Paleoclimate Reconstructions Research Articles

Reconstruction of Paleoclimate Based on Plant Leaf Fossils: Methods, Technological Advances, and Research Status

Plant leaf fossils serve as crucial "natural archives" in paleoclimate reconstruction research. This paper systematically reviews the methods, technological advances, and research status of paleoclimate reconstruction based on plant leaf fossils. Traditional research methods have evolved from Nearest Living Relative (NLR) analysis and Coexistence Approach to Leaf Margin Analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP), gradually establishing quantitative relationships between plant morphological characteristics and climate parameters. With technological advancement, research has expanded from macroscopic morphological analysis to microscopic structural studies, with stomatal density and stomatal index analysis providing new approaches for studying atmospheric CO₂ concentration changes. In recent years, the introduction of computer vision and deep learning technologies has significantly improved the efficiency and accuracy of leaf fossil analysis, driving the field toward intelligent and data-driven interdisciplinary integration. However, challenges remain, including sample scarcity, regional model applicability, and data bias. Future research will focus on multidisciplinary method integration, technological innovation, and big data analysis to further enhance the precision of paleoclimate reconstruction and deepen our understanding of climate changes throughout geological history.

Temporal Comparisons Involving Paleoclimate Data Assimilation: Challenges and Remedies

Abstract Paleoclimate reconstructions are increasingly central to climate assessments, placing recent and future variability in a broader historical context. Several estimation methods produce plumes of climate trajectories that practitioners often want to compare to other reconstruction ensembles or to deterministic trajectories produced by other means, such as global climate models. Of particular interest are “offline” data assimilation (DA) methods, which have recently been adapted to paleoclimatology. Offline DA lacks an explicit model connecting time instants, so its ensemble members are not true system trajectories. This obscures quantitative comparisons, particularly when considering the ensemble mean in isolation. We propose several resampling methods to introduce a priori constraints on temporal behavior, as well as a general notion, called plume distance, to carry out quantitative comparisons between collections of climate trajectories (“plumes”). The plume distance provides a norm in the same physical units as the variable of interest (e.g., °C for temperature) and lends itself to assessments of statistical significance. We apply these tools to four paleoclimate comparisons: 1) global mean surface temperature (GMST) in the online and offline versions of the Last Millennium Reanalysis (v2.1); 2) GMST from these two ensembles to simulations of the Paleoclimate Modelling Intercomparison Project past1000 ensemble; 3) Last Millennium Reanalysis, version 2.1 (LMRv2.1), to the PAGES 2k Consortium ensemble of GMST; and 4) the Northern Hemisphere mean surface temperature from LMRv2.1 to the Büntgen et al. ensemble. Results generally show more compatibility between these ensembles than is visually apparent. The proposed methodology is implemented in an open-source Python package, and we discuss the possible applications of the plume distance framework beyond paleoclimatology. Significance Statement Paleoclimate data assimilation is an emerging technique to reconstruct past climate variations. The currently dominant approximation, offline data assimilation, lacks the ability to connect information across time. This work proposes open-source solutions to this problem and applies them to three paleoclimate questions, before discussing broader implications.

Distribution of bacterial 3-OH-FAs in Chinese saline lakes and its implication for paleoclimate reconstruction

Distribution of bacterial 3-OH-FAs in Chinese saline lakes and its implication for paleoclimate reconstruction

A Novel Approach of Semi‐Quantifying Gypsum in Sedimentary Rocks by Visible and Near‐Infrared Diffuse Reflectance Spectroscopy

AbstractGypsum is one of the major evaporite minerals that can be used as a sensitive archive for past climate change, revealing variations in the hydrological cycle and dry‐wet climatic alternations. Measuring variations in gypsum content, rapidly and with high accuracy, will contribute to more extensive paleoclimate reconstructions. However, a fast, convenient, and non‐destructive method for quantifying gypsum in sedimentary rocks is still lacking. Diffuse reflectance spectroscopy (DRS) is a commonly employed technique for rapidly identifying and quantifying minerals; however, its application to semi‐quantifying gypsum in paleoclimate studies has received comparatively less attention. Here, we synthesized artificial and natural samples with precisely controlled gypsum content and analyzed the visible and near‐infrared DRS characteristics of the gypsum crystals. We report a linear correlation between gypsum content and the intensity of negative peaks in the DRS spectra at 1,540 nm (I1540) and 1,942 nm (I1942), converted by the second derivative of the Kubelka‐Munk (K‐M) remission functions. The robustness of this I1540/I1942‐based DRS proxy (Igyp) for semi‐quantifying gypsum in sediments was further validated against powder X‐ray diffraction results. Applying the new Igyp proxy to the Eocene gypsum sequence from the Xining Basin (China) shows a strong correlation with calibrated gypsum contents, demonstrating its potential for the identification and quantification of gypsum in sedimentary rocks. This method offers a promising new approach for gypsum analysis in paleoclimate studies.

Paleoenvironments and Paleoclimate Reconstructions of the Middle–Upper Eocene Rocks in the North–West Fayum Area (Western Desert, Egypt): Insights from Geochemical Data

This study deals with the reconstruction of the paleoenvironment and the paleoclimate situation of the middle–upper Eocene sediments in the northwest Fayum area. The reconstruction is based on comprehensive stratigraphical and geochemical analyses of major oxides and trace elements for selected sediment samples from the Gehannam Formation (Bartonian–Priabonian), the Birket Qarun and the Qasr El Sagha formations (Priabonian). The sedimentological features coupled with paleo-redox trace elemental ratios (Ni/Co, V/Cr, U/Th, V/(V + Ni), and Cu/Zn), paleosalinity (Sr/Ba, Mg/Al ×100, Ca/Al), and paleowater depth (Fe/Mn) proxies, indicate that deposition took place in a shallow marine agitated environment with high oxygen levels. Paleoclimate indicators (Sr/Cu, Rb/Sr, K2O3/Al2O3, Ga/Rb, C-value, CIA, and CIW) suggest warm and prevailing arid climatic conditions, with minor humid periods at some intervals. The observed low values of the total organic carbon (TOC) are attributed to significant high sediment influx, predominant oxygenated conditions, and poor primary productivity, which is further confirmed by low values of paleoprimary productivity proxies (P, Ni/Al, Cu/Al, P/Al and P/Ti, and Babio ratios). These findings enhance our understanding of the Eocene environments and provide insights into sedimentation processes during this period.

Paleoclimatic Events Since 25 kyr B.P. and the Regional Differences Documented by Phytoliths in the Central Songnen Plain, NE China

Identification of paleoclimate oscillation from various climate proxies across different regions is important for the mechanistic research of paleoclimate. Phytoliths from the lacustrine sediment of central NE China were extracted for paleoclimate reconstruction and abrupt event recognition. The combined phytolith assemblages; indices of Iw, Iph, D/P, Pi/P, and T/P; and the 66.4% PCA information with 95% confidence ellipse showed six global synchronously paleo-stages in the past 25,000 years: mixed coniferous broadleaf forest in a semi-humid cool climate (25,165–22,180 cal aB.P.), cold and arid steppe (22,180–18,080 cal aB.P.), semi-humid and semi-arid steppe (18,080–11,380); semi-humid cool grassland (11,380–7790 cal aB.P.), humid warm forest steppe (7790–4300 cal aB.P.), and semi-arid and cool meadow steppe (4300 cal aB.P. to the present). The global abrupt events of the 4.2-kiloyear event, 8.2-kiloyear event, Younger Dryas (YD), Heinrich1 (H1), and Heinrich2 (H2) were also captured by phytolith indices. The regional character of the reduction in humidity of the YD might have been affected by the combined influence of the Okhotsk High and the surrounding mountains. These findings not only strengthen phytolith palaeoresearch but also provide basic information for the mechanistic research of palaeoclimate in the edge area of Northeast Asia and promote global climate change research.

New probabilistic methods for quantitative climate reconstructions applied to palynological data from Lake Kinneret

Abstract. Quantitative local paleoclimate reconstructions are an important tool for gaining insights into the climate history of the Earth. The complex age–sediment–depth and proxy–climate relationships must be described in an appropriate way. Bayesian hierarchical models are a promising method for describing such structures. In this study, we present a new age–depth transformation in a Bayesian formulation by determining the uncertainty information of depths in lake sediments at a given age. This enables data-driven smoothing of past periods, which allows better interpretation. We introduce a systematic, machine-learning-based way to establish probabilistic transfer functions which connect spatial distributions of temperature and precipitation to the spatial presence of specific biomes. This includes consideration of various machine learning (ML) algorithms for solving the classification problem of biome presence and absence, taking into account uncertainties in the proxy–climate relationship. For the models and biome distributions used, a simple feedforward neural network provides the optimal choice of the classification problem. Based on this, we formulate a new Bayesian hierarchical model that generates local paleoclimate reconstructions. This is applied to plant-based proxy data from the lake sediment of Lake Kinneret (LK). Here, a priori information on the recent climate in this region and data on arboreal pollen from this lake are used as boundary conditions. To solve this model, we use Markov chain Monte Carlo (MCMC) sampling methods. During the inference process, our new method generates taxa weights and biome climate ranges. The former shows that less weight needs to be given to Olea europaea to ensure the influence of the other taxa. In contrast, the highest weights are found in Quercus calliprinos and Amaranthaceae, resulting in appropriate flexibility under the given boundary conditions. In terms of climate ranges, the posterior probability of the Mediterranean biome reveals the greatest change, with an average boreal winter (December–February) temperature of 10∘C and an annual precipitation of 700 mm for Lake Kinneret during the Holocene. The paleoclimate reconstruction for this period shows comparatively low precipitation of about 400 mm during 9–7 and 4–2 cal ka BP. The respective temperatures fluctuate much less and stay around 10 °C.

Proxy- and Model-Estimated Coupled Megadroughts in the Southwestern Regions of North and South America

Abstract The North American Southwest (NASW) and South American Southwest (SASW) are regions susceptible to prolonged and intense droughts that can span a decade or more (i.e., megadroughts). Although the drivers and impacts of megadroughts in each region and their co-occurrence have been examined in paleoclimate reconstructions, it is not known whether climate models simulate co-occurring megadroughts in these regions with characteristics and drivers that are similar to the real world. We compare the temporal characteristics of concurrent megadroughts and the Pacific Ocean conditions associated with these events in the Paleo Hydrodynamics Data Assimilation (PHYDA) product and the Community Earth System Model Last Millennium Ensemble (CESM-LME). We find that concurrent megadroughts in PHYDA and CESM-LME have similar temporal characteristics, but the relationship between hydroclimate conditions in the NASW and SASW is different between proxy-based estimates and the climate model. Further analyses reveal that changes in the tropical Pacific Ocean are weaker during concurrent megadroughts in the CESM-LME compared to those in PHYDA and that their teleconnection patterns and strengths are different. Reconstruction methodology is also found to be a factor in how the relationship between the tropical Pacific and each region is characterized. These results together indicate that while the CESM-LME simulates concurrent megadroughts with temporal characteristics similar to PHYDA, it does so for different reasons; this result leaves open the question of whether climate models used for future projections can accurately capture the risk of concurrent megadroughts in future projections.

Shifting Antarctic Circumpolar Current south of Africa over the past 1.9 million years.

The Antarctic Circumpolar Current (ACC) dominates the transfer of heat, salt, and tracers around the Southern Ocean (SO), driving the upwelling of carbon-rich deep waters around Antarctica. Paleoclimate reconstructions reveal marked variability in SO circulation; however, few records exist coupling quantitative reconstructions of ACC flow with tracers of SO upwelling spanning multiple Pleistocene glacial cycles. Here, we reconstruct near-bottom flow speed variability in the SO south of Africa, revealing systematic glacial-interglacial variations in the strength and/or proximity of ACC jets. These are superimposed by warmer-than-present "super-interglacials," whereby extreme slowdown in the midlatitude ACC (41°S) is opposed by faster flow at higher latitudes (>54°S), implying poleward strengthening of the ACC. Coupled with reconstructions of the subsurface-deep stable carbon isotope gradient, we show that the reorganization of ACC coincides with the upwelling of isotopically light deep waters around Antarctica, likely contributing to the interglacial rise in atmospheric carbon dioxide (CO2) levels.

Regional differences in millennial-scale climate variability in northeastern Tibet loess deposits spanning 34 ka to 8 ka

Paleoclimate reconstructions from East Asian loess records are often inconsistent, especially at the junction between the relatively humid East Asia and more arid Central Asia regions. We present two high-resolution paleoclimatic records spanning 34−8 ka from northeastern Tibet (based on grain size, element abundance, and magnetic susceptibility), which have been temporally constrained using optically stimulated luminescence dating. Both records, from sites <200 km apart, demonstrate a significant climate shift at ca. 15 ka. In the section located farthest south, this shift manifests as an increase in humidity. By contrast, the northernmost section shows a decreasing trend in effective humidity at ca. 15 ka. The differences between these records demonstrates how regional factors can lead to marked differences in reconstructed paleoclimate in loess records. Our work additionally reveals millennial-scale signals recorded in northeastern Tibet loess deposits, and that these signals reflect a nonlinear response of the East Asian summer monsoon to insolation and other climatic components (e.g., the North Atlantic system).

The Early Miocene Paleoclimate of Erzhilansay: Interpretation of Climatic Parameters Using Modern Methods

Studying paleoclimatic conditions across geological epochs is essential for understanding climate evolution and its influence on Earth’s biosphere. Leaf macrofossils serve as a crucial data source for reconstructing ancient climates due to their sensitivity to environmental changes. Advanced analytical methods, such as the Climate Leaf Analysis Multivariate Program (CLAMP) and the coexistence approach (CA), enable precise assessment of past climatic parameters using fossilized leaf remains. The Erzhilansay locality, dated to the early Miocene, represents a remarkable site with exceptionally preserved and diverse plant fossils, making it pivotal for paleoclimatic reconstructions. This study reveals that mean annual temperatures and summer temperatures in the early Miocene were relatively stable over millions of years. In contrast, winters were notably milder, exhibiting warmer and more consistent conditions. Precipitation levels were significantly higher, fostering the development of dense vegetation, unlike the arid environment seen today. These findings underscore the importance of employing integrated methodologies to reconstruct ancient climates and interpret geological-scale climate changes. The study also offers critical insights into climate dynamics, supporting the development of strategies to mitigate current environmental challenges.

TEMPORAL STABILITY OF CLIMATIC SIGNAL RECORDED BY STABLE CARBON ISOTOPE COMPOSITION OF TREE RINGS α-CELLULOSE—A CASE STUDY FOR SUWAŁKI REGION

ABSTRACTInvestigations of stable carbon isotope composition in α-cellulose extracted from tree rings of pines (Pinus sylvestris L.) growing in the unpolluted Suwałki region, northeastern part of Poland, are undertaken. The presented carbon isotope record covers the period of 1931–2003. Values of δ13C measured in the tree ring α-cellulose are compared to meteorological data. These δ13C values in tree ring cellulose respond to summer temperature, insolation, relative humidity, and precipitation. The best correlation is observed between relative humidity and carbon isotope data. The August relative humidity is found more influential on δ13C values than relative humidity for any other month or combination of months (r = –0.65). Relations between isotopic and meteorological data demonstrate that precipitation influences the stable carbon isotopic ratios to a lower extent than humidity. The intensity and duration of summer rainfall events can determine this effect. The temporal stability of climate-proxy connections is an important issue in paleoclimatic reconstruction. Therefore, the temporal stability of climatic signals recorded by stable carbon isotopes is analyzed in this research using the moving correlation function for moving intervals with a 25-year window. Based on those investigations the highest time stability of correlation was found for the carbon isotope and the August relative humidity. More variability is observed for the correlation of δ13C values with precipitation.

Southern Ocean and Southern African Monsoon Forcing of the Subtropical Indian Ocean Early Pliocene “Biogenic Bloom”

AbstractThe Pliocene epoch emerges as a pivotal juncture in Earth's climatic evolution, characterized by pronounced warmth and elevated atmospheric carbon dioxide compared to contemporary levels. While the broader climatic context of the Pliocene has garnered attention, there remains an outstanding gap in detailed paleoclimate reconstructions of the early Pliocene, a new potential target for data‐model intercomparison. Addressing this, we investigate the drivers of the early Pliocene “Biogenic Bloom” and implications for nutrient dynamics and climate. By analyzing high‐resolution biotic assemblage and geochemical records from the Agulhas Plateau, southwestern Indian Ocean (International Ocean Discovery Program, IODP Site U1475), we aim to elucidate the forcing and feedback mechanisms driving the early Pliocene marine ecosystems. We identify a distinct shift in coccolithophore assemblages at ∼4.6 million years ago, characterized by a notable change in dominance between the larger and smaller Reticulofenestra and high abundances of Noelaerhabdaceae < 5 µm. Our findings confirm the adaptive strategies of coccolithophore communities to prevailing environmental conditions, underscoring their evolutionary resilience by producing smaller coccoliths while increasing their abundances in a nutrient‐replete ocean. Surface water dynamics, particularly the subtropical front migration and expansion of Southern Ocean waters, in combination with the southern African monsoon variability, emerge as key drivers of phytoplankton productivity during the early Pliocene. We posit that a weakened biological carbon pump, due to increased phytoplankton production driven by intense ocean circulation and mixing during the early Pliocene, served as a potential precursor to the subsequent middle Pliocene abrupt climate extremes.

Paleoclimate reconstructions of Durankulak Lake (Northeastern Bulgaria) during the last 6000 years using pollen analysis and modern analog technique (MAT)

Paleoclimate reconstructions of Durankulak Lake (Northeastern Bulgaria) during the last 6000 years using pollen analysis and modern analog technique (MAT)

Pleistocene pedogenic carbonates from alluvial paleosols in eastern Sudan reveal a semi-arid and seasonal climate, similar to today

Pedogenic carbonates can provide important information regarding paleoclimatic conditions. Compared with East Africa, Pleistocene pedogenic carbonates in Sudan, particularly calcretes, have received very little attention, particularly with regard to local paleoclimatic reconstructions. Pleistocene alluvial sediments aged from ∼230 to <17 ka were deposited along the middle Atbara River in eastern Sudan. Intercalated in these alluvial deposits are paleosols in which different types of pedogenic carbonates occur. Petrographic, mineralogical and isotopic analyses were performed to reconstruct the regional paleoenvironmental conditions. The investigated pedogenic carbonates are appropriate for paleoclimatic reconstruction because they are free of inherited carbonate and diagenetic modification. The paleosols identified in a previous study as Aridisols/Calcisols contain calcrete horizons that consist of an orthic nodular horizon, sometimes overlain by a laminar horizon. Paleosols identified as Vertisols contain slickensides, and disorthic and septaric nodules. The paleosols show stable carbon and oxygen isotope values ranging between −9.12 and −5.12 ‰, and between −7.25 and −4.09 ‰, respectively. Supporting the previous study, the inferred climatic conditions were arid to semi‐arid, with a mixture of C3 and C4 vegetation cover, and paleoprecipitation greater than 350 mm/yr, similar to that of the present-day, with likely higher rainfall during the formation of Vertisols than Aridisols/Calcisols. The thickness and morphology of Pleistocene calcretes in eastern Sudan are similar to those in East Africa, suggesting similar climatic conditions during their formation. Well-and weakly-developed calcretes in Aridisols formed in distal and proximal floodplains, respectively, whereas well-developed vertic horizon in Vertisols formed in distal floodplains.

Lithogeochemistry of Upper Precambrian terrigenous rocks of Belarus. Communication 2. Provenance, paleogeodynamics, paleogeography, paleoclimate

This publication completes the consideration of the lithogeochemical features study of a pilot collection of the Riphean and the Vendian sandstones, siltstones and mudstones (last one identified based on the interpretation results) of the Belarus. Data on the age of detrital zircon published in recent years suggest that the source rocks for the Upper Precambrian deposits of this region were the Osnitsk-Mikashevichi and the Trans-Scandinavian igneous belts, the Volyn-Brest large igneous province, rapakivi granites, as well as various associations of rocks of Sarmatia, the Danopolonian orogen and Svecofennides. The distribution of clastic rocks data points of our collection on provenance, paleogeodynamic, paleogeographic and paleoclimatic discriminant diagrams, which based mainly on the lithogeochemical composition, allows us to draw a number of conclusions. We are considering that the Riphean and the Vendian strata of the Belarus are composed mainly of intraplate granitoids erosion products, as well as various felsic igneous rocks of island-arc and syncollisional genesis. The part of mafic rocks erosion products among them generally does not exceed 30%. It`s noticeable mainly in rocks of the Volyn series (products of the Volyn-Brest large igneous province erosion), as well as in some samples of the Nizov, Selyavy and Kotlin formations (fragments of mafic rocks from other sources?). Source to sink transporting was carried out mainly by large rivers. Paleogeodynamic settings varied from quite active to quite passive. The paleoclimate in the Riphean was most likely arid/semiarid, and in the Vendian it was humid, from subtropical in the early (except for the Glussk Formation) to tropical in the Late Vendian. The research results also make it possible to show some work features for known paleoclimate reconstruction methods and techniques.

The effect of burning on the dissolution behaviour and silicon and oxygen isotope composition of phytolith silica

The δ30Si and δ18O values of opal-A precipitated in plants (silica phytoliths) have been shown to be useful for paleoenvironmental reconstructions. Here, the effects of burning and partial dissolution of phytoliths on their isotopic compositions and dissolution behaviour were examined. Phytoliths were heated to 700 °C and then dissolution experiments were conducted in batch reactors under a range of pH (4–8) and temperature (4–19 °C) conditions. Heating caused a −2.6 ‰ shift in phytolith δ18O values. NMR results suggest that heating reduces the number of surface vicinal silanols, which likely results in the formation of strained SiOSi bonds which incorporate oxygen from 18O-depleted hydroxyl groups. During dissolution, the δ18O of burned phytoliths increased by up to 3.5 ‰ (average 1.8 ‰) until 15–45 % saturation was reached, and then adsorption of silica on the surface of the solid began to reduce the δ18O value of solid silica despite a net dissolution. The maximum increase in δ18O during dissolution of burned phytoliths is 1.8 ‰ smaller than previously observed for unburned silica subjected to partial dissolution under the same conditions. Heating did not cause a significant change in δ30Si values, and partial dissolution of burned phytoliths caused a slight increase in δ30Si values that was smaller in magnitude than for unburned phytoliths. Dissolution of burned phytoliths progressed more slowly than dissolution of fresh phytoliths in low pH and temperature conditions, but was faster than the dissolution of fresh phytoliths when pH > 6 and temperature = 19 °C. We propose that because fewer hydrolysis sites exist on the surface of burned phytoliths that the isolated silanols that remain after heating are difficult to deprotonate at low pH resulting in slower dissolution. However, at higher pH the breakage of strained SiOSi bonds in burned phytoliths may explain their higher dissolution rate relative to fresh phytoliths. We recommend caution in using the δ18O values of soil phytoliths in paleoclimate reconstructions as they can be altered during both heating and partial dissolution. For phytolith assemblages collected from archaeological hearths or grasslands prone to wildfires, the shift towards lower δ18O values caused by heating would result in overestimations of temperature using paleothermometer equations. Care must be taken to identify alteration by dissolution or burning, which may not always be visually evident.

High temporal resolution paleoclimate reconstruction by the analysis of growth patterns and stable isotopes of fossil shells of the long-lived bivalve Mercenaria stimpsoni from MIS 5e, 7 and 9

Paleoenvironments during past interglacial periods such as Marine Isotope Stages (MISs) 5e, 7 and 9 have been studied as possible analogues for current global warming. In central Japan, interglacial oceanic sediments of the Shimosa Group were deposited in the Paleo-Tokyo Bay between MIS 11 and MIS 5 when sea level was high. However, due to the scarcity of biogenic archives that recorded paleoenvironments over long intervals of time with high temporal resolution, seasonal variation of past seawater temperature in the bay during the Pleistocene warm periods remains unclear. Shells of the long-lived bivalve, Mercenaria stimpsoni (Stimpson's hard clam) can potentially provide such data from mid- to high-latitude northwestern Pacific coastal regions. Here we used growth patterns and oxygen isotope values of fossil shells of M. stimpsoni from the Shimosa Group to reconstruct the seasonal variation in seawater temperature of Paleo-Tokyo Bay during MIS 5e, 7, and 9 based on sclerochronological analysis.Our study demonstrates that fossil shells of this species lived over 100 years and grew most rapidly during the first ten years of life. During each studied interglacial, the highest seawater temperatures equaled approx. 20 °C, i.e., much lower than today in coastal regions of Chiba Prefecture (approx. 27 °C). Our results suggest that during interglacial periods when the sea level was high, cold-water masses of the Oyashio Current reached the Paleo-Tokyo Bay. The habitat of cold-water species including M. stimpsoni thus expanded southward following the distribution of this cold-water mass. Such climatic conditions likely lasted at least for 100 years, i.e., during the lifespan of this species.

Subsistence strategies and climate change as key factors in the vicinity of the Great Wall in northern China from 500 BCE

Whether, and in what ways, the association between changes in climate and the shifting of imperial frontiers (i.e. the Great Wall) could be mediated by the social responses of major ethnic groups is a question that remains unanswered. Ulanqab is a region in Inner Mongolia associated with a long history of Great Wall construction from the Warring States to the Ming dynasties (~500 BCE–1644 CE) and the Great Wall is often regarded as the boundary of the Central Plains dynasty. This paper uses Ulanqab as a case study to investigate the historical inter-relationship between changes in climate and subsistence strategies on the one hand, and the positioning of the Great Wall on the other. We determined the precise geographical coordinates of the Great Wall in this region during each dynastic period of Chinese history, and compared its location to (1) the empire’s boundaries in each dynasty, (2) evidence that is available on climate change from high-resolution paleo-climate reconstructions and (3) subsistence strategies (whether agriculture, pastoralism, or nomadism) that people adopted as recorded in historical documents. Geo-referenced information from associated archaeological sites was also used to determine the extent of habitation in different areas. We found that during the period of agriculturalist empires (the Han and Ming dynasties), the Great Wall was a frontier between farming and animal husbandry, and was located to the south of the Daqing Mountains. In contrast, during the period of pastoralist empires (the Zhao Kingdom [of the Warring States], Northern Wei and Jurched Jin periods), the Great Wall was the frontier between animal husbandry and nomadism, and was located to the north of the Daqing Mountains. These mountains (42.5°N) seem to have been the northern limit of human settlements that were based on animal husbandry and farming. We observed that, when precipitation and temperature increased, this resulted in an augmentation of agricultural production that most likely facilitated the northward expansion of the agriculturalist peoples. A decrease in precipitation, on the other hand, resulted in the shrinkage of pastures and food, triggering a southward expansion that was characteristic of the pastoralist peoples. This study attempts to provide new insights into the interrelationships among changes in climate, human societies and geopolitics in Chinese history.

Where did they come from, where did they go? Niche conservatism in woody and herbaceous plants and implications for plant-based paleoclimatic reconstructions.

The ecological conditions that constrain plants to an environmental niche are assumed to be constant through time. While the fossil record has been used previously to test for niche conservatism of woody flowering plants, additional studies are needed in other plant groups especially since they can provide insight with paleoclimatic reconstructions, high biodiversity in modern terrestrial ecosystems, and significant contributions to agriculture. We tested climatic niche conservatism across time by characterizing the climatic niches of living herbaceous ginger plants (Zingiberaceae) and woody dawn redwood (Metasequoia) against paleoniches reconstructed based on fossil distribution data and paleoclimatic models. Despite few fossil Zingiberaceae occurrences in the latitudinal tropics, unlike living Zingiberaceae, extinct Zingiberaceae likely experienced paratropical conditions in the higher latitudes, especially in the Cretaceous and Paleogene. The living and fossil distributions of Metasequoia largely remain in the upper latitudes of the northern hemisphere. The Zingiberaceae shifted from an initial subtropical climatic paleoniche in the Cretaceous, toward a temperate regime in the late Cenozoic; Metasequoia occupied a more consistent climatic niche over the same time intervals. Because of the inconsistent climatic niches of Zingiberaceae over geologic time, we are less confident of using them for taxonomic-based paleoclimatic reconstruction methods like nearest living relative, which assume a consistent climatic niche between extant and extinct relatives; we argue that the consistent climatic niche of Metasequoia is more appropriate for these reconstructions. Niche conservatism cannot be assumed between extant and extinct plants and should be tested further in groups used for paleoclimatic reconstructions.