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Stellar rotation at early ages plays a crucial role in the survival of primordial atmospheres around Earth-mass exoplanets. Earth-like planets orbiting fast-rotating stars may undergo complete photoevaporation within the first few hundred Myr driven by the enhanced stellar XUV [X-rays and extreme ultraviolet (EUV)] radiation, while planets orbiting slow-rotating stars are expected to experience difficulty in losing their primordial envelopes. Besides the action of stellar radiation, stellar winds induce additional erosion on these primordial atmospheres, altering their morphology, extent, and causing supplementary atmospheric losses. In this paper, we study the impact of activity-dependent stellar winds on primordial atmospheres to evaluate the extent to which the action of these winds can be significant in the whole planetary evolution at early evolutionary stages. We performed 3D magnetohydrodynamical (MHD) simulations of the interaction of photoevaporating atmospheres around unmagnetized Earth-mass planets in the time span between 50 and 500 Myr, analysing the joint evolution of stellar winds and atmospheres for both fast- and slow-rotating stars. Our results reveal substantial changes in the evolution of primordial atmospheres when influenced by fast-rotating stars, with a significant reduction in extent at early ages. In contrast, atmospheres embedded in the stellar winds from slow-rotating stars remain largely unaltered. The interaction of the magnetized stellar winds with the ionized upper atmospheres of these planets allows us to evaluate the formation and evolution of different MHD structures, such as double bow shocks and induced magnetospheres. This work will shed light on the first evolutionary stages of Earth-like exoplanets, which are of crucial relevance in terms of planet habitability. [ABSTRACT FROM AUTHOR]

The Early‐Middle Jurassic is one of the crucial coal‐forming geologic periods in the world and an important target for hydrocarbon exploration in the Turpan‐Hami Basin, China. The paleoenvironment and vegetation reconstruction of the Early‐Middle Jurassic have been investigated using elemental geochemistry and palynological analysis to reveal paleoclimate evolution. A total of 48 genera of pteridophyte spore and 35 genera of gymnosperm pollen were identified, and 5 palynological assemblages were longitudinally divided, which showed significant differences in geochemical behaviours. The paleoenvironment was a transition from suboxidation to anoxia and then to an oxidation environment under freshwater conditions. The paleowater in the northern Taibei Sag was deeper than that in the southern part during the Middle Jurassic, which coincided with the sedimentary background of the sublacustrine fan in the north and the shallow braided river delta in the south. The paleovegetation evolved from mixed lowland–upland forest in the Hettangian‐Toarcian, to lowland fern forest in the Aalenian‐Bajocian, to upland conifers forest in the early Bathonian, to upland Cheirolepidiaceae forest in the late Bathonian‐Callovian. The Toarcian and Bathonian‐Callovian arid climate and the Hettangian‐Pliensbachian and Aalenian‐Bajocian warm‐humid climate were responses to the continued global warming events and the intensification of the East Asian monsoon circulation, respectively. The influence of the Bathonian‐Callovian aridification event on the sedimentary response in the southern Taibei Sag will be delayed due to the gradual southward migration of the depositional centre. [ABSTRACT FROM AUTHOR]

The Carbonate Compensation Depth (CCD) refers to the depth within the ocean where the production and dissolution rates of carbonates reach equilibrium, widely likened to the oceanic calcareous 'snowline'. The reconstruction of deep-time CCD has significant implications for understanding ocean circulation, seawater chemical conditions, sediment distribution, and the surface carbon cycle. This paper critically reviews the methods for CCD reconstruction, summarizes the driving mechanisms of the Cenozoic CCD evolution and its association with the carbon cycle, and offers insights into future directions for CCD research. CCD reconstruction has evolved over the past half century from early qualitative to quantitative methods. These methodological improvements have markedly improved the accuracy and resolution of CCD. Existing studies have indicated a general trend of the CCD deepening across major ocean basins since the Cenozoic, interspersed with a minor shallowing phase during the mid-Miocene. The variations in the CCD are primarily influenced by factors such as ocean productivity, weathering, and shelf-basin partitioning. During climate events such as the Paleocene-Eocene Thermal Maximum, the CCD exhibits pulselike fluctuations. Future research should focus on precision and quantification while integrating model simulations to further explore the correlations and response mechanisms between the CCD and the paleoclimate as well as the carbon cycle. [ABSTRACT FROM AUTHOR]

The northern Tibetan Plateau is a climatically sensitive zone influenced by monsoon and westerly winds. In summer, water vapor transport can reach Qinghai Lake and the eastern section of the Qilian Mountains; in winter, westerly winds mainly control the climate. This article compares the wet/dry changes in the region during the mid-Holocene (MH) warm period, the medieval climate anomaly (MCA), the current warm period (CWP), and the future warm period from the perspective of paleoclimate. We found that the MH warm period was mainly affected by the orbit-controlled East Asian summer monsoon, and the region showed warm and humid climate characteristics. The MCA was mainly controlled by solar radiation, and there was a warm and dry phenomenon. The CWP and the future warm period are mainly controlled by the rise in temperature caused by the increase in greenhouse gases, and the climate is becoming more arid. The wet/dry patterns in the CWP and the future warm period in the next century on the northern Tibetan Plateau are similar to those in the MCA. Continued warming will lead to the expansion of the westerly belt and a gradually humid climate. The future wet/dry changes will be more similar to the MH warm period. [ABSTRACT FROM AUTHOR]

To understand the role of the East Asian summer monsoon (EASM) and the East Asian winter monsoon (EAWM) on the hydroclimate in northern Taiwan, a multiproxy study has been conducted. This study aims to achieve its goal by using micro-XRF data of Ti and sulfur (S), carbon isotopic compositions (δ13C) along with elemental concentrations of carbon (C), nitrogen (N) and S, and diatom analyses in the sediment core extracted from the Dream Lake (DL; 25°10′01.9″ N, 121°33′36.0″ E and elevation = 588 m above sea level), northern Taiwan. The radiocarbon dates revealed that the DL core covered the time interval from 4.5 to 0.4 cal kyr BP. The current records revealed wetter phases during 4.5–3.0 cal kyr BP, 2.0–1.7 cal kyr BP, and 1.0–0.4 cal kyr BP, characterized by the dominance of C3 plants in the DL catchment, increased runoff, and higher lake levels. Drier climates observed in the current study during 3.0–2.0 cal kyr BP and 1.7–1.0 cal kyr BP, marked by a reduction in C3 plants, decreased runoff, and lower lake levels. The northern Taiwan climate during the late Holocene was observed to be regulated by the interplay of EASM and EAWM. The wet climate conditions during 4.5–3.0 were due to the La Niña-like conditions, which led to a strong EASM resulting in high precipitation conditions. The dry climate conditions during 3.0–2.0 cal kyr BP have coincided with El Niño-like conditions during 3.0–2.4 cal kyr BP and a subsequently strong EAWM during 2.4–2.0 cal kyr BP. Both situations led to a reduction in precipitation in the region. Unlike the time frame from 4.5 to 3.0 cal kyr BP, wet climate conditions during 2.0–1.7 and 1.0–0.4 cal kyr BP have coincided with weak EAWM conditions, which led to an increase in precipitation in northern Taiwan. The dry climate noticed between 1.7 and 1.0 cal kyr BP appeared to be the impact of both El Niño-like conditions and strong EAWM. [ABSTRACT FROM AUTHOR]

In order to cope with the complexity and variability of the terrestrial environment, amphibians have developed a wide range of reproductive and parental behaviors. Nest building occurs in some anuran species as parental care. Species of the Music frog genus Nidirana are known for their unique courtship behavior and mud nesting in several congeners. However, the evolution of these frogs and their nidification behavior has yet to be studied. With phylogenomic and phylogeographic analyses based on a wide sampling of the genus, we find that Nidirana originated from central-southwestern China and the nidification behavior initially evolved at ca 19.3 Ma but subsequently lost in several descendants. Further population genomic analyses suggest that the nidification species have an older diversification and colonization history, while N. adenopleura complex congeners that do not exhibit nidification behavior have experienced a recent rapid radiation. The presence and loss of the nidification behavior in the Music frogs may be associated with paleoclimatic factors such as temperature and precipitation. This study highlights the nidification behavior as a key evolutionary innovation that has contributed to the diversification of an amphibian group under past climate changes. The Music frogs are revealed to possess adaptative flexibility under climate changes. Mud nests evolved as a key innovation during perennial high temperatures and precipitations but lost in certain descendants when the weather got dryer and colder. [ABSTRACT FROM AUTHOR]

The sedimentary infill of the Quibas karstic site (Early Pleistocene, southern Spain) represents the only continuous succession with remains of continental vertebrates in Europe from pre-Jaramillo to post-Jaramillo age. The Quibas site, with a significant paleontological record, is dated between 1.1 and 0.9 Ma and offers a unique opportunity to carry out a paleoclimatic reconstruction of the time period immediately after the arrival of the first humans to western Europe. For this reason, defining the dominant sedimentary processes in the different stratigraphic units and the associated paleoenvironment is essential. The Quibas site is made up of two karstic features with two stratigraphic sequences: Quibas-Cueva, containing six lithostratigraphic units, and Quibas-Sima, which contains seven lithostratigraphic units. The detailed description and analyses of the stratigraphic sections have allowed the characterization of various autochthonous and allochthonous facies of cave deposits. Paleoclimatic proxies, inferred from sedimentological analyses, reveal a record of several alternating humid and arid phases resulting from the Early Pleistocene glacial-interglacial cycles, allowing correlation to the marine oxygen isotope record. The lowermost units (pre-Jaramillo) were deposited during a long-lasting interglacial, correlated to MIS 33–31. It was followed by an increase in aridity in the intermediate units of Quibas-Sima and uppermost unit of Quibas-Cueva (Jaramillo), revealing the beginning of a glacial period at the start of the Jaramillo subchron (1 Ma), which can be correlated to MIS 30. The upper Jaramillo and post-Jaramillo units suggest these were deposited in alternating periods of aridity and humid conditions, although less humid than the pre-Jaramillo period, probably representing the MIS 29 interglacial, the MIS 28 glacial and the MIS 27 interglacial. [ABSTRACT FROM AUTHOR]

Proxy-based paleoclimate reconstructions in the central Zagros region suggest the occurrence of several climatic events during the Last Glacial Maximum (LGM) to Holocene. The central Zagros region is situated in a unique transition zone between mid-latitude temperate climate in the north and sub-tropical arid climate in the south and was affected in different climatic periods by the strengthening and weakening of the Indian monsoons, the inter tropical convergence belt, the westerlies and the low-pressure systems of the Mediterranean and the Atlantic Ocean. Our results suggest that a transition occurred from dry and dusty conditions during the LGM to a relatively wetter period with higher carbon accumulation rates in the Early Holocene (11600 cal yr BP). Between 30000 and 19000 cal yr BP, cold and dry climatic conditions with the dominance of Amaranthaceae and semi-desert steppe prevailed in the region. High values of magnetic susceptibility, decrease in organic matter, and increase in allogenic elements indicate the presence of cold and dry climate in the region during the LGM. The Holocene was characterized by relatively less dry and dusty conditions, which is consistent with orbital changes in insolation that affected much of the northern hemisphere. Numerous episodes of high aeolian input spanning a few decades to millennia are prevalent during the Holocene. Dry events identified in the area occurred at 10200, 9200, 8200, 5200, 4200, 3200, 2200, and 1600 cal yr BP. Also Younger Dryas, occurred in the region 12300-11600 years ago, and it was cold and dry period with a decrease amount of pollen and increase in dust. [ABSTRACT FROM AUTHOR]

Documenting the seasonal temperature cycle constitutes an essential step toward mitigating risks associated with extreme weather events in a future warmer world. The mid-Piacenzian Warm Period (mPWP), 3.3 to 3.0 million years ago, featured global temperatures approximately 3°C above preindustrial levels. It represents an ideal period for directed paleoclimate reconstructions equivalent to model projections for 2100 under moderate Shared Socioeconomic Pathway SSP2-4.5. Here, seasonal clumped isotope analyses of fossil mollusk shells from the North Sea are presented to test Pliocene Model Intercomparison Project 2 outcomes. Joint data and model evidence reveals enhanced summer warming (+4.3° ± 1.0°C) compared to winter (+2.5° ± 1.5°C) during the mPWP, equivalent to SSP2-4.5 outcomes for future climate. We show that Arctic amplification of global warming weakens mid-latitude summer circulation while intensifying seasonal contrast in temperature and precipitation, leading to an increased risk of summer heat waves and other extreme weather events in Europe's future. [ABSTRACT FROM AUTHOR]

CO2 absorbs and emits radiation, which allows it to act both as radiative forcing and feedback. Recent work has shown CO2's feedback effect becomes dominant in hothouse climates, giving rise to a non‐monotonic climate sensitivity around 310 K. However, CO2's feedback effect in colder climates is less clear. We use a line‐by‐line model to explore the CO2‐dependence of the longwave clear‐sky feedback and identify a dividing temperature. Above 290 K, feedback increases with CO2 concentration; below 290 K, feedback decreases with CO2 concentration. We explain this dependence in terms of spectral competition under CO2 increases. In hot climates, CO2's moderate feedback replaces near‐zero feedback from the H2O bands; in cold climates, CO2's moderate feedback replaces the large feedback from the surface. Given that global mean temperature is currently close to 290 K, our results suggest that feedback CO2‐dependence is weak at present but can be important in past and future climates. Plain Language Summary: CO2 traps heat, causing warming. But CO2 also emits heat to space, acting as radiative feedback. Recent work has shown CO2's feedback effect crucially helps to stabilize very hot climates, but how does it affect present‐day Earth? We show that in hot climates, more CO2 increases Earth's feedback, while in cold climates, more CO2 decreases it. To understand why, we explain that the surface is an effective emitter, CO2 is a moderate emitter, while H2O is a poor emitter. At high temperatures, adding CO2 to the atmosphere thus replaces feedback that would have otherwise come from H2O, increasing the overall feedback; at low temperatures, adding CO2 replaces feedback that would have otherwise come from the surface, decreasing the overall feedback. Currently, Earth's global‐mean temperature falls between these two temperature regimes, where CO2's effect on feedback is nearly zero. Our results explain why CO2's impact on feedback is small now but can be significant in past or future climates. Key Points: An increase in CO2 concentration strengthens Earth's feedback in hot climates, ∂λ/∂CO2 > 0, but weakens it in colder climates, ∂λ/∂CO2 < 0Whether feedback CO2‐dependence, ∂λ/∂CO2, is positive or negative primarily depends on the extent of the H2O windowFeedback CO2‐dependence and forcing temperature‐dependence, ∂λ/∂CO2 = −∂F2x/∂Ts, can be important for past or future climates [ABSTRACT FROM AUTHOR]

Context. Out of the more than 5000 detected exoplanets, a considerable number belong to a category called "mini-Neptunes". Interior models of these planets suggest that they have primordial H–He-dominated atmospheres. As this type of planet is not found in the Solar System, understanding their formation is a key challenge in planet formation theory. Unfortunately, quantifying how much H–He planets have, based on their observed mass and radius, is impossible due to the degeneracy of interior models. Aims. Another approach to estimating the range of possible primordial envelope masses is to use formation theory. As different assumptions in planet formation can heavily influence the nebular gas accretion rate of small planets, it is unclear how large the envelope of a protoplanet should be. We explore the effects that different assumptions regarding planet formation have on the nebular gas accretion rate, particularly by exploring the way in which solid material interacts with the envelope. This allows us to estimate the range of possible post-formation primordial envelopes. Thereby, we demonstrate the impact of envelope enrichment on the initial primordial envelope, which can be used in evolution models. Methods. We applied formation models that include different solid accretion rate prescriptions. Our assumption is that mini-Neptunes form beyond the ice line and migrate inward after formation; thus, we formed planets in situ at 3 and 5 au. We considered that the envelope can be enriched by the accreted solids in the form of water. We studied how different assumptions and parameters influence the ratio between the planet's total mass and the fraction of primordial gas. Results. The primordial envelope fractions for low- and intermediate-mass planets (total mass below 15 M⊕) can range from 0.1% to 50%. Envelope enrichment can lead to higher primordial mass fractions. We find that the solid accretion rate timescale has the largest influence on the primordial envelope size. Conclusions. Rates of primordial gas accretion onto small planets can span many orders of magnitude. Planet formation models need to use a self-consistent gas accretion prescription. [ABSTRACT FROM AUTHOR]

Among the global monsoon systems, the Asian summer monsoon (ASM) reaches the furthest north into eastern Asia and separates it into the monsoon- and westerlies-dominated regions. Paleoclimate studies revealed different hydroclimate patterns between the monsoon- and westerlies-dominated regions at glacial-interglacial and centennial timescales. The monsoon-westerlies boundaries are difficult to be quantified with the instrumental data. Herein, a monsoon-westerlies dipole pattern was identified by empirical orthogonal function (EOF) analysis of the Palmer Drought Severity Index (PDSI) for the 1900–2018 period on interdecadal timescales. This dipole pattern showed significant correlations with variations of the monsoon-related western Pacific sea surface temperature (SST) and the westerlies-related North Atlantic Oscillation (NAO). We then reconstructed the dipole pattern back to 1511 by tree rings, which was consistent with the reconstructed NAO at interdecadal timescale. Our reconstruction revealed long-term changes of monsoon-westerlies boundaries and provided evidence of their linkages with the NAO. Apart from anthropogenic forcing, climate internal variability also play a critical role in modulations of the dipole mode between ASM and westerlies at interdecadal timescale. [ABSTRACT FROM AUTHOR]

Quantitative investigations of ancient rivers usually provide insights into either instantaneous or mean flow conditions. There is a critical gap between these time scales of investigation, which reflects the intermittency of flow and sediment transport, and closing this gap is crucial to fully explore the dynamics and evolution of ancient fluvial landscapes. Here, we combined fluvial stratigraphic data sets, flow and sediment transport models, and paleoclimate general circulation model (GCM) results to develop new methods to estimate intermittency in the geological past, specifically flow intermittency factors (Iw) and sediment transport intermittency factors (Is), and we show how they can be used to explore past hydrograph shapes. We illustrated these methods using the Upper Cretaceous Last Chance Ferron Sandstone in Utah, western United States. For sand-transporting flow conditions in Last Chance Ferron rivers, we estimated Iw values of 0.54-0.90, which imply that channel-forming conditions were sustained for the majority of the year, consistent with perennial systems in which relatively large discharges were sustained. In contrast, for gravel-transporting flow conditions, Iw values of 0.28-0.38 suggest that the largest formative flows may have occupied Last Chance Ferron rivers for nearly a third of the year, which could be explained by a monsoonal system in which high-magnitude discharge events were sustained, or a subtropical system in which high-magnitude discharge events had short durations but high frequencies. Meanwhile, Is values of 0.075-0.15 suggest that annual sediment budgets could have been transported in as little as 10 days and up to 2 months, if channel-forming conditions were sustained, and these values highlight that small changes in the duration of channelforming conditions could significantly impact sediment budgets. Our results are consistent with independent facies- and proxy-based insights into Last Chance Ferron rivers, which point to a perennially wet system characterized by a monsoonal or subtropical discharge regime. Further, our results highlight new opportunities to use paleoclimate GCMs to constrain intermittency factors in the geological past. Going forward, paleoclimate GCMs will be particularly useful where the rock record is incomplete or inaccessible, or where stratigraphic approaches are limited, and they will enable us to tackle pertinent research questions pertaining to past surface processes on both Earth and other planets. [ABSTRACT FROM AUTHOR]

Siliciclastic muds (clay-and silt-sized sediment) concentrate physical and chemical weathering products. However, both rock composition and climate can affect the mineralogy and geochemistry of these sediments. We quantitatively assessed the influence of provenance and climate on muds collected from end-member climates to test, which, if any, of these potential weathering signatures are indicative of climate in finegrained, fluvial sediments. Granulometry, mineralogy, and geochemistry of the studied muds indicated that provenance and mineral sorting hinder interpretation of (paleo)climate signals. These issues also affect chemical index of alteration (CIA) values, as well as mafic-felsic-weathering (MFW), Al2O3-(CaO* + Na2O)-K2O (A-CN-K), and Al2O3-(CaO* + Na2O + K2O)-(FeOT + MgO) (ACNK-FM) ternary plots, decreasing their utility as paleoclimate proxies. CaO content is heavily weighted within the calculations, resulting in even felsic-sourced sediment commonly plotting as mafic owing to the relative enrichment in CaO from preferential sorting of Ca-rich minerals into the mudsized fraction during transport. These results cast doubt on the indiscriminate use of CIA values and ternary plots for interpreting chemical weathering and paleoclimate within muds, particularly from glacial systems. Most notably, the positive correlations between CIA and climatic parameters (mean annual temperature and mean annual precipitation) diminished when sediments that had formed in nonglacial settings were filtered out from the data sets. This implies that CIA may only be applicable when used in nonglacial systems in which the composition of the primary source material is well constrained-such as soil/paleosol profiles. Within this end-member climate data set, CIA was only useful in discriminating hothumid climates. [ABSTRACT FROM AUTHOR]

Reconstructing Pleistocene glaciation timing and extent is vital for understanding paleoclimate. Whereas late Pleistocene glaciation has been studied extensively in western North American mountain ranges, the glacial history of the western Elk Range in Colorado remains understudied, particularly in the East River watershed, a site of intense scientific focus. Here we use cosmogenic nuclide exposure and depth–profile dating methods to determine the timing of glaciation in the East River watershed. We use glacier modeling to reconstruct paleoglacier extents and quantify past climate conditions. Our findings indicate that the East River glacier retreated from its maximum position approximately 17–18 ka, moving to recessional positions between 13 and 15 ka, before experiencing more substantial retreat to high-elevation cirques around 13 ka. Glacier modeling suggests that the maximum ice extents at 17–18 ka could have been sustained by temperature depressions of approximately −6.5°C compared to modern conditions, assuming consistent precipitation. Additionally, the ice position at 13–15 ka could have been supported by temperature depressions of around −4.0°C. These results offer insights into the deglaciation timeline in the East River watershed and broader western Elk Range as well as paleoclimate conditions during the late Pleistocene, which may aid future research on critical zone evolution in the East River watershed. [ABSTRACT FROM AUTHOR]

High‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce seasonally resolved climate records from subarctic‐Canada using micron‐scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods—Marine Isotope Stages (MIS) 11, 9, and 5e. We find 3‰ lower δ18O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ18O and suggest low MIS 11 δ18O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. Our study highlights the potential for high‐latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them. Plain Language Summary: Few climate records pre‐dating the last ice age exist from high‐latitude North America, which inhibits our understanding of how regions with permafrost responded to past warming and how they might change in the future. Here, we help fill this data gap by using six speleothems (cave mineral deposits) from a cave in the Northwest Territories, Canada to produce climate records that span thousands of years during former warm periods of Earth's history. We find that speleothems that grew during an exceptionally warm super‐interglacial period 400,000 years ago have 3‰ lower oxygen isotope (δ18O) values compared to those that grew during a likely cooler interglacial 125,000 years ago. We explore potential explanations for the difference in δ18O across interglacials, and suggest that lower δ18O values during warmer periods reflect greater infiltration of cool‐season precipitation with longer annual ground thaw durations. This study highlights the importance of high‐latitude speleothems to provide detailed climate records beyond the range available from Greenland ice cores. Key Points: Long high‐latitude terrestrial climate records are rare in the Northern HemisphereHigh‐latitude speleothems can provide ultra‐high‐resolution climate records beyond the reach of Greenland ice coresMean oxygen isotopes of Arctic and subarctic speleothems likely are controlled by annual ground thaw durations [ABSTRACT FROM AUTHOR]

Semi-subterranean house occupation in the southern Columbia Plateau of Western North America was episodic over the latter half of the Holocene. Several analyses of radiocarbon chronologies for house features have emphasized environmental change as a primary catalyst of shifts in subsistence strategies and house settlement. Our analysis incorporates summed probability distributions of radiocarbon dates for house occupations, climatic conditions, and evidence of conflict to assess the relationship among the three variables. Climate change is outlined using previously published proxy data. Results of our analysis indicate that climate had a strong influence on the settlement systems of the southern Columbia Plateau. Along with the direct influence of climate on resource availability, conflict became more frequent when house communities became larger. Developing a greater understanding of the cause and effect, and timing of environmental and social changes will ultimately require more robust datasets for house occupations, simulations of demographic trajectories, and higher resolution temporal and spatial models of climate change on the Columbia Plateau. [ABSTRACT FROM AUTHOR]

Climate field reconstruction (CFR) refers to the estimation of spatiotemporal climate fields (such as surface temperature) from a collection of pointwise paleoclimate proxy datasets. Such reconstructions can provide rich information on climate dynamics and provide an out-of-sample validation of climate models. However, most CFR workflows are complex and time-consuming, as they involve (i) preprocessing of the proxy records, climate model simulations, and instrumental observations; (ii) application of one or more statistical methods; and (iii) analysis and visualization of the reconstruction results. Historically, this process has lacked transparency and accessibility, limiting reproducibility and experimentation by non-specialists. This article presents an open-source and object-oriented Python package called cfr that aims to make CFR workflows easy to understand and conduct, saving climatologists from technical details and facilitating efficient and reproducible research. cfr provides user-friendly utilities for common CFR tasks such as proxy and climate data analysis and visualization, proxy system modeling, and modularized workflows for multiple reconstruction methods, enabling methodological intercomparisons within the same framework. The package is supported with extensive documentation of the application programming interface (API) and a growing number of tutorial notebooks illustrating its usage. As an example, we present two cfr-driven reconstruction experiments using the PAGES 2k temperature database applying the last millennium reanalysis (LMR) paleoclimate data assimilation (PDA) framework and the graphical expectation–maximization (GraphEM) algorithm, respectively. [ABSTRACT FROM AUTHOR]

Summary: C4 photosynthesis is a key innovation in land plant evolution, but its immediate effects on population demography are unclear. We explore the early impact of the C4 trait on the trajectories of C4 and non‐C4 populations of the grass Alloteropsis semialata.We combine niche models projected into paleoclimate layers for the last 5 million years with demographic models based on genomic data.The initial split between C4 and non‐C4 populations was followed by a larger expansion of the ancestral C4 population, and further diversification led to the unparalleled expansion of descendant C4 populations. Overall, C4 populations spread over three continents and achieved the highest population growth, in agreement with a broader climatic niche that rendered a large potential range over time. The C4 populations that remained in the region of origin, however, experienced lower population growth, rather consistent with local geographic constraints. Moreover, the posterior transfer of some C4‐related characters to non‐C4 counterparts might have facilitated the recent expansion of non‐C4 populations in the region of origin.Altogether, our findings support that C4 photosynthesis provided an immediate demographic advantage to A. semialata populations, but its effect might be masked by geographic contingencies. [ABSTRACT FROM AUTHOR]

Using the climate model CLIMBER-X, we present an efficient method for assimilating the temporal evolution of surface temperatures for the last deglaciation covering the period 22000 to 6500 years before the present. The data assimilation methodology combines the data and the underlying dynamical principles governing the climate system to provide a state estimate of the system, which is better than that which could be obtained using just the data or the model alone. In applying an ensemble Kalman filter approach, we make use of the advances in the parallel data assimilation framework (PDAF), which provides parallel data assimilation functionality with a relatively small increase in computation time. We find that the data assimilation solution depends strongly on the background evolution of the decaying ice sheets rather than the assimilated temperatures. Two different ice sheet reconstructions result in a different deglacial meltwater history, affecting the large-scale ocean circulation and, consequently, the surface temperature. We find that the influence of data assimilation is more pronounced on regional scales than on the global mean. In particular, data assimilation has a stronger effect during millennial warming and cooling phases, such as the Bølling-Allerød and Younger Dryas, especially at high latitudes with heterogeneous temperature patterns. Our approach is a step toward a comprehensive paleo-reanalysis on multi-millennial time scales, including incorporating available paleoclimate data and accounting for their uncertainties in representing regional climates. [ABSTRACT FROM AUTHOR]

The Huangling region is located in the central part of the Chinese Loess Plateau, which is sensitive to climate change due to the transitional characteristics of the natural environmental zone in which it is located. In this study, we utilized a spore–pollen analysis of the Tianjiahe (TJH) profile in Huangling to apply the pollen–climate factor conversion function method. This approach allowed us to quantitatively reconstruct the paleotemperature and paleoprecipitation of the Huangling area during the Middle and Late Holocene. The results show that the Huangling area experienced four climatic stages during the Middle and Late Holocene, including mild and slightly humid → warm and humid → warm and slightly humid → warm and humid. Except for the period of 5.3–4.72 kaBP, during which the climate was relatively cool and dry compared to the present, the climate in the remaining period (4.72–0.03 kaBP) was warmer and more humid than that of the present. The above results provide an important insight for further exploring the mechanism of paleoclimate change and predicting future climate change. [ABSTRACT FROM AUTHOR]

Central Asia (CA) is one of the world's most significant arid regions, which is markedly impacted by global warming. A better understanding of the dynamical processes governing its Holocene climate variability is critical for a better understanding of possible future impacts of climate change in the region. To date, most of the existing CA paleoclimate records are from the summer precipitation-dominated eastern CA (ECA), with few records from the winter precipitation-dominated western CA (WCA). Here, we present a precisely dated (~6‰) and highly resolved (<4-y) record of hydroclimatic variations from the WCA covering the period between 7,774 and 656 y BP. Utilizing multiple proxies (δ18O, δ13C, and Sr/Ca) derived from a stalagmite from the Fergana Valley, Kyrgyzstan, we reveal a long-term drying trend in WCA, which is in contrast with the wetting trend in ECA. We propose that different responses of winter and summer westerly jets to seasonal solar insolation over the past 8,000 y may have resulted in an antiphased precipitation relationship between the WCA and ECA. Our data contain dominant quasiperiodicities of 1,400, 50 to 70, and 20 to 30 y, indicating close connections between the WCA climate and the North Atlantic. We further identified a series of droughts and pluvials on centennial-to-decadal timescales, which may have influenced regional societies and trans-Eurasian culture exchanges during historical and prehistorical times. [ABSTRACT FROM AUTHOR]

The soil water retention behavior of the loess–paleosol sequence has important significance for hydrology and paleoclimate. This report examines the soil–water retention curves and microstructures of the Luochuan loess–paleosol sequence, which has a thickness of around 43.7 m and includes the S0–L6 layers. The experimental results demonstrated that as burial depth increases, there is a significant change in the soil–water retention curve of loess–paleosol sequence. Simultaneously, the saturated volumetric water content and water loss rate gradually decrease, while the air entry value and residual water content increase. As a whole, the loess layer has a lower water-holding capacity than the adjacent paleosol layer. Accordingly, the microstructure of the loess–paleosol sequence changes considerably with the burial depth. The microstructure changes from overhead structure to matrix structure, the particle contact relationship changes from direct point contact to indirect surface contact, the degree of cementation changes from slight cementation to complete cementation, and the volumes of all pore types decrease. The results suggest that the loess layer deposited in cold and dry climate conditions can act as an aquifer, which is related to weak pedogenic weathering. In contrast, paleosol layers that were formed in warm, humid climates underwent significant pedogenic weathering and can behave as an aquiclude. Based on the previously mentioned results, the link between paleoclimate changes and the current hydrological system has been explored. This offers a theoretical foundation and guidance for future engineering and ecological construction operations, as well as water resources management in loess areas. [ABSTRACT FROM AUTHOR]

As prominent abrupt climatic events during the last deglaciation and the early Holocene, the Younger Dryas (YD) and the 8.2 ka events have been intensely discussed to reveal the relationship between their phases and intensities, and their underlying mechanisms based on massive marine and terrestrial archives. However, the related paleoclimate records with sufficient resolution and/or precise age constraints from the Southern Hemisphere, especially East Africa, are relatively sparse, hindering our comprehensive understanding about the phases of these two events. Here, we provide a precisely dated record of an aragonite-calcite stalagmite covering 11.3–13.5 ka BP from northwest Madagascar to unravel the arid conditions during the YD, in contrast to the pluvial conditions in the 8.2 ka event that has been evidenced before. Changes in austral summer precipitation related to the Intertropical Convergence Zone (ITCZ) have always been interpreted to be the primary means of controlling regional rainfall amounts and thus the δ18O variations in stalagmite. However, ITCZ's meridional migration alone is not enough to interpret the opposite hydroclimatic conditions during the YD and the 8.2 ka events in northwest Madagascar. The variation in convection intensity within the ITCZ combined with the rainfall dipole mode in East Africa, and the redistribution of the duration of the ITCZ's presence at different latitudes might be responsible for this phenomenon. In addition, sea surface temperature could play a nonnegligible role. [ABSTRACT FROM AUTHOR]

The presence of exceptionally old ice and relative ease of access make Antarctic blue-ice areas (BIAs) attractive paleoclimate archives. However, only a handful of BIAs, mostly situated in West Antarctica and along the Transantarctic Mountains, have been investigated for this purpose. Here, we present the age of surface ice from the Grove Mountains BIA in Princess Elizabeth Land, East Antarctica, determined by measuring 81 Kr in the trapped air. Two samples yield an average age of 143-29+33 kyr. Together with the reported terrestrial age of a chondrite, we conclude that the Grove Mountains BIA holds considerable potential for paleoclimate studies. [ABSTRACT FROM AUTHOR]

Subtle bedrock depressions called gnammas allow the water in ephemeral pools to maintain contact with bare rock, thus serving as natural rock‐weathering experiments. Following filling by precipitation, evaporation is often assumed to be the sole process of water loss from gnammas. We evaluated this assumption by monitoring evolving stable isotope compositions of gnamma waters hosted in granite of Colorado's Front Range. Surprisingly, we found that a significant fraction of the water was lost by seepage through the underlying bedrock. Seepage dominated, with only 10%–20% loss by evaporation. We propose a conceptual model of gnamma formation in which enhanced weathering of the bedrock beneath the gnamma increases the water holding capacity and permeability of the underlying rock that in turn promotes efficient water loss through seepage and further weathering of the surrounding rock. This model has implications for bare‐rock weathering and hence the evolution of landscapes over geologic timescales. Plain Language Summary: Rates and styles of rock weathering influence the evolution of soil, landforms, and climate over geologic timescales. Gnammas are depressions in solid bedrock that periodically fill with rainwater or snowmelt to form ephemeral pools that can provide critical but temporary water sources in arid, bare‐rock surface environments. In contrast to previous assumptions that gnamma water is lost solely by evaporation, our work shows that a significant fraction of the water can be lost by seepage into the underlying rock. These findings suggest a feedback between enhanced seepage into underlying bedrock and enhanced degradation of the surrounding rock that potentially explains the growth and persistence of these unique isolated ecosystems, and informs debates about the role of bare bedrock weathering in landscape evolution. Key Points: Water stable isotopes constrain the hydrologic evolution of gnammasGnammas lose water via seepage through the underlying bedrock, not only by evaporationSeepage may drive a feedback process that enhances bedrock weathering but limits gnamma size evolution [ABSTRACT FROM AUTHOR]

The evolutionary transition to powered flight remains controversial in bats, the only flying mammals. We applied aerodynamic modeling to reconstruct flight in the oldest complete fossil bat, the archaic Onychonycteris finneyi from the early Eocene of North America. Results indicate that Onychonycteris was capable of both gliding and powered flight either in a standard normodense aerial medium or in the hyperdense atmosphere that we estimate for the Eocene from two independent palaeogeochemical proxies. Aerodynamic continuity across a morphological gradient is further demonstrated by modeled intermediate forms with increasing aspect ratio (AR) produced by digital elongation based on chiropteran developmental data. Here a gliding performance gradient emerged of decreasing sink rate with increasing AR that eventually allowed applying available muscle power to achieve level flight using flapping, which is greatly facilitated in hyperdense air. This gradient strongly supports a gliding (trees-down) transition to powered flight in bats. Aerodynamic modeling based on the primitive, early Eocene bat Onychonycteris strongly supports a gliding transition to powered flight in mammals, which is facilitated under the hyperdense atmospheric conditions here inferred for the fossil age. [ABSTRACT FROM AUTHOR]

The surficial cycling of Mg is coupled with the global carbon cycle, a predominant control of Earth's climate. However, how Earth's surficial Mg cycle evolved with time has been elusive. Magnesium isotope signatures of seawater (d26Mgsw) track the surficial Mg cycle, which could provide crucial information on the carbon cycle in Earth's history. Here, we present a reconstruction of d26Mgsw evolution over the past 2 billion years using marine halite fluid inclusions and sedimentary dolostones. The data show that d26Mgsw decreased, with fluctuations, by about 1.4? from the Paleoproterozoic to the present time. Mass balance calculations based on this d26Mgsw record reveal a long-term decline in net dolostone burial (NDB) over the past 2 billion years, due to the decrease in dolomitization in the oceans and the increase in dolostone weathering on the continents. This underlines a previously underappreciated connection between the weathering-burial cycle of dolostone and the Earth's climate on geologic timescales. [ABSTRACT FROM AUTHOR]

The non-marine bivalve Ferganoconcha occurred widely in palaeolakes in the high-middle latitude of northern China, Siberia and Central Asia during the Early and Middle Jurassic and was an important member of these lacustrine ecosystems. The diagnostic features and phylogenetic position of Ferganoconcha are still under debate. Here, based on nearly one hundred of Ferganoconcha specimens from the lacustrine and fluvial facies of the Junggar Basin in northwestern China, it is clearly shown that its most important distinctive features are the thin and flatted to weakly inflated shell covered with wrinkled ornament and the ligament is well-developed. This kind of shell indicate that the Ferganoconcha is a weak suspension feeder, burrowing rapidly and living in fine-soft substrata of the 'low energy' environments. In addition, we conclude that the dispersal pattern of the Ferganoconcha generally followed the cool to temperate and humid paleoclimate zone in northern China during the Early to Middle Jurassic, making the genus a possible palaeclimatic indicator. [ABSTRACT FROM AUTHOR]

A speleothem collected from Palco Cave (Puerto Rico) spans the 8.2 ka event, a time interval associated with fluctuations of Atlantic Ocean circulation and possible drying in the Caribbean region. While stalagmite δ18O, δ13C, and Mg/Ca data do not show a sustained change in mean state over the 8.2 ka event, the proxies provide robust evidence for three abrupt fluctuations toward drier conditions in rapid succession, each lasting less than two decades, occurring at 8.20, 8.14, and 8.02 ka BP. A cave monitoring program at Palco Cave supports the interpretation of the speleothem proxy records. Because changes in the position of the Intertropical Convergence Zone (ITCZ) are directly coupled to sea-surface temperature variations in the North Atlantic, we hypothesize that cold events in the North Atlantic temporarily limited the northward migration of the ITCZ and tropical rain belt in boreal summer during these abrupt drying periods. The speleothem record suggests that the 8.2 ka event was associated with rapid rainfall fluctuations in the northern Caribbean followed by a comparably warm and wet phase after the 8.2 ka event. This enhanced variability during the transitional period of the deglaciation appears to be linked to a fast coupling between interacting oceanic and atmospheric processes. This involves, in particular, the Atlantic Meridional Overturning Circulation in modulating interhemispheric heat transport. [ABSTRACT FROM AUTHOR]

This study presents a methodological advancement in the field of clumped‐isotope (∆47) thermometry, specifically tailored for application to freshwater ostracods. The novel ostracod clumped isotope approach enables quantitative temperature and hydrological reconstruction in lacustrine records. The relationship between ∆47 and the temperature at which ostracod shell mineralized is determined by measuring ∆47 on different species grown under controlled temperatures, ranging from 4 ± 0.8 to 23 ± 0.5ºC. The excellent agreement between the presented ∆47 ostracod data and the monitored temperatures confirms that ∆47 can be applied to ostracod shells and that a vital effect is absent outside the uncertainty of measurements. Results are consistent with the carbonate clumped‐isotope unified calibration (Anderson et al., 2021, https://doi.org/10.1029/2020gl092069), therefore, an ostracod‐specific calibration is not needed. The ostracod clumped‐isotope thermometer represents a powerful tool for terrestrial paleoclimate studies all around the world, as lakes and ostracods are found in all climatic belts. Plain Language Summary: In the framework of global warming, the reconstruction of past climatic conditions is important to understand the future evolution of climate and its impact. Lake sediments can be used as archives to quantify these effects. This study presents a novel paleo‐thermometer based on the application of clumped‐isotope technique (i.e., measurement of the number of 13C–18O bonds in carbonate minerals that depends on the temperature of carbonate precipitation) on carbonatic microcrustacea, named ostracods that commonly live in lakes. By using ostracods that formed their shells at known temperatures, we demonstrate that they can be easily used to reconstruct water temperature and hydrological conditions (precipitation/evaporation). The ostracod clumped‐isotope thermometer represents a powerful tool for terrestrial paleoclimate studies around the world, as lakes and ostracods are located in all climatic belts. Key Points: ∆47—ostracod signal accurately records the shell calcification temperature∆47—ostracod signal is not affected by the so called "vital effect"The unified calibration of Anderson et al. (2021) can be used to convert the ∆47—ostracod signal into accurate temperatures [ABSTRACT FROM AUTHOR]

El Juyo is a Cantabrian Lower Magdalenian cave site located approximately 8 km west of the city of Santander. The excavations covered an area over 40 m2, and the stratified deposits reach 3.5 m thick, with an estimated duration of Magdalenian occupation of around 1,000 years. Here, we present the first study of the herpetofaunal assemblages from El Juyo and explore their significance in terms of quantitative palaeoclimatic and palaeoenvironmental reconstructions using different quantitative methods. The palaeoherpetofaunal assemblages documented at El Juyo have a much lower diversity than present day. All methods applied to these assemblages characterised the climate as colder (between −8.5 and −3.7°C) and dryer (between −415 and −344 mm) than today, whereas landscape reconstructions suggest humid open area together with a potentially good representation of woodland areas in the vicinity of the site. This indicates that the climate during the Dryas I was much colder and dryer than today, even if the proximity of the sea may have mitigated in some way the harshness of the climate in this area. Rainfall seasonality pattern changed between the coldest periods of the Dryas I and today from more abundant precipitation during summer to late fall and winter maximum. [ABSTRACT FROM AUTHOR]

The frequency and duration of Late-Holocene hydrologic extremes in northern Guatemala were investigated using multiple sedimentological and geochemical proxies preserved in a sediment core collected from Lake Petén Itzá. A general trend of increasing aridity in the Maya Lowlands during the past 2000 years was punctuated by several multidecadal- to centennial-scale drought events recorded in the Petén Itzá sediments. In particular, the period spanning the Maya Terminal Classic Period and the Medieval Climate Anomaly (MCA), between 800 and 1300 CE, was marked by several extreme droughts and included the driest conditions of the past 2000 years between 950 and 1100 CE. Similarities between our data and other existing regional paleoclimate records suggest regional drying events during this time may have been driven by a common mechanism. Specifically, comparisons between these records and tropical Atlantic sea surface temperatures (SSTs) suggest that the dry intervals may have been driven by a westward expansion of the North Atlantic Subtropical High pressure system. This period was unique in the general agreement between regional proxy records, which are otherwise notably heterogeneous during the Late-Holocene. During the Little Ice Age (LIA; 1400–1800 CE) mean precipitation at Petén Itzá was further reduced, and multidecadal drying events were recorded between 1500–1530, 1600–1640, and 1770–1800 CE. However, regional hydroclimatic coherency was weaker during the LIA, suggesting that additional climatic mechanisms played a more important role in local-scale hydrology during that time. [ABSTRACT FROM AUTHOR]

Databases of 3D paleoclimate model simulations are increasingly used within global biogeochemical models for the Phanerozoic Eon. This improves the accuracy of the surface processes within the biogeochemical models, but the approach is limited by the availability of large numbers of paleoclimate simulations at different pCO2 levels and for different continental configurations. In this paper we apply the Frame Interpolation for Large Motion (FILM) Deep Learning method to a set of paleoclimate model simulations to upscale their time resolution from one model run every ~25 million years to one model run every 1 million year (Myr). Testing the method on a 5 Myr time-resolution set of continental configurations confirms the accuracy of our approach when reconstructing intermediate frames from configurations separated by up to 40 Myrs. We then apply the method to upscale the paleoclimate datastructure in the SCION climate-biogeochemical model and demonstrate that upscaled outputs for global distributions of surface temperature and runoff follow a logical progression between the original keyframes. When updated to use the high-time-resolution climate datastructure, the SCION model predicts climate shifts that were not present in the original model outputs due to its previous use of wide-spaced datasets and simple linear interpolation. We conclude that a time resolution of ~10 Myr in paleoclimate simulations is likely sufficient for investigating the long-term carbon cycle, and that Deep Learning methods may be critical in attaining this time-resolution at a reasonable computational expense, as well as for developing new fully-continuous methods in which 3D continental processes--such as species distribution--are able to translate over a moving continental surface in deep time. Nonetheless, the efficacy of Deep Learning methods in interpolating runoff data, compared to that of paleogeography and temperature, is diminished by the heterogeneous distribution of runoff. Consequently, interpolated climates should be confirmed by running a paleoclimate model for any sound scientific conclusions. [ABSTRACT FROM AUTHOR]

The Wanakah Formation and Tidwell Member of the Morrison Formation record intervals of paedogenesis in the Paradox Basin and Central Colorado trough, western Colorado during the Middle-Late Jurassic. Detailed field description of paleosols and paedogenic carbonates at different stratigraphic horizons from three localities document four main pedotypes: vertisols, gleysols, oxisols, and protosols. Generally, gleysols reflect reducing conditions, protosols and oxisols reflect oxidizing conditions, and vertisols reflect fluctuations in oxidizing/reducing conditions (seasonality). Major elemental geochemical ratios in samples from these paleosols suggest variable redox conditions and a sub-humid to humid paleoclimate with seasonal precipitations during paleosol development. Estimated mean annual temperature based on elemental analyses of paleosol B in paleosols from Ribbon Trail and Escalante Canyon in western Colorado suggest mesic – thermic paleoclimate. Mean annual precipitation indicates sub-humid to humid regional palaeoclimatic conditions marked by seasonal precipitation. Clay mineralogy of these paleosols, determined by X-ray diffraction, shows the abundance of illite most likely formed from smectite alteration due to episodic wetting and drying. δ13C and δ18O isotope analyses of carbonate veins in these paleosols suggest that they formed recently from meteoric water and therefore are not considered for palaeoclimatic reconstructions. Mean annual temperature and mean annual precipitation estimates in the Wanakah Formation and Tidwell Member of the Morrison Formation provide new information on the local and regional palaeoclimatic and paleoenvironmental conditions during the Middle Jurassic in western Colorado as well as data for comparison with the Upper Morrison paleoclimate from northern and southern localities in the western United States. [ABSTRACT FROM AUTHOR]

Based on the spectral analysis results obtained for air temperature and ice cover on the East Siberian Sea shelf reconstructed for the past five thousand years, empirical forecast models have been constructed to record the "natural trend scenario" of these climatic parameters in the coming centuries. Based on the forecast construction results, the duration of the ice-free period, as well as the near-surface air temperature, will tend to increase in the future. The studies conducted make it possible to suggest the anthropogenic influence on the temperature and ice conditions in the studied region in the industrial period. Taking into account this factor, it can be assumed that the studied natural phenomena will have a higher rate than is indicated by the models. [ABSTRACT FROM AUTHOR]

Premise: Leaf epidermal cell morphology is closely tied to the evolutionary history of plants and their growth environments and is therefore of interest to many plant biologists. However, cell measurement can be time consuming and restrictive with current methods. CuticleTrace is a suite of Fiji and R‐based functions that streamlines and automates the segmentation and measurement of epidermal pavement cells across a wide range of cell morphologies and image qualities. Methods and Results: We evaluated CuticleTrace‐generated measurements against those from alternate automated methods and expert and undergraduate hand tracings across a taxonomically diverse 50‐image data set of variable image qualities. We observed ~93% statistical agreement between CuticleTrace and expert hand‐traced measurements, outperforming alternate methods. Conclusions: CuticleTrace is a broadly applicable, modular, and customizable tool that integrates data visualization and cell shape measurement with image segmentation, lowering the barrier to high‐throughput studies of epidermal morphology by vastly decreasing the labor investment required to generate high‐quality cell shape data sets. [ABSTRACT FROM AUTHOR]

Climate (in)stability can manifest in the size of mollusks attesting to variable impacts on growth, seasonal exploitation, and cultural persistence. We present population statistics of the height of a bivalve species (Donax obesulus) collected from sites dating to the Early Horizon (EH, 900–200 BCE) in the Nepeña Valley and the Middle Horizon (MH, 600–1000 CE) in the Jequetepeque Valley of northern coastal Peru and compare them with a paleoclimate record and a sample of modern shells (collected in 2012, 2014, and 2016) from the Nepeña Valley. We observe diachronic variation in the size of D. obesulus with larger bivalves during the EH and smaller shells during the MH and in the modern sample. D. obesulus size remains relatively static during the MH at one site through two sub-phases. These bivalve populations were likely impacted by both climate and cultural circumstances. A proxy for runoff from El Niño related rainfall (%lithic flux) from a previously published nearby marine sediment core is elevated during the EH and Late Moche phase of the MH and correlates with shell height. During the Transitional phase of the MH and the modern interval, however, there are periods of comparatively reduced El Niño activity and shell height compared to the EH. [ABSTRACT FROM AUTHOR]

The Qiongdongnan Basin, located in the sea between Hainan Island and the Xisha Islands, is a faulted Cenozoic basin on the northern continental margin of the South China Sea. The Changchang Sag, situated in the eastern part of the central depressional zone in the deepwater area of the Qiongdongnan Basin, exhibits a near EW-striking morphology and represents an important potential target for oil/gas exploration. However, the age of the interface of the Lingshui Formation remains controversial, which hinders a comprehensive understanding of the tectonic evolution and hydrocarbon accumulation pattern in the Changchang Sag. This study focuses on well A, located in the depositional center of the Changchang Sag, and employs cyclostratigraphic analysis to identify cyclic signals of the Milankovitch cycles recorded in the sedimentary strata. Spectral analysis of natural gamma logging data from this well reveals the presence of 405 kyr long eccentricity cycles, 100 kyr short eccentricity cycles, 39.3 kyr obliquity cycles, and 20.58 kyr age precession cycles. By employing astronomical tuning, a "floating" astronomical time scale of the Lingshui Formation spanning 5.483 million years (Myr) is established. The top interface of the Oligocene in the International Geological Time Scale 2020 (GTS2020), with a geological age of 23.03 Ma, is used as the time anchor to establish a high-precision absolute astronomical age framework for the Lingshui Formation. The results indicate that the bottom interface of the first member of the Lingshui Formation is dated at 23.79 Ma, the bottom interface of the second member is dated at 25.08 Ma, and the bottom interface of the third member is dated at 28.51 Ma. Additionally, the average sedimentation rate during this period is estimated to be 9.261 cm/kyr. Furthermore, paleoclimate and paleoenvironmental reconstructions were carried out through quantitative analysis of spore and pollen assemblages, as well as foraminifera within the Lingshui Formation. These analyses suggest that the deposition of the Lingshui Formation occurred under warm and humid temperate climatic conditions. The results of paleoclimate proxy analysis and comparative fitting analysis of the astronomical time scale confirm that the climate evolution during this period was influenced by astronomical orbital forces, such as eccentricity and precession. [ABSTRACT FROM AUTHOR]

The Vedde Ash, originating from the Katla central volcano, Iceland, and taken to be dispersed across the North Atlantic and Europe at ~ 12 ka BP, is widely used as a geochronological marker. However, distal tephra layers with compositions like the Vedde Ash but of younger ages question the reliability of Vedde-like tephra layers as robust age control. Vedde-like tephra layers are rare in Icelandic sedimentary sequences and, where present, lack firm age control. Providing well-constrained local records of Early Holocene Katla layers is therefore critical to assess uncertainties related to the use of the Vedde Ash. Here we report three visible and stratigraphically separated Early Holocene Katla tephra layers from Torfdalsvatn, a lake in north Iceland, each with chemistry similar to the Vedde Ash. Using high-resolution 14C chronologies, we provide ages (± 1σ) for these tephra layers of 11,315 ± 180, 11,295 ± 195, and 11,170 ± 195 cal a BP. These observations reinforce that multiple explosive eruptions of Katla occurred over a 1000-year interval in the Early Holocene and challenge the precision of some paleoclimate records using the Vedde Ash as a geochronometer where age control is equivocal. This may lead to a re-evaluation of age models for some Early Holocene North Atlantic records. [ABSTRACT FROM AUTHOR]

For Paleoclimate data assimilation (PDA), a hybrid gain analog offline ensemble Kalman filter (HGAOEnKF) is proposed. It keeps the benefits of the analog offline ensemble Kalman filter (AOEnKF) that constructs analog ensembles from existing climate simulations with joint information of the proxies. The analog ensembles can provide more accurate prior ensemble mean and "flow‐dependent" error covariances than randomly sampled ensembles. HGAOEnKF further incorporates the benefits of static prior error covariances that better capture large‐scale error correlations and mitigate sampling errors than the sample prior error covariances, through a hybrid gain approach within an ensemble framework. Observing system simulation experiments are conducted for various data assimilation methods, using ensemble simulations from the Community Earth System Model‐Last Millennium Ensemble Project. Results show that using the static prior error covariances estimated from a sufficiently large sample set is beneficial for the traditional offline ensemble Kalman filter (OEnKF) and AOEnKF. HGAOEnKF method is superior to the OEnKF and AOEnKF with and without static prior error covariances, especially for the reconstruction of extreme events. The advantages of HGAOEnKF over OEnKF and AOEnKF with and without static prior error covariances are persistent with varying sample sizes and presence of model errors. Plain Language Summary: Paleoclimate data assimilation (PDA) combines information from the climate simulations and proxy data, aiming to provide an optimal estimate of past climates. The relatively low predictive skill of the climate model and the noisy and sparse paleoclimate proxies have imposed great challenges on PDA. Previous studies have shown that offline ensemble assimilation methods are much more computationally efficient than online ensemble assimilation ones, and the offline analog ensemble can also provide "flow‐dependent" prior error covariances. However, the sample prior error covariances estimated from an ensemble with limited members can be contaminated by sampling errors. Hybridization of the "flow‐dependent" prior error covariances with the static ones can remedy the sampling error, and also infuse better representation of large‐scale error correlations from the static ones. Thus a hybrid gain analog offline ensemble Kalman filter (EnKF) is proposed, which retains the advantages of the analog ensemble and further adapts the benefits of static prior error covariances. The hybrid gain analog offline EnKF is superior to the traditional offline EnKF and the offline EnKF with analog ensembles. Key Points: Static B using sufficiently large samples can better capture large‐scale error correlations and mitigate sampling errors than the sampled BHybrid gain analog offline ensemble Kalman filter (HGAOEnKF) uses the ensemble mean prior from the analog ensemble and hybrid gains combining the static B and "flow‐dependent" BHGAOEnKF has advantages over OEnKF and analog offline ensemble Kalman filter with varying sample sizes and presence of model errors, especially for extreme years [ABSTRACT FROM AUTHOR]

We report the discovery of two mini-Neptunes in near 2:1 resonance orbits (P = 7.610303 d for HIP 113103 b and P  = 14.245651 d for HIP 113103 c) around the adolescent K-star HIP 113103 (TIC 121490076). The planet system was first identified from the TESS mission, and was confirmed via additional photometric and spectroscopic observations, including a ∼17.5 h observation for the transits of both planets using ESA CHEOPS. We place ≤4.5 min and ≤2.5 min limits on the absence of transit timing variations over the 3 yr photometric baseline, allowing further constraints on the orbital eccentricities of the system beyond that available from the photometric transit duration alone. With a planetary radius of R p  =   |$1.829_{-0.067}^{+0.096}$| R⊕, HIP 113103 b resides within the radius gap, and this might provide invaluable information on the formation disparities between super-Earths and mini-Neptunes. Given the larger radius R p  =  |$2.40_{-0.08}^{+0.10}$| R⊕ for HIP 113103 c, and close proximity of both planets to HIP 113103, it is likely that HIP 113103 b might have lost (or is still losing) its primordial atmosphere. We therefore present simulated atmospheric transmission spectra of both planets using JWST, HST , and Twinkle. It demonstrates a potential metallicity difference (due to differences in their evolution) would be a challenge to detect if the atmospheres are in chemical equilibrium. As one of the brightest multi sub-Neptune planet systems suitable for atmosphere follow up, HIP 113103 b and HIP 113103 c could provide insight on planetary evolution for the sub-Neptune K-star population. [ABSTRACT FROM AUTHOR]

Understanding the future evolution of permafrost requires a better understanding of its climatological past. This requires permafrost models to efficiently simulate the thermal dynamics of permafrost over the past centuries to millennia, taking into account highly uncertain soil and snow properties. In this study, we present a computationally efficient numerical permafrost model which satisfactorily reproduces the current ground temperatures and active layer thicknesses of permafrost in the Arctic and their trends over recent centuries. The performed simulations provide insights into the evolution of permafrost since the 18th century and show that permafrost on the North American continent is subject to early degradation, while permafrost on the Eurasian continent is relatively stable over the investigated 300-year period. Permafrost warming since industrialization has occurred primarily in three "hotspot" regions in northeastern Canada, northern Alaska, and, to a lesser extent, western Siberia. We find that the extent of areas with a high probability (p3m>0.9) of near-surface permafrost (i.e., 3 m of permafrost within the upper 10 m of the subsurface) has declined substantially since the early 19th century, with loss accelerating during the last 50 years. Our simulations further indicate that short-term climate cooling due to large volcanic eruptions in the Northern Hemisphere in some cases favors permafrost aggradation within the uppermost 10 m of the ground, but the effect only lasts for a relatively short period of a few decades. Despite some limitations, e.g., with respect to the representation of vegetation, the presented model shows great potential for further investigation of the climatological past of permafrost, especially in conjunction with paleoclimate modeling. [ABSTRACT FROM AUTHOR]

The three leading modes of the North Atlantic atmospheric circulation explain about 70% of the winter climate variability. Although climate models generally can capture these modes, biases may induce large uncertainties in regional climate predictions. Here, we evaluate the leading winter modes simulated by CMIP5‐PMIP3 and CMIP6‐PMIP4 models from the last millennium to future scenarios in comparison with historical reanalysis and paleo‐reconstructions. The models generally have a good representation of the average spatial pattern of the North Atlantic Oscillation (NAO) while showing a larger spread in performance for the East Atlantic and Scandinavian patterns. In contrast to historical reanalysis, the simulated NAO pattern tends to be rather stationary under various climate states over the years 861–2100. Such underestimated spatial variability in the simulated NAO is directly related to the biased spatial shifts in NAO‐related regional temperature and precipitation changes, inducing uncertainties in climate projections over the North Atlantic sector. Plain Language Summary: The North Atlantic Oscillation (NAO) is the most dominant weather pattern over the North Atlantic‐European sector with profound influence on regional climate. The NAO pattern describes the changes in a low‐pressure system over Iceland and a high‐pressure system over the Azores, which are commonly known as the NAO centers of action. However, the NAO centers of action are not always fixed in these two locations, but show spatial movement over time. In this study, we compare the winter weather patterns over the North Atlantic region from the last millennium to future scenarios in climate models with reanalysis products and paleoclimate reconstructions. We find that models generally can capture the spatial structure of the NAO very well but with little changes in its location and shape over time in contrast to historical reanalysis. These biased NAO patterns in climate models can shift the modeled regional temperature and precipitation patterns associated with the NAO. This remains a challenge for the reliability of future climate projections over the North Atlantic region. Key Points: We compare the spatial variability of modeled North Atlantic climate modes over the years 861–2100 with reanalysis and reconstructed dataThe North Atlantic Oscillation (NAO) in 13 Coupled Model Intercomparison Project‐Paleoclimate Modelling Intercomparison Project models shows underestimated spatial variability compared to historical reanalysisProjections of regional temperature and precipitation may show biased patterns due to the underestimated spatial shifts in simulated NAO [ABSTRACT FROM AUTHOR]

Geological reservoir δ30Si values have increasingly been applied as paleoclimate and paleoproductivity proxies. Many of these applications rely on the assumption that the surface Earth Si isotope budget is in mass balance with bulk silicate Earth, such that trends in δ30Si over time can be attributed to changes in flux to or from key silica reservoirs. We compiled δ30Si data from modern reservoirs representing the major sources and sinks of surface Earth reactive silica, to which we applied an inverse model to test assumptions about mass balance. We found that δ30Si values of reverse weathering products must closely match those of diatoms, conflicting with previous assumptions. Model results also revealed that of the 19 to 21 teramoles per year Si released during silicate mineral weathering, ~10 to 18 teramoles per year is stored in terrestrial silica sinks, consistent with assumptions of incongruentweathering reactions. Our results demonstrated that the modern silica cycle summary is in isotopic mass balance. [ABSTRACT FROM AUTHOR]

Aptian is characterized by widespread deposition of organic-rich sediment. The Aptian bitumen limestone horizon, which is thin decimetre-thick sequences, locally crops out in the Kırcaova area, Eastern Black Sea Region (Eastern Pontides). They are well correlated with Aptian bitumen limestone in the other Tethys Reams. They are proposed as episodes of increased organic matter. However, background factors controlling organic matter enrichment are poorly known. In this study, we present new inorganic geochemistry, including trace elements, rare earth elements (REE), redox-sensitive elements (RSE), stable-isotopes (δ18O and δ13C), and total organic carbon (TOC). We integrated new geochemical data with existing stratigraphy, paleontology, and organic chemistry data to provide new insight into the depositional environment and paleoclimate conditions during Aptian. The lacustrine bitumen limestone (LBL) samples have varied δ13C (ave. -1.45‰) and δ18O (ave.-4.50‰). They possess distinct REE patterns, with an average of REE (ave. 14.45 ppm) and Y/Ho (ave. 35) ratios. In addition, they have variable Nd/YbN (0.28–0.81; ave. 0.56) and Ce/Ce* (0.68–0.97; ave. 0.86), and relatively high Eu*/Eu (1.23–1.53; ave. 1.35). They display seawater signatures with reduced oxygen conditions. The enrichment in RSE (Mo, Cu, Ni, and Zn) and the low Mo/TOC (0.70–3.69; ave. 2.41) support a certain degree of water restriction. The high Sr/Ba, Sr/Cu, Ga/Rb, and K/Al records of the LBL facies suggest hot house climatic conditions. The sedimentary environment was probably an isolated basin that is transformed from the marine basin. In addition to depositional conditions, the regional parameters such as the climate, increased run-off period, nutrient levels, alkalinity level, and dominant carbonate producers favored the enrichment in organic matter of LBL facies. Thus, extreme greenhouse palaeoclimate conditions have an important role in organic matter enrichment in the isolated basin. Our results are conformable with the published data from marine, semi-restricted basin, and lacustrine settings in the different parts of the Tethys margin. Thus, this approach provides the first insight into the Aptian greenhouse paleo-climate conditions of the Eastern Black Sea Region, NE Turkey. [ABSTRACT FROM AUTHOR]

For Upper Jurassic–Lower Cretaceous rocks of the Bazhenov Formation, a significant positive linear correlation of the content of Th, Hf, Sc, and La with the Al2O3 content was revealed, and their terrigenous genesis was confirmed. It has been determined that the samples, in which the distribution of Sc/Al2O3 and La/Al2O3 values does not satisfy the linear correlation, represent the mixed clayey–siliceous rocks (with P2O5 > 1 wt %) or the substantially pyritized rocks (with the pyrite content exceeding the OM content and C/S ≤ 1), as well as siliceous mudstones (with the SiO2 content > 70 wt %). It is concluded that, in addition to carbonatized rocks, rocks of the above-mentioned types, as well as rocks subjected to the late diagenetic kaolinization, should be excluded before analyzing the geochemical indicators for reconstructing the formation conditions of the Bazhenov Formation. The formation conditions of these rocks were reconstructed based on the analysis of values of several geochemical modules and indicators. Based on the study of CIA and CIW variations, it was confirmed that the Late Jurassic–Early Cretaceous climate in the West Siberian sedimentary basin was warm and semiarid, and it did not change significantly during the entire period under consideration. For rocks of the Bazhenov Formation, several indicators, such as (La/Yb)N and Eu/Eu*, as well as the distribution of trace elements in the Th‒La‒Sc triangular diagram, suggest that rocks of the Bazhenov Formation were deposited in the central and southeastern regions, with the dominant impact of source areas of mafic rocks. [ABSTRACT FROM AUTHOR]

Climate field reconstructions (CFRs) combine modern observational data with paleoclimatic proxies to estimate climate variables over spatiotemporal grids during time periods when widespread observations of climatic conditions do not exist. The Common Era (CE) has been a period over which many seasonally‐ and annually‐resolved CFRs have been produced on regional to global scales. CFRs over the CE were first produced in the 1970s using dendroclimatic records and linear regression‐based approaches. Since that time, many new CFRs have been produced using a wide range of proxy data sets and reconstruction techniques. We assess the early history of research on CFRs for the CE, which provides context for our review of advances in CFR research over the last two decades. We review efforts to derive gridded hydroclimatic CFRs over continental regions using networks of tree‐ring proxies. We subsequently explore work to produce hemispheric‐ and global‐scale CFRs of surface temperature using multi‐proxy data sets, before specifically reviewing recently‐developed data assimilation techniques and how they have been used to produce simultaneous reconstructions of multiple climatic fields globally. We then review efforts to develop standardized and digitized databases of proxy networks for use in CFR research, before concluding with some thoughts on important next steps for CFR development. Plain Language Summary: Few observational records of meteorological variables like surface temperature and precipitation extend beyond 100–150 years. The length of observational records is therefore insufficient for learning how climate varies over decades to centuries, or for estimating many climate extremes. In contrast, annually‐resolved climate proxies, such as tree rings, ice cores, and corals, when used in concert with observational records, can provide information on how climate conditions have changed over decades to millennia. These proxies are also abundant enough over the last two millennia to create reconstructions in both space and time, or maps of climate conditions at seasonal or annual intervals. These kinds of reconstructions are called climate field reconstructions (CFRs) and we review their scientific history back to the 1970s when they were first attempted. We survey the underlying methods that are used to derive these reconstructions and how they have been applied, with a specific focus on the last two decades when the number of CFRs has greatly increased. We conclude with a survey of the data networks that are being cultivated for CFRs and some reflections on how the science can move forward. Key Points: Reconstructions of climate fields are valuable paleoclimatic products that have been developed since the 1970sImportant similarities and differences exist across the approaches used to derive hydroclimate and temperature climate field reconstructions (CFRs) targeting the Common Era (CE)Controlled and systematic comparisons of CFRs should be a priority for the CE paleoclimate community [ABSTRACT FROM AUTHOR]

Using past episodes of climate change as a source of evidence to inform our projections about contemporary climate change requires establishing the extent to which episodes in the deep past are analogous to the current crisis. However, many scientists claim that contemporary rates of climate change (e.g., rates of carbon emissions or temperature change) are unprecedented, including compared to episodes in the deep past. If so, this would limit the utility of paleoclimate analogues. In this paper, I show how a data adjustment procedure called "temporal scaling," which must be applied to both contemporary and past rate data, complicates the claim that contemporary rates are truly unprecedented. On top of giving actionable recommendations to scientists, this paper advances the philosophical literature concerning the use of models that are known to be somewhat disanalogous to their target systems. [ABSTRACT FROM AUTHOR]

Sea‐ice extent is predicted to decrease in a warming climate. However, despite global warming over the past century, total Antarctic sea ice remained relatively stable from 1979 until 2015, before strongly melting. Here we explore the long‐term sea ice variability by reconstructing Antarctic sea ice since 1700 CE, based on paleoclimate records and data assimilation. Our results indicate a decline in southern hemisphere sea‐ice extent over the 20th century, driven by a reduction of 0.26 million km2 in the Weddell Sea that reached values at the end of the century lower than any other reconstructed period. The Ross Sea experienced an increasing sea‐ice cover trend due to a low‐pressure system located off the Amundsen Sea coast, offset by a decreasing trend in the Bellingshausen‐Amundsen Sea. Models failed to account for the Ross Sea increase, resulting in an overly uniform estimate of Antarctic sea ice loss over the 20th century. Plain Language Summary: Despite global warming, the Antarctic sea‐ice extent remained relatively constant over the satellite era until 2015 before a strong reduction. Numerous studies analyzed this intriguing behavior but no consensus emerged, mainly because of the shortness of observations. Here, we reconstruct the Antarctic sea‐ice over the past 300 years based on paleoclimate observations, in particular ice‐core records, combined with the physics of climate models using a so‐called data‐assimilation technique. We show that there has been a decline in the Antarctic sea‐ice extent during the 20th century. Specifically, the Atlantic sector displays a significant sea‐ice extent reduction, reaching its lowest level at the end of our reconstruction compared to the past three centuries. Our results indicate sea‐ice extent trends over the 20th century of variable signs in the Pacific sector, with a sea ice increase in western Pacific while a decrease is noticed in western Pacific. These heterogeneous spatial changes are mainly related to changes in the low‐pressure system located off the West Antarctic coasts. According to our analysis, climate models are not able to simulate the observed sea ice expansion in the eastern Pacific, leading to a too large and too homogenous Antarctic loss during the 20th century. Key Points: The Antarctic sea‐ice extent experienced a reduction over the 20th centuryThe sea‐ice extent in Weddell Sea reached its lowest level over the past 300 years at the end of the 20th centuryModels are unable to simulate the reconstructed sea ice increase in the Ross Sea, leading to an overestimation of the Antarctic sea ice loss [ABSTRACT FROM AUTHOR]