mid-Pleistocene Climate Transition Research Articles

Tectonic and high-latitude climate controls on Quaternary sedimentary processes on the northern coast of Bohai Bay

Separating the relative roles of tectonics and climate change in geological evolution is complicated. The northern coast of Bohai Bay (NCBB), with a thick accumulation of Quaternary lacustrine sediments, is a subsiding area and is well suited to studying tectonic versus climatic controls on sedimentary processes. We used magnetostratigraphy and sedimentological analyses of borehole core JL01 from the NCBB to provide new insights into the effects of tectonic processes and climate changes in this region. The results show the following: (1) A shallow lacustrine delta, a deep-water lacustrine sedimentary system and a subaqueous fan-delta sedimentary system developed during 2.1–1.4 Ma, 1.4–0.78 Ma, and from 0.78 Ma to the present, respectively, corresponding to the rift-initiation, rift-climax, and late-rift tectonic stages of the evolution of an extensional basin, respectively. These stages constitute a low-order tectono-sedimentary cycle. (2) Tectonic and orbital-scale climate changes can be distinguished, particularly the 2.5 Ma climatic transition and a significant shift from 41- to 100-kyr cyclicity across the Mid-Pleistocene climatic transition. These changes indicate that the sedimentary processes of the NCBB were influenced by high-latitude climate forcing since the Late Pliocene. Our results demonstrate that detailed sedimentary facies analyses can provide valuable information about the effects of tectonics and climate changes on basin sedimentary evolution. This approach can be applied to other regional basins worldwide.

Mineralogical and magnetic variations of periglacial loess in SE Tibet reveal mid-Pleistocene expansion of Tibetan glacial activity

The formation and evolution of the cryosphere on the Tibetan Plateau is of great significance in understanding the Earth's carbon and climatic system. Periglacial loess deposits in southeastern Tibet offer a means to constrain this history as they contain critical information on glacial grinding and frost shattering processes in high-altitude mountain regions through time, which yield lithogenic fractions of largely loess silts and sands. Based on combined analyses of lithogenic magnetic properties and mineralogical composition, here we find that increasing high mountain production and supply of fresh detrital components since the mid-Pleistocene climate transition (MPT, 1.2–0.7 Ma) led to a substantial increase of the lithogenic susceptibility and decrease in chemical weathering intensity of periglacial loess in southeastern Tibet. The agreement of these findings with similar results from eolian loess on the northern margins of the Tibetan Plateau suggests a plateau-wide glacier expansion during the MPT. Enhanced glacial erosion and freeze-thaw activities occurred in the high-altitude mountain regions of the plateau during the MPT, thereby providing vast amounts of fresh detritus for the formation of loess deposits. High and constant values of lithogenic magnetic parameters in the loess deposits after 0.7–0.6 Ma further indicate that the Middle Pleistocene is a critical period for the establishment of modern-like glacial and periglacial landforms on the Tibetan Plateau. Our results further suggest that enhanced Quaternary glaciation in SE Tibet occurred earlier than in the north, which we attribute to climate cooling combined with regional seasonal snowline lowering. As such, a close relationship exists between global climate changes, development of pan-Tibetan glaciations, and large-scale dust emission.

Genome assembly of autotetraploid Actinidia arguta highlights adaptive evolution and enables dissection of important economic traits

Actinidia arguta, the most widely distributed Actinidia species and the second cultivated species in the genus, can be distinguished from the currently cultivated Actinidia chinensis on the basis of its small and smooth fruit, rapid softening, and excellent cold tolerance. Adaptive evolution of tetraploid Actinidia species and the genetic basis of their important agronomic traits are still unclear. Here, we generated a chromosome-scale genome assembly of an autotetraploid male A. arguta accession. The genome assembly was 2.77 Gb in length with a contig N50 of 9.97 Mb and was anchored onto 116 pseudo-chromosomes. Resequencing and clustering of 101 geographically representative accessions showed that they could be divided into two geographic groups, Southern and Northern, which first diverged 12.9 million years ago. A. arguta underwent two prominent expansions and one demographic bottleneck from the mid-Pleistocene climate transition to the late Pleistocene. Population genomics studies using paleoclimate data enabled us to discern the evolution of the species’ adaptation to different historical environments. Three genes (AaCEL1, AaPME1, and AaDOF1) related to flesh softening were identified by multi-omics analysis, and their ability to accelerate flesh softening was verified through transient expression assays. A set of genes that characteristically regulate sexual dimorphism located on the sex chromosome (Chr3) or autosomal chromosomes showed biased expression during stamen or carpel development. This chromosome-level assembly of the autotetraploid A. arguta genome and the genes related to important agronomic traits will facilitate future functional genomics research and improvement of A. arguta.

Mid-Pleistocene links between Asian dust, Tibetan glaciers, and Pacific iron fertilization

Increasing Asian dust fluxes, associated with late Cenozoic cooling and intensified glaciations, are conventionally thought to drive iron fertilization of phytoplankton productivity in the North Pacific, contributing to ocean carbon storage and drawdown of atmospheric CO2. During the early Pleistocene glaciations, however, productivity remained low despite higher Asian dust fluxes, only displaying glacial stage increases after the mid-Pleistocene climate transition (~800ka B.P.). We solve this paradox by analyzing an Asian dust sequence, spanning the last 3.6 My, from the Tarim Basin, identifying a major switch in the iron composition of the dust at ~800ka, associated with expansion of Tibetan glaciers and enhanced production of freshly ground rock minerals. This compositional shift in the Asian dust was recorded synchronously in the downwind, deep sea sediments of the central North Pacific. The switch from desert dust, containing stable, highly oxidized iron, to glacial dust, richer in reactive reduced iron, coincided with increased populations of silica-producing phytoplankton in the equatorial North Pacific and increased primary productivity in more northerly locations, such as the South China Sea. We calculate that potentially bioavailable Fe2+ flux to the North Pacific was more than doubled after the switch to glacially- sourced dust. These findings indicate a positive feedback between Tibetan glaciations, glaciogenic production of dust with enhanced iron bioavailability, and changes in North Pacific iron fertilization. Notably, this strengthened link between climate and eolian dust coincided with the mid-Pleistocene transition to increased storage of C in the glacial North Pacific and more intense northern hemisphere glaciations.

Ecological shifts and hominin adaptations during the Mid-Pleistocene Climate Transition in Northeast Asia as evidenced by isotopic analysis (δ13C, δ18O) of mammalian enamel from Early Paleolithic sites in the Nihewan Basin, China

The Nihewan Basin in North China is one of the most important early archaeological sequences for our understanding of the ecological ranges exploited by hominins and how their adaptive behaviors were shaped by local, regional, and global environmental fluctuations. This study contributes to the topic by conducting stable isotope (δ13C, δ18O) analyses of mammalian tooth enamel from several Early Pleistocene assemblages in the Nihewan Basin dated to ca. 1.2–1.1 Ma, and exploring the links between hominin behavioral adaptations and ecological changes during the Mid-Pleistocene Climate Transition in Northeast Asia mainland. Our isotopic analysis of bulk samples (n = 215) indicates that the Nihewan Basin regional environment underwent significant changes, from landscapes dominated by wet and closed pure C3 vegetation no later than 1.2 Ma, to those dominated by dry and open C3/C4 mixed vegetation during 1.2–1.1 Ma. Additionally, the isotopic analysis of sequential samples (n = 16) suggests seasonal variations. These isotope results interpreted in the context of hominin behavioral traits indicate that hominins exhibited cognitive and technical flexibility in the face of complex and unstable regional ecological settings, suggesting that they adjusted to the environmental fluctuations characteristic of high-latitude arid/semi-arid regions such as the Nihewan Basin over or prior to the Mid-Pleistocene Climate Transition.

New study sheds light on the impressive intraspecific variation of Quaternary Asiatic black bears in China

Asiatic black bears have long been recognized as key members of the Quaternary mammalian fauna in South China. Despite this, for decades, taxonomic remarks since the Early Pleistocene Ursus thibetanus have been controversial, and the intraspecific variations of it remain unresolved. We here described a nearly complete black bear skull from the late Mid-Pleistocene or the early Late-Pleistocene (ca. 134 ± 22–133 ± 30 ka) of the Sifangdi Cave, Yanjinggou area, Chongqing. The studied material was compared with other U. thibetanus materials from the Quaternary localities in China.Morphological analyses revealed impressive intraspecific variations and that U. t. kokeni can be deemed as an invalid paleosubspecies, which discernibly corresponds to all living subspecies of U. thibetanus. Based on isolated teeth and several skulls from various localities, we proposed that U. thibetanus primitinus was a black bear with small-sized skull and upper molars, while U. thibetanus since the Mid-Pleistocene was a larger black bear with significantly larger cranium and upper molars, in accordance with extant subspecies. Furthermore, in response to the prominent Mid-Pleistocene climate transition and ecosystem changes, it is evident that black bears tend to have increased their body sizes, expanded their living territories, and perhaps even arrived at the localities in North China since the Mid-Pleistocene.

Centres of endemism of Noctuidae (Lepidoptera) in the Palaearctic arid mountains: biogeographical and phylogenetic implications

The oreal fauna is connected with orographically limited non-arboreal habitats. Its chorological centres can be recognised by the high species-diversity of numerous typical genera, and by the accumulated occurrence of endemic species and/or subspecies of disjunct species. The oreal fauna is partitioned to the alpine type, as the faunal type of humid high-mountains with strong connections to the tundral zonobiome, and the xeromontane type, as the faunal type of arid high-mountains with close connections to the eremic zonobiomes. As the results of revisions of several Noctuinae genera, species groups and/or sister species were recognised and their distributions were mapped. The restricted areas of allopatric sister species, often described by us as new for science, fulfil the criteria of the “areas of endemism”. Core areas of the Palaearctic xeromontane Noctuidae, outlined by the distribution of endemic species, have been proven by the occurrence of allopatric subspecies of polytypic species, and/or by the presence of allopatric sister species. In the revised genera of Noctuidae several types of allopatric speciation have been identified based on the analysis of the areas of endemism and of vicariance patterns. As a result of these analyses, it is proved that allopatric sister species, as elementary monophyletic supraspecific units, are suitable for phylogenetic biogeographical surveys. Although the major part of the xeromontane fauna appears to be range-restricted, a considerable fraction of the species could have expanded into the steppic zonobiome due to adaptive changes of their life cycles. High diversity of cold-adapted species originated from the Sino-Himalayan mountains by passing two main filtercorridors. One track of this bifurcation was directed across the “Rhododendron-corridor” to the Holarctic taiga zone while the other one, across the “Xeromontane filter-corridor” to the mountain systems of Central and Inner Asia. This bifurcation becomes apparent from the taxonomic division of the genera, composing both of these main faunal types. Supposedly, the faunal movements of the xeromontanean species in the West Palaearctic had been shaped by the Messinian salinity crisis and, additionally, significantly influenced by the Mid-Pleistocene climatic transition which deeply transformed the zonality of the vegetation by cooling and aridisation of vast areas.

Centres of endemism of Noctuidae (Lepidoptera) in the Palaearctic arid mountains: biogeographical and phylogenetic implications

The oreal fauna is connected with orographically limited non-arboreal habitats. Its chorological centres can be recognised by the high species-diversity of numerous typical genera, and by the accumulated occurrence of endemic species and/or subspecies of disjunct species. The oreal fauna is partitioned to the alpine type, as the faunal type of humid high-mountains with strong connections to the tundral zonobiome, and the xeromontane type, as the faunal type of arid high-mountains with close connections to the eremic zonobiomes. As the results of revisions of several Noctuinae genera, species groups and/or sister species were recognised and their distributions were mapped. The restricted areas of allopatric sister species, often described by us as new for science, fulfil the criteria of the “areas of endemism”. Core areas of the Palaearctic xeromontane Noctuidae, outlined by the distribution of endemic species, have been proven by the occurrence of allopatric subspecies of polytypic species, and/or by the presence of allopatric sister species. In the revised genera of Noctuidae several types of allopatric speciation have been identified based on the analysis of the areas of endemism and of vicariance patterns. As a result of these analyses, it is proved that allopatric sister species, as elementary monophyletic supraspecific units, are suitable for phylogenetic biogeographical surveys. Although the major part of the xeromontane fauna appears to be range-restricted, a considerable fraction of the species could have expanded into the steppic zonobiome due to adaptive changes of their life cycles. High diversity of cold-adapted species originated from the Sino-Himalayan mountains by passing two main filtercorridors. One track of this bifurcation was directed across the “Rhododendron-corridor” to the Holarctic taiga zone while the other one, across the “Xeromontane filter-corridor” to the mountain systems of Central and Inner Asia. This bifurcation becomes apparent from the taxonomic division of the genera, composing both of these main faunal types. Supposedly, the faunal movements of the xeromontanean species in the West Palaearctic had been shaped by the Messinian salinity crisis and, additionally, significantly influenced by the Mid-Pleistocene climatic transition which deeply transformed the zonality of the vegetation by cooling and aridisation of vast areas.

Expanded North Pacific Subtropical Gyre and Heterodyne Expression During the Mid‐Pleistocene

AbstractThe Kuroshio Current (KC) and Kuroshio Current Extension (KCE) form a western boundary current as part of the North Pacific Subtropical Gyre. This current plays an important role in regulating weather and climate dynamics in the Northern Hemisphere in part by controlling the delivery of moisture to the lower atmosphere. Previous studies indicate the KCE responded dynamically across glacial and interglacial periods throughout the Pliocene‐Pleistocene. However, the response of the KCE during Pleistocene super‐interglacials has not been examined in detail. We present a ∼2.2 Ma record of X‐ray fluorescence elemental data from Ocean Drilling Program Hole 1207A and employ hierarchical clustering techniques to demonstrate paleoenvironmental changes around the KCE. Time‐frequency analysis identifies significant heterodyne frequencies, which suggests there were nonlinear interactions between high‐latitude and low‐latitude climate regulating expansion and contraction of the North Pacific Subtropical Gyre prior to the onset of the Mid‐Pleistocene Climate Transition (MPT). We observe two periods of elevated ln Ca/Ti, which may represent sustained warmth with northward migrations of the KCE in the northwestern Pacific. These intervals correspond to Marine Isotope Stages 29‐25, 15, and 11‐9 and occur around recent climatic transitions, the MPT and Mid‐Brunhes Event. Northward expansion of the subtropical gyre during these exceptionally warm interglacials would have delivered more heat and moisture to the high latitudes of the northwest Pacific. Furthermore, enhanced evaporation from the warm KCE vented to the lower atmosphere may have preconditioned the Northern Hemisphere for ice volume growth during two of the most recent periods of climate transition.

Late Miocene–Quaternary seismic stratigraphic responses to tectonic and climatic changes at the northeastern margin of the South China Sea

Abstract Tectonic and climate evolution could be well archived in deep-water stratigraphy. Based on newly acquired high-resolution two-dimensional (2-D) multichannel seismic profiles and multibeam bathymetry, together with Ocean Drilling Program/International Ocean Discovery Program (ODP/IODP) data, this study investigated the late Miocene–Quaternary deep-water seismic stratigraphy, sedimentary evolution, and responses to regional tectonic and climatic variations at the northeastern margin of the South China Sea. The late Miocene–Quaternary stratigraphy consists of three units (i.e., SU-1, SU-2, and SU-3 from bottom to top) that are dated to 10.5–6.5 Ma (stage 1), 6.5–0.9 Ma (stage 2), and 0.9 Ma–present (stage 3), respectively. SU-1 is dominated by sheeted drifts with slight thickness variation, but SU-2 and SU-3 mainly consist of mounded, lenticular contourite drifts and channel-like moats. This suggests that the bottom currents intensified from stage 1 to stage 2, which was probably caused by the sill uplifting at the Luzon Strait under the influence of tectonic collision between the Luzon arc and Eurasia since ca. 6.5 Ma. SU-2 and SU-3 are separated by a basinwide high-amplitude seismic reflection, across which the average sedimentation rate shows a dramatic increase from ~28 m/m.y. in SU-2 to ~144 m/m.y. in SU-3. The high sediment supply since 0.9 Ma could be linked to the mid-Pleistocene climate transition, which resulted in abundant rainfall that promoted the Taiwan orogen to contribute more sediments to the South China Sea. This study indicates that the deep-water stratigraphy recorded the tectonic collision around the sole deep-water gateway (i.e., Luzon Strait) and mid-Pleistocene climate transition event at the northeastern South China Sea margin, which has important implications for understanding the relationships among the tectonic, paleoclimatic, paleoceanographic, and deepwater sedimentary processes in the largest marginal basin of the western Pacific Ocean.

More opportunities more species: Pleistocene differentiation and northward expansion of an evergreen broad-leaved tree species Machilus thunbergii (Lauraceae) in Southeast China

BackgroundThe broad continuum between tropical and temperate floras in Eastern Asia (EAS) are thought to be one of the main factors responsible for a prominent species diversity anomaly of temperate plants between EAS and eastern North America (ENS). However, how the broad continuum and niche evolution between tropical and temperate floras in EAS contributes to lineage divergence and species diversity remains largely unknown.ResultsPopulation genetic structure, demography, and determinants of genetic structure [i.e., isolation-by-distance (IBD), isolation-by-resistance (IBR), and isolation-by-environment (IBE)] of Machilus thunbergii Sieb. et Zucc. (Lauraceae) were evaluated by examining sequence variation of ten low-copy nuclear genes across 43 populations in southeast China. Climatic niche difference and potential distributions across four periods (Current, mid-Holocene, the last glacial maximum, the last interglacial) of two genetic clusters were determined by niche modelling. North and south clusters of populations in M. thunbergii were revealed and their demarcation line corresponds well with the northern boundary of tropical zone in China of Zhu & Wan. The divergence time between the clusters and demographic expansion of M. thunbergii occurred after the mid-Pleistocene climate transition (MPT, 0.8–1.2 Ma). Migration rates between clusters were asymmetrical, being much greater from north to south than the reverse. Significant effects of IBE, but non-significant effects of IBD and IBR on population genetic divergence were detected. The two clusters have different ecological niches and require different temperature regimes.ConclusionsThe north-south genetic differentiation may be common across the temperate-tropical boundary in southeast China. Divergent selection under different temperature regimes (possibly above and below freezing temperature in winter) could account for this divergence pattern. The broad continuum between tropical and temperate floras in EAS may have provided ample opportunities for tropical plant lineages to acquire freezing tolerance and to colonize the temperate regions during the late-Cenozoic global cooling. Our findings shed deeper insights into the high temperate plant species diversity in EAS.

Shelf-margin architecture and deposition variability across the mid-Pleistocene climate transition, northeastern South China Sea

The shelf-margin prism of the Upper Pliocene to Pleistocene in the northeastern South China Sea has recorded significant signatures of glacio-eustatic cycles and paleo-climatic conditions. Integrated analysis of 3D seismic, well-logging, and borehole dating data in the study area provided a detailed depiction of the high-resolution sequence architecture and depositional evolution as they responded to the glacio-eustatic cycles and climate changes. The shelf-margin section of the Upper Pliocene to Pleistocene is comprised of a composite sequence bounded by a regional unconformity, which can be further divided into five sequences confined by subordinate unconformities. The two lower sequences (S1-S2) with similar and simple internal structures, are displayed as having roughly equal thicknesses (ca. 50 m) and gently seaward-dipping foresets. In contrast, the upper three sequences (S3-S5) are characterized by the development of high (200–600 m) and steep (2–5°) shelf-margin clinoforms, which can be further divided into fifteen clinothems. The sequences generally embody four systems tracts, showing different stratal stacking patterns, and the linking contemporaneous depositional systems including fluvial channels, deltaic and slope fan systems are documented. Based on the chronostratigraphic framework, comparisons have been made between the sequence cycles and the global oxygen isotopic records. The results suggest that the formation of different order sequences may have been in response to the glacio-eustatic cycles paced by the Milankovitch orbital cyclicity. The abrupt changes in the sequence and depositional architectures between S1-S2 and S3-S5 are assumed to be related to the significant increases in the amplitudes and durations of the glacio-eustatic fluctuations across the mid-Pleistocene climate transition (MPT). Intensively variable climatic conditions with strengthened monsoons during and after the MPT could have potentially led to an abundant sediment supply, which may have enhanced the development of shelf to shelf-edge delta systems with the large-scale prograding clinoforms.

Hominin site distributions and behaviours across the Mid-Pleistocene climate transition in China

Knowledge about the Early and Middle Pleistocene hominin record of China is steadily increasing owing to the on-going implementation of palaeoanthropological surveys and excavations. Yet, relatively little attention has been paid to the effects of climate variability on hominin populations in China and its influence on archaeological site distributions and hominin behaviours. The Mid-Pleistocene climate transition (MPT), dating to between ∼1.2–0.7 Ma in Eastern Asia, is characterized by significant changes in the length and intensity of glacial-interglacial cycles and in monsoon intensity and terrestrial conditions, which have been implicated in influencing the occupation history of basins within China. Here, the MPT is examined relative to archaeological site distributions across China to determine potential long-term geographic and behavioural effects on hominin populations before, during and after this critical period. Changes in the geographic distribution of hominins are demonstrated across the MPT, with significant shifts in the number of sites in high and low latitudes, likely as a response to changing ecosystems. Technological innovations, including the development of Large Cutting Tools, occur in the MPT and afterwards, possibly a response to the formation of open habitats in South China. Geographic and behavioural shifts in the hominin record challenge traditional views about the long-term, conservative nature of the biological and cultural evolution of hominins in Eastern Asia, and instead demonstrate dynamic responses of populations to ecosystem changes across the Early and Middle Pleistocene.

Technological innovations at the onset of the Mid-Pleistocene Climate Transition in high-latitude East Asia.

The interplay between Pleistocene climatic variability and hominin adaptations to diverse terrestrial ecosystems is a key topic in human evolutionary studies. Early and Middle Pleistocene environmental change and its relation to hominin behavioural responses has been a subject of great interest in Africa and Europe, though little information is available for other key regions of the Old World, particularly from Eastern Asia. Here we examine key Early Pleistocene sites of the Nihewan Basin, in high-latitude northern China, dating between ∼1.4 and 1.0 million years ago (Ma). We compare stone-tool assemblages from three Early Pleistocene sites in the Nihewan Basin, including detailed assessment of stone-tool refitting sequences at the ∼1.1-Ma-old site of Cenjiawan. Increased toolmaking skills and technological innovations are evident in the Nihewan Basin at the onset of the Mid-Pleistocene Climate Transition (MPT). Examination of the lithic technology of the Nihewan sites, together with an assessment of other key Palaeolithic sites of China, indicates that toolkits show increasing diversity at the outset of the MPT and in its aftermath. The overall evidence indicates the adaptive flexibility of early hominins to ecosystem changes since the MPT, though regional abandonments are also apparent in high latitudes, likely owing to cold and oscillating environmental conditions. The view presented here sharply contrasts with traditional arguments that stone-tool technologies of China are homogeneous and continuous over the course of the Early Pleistocene.

Influence of tectonic uplift of the Qinling Mountains on the paleoclimatic environment of surrounding areas: Insights from loess–paleosol sequences, Weihe Basin, central China

The southern edge of the Chinese Loess Plateau affected by the stepwise uplift of the Qinling Mountains is a transitional climatic area between the different climatic environments and sedimentary characteristics to the north and south sides of the Qinling Mountains. The study of different Quaternary loess deposits in this region is conducive to improving our understanding of the micro-scale climatic effects of tectonic developments. Here, we use a series of experimental methods on a well-preserved loess–paleosol sequence in the South Jingyang Plateau to obtain proxy data, including grain-size, magnetic susceptibility, loss on ignition, and geochemical elemental. Changes in grain-size, magnetic susceptibility and loss on ignition indicate that the East Asian monsoon has undergone significant changes due to the continued global cooling and mid-Pleistocene climate transition during the deposition process of XSD loess, i.e., the intensities of the winter and summer monsoons were simultaneously enhanced. Elemental correlations and factor analysis indicate the sedimentary environment and provenance of the deposits, while elemental enrichment and element ratios, including Si/Ti, Al/Ti, Rb/Sr and Zr/Rb, are consistent with changes in the intensity of pedogenic and of the East Asian monsoon as reflected by climate proxies, illustrating that XRF core scanning analysis technology has great potential in the field of Quaternary environmental changes of loess. Furthermore, the stepwise uplift of the Qinling Mountains, which has blocked the winter and summer monsoons to a certain extent, has had a significant impact on the relative degree of loess accumulation and pedogenic in the northern piedmont, southern piedmont and intermontane basin of the Qinling Mountains and also appears to have promoted settlement by early humans. Hence, the study of paleoclimate in areas of active tectonic movement has the potential to promote our understanding of micro-scale climate change in this region in the future.

Glacial Indonesian Throughflow weakening across the Mid-Pleistocene Climatic Transition

The Indonesian Throughflow (ITF) controls the oceanic flux of heat and salt between the Pacific and Indian Oceans and therewith plays an important role in modulating the meridional overturning circulation and low latitude hydrological cycle. Here, we report new sea surface temperature and aridity records from the west coast of Australia (IODP Site U1460), which allow us to assess the sensitivity of the eastern Indian Ocean to the major reorganization of Earth’s climate that occurred during the Mid-Pleistocene Transition. Our records indicate glacial coolings at 1.55 and 0.65 million years ago that are best explained by a weakening of the ITF as a consequence of global sea level and tectonic changes. These coincide with the development of pronounced gradients in the carbon isotope composition of the different ocean basins and with substantial changes in regional aridity, suggesting that the restrictions of the ITF influenced both the evolution of global ocean circulation and the development of the modern hydrological cycle in Western Australia.

Magnetostratigraphic and archaeological records at the Early Pleistocene site complex of Madigou (Nihewan Basin): Implications for human adaptations in North China

The Nihewan Basin in North China contains the densest concentration of early Pleistocene Paleolithic sites outside Africa. This paper introduces a new archaeological site complex at Madigou (MDG) that was systematically excavated from 2011 to 2014 in the northeastern part of the Nihewan Basin. The site contains fossils and well-preserved stone artefacts in fluvio-lacustrine sediments. Our magnetostratigraphic results situate the MDG sedimentary sequence in the early Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. The MDG artifact layers are positioned within the pre-Jaramillo Matuyama chron, with an estimated age of ca. 1.2 Ma, close to the onset of Mid-Pleistocene climate transition. The MDG core and flake technology includes bipolar flaking of siliceous dolomite cobbles, and freehand flaking of chert and brecciated chert block fragments. Mammalian fauna and pollen compositions indicate that the MDG hominins lived in an open habitat varying from lightly-wooded grassland to an ecosystem dominated by sparse steppe near the shore of the Nihewan paleolake. Our combined results in the fields of archaeology, paleontology, palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of Mid-Pleistocene climate transition.

Diverse manifestations of the mid-Pleistocene climate transition

The mid-Pleistocene transition (MPT) is widely recognized as a shift in paleoclimatic periodicity from 41- to 100-kyr cycles, which largely reflects integrated changes in global ice volume, sea level, and ocean temperature from the marine realm. However, much less is known about monsoon-induced terrestrial vegetation change across the MPT. Here, on the basis of a 1.7-million-year δ13C record of loess carbonates from the Chinese Loess Plateau, we document a unique MPT reflecting terrestrial vegetation changes from a dominant 23-kyr periodicity before 1.2 Ma to combined 100, 41, and 23-kyr cycles after 0.7 Ma, very different from the conventional MPT characteristics. Model simulations further reveal that the MPT transition likely reflects decreased sensitivity of monsoonal hydroclimate to insolation forcing as the Northern Hemisphere became increasingly glaciated through the MPT. Our proxy-model comparison suggests varied responses of temperature and precipitation to astronomical forcing under different ice/CO2 boundary conditions, which greatly improves our understanding of monsoon variability and dynamics from the natural past to the anthropogenic future.

Magnetostratigraphic dating of the hominin occupation of Bailong Cave, central China

Intermontane basins in the southern piedmont of the Qinling Mountains are important sources of information on hominin occupation and settlement, and provide an excellent opportunity to study early human evolution and behavioral adaptation. Here, we present the results of a detailed magnetostratigraphic investigation of the sedimentary sequence of hominin-bearing Bailong Cave in Yunxi Basin, central China. Correlation to the geomagnetic polarity time scale was achieved using previously published biostratigraphy, 26Al/10Be burial dating, and coupled electron spin resonance (ESR) and U-series dating. The Bailong Cave hominin-bearing layer is dated to the early Brunhes Chron, close to the Matuyama-Brunhes geomagnetic reversal at 0.78 Ma. Our findings, coupled with other records, indicate the flourishing of early humans in mainland East Asia during the Mid-Pleistocene climate transition (MPT). This suggests that early humans were adapted to diverse and variable environments over a broad latitudinal range during the MPT, from temperate northern China to subtropical southern China.

Mid-Pleistocene climate transition: Characteristic, mechanism and perspective

Milankovich theory suggested that orbitally induced summer insolation change at high-latitude region of Northern Hemisphere played a key role in driving the ice cycles during the Pleistocene. However, a significant shift of the Pleistocence climate from 41-ka to 100-ka cycles (namely mid-Pleistocene transition, MPT) cannot be simply attributed to the astronomical forcing due to insignificant insolation change induced by eccentricity forcing. Here we summarized multiple proxies generated from the ocean and land to address Pleistocene climate changes such as global ice volume, sea surface temperature, sea level, aridity of dust sources, and monsoon-related hydrological cycles. The temporal and spatial characteristics of the MPT phenomenon, in terms of the timing, duration, amplitudes and frequencies, were addressed using spectral and wavelet results. Most records reveal that the MPT was commenced as the onset of the ~100-ka cycles at ~1.2 Ma, and ended by the establishment of the dominant 100-ka cycles at ~0.7 Ma. However, some hydroclimatic proxies from the Mediterranean Sea, South China Sea and Chinese caves show a relatively strong 23-ka cycles during the middle to late Pleistocence. Such a difference may be attributable to varied sensitivity of proxy indicators to the insolation and glacial forcing. Globally, temperature and sea level signals that are affected by changing ice volume usually demonstrate a distinctive and consistent MPT. By contrast, regional hydroclimatic proxies at mid-to-low latitudes are likely dominated by the precession cycles (i.e. high-resolution, absolutely dated Chinese speleothem records). The MPT associated with the onset of ~100-ka cycles has inspired the paleocommunities to address its driving mechanism from both data and model perspectives. Several hypotheses have been proposed to explain the MPT in the past two decades, including nonlinear response to external forcing and complicated internal feedbacks. The nonlinear response to the astronomical forcing including eccentricity (100-ka cycle), interplay between obliquity (41-ka cycle) and precession (23- and 19-ka cycles) can produce the 100-ka ice-age cycles. However, model results suggest that the MPT and subsequent ″100 ka world″ are likely caused by changes in atmospheric CO2 concentration, bedrock exposure or ocean circulations. Taking these different hypotheses together, it was suggested that the solar insolation caused by changing Earth′s orbital parameters as external forcing, drives the glacial-interglacial climate cycles, whilst the nonlinear responses to atmospheric CO2 decrease and to different regolith boundary conditions as internal feedbacks have played key roles in triggering the climate transition and amplifying the glacial-interglacial oscillations. While most proxies from the land and ocean demonstrate a remarkable MPT from 41- to 100-ka cycles, regional high-resolution proxy records indicated that hydroclimatic changes at mid-to-low latitudes exhibit insignificant MPT and weak ~100-ka cycles after the MPT. In the future, more data assimilation should be focused on the hydroclimatic changes particularly in monsoon-affected regions to decipher the diverse responses in a regional scale. Meanwhile, simulations using high-resolution regional climate system models should be performed to quantify the responses of different climate parameters to external forcing and internal feedback. Through intensively data-model comparison, new insights into past climate variability and dynamics will permit a better projection of future climate change under the global warming context.