Palaeoclimate Reconstructions Research Articles

The Current Phyto-Scape and Foodplants of Holley Shelter, KwaZulu-Natal (South Africa) and Its Potential for Past Foragers

AbstractCurrent phyto-scapes (plant populations in their geo-spatial context) are not exact replicas of past foraging potential, yet they provide valuable data about the carrying capacity or potential of a foraging-scape. Knowledge about contemporary micro-ecologies and ethno-historical plant use can inform on behavioral aspects, should such plants be found in archaeological deposits. It is in this context that we explore existing information (data and literature) to establish the current vegetation types and micro-ecologies around Holley Shelter, KwaZulu-Natal, South Africa, that contains Middle and Later Stone Age occupations. We present the first plant species inventory consisting of > 1500 taxa growing approximately a day’s foraging distance from the site, compiled from records provided by the South African National Biodiversity Institute and other sources. From this list, we generated separate checklists for foodplants (n = 450) and plants that have other uses (n = 337), to gain insight into the site’s current phyto-fitness potential. The resulting database is intended as a modern proxy for future work on the site’s archaeo-botany and palaeo-climatic reconstructions. The data is also applicable to other sites on the Savanna/Grassland Biomes of southern Africa with records of the same species. Here we use the foodplant checklist and what is known about the edible plant parts, their seasonality and the distribution of some species to speculate about land-use patterns. These hypotheses can be tested for the past with future archaeo-botanical work. We demonstrate that, compared to archaeological sites in the Eastern and Western Cape for which comparable data exist, Holley Shelter is rich in foodplants, and especially so in plant foods that are known to buffer against famine during the periodical droughts of inland South Africa.

The ostracod distribution in the Sea of Galilee (Levant): species distribution and post-mortem dispersal of valves and carapaces

The Sea of Galilee is a unique large freshwater or slightly oligohaline natural lake in the Levant. Therefore, it represents an important aquatic habitat in the region that also provides invaluable ecosystem services for the local communities. To improve our knowledge of the lake’s ecosystem and the use of disarticulated ostracod valves and preserved carapaces, micro-crustacean remains commonly used in palaeolimnology and palaeoceanography, as proxies for palaeoenvironmental reconstructions, and to examine the post-mortem dispersal of ostracod remains, 68 surface-sediment samples were collected from the lake bottom in 2012 and analysed for the ostracod assemblages. Both, the noded and smooth, forms of Cyprideis torosa dominate in the Sea of Galilee, with the former more abundant than the latter. Relatively abundant and found at half of the 68 sampling locations or more, are also Ilyocypris hartmanni, I. cf. nitida, Darwinula stevensoni and Neglecandona angulata. In addition, ten less abundant ostracod taxa were recorded in the lake. Of all 15 taxa recorded in our study, ten were also recorded in a study of the Sea of Galilee’s ostracod fauna conducted already in the 1960s. The newly recorded five taxa are relatively rare, and they were mostly found in the region of the Jordan River delta or near the southeastern shore of the lake which were not included in the survey of the 1960s. Thus, there is no evidence for a significant change in the ostracod fauna of the lake over the last half-century. In comparison to the ostracod assemblage from a late Pleistocene archaeological excavation site at the southwestern margin of the lake, the assemblage from the recent survey is slightly less diverse, probably because of the long duration of ca. 5000 years integrated by the sedimentary section of the archaeological site and also due to nearby freshwater inflows from which valves and carapaces were probably washed to the site’s location. Our study also shows that ostracod valves and carapaces are typically relatively abundant in most of the surface-sediment samples collected from locations at 18 m or shallower. In contrast, very few valves and carapaces were recorded at depths greater than 18 m, which is a zone affected by seasonal anoxia in the Sea of Galilee. These few ostracod remains were apparently transported by currents and waves to the central, deeper part of the lake, but their low number shows that such post-mortem dispersal of ostracod remains is insignificant in the deeper part of the lake. Thus, our study provides support for palaeoenvironmental and palaeoclimate reconstructions based on ostracod records from single sediment cores obtained from depths unaffected by post-mortem transport and seasonal or permanent anoxia.

Maastrichtian palaeoenvironments and palaeoclimate reconstruction in southern South America (Patagonia, Argentina) based on fossil fungi and algae using open data resources

ABSTRACT The use of non-pollen palynomorphs (NPP), particularly fossil fungi and algae, as palaeobiological proxies for Late Cretaceous palaeoenvironmental and palaeoclimatic reconstructions of warm-to-hot greenhouse conditions, can enhance our understanding of climate change impacts on modern Patagonian environments. This study aimed to reconstruct the Maastrichtian palaeoenvironment and palaeoclimate in the Cañadón Asfalto Basin (CAB, Chubut Province) by testing these NPPs as proxies using the Nearest Living Relative method (NLR). Moreover, using modern ecological requirements from open-source databases, such as GBIF and processing it with an open-source, cross-platform tool like QGIS, linked with Köppen-Geiger shapefiles, provided evidence of climate-driven palaeo-distribution patterns of fungal and algal diversity at CAB. Applying modern ecological requirements and biogeographic distribution data, we reconstructed the palaeoclimate as temperate with evenly distributed precipitation and warm summers, corresponding to the Cfb climate zone in Köppen-Geiger classifications. Additionally, our methodology produced reliable results regarding Cenozoic floras’ physiognomies based on fossil fungi, revealing a transition from sparsely wooded areas with palms and prairies to complex forest ecosystems with palms, deciduous trees, and shrubland. Furthermore, testing Cretaceous algae with the NLR method, for the first time, provided comprehensive insights into past water body characteristics, including trophic state and water quality.

The Stability of Manganese Oxides Under Laser Irradiation During Raman Analyses: I. Compact Versus Channel Structures

ABSTRACTManganese oxides/oxyhydroxides (MnOx) are based on Mnn+O6 and Mnn+O4 polyhedra arranged such as to form compact, channel or layered structures. In geology, they are precious archives of past redox conditions for palaeoclimatic reconstructions; in material sciences, they are used for a variety of applications, from pigments to environmental remediation and energy storage. Thus, the fast, remote and non‐destructive identification of MnOx is critical in several disciplines. Micro‐Raman spectroscopy is often used for this purpose, although a systematic characterization of their stability under the laser beam is still lacking. In this work, we present our results on the behaviour of the most common MnOx having compact and channel structures when a 532‐nm laser with intensity between ~23 μW/μm2 and ~36.8 mW/μm2 is used. The compact structures of manganosite (NaCl‐like) and hausmannite (spinel‐like) are stable up to ~36.8 mW/μm2. The stability of oxides with channel structures depends on channel size, charge of channel cations and valence state of Mn. Hausmannite is the final degradation product of all MnOx with channel structures, irrespective of the starting phase. Pyrolusite, manganite, hollandite and romanéchite are relatively stable under the laser beam, and the transition to the spinel structure occurs above 2.5 mW/μm2 while the degradation of cryptomelane and todorokite starts ~226 μW/μm2. The analysis of MnOx thus needs very accurate experimental conditions to avoid misleading and incorrect phase identifications. Based on our data, we propose an analytical protocol for a proper characterization of these minerals via Raman spectroscopy.

Tsuga leaves from the Neogene Baoshan Basin in southwest China and their palaeoecological implications

Tsuga (Endl.) Carrière (Pinaceae) has a rich fossil record represented by pollen, leaves, wood and seed cones. Although fossil leaves of the genus have been widely documented, most of them have not been examined microscopically, which may limit their taxonomic resolution. In this study, three-dimensionally preserved leaves and leaf fragments of Tsuga from the Neogene (latest Miocene to Pliocene) Baoshan Basin in western Yunnan, southwest China, were examined both morphologically and micromorphologically. The fossil leaves are characterized by flattened and bifacial shape, round to obtuse apex and petiolate base, adaxially sunken and abaxially elevated midvein, adaxial surface without stomata and with elongated, smooth-margined epidermal cells, and abaxial surface with two stomatal bands along the midvein, each stomatal band consisting of 6–8 longitudinal stomatal lines. Based on comparisons with extant species of the genus, we found that the fossil leaves show the closest affinity to Tsuga dumosa (D. Don) Eichler, an extant species growing in the modern western Yunnan. As modern species of Tsuga prefer humid conditions, our fossil find suggests a humid climate in the Baoshan Basin at the time of fossil deposition, probably due to the influence of the Indian summer monsoon from the southwest. This is consistent with previous results of quantitative palaeoclimate reconstructions using spore/pollen fossil assemblages. Our study provides new fossil evidence for the origin of modern conifer diversity in southwest China. It highlights the importance of microscopic studies in the taxonomic resolution of fossil leaves of Pinaceae.

Quantification of Middle to Late Holocene precipitation in the Gonghe Basin, northeastern Qinghai-Tibetan Plateau, from the geochemistry of aeolian surface soil

The Northeastern Qinghai-Tibetan Plateau (QTP) is situated in the climatically sensitive intersection of the Asian summer and winter monsoons and the westerlies. However, due to the lack of a well-defined relationship between aeolian deposits and climatic factors in this region, there are few quantitative palaeoclimate reconstructions from these deposits. This deficiency prevents a comprehensive understanding of the precipitation history of the alpine and arid/semi-arid intermontane basins in this region, although the regional landscape is dominated by deserts/dunefields. We studied the relationship between two geochemical indices, C (the ratio of (Fe + Al + Mn + Cr + Co + Ni) to (Ca + Mg + Na + K + Sr + Ba)) and Re (the ratio of (CaO + MgO + K2O + Na2O) to (Fe2O3+MnO2)) of the aeolian topsoils and potential modern climatic variables across the Gonghe Basin in the northeastern QTP. We found that the mean annual precipitation (MAP) is the dominant climatic control of the variations of C and Re in the surface aeolian deposits, accounting for 70.9% and 53.1% of the total explained variances, respectively. Accordingly, we established two climofunctions based on C and Re to quantitatively reconstruct the MAP evolution during the Middle–Late Holocene, from the alternating aeolian sand-palaeosol sequences in the Gonghe Basin. The results revealed five intervals of enhanced MAP, with similar results obtained from the two sections, which document millennial–centennial-scale climatic fluctuations during the Middle–Late Holocene. These fluctuations are consistent with climate records from tree rings and lake sediments in this region, within the dating errors. This consistency supports the reliability of our methodology of quantitative reconstruction based on geochemical climofunctions for aeolian deposits. Our findings demonstrate a robust approach for the quantitative reconstruction of palaeo-precipitation using geochemical parameters from aeolian topsoils in an alpine and arid/semi-arid intermontane basin, and they provide new evidence for understanding significant Holocene environmental events recorded in different geological archives within the transitional region of the monsoon and the westerlies.

Pollen atlas and morphological analysis of the selected types from southeastern Tibet, China

The accuracy of fossil pollen identification is crucial for understanding past plant diversity, vegetation landscape and associated climate change, while dispersed/fossil pollen assignments heavily rely on how robust modern pollen reference is. There is high species richness in southeastern Tibet, China, however, pollen morphological studies in this area are still poorly documented. Here, we present pollen atlas of 57 species (40 genera, 22 families) collected from the Ranwu Lake Basin. Pollen grains were imaged with light microscope (LM, 100X oil-immersion objective lens) and scanning electron microscope (SEM). All pollen types are ordered and presented according to different aperture types and sculpture patterns, facilitating comparison with fossil pollen. Moreover, we selected some representative species mainly based on potential palaeoecological importance, including Sibiraea (Rosaceae), Koenigia cathayana (Polygonaceae), Stellera chamaejasme (Thymelaeaceae), Hordeum vulgare subsp. vulgare and Poa annua (Poaceae), to discuss their pollen identification characteristics for the first time and assess potential applications in Quaternary palaeoecological interpretation. This study enriches modern pollen atlas for Quaternary pollen analysis in the study area and the adjacent regions. Our results provide robust modern reference in pollen-based reconstruction of vegetation history, palaeoclimate and palaeoenvironment, and tracing pollen signal of local human activities as well.

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.

Disease, climate, environment and the fortunes of Buddhism during the Tibetan Empire 618–842 CE

The official adoption of Buddhism by the Tibetan state in the mid-8th Century (761-762 CE) was relatively late compared to its permeation from northern India to elsewhere in south and east Asia, due to the country’s geographical isolation. Whilst reasons for its adoption remain uncertain, it is thought that the religion provided a strong unifying influence permitting both the consolidation and subsequent expansion of the Tibetan Empire. Early historical records suggest that the religion was prohibited in 739-741 CE and again in 841-842 CE, the latter coinciding with the fall of the Tibetan Empire. This research presents a detailed examination of Tibetan and Chinese historical records and also of recent fine-resolution palaeoclimatic reconstructions to demonstrate that the ‘oscillating fate’ of Buddhism during the Tibetan Empire (618-842 CE), was not only linked to the economic fortunes of the Tibetan state as previously envisaged, but also inextricably to disease, the long-term regional climatic deterioration and possibly also to a series of natural disasters, many of which were recorded in the north and north-west of the Tang Empire adjacent to Tibet, as well as in Tibet itself. These ‘disasters’ noted in the historic records, and both catalogued and quantified here, indicate extreme pressures placed on the rural economy of the Tibetan Plateau and adjoining areas by crop failures, the death of many livestock and associated widespread famine and human mortality. The ‘chaos & disorder’ of the latter stages of the reign of Emperor Ralpachen (815-836/838 CE), as well as the Second Prohibition of Buddhism by the last Tibetan Emperor Lang Darma can therefore now not only be related to climatic-environmental deterioration, but also to the likely loss of public faith in both Tibetan Emperors and in Buddhism. It is possible that in the eyes of superstitious Tibetans, neither their rulers nor the state religion could address an accelerating spiral of crises. Devine displeasure could have been further signified by a devastating earthquake in Tibet sometime between 839-842 CE and the subsequent ‘implosion’ of the Tibetan Empire should no longer be considered surprising.

Fire-induced shifts in stalagmite organic matter mapped using Synchrotron infrared microspectroscopy

Understanding organic matter (OM) in cave mineral deposits (speleothems) is essential for interpreting land use and climatic changes, and the incorporation of trace elements associated with organic compounds. However, the sources and composition of OM in speleothems are poorly understood due to challenges associated with measuring OM at low concentrations and the destructive nature of most speleothem OM analysis techniques. Synchrotron Fourier-transform infrared (FTIR) microspectroscopy is a promising non-destructive technique that can be used to investigate stalagmite OM composition. We use FTIR to analyse vegetation, soil, calcium carbonate and ash end-members and demonstrate the use of Synchrotron infrared microspectroscopy (IRM) mapping to detect temporal changes in the OM composition of a stalagmite from a shallow cave in south-west Western Australia. Our analysis reveals predominant FTIR peaks in the stalagmite linked to amides and CH2 groups, suggesting potential microbial contributions, with smaller proportions of aromatic, CH3 and CO groups. High-resolution transmission electron microscopy revealed that this OM is likely hosted in sets of nanopores spaced hundreds of nanometers apart, aligned along calcite crystallographic orientations. Furthermore, we assess the impact of known wildfire events as discrete short term environmental changes on the stalagmite’s OM composition. The temporal variability in OM functional group composition after fires implies complex fire-soil-vegetation-microbial interactions. This research demonstrates the effectiveness of Synchrotron IRM mapping in providing insights into the short and long-term environmental influences on stalagmite OM composition. Expanding this research to other regions and climates could further enhance the interpretation of OM changes in speleothem-based palaeoclimate reconstructions.

Hydrological Regime of Rivers in the Periglacial Zone of the East European Plain in the Late MIS 2

At the end of the Pleniglacial and the first half of the Late Glacial period, approximately between 18 and 14 ka BP, rivers of the central and southern parts of the East European Plain had channels up to 10 times as large as the present day channels of the same rivers. These ancient channels, called large meandering palaeochannels, are widespread in river floodplains and low terraces. The hydrological regime of these large rivers is of great interest in terms of the palaeoclimatology of the late Marine Isotope Stage 2 (MIS 2). In this study, we aimed at quantitative estimation of maximum flood discharges of rivers in the Dnepr, Don and Volga basins in the late MIS 2. To approach this, we used massive measurements of the morphometric characteristics of large palaeochannels on topographic maps and remote sensing data—palaeochannel width, meander wavelength and their relationships with river flow parameters. The runoff depth of the maximum flood, which corresponds to the maximum depth of daily snow thaw during the snowmelt period, was obtained for unit basins with an area of <1000 km2. The mean value for the southern megaslope of the East European Plain was 44.2 mm/day (6 times the modern value), with 46 mm/day for the Volga River (5.5 times), 45 mm/day (6.3 times) for the Don River and 39 mm/day (8 times the modern value) for the Dnepr River basins. In general, the Dnepr basin was drier than the Don and Volga basins, which corresponds well to the modern distribution of humidity. At the same time, the westernmost part of the Dnepr River basin was relatively wet in the past, and the decrease in humidity from the past to the modern situation was greater there than in the eastern and central regions. The obtained results contradict the prevailing ideas, based mainly on climatic modeling and palynological data, that the climate of Europe was cold and dry during MIS 2. The reason is that palaeoclimatic reconstructions were made predominantly for the LGM epoch (23–20 ka BP). On the East European Plain, the interval 18–14 ka BP is rather poorly studied. Our results of paleoclimatological and palaeohydrological reconstructions showed that the Late Pleniglacial and the first half of the Late Glacial period was characterized by a dramatic increase in precipitation and river discharge relative to the present day.

Middle-Late Holocene climate change in an East Asian sandy land: Perspectives from the phytolith record of different geomorphic units

The accuracy of the regional palaeoclimate reconstruction is vital for ecological restoration and future climate predictions. Clarifying the regional climate signal on different geomorphological units within the same region plays a key role in regional climate researches. Here, we select the Horqin Sandy Land as the research area, and collect sedimentary from two typical geomorphological units (interdune lowlands: ML profile, DBS profile; dunes: CS profile, FX profile) as the research objects. The regional averaging method is employed to isolate distinct climate signals originating from interdune lowlands (IC-Score (Peat)) and dunes (IC-Score (Dune)), alongside an amalgamated climate signal (IC-Score (Peat&Dune)) synthesized from these two geomorphological units. This methodological approach facilitates the identification of variations in climate signals that collectively encapsulate the broader regional context. Meanwhile, local microclimate signals from dunes (IC-D-Value (Dune)) and interdune lowlands (IC-D-Value (Peat)) were separately analyzed to examine microclimate changes on different geomorphological units. The results indicate that different sedimentary carriers on various geomorphological units capture the local climate characteristics of their own units while recording regional climate changes. IC-D-Value (Peat) reflects ‘warm-humid’ climate, and IC-D-Value (Dune) represents ‘cold-dry’ climate. Climate signals derived from diverse geomorphological units exhibit the capacity to portray overarching regional climate patterns, yet they manifest variations concerning both semi-quantitative and quantitative climate parameters, notably temperature and precipitation. A regional average method is used to synthesize climate signals from different geomorphological units, which is more advantageous in documenting regional climate change. Regional climate signal reveals a change from warm-humid (9300 ∼ 4000 cal yr BP) to cold-dry (4000 ∼ 2000 cal yr BP) and then to slightly warm-humid (2000 ∼ 560 cal yr BP). Furthermore, regional climate signal shows the significant ∼ 2000-yr，∼1000-yr, ∼500-yr periodicities since 7300 cal yr BP, and solar activities are identified as one of the important driving factors.

Palaeolake Jeinimeni and ice-marginal geomorphology of the central Patagonian Lago General Carrera/Buenos Aires ice-lobe (46.5°S)

Robust geomorphological interpretations of ice-marginal glacial, meltwater and palaeolake landforms are needed to constrain models of landform evolution that can be used to underpin high-resolution geochronologies of deglaciation. The Lago General Carrera/Bueno Aires (LGCBA) ice lobe of the former Patagonian Ice Sheet is one of the most researched in Patagonia, yet there remain contrasting landform evolution models partly because the spatiotemporal relationships between landforms in the LGCBA basin and tributary valleys have not been fully investigated. To this end we present a detailed, high-resolution glacial geomorphological map of the Los Antiguos sector of the LGCBA basin, and the tributary Río Jeinimeni valley, alongside sediment-landform assemblages from a broad suite of ice-marginal, subglacial, glaciolacustrine, glaciofluvial and paraglacial landforms. We introduce evidence for a previously unmapped ice-dammed lake within the Jeinimeni valley, which may have existed during the Last Glacial Maximum. Multiple isolated, ice-marginal proglacial lakes, which formed during the recession of the LGCBA ice lobe, were also mapped. The landform evidence is synthesised into a refined landscape evolution model for the LGCBA basin and Jeinimeni valley during the Last Glacial Interglacial Transition. The data presented demonstrate that previously reconstructed high LGCBA lake-level stands above 500 m asl were likely glaciolacustrine landforms created by ice-marginal lakes dammed by the LGCBA ice lobe. The mapping in the Jeinimeni valley highlights the potential for renewed dating investigations of landforms in tributary valleys to provide maximum limiting ages for the retreat of their associated glaciers. Furthermore, the identification of glaciolacustrine varved sediments associated with palaeolake Jeinimeni and the Los Antiguos sector of the LGCBA palaeolake, highlights the potential of these annually-resolved archives to infer spatiotemporal dynamics of main ice-lobe/tributary glaciers to improve palaeoenvironmental and palaeoclimatic reconstructions in the region.

Multiproxy studies on the spatially distinct surface samples to reconstruct palaeoecology and palaeoclimate from the Core Monsoon Zone of India

Palaeoclimatic reconstructions necessitate an understanding of the various biotic and abiotic responses to develop a modern analogue. The interpretation and calibration of the modern data allow us to check the lead-lag effect in different proxy parameters, which could be applied for robust palaeoclimatic reconstructions. We, in the present study, analysed pollen and diatom (biotic proxies), as well as grain size, magnetic susceptibility and geochemistry (abiotic components) of the modern soil samples, collected from the states of Madhya Pradesh and Chhattisgarh, the Core of the Monsoon Zone (CMZ) in central India. The weathered materials of the Palaeocene Cretaceous extrusive rocks and sedimentary rocks of the Late Triassic to the Upper Carboniferous are underlying the soil cover in these areas, respectively. The study revealed that the overall pollen and diatom preservation is comparatively good in the areas where the Palaeocene Cretaceous extrusive rocks are found except for the areas of human settlements, whereas the preservation of pollen and diatom was comparatively poor in areas where sedimentary rocks of the Late Triassic to Upper Carboniferous are found. The most plausible reason for this difference is the availability of nutrients which are supplied more abundantly by the easily weatherable Deccan basalt rocks compared to their sedimentary counterparts. The present study will serve as baseline information about biotic-abiotic interactions operating in the central Indian Core Monsoon Zone (CMZ). Since the intensity and duration of the rainfall in the CMZ are largely governed by the annual Indian summer monsoon rainfall (AISMR), therefore, the present study could help trace the weak or intense monsoon periods (break and active spells, respectively) of the past hundreds to thousands of years by studying the sediment profiles/cores.

Diatom-based indications of an environmental regime shift and droughts associated with seasonal monsoons during the Holocene in Biển Hồ maar lake, the Central Highlands, Vietnam

The interactions of the different monsoon systems across Southeast Asia create extreme climate phenomena. Central Vietnam, located near the centre of this transitional region, has encountered numerous effects. As a result, its sediments from lakes or speleothems are valuable archives for interpreting past climate variability. However, there is still a lack of high-resolution paleoenvironmental and palaeoclimatic reconstructions during the Holocene in Vietnam. Our study presents a paleoenvironmental diatom-based record of sediment cores collected from Biển Hồ maar lake (14°03′N, 108°00′E) in the Central Highlands of Vietnam covering nearly the entire Holocene. Based on changes in diatom assemblages in the sediment sequence, we identified two periods of the Early Holocene (~11,700–7800 cal BP) and the Mid- to Late-Holocene (~7800–360 cal BP), which mark a remarkable shift in the environment around Biển Hồ. Alternations of key diatom species during the Early Holocene indicate intensity variations between water-mixing and thermal stratification mechanisms in meso-eutrophic conditions. During the Mid- to Late-Holocene, the complete dominance of Aulacoseira granulata var. granulata implies year-round destratification and intense mixing of the lake water column in a permanently eutrophic environment. Its morphological variability reveals intervals of dry environmental conditions driven by pronounced droughts across the Asian continent.

Forest or grassland? Late Pliocene vegetation and climate of the Yushe Basin, Northern China

The Pliocene warm period is regarded as an analogue of future warming, and quantitative reconstruction of palaeovegetation and palaeoclimate during this period is helpful for predicting vegetation and climate changes in the future. Here, we quantitatively reconstructed the late Pliocene vegetation and climate based on phytolith assemblages from the Upper Zhangcun Formation in the Yushe Basin, Northern China. The results show that the vegetation was dominated by grasses with few trees, which conflicts with the pollen assemblage results. The possible reason for this contradiction is that phytoliths tend to mirror local, shoreline vegetation (grasses with few aquatic plants), while pollen tend to mirror both local and regional vegetation (trees in surrounding mountains and piedmont, grasses on lakeshores and aquatic plants in wetlands) in a small structurally confined lake. The phytolith-based quantitative reconstruction of mean annual precipitation (812–1673 mm) and warm season precipitation (417–1197 mm) provides values that are higher than those at present, revealing an increase in Asian monsoon rainfall during the late Pliocene, which is consistent with the pollen results, although the reconstructed vegetation is different. This study highlights the usefulness of phytoliths in reconstructing Cenozoic vegetation and climate and underlines the importance of landforms in determining phytolith and pollen assemblages in sediments.

A New Perspective on the Applicability of Diffuse Reflectance Spectroscopy for Determining the Hematite Content of Fe-Rich Soils in the Tropical Margins of China

Hematite and goethite are widely occurring chromogenic iron oxides in soils and sediments that are sensitive to climatic dry/wet shifts. However, only by accurately quantifying the content or ratio of hematite and goethite can they be applied reliably to palaeoclimate reconstruction. Compared to the Loess Plateau of China, hematite in the soils of southern China has not been sufficiently studied. We used diffuse reflectance spectroscopy (abbreviation DRS, including the first-derivative curves and the second-derivative curves of the Kubelka–Munk remission functions), combined with ignition at 950 °C, and X-ray fluorescence (XRF) to quantify the hematite content of four tropical-margin iron-rich soil profiles with different matrix compositions in the Leizhou Peninsula, China. We also examined the application of hematite quantification parameters in soils with different matrix compositions under the same climatic conditions. Our main findings are as follows: (i) DRS first-derivative curves can reflect the presence of goethite and hematite in soils, and their relative contents can be compared within the same profile. (ii) The second-derivative curve of the Kubelka–Munk remission functions can reflect the relative proportions of goethite and hematite and provide information about the degree of Al substitution. (iii) Combined with calibration equations, soil redness can reliably quantify the hematite content, but it is necessary to consider the effect of mucilage envelopes in the process of hematite formation. Additionally, we summarize various methods used for quantifying hematite, and the influence of soil matrix compositions, with the aim of providing a reference for hematite quantification elsewhere. We also propose a new indicator (ΔHmRed/HmRed) to help detect iron hydroxide/iron oxide changes in soils.

Talus rock glaciers in the Cairngorm Mountains

ABSTRACT Although several relict talus rock glaciers (TRGs) of Lateglacial age have been identified in the British Isles, all have been refuted by some authors and their absence attributed to the lack of permafrost. The evidence provided by palaeoclimatic reconstructions and periglacial features, however, implies that Lateglacial permafrost was present throughout Scotland during the Loch Lomond Stade (LLS; ∼12.9–11.7 ka). Across much of the Scottish Highlands, the absence of Lateglacial TRGs is attributable to occupation of potential sites by glaciers during the LLS. In the Cairngorms, however, where limited snowfall at that time left some corries glacier-free, there is convincing evidence for TRG formation. Three examples illustrating different degrees of TRG development are described; all occur at high-level (>840 m) sites that remained glacier-free during the LLS, and all lack plausible alternative explanations. The apparent scarcity of relict TRGs even in the Cairngorms may reflect the development of ‘cold’ permafrost and/or a lengthy time lag between permafrost development and the accumulation of a sufficient volume and thickness of ground ice to permit permafrost creep and deformation of an overlying mantle of bouldery debris. In consequence, relict TRGs may occur only at favourable high-level sites where permafrost developed earliest.

Bayesian multi-proxy reconstruction of early Eocene latitudinal temperature gradients

Abstract. Accurately reconstructing large-scale palaeoclimatic patterns from sparse local records is critical for understanding the evolution of Earth's climate. Particular challenges arise from the patchiness, uneven spatial distribution, and disparate nature of palaeoclimatic proxy records. Geochemical data typically provide temperature estimates via transfer functions derived from experiments. Similarly, transfer functions based on the climatic requirements of modern taxa exist for some fossil groups, such as pollen assemblages. In contrast, most ecological and lithological data (e.g. coral reefs and evaporites) only convey information on broad climatic requirements. Historically, most large-scale proxy-based reconstructions have used either geochemical or ecological data, but few studies have combined multiple proxy types into a single quantitative reconstruction. Large spatial gaps in existing proxy records have often been bridged by simple averaging, without taking into account the spatial distribution of samples, leading to biased temperature reconstructions. Here, we present a Bayesian hierarchical model to integrate ecological data with established geochemical proxies into a unified quantitative framework, bridging gaps in the latitudinal coverage of proxy data. We apply this approach to the early Eocene climatic optimum (EECO), the interval with the warmest sustained temperatures of the Cenozoic. Assuming the conservation of thermal tolerances of modern coral reefs and mangrove taxa, we establish broad sea surface temperature ranges for EECO coral reef and mangrove sites. We integrate these temperature estimates with the EECO geochemical shallow marine proxy record to model the latitudinal sea surface temperature gradient and global average temperatures of the EECO. Our results confirm the presence of a flattened latitudinal temperature gradient and unusually high polar temperatures during the EECO, which is supported by high-latitude ecological data. We show that integrating multiple types of proxy data, and adequate prior information, has the potential to enhance quantitative palaeoclimatic reconstructions, improving temperature estimates from datasets with limited spatial sampling.

Palaeoglacier and palaeoclimate reconstruction since the Neoglacial of the central Gangdise Mountains, southern Tibetan Plateau

Palaeoglacier modelling is a crucial approach for reconstructing palaeoclimate. Although the timing of glaciations during the Little Ice Age (LIA) and Neoglacial in the central Gangdise Mountains has been partially determined, there are still undated fresh-looking moraines. This study utilized coupled mass balance and ice flow models to simulate the palaeoclimate during the five LIA glacial events (LIA-1 to LIA-5) and two Neoglacial glacial events (Neo-1 and Neo-2). The results revealed that the glacial volumes in the Gangdise Mountains during the LIA and Neoglacial periods ranged from ∼1.10 to 1.57 km3. Comparing the reconstructed climate with other proxies, it was found that Neo-2 and Neo-1 exhibited temperatures 0.54 to 0.82 °C and 0.7 to 1.0 °C lower than the present, respectively, with precipitation levels at 110–140% of the present. The temperatures during the LIA periods were 0.36 to 1 °C lower than the present, with precipitation levels at 80–120% of the present. The interannual variability of climate at decadal or centennial scales may have played a significant role in the formation of the LIA moraines.