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Dating the arrival of the first hominins in Java The World Heritage archaeological site at Sangiran on the island of Java in Indonesia has major importance for the understanding of human arrival and evolution in Asia. However, the timing of the first appearance of Homo erectus at the site has been controversial. Using a combination of dating techniques for hominin-bearing sediments, Matsu'ura et al. resolved the arrival of H. erectus at ∼1.3 million years ago (see the Perspective by Brasseur). This dating suggests that the earliest hominins in Sangiran are at least 200,000 years younger than has been thought and may represent an important step to the resolution of the controversy. Science , this issue p. 210 ; see also p. 147

Leads, lags, or synchronies in climatic events among different regions are key to understanding mechanisms of climate change, as they provide insights into the causal linkages among components of the climate system. The well-studied transition from the Lateglacial to early Holocene (ca. 16–10 ka) contains several abrupt climatic shifts, making this period ideal for assessing the spatio-temporal structure of climate change. However, comparisons of timings of past climatic events among regions often remain hypothetical because site-specific age scales are not necessarily synchronised to each other. Here we present new pollen data (n = 510) and mean annual temperature reconstruction from the annually laminated sediments of Lake Suigetsu, Japan. Suigetsu's 14C dataset is an integral component of the IntCal20 radiocarbon calibration model, in which the absolute age scale is established to the highest standard. Its exceptionally high-precision chronology, along with recent advances in cosmogenic isotope studies of ice cores, enables temporally coherent comparisons among Suigetsu, Greenland, and other key proxy records across regions. We show that the onsets of the Lateglacial cold reversal (equivalent to GS-1/Younger Dryas) and the Holocene were synchronous between East Asia and the North Atlantic, whereas the Lateglacial interstadial (equivalent to GI-1/Bolling-Allerod) started ca. two centuries earlier in East Asia than in the North Atlantic. Bimodal migration (or ‘jump’) of the westerly jet between north and south of the Tibetan plateau and Himalayas may have operated as a threshold system responsible for the abruptness of the change in East and South (and possibly also West) Asia. That threshold in Asia and another major threshold in the North Atlantic, associated with switching on/off of the Atlantic meridional overturning circulation (AMOC), were crossed at different times, producing a multi-centennial asynchrony of abrupt changes, as well as a disparity of climatic modes among regions during the transitional phases. Such disparity may have disturbed zonal circulation and generated unstable climate during transitions. The intervening periods with stable climate, on the other hand, coincided with the beginnings of sedentary life and agriculture, implying that these new lifestyles and technologies were not rational unless climate was stable and thus, to a certain extent, predictable.

Volcanoes in the East Asian/Pacific region have been the source of some of the largest magnitude eruptions during the Late Quaternary, and accurately evaluating their eruptive histories is essential for hazard assessments. To overcome difficulties in resolving and precisely dating eruptions in the near‐source realm, the high‐resolution (varved) sediments of Lake Suigetsu (central Honshu, Japan) were examined for the presence of non‐visible (cryptotephra) layers from 50 ka up until the 30 ka Aira‐Tanzawa (AT) caldera‐forming event of Aira volcano. Cryptotephra layers are four times more frequently preserved than visible markers in the Suigetsu sediments, meaning that this archive provides a unique and unprecedented record of eruptions that were dispersed over the densely populated regions of central Honshu. Major and trace element volcanic glass chemistry is used to fingerprint the ash layers and pinpoint their volcanic origin. Tephras are found throughout the investigated sediments, but the highest abundance of ash fall events are recorded between 39 and 30 ka, capturing a period of intense volcanism at calderas on Kyushu Island (Japan). The augmented Suigetsu tephrostratigraphy records at least seven eruptions from Aso caldera (southern Kyushu) that post‐date the widespread ACP‐4 Plinian eruption (ca. 50 ka) and four explosive events from Aira (central Kyushu) that occurred leading up to the catastrophic caldera‐forming AT eruption (ca. 30 ka).

Tephra (volcanic ash) layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales. Highly productive arc regions, like those in East Asia, offer a considerable number of widespread isochrons, but before records can be confidently correlated using these layers, a refined and integrated framework of these eruptive events is required. Here we present the first high-resolution Holocene cryptotephra study in East Asia, using the Lake Suigetsu sedimentary archive in central Japan. The Holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques, which integrates the deposits from explosive eruptions from North Korea/China, South Korea and along the Japanese arc. This Lake Suigetsu tephrostratigraphy is now the most comprehensive record of East Asian volcanism, and the linchpin site for correlating sequences across this region. Major element glass geochemical compositions are presented for the tephra layers in the sequence, which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions. This study has significantly extended the ash dispersal of many key Holocene marker layers, and has identified the first distal occurrence of isochrons from Ulleungdo and Changbaishan volcanoes. Utilising the high-precision Lake Suigetsu chronology, we are able to provide constrained eruption ages for the tephra layers, which can be transferred into other site-specific age models containing these markers. This new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in Japan, and could be used to precisely assess the regional and hemispheric synchronicity of these events.

Fossil pollen grains have long been recognised as potentially ideal materials for radiocarbon dating. In recent years, the development of cell sorter technology has made it possible to date fossil pollen grains. Although various approaches have been proposed, none of them is being practiced routinely because of the difficulty in stably and efficiently extracting small fossil grains at high enough purity from a variety of sediments. Here we show a new method which allows routine extraction and reliable radiocarbon dating of fossil pollen grains, even from organic-rich sediments. The improved physicochemical pre-treatment enables efficient enrichment from large volume of organic-rich sediments without the use of an oxidant. We also propose new sorting criteria consisting of multi-step ‘gates’, each of which is based upon fluorescence characteristics and scattered light of the particles. The sorting method, combined with the improved physicochemical pre-treatments, makes it possible to separate small fossil pollen grains from impurities such as green algae, micro charcoal, spores and plant fragments using a cell sorter. In particular, relatively small fossil pollen grains, with which previously proposed methods tended to suffer, could be extracted from organic-rich lacustrine sediments and organic peats in a remarkably high purity and velocity using our method. Radiocarbon ages subsequently measured on fossil pollen concentrates prepared by our method show very good agreement with those of terrestrial leaf fossils extracted from the same sediments of Lake Suigetsu, which directly record atmospheric 14C. The extraction method provides a new opportunity to routinely determine ages of sediments that do not contain contemporaneous macrofossil remains, and allow us to increase the precision of age models by strategically selecting horizons for dating prior to incorporation into Bayesian chronological modelling.

We conducted diatom analyses of a core from the Pleistocene marine sequence drilled at the Chiba Section, central Japan, to reveal detailed paleoceanographic variations across the Early–Middle Pleistocene boundary. Diatom valves are most abundant at 4.5 m below the Matuyama–Brunhes magnetic polarity boundary, followed by the second highest abundance at 18.6 m above the boundary, which is consistent with the sea-level changes inferred from planktonic δ 18 O data. The highest abundance is correlated with the Marine Isotope Stage (MIS) 19.3 sea-level highstand, and the second-highest with the MIS 19.1 highstand. The abundance of the extinct species Actinocyclus ingens is quite low around these sea-level highstands, whereas it is greatest at the core depth with the minimum diatom total valves, which is correlated to the MIS 19.2 lowstand. Cold-water diatom species that are characteristic of the Oyashio Current are dominant but coexist with warm-water species of the Kuroshio Current below a core depth just postdating MIS 19.2. Above this depth, warm diatom species of the Kuroshio Current become dominant. The change in dominant diatoms suggests that the Kuroshio Front shifted northward just after MIS 19.2 and remained in the northern area until at least early MIS 18. This shift caused a rapid increase in sea-surface temperature by 4–5 °C within a sediment thickness of 1.3 m (representing ∼300 years).

Marker grain method is commonly used by palynologists to quantify absolute pollen concentration in sediments. DuPont NEM plastic microbeads and Lycopodium spore tablets are two of the most commonly used marker grains. The DuPont NEM series has an obvious advantage over Lycopodium tablets because Lycopodium is not guaranteed ‘exotic’ in many ecosystems (especially in the past). Moreover, NEM also has high visibility, easily identifiable spherical shape, and availability in different size ranges. However, the production of NEM has been discontinuous since more than a decade, and palynologists of the world are using the precious remainders of their own stock in very small (=suboptimal) quantities. Here we propose a solution. Microspheres of black ceramic can be used as marker grains for a wide range of microfossil analyses (in this paper, however, we mainly discuss the use of the material for pollen analysis because of the expertise of the authors). The ceramic spheres are tolerant to all chemicals commonly used during pollen extraction processes and is extremely resistant to physical stresses. The particles are matt black, spherical, available in a wide range of size clusters, have a density very close to that of fossil pollen grains (1.424 g/cm3 vs. 1.494 g/cm3 in average), and don't change color and density over a long storage in acidic liquids. The behavior of ceramic spheres was closer to the pollen grains than the Lycopodium spores regardless of the pollen concentration and composition in sediments. In combination, these properties make the black ceramic spheres an even better solution for palynologists than DuPont NEM microbeads or Lycopodium spore tablets. The absolute pollen concentrations estimated from ceramic spheres and those estimated from volume method were indistinguishable within errors. On the other hand, when the samples were relatively poor in fossil pollen grains, the concentrations calculated by Lycopodium method tended to be significantly overestimated. The ceramic microbeads are available either as a dry powder in different size ranges, or as a mixture of two size ranges blended in a defined ratio and dispersed in a buoyancy-neutral liquid, ready to be added to sediment samples. Mixing two different size ranges in a known ratio serves to detect any laboratory failures that differentially favor recovery of larger or smaller pollen types.

The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60% from 4826 to 8134. Much of the improvement in data coverage has come from northern Asia, and the database has consequently been renamed the Eurasian Modern Pollen Database to reflect this geographical enlargement. The EMPD can be viewed online using a dedicated map-based viewer at https://empd2.github.io and downloaded in a variety of file formats at https: //doi.pangaea.de/10.1594/PANGAEA.909130 (Chevalier et al., 2019)., Swiss National Science Foundation (SNSF) 200021_169598, University of Lausanne

The eruptive histories of Ulleungdo (South Korea) and Changbaishan (North Korea/China border) volcanoes are not well constrained since their proximal stratigraphies are poorly exposed or largely inaccessible. However, determining the past behaviour of these volcanoes is critical since future eruptions are likely to disperse ash over some of the world’s largest metropolitan regions. Alkaline tephra deposits erupted from both centres are routinely identified in marine cores extracted from the Sea of Japan, as well as high-resolution lacustrine records east of the volcanoes. Here, we review the distal ash occurrences derived from Ulleungdo and Changbaishan and provide new data from the Lake Suigetsu (central Honshu, Japan) sediment core, in order to provide a more complete and constrained eruption framework. The intensely-dated Lake Suigetsu archive provides one of the most comprehensive distal eruption records for both centres, despite being located ca. 500 km E of Ulleungdo and ca. 1000 km SSE of Changbaishan. The Suigetsu record is utilised to precisely date and geochemically fingerprint (using major, minor and trace element glass compositions) ash fall events that reached central Honshu. Here, we identify a new non-visible (cryptotephra) layer in the Suigetsu sediments, which reveals a previously unreported explosive event from Changbaishan at 42,750 – 42,323 IntCal13 yrs BP (95.4 % confidence interval). This event is chronologically and geochemically distinct from the B-J (Baegdusan-Japan Basin) tephra reported in the Sea of Japan (ca. 50 ka). Furthermore, we also confirm that the widespread U-Ym tephra erupted from Ulleungdo reached central Japan, and is herein dated to 40,332 – 39,816 IntCal13 yrs BP (95.4 % confidence interval). This terrestrial 14C-derived age of the U-Ym can be used to constrain the chronology of marine records containing the same marker layer. This reviewed and integrated tephrostratigraphic framework highlights the pivotal role that distal sedimentary records can play in evaluating the eruptive histories and hazard potential of Ulleungdo and Changbaishan.

Detailed sea-level variation was investigated for Marine Isotope Stage (MIS) 19, based on diatom and grain size analyses of a marine sequence in a core of the Osaka Group. Diatom sea-level proxies represent precession-related signals correlated with highstands MIS 19.3 and 19.1, and lowstand MIS 19.2. Astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka−1. A rapid sea-level fall event was found in the earliest MIS 19, demonstrated by several independent sea-level proxies of diatom and grain size. This event began with a rapid sea-level drop, followed by a gradual recovery, at about 783–782 ka. A maximum abundance of pelagic diatom taxa at a core depth of 402.20 m evidently shows the highest sea-level peak in MIS 19, supported by many other proxies. Based on the diatom data, sea-level change across MIS 19.1 is characterized by centennial to millennial fluctuations. The sea-level fall event began just after the onset of a cooling event previously reported from the same core. Observations of a comparable sea-level fall signal in many deep-sea core records suggest the event is global.

Akita-sugi (Cryptomeria japonica, Japanese cedar that is grown in Akita) forests are among the most important for commercially valuable timber in Japan. Historically, these forests have been severely exploited, although now some parts of them are conserved. It is important to know the detailed history of the forests in order to utilize them sustainably in the future. This study analyzes the pollen in an annually laminated lake sediment core from Ichi-no-Megata on the Oga peninsula, Akita, Japan, to understand the history of Akita-sugi cedar forests. An age-depth model was developed based on the results of an accelerator mass spectrometer dating of 13 plant macrofossils from the surface to 422 cm in depth, the Towada-a tephra and other well-known event layers. The dominant pollen taxa were Cryptomeria and Fagus crenata by ad 1000. The first increase of Cryptomeria was detected around 1700 bc. By the 1st century ad, Cryptomeria forest was established. At that time, Cryptomeria was mixed with deciduous trees, mainly F. crenata. The pollen analysis found evidence that the main loss of woodland occurred during the 11th century ad, when forest lands were cleared for agriculture. Substantial natural forests nevertheless remained until the 16th century, after which forest resources were exhausted. Conservation and plantation activities took place later, but human activity in response to severe famines prevented the recovery of the forests. After the famine periods, the remaining forests recovered to their previous condition, but after World War II, the natural forests shrank further and plantation forests without deciduous trees were established over large areas.

We present a detailed stratigraphy of the lithology, sedimentary facies, magnetic susceptibility, and chemical composition of a 54-m thick core sequence drilled adjacent to the Chiba section, a candidate for the Global Boundary Stratotype Section and Point of the early–middle Pleistocene boundary. Siltstones rich in trace fossils are dominant throughout the core, except for the lowermost sand beds. The Byakubi tephra is divided into three units, of which the uppermost (39.54–39.49 m core depth) is identified as a primary bed showing evidence of fallout. The preliminary Matuyama–Brunhes magnetic polarity boundary lies 1 m above the top of the fallout unit. Maximum and minimum susceptibility axes for anisotropy of magnetic susceptibility have shallow ( 73°) inclinations, respectively, throughout the core. The results suggest that sedimentary structures formed in calm environments remain undisturbed in the sediment. Clustered maximum axis directions indicate the influence of a persistent NW–SE contour current. The homogeneous depositional environment for the siltstone interval is supported by relatively smooth variations in magnetic susceptibility and chemical composition. Stratigraphic correlation with published oxygen isotope data indicates that the depositional age of the core may extend from the end of marine oxygen isotope stage (MIS) 20 to just after mid-MIS 19, from which an average sedimentation rate of 2–2.5 m/ky is estimated. These results suggest that the Chiba section has a high potential to provide an excellent stratotype for the early–middle Pleistocene boundary.

Large Magnitude (6–8) Late Quaternary Japanese volcanic eruptions are responsible for widespread ash (tephra) dispersals providing key isochrons suitable for the synchronisation and dating of palaeoclimate archives across East Asia, the NW Pacific and beyond. The transfer of geochronological information using these eruption deposits demands robust tephra correlations underpinned by detailed and precise volcanic glass geochemical data. Presented here is a major (electron microprobe; EMP) and trace element (Laser ablation inductively coupled plasma mass spectrometry; LA-ICP-MS) characterisation of near-source deposits from a series of large magnitude Japanese eruptions spanning approximately the last 150 ka. These data offer new insights into diagnostic compositional variations of the investigated volcanic sources spanning the Japanese islands. Whilst in the case of the highly productive Aso caldera (Kyushu), we are able to explore compositional variations through successive large magnitude eruptions (50–135 ka). These near-source volcanic glass data are used to validate and refine the visible tephrostratigraphy of the intensely dated Lake Suigetsu sedimentary record (SG06 core), Honshu Island, whilst also illustrating key tephrostratigraphic tie points to other East Asian palaeoclimate records (e.g. Lake Biwa). The identification of widespread Japanese tephrostratigraphic markers in the SG06 sediment record enables us to place chronological constraints on these ash dispersals, and consequently explosive volcanism at source volcanoes situated along the Kyushu Arc, including Kikai, Ata and Aso calderas. The proximal Aso-4 Ignimbrite (Magnitude 7.7) deposit is dated here by 40Ar/39Ar at 86.4 ± 1.1 ka (2σ), and provides a chronological anchor (SG06-4963) for the older sediments of the Lake Suigetsu record. Finally, trace element glass data verify visible ash fall layers derived from other compositionally distinct source regions of Japanese volcanism, including activity along the northern Izu-Bonin arc and North East Japan Arcs. These findings underline the Lake Suigetsu record as central node in the Japanese tephrostratigraphic framework. Highlights • Near-source and distal (Lake Suigetsu) characterisation of Late Quaternary widespread Japanese Tephrostratigraphic markers. • Grain-specific major and trace element volcanic glass analyses (EMP & LA-ICP-MS). • Chemical discrimination of Japanese volcanic source regions for the purposes of Tephrochronology. • Unlocking the Lake Suigetsu (SG06 core) visible tephra layers for reliable archive synchronisation. • Proximal 40Ar/39Ar age of 86.4 ± 1.1 ka (2σ) for the Magnitude 7.7 caldera forming Aso-4 eruption.

The chronology of the World Heritage Site of Sangiran in Indonesia is crucial for the understanding of human dispersals and settlement in Asia in the Early Pleistocene (before 780,000 years ago). It has been controversial, however, especially regarding the timing of the earliest hominin migration into the Sangiran region. We use a method of combining fission-track and uranium-lead dating and present key ages to calibrate the lower (older) Sangiran hominin-bearing horizons. We conclude that the first appearance datum for the Sangiran hominins is most likely ~1.3 million years ago and less than 1.5 million years ago, which is markedly later than the dates that have been widely accepted for the past two decades.

Recent high-resolution magnetic and microfossil data from a long core penetrating the Osaka Group, Japan are astronomically tuned and reassessed to reveal detailed stratigraphic features across the Matuyama–Brunhes (MB) polarity transition during Marine Isotope Stage (MIS) 19. The sediments have a uniform and high average accumulation rate of 63 cm/ky. Astronomical tuning based on six calibration points, including a clear MIS 19.2 sea-level lowstand, dates the main MB boundary (MBB) to 777.6 ka, the sea-level peak of the MIS 19.3 highstand to 780.7 ka, and the climatic thermal maximum (TM) to 776.4 ka. The MB transition began with a short-lived normal polarity episode that occurred before the highstand at MIS 19.3, and terminated with multiple rapid reversals that occurred between highstand MIS 19.3 and lowstand 19.2. The TM just postdates the termination of the MB transition, and occurs about 4000 years after the sea-level peak. The delayed TM is also observed at Gesher Benot Ya'aqov, Israel and on the Mediterranean coast, and possibly at Lake Baikal. In high-resolution records from Chinese loess–paleosols and deep-sea sediments, the rapid reversal zone of the MBB has a very similar climatostratigraphic character. These magneto-climatostratigraphic features in MIS 19 are useful for correlating between terrestrial and marine sediments. The delay in warming relative to the sea-level highstand seems to have been due to a cloud-albedo effect induced by an increase in galactic cosmic ray flux during an extremely low magnetic field intensity interval.

Suborbital-scale climate variations, possibly caused by solar activity, are observed in the Holocene and last-glacial climates. Recently published bicentennial-resolution paleoceanic environmental records reveal millennial-scale high-amplitude oscillations postdating the last geomagnetic reversal in the Marine Isotope Stage (MIS) 19 interglacial. These oscillations, together with decoupling of post-reversal warming from maximum sea-level highstand in mid-latitudes, are key features for understanding the climate system of MIS 19 and the following Middle Pleistocene. It is unclear whether the oscillations are synchronous, or have the same driver as Holocene cycles. Here we present a high resolution record of western North Pacific submarine anoxia and sea surface bioproductivity from the Chiba Section, central Japan. The record reveals many oxic events in MIS 19, coincident with cold intervals, or with combined cold and sea-level fall events. This allows detailed correlations with paleoceanic records from the mid-latitude North Atlantic and Osaka Bay, southwest Japan. We find that the millennial-scale oscillations are synchronous between East and West hemispheres. In addition, during the two warmest intervals, bioproductivity follows the same pattern of change modulated by bicentennial cycles that are possibly related to solar activity.

The weakening of the geomagnetic field causes an increase in galactic cosmic ray (GCR) flux. Some researchers argue that enhanced GCR flux might lead to a climatic cooling by increasing low cloud formation, which enhances albedo (umbrella effect). Recent studies have reported geological evidence for a link between weakened geomagnetic field and climatic cooling. However, more work is needed on the mechanism of this link, including whether the umbrella effect is playing a central role. In this research, we present new geological evidence that GCR flux change had a greater impact on continental climate than on oceanic climate. According to pollen data from Osaka Bay, Japan, the decrease in temperature of the Siberian air mass was greater than that of the Pacific air mass during geomagnetic reversals in marine isotope stages (MIS) 19 and 31. Consequently, the summer land-ocean temperature gradient was smaller, and the summer monsoon was weaker. Greater terrestrial cooling indicates that a reduction of insolation is playing a key role in the link between the weakening of the geomagnetic field and climatic cooling. The most likely candidate for the mechanism seems to be the increased albedo of the umbrella effect.

The climatic effects of cloud formation induced by galactic cosmic rays (CRs) has recently become a topic of much discussion. The CR–cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux. This hypothesis, however, is not well-tested using robust geological evidence. Here we present paleoclimate and paleoenvironment records of five interglacial periods that include two geomagnetic polarity reversals. Marine oxygen isotope stages 19 and 31 contain both anomalous cooling intervals during the sea-level highstands and the Matuyama–Brunhes and Lower Jaramillo reversals, respectively. This contrasts strongly with the typical interglacial climate that has the temperature maximum at the sea-level peak. The cooling occurred when the field intensity dropped to 40% increase in CR flux. The climate warmed rapidly when field intensity recovered. We suggest that geomagnetic field intensity can influence global climate through the modulation of CR flux.

We report climate and sea-level variation for the marine oxygen isotope stage (MIS) 21, encompassing the end of the Mid-Pleistocene climate transition (MPT), based on pollen, diatom, and sulfur records from a 50-m thick sequence in a core from Osaka Bay. An extremely warm climate coincided with the sea level highstand of substage 21.5, when the warm-temperate element Quercus ( Cyclobalanopsis ) exceeds 40% of total arboreal pollen. This was followed by a warm-temperate to temperate and humid climate that continued until the end of MIS 21. A linear age model shows that climate was dominated by precessional cyclicity, with an inverse correlation between temperature and precipitation. The postglacial sea-level rise reached its highest peak in substage 21.5, when paleo-Osaka Bay reached its maximum extent including Kyoto and Nara Basins. At this time pelagic diatoms were dominant in the central part of the bay. Sea level dropped below the Osaka Bay sill (about − 60 m at present) during substage 21.4, followed by a rise above the sill in substage 21.3, and a drop at 21.2. Sea level remained below the sill during substage 21.1. The thermal maximum and sea level peak occurred just after the rapid postglacial sea level rise, after which there was a gradual decline in temperature and sea level accompanied by precession-related oscillations; these features are typical of the post-MPT interglacials dominated by 100-ka cyclicity. These features may be a sign of termination of the MPT.

奈良盆地西部の生駒市高山町稲葉に分布する大阪層群海成粘土層Ma2層から産出した花粉化石と大型植物化石に基づき，Ma2層が堆積した前期更新世MIS 25の古植生と古気候を推定した．当時の植生は，ブナ属やコナラ亜属を主体とする落葉広葉樹林が卓越していた．植物化石群のうち，最も温暖な地域に生育するハスノハカズラと，最も冷涼な地域に生育するサワラの分布域の気候から，当時の奈良盆地西部の気温条件を年平均気温約10～13℃と推定した．Ma2層に含まれるブナ属殻斗化石は，小型で基部が隆起する殻斗鱗片から，シキシマブナと同定した．微分干渉顕微鏡による観察から，シキシマブナ由来である可能性が高い同層準のブナ属花粉は，小さな粒径と粗い表面模様を持つ点で，現生のブナ属と異なることがわかった．また，奈良盆地と大阪湾周辺のMa2層のメタセコイア化石産出状況を比較・再検討した結果，大型植物化石の産出の有無や花粉の産出率に地域差があることが明らかになった．

This study presents a high-resolution palynological analysis of a sedimentary core from Osaka Bay (Japan) straddling Marine Oxygen Isotope Stage (MIS) 19, i.e. across the Matuyama–Brunhes magnetic polarity Boundary (MBB). Comparison with the standard marine oxygen isotope curve ([Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., Lancelot, Y., 1994. The astronomical theory of climate and the age of the Brunhes–Matuyama magnetic reversal. Earth and Planetary Science Letters 126, 91–108.]) demonstrates that variations in vegetation and the basinal environment coincided with global ice volume changes. The late MIS 20 is characterized by boreal climate with coniferous forest. In MIS 19, the forest was generally dominated by Fagus and Quercus (Lepidobalanus), suggesting onset of humid climatic conditions slightly cooler than the present. Excluding coastal vegetation components, climate during MIS 19 can be subdivided into three stages. The early stage, including substage 19.3, is characterized by high seasonality in precipitation. This contrasts with the very abundant, year-round precipitation that is inferred for the late stage, from substage 19.2 to substage 19.0, which is characterized by cool-temperate coniferous taxa including Cryptomeria. The very high precipitation rates of the latter persisted at least up to substage 18.4. There was no apparent vegetational response to the sea level highstand of 19.3. In contrast, a short-lived thermal maximum event took place ca. 6–7 kyr later, i.e. in middle MIS 19. This event is characterized by increases in the warm-temperate element Quercus (Cyclobalanopsis). The MBB, the recommended criterion for defining the Lower–Middle Pleistocene boundary, took place in middle MIS 19. These lines of evidence indicate that the occurrence of the MBB corresponded with a shift towards warmer and wetter climatic conditions. Similar warming and wetting events across the MBB are also observed in pollen records from southern Italy and central Japan. This possibly provides long-distance correlation, and may suggest a connection between the Earth's magnetic field and climate.

Marine oxygen isotope stage (MIS) 19 has an abnormal climate where the temperature maximum postdated by about 5 kyr the sea-level peak in mid-latitudes, and includes the Matuyama–Brunhes magnetic polarity transition that persisted for several kyr. The stratigraphy of this stage must be precisely understood as a candidate for the Early–Middle Pleistocene boundary. The marine clay layer correlated with MIS 19 in the Osaka Group is able to provide millennial-scale magneto–climatostratigraphy because of its high accumulation rate of about 60 cm/kyr. A new age model based on a diatom sea-level proxy curve tuned to oxygen isotope stack LR04 reveals that the sedimentation rate is almost uniform. The following dated events provide a useful time scale: (1) Two high sea-level intervals that span 784–778 ka and 768–762 ka, correlated with substages 19.3 and 19.1, respectively. The first interval includes a sea-level peak at 780 ka. (2) The warmest temperature interval spans 777–774 ka. (3) The low-palaeointensity interval (LPI) spans 784–776 ka and includes multiple polarity swings. We confirm that the LPI is a useful time measure, applying to the preliminary palaeomagnetic results from the Chiba section of the Kazusa Group in eastern Japan. The beginning of the warmest temperature interval almost coincides with the end of the LPI at 777–776 ka and may provide an important datum level near the Early–Middle Pleistocene boundary.

A detailed paleomagnetic study conducted in the Sangiran area, Java, has provided a reliable age constraint on hominid fossil-bearing formations. A reverse-to-normal polarity transition marks a 7-m thick section across the Upper Tuff in the Bapang Formation. The transition has three short reversal episodes and is overlain by a thick normal polarity magnetozone that was fission-track dated to the Brunhes chron. This pattern closely resembles another high-resolution Matuyama–Brunhes (MB) transition record in an Osaka Bay marine core. In the Sangiran sediments, four successive transitional polarity fields lie just below the presumed main MB boundary. Their virtual geomagnetic poles cluster in the western South Pacific, partly overlapping the transitional virtual geomagnetic poles from Hawaiian and Canary Islands’ lavas, which have a mean 40 Ar/ 39 Ar age of 776 ± 2 ka. Thus, the polarity transition is unambiguously the MB boundary. A revised correlation of tuff layers in the Bapang Formation reveals that the hominid last occurrence and the tektite level in the Sangiran area are nearly coincident, just below the Upper Middle Tuff, which underlies the MB transition. The stratigraphic relationship of the tektite level to the MB transition in the Sangiran area is consistent with deep-sea core data that show that the meteorite impact preceded the MB reversal by about 12 ka. The MB boundary currently defines the uppermost horizon yielding Homo erectus fossils in the Sangiran area.