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During Deep Sea Drilling Project (DSDP) Leg 21, Cenozoic and latest Cretaceous sediments were recovered at Site 208 on the Lord Howe Rise, Southwest Pacific. We provide new biostratigraphic, magnetostratigraphic and chemostratigraphic data from Site 208 to constrain the stratigraphy around the Cretaceous-Paleogene (K-Pg) boundary and to determine the depth of the K-Pg boundary more precisely. Biostratigraphic data from calcareous nannofossils indicate a near-continuous succession of sediments from the mid-Maastrichtian (Late Cretaceous) to lowermost Thanetian (Paleocene) at depths of 540–590 m below seafloor (mbsf). The biostratigraphic data suggest that the K-Pg boundary corresponds to a siliceous claystone at the base of an interval of silicified sediments (576.0–576.8 mbsf). Carbonate carbon isotopic composition (δ13Ccarb) reveals a negative shift across this interval, which is consistent with global patterns of δ13C across the K-Pg boundary. Osmium concentration and Os isotopic composition (187Os/188Os) can also be used to identify the K-Pg boundary interval, as it is marked by a peak in Os concentration and a drop in 187Os/188Os values to 0.12–0.15, both of which are the result of the Chicxulub impact event. Our 187Os/188Os data show trends similar to those of coeval global seawater with the lowest value of 0.12–0.16 in the siliceous claystone (576.8 mbsf). However, the concentration of Os is low (

The Indian Summer Monsoon (ISM) brings seasonal winds and rains to the Indian subcontinent. The winds cause surface ocean mixing in the southern Bay of Bengal (BoB), bringing nutrients to the surface that fuel ocean productivity and export of carbon to the sea floor. To improve the understanding of the role of monsoon winds in low-latitude surface ocean productivity and carbon export, the Plio-Pleistocene interval is ideal because boundary conditions were evolving. We aim to reconstruct variability in surface ocean and export productivity across the late-Pliocene and early-Pleistocene in response to ISM wind-driven mixing in the southern BoB. Here we analyse sediments from IODP Site U1443 (Exp. 353) from ~1.9-2.8 million years ago. A new benthic oxygen isotope (δ18O) stratigraphy (at ~3-thousand-year resolution) and age model tied to the global benthic δ18O stack are presented. We utilise these sediments to obtain bulk sediment X-ray fluorescence (XRF) core scanning elemental data and coccolithophore assemblages to infer changes in summer monsoon runoff and surface ocean productivity influenced by monsoon wind strength. We use % Florisphaera profunda (coccolithophore assemblage) along with bulk sediment XRF Br as productivity indicators and a “terrigenous” bulk sediment XRF elemental composition stack as a wind strength and runoff indicator. We observe increased productivity during glacials (MIS 96, 98, 100), coinciding with increased terrigenous input. This observation is coherent with previous low-latitude productivity records from the equatorial Pacific. However, in contrast to equatorial Pacific productivity records, influenced by obliquity, our southern BoB records show robust surface productivity (% F. profunda) and summer monsoon runoff (terrigenous stack) peaks in both the obliquity and precession bands. We will discuss linkages between monsoon wind and runoff across the Plio-Pleistocene in context with other monsoon records.

Shock metamorphism of minerals in meteorites provides insights into the ancient Solar System. Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite-group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre-impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X-ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation-induced plastic deformation in the crystal. Finally, we propose a strategy to re-construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu., 25 pages, 9 figures, 1 table, 1 supporting information, accepted for publication in Journal of Geophysical Research Planets

Both molybdenum (Mo) and tungsten (W) form soluble oxyanions in oxic seawater, whereas Mo forms insoluble thiomolybdate and W forms soluble thiotungstate in sulfidic seawater. Thus, concentrations and stable isotope ratios of Mo and W in sediments may fluctuate due to changes in redox conditions and can be used to estimate paleoenvironmental changes. The modern Japan Sea is oxic from the surface to the bottom, whereas deep water became anoxic several times from the late Pleistocene to the Holocene. Detailed information on redox conditions is still lacking. In this study, we analyzed a sediment core that was collected from offshore Iwanai, Hokkaido (43°22ʹ36ʺ N, 140°04ʹ10ʺ E, water depth 900 m). To the best of our knowledge, our study is the first to report stable isotope data of Mo and W in sediments of the Japan Sea. We observed maxima in the Mo concentration of up to 29 ppm in the sediment layers of 11–10 ka, 17–14 ka (the last glacial maximum), 31 ka, and 45 ka in accordance with the maxima of total sulfur, thereby indicating the deposition of thiomolybdate MoOxS₄₋x²⁻ (0 ≤ x ≤ 3). δ⁹⁸Mo, however, was between –0.19 and 0.69‰ at these ages, suggesting that the H₂S concentration in bottom water never exceeded 11 μmol kg⁻¹. The concentration and isotopic ratio of W were relatively constant throughout the core; W = 1.2 ± 0.2 ppm and δ¹⁸⁶W = 0.03 ± 0.03‰ (ave ± sd). The authigenic Mo and W ratio, Moauth/Wauth (mol/mol), was 10.5 ± 7.3 except for the above four ages, supporting the control of Mn and Fe (oxyhydr)oxides on Moauth and Wauth under oxic conditions.

Molybdenum (Mo) is a redox-sensitive element and its concentrations and stable isotope compositions are widely used as a redox proxy in paleoceanography. Tungsten (W) is an emerging new isotope proxy, which has potential as a tracer for hydrothermal and early diagenetic processes. We present a new method for the precise and accurate analysis of Mo and W concentrations and isotope compositions from one single sample aliquot, thus saving mass of a sample and making the results directly comparable without concerns related to analytical or natural sample heterogeneity. After acid digestion, Mo and W are separated from the sample matrix using chelating resin NOBIAS Chelate-PA1 and anion exchange resin AG1 X8. Matrix removal is highly efficient: the remaining percentage is 10−2 to 10−5% with respect to the initial weight. Subsequently, samples are measured for Mo and W concentrations and isotope compositions using multi-collector inductivity coupled plasma mass spectrometry (MC-ICP-MS). For mass bias correction and determination of concentrations, we use standard-sample bracketing and in addition an external correction method employing ruthenium (Ru) for Mo and rhenium (Re) for W. This double correction approach results in an external reproducibility of or below 0.10‰ (2SD) for δ98Mo and 0.05‰ for δ186W based on ICP standard solutions (NIST SRM 3134 lot No. 130418 for Mo and NIST SRM 3163 lot No. 080331 for W). We present data for Mo and W in 12 geological reference materials including igneous rocks, sedimentary rocks, marine sediments, and manganese nodules. For Mo our method reproduces published values for the geological standard materials within analytical error of published values. For W, although published data do not always agree for a given geological standard material, our data agree within error with more recent data. We interpret a cause of the deviations is due to unknown effects of a desolvating nebulizer for MC-ICP-MS.

X-ray fluorescence (XRF) core scanner elemental count data are useful for high-resolution paleoceanographic studies. However, because several factors, such as changes in physical core properties, significantly affect element count intensities, the appropriate calibration of the count data is required. Besides, the existing approaches for calibration were not widely employed and require rigorous testing based on sediment variety. In this study, we analyzed high-resolution element intensity (cps) using a wet muddy marine sediment piston core that was collected from the northeast Gulf of Alaska and tested several approaches with ratio and log-ratio methods, and the reliability was evaluated by comparison with the concentrations that were measured by WD-XRF and an elemental analyzer. The results show that the lighter elements (Ti and K) exhibited a significantly weak relationship between raw counts measured by ITRAX and concentrations that were measured by the WD-XRF, indicating that some factors artificially influence ITRAX intensity data. The Cl intensity that is expressed as the water content in marine sediment increased significantly in the upper 202 cm by 42% and the top 25 cm by 73% as compared to the down-core (below 202 cm), which deviates the X-ray scattering and element-counts. The calibration of raw data through coherent/incoherent X-ray scattering ratio (CIR) and additive- and centered-log ratio reduces the offsets. The calibration by CIR performed best for Sr, Fe, Mn, Ti, Ca, K, and Br (0.56 &lt, R2 &lt, 0.91), and the correlation with concentration significantly increased for Ti and K of 100% and 56%, respectively. Therefore, the study suggests that the correction of raw counts through CIR is an effective approach for wet marine sediment when core physical properties have greater variability.

The southwestern Ryukyu Trench represents the ultimate sink of sediments shed from Taiwan into the Philippine Sea, which are mainly transported to the trench by turbidity currents via submarine canyons. Here, we present trench turbidites intercalated with hemipelagites in a gravity pilot core and a piston core acquired on the Ryukyu Trench floor at 6147 m water depth. We performed X-ray fluorescence core scans (ITRAX profiles), magnetic measurements, and organic geochemistry analyses to discriminate turbidites from hemipelagites. We identified 36 turbidites (0.9–4.2 cm thick) based on visual core descriptions and Ca/Fe ratios in the ITRAX profiles. Three of these turbidites show magnetic signatures indicating the presence of pyrrhotite and peaks in the magnetic susceptibility profile, suggesting that Taiwan-sourced sediments are transported to the Ryukyu Trench by long-runout turbidity currents. Pyrrhotite is also present in hemipelagites of the upper part of the retrieved cores, indicating a dominant sediment source in Taiwan over the last several thousand years. Ca/Fe and Zr/Rb ratios in the ITRAX profiles mark distal turbidites (about 1–3 cm thick), and Zr/Rb peaks mainly reflect grain size changes. Detailed analyses of a representative turbidite show good correlation between Ca/Fe and Zr/Rb peaks with upward-coarsening and upward-fining trends that delimit the turbidite. Sedimentary organic matter in hemipelagites is characterized by higher total organic carbon and total nitrogen contents and higher δ13C values than that in turbidites. Our multi-proxy approach employing high-resolution XRF core scans to differentiate turbidites from hemipelagites contributes to establishing a comprehensive view of modern trench sedimentation from Taiwan to the southwestern Ryukyu Trench.

X-ray fluorescence (XRF) scanning of marine sediment has the potential to yield near-continuous and high-resolution records of elemental abundances, which are often interpreted as proxies for paleoceanographic processes over different time scales. However, many other variables also affect scanning XRF measurements and convolute the quantitative calibrations of element abundances and comparisons of data from different labs. Extensive interlab comparisons of XRF scanning results and calibrations are essential to resolve ambiguities and to understand the best way to interpret the data produced. For this study, we sent a set of seven marine sediment sections (1.5 m each) to be scanned by seven XRF facilities around the world to compare the outcomes amidst a myriad of factors influencing the results. Results of raw element counts per second (cps) were different between labs, but element ratios were more comparable. Four of the labs also scanned a set of homogenized sediment pellets with compositions determined by inductively coupled plasma-optical emission spectrometry (ICP-OES) and ICP-mass spectrometry (MS) to convert the raw XRF element cps to concentrations in two ways: a linear calibration and a log-ratio calibration. Although both calibration curves are well fit, the results show that the log-ratio calibrated data are significantly more comparable between labs than the linearly calibrated data. Smaller-scale (higher-resolution) features are often not reproducible between the different scans and should be interpreted with caution. Along with guidance on practical calibrations, our study recommends best practices to increase the quality of information that can be derived from scanning XRF to benefit the field of paleoceanography.

The South Asian or Indian Summer Monsoon (ISM) brings seasonal winds and rains to the Indian subcontinent and affects billions of people. It is likely that the global monsoon will strengthen in a 1.5 °C warming scenario (IPCC special report (2018)), however our ability to predict ISM behaviour in the future is restricted due to lack of understanding of its behaviour under varying climatic conditions before instrumental records began. Thus, reconstructing the palaeo-monsoon using proxies gives insight into past and potentially future controls on the ISM. We present new data covering the interval ~5 to ~2 million years ago (Ma), during the Pliocene and early Pleistocene when the long-term Cenozoic cooling trend culminated in intense northern hemisphere glaciations from 2.7 Ma. At this time, global temperatures are suggested to have been 2-3 °C warmer than today and atmospheric CO2 was over 400 ppm (similar to today). This study focuses on sediments from Site U1443 ( 5°N, 90°E), drilled during International Ocean Discovery Program (IODP) Expedition 353 in the Bay of Bengal (BoB) for the Pliocene – early Pleistocene. We present X-ray fluorescence (XRF)-derived bulk sediment geochemical data and suggest that erosional flux (terrigenous elements/total counts) as well as productivity (Br/Cl) varied in response to runoff strength, precipitation, and wind stress at the study site to reconstruct ISM variability. Additionally, new nannofossil assemblage and morphometric data, collected using the automated system SYRACO, are used to reconstruct BoB stratification and productivity and thereby assess ISM dynamics. A new benthic oxygen isotope-based age model will allow us to place the Site U1443 records into the context of existing climate and monsoon records and evaluate ISM response due to external and internal climate forcing factors.

International audience; Microplastics have become widely dispersed throughout the marine environment in and around Japan since the 1960s, which correspond to the onset of mass plastic production and use in this country. Our study documents a possible abrupt microplastics depositional event in continental shelf and deep-sea environments triggered by a tsunami. The sediment layers contaminated by microplastics correspond with sedimentary horizons where 137Cs signals were measured, indicating deposition after 1960s nuclear tests. The microplastics were observed in the 2011 Tohoku-Oki tsunami deposits. Tsunamis can thus contribute to the wide dispersal of microplastics from coastal to deep-sea areas, and these anthropogenic particles can be used to date very recent turbidite deposits.

Oxygen isotope ratios of the core region of otoliths were examined in Anguilla japonica glass eels collected from two rivers in Japan to verify the possible temperature and depth layer experienced by these eels when they were at the egg stage in their spawning area. To determine the relationship between otolith δ18O values and water temperature, the otoliths of glass eels reared under four different temperatures (15, 20, 25 and 30 °C) were analyzed. The otolith δ18O values showed an inverse relationship to ambient water temperature. Linear regression of the fractionation between otolith oxygen isotopic ratio from the δ18O of seawater and water temperature produced a precisely determined relationship from 15 to 30 °C: δ18Ootolith,PDB − δ18Oseawater,SMOW = −0.153 × T (°C) + 1.418. The δ18O core,PDB values of the otolith core region of the glass eels from the two locations were −2.53 ± 0.12 and −2.59 ± 0.07 respectively, and could be converted to water temperatures of 26.3 ± 0.8 °C and 26.7 ± 0.4 °C, respectively, using the equation and assuming a seawater δ18Oseawater,SMOW = 0.06‰. The water depth corresponding to these temperatures is ∼150 m in the water column in the spawning area of Japanese eels, which corresponds to the upper-most part of the thermocline and chlorophyll maximum in the vertical hydrographic profile. These results were consistent with the field studies that egg development after the beginning of otolith formation and hatching occurs around the upper-most part of thermocline, suggesting that stable isotope micro-analysis is a powerful method to extrapolate unknown spawning ecology of fishes.

A continuous reconstruction of quantitative paleotemperatures in the Holocene was conducted by using alkenone sea surface temperature (SST) measurements from coastal sedimentary cores because of the strong correlation of SST with atmospheric temperature (AT) in the coastal bay area. This analysis enabled us to estimate a record of temperatures in western Japan with high and low time resolution during the last 3000 and 10,000 years, respectively. The reconstructed SSTs were validated by historical documents and records after 600 AD. A long-term trend of declining SSTs can be attributed mainly to changes in solar radiation and sea level and, to a lesser extent, changes in the Asian monsoon. Interestingly, the profile was quite different from those reported from the open ocean. During the last three millennia, the SSTs (ATs) fluctuated by 2.1 °C, with a maximum in 820 AD (24.3 °C [25.9 °C]) and two minima in 760 BC (22.2 °C [23.8 °C]) and 990 AD (22.4 °C [24.0 °C]). Low temperatures were also observed in 220–110 BC, 560–620 AD, and other periods. Historical documents suggest a notable cold period from the late 18th to early 19th centuries. The overall mean value (23.6 °C) was comparable to the average value in the mid-20th century, whereas the top sediments had an SST of 24.6 °C, which is higher than the maximum observed in the previous 3000 years. Although a cold climate was definitely observed in 1440–1730 AD, which almost corresponded to the Little Ice Age, the Medieval Warm Period was not identified in this study. These temperature fluctuations cannot be explained by a single cause but rather by more than one external and internal driver of climate variability (e.g., volcanic forcing, ocean-atmosphere interactions, and solar forcing). With respect to the influence of climate on human activity, major shifts in social systems appeared to coincide with cold periods in western Japan.

Recent studies have revealed an intensification of the Indian Summer Monsoon (ISM) over the past 700 years, but its influence on the sediments in the northern Andaman Sea is unclear. To examine this influence, we used radiocarbon-dated sediment core StMY6, acquired 100 km offshore in the northern Andaman Sea from the Ayeyarwady River mouth, and obtained a 700-year-long record of the grain-size distribution and geochemistry of the sedimentary sequence. The ISM influences precipitation surrounding the Ayeyarwady River, and thus the river water and sediment discharges to the northern Andaman Sea near the river mouth in the Ayeyarwady River and the weathering intensity in the river catchment. Based on the system, we propose that higher sedimentation rates and larger modal grain size (the most abundant size in the grain-size distribution of sediments) and lower carbonate concentrations after about AD 1600 can be attributed to higher ISM intensity. Profiles of total organic carbon (TOC) content and carbon/nitrogen (C/N) ratios, however, did not show any trends after about AD 1600, which suggests that the ISM has had little influence on these proxies at this site.

International audience; New proxy records from deep-sea sediment cores from the northwestern continental margin of Western Australian reveal a 5.3 million year (Ma) history of aridity and tropical monsoon activity in northwestern Australia. Following the warm and dry early Pliocene (~5.3 Ma), the northwestern Australian continent experienced a gradual increase in humidity peaking at about 3.8 Ma with higher than present-day rainfall. Between 3.8 and about 2.8 Ma, climate became progressively more arid with more rainfall variability. Coinciding with the onset of the Northern Hemisphere glaciations and the intensification of the Northern Hemisphere monsoon, aridity continued to increase overall from 2.8 Ma until today, with greater variance in precipitation and an increased frequency of large rainfall events. We associate the observed large-scale fluctuations in Australian aridity with variations in Indian Ocean sea surface temperatures, which largely control the monsoonal precipitation in northwestern Australia. Plain Language Summary Australia is the driest inhabited continent on the planet, with its moisture mostly sourced from the tropical monsoon in the north and the southern westerlies in the south. The continent has experienced large climate fluctuations in the geologic past, but long continuous records of paleoenvironmental changes are lacking, particularly prior to~0.55 Ma. Here, we address this paucity by presenting a continuous and fluctuating record of continental aridity and monsoonal activity in northwestern Australia since the Pliocene (5.3 Ma). These records are based on bulk-chemical X-Ray Fluorescence scans and particle-size distributions of the terrigenous fraction in two marine sediment cores from the NW Western Australian continental margin. A comparison with present-day sources of windblown and fluvial sediments taken near the NW Western Australian coast corroborates our interpretation of the terrigenous fraction in the marine sediment cores. We show how the northwestern part of the Australian continent has experienced large climate fluctuations since 5.3 Ma, expressed by large aridity contrasts and great changes in monsoonal precipitation that are driven by Indian Ocean sea-surface temperatures.

The marine organic carbon content in sediments is a useful tool for reconstructing past productivity in the ocean. Bromine has been proposed as a useful proxy for marine organic carbon, since bromine is more concentrated in marine organic matter compared to terrestrial organic matter. Here, we present a high-resolution Quaternary record of marine organic carbon in the hemipelagic sediments of the Japan Sea obtained during Integrated Ocean Drilling Program (IODP) Expedition 346. We measured the bromine content in the sediments using an XRF core scanner (ITRAX). The total organic carbon content, total nitrogen, and stable carbon isotope values were also measured for discrete samples from the same sediments. The total organic carbon/total nitrogen ratio and the stable carbon isotope ratio of the total organic carbon are used to estimate the marine organic carbon content within the total organic carbon. The Br counts and marine organic carbon content show a high correlation, which we used to construct a calibration equation of the marine organic carbon content from the Br counts. Using the calibration equation, we reconstructed the changes in the marine organic carbon content during the Quaternary with a time resolution of ~ 50 years using sediment cores from IODP Site U1424 in the east central Japan Sea. The method to estimate the marine organic carbon content from the Br counts measured by the XRF core scanner proposed in this paper will be a useful tool to reconstruct the organic carbon content with high resolution and high speed.

Past and ongoing precipitations of Mn-carbonate (rhodochrosite) have occurred in the freshwater Lake Ohnuma, which is situated about 8 km south of the Hokkaido-Komagatake volcano, southwest Hokkaido (northern Japan). Lake sediments from a surface and a longer ∼4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro-XRF fluorescence analyses. The three tephra ash layers from the Hokkaido-Komagatake volcano, characterized by peaks of Al, Si, K, Ca, and Ti, correspond to regionally recognized tephras (1640, 1929 and 1996 CE) based on ashfall isopachs and 137Cs, 210Pb and 14C ages determined from the two cores. The sedimentation rate showed a drastic change around 1929 CE; ∼0.3 cm/yr for 1640–1929 CE and ∼2.7 cm/yr for 1929–2012 CE. The Mn content record of Lake Ohnuma sediments, composed of rhodochrosite laminae, showed a periodic variation with a decadal–centennial scale over the interval 1640–2012 CE. Sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated, followed by the crystal growth of rhodochrosite within the anoxic sediments. On the basis of these results, high Mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff. The Ti/Si ratios are representative of the relative abundance of detrital inputs from the watershed. The combined signals of elevated Mn content and Ti/Si ratio for 1935–2012 CE indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed, associated with the post-1970s intensive land use such as livestock farming. For 1640–1935 CE, the Lake Ohnuma record shows an antiphase relationship between the Mn content and Ti/Si ratio, which implies that the detrital inputs reflected the strength of the East Asian summer monsoon (EASM), and the reduced rainfall runoff resulted in weaker mixing, followed by depleted O2 in the water column. The antiphase variation in Mn content and Ti/Si ratio suggest weak EASM during the Little Ice Age (∼1850 CE), followed by strong EASM between 1860 and 1929 CE.

Although the climate in the Arabian Sea is controlled primarily by the southwest monsoon, the southwest monsoon has little influence in the Gulf of Aden. To examine the different responses to monsoons between the Gulf of Aden and areas outside the gulf, a comprehensive data set of bulk organic and inorganic geochemistry, sea surface temperature, and δ15N of pheopigments was obtained from deep-sea sediment cores recovered from inner and outer regions of the gulf. The results indicated that during the past 220 kyr, the influence of the southwest monsoon was stronger in the outer region of the gulf than in the inner region, which implies that the southwest monsoon trajectory has not changed substantially during that time period. Furthermore, influxes of O2-depleted water from the Southern Ocean and the lateral advection of upwelled seawater also had limited influence in the inner region. In contrast, concentrations of lithogenic materials transported by the southwest monsoon were similar in the two regions. δ15N of pheopigments indicated that during the last glacial maximum, the southwest monsoon was weaker and the northeast monsoon was stronger than at present. A stronger southwest monsoon during interglacials enhanced primary productivity and may have caused anoxic conditions to develop in the Arabian Sea, as indicated by redox proxies in the outer region. Anoxic conditions also formed during MIS 3, but no increase in the primary productivity is indicated; therefore, another mechanism, such as an influx of O2-depleted water from the Southern Ocean, may have been the cause.

The provenance of hemipelagic sediments in the Shikoku Basin during late Cenozoic time was studied through the temporal variations in the Sr–Nd–Pb isotopic compositions of detrital sediments from Integrated Ocean Drilling Program Site C0011 from the late Miocene (7 Ma) to the present. Detrital sediments at Site C0011 are interpreted as a mixture of sediments originating from the southwest Japan arc and lands around the East China Sea. Sediments from the East China Sea were transported by the Kuroshio, while Japanese sediments were transported by turbidity currents, bottom currents, and ocean surface currents. The isotopic evidence suggests that the main source of hemipelagic sediments gradually changed from the East China Sea to Japan from 4.4 to 2.9 Ma, in accordance with the northward movement of Site C0011 with the Philippine Sea plate in this period. A contemporaneous increase in grain size also supports this interpretation. The beginning period of these changes, 4.4 Ma, conforms closely to the postulated advent or acceleration of trench-normal subduction of the Shikoku Basin lithosphere.

We analyzed long-chain (C25–C36) n-alkanes and pollen grains in sediments from the Gulf of Aden covering the last 212 kyr to reconstruct the surrounding terrestrial environment, a critical region for the dispersal of Homo sapiens. Substantial increases in the flux of n-alkanes during 200–185, 120–95, and 70–50 ka were interpreted to indicate enhanced vegetation biomass in the Arabian Peninsula and the northern part of the Horn of Africa or increase in lithogenic material inputs. Periods of enhanced n-alkane flux occurred during or immediately after pluvial episodes, indicating that the increased precipitation may have induced substantially enhanced vegetation biomass, creating favorable conditions for Homo sapiens. Additionally, vegetation may have increased due to moderate precipitation unrecorded by speleothems or in accordance with the lowering of sea level, indicating that the dispersal might have been possible even after the shift to an arid environment indicated by the speleothems.

Centennial-scale variability of the East Asian winter monsoon during the Holocene is poorly understood because suitable archives and proxies are lacking. Here we present a high-resolution (∼30-yr spacing) planktonic foraminiferal δ O 18 record of Neogloboquadrina incompta (dextral form), which reflects sea surface temperature during the winter season, for the last 6000 yrs from marine sediments in the western North Pacific. Stronger winter monsoons indicated by cooler winter SSTs correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial-scale variability. The variability also shows good correlation with δ O 18 records in lake sediments and ice cores from the Yukon Territory, Canada, spanning the last 4500 yrs, suggesting east–west climate coupling across the North Pacific. Furthermore, the climate changes across the North Pacific co-vary over widespread regions, such as the eastern tropical Pacific and the northern Red Sea, and the reconstructed solar activity. The cross-spectral and wavelet analyses show that the East Asian winter monsoon shares some cyclicity with the solar variability. Our results suggest that the solar activity is a fundamental forcing producing the centennial-scale EAWM variability mediated by the large-scale climate linkages.

The Pacific Decadal Oscillation (PDO) is a dominant climate mode in the Pacific Ocean and thought to be related to seasonal to decadal changes in sea surface conditions. Colonies of long-living Porites coral, widely used to reconstruct monthly to century-scale tropical sea surface temperature and sea surface salinity records, were discovered near Koshiki Island, Japan (31 degrees N, 129 degrees E). A monthly resolved, 106 year 18O record revealed that distinct decadal-scale variability was significantly correlated with the PDO index. Our comparison showed 1 to 3 years lead-lag correlation of summer coral 18O with the winter PDO index, suggesting that the East Asian summer monsoon (EASM) may act as the driving force of winter PDO variability over the last 100 years. Cross-spectral analysis between the winter PDO index and summer coral 18O suggested that recent and future global warming may lead to a more frequent and/or stronger teleconnection between EASM and PDO.

Cyclic changes in volume transport of the Tsushima Warm Current (TWC) have been argued from diatom records in the southern Japan Sea off the Japanese islands during the Holocene. Although this phenomenon has not yet been confirmed by various proxy data, determining whether or not these oceanographic changes occurred is crucial for clarifying the nature of oceanographic changes in the southern Japan Sea. Here, we conducted a coupled analysis of Mg/Ca ratios and oxygen isotopes (δ18O) in shallow-dwelling Neogloboquadrina incompta from 13 core-top sediments in southern Japan, and developed a new equation for Mg/Ca temperature calibration (Mg/Ca = 0.311 × exp (0.07 × T)) as a proxy for spring sea surface temperature (SST). Using the newly developed, species-specific Mg/Ca-paleothermometry, we reconstructed SST variability for the past 6800 years from core YK10-7-PC09 in the southern Japan Sea. The Mg/Ca-derived SST record clearly represented five warmer periods at 6200–6000, 4900–4500, 4200–3800, 2600–2100, and 900–400 cal. year BP, almost consistent with previously published diatom records. These warmer events also corresponded to the periods in which warm molluscan assemblages increased at the northern end of the TWC, suggesting that periods of higher SST can be seen as reflecting the increased volume transport of the TWC. We interpreted the results of a model study showing that higher solar irradiance provoked positive Arctic Oscillation (AO)-like spatial patterns and the negative phase of the Pacific Decadal Oscillation (PDO) to mean that increased (reduced) TWC volume transport on the multi-centennial to millennial time scales was caused by high (low) solar insolation via a potential link between AO and PDO. Given that larger and more frequent volcanic eruptions occurred in the mid Holocene than in the late Holocene, volcanic forcing on the TWC volume transport changes would have been more significant during the former, as seen in the highly variable SST from this period and distinct decreases in SST around ~5900 cal. year BP and ~6400 cal. year BP. The millennial-scale fluctuations seen in SSTs in the southern Japan Sea would have had a large impact on the evolution of vegetation and human adaptation in the northern Japanese islands, adjacent to the Japan Sea, over the last 6800 years.