for this article on the Journal blog.

Holocene aeolian-fluvial interactions patterns and their response to climate changes in the Paiku Co basin, Southern Tibetan Plateau

Aeolian-fluvial processes are crucial in shaping landforms. Despite the advancements in understanding the sedimentary processes of aeolian-fluvial interactions, the sedimentary patterns of these interactions are complex in spatiotemporal scale, and the records of Holocene small-scale aeolian-fluvial interaction sedimentary is insufficient, especially in the Tibetan Plateau region. Therefore, this study focuses on analyzing the sedimentary patterns of aeolian-fluvial interactions and their response to climate change in the Paiku Co basin of the southern Tibetan Plateau (TP). Through the examination of aeolian-fluvial sequences, Optically Stimulated Luminescence (OSL) dating is utilized to establish a chronological framework. Furthermore, proxy indices are explored to identify potential sediment models and their reactions to climate change. The findings indicate that fluvial activity predominated during a relatively warm and wet period around 5.1–4.6 ka, while thicker aeolian sands accumulated extensively during 4.6–4.1 ka as the climate transitioned to cold and dry conditions. On a millennial scale, the aeolian-fluvial interaction sedimentation is characterized by alternating deposition of clay layers and medium to fine sand. This sedimentation pattern is predominantly influenced by climate change. Overall, the findings shed light on the complex coupling between aeolian and fluvial processes in response to past climate changes, which has important implications for understanding the landscape evolution and environmental changes in this sensitive high-altitude region.

Multidimensional multiscale complexity analysis of sediment dynamics in the Yanhe Watershed of the loess Plateau, China

The Yanhe Watershed, emblematic of the loess hilly-gully landscape and ecological fragility in China's Loess Plateau, has experienced significant soil erosion and extensive soil-water conservation measures. To elucidate sediment dynamics and identify influencing factors in this region from 1960 to 2020, a novel multidimensional multiscale complexity analysis (MMCA) method was developed, based on entropy and complexity perspectives. This method integrated the refined composite multiscale fuzzy entropy (RCMFE) with multidimensional complexity analysis, offering a nuanced evaluation of sediment complexity and its implications for water resource management and ecological restoration. The findings revealed two distinct stages of sediment complexity variations: 1971–1988 and 2000–present. During the first period, the operation of the Wangyao Reservoir predominantly influenced sediment dynamics, initially reducing sediment complexity through sediment interception but later increasing it during discharge phases, particularly at larger scales. After 2002, extensive vegetation restoration efforts significantly reduced sediment complexity but raised concerns about long-term ecosystem resilience. Over the past decade, urbanization and climate change have exacerbated sediment instability, especially over semi-annual scales. This study advocates for management strategies that prioritize ecosystem sustainability and address the challenges posed by climate change and urbanization, facilitating improved soil and water conservation efforts in the Yanhe Watershed and similar regions in the Loess Plateau.

Automatic Detection and Identification of Calcareous Nannofossils in Chalk Using Deep Learning: A Proof-of-Concept Study for Biostratigraphy and Climate Research

Calcareous nannofossils serve as crucial indicators for establishing the biostratigraphic age of chalk macrofossil specimens in natural science collections. Better age control of specimens collected several hundred years ago enables us to uncover the dark data hidden within these collections and incorporate these data into current research projects, examining ecosystem response to past climate change. However, the manual identification of these microscopic organisms is laborious and subjective, and so we are harnessing deep learning techniques for automatic nannofossil detection and identification. This approach required the construction of a robust dataset, currently comprising over 100,000 labelled images, complemented by the development of multiple specialised deep learning models. While some models focus on detecting target species, others are dedicated to species classification. Evaluation on an independent test set showcases the efficacy of our methodology, with the current detection model achieving a balanced accuracy of 93%. Similarly, the classification model demonstrates robust performance, attaining an average balanced accuracy of 96%. Furthermore, as well as assisting with our biostratigraphic studies, the dataset of accurately labelled images has enabled us to test other aspects of ecosystem response. For example, examining morphometric changes in nannofossils over geological time can provide valuable insights into the potential impact of current global warming on modern phytoplankton assemblages (Mancini et al. 2021). This is particularly important for coccolithophores (Young et al. 2005), which play a critical role as primary producers in the global carbon cycle. A decrease in their size could lead to bottom-up ecosystem impacts and reduced carbon sequestration (Poulton et al. 2007, Krumhardt et al. 2017). Using our dataset, we conducted a deep-learning-enhanced automatic morphometric analysis focusing on the nannofossil species, Tranolithus orionatus. Our analysis revealed that two key morphometric parameters, minor axis and area size, showed statistically significant differences between the Cenomanian stage (approximately 100.5 to 93.9 million years ago) and the post-Cenomanian stages of the Late Cretaceous (approximately 93.9 to 66.0 million years ago). Kolmogorov-Smirnov tests (Massey 1951) between the two samples yielded p-values of 0.039 for the minor axis and 0.031 for the area size. Understanding these morphometric changes is crucial due to the close parallels between current climate projections and the warming and greenhouse climate of the Late Cretaceous, particularly the Cenomanian-Turonian boundary event (Arthur et al. 1990). Insights into how organisms changed morphologically during past periods of environmental stress can help us more effectively predict future responses of organisms under similar conditions (Razmjooei et al. 2020). These findings underscore the effectiveness of our approach in automating the identification and recognition of chalk nannofossils, helping to unlock natural science collections and to address key questions related to marine response to past climate change.

Tree-ring anomalies as time markers for ice-core chronologies, with special reference to 5281 BCE as the possible date of the Kikai volcanic event

The synchronization of Greenland and Antarctica ice core data with tree-ring data, other proxies, and direct observations of natural processes and events is important to understand past climatic variation and environmental change. One of the methods that is used to correct the dating of ice layers is to match volcanic eruption footprints in ice cores with tree rings, manifested as sulphate spikes and anomalous rings, respectively. In this study, we inventoried the occurrence of tree-ring anatomical anomalies and extremes in ring width during three 200-year periods. These periods included three of the eight largest Holocene volcanic eruptions, each with a Volcanic Explosivity Index (VEI) of 7. The initial period spanned from 6560 to 6360 BCE and included the eruption of Ilyinsky Volcano in Kamchatka. The second period was from 5780 to 5580 BCE, during which Mount Mazama Volcano in North America erupted. The third period was from 5380 to 5180 BCE when the Kikai Volcano in the Japanese Islands erupted. Throughout the first two periods, no substantial tree-ring anomalies were observed suggesting the absence of any significant climate consequences of a major volcanic eruption. However, in the 5380–5180 BCE period, a clear sharp decline in tree growth and an exceptionally high frequency of tree-ring anomalies were identified in 5281 BCE and the subsequent 5 years. We propose that the exceptionally narrow light rings in these 6 years are indicative of the climatic impact resulting from the Kikai volcanic eruption. We suggest utilising the year 5281 BCE as the reference year for synchronising the Greenland and Antarctica ice core chronologies. In the case that our assumption is correct, this would imply the necessity to adjust the time of the event to an earlier date compared to the dates indicated by the existing ice core chronologies of the GICC05 (Greenland Ice Core Chronology 2005), adjusted according to Kobashi (2017), and WD2014 used for creating HolVol 1.0 (Holocene ice-core volcanic eruption catalogue from 9500 BCE - 1900 CE) by 67 and 54 years, respectively, for the period around 5300 BCE. A verification of our assumption could be conducted by examining the nearby Miyake event, a spike in cosmogenic radiocarbon, of 5258 BCE. Ice core layers displaying potential signs of this event should be approximately 25 years later than the markers of the Kikai volcanic eruption.

A model framework for atmosphere–snow water vapor exchange and the associated isotope effects at Dome Argus, Antarctica – Part 1: The diurnal changes

Abstract. Ice-core water isotopes contain valuable information on past climate changes. However, such information can be altered by post-depositional processing after snow deposition. Atmosphere–snow water vapor exchange is one such process, but its influence remains poorly constrained. Here we constructed a box model to quantify the atmosphere–snow water vapor exchange fluxes and the associated isotope effects at sites with low snow accumulation rates, where the effects of atmosphere–snow water vapor exchange are suspected to be large. The model reproduced the observed diurnal variations in δ18O, δD, and deuterium excess (d-excess) in water vapor at Dome C, East Antarctica. According to the same model framework, we found that under average summer clear-sky conditions, atmosphere–snow water vapor exchange at Dome A can cause diurnal variations in atmospheric water vapor δ18O and δD of 4.8 ‰ ± 2.6 ‰ and 29 ‰ ± 19 ‰, with corresponding diurnal variations in surface snow δ18O and δD of 0.80 ‰ ± 0.35 ‰ and 1.6 ‰ ± 2.7 ‰. The modeled results under summer cloudy conditions display similar patterns to those under clear-sky conditions but with much smaller magnitudes of diurnal variations. However, under winter conditions at Dome A, the model predicts few to no diurnal changes in snow isotopes, consistent with the stable boundary condition in winter that inhibits effective vapor exchange between the atmosphere and snow. In addition, after 24 h and continuous simulations of 11 d, the model predicts significant enrichments in snow isotopes under summer conditions, while in winter, the depletions also accumulate after each 24 h simulation but with a much smaller magnitude of change compared to the results from summer simulations. If the modeled snow isotope enrichments in summer conditions and the depletions in winter conditions represent the general situation at Dome A, this likely suggests that atmosphere–snow water vapor exchange tends to increase snow isotope seasonality, and the annual net effect would be overall enrichments in snow isotopes since the effects in summer appear to be greater than those in winter. This trend will need to be further explored in the future with more comprehensive model studies and/or field observations and experiments.

Contrasting Patterns of Genetic Diversity in European Mammals in the Context of Glacial Refugia

Phylogeographic studies have been conducted on many different mammal species in order to track their recent demographic histories. The climatic fluctuations associated with the Last Glacial Maximum (LGM) appear to have had a profound influence on the geographic patterning of genetic diversity in mammals. However, most phylogenetic studies have focused on single species. Few have used a holistic approach covering multiple taxa to explore common patterns. Here, we conducted meta-analyses of mitochondrial DNA control region sequences, identifying haplotype diversity and private allelic richness patterns in a geographic context. Four general patterns emerged among European mammals: an east–west decline in variation, a Western-Central belt of the highest diversity, southern richness, and homogeneity with no geographic pattern. These patterns likely reflect the refugial origins of modern populations. The east–west variation decline suggests species with eastern LGM refugia; the Western-Central belt of the highest diversity may harbor taxa with cryptic northern refugia, while southern richness may correspond to traditional southern refugia. Species with homogeneity and no geographic pattern may have been panmictic without a specific refugium or may reflect the occurrence of both southern and cryptic northern refugia. Surprisingly, the “no pattern” phenomenon is seldom discussed and may frequently have been discounted. Our study emphasizes the importance of considering multiple taxa, providing valuable insights into the responses of European mammals to past climatic changes.

Exploring societal responses to past climate changes

Exploring societal responses to past climate changes

The potential to reduce runoff generation through improving cropping and tillage practices in a sub-humid continental climate

Agricultural sustainability is threatened by both water deficit and water excess, especially at the presence of extreme meteorological events resulting from climate change. However, there has been lack of demonstrations on management options with long-term values for agricultural adaptation to runoff. Using 20 years of monitoring data (1993‒2012) for two experimental fields in the Canadian Prairies as a case study, we quantified the effects of rainfall characteristics, crop type and biomass, and tillage on growing-season runoff generation using regression analyses and thereafter scenario comparisons. With growing-season gross rainfall ranging between 183 and 456 mm, runoff responses varied between 0 and 59 mm. Over the 20-year study period, 70%‒74% of the growing-season runoff was generated by rainfall events > 100 mm. Compared to high-intensity tillage, long-term conservation tillage reduced both overall runoff and runoff in large events likely by improving water infiltration. Under both tillage methods, growing-season runoff significantly increased with increasing rainfall but decreased with increasing biomass (R2 range: 0.40‒0.58; p range: 0.0007‒0.02). At the event level, the rainfall-runoff relationship followed a piecewise regression model (Cd = 0.82; p < 0.0001; “breakpoint” rainfall event = 105 mm), in which runoff increased slowly before reaching the “breakpoint” but rose sharply afterwards. Due to a greater biomass, canola resulted in less runoff than wheat. Scenario analyses showed that increasing crop biomass by 50% under the current average rainfall conditions could reduce runoff by 81‒86% in wheat and 100% in canola. The reduction may be attributed to the combined effects of crop on interception, evapotranspiration, and infiltration. In conclusion, although in a sub-humid continental climate like the Canadian Prairies there are generally low amounts of rainfall runoff, this study demonstrates significant runoff in some years, especially following large rainfall events. Runoff generation can be significantly reduced through improving cropping and tillage practices, and such effects on regional water retention should be further assessed by considering the past and future changes in climate and management.

An OSL-dated, stacked Holocene dust mass accumulation rate record on the Chinese Loess Plateau and its implications for Northern Hemisphere dust activity

Accurate reconstruction of geological dust activity is crucial for understanding past climate change and its interaction with dust cycle. Loess on the Chinese Loess Plateau (CLP) is an ideal and sensitive material for revisiting past dust activity. Previously, the changes in the dust mass accumulation rate (MAR) over various time scales were widely established on the CLP. However, few absolutely dated dust records have been obtained and synthesized for the Holocene. This study addresses this gap by compiling 23 optically stimulated luminescence-dated Holocene loess sections across the CLP. We developed a high-quality chronology via Bayesian age-depth modeling and derived a MAR record for each section. Then, we obtained a mean MAR record for the CLP by stacking individual records. We propose that, in contrast to site-specific MARs, stacked MARs represent the mean dust accumulation conditions for the entire CLP and can be used to track relatively large-scale dust activity and climate change. The stacked MAR record suggests a moderate weakening trend of dust accumulation from ∼11.5 to 7.5 thousand years ago (ka BP), followed by a pronounced strengthening trend from ∼7.5 to 3.0 ka BP. A comparison with other regional dust records reveals a shift in dust activity at ∼8–6 ka BP in northern China and western Mongolia. We argue that the East Asian winter and summer monsoons jointly contributed to Holocene mean dust MAR variations on the CLP by changing dust transport wind energy and dust source aridity, respectively. A comparison of Holocene dust records in Asia with those in the northwestern Pacific Ocean and Greenland suggests asynchronous variations in dust activity between proximal and distal Asia-sourced dust deposition. This is because, unlike proximal deposition, distal deposition can be controlled not only by the dust source conditions but also by the intensity and the position of the Westerlies.

Technological and Dietary Responses to Holocene Climate Events in the Northern Great Basin

ABSTRACT Environmental instability caused by extended periods of drought no doubt impacted past human populations by limiting economic options and driving changes in social and technological organization. Here we examine two sets of Great Basin sites with occupations spanning the middle and late Holocene droughts: one associated with lowland springs and another with upland springs. We use dietary markers retrieved via starch granule analysis to evaluate whether artifact form relates to resources processed, how changes in tool form might be related to past changes in climate, environment, and social organization, and what, if any, differences mark upland vs. lowland resource use. Our data suggest that changes in tool form track with environmental fluctuations and that in both upland and lowland settings diets focused primarily on tubers and high-return seeds and that these profitable and stable food sources likely anchored populations during periods of drought.

Deciphering the evolution and biogeography of ant-ferns Lecanopteris s.s

Southeast Asia is a biodiversity hotspot characterized by a complex paleogeography, and its Polypodiopsida flora is particularly diverse. While hybridization is recognized as common in ferns, further research is needed to investigate the relationship between hybridization events and fern diversity. Lecanopteris s.s., an ant-associated fern, has been subject to debate regarding species delimitations primarily due to limited DNA markers and species sampling. Our study integrates 22 newly generated plastomes, 22 transcriptomes, and flow cytometry of all native species along with two cultivated hybrids. Our objective is to elucidate the reticulate evolutionary history within Lecanopteris s.s. through the integration of phylobiogeographic reconstruction, gene flow inference, and genome size estimation. Key findings of our study include: (1) An enlarged plastome size (178–187 Kb) in Lecanopteris s.s., attributed to extreme expansion of the Inverted Repeat (IR) regions; (2) The traditional ‘pumila’ and ‘crustacea’ groups are paraphyletic; (3) Significant cytonuclear discordance attributed to gene flow; (4) Natural hybridization and introgression in the ‘pumila’ and ‘darnaedii’ groups; (5) L. luzonensis is the maternal parent of L. ‘Yellow Tip’, with L. pumila suggested as a possible paternal parent; (6) L. ‘Tatsuta’ is a hybrid between L. luzonensis and L. crustacea; (7) Lecanopteris s.s. first diverged during the Neogene and then during the middle Miocene climatic optimum in the Indochina and Sundaic regions. In conclusion, the biogeographic history and speciation of Lecanopteris have been profoundly shaped by past climate changes and geodynamics of Southeast Asia. Dispersals, hybridization and introgression between species act as pivotal factors in the evolutionary trajectory of Lecanopteris s.s.. This research provides a robust framework for further exploration and understanding of the complex dynamics driving the diversification and distribution patterns within Polypodiaceae subfamily Microsoroideae.

Past climate change effects on human evolution

Past climate change effects on human evolution

Decoupled terrestrial temperature and hydroclimate during the Plio-Pleistocene in the East Asian monsoonal region

The independent reconstructions of temperature and hydroclimate records are crucial to understanding past changes in Earth's climate. However, the temperature and hydroclimate history of East Asia during the late Cenozoic remains largely unknown. Here, we reconstructed terrestrial temperature and hydroclimate patterns in the East Asian monsoonal regions using GDGTs (glycerol dialkyl glycerol tetraethers) in a sediment core from North China spanning 5.5 million years (Ma). Our data show a decoupled terrestrial temperature and hydroclimate evolution over the past 5.5 Ma. The methylation index of branched GDGTs (brGDGTs), i.e. MBT'5ME-inferred temperature, significantly decreases at ∼2.6 Ma and likely reflects a response to Northern Hemisphere glaciation (NHG), in agreement with multiple marine temperature records. The MBT'5ME temperature record shows a decline of approximately 6.5 °C at around 2.6 Ma, which is larger than the decline recorded in marine sequences. Interestingly, this temperature decline occurs much later than the large GDGT-inferred (i.e., Ri/b and GDGT-0/Cren) increase in rainfall at ∼4.0 Ma, which aligns with the strengthening of Pacific zonal and meridional sea surface temperature (SST) gradients as well as the increased marine-land temperature gradients. Our study thus suggests differing mechanisms driving temperature and hydroclimate evolution in East Asia during the Plio-Pleistocene.

Global Distribution of Mammalian Cradles and Museums is Driven by Past Climate Dynamics and Present Water–Energy Balance

ABSTRACTAimTo describe worldwide distribution of mammalian cradles and museums using the rates of phylogenetic lineage turnover as a surrogate. Additionally, we investigated the influences of current water–energy dynamics, climate instability, past climate changes and elevational ranges on the distribution of these evolutionary zones.LocationGlobal.Time PeriodCurrent.Major Taxa StudiedTerrestrial mammals.MethodsWe developed a new methodology that consists of calculating the spatial phylogenetic turnover for non‐overlapping temporal segments of phylogenetic trees. By calculating the relative turnover in each tree segment, we quantified the rate of accumulation of phylogenetic turnover through time. We depicted cold and hotspots of rates of lineage turnover using bivariate maps and examined the effects of environmental factors using a path model.ResultsThe distributions of cradles and museums of biodiversity are primarily driven by water–energy dynamics. Environments with higher water availability than energetic demand predominantly act as cradles, as seen in tropical rainforests, while xeric‐like environments predominantly serve as museums. Conversely, regions undergoing higher historical climate changes become cradles, such as in higher northern latitudes, while climatically stable areas function as museums. Mountains play a dual role, acting as both cradles and museums by generating new lineages along their elevation bands while simultaneously providing climate refuges for ancient mammal lineages.Main ConclusionsOur findings demonstrate that cradles and museums are not merely a dichotomy but exist along an evolutionary continuum. Furthermore, they reveal how spatial patterns of mammalian cradles and museums are intricately shaped by biogeographical processes governed by environmental forces. Uncovering these hidden effects provides insights into the ecological mechanisms by which ongoing climate changes continually shape evolutionary assemblages over time.

Synergistic effects of climate and land use change on khulan (Equus hemionus hemionus) habitat in China

Climate and land use change are the primary drivers causing the reduction of habitat range for many species worldwide, especially wide-ranging and large-bodied ungulates. For instance, khulan (Equus hemionus hemionus), a flagship species inhabiting desert regions of Asia, exhibits heightened vulnerability to habitat loss and fragmentation due to their extensive habitat requirements. We simulated suitable khulan habitats in China across 20 scenarios, including the past (1980–2000), current (2001–2022), and future (2050 s and 2070 s) climate and land use change scenarios. For each scenario, we identified the suitable habitat area and evaluated the effectiveness of protected areas (PAs). Our findings revealed a decline in khulan habitat area from 133,006 km2 in the past to 60,141 km2 at present. Future scenarios indicate further reductions in potential khulan habitat, with more negative impacts resulting from climate change than land use change. Northern Xinjiang is expected to persist as a primary area of both in-situ and ex-situ refugia for khulan in future scenarios. Although suitable habitat within existing PAs is smaller than that outside, the rates of habitat loss and fragmentation outside the PAs surpass those inside PAs. These findings emphasize the importance of effective management strategies for PAs as crucial goals for ongoing conservation efforts for the khulan. Our models suggest that future suitable habitat for khulan will be situated along the international border between China and Mongolia, adjacent to protected areas in Mongolia utilized by khulan. Enhancing connectivity between these habitats could significantly contribute to improving both the climate and genetic resilience of khulan populations.

Arvicolinae rodents of Galería de las Estatuas (Sierra de Atapuerca, Burgos) and insights into MIS 5- to −4 climatic conditions in Northern Iberia

Well-dated Middle Palaeolithic sequences that lie beyond the limit of radiocarbon dating (i.e., >50,000 years ago) are critical for understanding the long-term palaeoecological changes that took place during Neandertal occupation of Europe and the Iberian Peninsula. Among the two pits excavated in Galería de las Estatuas site, GE (Sierra de Atapuerca, Burgos, Spain) represents such sequence, having been previously dated using a combination of single-grain optically stimulated luminescence (OSL) and U-series. This site is one of the few across Eurasia to have yielded both Neandertal remains and genetic evidence of Neandertal population replacements during marine isotope stage (MIS) 5 to the beginning of MIS 4 (120,000 to 70,000 years ago). Understanding the prevailing climatic and environmental conditions during the period of Neandertal occupation is therefore of great importance. Small mammal remains are one of the best proxies to interpret past environmental and climatic changes, and among these, the Arvicolinae species (Cricetidae, Rodentia) are particularly useful.Here we provide a revision of the small mammal associations at both Galería de las Estatuas pits undertaking detailed study of Arvicolinae species composition in both excavation pits. Additionally, we present new single-grain OSL dating results to refine the existing chronostratigraphic framework and better contextualise the past climatic changes inferred from the small mammal record. Our results indicate that the lower levels were formed in cold-temperate conditions, with a predominance of an open landscape and Atlantic-type climatic regime. Progressively upward through the sequences, we observe warmer and more humid conditions, with a stronger Mediterranean climate regime and increased development of forest areas, although still with a predominance of open meadows. Finally, both sedimentary sequences seem to end with a deterioration of these climatic conditions, and show a drier environment, dominated by open landscapes and a return to an Atlantic climatic regime. We conclude that at least two marked climatic changes can be identified at each pit (GE-I and GE-II), from MIS 5.4 through to the beginning of MIS 4, by studying the small mammal record together with OSL dating.

Isothermal thermoluminescence dating of speleothem growth – A case study from Bleßberg cave 2, Germany

Speleothems are a key archive of past climatic and environmental changes. 230Th/U dating is the most commonly used method to determine speleothem ages. However, incorporation of non-radiogenic thorium may hamper 230Th/U dating, and samples older than 600 ka also remain out-of-reach. Calcite exhibits a thermoluminescence (TL) signal at 280 °C with a high characteristic saturation dose, and provides significant potential to date carbonate samples over several million years. Hitherto, the application of TL dating for calcite has mainly been hindered by two factors: 1) a spurious TL signal occurring in the high temperature range, and 2) non-uniform dose rate due to U-series disequilibrium. Here we test an isothermal TL (ITL) dating method on a speleothem sample from Bleßberg cave 2, Germany. We show that the ITL signal measured at 240 °C can completely remove the 280 °C TL peak with a negligible TL contribution from the higher temperature range, thus reducing the influence from the spurious signal. The time-dependent dose rate variation can be simulated using the initial radioactivity of 238U, 234U, 230Th and their decay constants. We use the 230Th/U dating method to provide precise and accurate radiometric ages documenting that the speleothem grew between 425.5 ± 5.4 and 320.5 ± 9.7 ka. The ITL ages (421 ± 23 to 311 ± 23 ka) of four subsamples from the speleothem are consistent with the 230Th/U ages at isochronous sampling positions, showing the general reliability of the ITL dating method. ITL dating provides a pathway to construct chronologies for palaeoclimate reconstructions for speleothems beyond the range of the 230Th/U-method and for samples that are unsuitable for U-series dating methods.

Gelada genomes highlight events of gene flow, hybridisation and local adaptation that track past climatic changes.

Theropithecus gelada, the last surviving species of this genus, occupy a unique and highly specialised ecological niche in the Ethiopian highlands. A subdivision into three geographically defined populations (Northern, Central and Southern) has been tentatively proposed for this species on the basis of genetic analyses, but genomic data have been investigated only for two of these groups (Northern and Central). Here we combined newly generated whole genome sequences of individuals sampled from the population living south of the East Africa Great Rift Valley with available data from the other two gelada populations to reconstruct the evolutionary history of the species. Integrating genomic and paleoclimatic data we found that gene-flow across populations and with Papio species tracked past climate changes. The isolation and climatic conditions experienced by Southern geladas during the Holocene shaped local diversity and generated diet-related genomic signatures.