Climate Reconstructions Research Articles

Evolution of weathering intensity in the Qaidam Basin, northeastern Tibetan Plateau, since the middle Miocene: Insights from clay mineral records

Terrestrial silicate weathering records from the tectonically active Tibetan Plateau are crucial to explore the interactions among climate change, tectonic uplift and chemical weathering during the Cenozoic. However, the complex sedimentary facies changes and frequent occurrence of coarse lithologies related to intense tectonic uplift of the Tibetan Plateau have largely limited the reliability of bulk chemical weathering indexes to reveal the silicate weathering history. Here, we present detailed records of clay minerals and geochemical compositions from clay-sized (< 2 μm) sediments collected from the well-dated Huaitoutala section (ca. 15.3–1.8 Ma) in the NE Qaidam Basin to reconstruct the chemical weathering history of the NE Tibetan Plateau during the late Cenozoic. The relatively high (illite–smectite mixed layers + smectite)/(chlorite + illite) ratio indicates a strong silicate weathering intensity from 15.3 to 12.6. Ma, while a continuous decrease in this ratio since 12.6 Ma reflects a long-term decreasing intensity of silicate weathering. By comparing the clay mineral records with the climatic reconstruction and the tectonic events in the NE Tibetan Plateau, the results reveal that middle Miocene global cooling-related drying exerted a significant influence on the decreasing weathering intensity since ca. 12.6 Ma. Furthermore, the late Cenozoic episodic and persistent uplift of the NE Tibetan Plateau may have exerted an additional influence on the long-term decrease in weathering intensity. Specifically, the dramatic fluctuation in the silicate weathering intensity during ∼11–9.6 Ma is mainly due to uplift-induced provenance changes. Moreover, the fluctuating increase in the silicate weathering intensity during ∼8–5 Ma may have been caused by intensified East Asian summer monsoon precipitation. Our study suggests that both climate change and tectonic deformation controlled the chemical weathering intensity in the NE Tibetan Plateau during the late Cenozoic.

Summer temperatures from the Middle Pleistocene site Schöningen 13 II, northern Germany, determined from subfossil chironomid assemblages

We present the first climatic and environmental reconstruction based on subfossil chironomid head capsules from the Middle Pleistocene Reinsdorf sequence, Schöningen, northern Germany, corresponding to Marine Isotope Stage 9e‐a. The sequence is characterized by interglacial forest successions followed by alternating woodland and steppe phases. Higher levels of runoff formed lacustrine habitats during post‐interglacial, cool steppe (woodland) phases. These were characterized by diverse chironomid assemblages with up to 27 chironomid morphotypes occurring simultaneously. Warmer forest phases were mostly void of chironomids when the site Schöningen 13 II fell dry owing to higher vegetational coverage and therefore lower runoff. Transitional periods between woodland and steppe phases show higher abundances of profundal, bottom‐dwelling chironomid taxa, suggesting oligo‐mesotrophic aquatic conditions, while steppe phases are dominated by shallow‐lake taxa with higher tolerance to increasing productivity. We applied temperature inference models to the chironomid assemblages based on a Swiss–Norwegian and a Swiss–Norwegian–Polish chironomid–temperature calibration data set to reconstruct mean July air temperatures for the Reinsdorf sequence. The Swiss–Norwegian–Polish training set (TS) seems better suited owing to a longer temperature gradient and the presence of the dominant taxon, Propsilocerus lacustris‐type, which is missing from the Swiss–Norwegian TS. In sections of the record with low taxon richness (Shannon index &lt;2) and a dominance of P. lacustris‐type, indicating increased nutrient impact, summer temperatures may have been overestimated by the Swiss–Norwegian–Polish TS. In the other sections, the chironomid‐based reconstructions based on the Swiss–Norwegian–Polish TS were in line with ostracod and plant remains‐based temperature reconstructions, suggesting summer temperatures of the post‐interglacial Reinsdorf oscillations between 16.5 and 22 °C. Our results show that summer air temperatures were lower during warmer, wetter transitional zones (−0.5–0.2 °C colder/warmer than today) and increasing during cooler, dry steppe phases (1 °C warmer than today), most likely caused by higher continentality.

Multiscale ocean dynamics control the sedimentary source-to-sink processes in the southwestern Okinawa Trough (East China Sea)

The sedimentary source-to-sink processes remain under debate in the southwestern Okinawa Trough due to its complex oceanographic context. We employe a multidisciplinary approach combining marine sedimentology and physical oceanography to address the sedimentary source-to-sink processes. This study shows that the East China Sea shelf has been the provenance of the southwestern Okinawa Trough during the past 3000 a, judged from the detrital zircon U-Pb geochronology. Numerical simulations indicated that the bottom currents are the primary drivers that transport sediments from the East China Sea shelf continuously entering the southwestern Okinawa Trough. This study confirms that the source-to-sink system in the southwestern Okinawa Trough is controlled by multiscale ocean processes, and verifies that the sediments are mainly sourced from the East China Sea shelf in the past 3000 a. These arguments greatly improve our understanding on the sediment dispersal and have important implications on the climatic and oceanographic reconstructions.

Reconciling East Asia's mid-Holocene temperature discrepancy through vegetation-climate feedback

The term “Holocene temperature conundrum” refers to the inconsistencies between proxy-based reconstructions and transient model simulations, and it challenges our understanding of global temperature evolution during the Holocene. Climate reconstructions indicate a cooling trend following the Holocene Thermal Maximum, while model simulations indicate a consistent warming trend due to ice-sheet retreat and rising greenhouse gas concentrations. Various factors, such as seasonal biases and overlooked feedback processes, have been proposed as potential causes for this discrepancy. In this study, we examined the impact of vegetation-climate feedback on the temperature anomaly patterns in East Asia during the mid-Holocene (∼6 ka). By utilizing the fully coupled Earth system model EC-Earth and performing simulations with and without coupled dynamic vegetation, our objective was to isolate the influence of vegetation changes on regional temperature patterns. Our findings reveal that vegetation-climate feedback contributed to warming across most of East Asia, resulting in spatially diverse temperature changes during the mid-Holocene and significantly improved model-data agreement. These results highlight the crucial role of vegetation-climate feedback in addressing the Holocene temperature conundrum and emphasize its importance for simulating accurate climate scenarios.

Effects of varied modern pollen-climate calibration-set establishment approaches on quantitative climate reconstructions

A representative modern calibration dataset is an essential prerequisite for a reliable quantitative reconstruction of paleoclimate. However, there has been a notable lack of systematic research on the optimal filtering of calibration sets. Four representative high-resolution pollen records were selected to repeatedly reconstruct paleoclimate using multiple approaches such as geographical distance, analogues and climate gradient. Comparisons of pollen-based reconstructions indicate that these varied approaches exhibit significant discrepancy in model performance and reconstruction accuracy under different geographical circumstances and time scales. Generally, in terms of calibration-set selection, the geographical distance method demonstrates greater efficiency for the plain region, but exhibit limitations in areas characterized by significant topographic changes. Analogue-calibration has been found to be more suitable for the edge of the database and also has been proven superior to other two methods for reconstructions exceed Holocene. Selecting calibration sets based only on climate gradients is inappropriate for independent applications, but may act as a limitation for other methods. This preliminary research can contribute to a more precise projection of potential future climate changes by providing essential data input or validating hindcasts for Earth system models.

The role of dispersal limitation in the forest biome shifts of Europe in the last 18,000 years

AbstractAimHow the ability of plants to move towards newly favourable habitats (dispersal limitation) impacts the change of biome distribution and transition under fast climate warming is still debated. Analysing vegetation change in the past may help to clarify the relative importance of underlying ecological processes such as climate, biotic interactions, and dispersal. In this study, we investigated how dispersal limitation affected the distribution of European forests in the last 18,000 years.LocationSouthern and Central Europe.TaxonSpermatophyta.MethodsUsing the LPJ‐GM 2.0 model (an extension of LPJ‐GUESS), we simulated European vegetation from the end of the Last Glacial Maximum (18.5 ka) to the current time (0 ka). Using biome reconstructions from pollen data as reference, we compared the performance of two dispersal modes: with no migration constraints or seed limitation (free dispersal mode), and with plant establishment depending on seed dynamics and dispersal (dispersal limitation mode).ResultsThe model run, including migration processes, was better at capturing the post‐glacial expansion of European temperate forests (and the longer persistence of boreal forests) than the setting assuming free dispersal, especially during periods of rapid warming. This suggests that a number of (temperate) tree taxa experienced delayed occupancy of climatically suitable habitats due to a limited dispersal capacity, i.e., post‐glacial migration lags.Main ConclusionsOur results show that including migration processes in model simulations allows for more realistic reconstructions of forest patterns under rapid climate change, with consequences for future projections of carbon sequestration and climate reconstructions with vegetation feedback, assisted migration and forest conservation.

Open paleoenvironment and dry climate in south India immediately before the Youngest Toba Tuff eruption (~75 ka) are suggested by Vondrichnus structures at the Jwalapuram locality, Jurreru valley

Abstract The Younger Toba Tuff (YTT) eruption is regarded as one of the largest of its time and possibly responsible for changing past climate and vegetation from C3 to C4 in the Indian subcontinent. A paleosol constituting a Toba pre-tephra horizon at the Jwalapuram locality, exhibits the preservation of biogenic structures identified as Vondrichnus planoglobus and Vondrichnus obovatus. This study investigated their paleoecological and paleoenvironmental significance. These structures are hard and compact, rounded to sub-rounded, spherical to sub-spherical bodies with empty chambers, surrounded by carbonate layers, and preserved in close proximity to termite pipes and nests and rhizolith structures. Their occurrence in the Jwalapuram area is significant, as the locality has been well documented as suitable for reconstruction of past climate and vegetation in light of the impact of the YTT eruption. Based on the present findings, we assume that the investigated locality would likely have an insect population and bush to scrub vegetation, indicating a dry environment immediately before the YTT eruption.

On Local Structure Equilibration of Ca2+ in Solution by Ab Initio Molecular Dynamics.

Analyzing the stable isotopic ratio of Ca offers valuable insights into a wide range of applications from climate reconstruction to bone cancer diagnosis and agricultural nutrient improvement. While the first hydration shell of Ca in solution is expected to play a major role in its fractionation properties, the coordination of Ca in water remains a subject of debate. In this work, Ca2+ in water has been modeled by means of ab initio molecular dynamics simulations using various exchange and correlation functionals and at different temperatures. Results show a significant effect of the functional on the average Ca2+ coordination, depending on its tendency to over- or understructure liquid water. The BLYP functional with Grimme-D2 correction was judged as the most accurate among those tested based on its accuracy to reproduce water structural and diffusion properties. Using this functional, the effect of temperature has been systematically investigated, focusing on means to limit the uncertainty in our assessments of the average coordination of Ca2+ ions by (1) estimating the number of water exchanges in the simulations and (2) implementing a statistical approach based on Markov chains. The findings indicate, especially, that our simulations at 300, 350, and 400 K do not yield converged results due to potential equilibration problems. These observations impose substantial constraints on the trustworthiness of numerous estimates in the existing literature that depend on trajectories with insufficient exchanges. We estimate Ca2+ coordination values of 6.8 ± 0.1, 6.8 ± 0.1, 6.7 ± 0.2, and 6.7 ± 0.2 at 600, 550, 500, and 450 K respectively. At lower temperatures (300, 350, and 400 K), while obtaining definitive values for Ca2+ coordination remains challenging, our research does indicate a potential temperature-related influence on coordination with an average Ca2+ coordination at 300 K as low as 6.2.

Detrending tree-ring widths in closed-canopy forests for climate and disturbance history reconstructions

Canopy disturbance events in forests often increase light availability and growth rates for surviving trees. Using ring widths, release-detection methods identify the initiation of rapid growth associated with these events enabling reconstructions of forest disturbance history. Conversely, dendroclimate reconstructions minimize these rapid growth responses by detrending entire ring-width time series to resolve underlying climate signals. Incorporating advantages from both of these approaches, we present a canopy disturbance detrending method that quantifies the subsequent, additional growth from release events as a discrete time series. Our method uses radial-growth averaging to detect release events and then power transformation and age-dependent smoothing splines to detrend individual release events, separating canopy disturbance responses from climatic effects. We test our canopy disturbance detrending method on both a coniferous and a broadleaf ring-width chronology from two contrasting temperate forests in eastern North America with known disturbance histories. The resulting disturbance growth time series agrees with the documented forest histories for each forest. Removing the effects of canopy disturbance from the ring-width series in each chronology improves climate correlations with monthly values of temperature and precipitation and may recover more low-frequency variation with past climate compared to other common detrending methods. Our method provides an alternative approach for detrending disturbance events in closed-canopy forests that should be accessible and useful for both ecological and climatological reconstructions.

New fossil woods (upper Pleistocene) from the lower-middle Uruguay river basin (South America) reveal the past distribution of Aspidosperma (Apocynaceae)

The present work describes the taxonomic and paleobiogeographic study of two fossil woods related to extant Aspidosperma. The silicified specimens come from the fossil localities of Santa Ana (30°54′S, 57°55′W) and Concordia (31°19′S, 57°59′W), Entre Ríos Province, Argentina, belonging to the El Palmar Formation (Late Pleistocene). This unit represents the sedimentary body of the upper fluvial terrace generated by the Uruguay River in its middle basin in eastern Argentina. The anatomical features that distinguish the woods are growth rings delimited by axial parenchyma and fibers, semi-ring to-diffuse-porous woods; mainly solitary vessels; simple perforation plates; alternate, bordered, and vestured intervessel pits; scarce paratracheal and diffuse apotracheal axial parenchyma; homocellular, and uniseriate to-triseriate rays; non-septate fibers. Climate reconstruction modelled at the regional scale (Ecological Niche Modeling) revealed variations in macroecological diversity patterns of the nearest living relatives (Aspidosperma australe and A. polyneuron) over the last ca. 130,000 years. Optically stimulated luminescence dating of sediments from the upper part of the El Palmar Formation in the type area reveals that the unit spans from the Last Interglacial period (warm substage, MIS marine isotope stage 5a), to the penultimate interglacial (MIS 7). This period was characterized by warmer and wetter conditions than those observed today. The eco-anatomical characteristics of the fossil record reflect this type of environment. The modern analogues of the fossils studied here are now part of the forests that integrate the Atlantic forest and Araucaria forest biogeographic provinces in South America.

A tree ring-based spring temperature reconstruction for the Hindu Kush region in northern Pakistan

Annually resolved and absolutely dated proxy archives are necessary for contextualizing the rate and amplitude of anthropogenic climate change. High-resolution climate reconstructions are particularly important for remote regions where instrumental meteorological observations are limited in space and time. Here, we develop a robust, 260-year-long tree-ring width chronology from 32 Himalayan cedars (Cedrus deodara D. Don), which grew around 3000 m asl in the Kumrat Valley of the Hindu Kush region in northern Pakistan. Growth-climate response analyses reveal a significant negative correlation of -0.631 between our new standard chronology and March-April minimum temperatures (p < 0.001, n = 51). This inverse relationship between radial tree growth and early spring temperatures, together with positive correlations against precipitation totals at the onset of the growing season, suggest that warming-induced drought is the most limiting factor of sub-alpine forest growth in the Kumrat Valley. We then use the inverse growth-temperature association to reconstruct March-April minimum temperatures from 1812 to 2018 CE. The reconstruction explains 40 % of the instrumental record back to 1967, and exhibits the coldest and warmest spring conditions in 1815–1864 (6.67 ± 0.21°C) and 1918–1927 (8.11 ± 0.43°C), respectively. This pioneering study is indicative of the dendroclimatological potential in the Hindu Kush, where samples from living and relict trees of different species and elevational bands should be collected for advanced temperature and hydroclimate reconstructions.

Drought, temperature, and moisture availability: understanding the drivers of isotopic decoupling in native pine species of the Nepalese Himalaya.

The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ18OTR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460-2000m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ18OTR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ18OTR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993-1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ18OTR-climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions.

A global compilation of diatom silica oxygen isotope records from lake sediment – trends and implications for climate reconstruction

Abstract. Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ18O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ18OBSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial–interglacial cycles. The best coverage in number of records (N = 37) and data points (N = 2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times &lt; 100 years. For mid- to high-latitude (&gt; 45° N) lakes, we find common δ18OBSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

Quantitative Holocene climate reconstruction and anthropogenic impact analysis based on the pollen records in peat sediment in Southern China

The quantitative reconstruction of Holocene paleoclimate is pivotal for unraveling the evolution of East Asian Monsoon (EAM). Some recent studies have highlighted the escalating human activities in the late Holocene, which could potentially pose significant challenges to the precise quantitative reconstruction of paleoclimate. In this study, we undertake a quantitative reconstruction of Holocene climate and human influence index (HII) based on pollen data from the Shiwangutian (SWGT) in Southern China. This is achieved by developing and applying a pollen-based calibration model utilizing Locally Weighted Average-Partial Least Squares Regression (LWWA-PLS) and the Modern Analogue Technique (MAT). Our findings reveal that evergreen forests experienced expansion between 11.6 and 9.0 cal ka BP, coinciding with elevated Mean Annual Precipitation (Map) and Mean Annual Temperature (Mat) levels. These patterns signify a progressively warm and wet climate during this period. Subsequently, evergreen forests achieved their maximum abundance between 9.0 and 4.0 cal ka BP, aligning with a notable increase in vegetation richness, indicating a warmer and wetter climate during the mid-Holocene. Notably, during the interval of 6.0–4.0 cal ka BP, the Map, Mat, and Precipitation of Warmest Month (Mpwa) reached the Holocene optimum, approximately 14% higher than modern. Consequently, we deduce that in the early and middle Holocene, when the monsoon was particularly strong, synchronous changes in precipitation fostered the regional expansion of evergreen broad-leaved forests. Furthermore, the record demonstrates a substantial reduction in forest cover and a noteworthy increase in the HII value since 4.0 cal ka BP, likely attributable to anthropogenic impacts. Our analysis suggests that the influence of anthropogenic activities surpassed that of natural climate factors in shaping regional vegetation cover. These findings offer insights into potential drivers of climate change. As a preliminary conclusion, we propose that the summer insolation, ice sheets, and meltwater fluxes were the primary controlling factors for climate variations during the early to mid-Holocene in Southern China.

Climate reconstruction of the Little Ice Age maximum extent of the tropical Zongo Glacier using a distributed energy balance model

Climate reconstruction of the Little Ice Age maximum extent of the tropical Zongo Glacier using a distributed energy balance model

A discussion on carbon and oxygen isotopes of secondary carbonates in loess-paleosol sequences

Although carbon and oxygen isotopic compositions of carbonates are valuable for Quaternary climate reconstruction due to their sensitivity to paleoclimate changes, a comprehensive understanding regarding the formation, factors influencing isotopic variations, and age uncertainties of secondary carbonates in loess deposits remains elusive. This study investigates the microstructure and stable isotopes of secondary carbonates, specifically calcified root cells (CRC) and needle-fiber calcite (NFC), found within the loess deposits of the last glacial period in the northwestern region of the Chinese Loess Plateau. The average δ13C values of soil total organic matter, CRC, NFC, and total inorganic carbonates in the YuanBao sections are −22.1‰, −14.9‰, −7.0‰, −4.6‰, respectively. Radiocarbon dating results reveal that both CRC and NFC were not of synsedimentary origin. The pronounced negativity of the carbon isotopic composition and the microstructures offer insights that CRC formation is closely tied to C3 plants. The synchronous depletion of δ13CCRC and δ18OCRC values during the transition period from the last glacial to the Holocene, underscores the sensitivity of isotopic composition of CRC to local environmental changes, making it a potential candidate for paleo-climate studies. Additionally, CRC formed during the glacial period provides a close approximation to the true sedimentation age. The radiocarbon dating of NFC highlights a significant fluctuation in carbon source translocation depth, resulting in a pronounced temporal and spatial decoupling between NFC formation and the surrounding deposits. Consequently, values of δ13CNFC and δ18ONFC seem to exhibit no significant trend across the limited depth range in this research. We propose that, when using NFC for paleoclimate reconstruction, careful consideration of variations in translocation depths of carbon sources is imperative to prevent misestimations. NFC could potentially be more fitting for broader temporal-scale paleoclimate reconstructions rather than high-resolution investigations.

Tree-ring hydrological research in the Himalaya: State of the art and future directions

Recent developments in tree-ring research offer great potential for reconstructing past climate changes; determining the frequencies of natural hazards; and assessing the availability of freshwater resources over timescales that extend well into the pre-instrumental period. Here, we review the state of dendrochronological research in the Himalaya and outline future directions for tree-ring-based hydrological reconstructions in a region that has a pressing societal need to understand the causes and consequences of past, present and future changes in the hydrological cycle. We used ‘tree ring’ and ‘Himalaya’ as keywords to identify scholarly articles from the Web of Science that were published between 1994 and 2022. The resulting 173 publications were separated by their spatial coverage into the western, central and eastern Himalaya, as well as their scientific purpose (e.g. reconstructing growth-climate relationships, temperature, precipitation, streamflow, floods, droughts, etc.). Our analysis shows that dendrochronological research in the Himalaya primarily focused on understanding growth-climate relationships using annual tree-ring widths measurements obtained for coniferous species, and their application in climate reconstructions. Reconstructions of hydrological processes such as streamflows, and extremes such as glacial and landslide lake outburst floods, have received less attention. Recent advances in dendrochronology, including blue intensity (BI), quantitative wood anatomy (QWA), and tree-ring stable isotopes (TRSI) should be combined to improve the resolution and accuracy of hydrological reconstructions in all parts of the Himalaya. Such studies may allow us to better understand the effects of climate change and the Himalayan water resources for its lowland surroundings. They may also facilitate decision-making processes for mitigating the impacts of climate change on natural hazards, and for better managing water resources in the region.

Rethinking the Holocene temperature conundrum

Recent scholarship argues for more research to resolve the ‘Holocene temperature conundrum’, an apparent discrepancy between decreasing proxy-reconstructed and increasing model-simulated long-term temperature trends during the late Holocene. Here, we argue that the observed proxy-model offset likely results from inappropriate comparisons of different seasonal and spatial signals in the reconstructed and simulated palaeo-data. Since proxy archives have been used to reconstruct global annual mean temperatures, they have been compared against model simulations of the same seasonal and spatial domains. However, we suggest that most of the proxy-based large-scale reconstructions are biased towards Northern Hemisphere summer temperatures, and as such model comparisons have predominantly focused on the wrong target data. Further to advancing our understanding of long-term temperature trends, we recommend prioritising the refinement of proxy networks and climate reconstructions to preserve the full spectrum of naturally forced, interannual to multi-millennial variations needed to contextualise recent anthropogenic changes against past Holocene ranges.

Diatom-based inferences of environmental changes from an alpine lake on the southeast edge of the Tibetan plateau over the last 4000 years

To better understand how global and regional-scale climate has changed, high-resolution records for environmental changes are still needed in southwestern (SW) China during the Late Holocene epoch. This study presents a well-dated high-resolution diatom analysis from a 1.66-m-long sediment core taken from Lake Cuogeda (CGD) on the southeast (SE) edge of the Tibetan Plateau to document environmental changes over the past ∼4000 years. Diatom and other geochemical proxies show that, from 3850 to 3430 cal yr BP (before present, 0 BP=1950 AD, 1900 to 1480 BC), the environment of Lake CGD is acidic, oligotrophic, and enriched with humic acids. And the lake ice cover duration is short during this period. During 3430–1550 cal yr BP (1480 BC-400 AD), Lake CGD has less humic acid and a relatively high pH environment. The ice cover duration is longer, and the temperature drops during this period. Our multi-indicator recorded two environment fluctuations at ∼2800 cal yr BP (850 BC) and 2210–1950 cal yr BP (260 BC-0 AD). From 1550 to 3.6 cal yr BP (400–1946 AD), the lake ecosystem changed to a higher pH condition and had a prolonged freezing time. From 3.6 cal yr BP (1946 AD) to the present, Lake CGD’s water was acidic, with an environment of shorter duration of ice cover and stronger lake water turbulence. Comparisons between the CGD records and other climate reconstructions underscore the relevance of the CGD record for regional and global environments. Comparisons indicate that the environment evolution pattern of SW China during the Late Holocene was greatly affected by solar radiation and North Atlantic sea surface temperature.

Climate and Vegetation of the Miocene of Tierra del Fuego: Filaret Formation

AbstractThe changing climate during the Cenozoic affected the diversity of plants in Patagonia, as species richness tends to increase during warm periods and decrease during cold periods. Precipitation is a significant factor shaping diversity, as shown in the case of central Chile during the Miocene. This study presents a reconstruction of the climate and vegetation in Tierra del Fuego Island, located approximately 52°S, using fossil flora recovered from the Filaret Formation to understand the Miocene epoch, characterized by contrasting global climatic changes. Filaret flora comprises twenty‐seven morpho‐taxa, including nine Nothofagus species and other Gondwanan and Neotropical families, such as Atherospermataceae and Anacardiaceae, in agreement with a forest habitat. Leaf physiognomy climate reconstruction suggests microthermal conditions, with a mean annual temperature of 9.4–11°C and annual precipitation ranging from 985 to 1,130 mm. These conditions are warmer and wetter than the modern record of the area, with a MAT of 6°C and mean annual precipitation of 300 mm. As the Filaret fossil record suggests, the forest habitat under a microthermal climate is consistent with the global climatic reconstruction of the Early Miocene. This Miocene landscape on Tierra del Fuego was possible because the Andes could not rain‐shadow humid westerly winds by this timeframe.