Yakushima is a small, mountainous island off southern Kyushu, Japan. Its proximity to active volcanos and subduction zones leaves Yakushima vulnerable to large megathrust earthquakes and tsunamis, in addition to powerful typhoons and storm surges. These hazardous events deposit beach boulders: large rocks moved above sea-level by powerful waves. By radiocarbon dating the fossilized coral within these boulders, one can derive age estimates of the hazard events. Reliably estimating the magnitude and timing of geological events in the historical record is vital for future hazard prediction and mitigation. In this study, we estimated the deposition age of ten boulders on the north coast of Yakushima to infer potential paleo tsunamis and storm surges. We found that large wave events have occurred frequently throughout the Holocene. Based on the boulders’ ages, we identified four potential deposition events at 1986–2692 cal yr BP, 3522–4075 cal yr BP, 4773–5232 cal yr BP, and 6187–6638 cal yr BP. These deposits are likely a result of storm surges, or tsunamis from nearby volcanic activity or subduction earthquakes. Another set of boulders dated to 5125–5738 cal yr BP were likely exposed due to a decline in sea-level following the Holocene high sea-level stand. Further modelling could determine the wave height necessary to move the boulders and distinguish between storm and tsunami deposits. This is especially pertinent given the high frequency of coastal geohazards, and the likelihood of similar hazards impacting southeast Japan in the future.

At the Intertropical Convergence Zone (ITCZ), the northern and southern Tradewinds converge, and this region is characterized by low atmospheric pressure and high precipitation. The climate in the Timor Sea is characterized by seasonal precipitation changes driven by meridional migrations of the ITCZ and the monsoonal front. The ITCZ shifts in response to changes in the thermal balance between the northern and southern hemispheres. Thus, reconstruction of paleo-precipitation in the Timor Sea is expected to reveal past changes in both regional and global climate, the latter through inference of the ITCZ position. To reconstruct paleo-precipitation in the Timor Sea, we performed extensive radiocarbon analysis on both planktonic foraminifera and total organic carbon (TOC), which is derived from terrestrial and marine sources. Increased precipitation enhances the fraction of relatively old, terrestrial carbon to the core site, which in turn increases the difference between the ages of TOC and planktonic foraminifera. Variations in radiocarbon ages reveal that during northern hemisphere cooling intervals such as Heinrich Stadial 1 and the Younger Dryas, the ITCZ was in a southern position, thus increasing precipitation in the Timor Sea. However, the Timor Sea was dryer during the Bølling–Allerød warming as the ITCZ shifted northward.

In this study, we investigate the distribution of radiocarbon and uranium in the calcified opercula of Turbo sp. collected from Ryukyu region and Chiba, Japan, to explore the potential of U/Th dating using mollusks collected from the Japanese archipelago. We acquired high-resolution radiocarbon and uranium concentration measurements using single-stage accelerator mass spectrometry and laser ablation−inductively coupled plasma−mass spectrometry. Our results show that uranium in the opercula of modern Turbo sp. is unevenly distributed at concentrations 1000 times less than those in coral skeletons. Radiocarbon found in the calcified opercula samples record ambient seawater radiocarbon values as well as coral skeletons. Uranium in the calcified opercula of Holocene Turbo marmoratus were also unevenly distributed and concentrated within the opercula in a different manner than observed in modern samples, suggesting uranium exchange after death. Our results suggest variable uptake of uranium isotopes into mollusk shells and highlights the need for rigorous sample selection criteria when choosing mollusks species for U/Th dating around Japan.

Analysis of the chronological data and observation of a lagoonal sediment core reveal sand washover events between around 2.4 to 2.5 cal. ky BP in the Isumi River lowland. We conducted radiocarbon dating with AMS and constructed an age-depth model using the latest calibration curve and appropriate model routine. In the middle to lower part of the core, dark-gray sand layers are repeatedly deposited. Sand layers may exhibit an erosional surface at the base with fining upward grading. The overwash layers are composed of well-rounded sand with occasional gravel, indicative of transportation. overwash sediment characteristics are consistent with proximal marine deposits, suggesting an ocean origin (though riverine sediment is also similar in character). The age-depth model indicates very high sediment accumulation rates associated with overwash deposits. Based on the amount of accumulated sediment, relatively large-scale redeposition events occurred during this period but more information is needed to constrain the mechanism(s) causing the events. We also present a local reservoir age correction compatible with the Marine20 calibration curve.

Differential sources of sedimentary organic compounds in a volcanic region were revealed by determining radiocarbon content (Δ14C) of organic compounds in surface sediments from Lake Kawaguchi, at the northern foot of Mount Fuji, central Japan. The Δ14C values of C16 fatty acid (−124‰) and chlorophyll a (Chl a) (−133‰) were similar to the Δ14C of dissolved inorganic carbon (DIC) in surface water (−117‰), suggesting that a significant portion of these compounds originated from modern primary producers with a reservoir age of ~1000 years. On the other hand, a large offset between the Δ14C values of Chl a (−133‰) and those of 132, 173-cyclopheophorbide-a-enol (−169‰) and pheophytin a (−179‰) suggested contributions from older pigments. In addition, the Δ14C of long-chain (C24, C26, and C28) fatty acids (−183 to −75‰) showed a large offset from that of a plant leaf remain (0‰) within sediments, demonstrating that the long-chain fatty acids were affected by substantial contributions from pre-aged terrestrial materials. Overall, the sedimentary organic compounds gave 14C ages older than the plant leaf fragment within sediments; however, the similarity between Δ14C of the C16 fatty acid and DIC implies potential for applying compound-specific radiocarbon analysis as a dating tool in volcanic lake environments.

The trajectory of the Kuroshio, the western boundary current in the north Pacific, influences regional climate. It intrudes into the South China Sea (SCS) through the Luzon Strait, resulting in the exchange of water, nutrients, heat, and salt between the Pacific and SCS. It has been reported that the trajectory of the Kuroshio has varied with decadal climate changes. However, there has been no report of an observation-based estimate of the variation in the Luzon Strait transport. Here, a 50-year, high-resolution coral skeletal radiocarbon (Δ14C) dataset from 1946 to 1994 is reported from Currimao, northwest of Luzon Island. Δ14C has been used as a sensitive tracer of seawater, and our data indicates a significant increase in Δ14C from 1946 to 1994 related to atmospheric nuclear bomb testing, with more rapid increase in the SCS than in the Pacific. The unusual, rapid Δ14C increase in the 1950s found in our SCS corals together with seasonal variation in Δ14C will helps constrain physical oceanographic models for the western Pacific, including the SCS.

The South Pacific Ocean contributes to the global carbon cycle by exchanging CO2 between the atmosphere and intermediate to deep water masses. The path of the Antarctic Intermediate Water (AAIW) in the South Pacific gyre has been inferred from salinity, oxygen, and nutrient measurements, but radiocarbon (14C) measurements—a direct tracer of the carbon cycle—remain sparse. Here, we present the first radiocarbon profiles in the western Coral Sea and compare our measurements with South Pacific stations from GLODAPv2, a database of ocean hydrochemistry. Surface and subsurface waters in the Coral Sea cannot be attributed to a single source based on their Δ14C signatures, and we observe a penetration of bomb-produced 14C. AAIW in the western Coral Sea shows Δ14C values comparable to those in the South Pacific gyre, consistent with circulation of AAIW in the lower part of the southern equatorial current. The deep waters of the western Coral Sea have significantly higher 14C than the South Pacific at the same isopycnal, consistent with a northward intrusion of Circumpolar Deep Water from the Tasman Sea, along with a westward influx of deep waters from the Central Pacific. In accordance with silicate concentrations published previously, this shows the dual origin of deep waters in the Coral Sea.

Reconstructing past ocean currents in the coastal regions is necessary to better understand the relationship between oceanographic changes and coastal ecosystems. It is known that variations have occurred with large-scale climate changes such as ENSO (El Niño Southern Oscillations) and PDO (Pacific Decadal Oscillations). Thus, reconstruction of past seawater conditions in coastal regions is needed to better understand the relationship between oceanographic changes and coastal ecosystems. Seawater radiocarbon is a unique proxy to understand the properties of water masses. Reef-building corals have been employed extensively and successfully in conducting this type of research into past ocean circulation histories. However, their distribution is limited to the low latitudes and hence alternative archives are required for studies in mid to high-latitude locations. Here, we use abalone shell samples obtained from Otsuchi Bay located in the Tohoku region on the Pacific coast of Northern Japan. Radiocarbon in abalone shells was compared with dissolved inorganic carbon in two-year-long records of river water as well as seawater. The data indicate that abalone shells can be used to reconstruct past seawater radiocarbon variations in northern Japan where coral skeletons are not available for ocean mixing studies.

We analyzed rare wooden Komainu found at Akagami Shrine in Akita prefecture, Japan. The formation of historical objects is often thoroughly recorded in documents, although the formation age of this particular Komainu sculpture is still unknown due to its antiquity. Thus, age determination exercises have been conducted using radiocarbon (14C)-wiggle-matching techniques. Although only a limited quantity was available for sampling, we have successfully measured 14C samples in the sculptures along with several sets of tree rings. We interpret the Komainu sculptures age considering the age of the trees and the result obtained from the wooden construction materials used for the Akagami shrine. The results obtained from Komainu show a range from 550 CE to 1020 CE, which is consistent with the dates of the shrine’s formation. Thus, the multiple 14C-wiggle-matching method can determine precise calendar ages of wood, as well as provide some supportive information for the periods when there are no reliable historical documents.

Radiocarbon natural abundances (Δ14C) are being increasingly used to trace carbon cycling in stream ecosystems. To understand the ultimate sources of carbon, we determined the stable carbon isotope ratios (δ13C) and Δ14C values of dissolved inorganic and organic carbon (DIC and DOC, respectively) and of particulate organic carbon (POC) in two small streams in central Japan, one of which flows over limestone bedrock (Seri) and the other does not (Fudoji). Investigations over four seasons revealed that the Δ14C values of the DIC (from −238‰ to −174‰ for Seri and −23‰ to +10‰ for Fudoji) were less variable than those of the other carbon fractions (DOC: from −400‰ to −138‰ for Seri and −2‰ to +103‰ for Fudoji; POC: from −164‰ to −60‰ for Seri and −55‰ to +37‰ for Fudoji). Based on mass balance calculations using the δ13C and Δ14C values, the proportions of carbon in the DIC originated from (1) atmospheric CO2 were 47% to 57% for Seri and 74% to 90% for Fudoji, (2) organic matter degradation were 29% to 35% for Seri and 4% to 21% for Fudoji, and (3) carbonate rock were 14% to 22% for Seri and 4% to 6% for Fudoji. We compared the results with previous studies that had been conducted in larger rivers and showed that in small streams, the dissolution of atmospheric CO2 and weathering of carbonate rock are more important factors in the carbon cycling than the biological degradation of organic matter.

This study applied compound-specific radiocarbon analysis (CSRA) to a 186-m-long sediment core (U1357A) taken from Adélie Basin located on the continental shelf off Wilkes Land, East Antarctica. The CSRA targeted C16 fatty acid as well as C16., fatty acid and cyclopheophorbide-a-enol isolated from the sediment. Due to their high degradation rate, these compounds are expected to occur in low abundances in relict organic matter deposited at this site. Twelve compound-specific (CS) 14C ages were obtained that are mostly consistent with their stratigraphic order. The CS 14C results of all samples are Holocene in age (9800 to 440 cal BP). These results suggest that significant sedimentation started ∼10,000 cal BP. Moreover, the data suggest that 14C measurements of C16:1 fatty acid and cyclopheophorbide-a-enol are useful for dating sediments from the Southern Ocean.

Shallow-water tropical corals can be used to calibrate the radiocarbon timescale. In this paper, we present a new data set based on the comparison between 14C ages and U-Th ages measured in fossil corals collected offshore the island of Tahiti during the Integrated Oceanic Drilling Program (IODP) Expedition 310. After applying strict mineralogical and geochemical screening criteria, the Tahiti record provides new data for 2 distinct time windows: 7 data for the interval between 29 and 37 cal kyr BP and 58 for the last deglaciation period, notably a higher resolution for the 14–16 cal kyr BP time interval. There are 3 main outcomes of this study. First, it extends the previous Tahiti record beyond 13.9 cal kyr BP, the oldest U-Th age obtained on cores drilled onshore in the modern Tahiti barrier reef. Second, it strengthens the data set of the 14–15 cal kyr BP period, allowing for better documentation of the 14C age plateau in this time range. This age plateau corresponds to a drop of the atmospheric 14C synchronous with an abrupt period of sea-level rise (Melt Water Pulse 1 A, MWP-1 A). The Tahiti 14C record documents complex changes in the global carbon cycle due to variations in the exchange rates between its different reservoirs. Third, during the Heinrich event 1, the Tahiti record disagrees with the Cariaco record, but is in broad agreement with other marine and continental data.

The varved sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity from which to derive a terrestrial record of atmospheric radiocarbon across the entire range of the 14C dating method. Previous work by Kitagawa and van der Plicht (1998a,b, 2000) provided such a data set; however, problems with the varve-based age scale of their SG93 sediment core precluded the use of this data set for 14C calibration purposes. Lake Suigetsu was re-cored in summer 2006, with the retrieval of overlapping sediment cores from 4 parallel boreholes enabling complete recovery of the sediment profile for the present “Suigetsu Varves 2006” project (Nakagawa et al. 2012). Over 550 14C determinations have been obtained from terrestrial plant macrofossils picked from the latter SG06 composite sediment core, which, coupled with the core's independent varve chronology, provides the only non-reservoir-corrected 14C calibration data set across the 14C dating range.

Here, physical matching of archive U-channel sediment from SG93 to the continuous SG06 sediment profile is presented. We show the excellent agreement between the respective projects' 14C data sets, allowing the integration of 243 14C determinations from the original SG93 project into a composite Lake Suigetsu 14C calibration data set comprising 808 individual 14C determinations, spanning the last 52,800 cal yr.

Calibration is a fundamental stage of the radiocarbon (14C) dating process if one is to derive meaningful calendar ages from samples' 14C measurements. For the first time, the IntCal09 calibration curve (Reimer et al. 2009) provided an internationally ratified calibration data set across almost the complete range (0 to 50,000 cal BP) of the 14C timescale. However, only the last 12,550 cal yr of this record are composed of terrestrial data, leaving approximately three quarters of the 14C timescale necessarily calibrated via less secure, marine records (incorporating assumptions pertaining to the temporally variable “marine reservoir effect”). The predominantly annually laminated (varved) sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity to derive an extended terrestrial record of atmospheric 14C across the entire range of the method, through pairing of 14C measurements of terrestrial plant macrofossil samples (extracted from the sediment) with the independent chronology provided through counting of its annual laminations.

This paper presents new data (182 14C determinations) from the upper (largely non-varved) 15 m of the Lake Suigetsu (SG06) sediment strata. These measurements provide evidence of excellent coherence between the Suigetsu 14C data and the IntCal09 calibration curve across the last ~12,000 cal yr (i.e. the portion of IntCal based entirely on terrestrial data). Such agreement demonstrates that terrestrial plant material picked from the Lake Suigetsu sediment provides a reliable archive of atmospheric 14C, and therefore supports the site as being capable of providing a high-resolution extension to the “wholly terrestrial” (i.e. non-reservoir-corrected) calibration curve beyond its present 12,550 cal BP limit.

We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12C4+ beam currents generated by small standards and ion beam currents (15–30 μA) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14C/12C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 μA, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 μg of modern and 1 μg of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.

We have examined the variation of carbon-14 content in annual tree rings, and investigated the transitions of the characteristics of the Schwabe/Hale (11-year/22-year) solar and cosmic-ray cycles during the last 1200 years, focusing mainly on the Maunder and Spoerer minima and the early Medieval Maximum Period. It has been revealed that the mean length of the Schwabe/Hale cycles changes associated with the centennial-scale variation of solar activity level. The mean length of Schwabe cycle had been ~14 years during the Maunder Minimum, while it was ~9 years during the early Medieval Maximum Period. We have also found that climate proxy record shows cyclic variations similar to stretching/shortening Schwabe/Hale solar cycles in time, suggesting that both Schwabe and Hale solar cycles are playing important role in climate change. In this paper, we review the nature of Schwabe and Hale cycles of solar activity and cosmic-ray flux during the Maunder Minimum and their possible influence on climate change. We suggest that the Hale cycle of cosmic rays are amplified during the grand solar minima and thus the influence of cosmic rays on climate change is prominently recognizable during such periods.

Whisker-originated short in the self-aligned contact (SAC) W polymetal gate was directly observed for the first time. Short points between gate electrodes and poly-Si plugs in the test structure were identified by emission microscope and cross-sectional TEM samples of those points were made by using focused ion beam (FIB).

Whiskers are formed during high-temperature processing such as LP-CVD SiN. We have proposed that NH3 de-oxidation step inserted in the SiN deposition sequence is effective for suppressing whisker growth. [1] In this study it was also confirmed that 600°C NH 3 pre-flow improved leakage current between gate electrode and contact plugs.

Uranium series and radiocarbon ages were measured in corals from the uplifted coral terraces of Huon Peninsula (HP), Papua New Guinea, to provide a calibration for the 14C time scale beyond 30 ka (kilo annum). Improved analytical procedures, and quantitative criteria for sample selection, helped discriminate diagenetically altered samples. The base-line of the calibration curve follows the trend of increasing divergence from calendar ages, as established by previous studies. Superimposed on this trend, four well-defined peaks of excess atmospheric radiocarbon were found ranging in magnitude from 100% to 700%, relative to current levels. They are related to episodes of sea-level rise and reef growth at HP. These peaks appear to be synchronous with Heinrich Events and concentrations of ice-rafted debris found in North Atlantic deep-sea cores. Relative timing of sea-level rise and atmospheric 14C excess imply the following sequence of events: An initial sea-level high is followed by a large increase in atmospheric 14C as the sea-level subsides. Over about 1800 years, the atmospheric radiocarbon drops to below present ambient levels. This cycle bears a close resemblance to ice-calving episodes of Dansgaard-Oeschger and Bond cycles and the slow-down or complete interruption of the North Atlantic thermohaline circulation. The increases in the atmospheric 14C levels are attributed to the cessation of the North Atlantic circulation.

In the SELenological and ENgineering Explorer (SELENE) project which is the Japanese lunar program to be launched in 2003 by the Institute of Space and Astronautical Science (ISAS) and National Space Development Agency of Japan (NASDA), we measure angular distance between a radio transmitter on a relay satellite, that on the Moon and quasars by differential VLBI and determine amplitudes of the physical librations, gravitational harmonic coefficients of the Moon and lunar ephemeris with an accuracy one or two orders higher than before in cooperation with 4-way Doppler measurements and two-way Doppler and ranging measurements using the lunar orbiter and the relay satellite. We are proposing another selenodetic mission, In situ Lunar Orientation Measurement (ILOM) to study lunar rotational dynamics by direct observations of the lunar physical libration from the lunar surface with an accuracy of 1 milliarcsecond in a post-SELENE project which will be launched about three years after SELENE. Year-long trajectories of the stars provide information on various components of the physical librations and we will also try to detect the lunar free librations in order to investigate the lunar mantle and the liquid core.