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Changes in the magnitude of millennial-scale climate variability (MCV) during the Late Pleistocene occur as a function of changing background climate state over tens of thousands of years, an indirect consequence of slowly varying incoming solar radiation associated with changes in Earth’s orbit. However, whether astronomical forcing can stimulate MCV directly (without a change in the background state) remains to be determined. Here we use a comprehensive fully coupled climate model to demonstrate that orbitally driven insolation changes alone can give rise to spontaneous millennial-scale climate oscillations under intermediate glacial conditions. Our results demonstrate that an abrupt transition from warm interstadial to cold stadial conditions can be triggered directly by a precession-controlled increase in low-latitude boreal summer insolation and/or an obliquity-controlled decrease in high-latitude mean annual insolation, by modulating North Atlantic low-latitude hydroclimate and/or high-latitude sea ice–ocean–atmosphere interactions, respectively. Furthermore, contrasting insolation effects over the tropical versus subpolar North Atlantic, exerted by obliquity or precession, result in an oscillatory climate regime, even within an otherwise stable climate. With additional sensitivity experiments under different glacial–interglacial climate backgrounds, we synthesize a coherent theoretical framework for climate stability, elaborating the direct and indirect (dual) control by Earth’s orbital cycles on millennial-scale climate variability during the Pleistocene.

Abundant evidence from marine, ice-core and terrestrial records demonstrates that Earth’s climate has experienced co-evolution of orbital- and millennial-scale variability through the Pleistocene. The varying magnitude of millennial climate variability (MCV) was linked to orbitally paced glacial cycles over the past 800 kyr. Before this interval, global glaciations were less pronounced but more frequent, yet scarcity of a long-term integration of high-resolution continental and marine records hampers our understanding of the evolution and dynamics of MCV before the mid-Pleistocene transition. Here we present a synthesis of four centennial-resolved elemental time series, which we interpret as proxies for MCV, from North Atlantic, Iberian margin, Balkan Peninsula (Lake Ohrid) and Chinese Loess Plateau. The proxy records reveal that MCV was pervasive and persistent over the mid-latitude Northern Hemisphere during the past 1.5 Myr. Our results suggest that the magnitude of MCV is not only strongly modulated by glacial boundary conditions on Earth after the mid-Pleistocene transition, but also persistently influenced by variations in precession and obliquity through the Pleistocene. The combination of these four proxies into a new MCV stack offers a credible reference for further assessing the dynamical interactions between orbital and millennial climate variability.

Application of X-ray fluorescence core-scanning (XRF-CS) on both marine and lake sediments has achieved remarkable results. However, its application has not been widely extended to the research on speleothems. In this study, we measure the Sr abundance and the Sr/Ca ratios of three stalagmites (two aragonite stalagmites, one calcite stalagmite) using the state-of-the-art fourth-generation Avaatech high-resolution XRF core scanner. Through comparisons among different scan paths and among different scan resolutions, as well as comparisons with inductively coupled plasma optical emission spectrometer (ICP-OES), Itrax XRF, and Artax XRF results, we confirm that the Avaatech XRF core scanner could precisely, quickly, and non-destructively analyze the high-resolution Sr abundance of speleothems. Furthermore, we combine the stalagmite δ18O records to explore the paleoclimatic significance of the measured stalagmite Sr/Ca.

Eolian dust is a major terrigenous component in North Pacific Ocean pelagic sediments and is an important recorder of Asian terrestrial environmental evolution and Northern Hemisphere atmospheric circulation. In order to extract and quantify wind‐borne mineral signals and develop a reliable eolian dust proxy for pelagic sediments, we investigated sediments from Ocean Drilling Program Hole 885A, North Pacific Ocean, by integrating results from environmental magnetism, transmission electron microscopy, and diffuse reflectance spectroscopy (DRS). Our results indicate that ferrimagnetic and antiferromagnetic minerals coexist in the sediments. The former includes biogenic magnetite, nano‐sized single domain (titano) magnetite inclusions embedded in silicate hosts, submicron vortex state magnetite, and ultrafine superparamagnetic maghemite. The latter includes hematite and goethite. Our results indicate that magnetic properties can be used to determine an overall trend of increased eolian dust inputs, with additional significant influence from biogenic and volcanogenic components. In contrast, a newly proposed parameter RelHm+Gt(combined hematite and goethite concentration) obtained from DRS measurements extracts precisely the eolian signal and precludes other components. Our DRS results indicate that hematite/goethite and siliceous fractions deposited at Hole 885A were jointly delivered to the North Pacific Ocean from Asian dust sources. Therefore, we suggest that RelHm+Gtis a reliable eolian dust proxy for pelagic sediments in this region. Ferrimagnetic and antiferromagnetic minerals were identified systematically in North Pacific Ocean pelagic sedimentsFerrimagnetic minerals record the overall trend of increased eolian dust inputs since the late PlioceneA parameter obtained from diffuse reflectance spectroscopy is proposed to trace eolian dust in pelagic sediments

The seasonal rainfall regime is a key factor control on local ecological and social processes and is commonly thought to be stable under long‐term climate changes. Here we present a unique high‐resolution rainfall record from the Thai‐Malay Peninsula, combined with a state‐of‐the‐art transient climate simulation, demonstrating a fundamental rainfall regime shift from summer to winter during the Holocene. Transient model simulation and new sensitivity experiments further reveal that westward migration of the boundary between summer and winter rainfall regimes results in a summer to winter rainfall regime shift forced by distinct changes in summer and winter monsoons. Our findings suggest that the seasonal rainfall regime could be unstable under climate change around the boundaries of rainfall regimes in the tropics and possibly worldwide, which might be more critical for shaping both past and future ecological environments. The observed seasonal rainfall regime, which varies over time, challenges the assumption of stable seasonal patterns in reconstructions of paleorainfall, suggesting that a reappraisal of the understanding of past ecological‐social changes with respect to rainfall may be needed. In this study, we have used a high‐resolution rainfall record from the Thai–Malay Peninsula and a state‐of‐the‐art transient paleoclimate simulation to describe a novel summer to winter rainfall regime shift during the Holocene era in the tropics, which may apply to regime‐boundary regions worldwide and thus provide a new perspective on dramatic ecological and social changes recorded around regime boundary regions for both past and future studies. A unique rainfall record in the Thai‐Malay and a transient simulation suggest a summer to winter rainfall regime shift during the HoloceneTransient paleoclimate simulation simulation reveals that this shift was caused by westward migration of the boundary between summer and winter rainfall regimesThis regime shift could occur in regions around the boundaries of rainfall regimes in the tropics and possibly worldwide A unique rainfall record in the Thai‐Malay and a transient simulation suggest a summer to winter rainfall regime shift during the Holocene Transient paleoclimate simulation simulation reveals that this shift was caused by westward migration of the boundary between summer and winter rainfall regimes This regime shift could occur in regions around the boundaries of rainfall regimes in the tropics and possibly worldwide

Orbitally modulated insolation is thought to be among the key mechanisms driving ice sheet change. Yet, late Pleistocene ice sheets attained maximum marginal extents prior to summer insolation minima, suggesting that additional mechanisms influenced ice growth and decay. Continuous orbital‐scale terrestrial temperature records can help define the role that temperature near ice sheet margins plays on the timing and structure of glacial maxima. We hypothesize, based on a 360 kyr long air temperature record from the Chinese Loess Plateau and shorter records from North America and Europe, that midlatitude terrestrial temperature influenced the rate of ice sheet growth prior to and during glacial maxima; cold conditions prior to glacial maxima enhanced ice sheet growth, while warming during glacial maxima inhibited further growth, despite low summer insolation. Thus, the midlatitude surface energy budget may be an important component of understanding and modeling ice volume, particularly for intervals prior to and during glacial maxima, when ice sheet margins reached midlatitudes. Orbital‐scale proxy and model land surface temperature respond directly to orbital forcingNorthern Hemisphere midlatitude land surface temperature influences ice sheet ablation rateBalance between insolation and land surface temperature causes ice sheet stability at glacial maxima

It is generally accepted that the glacial‐interglacial variations of the East Asian winter monsoon (EAWM) are controlled by the volume of the Northern Hemisphere ice sheets (NHIS), but the fact that they exhibit different evolution patterns during glacial inceptions is often overlooked. By generating an independent chronology framework and integrating multi‐proxy records from the loess sections on the central Chinese Loess Plateau, here we show that the rapid intensifying of the EAWM during glacial inceptions reflects millennial perturbations in the large‐scale atmospheric circulation in East Asia in response to insolation‐triggered abrupt North Atlantic cooling. This climate teleconnection between North Atlantic and East Asia is found to be particularly effective only when the NHIS reaches a critical large size. Our integrated multi‐proxy records thus highlight the key role of ice volume in modulating the response of the EAWM to insolation‐triggered North Atlantic cooling during the interglacial‐glacial transitions. The strength of the East Asian winter monsoon is thought to be dynamically linked to the volume of the Northern Hemisphere ice sheets during the Quaternary glacial‐interglacial cycles. Nevertheless, paleoclimatic records generally indicate a rapid shift in the East Asian winter monsoon intensity in the mid‐way of the gradual build‐up of the Northern Hemisphere ice sheets, meaning that our current understanding of the East Asian winter monsoon dynamics remains elusive. By generating an independent chronology framework and integrating multi‐proxy records from the loess sections on the central Chinese Loess Plateau, here we show that the rapid intensifying of the East Asian winter monsoon during glacial inceptions, previously demonstrated as a direct response to the build‐up of the Northern Hemisphere ice sheets, actually reflects millennial perturbations in the large‐scale atmospheric circulation in East Asia caused by insolation‐triggered abrupt North Atlantic cooling when Northern Hemisphere ice sheets reach a critically large size. Our results thus offer new insights into how the climate teleconnections between high‐ and middle‐latitudes of the Northern Hemisphere have controlled the East Asian winter monsoon during glacial inceptions. Microcodium 87Sr/86Sr record captures the cooling trend in East Asia at the interglacial‐glacial transitionsDecoupled evolution of East Asian winter monsoon and temperature occurred during glacial inceptionsIce volume modulates the response of East Asian winter monsoon to insolation‐triggered North Atlantic cooling during glacial inceptions Microcodium 87Sr/86Sr record captures the cooling trend in East Asia at the interglacial‐glacial transitions Decoupled evolution of East Asian winter monsoon and temperature occurred during glacial inceptions Ice volume modulates the response of East Asian winter monsoon to insolation‐triggered North Atlantic cooling during glacial inceptions

Eolian dust plays an important role in the Earth’s climate system. Environmental magnetism has been widely used to trace dust variations at different spatial and temporal scales. However, the magnetic properties of sediments from key dust sources have not been well determined. In this study, surface samples from potential dust sources in inner Eastern Asia were systematically investigated. Our results indicate that ferrimagnetic and antiferromagnetic minerals are both present in surface sediments and that they have broad grain size distributions. Ferrimagnetic components are dominated by partially oxidized coarse-grained (pseudo-single domain and multi-domain) lithogenic magnetite particles with minor contributions from pedogenic fine-grained (single domain and superparamagnetic) particles. Antiferromagnetic hematite can be classified into three groups in terms of diffuse reflectance spectroscopy (DRS) band positions (P560 nm, P545 nm, and P535 nm, where numbers indicate the DRS band wavelength for hematite). The first group (P560 nm) is the coarse-grained hematite of lithogenic origin and is mostly confined to western China. The P535 nmgroup is of pedogenic origin. The P545 nmgroup is an intermediate phase that is present both in surface samples from the source regions and in loess. Therefore, the P545 nmand P535nmgroups are related to eolian inputs to the Chinese Loess Plateau and pedogenic processes, respectively. In addition, significant differences exist between the magnetic properties of eolian material from sources and depositional regions due to gravitational sorting. These insights provide strong constraints on interpretation of dust signals recorded by the Chinese loess and marine sediments from the North Pacific Ocean.

Record of long‐term land temperature changes remains ephemeral, discontinuous, and isolated, thus leaving the common view that Pleistocene land temperature evolution should have followed ocean temperatures unconfirmed. Here, we present a continuous land surface temperature reconstruction in the Asian monsoon region over the past 3.0 Myr based on the distribution of soil bacterial lipids from the Chinese Loess Plateau. The land temperature record indicates an unexpected warming trend over the Pleistocene, which is opposite to the cooling trend in Pleistocene ocean temperatures, resulting in increased land‐sea thermal contrast. We propose that the previously unrecognized increase of land‐sea thermal contrast during much of the Pleistocene is a regional climate phenomenon that provides a likely mechanism in favor of the long‐term enhancement of the Pleistocene East Asian summer monsoon. Numerous sea surface temperature (SST) records indicate long‐term gradual cooling over the Pleistocene, whereas the East Asian summer monsoon (EASM) appears to have strengthened during this period. Land‐sea thermal contrast is thought to have an important influence on the intensity of the EASM, but the lack of land surface temperature (LST) records from monsoonal regions prevents the assessment of its role in driving monsoonal changes. Here, we present a 3‐Myr‐long LST record from the Chinese Loess Plateau, displaying a unique long‐term warming trend over the Pleistocene, different from the trajectories of SST records. We propose that the decoupling of long‐term land and sea temperatures, and thus the increase of land‐sea thermal contrast, provides a simple interpretation for the otherwise paradox, strengthening of the EASM over the Pleistocene. This study presents much needed original LST data that support novel interpretations on a mechanism for important paleoclimate phenomenon in East Asia with implications to the entire terrestrial ecosystem during the critical period of earth history. Three million years of continuous land surface temperatures reconstructed based on soil bacterial lipidsThe land temperature record indicates an unexpected warming trend over the PleistoceneIncreasing land‐sea thermal contrast facilitated the long‐term intensification of Pleistocene East Asian summer monsoon Three million years of continuous land surface temperatures reconstructed based on soil bacterial lipids The land temperature record indicates an unexpected warming trend over the Pleistocene Increasing land‐sea thermal contrast facilitated the long‐term intensification of Pleistocene East Asian summer monsoon

Hf‐Nd‐Sr isotopic fingerprinting has been employed as a powerful method for distinguishing dust sources. However, the Hf and Sr isotopic compositions of dust are highly dependent on particle size to accurately identify dust provenance. Here we compare the Hf‐Nd‐Sr isotopic compositions of clay‐sized fractions from dust sources (the Mongolian Plateau) to sinks (Beijing and Greenland). Our results document that clay‐sized Hf‐Nd‐Sr isotopic compositions of Mongolian dust are controlled by two isotopic/geochemical provinces: Southern Mongolian Gobi (SMG) and Northern Mongolian Plateau (NMP). Our data indicate that the SMG is potentially an important dust source to the loess in Beijing and Hulun Buir and could be a contributing source of dust to Greenland, whereas the NMP contributes little dust to the Chinese loess and the Greenland. Furthermore, we demonstrate that the deserts of northwest China are one of the main dust contributors to Beijing and Greenland, but not to Hulun Buir. The clay‐sized radiogenic isotopic compositions link to the geological settingThe Southern Mongolia Gobi could be a contributing source to GreenlandThe Hf‐Nd‐Sr isotope constrains on provenances and pathway of mineral dust

Abstract: The expansion of inland Asia deserts has considerably influenced the environmental, social and economic activities in Asia. Aridification of inland Asia, especially timing of the initiation of Asian desertification, is a contentious topic in paleoclimatology. Late Cenozoic eolian loess-red clay sequences on the Chinese Loess Plateau, which possess abundant paleoclimatic and paleo-environmental information, can be regarded as an indicator of inland Asia desertification. Here we present a detailed magnetostratigraphic investigation of a new red clay sequence about 654 m in Zhuanglang located at the western Chinese Loess Plateau. Sedimentological, geochemical, mineralogical, and quartz morphological lines of evidence show that the red clay is of eolian origin. Magnetostratigraphic correlations indicate that this core sequence spans from 25.6 to 4.8 Ma, and typical eolian red clay appears as early as 25 Ma. This extends the lower limit of the red clay on the Chinese Loess Plateau from the previously thought early Miocene back into the late Oligocene. This new red clay record further implies that the inland Asia desertification was initiated at least by the late Oligocene. This sequence provides a unique high-resolution geological record for understanding the inland Asia desertification process since the late Oligocene.

Recent progress both in studies of Chinese loess and deep-sea sediments have provided robust and longer records of winter monsoon variation and ice volume change back to the Late Miocene. However, when and how the winter monsoon became coupled with global ice volume change remains uncertain. Here we compare quartz grain size (a reliable winter monsoon proxy) generated from two loess-palaeosol and red clay sequences with a stacked benthic δ18O record (a global ice volume proxy). Our results indicate that at longer (>500 ka) timescales, the winter monsoon became strongly coupled with global ice volume change at 2.1 Ma, while at orbital timescales the winter monsoon variations started to be influenced by global ice volume change at c. 3.3 Ma. Correlation coefficients between these two records further indicate that winter monsoon intensity was strongly coupled with global ice volume change during intervals of 0–1.1 Ma, 1.4–1.8 Ma, and 2–2.85 Ma. In spite of these close connections amplitude mismatches between these two records are evident in terms of both long-term trend and glacial–interglacial fluctuations, suggesting that additional processes might have played a role in modulating the response of the winter monsoon variation to ice volume forcing.

The potential links between uplift of the Himalaya and Tibetan Plateau and desertification of inland Asia have been a long-considered problem in geology. Although a close link between the two has been suggested by theoretical climatic simulations, not enough geological data has existed to test the theory. Here, we conducted semi-quantitative field observations of a Neogene fluvial sequence at the Yecheng section on the southwestern margin of the Tarim Basin in order to confirm the origin and mode of deposition of the aeolian siltstone, determine the onset timing, evaluate quantitatively the temporal evolution of its deposition and its relationship to the tectonically driven surface uplift of NW Tibet. The results suggest a close link between the uplift of northwestern Tibet, alluvial fan formation, dust emission from Taklimakan Desert and the deposition of loess on the alluvial fans.

Earth's climate system has experienced substantial millennial‐scale oscillations characterized by abrupt changes superimposed on orbital‐scale changes. However, the dynamic connection between millennial and orbital timescales remains elusive. Here, we provide a summer monsoon precipitation δ18O record spanning from ∼8 to ∼60.5 ka based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau. This record shows distinct precessional variations (23 ka) punctuated by prominent millennial‐scale oscillations. It is generally consistent with speleothem δ18O and other loess‐based records, reflecting the East Asian summer monsoon changes. More importantly, our result also shows that large increases in the magnitude of millennial‐scale variability correspond to the Northern Hemisphere summer insolation minimum. We propose that precession‐induced low‐latitude summer insolation modulates the amplitudes of millennial‐scale summer monsoon variability by changing the mean monsoon state during the last glaciation. Understanding the dynamic connections between different timescales is crucial to predicting future climate variability. Here, we provide a summer monsoon precipitation δ18O record based on the oxygen isotopic composition of microcodium from loess deposits on the Chinese Loess Plateau, showing that large increases in the magnitude of millennial‐scale variability correspond to Northern Hemisphere summer insolation minimum. We propose that low‐latitude summer insolation modulates the amplitudes of millennial monsoon variability during the last glaciation. Our work provides clues for deciphering the dynamic connections between orbital and millennial timescales. A summer precipitation δ18O record on the Chinese Loess Plateau during the last glaciation was reconstructed based on microcodium δ18OThe record shows distinct precessional variations punctuated by millennial‐scale oscillations, consistent with other monsoon recordsThe magnitude of millennial‐scale East Asian summer monsoon variability was found to be modulated by low‐latitude insolation during the last glaciation A summer precipitation δ18O record on the Chinese Loess Plateau during the last glaciation was reconstructed based on microcodium δ18O The record shows distinct precessional variations punctuated by millennial‐scale oscillations, consistent with other monsoon records The magnitude of millennial‐scale East Asian summer monsoon variability was found to be modulated by low‐latitude insolation during the last glaciation

Trace elements in a speleothem have been considered to be effective proxies to characterize hydroclimatic changes. In this study, we present speleothem trace element records of the penultimate glacial‐interglacial transition from 138 to 125.8 ka BP from the Shangxiaofeng cave in northeastern China. We used two analytical methods, namely, inductively coupled plasma optical emission spectrometry (ICP‐OES) and the Avaatech high‐resolution X‐ray fluorescence (XRF) core scanner. Both methods showed good consistency for Sr/Ca but not for Mg/Ca because of the high Mg detection limit of XRF. By comparing the trace element ratios (Sr/Ca and Mg/Ca) with δ13C and by analyzing the slope of the regression line of ln(Sr/Ca) versus ln(Mg/Ca), we found that trace element variations were dominated by hydroclimate‐related prior calcite precipitation (PCP) and water‐rock interaction (WRI). A gradually decreasing trend of Sr/Ca, Mg/Ca, and δ13C records during the glacial‐interglacial transition indicated that the hydroclimate moved toward a moist condition with an intensified East Asian summer monsoon (EASM) and transgression of the coastline. The transgression shortened the distance between the cave site and the coastline, possibly contributing to persistent rainfall enhancement at the study site. The climate gradually turned wet during the penultimate deglaciation in Northern ChinaCoastline regression could contribute to regional humidification during the deglaciationThe X‐ray fluorescence measurement of Mg in stalagmites is not reliable and should be crosschecked The climate gradually turned wet during the penultimate deglaciation in Northern China Coastline regression could contribute to regional humidification during the deglaciation The X‐ray fluorescence measurement of Mg in stalagmites is not reliable and should be crosschecked