Paleoclimate Reconstructions Research Articles

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.

A solution for constraining past marine Polar Amplification

Most climate proxies of sea surface temperatures suffer from severe limitations when applied to cold temperatures that characterize Arctic environments. These limitations prevent us from constraining uncertainties for some of the most sensitive climate tipping points that can trigger rapid and dramatic global climate change such as Arctic/Polar Amplification, the disruption of the Atlantic Meridional Overturning Circulation, sea ice loss, and permafrost melting. Here, we present an approach to reconstructing sea surface temperatures globally using paired Mg/Ca - δ18Oc recorded in tests of the polar to subpolar planktonic foraminifera Neogloboquadrina pachyderma. We show that the fidelity of Mg/Ca-based paleoclimate reconstructions is compromised by variations in seawater carbonate chemistry which can be successfully quantified and isolated from paleotemperature reconstructions using a multiproxy approach. By applying the calibration to the last glacial maximum, we show that marine polar amplification has been underestimated by up to 3.0 ± 1.0 °C in model-based estimates.

A framework for reconstructing marine heatwaves from individual foraminifera in sedimentary archives

Marine heatwaves (MHWs) are warm sea surface temperature (SST) anomalies with substantial ecological and economic consequences. Observations of MHWs are based on relatively short instrumental records, which limit the ability to forecast these events on decadal and longer timescales. Paleoclimate reconstructions can extend the observational record and help to evaluate model performance under near future conditions, but paleo-MHW reconstructions have received little attention, primarily because marine sediments lack the temporal resolution to record short-lived events. Individual foraminifera analysis (IFA) of paleotemperature proxies presents an intriguing opportunity to reconstruct past MHW variability if strong relationships exist between SST distributions and MHW metrics. Here, we describe a method to test this idea by systematically evaluating relationships between MHW metrics and SST distributions that mimic IFA data using a 2000-member linear inverse model (LIM) ensemble. Our approach is adaptable and allows users to define MHWs based on multiple duration and intensity thresholds and to model seasonal biases in five different foraminifera species. It also allows uncertainty in MHW reconstructions to be calculated for a given number of IFA measurements. An example application of our method at 12 north Pacific locations suggests that the cumulative intensity of short-duration, low-intensity MHWs is the strongest target for reconstruction, but that the error on reconstructions will rely heavily on sedimentation rate and the number of foraminifera analyzed. This is evident when a robust transfer function is applied to new core-top oxygen isotope data from 37 individual Globigerina bulloides at a site with typical marine sedimentation rates. In this example application, paleo-MHW reconstructions have large uncertainties that hamper comparisons to observational data. However, additional tests demonstrate that our approach has considerable potential to reconstruct past MHW variability at high sedimentation rate sites where hundreds of foraminifera can be analyzed.

El Niño-like tropical pacific ocean cooling pattern during the last glacial maximum

Many state-of-the-art climate models are unable to reproduce the observed 20th century surface warming pattern in the tropical Pacific Ocean, casting doubt on the robustness of future projections. Here, we examine past changes in the tropical Pacific upper ocean spatial pattern using paleoclimate reconstructions from proxies and simulations from a multi-model ensemble. The proxy results demonstrate that during the Last Glacial Maximum, when atmospheric carbon dioxide concentrations were lower than present, temperatures in the western tropical Pacific Ocean decreased more than in the east, leading to an El Niño-like cooling pattern. This result contrasts with the zonally uniform cooling pattern observed in model simulations, highlighting the common issue of models overestimating the sensitivity of eastern tropical Pacific sea surface temperatures to greenhouse forcing. Our proxy results imply that the western Pacific may warm more than the east in response to future climate change, producing a La Niña-like surface warming pattern.

High-precision cyclic correlation as a basis for detailed paleoclimatic reconstructions for the Pliocene-Quartenary sections of Eurasia

An astrochronological (cyclostratigraphic) binding of the lithological and geochemical characteristics of Pliocene-Quaternary sediments of the Eurasian sections to the Milankovich cycles (eccentricity, obliquity of the ecliptic, precession) was carried out, an analysis of the relationship between the established variations in climate and paleotemperature with the moments of coincidence of different-order cycles of eccentricity and their paleoclimatic characteristics was given. The results of the implementation of the results obtained during the practice in geology at the Moscow State University in Chashnikovo are shown. During the research, materials from the exposition space of the Department of Regional Geology and Earth History and the Museum of Earth Science were used. The results of the study were used in conducting an educational practice in geology in Chashnikovo, and can also be used in the dismemberment and regional and global correlation of sections, in conducting geological surveys, creating cyclostratigraphic scales of the plains and mountainous regions of Eurasia, as well as in the creation and further development of the exposition space of museums — Moscow State University Gymnasium for example.

Constraining the sources of archaeal tetraether lipids in multiple cold seep provinces of the Cascadia Margin

Archaeal isoprenoid glycerol dialkyl glycerol tetraether lipid (iGDGT) abundance profiles and carbon isotopic compositions reflect the relative distributions of archaeal sources, including planktonic, benthic, and methane-cycling contributions. Here, we analyze the carbon isotope ratios of iGDGTs purified from sediments of three different cold seep sites in Cascadia Margin, off the coast of Washington, USA. Together with relative abundance and glycerol configurations, we use the carbon isotope ratios to estimate the contributions of multiple archaeal sources to the sedimentary iGDGT assemblages and their impact on values of the TEX86 and methane indices. Using a Bayesian mixing model, we robustly characterize three potential endmembers by determining their characteristic lipid distributions, inferred contributions to the total sediment inventory, and carbon isotopic signatures. Despite the geographic proximity of the sample locations, we find site-specific heterogeneity in relative iGDGT abundances and δ13C values. Planktonic and benthic methane-cycling sources predominate in all cases (contributing > 98 % of iGDGTs), while benthic non-methane cycling archaea contribute minimally to the sedimentary lipid pool. Environments with higher methane influence show an increased presence of anti-parallel iGDGTs, indicating that methane-cycling archaea may dominantly or exclusively synthesize iGDGTs in this configuration. Our results quantify the relationship between the methane index (MI) and methane impact in systems dominated by planktonic and benthic methane-cycling archaea. Within the framework of the TEX86 temperature proxy, this permits a quantitative demonstration that it is overly simplistic to apply a MI cutoff threshold as a binary indicator to determine methane influence, and caution is needed when taking this approach in paleoclimate reconstructions.

Paleobotanical Evidence for Mediterranean Climates in the Western Canadian Paleoarctic During the Late Middle Eocene

AbstractPaleogene age deposits east of the Fifteenmile River, northwest of Dawson City, Yukon, Canada preserve a diverse high‐latitude fossil flora. Here, we provide new data on the age of the fossil site based on laser ablation–inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) U‐Pb dating of tephra zircons, paleobotanical paleoclimate reconstructions, and growing season length estimates based on photoperiod. These new data indicate an age of the Fifteenmile River fossil locality as late middle Eocene and likely within the Middle Eocene Climatic Optimum episode. The paleoflora‐based paleoclimate reconstruction indicates the region was relatively wet and warm with non‐freezing winters, but also experienced seasonal dryness, with an approximate 7 months long growing season as suggested by photoperiod. We interpret this paleoclimate as summer dry and winter wet—a climate analogous to modern day warm Mediterranean climates in the Köppen‐Geiger climate classification system. These findings provide a new perspective on the past climate and environment of high‐latitude ecosystems during warm greenhouse intervals and contribute to our understanding of the Earth's climate history and its potential future changes.

The Pivotal Role of Evaporation in Lake Water Isotopic Variability Across Space and Time in a High Arctic Periglacial Landscape

AbstractRapidly changing climate is disrupting the High Arctic's water systems. As tracers of hydrological processes, stable water isotopes can be used for high quality monitoring of Arctic waters to better reconstruct past changes and assess future environmental threats. However, logistical challenges typically limit the length and scope of isotopic monitoring in High Arctic landscapes. Here, we present a comprehensive isotopic survey of 535 water samples taken in 2018 and 2019 of the lakes and other surface waters of the periglacial Pituffik Peninsula in far northwest Greenland. The δ18O, δ2H, and deuterium‐excess values of these samples, representing 196 unique sites, grant unprecedented insight into the environmental drivers of the regional hydrology and water isotopic variability. We find that the spatial variability of lake water isotopes can best be explained through evaporation and the hydrological ability of a lake to replace evaporative water losses with precipitation and snowmelt. Temporally, summer‐long evaporation can drive lake water isotopes beyond the isotopic range observed in precipitation, and wide interannual changes in lake water isotopes reflect annual weather differences that influenced evaporation. Following this, water isotope samples taken at individual times or sites in similar periglacial landscapes may have limited regional representativeness, and increasing the spatiotemporal extent of isotopic sampling is critical to producing accurate and informative High Arctic paleoclimate reconstructions. Overall, our survey highlights the diversity of isotopic compositions in Pituffik surface waters, and our complete isotopic and geospatial database provides a strong foundation for future researchers to study hydrological changes at Pituffik and across the Arctic.

Bayesian Errors‐in‐Variables Estimation of Specific Climate Sensitivity

AbstractEstimation of climate sensitivity is fundamental to assessing how global climate will warm as atmospheric concentration increases. Geological archives of environmental change provide insights into Earth's past climate, but the incomplete nature of paleoclimate reconstructions and their inherent uncertainties make estimation of climate sensitivity challenging. Thus, quantifying climate sensitivity and assessing how it changed through geological time requires statistical frameworks that can handle data uncertainties in a principled fashion. Here we demonstrate some of the hurdles to estimating climate sensitivity, with a focus on current statistical techniques that may underestimate both climate sensitivity and its associated uncertainty. To solve these issues, we present a Bayesian error‐in‐variables regression model, which can yield estimates of climate sensitivity without bias. The regression model is flexible and can account for data point uncertainties with a known parametric form. The utility of this approach is demonstrated by estimating specific climate sensitivity with uncertainty for the Eocene.

Carbonate mud production in lakes is driven by degradation of microbial substances

Carbonate mud is crucial in the global carbon cycle and serves as a key sedimentary archive for paleoclimate reconstruction. Understanding the mechanisms behind its formation is crucial for explaining long-term carbon storage, including atmospheric carbon dioxide transfer to the hydrosphere and variations in mud production over geological timescales. Various mechanisms explain carbonate mud formation in both lake and marine sediments. Using bio-physicochemical methods on deep sediments of Lake Ilay, Jura, France, we propose a model of micrite formation. Our study shows that micrite mineralization occurs in sediments due to the degradation of ooze rich in exopolymeric substances throughout the sediment core’s depth. This mineralization continues as long as exopolymeric substances are present, persisting for at least 2000 years. Cryo-Scanning electron microscope imaging reveals calcite nucleation at degraded exopolymeric substance nodes, advancing with substance degradation and calcium release. These findings provide insights into fossil carbonate mud origins and formation processes.

Biogeochemical cycling of trace elements and nutrients in ferruginous waters: Constraints from a deep oligotrophic ancient lake

AbstractIron‐rich, ferruginous waters were the dominant geochemical regime for most of Earth's history. Modern ferruginous waters are found in stratified, sulfur‐poor lakes, and serve as crucial analogs for biogeochemical cycling throughout Earth's past. Here we present the first depth‐resolved data of physical structure, nutrients and trace elements from Lake Poso (Indonesia), a deep oligotrophic ancient lake. Lake Poso is ferruginous, with anoxia below ~ 90 m depth, placing it among the world's largest ferruginous lakes. Physical stratification is weaker than other tropical anoxic lakes, indicating sensitivity for paleoclimate reconstructions. Trace elements and nutrients are predominantly shaped by the oxic–anoxic transition. Manganese– and Fe oxyhydroxide–driven biogeochemical cycling occurs at distinct depth horizons, with Co and Ni controlled by Mn and showing shallow release in anoxic waters, while V, Cr, P, and As are controlled by Fe, with release in surface sediments and diffusive transport. Chromium is nonquantitatively removed in anoxic waters, in contrast to widespread assumptions in Cr‐based paleoreconstructions. Oxycline U and Se removal corresponds to a local N minimum, suggesting biological reduction and/or uptake. These first ferruginous water Se data also show removal in sediments, indicating sediment signals reflect multiple removal processes and informing Se‐based paleoreconstructions, while the absence of sediment U removal contrasts other anoxic basins. A comparison with other ferruginous lakes demonstrates how local influences drive deviations from expectations in other systems, and highlight common, generalizable ferruginous basin features. Therefore, these data will guide research in ferruginous settings across space and time, and improve paleoreconstructions from ferruginous sediment records.

Radiocarbon dating of the natural groundwater in the Ob-Zaisan folded region (Russia)

Groundwater in the Ob-Zaisan folded region (Russia) has significant differences in the stable isotope composition of oxygen and hydrogen, which cannot be explained by the geographical and relief features of the region. A probable reason for these differences could be climatic changes in the study area over the past tens of thousands of years. The method of the radiocarbon dating can be perfectly suited in order to determine such small geological ages. The dating of waters using 14C data gives an understanding of their residence time. It will make it possible to differentiate periods of recharge and accumulation of water in aquifers and track the changes of the water stable isotope composition over time. The estimated water age ranges from 650 to 19,000 years. The enrichment of δD and δ18O values with the decreasing of the water age indicates a gradual warming of the Novosibirsk region climate. These results logically complement the meteorological observations over the last century and may be useful for paleoclimate reconstructions of the region.

The Origin and Nature of Magnetic Particles From Soils and Sediments Constrained by Hydrodynamics and Geochemistry Around a Tropical Lagoon System

AbstractMagnetic iron oxides are commonly enriched in soils and sediments on Earth's surface. Magnetic properties are widely employed in soil taxonomy, sediment tracing and paleoclimate reconstruction as indicators of associated pedogenic and depositional processes. However, in coastal regions, frequent shifts in pedogenesis and diagenesis accompanied by changes in hydrodynamic and geochemical conditions from land to sea can influence the formation and preservation of magnetic particles in sediment sequences. To discern the origin and nature of magnetic particles driven by these processes, we systematically examined soils and sediments around a tropical lagoon that has been closing for two hundred years. We found that the finest superparamagnetic particles are enriched along with hematite from inland soils with high‐Fe and high‐Al backgrounds, which was driven by pedogenesis. Single‐domain ferrimagnetic particles are enriched along with amorphous iron oxides in the lagoon with high‐Mg and high‐Mn backgrounds, which was driven by early diagenesis in quiet and reducing depositional environments. Coarse titanomagnetite particles are strongly enriched in inshore sediments with high‐Si and high‐Ti backgrounds, which was driven by seawater elutriation. However, magnetic particles in barrier bar soils have mixed features depending on the neighboring environment. Identifying magnetic particles derived from different soils and sediments in tropical coastal regions can assist in tropical coastal paleoclimate and paleoenvironment reconstruction on the basis of magnetic properties along coastal sediment sequences.

Biological control of ultra-skeleton mineralization in coral

Abstract Understanding the mineralization of coral is significant for the formation of coral reefs and paleoclimatic reconstructions. However, the fundamental mechanisms involved in biomineralization are poorly understood. A combination of Raman spectral and cross-polarized reflected light microscopy imaging was used to examine the three-dimensional spatial distribution of the skeletal ultrastructures and their associated mineral, organic, and water chemistry in coral, which enable insight into the spatial growth features of the ultrastructures and possible formation processes. A possible mechanism is proposed that controls the formation of skeletal ultrastructures, which likely involves compartmentalized calcifying cells and their related cellular activities. This could clarify the association between coral skeletal mineralization and biology, and it may be beneficial to better protection and application of coral reefs.

Absolute 230Th/U chronologies and Δ47 thermometry paleoclimate reconstruction from soil carbonates in Central Asian loess over the past 1 million years

Pleistocene loess records of the Khovaling Loess Plateau (KLP) in Tajikistan provide rich collections of lithic artifacts demonstrating past human presence in the region. To understand the timing of human activity and environmental conditions prevailing at that time U–Th dating and clumped/stable C/O isotope measurements have been applied to modern and Pleistocene soil carbonates (SCs) collected at several sites on the KLP and surroundings. U–Th ages were corrected by two methods: 1) assuming an initial [230Th/232Th] activity ratio of 0.85 ± 0.25 based on gamma spectrometry of loess/paleosol samples, and 2) the isochron technique using leachates and fully dissolved subsamples. Diagenetic alteration and potential U/Th mobilization and related isotope fractionation due to alpha-recoil was also modelled and found to be minor in the studied soil carbonates. Compared to model ages as references, uncorrected 230Th ages are only acceptable if measured [230Th/232Th] activity ratios of leachates are high (>30), while 230Th ages derived using method 1 are mostly overcorrected. It appears that SCs can be reliably dated by the U-series disequilibrium method in this sedimentary setting, but isochron dating cannot be spared. Application of the isochron method is required to derive 230Thmodel ages, which ensures that the non-zero initial 230Th and possible U–Th gain/loss due to alpha-recoil can be simultaneously corrected and reliable U–Th ages obtained. U–Th ages of Pleistocene SCs clearly demonstrate post-pedogenic ingrowth of multiple, non-contemporaneous populations of SCs within loess/paleosol units, and that SC formation happened in many cases under cold, presumably dry glacial climate conditions. Considering that U–Th ages of SCs provide minimum ages of the sediment in which they form, these ages can be useful in developing loess stratigraphic models and for correlation of paleosols with marine isotope stages. This implies that the age of a given paleosol and any lithic artifacts it may contain, indicating human activity, cannot be younger than the age of SCs formed in that paleosol. This is due to the nature of soil carbonates, which can be the product of both syn- and post-depositional processes.Clumped isotope thermometry of SCs collected from modern soils at three sites in Tajikistan provide evidence for SCs dominantly recording summer season soil temperatures, while the calculated soil water oxygen isotope signatures reflect annual signals and carbonate precipitation from source waters incorporating rainfall from prior to and during SC formation. In contrast, some Pleistocene SCs record soil temperatures and stable isotope compositions more appropriate to glacial conditions, confirming the findings of U–Th ages, and highlighting the primary role of aridity-driven soil moisture changes in SC precipitation in this setting. Considering the interpretative complexities of SC stable isotope compositions, involving issues such as SC formation depth within a soil/paleosol profile, seasonality of SC growth and violation of the law of superposition, SC stable isotope proxy records of past climates cannot be considered as a set of clearly sequential data through time. This implies that such SC-based stable isotope records must be accompanied by U–Th dating of carbonates to be meaningful.

Local hydrology control of radiocarbon in stalagmites from the Kyusendo Cave, Kumamoto, Japan

Stalagmite is an important archive of paleoclimate especially in the region of the East Asian Monsoon. Despite the widespread use of radiocarbon (14C) dating to explore past environmental changes, the contribution of a14C-free carbon fraction leached from soil and/or host rocks during stalagmite formation, known as the dead carbon fraction (DCF), impedes its application to stalagmite chronology. Thus, uranium series dating is preferentially used to determine stalagmite ages. However, both U/Th and 14C dating can be applied to stalagmite samples, U/Th can be used to calibrate the radiocarbon ages by assuming a relatively constant DCF contribution over time. Studies exploring DCF changes from glacial to interglacial periods remain scarce, suggesting that temporal and speleothem-specific DCF studies are needed. Here, we present findings on DCF changes over the last 38 ka in speleothems obtained from southwestern Japan. Our analysis includes measurements of both 14C in drip water and speleothem calcite alongside U/Th dating of three stalagmites collected from Kyusendo Cave, located in southern Japan. The DCFs reconstructed from these stalagmites exhibited variations of 37.8%–73.9% between 4.2 and 38.3 ka, which exceeded the typical DCF values reported previously. Intra-test variations of the DCF values in Kyusendo Cave also revealed differences of up to 30%–40% among the three stalagmites. A higher drip water DCF and dripping rate showed a strong negative correlation, indicating that variations in DCF may reflect changes in local hydrology. The study findings suggest that speleothem-specific and temporally varied DCF should be considered in paleoclimate reconstructions using speleothems.

Deep desert aquifers as an archive for Mid- to Late Pleistocene hydroclimate: An example from the southeastern Mediterranean

Many efforts have been made to illuminate the nature of past hydroclimates in semi-arid and arid regions, where current and future shifts in water availability have enormous consequences on human subsistence. Deep desert aquifers, where groundwater is stored for prolonged periods, might serve as a direct record of major paleo-recharge events. To date, groundwater-based paleoclimate reconstructions have mainly focused on a relatively narrow timescale (up to ∼40 kyr), limited by the relatively short half-life of the widely used radiocarbon (5.73 kyr). Here we demonstrate the usage of deep regional aquifers in the arid southeastern Mediterranean as a hydroclimate archive for earlier Mid-to-Late Pleistocene epochs. State-of-the-art dating tools, primarily the 81Kr radioisotope (t1/2 = 229 kyr), were combined with other atmosphere-derived tracers to illuminate the impact of four distinguishable wetter episodes over the past 400 kyr, with differences in climatic conditions and paleo-recharge locations. Variations in stable water isotope composition suggest moisture transport from more proximal (Mediterranean) and distal (Atlantic) sources to different parts of the region at distinct times. Large variability in the computed noble gas-based recharge temperature (NGT), ranging ~15–30 °C, cannot be explained by climate variations solely, and points to different recharge pathways, including geothermal heating in the deep unsaturated zone and recharge from high-elevation (colder) regions. The obtained groundwater record complements and enhances the interpretation of other terrestrial archives in the arid region, including a contribution of valuable information regarding the moisture source origin as reflected in the deuterium-excess values, which is unattainable from the common practice analysis of calcitic cave deposits. We conclude that similar applications in other deep (hundred-m-order) regional groundwater systems (e.g., the Sahara desert aquifers) can significantly advance our understanding of long-term (up to 1 Myr) paleo-hydroclimate in arid regions, including places where no terrestrial remnants, such as cave, lake, and spring sediments, are available.

Characterization of biotic and abiotic signatures of modern lake sediments of western India, and its palaeo-environmental implications

A multi-proxy study of biotic and abiotic components was conducted on surface sediment samples from six lakes/wetlands located along the western transitional boundary of the contemporary Indian Summer Monsoon (ISM) in the Indian Subcontinent. The primary goal is to assess the suitability of various proxies as representatives of modern vegetation, environmental and climatic conditions. The collected data indicate significant variations in the composition and density of pollen in response to climate-induced and anthropogenic ecological changes throughout the northwest India transect. The palynological studies from eastern Rajasthan shows high forest elements in comparison to western Haryana and western Uttar Pradesh. In addition, the palynological data was juxtaposed with other biotic proxies such as diatom and isotopic studies, along with geochemical proxies and paleomagnetic data of the surface lake sediments. The presence of marker pollen taxa including Cerealia type Poaceae, Chenopodiaceae, and Brassicaceae, allows for distinct recognition of anthropogenic activities throughout the whole transect. The diversity and distribution of diatoms also support the palynological data in response to climate-induced and anthropogenic ecological changes. Furthermore, grain size, geochemistry (TOC/TN ratio with stable carbon isotope), and magnetic susceptibility data offer crucial insights about the sediment's depositional settings and general mineralogical composition. Stable carbon isotope data shows C3 dominance in relatively humid areas and C4 dominance in semi-arid areas, suggesting climate-driven control over sediment organic matter composition. Canonical correspondence analysis (CCA) indicates that biotic variables (pollen, diatom, stable isotopic composition) are significantly controlled by modern precipitation and temperature. Redundancy analysis reveals a significant influence of current average temperature and precipitation on major element oxide variations in surface lake sediments. Therefore, we propose using palynological, stable carbon isotope, diatom data, along with grain size, environmental magnetism, and geochemistry, to establish a multiproxy modern analogue for quantitative palaeoclimatic reconstructions. As a result, this study provides the first modern analogues from a climate-sensitive region that separates the area under ISM influence from an area with meager precipitation in western India.

Applying paleoclimatic reconstruction of greenhouse gases and correlation analysis of global and Yangtze Estuary SST changes with industrial revolution

This study explores the differences of different proxies in paleoclimatological reconstruction. It was found that N2O content increased first and then decreased after the first industrial revolution, while CO2 and CH4 content increased. After the Second Industrial Revolution, the three kinds of greenhouse gases all increased sharply, and the amplitude was relatively consistent. The analysis shows that the annual variation of the Changjiang Estuary is larger than that of the whole world, showing a canine shape. Compared with other historical thermal events, it is found that global change is directly related to the Industrial Revolution.

Aridity record of the Arabian Peninsula for the last 200 kyr: Environmental magnetic evidence from the western equatorial Indian ocean

The evolution of aridity and its forcing mechanisms in the Arabian Peninsula are of significance for better understanding the environmental response of the region to global change and the impact of past climate shifts in human evolution. Paleoclimatic reconstructions for the region are predominantly derived from fragmentary terrestrial records. Here, we present a detailed environmental magnetic record for marine sediments from the western equatorial Indian Ocean, which constitute the terminal sink for eolian material originated from the Arabian Peninsula. The dominant magnetic minerals identified in the studied sediments include magnetite, maghemite, and hematite. The hard isothermal remanent magnetization (HIRM), widely used as a proxy for the abundances of the high coercivity mineral hematite, has been used to track variations in the concentration of Arabian dust over the last 200 kyr. Dust concentrations are lowest during interglacial periods of maximum boreal summer isolation, and coincide with intervals during which lake and fluvial systems developed and speleothems formed across most of southern and central Arabia. Our results point to a sharp decrease in the production of dust due to the expansion of vegetation cover up to 30°N during these periods. West African Monsoon appears to be the major source of increased rainfall across Arabia, while the Indian Summer monsoon likely contributed to enhance rainfall in the south and southeastern parts of the peninsula. Variation in the supply of Arabian dust were also driven by changes in high-latitude ice volume and atmospheric CO2, as indicated by highest dust concentration found during glacial periods. We interpret that the expansion of high-latitude ice sheets increased the global meridional temperature gradient, weakened the monsoon system, and resulted in a more southerly, colder and descending subtropical westerly jet, leading to the retreat of vegetation cover and the enhanced production of dust from the Arabian deserts. Our results highlight a link between the production of Arabian dust and orbital-scale climate variability, including both monsoon and northern hemisphere ice sheets dynamics.