Climate Proxies Research Articles

Global Evidence of Obliquity Damping in Climate Proxies and Sea-Level Record during the Last 1.2 Ma: A Missing Link for the Mid-Pleistocene Transition

A recent research has identified an inverse amplitude link between obliquity damping and short eccentricity amplification during the Mid-Late Pleistocene based on LR04 δ18O and equatorial Pacific Site 846 sea surface temperature records that is associated with the Earth’s long-term cooling. In the present study, new evidence of this anticorrelation is presented from Antarctic δD-CO2-CH4 records, global benthic–planktic δ18O, and regional (Atlantic, Pacific, Mediterranean, and Indian) climate-related proxies. Based on a critical review of theoretical constraints (Earth’s oblateness changes and ice-volume phase lag in the obliquity band <5.0 kyr), this widespread and symmetric (bipolar) obliquity response damping has been interpreted as an effect of the obliquity–oblateness feedback, which could be the latent physical mechanism at the origin of the Mid-Pleistocene Transition (MPT). Indeed, results and considerations of the present work suggest that fast and positive/negative net variation in the Earth’s oblateness in the obliquity band was controlled by a dominant glacio-eustatic water mass component and, assuming a rapid response of the ice volume to surface temperature changes, the mean obliquity lag response is estimated to be <5.0 kyr over the past 800 kyr. These elements may explain the interglacial/glacial damping observed in the obliquity response. The consolidation of the Earth’s long-term icy state in the subtrend IV, culminating with the post-MPT obliquity damping, might have contributed to the strengthening of the short eccentricity response by mitigating the obliquity ‘ice killing’ during obliquity maxima (interglacials), favouring the obliquity-cycle skipping and a feedback-amplified ice growth in the short eccentricity band (obliquity damping hypothesis). This suggests a different impact of the climate friction than what is generally believed, which is presumably the latent physical mechanism that triggers the transient ‘competitive’ interaction between obliquity and short eccentricity started early during the Piacenzian.

Assessment of climate extremes at the regional scale during the last millennium using an annually resolved stalagmite record

In public awareness, extraordinary floods, heat-waves, or drought episodes rank amongst the most tangible indications of a changing climate. Forecasting the magnitude of such extreme events at regional and local scales is a major challenge. Development of reliable small-scale climate models requires testing against past climate records, but these are often incomplete, or cover only partial aspects in a spectrum of environmental parameters, e.g., due to seasonal bias as it is the case for tree-ring records. Here, we study a stalagmite from the “Kleine Teufelshöhle” (KTH) in the Franconian karst (Germany) to obtain independent information on local climate conditions at multi-annual to multi-decadal time scales. Radiocarbon and 230Th/U dating provide constraints for linear growth models, which were then successfully refined by correlating high spatial resolution O isotope data for the KTH stalagmite with a published regional tree-ring width record at annual resolution for the past 1000 years. Besides the availability of the tree-ring record, the KTH site offers the additional advantage that direct comparison between tree-ring and speleothem climate proxies with historical documents is possible due to the proximity of the speleothem and tree-ring sites to the former “Free imperial city” of Nuremberg. Historical documents provide precisely dated records of extreme events, in particular for destructive floods. Higher O isotope values in the stalagmite characterize the “Litte Ice Age" (LIA), an interval coinciding with frequent and devastating floods, sometimes associated with river blockage related to accumulation of ice rafts. Prior to approximately 1500 Common Era (CE), O isotope values were generally lower and only show minor overlap with historical flooding accounts. Conversely, some known drought events for Central Europe as well as the climatic influence of large-volume volcanic eruptions with hemispheric to global impact may be recorded in the speleothem as negative excursions in speleothem O isotopic values. The correlated tree-ring and speleothem data for the first time provide a complementary paleohydrology record that is uniquely suited to resolve extreme short-term climate events at the regional scale.

Contrasting lake changes in Tibet revealed by recent multi-modal satellite observations

The limited anthropogenic activities on the Tibetan Plateau make this an ideal natural laboratory to elucidate how climate change impacts lake changes. Previous studies have mainly focused on decadal lake changes, yet their rapid evolutions at short temporal intervals and the associated atmospheric origins remain elusive. Here, we produce a new lake area change dataset at monthly sampling over 2015–2020 from 16,801 satellite images. Our estimates achieve an accuracy of <30 m, as evidenced by in-situ GPS field survey validations of representative lake shorelines. We found contrasting patterns in recent rapid area changes: deaccelerating in the north and accelerating in the south. Such contrasting pattern was unprecedented in the last two decades and is likely caused by recent precipitation anomalies, indicating that lakes in TP may experience a tipping point. Lakes are found to store only a small portion (<5 %) of net precipitation in summer, increased to ∼11 % for years with heavy precipitation, which helps understand the water mass budget for lakes over there. Our study highlights the importance of investigating short-term lake area changes as a climate proxy to study their rapid responses to intra- and inter-annual climate variability.

The late Quaternary palynological record of the northern Yangtze Delta: Implication for palaeoclimate change in East Asia

Marine Isotope Stage (MIS) 3 is the latest interstadial period with unstable climate regimes that provides an indispensable key to better predict future climate change. However, paleoclimate reconstruction in the Yangtze Delta covering MIS 3 remains elusive due to limited archives with reliable age. Here, we derived a 53,000–year–long paleoclimate record from the northern Yangtze Delta, using luminescence age–based palynological data of a coastal sediment core (YZ07). The results show that the climate was relatively warm and wet during ∼53.0–37.5 ka, followed by a slightly cool but wetter condition between ∼37.5 ka and ∼33.2 ka. Afterwards, a cool and dry climate prevailed from ∼33.2 ka to ∼30.7 ka. Three cold events were identified around 48.0 ka, 39.0 ka and 31.0 ka, corresponding to the timings of Heinrich Event (HE 5), HE 4 and HE 3, respectively. From ∼30.7 ka to ∼11.5 ka, broadleaved forests and wetland herbs obviously contracted in the Yangtze Delta region, indicating cold and dry climate conditions. From the late Pleistocene to Holocene, the pollen variations in this core site were linked to coastal geomorphology under climate–induced sea–level changes. Besides, our findings suggest that the percentages of emergent vegetation in this work were negatively correlated with El Niño–Southern Oscillation (ENSO)–linked flood events during the Holocene. Overall, from mid–MIS 3 to MIS 2, the climate exhibits a ‘warm–cool–cold’ pattern in the Yangtze Delta, broadly concordant with other climate proxies in East Asian monsoon domain and beyond on suborbital or millennial timescales. We argue that the northern hemisphere summer insolation may be responsible for the paleoclimate variability and paleovegetation successions in the Yangtze Delta. However, the variability of precipitation in MIS 3 might be governed by interhemispheric insolation forcing, which accounts for a wetter climate phase occurring during late MIS 3 rather than mid–MIS 3.

Show me? Inspire me? Make me? An institutional theory exploration of social and environmental reporting practices

PurposeAlbeit gradual and uneven, the emergence of social and environmental reporting by publicly held corporations has been a major development in the last few decades. This paper aims to explore patterns of the emergence of these disclosures. Using an institutional theory lens, this paper considers mimetic, normative and coercive possibilities.Design/methodology/approachUS publicly traded company data from 2013 to 2019 is used to test the hypotheses. Mimetic forces are proxied with corporate board interlock frequency. Normative ones use the extent of gender diversity on corporate boards. Measures of business climate and industry regulatory sensitivity proxy coercive potentiality.FindingsStudied in isolation, each of the three forces through which organizations pursue the heightened legitimacy of enhanced environmental and social disclosures has credibility. The strongest support exists for mimetic and normative mechanisms, perhaps because the US government has been reluctant to make these expanded disclosures mandatory.Research limitations/implicationsIn the world of voluntary action, more attention to diffusion is needed. For these purposes, better proxies will be needed to study change. Social and environmental information should be separated for individual analysis.Practical implicationsAt least in the USA, companies are attentive to what other companies are doing. There is something to be said for the ethical dimension of corporate transparency.Social implicationsGovernmental action in this area has not been effective, at current levels. Corporate leadership is essential. Critical information is shared about disclosure by board members.Originality/valueAlthough institutional theory makes several appearances in this area, to the best of the authors’ knowledge, the current study is the first empirical archival study to examine the three forces simultaneously, providing evidence as to the relative magnitude of each institutional force on environmental and social disclosures. Should these disclosures not be mandated by government, this study shows pathways for enhanced disclosures to continue to spread.

Were climatic forcings the main driver for mid-holocene changes in settlement dynamics on the Varamin Plain (Central Iranian Plateau)?

Settlement crises in ancient cultures of Western Asia are commonly thought to be caused by climatic events such as severe droughts. However, the insufficient climate proxy situation in this region challenges the inference of clear relationships between climate and settlement dynamics. We investigate the Holocene climatic changes on the Varamin Plain in the context of the climatic history of Western Central Asia by using a transient comprehensive Earth System Model simulation (8 ka BP to pre-industrial), a high-resolution regional snapshot simulation and a synthesis of pollen-based climate reconstructions. In line with the reconstructions, the models reveal only slightly varying mean climatic conditions on the Varamin Plain but indicate substantial changes in seasonality during the Holocene. Increased precipitation during spring, combined with lower temperature and potentially stronger snow accumulation on the upstream Alborz mountains may have led to an increased water supply on the alluvial fan during the vegetation period and thus to more favourable conditions for agricultural production during the Mid-Holocene compared to modern times. According to the model, dry periods on the Central Iranian Plateau are related to particularly weak Westerly winds, fostering the subsidence in the mid-troposphere and hampering precipitation over the region. The model reveals that dry periods have spatially heterogenous manifestations, thus explaining why they do not appear in all proxy records in the wider study region. In fact, the climatic signal may depend on local environmental conditions. The interaction of the topography with the atmospheric circulation leads to additional spatial heterogeneity. Although our results provide several indications for a connection between climate and settlement dynamics, the small overall changes in moisture call into question whether climate is the main driver for settlement discontinuities on the Central Iranian Plateau. To shed further light on this issue, more high-resolution long-term proxy records are needed.

Snow‐Atmosphere Humidity Exchange at the Ice Sheet Surface Alters Annual Mean Climate Signals in Ice Core Records

AbstractSurface processes alter the water stable isotope signal of the surface snow after deposition. However, it remains an open question to which extent surface post‐depositional processes should be considered when inferring past climate information from ice core records. Here, we present simulations for the Greenland Ice Sheet, combining outputs from two climate models with an isotope‐enabled snowpack model. We show that surface vapor exchange and associated fractionation imprint a climate signal into the firn, resulting in an increase in the annual mean value of δ18O by +2.3‰ and a reduction in d‐excess by −6.3‰. Further, implementing isotopic fractionation during surface vapor exchange improves the representation of the observed seasonal amplitude in δ18O from 65.0% to 100.2%. Our results stress that surface vapor exchange is important in the climate proxy signal formation and needs consideration when interpreting ice core climate records.

Elevational clines predict genetically determined variation in tropical forest seedling performance in Borneo: implications for seed sourcing to support reforestation

While much research has focused on genetic variation in plants in relation to abiotic clines in temperate and boreal forests, few studies have examined similar relationships in tropical forests. Genetic variation in desirable performance traits of trees, such as drought tolerance, fast‐growth, and carbon sequestration rates, is widely used to improve reforestation efforts in nontropical systems. However, evolutionary processes such as local adaptation are poorly understood in tropical forests making it difficult to locate desired phenotypes. To test for genetic variation in growth rate in relationship to climatic clines, we conducted a common garden study over 18 months in a nursery using four dipterocarp tree species, represented by 9–12 half‐sib families, sourced across an elevational gradient ranging from lowland to hill forests (circa 130–470 m above sea‐level) in Malaysian Borneo. We found genetic variation in growth for all four species with fast‐growing half‐sib families growing 42–88% faster than poorly performing half‐sib families. Furthermore, in three species we found that elevation of seedling origin predicted seedling performance; in Shorea fallax and S. johorensis, half‐sib families originating from low elevations performed the best. In S. argentifolia half‐sib families' seedlings from low elevations grew slowly. Because elevation is a good proxy for climate, the finding of elevational clines predicting genetic variation in growth provides evidence of evolution affecting the function of tropical tree species. Our research highlights opportunities to better understand evolutionary processes in tropical forests and to use such information to improve seed source selection in reforestation.

Winter hydroclimate contrasts between southern and northern Europe at ∼ 5.2 ka

Winter climate variations in midlatitude regions have far-reaching effects on both natural and human systems worldwide. However, most climate reconstructions focus on either annual or summer climate conditions. Here we present a stalagmite stable isotope record from Urşilor Cave (Romania) where the δ18O values are controlled by winter temperature. Because of its East-Central Europe (ECE) location, the cave site is well suited to capture variations in precipitation and temperature in response to changes in the North Atlantic region. Present day precipitation and temperature in this region are controlled by two teleconnection patterns, the Arctic Oscillation (AO) and the East Atlantic (EA). By analyzing composite maps for four different scenarios of AO and EA phase, we suggest that between 5.6 and 5.2 ka the positive phases of AO and EA became increasingly dominant. This shift led to generally warmer winters in northern Europe, but drier conditions in southern Europe and the Levant. Considering the compound effect of AO and EA on the hydroclimate of ECE, our study highlights the importance of examining the combined impact of teleconnection patterns on climate proxies influenced by various forcing mechanisms.

Stratigraphy, sedimentology, and paleoclimatic proxies of the Upper Jurassic Morrison Formation of central Montana: Geology of the Intermountain West

Since the discovery of dinosaurs in the late 19th century, the Upper Jurassic Morrison Formation has received considerable scholarly attention. However, the formation in central Montana needed to be sufficiently investigated. Recent dinosaur excavations from exposed Morrison strata on the southern flank of Spindletop dome near the town of Grass Range, Montana, prompted a review of the formation’s geology, paleobotany, and paleoclimate. A review of historical stratigraphic measurements of the formation in Montana reveals a considerable variance in measured thicknesses. Stratigraphic measurements and regional log data indicate that the formation averages 71 m thick across central Montana. A new regional isopach map of the formation from well-log data illustrates a broad distributive fluvial system that migrated from the southwest toward the northeast. The formation is divided into two informal facies in the study area: lower and upper depositional facies. The lower depositional beds represent the mud-rich distal-most distributive fluvial facies that overlies the stranded muddy tidal flat of the Swift Formation. An increased sandstone:mudstone ratio and small isolated fluvial channel and crevasse splay beds indicate that the upper depositional beds represent the slow progression of the distributive fluvial system. However, a review of the regional field stratigraphy and well-log data did not provide a regional correlatable facies change to warrant subdividing the formation into members.The stratigraphic positions and climatic interpretations for lithologic, faunal, and floral paleoclimatic proxies are specified. The compilation of climate proxy data from central Montana demonstrates that the climate in this region was wetter than in southern parts of the Morrison foreland basin. The climatic proxies signify that the environmental conditions were variable during the Late Jurassic in central Montana, displaying changing temperatures with mesic and xeric intervals of unknown duration.

Dolphin social phenotypes vary in response to food availability but not the North Atlantic Oscillation index.

Social behaviours can allow individuals to flexibly respond to environmental change, potentially buffering adverse effects. However, individuals may respond differently to the same environmental stimulus, complicating predictions for population-level response to environmental change. Here, we show that bottlenose dolphins (Tursiops truncatus) alter their social behaviour at yearly and monthly scales in response to a proxy for food availability (salmon abundance) but do not respond to variation in a proxy for climate (the North Atlantic Oscillation index). There was also individual variation in plasticity for gregariousness and connectedness to distant parts of the social network, although these traits showed limited repeatability. By contrast, individuals showed consistent differences in clustering with their immediate social environment at the yearly scale but no individual variation in plasticity for this trait at either timescale. These results indicate that social behaviour in free-ranging cetaceans can be highly resource dependent with individuals increasing their connectedness over short timescales but possibly reducing their wider range of connection at longer timescales. Some social traits showed more individual variation in plasticity or mean behaviour than others, highlighting how predictions for the responses of populations to environmental variation must consider the type of individual variation present in the population.

New data on Biphyllidae (Coleoptera: Cucujiformia: Cleroidea) from Baltic amber: more diverse assemblage than previously assumed and its climatic interpretation

ABSTRACT Two new extinct species of false skin beetles (Biphyllidae) are described and illustrated based on inclusions in Baltic amber: Biphyllus lar sp. nov. and Coelodiplus uuu-impressa gen. et sp. nov. The new Eocene fossils are compared with the related extant and extinct representatives of the family. A new monotypic genus is erected for one fossil; another Eocene species is classified within the extant genus Biphyllus Dejean, 1821. The holotype of Diplocoelus probiphyllus Vitali, 2010 (Baltic amber) is re-examined and its diagnosis is emended. The present paper brings the total number of described biphyllid species from European succinite to three. A key to all documented fossil species of the family is provided. Several aspects of insect use as paleoenvironment and climate proxies are briefly discussed. On the basis of the revealed biphyllid palaeofauna and analysis of the climatic extremes of the modern distribution of the family in the Northern Hemisphere, the lowest possible annual temperature in the area of amberiferous forests of Eocene Northern Europe is hypothesised.

Climate and atmospheric circulation during the Early and Mid‐Holocene inferred from lake‐carbonate oxygen‐isotope records from western Ireland

ABSTRACTThe Early to Mid‐Holocene experienced marked climate change over the northern hemisphere mid‐latitudes in response to changing insolation and declining ice volume. Oxygen isotopes from lake sediments provide a valuable climate proxy, encoding information regarding temperature, hydroclimate and moisture source. We present oxygen‐isotope records from two lakes in western Ireland that are strongly influenced by the North Atlantic. Excellent replication between the records suggests they reflect regional, not local, influences. Carbonate oxygen‐isotope values peaked at the start of the Holocene, between 11.2 and 11.1 cal ka bp, and then decreased markedly until 6 cal ka bp at both sites. Palaeoecological evidence supports only modest change in temperature or hydroclimate during this interval and we therefore explain the decrease primarily by a reduction in the oxygen‐isotope composition of precipitation (δ18Oppt). We show a similar decrease in δ18O values in a forward model of carbonate isotopes between 12–11 and 6–5 cal ka bp. However, the inferred reduction in δ18Oppt between the Early and Mid‐Holocene in the model is mainly linked to a decrease in the δ18O of the ocean source water from ice sheet melting whereas the lake carbonate isotope records are more consistent with changes in the transport pathway of moisture associated with atmospheric circulation change as the dominant cause.

Environmental controls on the distribution of GDGT molecules in Lake Höglwörth, Southern Germany

Tetraether lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs), are an increasingly used proxy for reconstructing paleoclimatic and paleoenvironmental dynamics. On a global scale, environmental drivers controlling the distribution of GDGTs in lake systems have been described extensively. However, the drivers that control down-core sedimentary GDGT composition within single lake systems are still poorly constrained. Here, we analysed GDGTs in a sediment core collected from Lake Höglwörth (Bavaria, Germany) covering the last ∼1100 years. The increase in ratio ΣIIIa/ΣIIa values (a ratio which captures the variation of 3 structural isomers of penta- and hexamethylated brGDGTs respectively) reflects a higher contribution of branched (br) GDGTs from aquatic sources after 1800 CE. This is synchronous with a high nutrient input as a result of increased local anthropogenic activities. The climate proxy methylation of branched tetraethers (MBT'5ME) reveals a pattern that deviates from the anticipated temperature changes during the last millennium. Instead, high MBT'5ME values from ∼880 to 1120 CE coincide with a period of increased soil input, resulting from lake damming and/or construction of the Höglwörth monastery. Decreased values after 1800 CE until present date correspond to a higher contribution of aquatic brGDGTs, with changes in the dependency between Ia and IIa suggesting a direct influence of bacterial community changes on the MBT'5ME. The proxy cyclisation of branched tetraethers (CBT') shows a linear increase with time, and a stepwise increase at 1700 CE, when a creek stream inflow channel was rerouted. Over time, MBT’5ME decreases gradually, while CBT’ and ΣIIIa/ΣIIa increase. This is hypothesized to be potentially caused by decreasing water depth over time and/or post- or syn-sedimentary production of GDGTs. The degree of cyclization (DC') shows variations on shorter timescales, possibly driven by the lake mixing regime and water column redox conditions. Our results indicate that caution must be taken when interpreting GDGTs for paleoclimate and paleoenvironmental reconstruction considering the possible influence of shifts in the provenance of brGDGTs. Further studies focusing on both sedimentary and intact polar lipids are highly recommended to constrain the source (water column, or sedimentary production) of GDGTs in lake sediments.

Assessing Seasonal and Inter‐Annual Marine Sediment Climate Proxy Data

AbstractThree recently published papers including Napier et al. (2022, https://doi.org/10.1029/2021PA004355) utilize novel microanalytical approaches with varved marine sediments to demonstrate the potential to reconstruct seasonal and inter‐annual climate variability. Obtaining paleoclimate data at a resolution akin to the observational record is vitally important for improving our understanding of climate phenomena such as monsoons and modes of variability such as the El Niño Southern Oscillation, for which appraisals of past inter‐annual variability is critical. The ability to generate seasonal and inter annual resolution sea surface temperature proxy time series spanning a thousand years or more is revolutionary and has the potential to fill gaps in our knowledge of climate variability. Although generally limited to sediments from regions with oxygen depleted bottom waters, there is great potential to integrate shorter seasonal resolution climate “snap shots” from other archives such as annually banded corals into composite time series. But as paleoceanographic data are used more by the observational and modeling fields, we make the case for conducting a thorough case‐by‐case assessment of the processes that influence the climate signal recovered from proxies, using careful replication to validate new approaches. Understanding or exploring the potential influence of processes which effectively filter the climate signal will lead to more quantitative paleoceanographic data that will better serve the broader climate science community.

Satellite-Based Distribution of Inverse Altitude Effect of Global Water Vapor Isotopes: Potential Influences on Isotopes in Climate Proxies

The widely-distributed altitude effect of stable isotopes in meteoric water, i.e., the negative correlation between stable hydrogen (or oxygen) isotope compositions and altitude, is the theoretical basis of isotope paleoaltimetry in climate proxies. However, as many recent local observations have indicated, the inverse altitude effect (IAE) in meteoric water does exist, and the regime controlling IAE is still unclear on a global scale. Based on a remote sensing product of the Infrared Atmospheric Sounding Interferometer (IASI), we examined the global frequency of IAE in water vapor isotopes, and the possible influences on isotopes in precipitation and climate proxies. According to the satellite-based δD values in water vapor at 2950 m and 4220 m above sea level, frequent IAEs are observed on a daily scale in North Africa, West and Central Asia, and North America, and IAEs are more likely to occur during the daytime than during the nighttime. We also converted water vapor δD to precipitation δD via equilibrium fractionation and then analyzed the potential presence of IAE in precipitation, which is more associated with climate proxies, and found that the spatial and temporal patterns of water vapor can be transferred to the precipitation. In addition, different thresholds of δD difference were also tested to understand the impact of random errors. The potential uncertainty of the changing isotope and altitude gradient should be considered in paleo-altitude reconstructions.

Experiments of the efficacy of tree ring blue intensity as a climate proxy in central and western China

Abstract. To investigate the potential value of tree ring blue intensity as a robust climate proxy in central and western China, four species from five sites were assessed. As well as latewood inverted blue intensity, we also examined earlywood blue intensity. To explore the sensitivity of using different extraction parameter settings using the software CooRecorder, seven percentile (P) variant settings for earlywood blue intensity and latewood inverted blue intensity were used, namely P50 : 50, P60 : 40, P70 : 30, P80 : 20, P85 : 15, P90 : 10, and P95 : 5. Age-dependent spline was used for all, and the positive trends were not retained. Correlation analysis was applied between the tree ring parameter chronologies and monthly/seasonal mean temperature, precipitation, and self-calibrated Palmer drought severity index variables. Linear regression was also used to further highlight the potential of developing climate reconstructions using these species. Only subtle differences were found between the different percentile extraction variants. As has been shown for many other Northern Hemisphere studies, latewood inverted blue intensity expresses a strong positive relationship with growing-season temperatures (the two southern sites explain almost 56 % of the temperature variance when combined). However, the low latitude of these sites shows an exciting potential for regions south of 30∘ N that are traditionally not targeted for temperature reconstructions. Earlywood blue intensity also shows good potential to reconstruct hydroclimate parameters in some humid areas.

On the timing of megafaunal extinction and associated floristic consequences in Australia through the lens of functional palaeoecology

The timing and cause of megafaunal extinctions are an enduring focus of research interest and debate. Despite the developments in the analysis of coprophilous fungal spores (CFS), the proxy for reconstructing past megaherbivore changes, the environmental consequences of this fauna loss remain understudied. This is partly due to the general obscurity of such a signal in pollen records, as well as limitations in disentangling human and extinction ecological impact, and the lack of spatial information of megafauna changes in site-level sedimentary records. In Australia, the debate centres on the possibility that habitat loss through climate change, vegetation-fire change, human intervention, or a combination of these factors led to the extinction of some large animals during the Late Pleistocene. Pollen and plant isotope studies have also demonstrated that vegetation-fire responses following the Late Pleistocene megafaunal extinctions were characterized by increased vegetation density and fire activity due to reduced grazing/browsing pressure. Here, we use a well-dated marine sedimentary core record from the Murray Darling Basin in southern Australia and apply palynological and functional palaeoecological approaches to reconstruct the Late Pleistocene megafaunal abundance changes, the timing and potential cause of extinction across the basin and investigate if extinction was associated with any signal of trait-based vegetation changes. We infer megafaunal abundance changes from the abundance of CFS and compare this with climatic proxies from the same core. We then link modern observations of fruit, seed and fire response traits of plant genera within the basin to the fossil pollen record to reconstruct palaeo vegetation community traits and determine if extinction was associated with any changes in plant community trait composition. Closely-spaced 14C dates obtained from planktonic foraminifera and δ18O tie points place a major decline in CFS, and thus the timing of extinction, within the basin at ∼43.3 ka. While climate-driven environmental changes largely controlled megafaunal presence, human arrival and frequent landscape burning are considered the most likely primary cause of extinction or, at the very least, megafauna decline in the Murray Darling Basin. We also found that the proposed period of megafaunal decline was also accompanied and followed by a decline in the prevalence of plants with larger seeds and fruits that were likely to have been once dispersed by megaherbivores. Our study supports the idea of a human-driven megafaunal extinction in mainland Australia and that the extinction caused changes in vegetation due to reduced plant dispersal and herbivory. However, high fire activity primarily linked to these vegetation changes was not observed, as humans were already practicing landscape burning before the period of megafaunal extinction and likely continued to do so afterward.

Holocene climate change in southern Oman deciphered by speleothem records and climate model simulations

Qunf Cave oxygen isotope (δ18Oc) record from southern Oman is one of the most significant of few Holocene Indian summer monsoon cave records. However, the interpretation of the Qunf δ18Oc remains in dispute. Here we provide a multi-proxy record from Qunf Cave and climate model simulations to reconstruct the Holocene local and regional hydroclimate changes. The results indicate that besides the Indian summer monsoon, the North African summer monsoon also contributes water vapor to southern Oman during the early to middle Holocene. In principle, Qunf δ18Oc values reflect integrated oxygen-isotope fractionations over a broad moisture transport swath from moisture sources to the cave site, rather than local precipitation amount alone, and thus the Qunf δ18Oc record characterizes primary changes in the Afro-Asian monsoon regime across the Holocene. In contrast, local climate proxies appear to suggest an overall slightly increased or unchanged wetness over the Holocene at the cave site.

Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate.

Earth system models and various climate proxy sources indicate global warming is unprecedented during at least the Common Era1. However, tree-ring proxies often estimate temperatures during the Medieval Climate Anomaly (950-1250CE) that are similar to, or exceed, those recorded for the past century2,3, in contrast tosimulation experiments at regional scales4. This not only calls into question the reliability of models and proxies but also contributes to uncertainty in future climate projections5. Here we show that the current climate of the Fennoscandian Peninsula is substantially warmer than that of the medieval period. This highlights the dominant role of anthropogenic forcing in climate warming even at the regional scale, thereby reconciling inconsistencies between reconstructions and model simulations. We used an annually resolved 1,170-year-long tree-ring record that relies exclusively on tracheid anatomical measurements from Pinus sylvestris trees, providing high-fidelity measurements of instrumental temperature variability during the warm season. We therefore call for the construction of more such millennia-long records to further improve our understanding and reduce uncertainties around historical and future climate change at inter-regional and eventually global scales.