Terrestrial plant macrofossils from the sedimentary record of Lake Suigetsu, Japan, provide the only quasi-continuous direct atmospheric record of radiocarbon (14C) covering the last 50 ka cal BP (Bronk Ramsey et al. 2012). Since then, new high precision data have become available on U-Th dated speleothems from Hulu Cave China, covering the same time range (Cheng et al. 2018). In addition, an updated varve-based chronology has also been published for the 2006 core from Lake Suigetsu (SG06) based on extended microscopic analysis of the sediments and improved algorithms for interpolation (Schlolaut et al. 2018). Here we reanalyze the radiocarbon dataset from Suigetsu based on the new varve counting information and the constraints imposed by the speleothem data. This enables the new information on the calendar age scale of the Suigetsu dataset to be used in the construction of the consensus IntCal calibration curve. Comparison of the speleothem and plant macrofossil records provides insight into the mechanisms underlying the incorporation of carbon into different types of record and the relative strengths of different types of archive for calibration purposes.

Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for ${\geqslant}$kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This diagnostic has been implemented using the Thomson scattering probe beam and the resultant path-integrated magnetic field has been compared with that of proton radiography. Accurate measurement of magnetic fields is essential for satisfying the scientific goals of many current laser–plasma experiments.

We used a change point analysis on a late Pleistocene–Holocene lake-sediment record from the Chew Bahir basin in the southern Ethiopian Rift to determine the amplitude and duration of past climate transitions. The most dramatic changes occurred over 240 yr (from ~15,700 to 15,460 yr) during the onset of the African Humid Period (AHP), and over 990 yr (from ~4875 to 3885 yr) during its protracted termination. The AHP was interrupted by a distinct dry period coinciding with the high-latitude Younger Dryas stadial, which had an abrupt onset (less than ~100 yr) at ~13,260 yr and lasted until ~11,730 yr. Wet-dry-wet transitions prior to the AHP may reflect the high-latitude Dansgaard-Oeschger cycles, as indicated by cross-correlation of the potassium record with the NorthGRIP ice core record between ~45–20 ka. These findings may contribute to the debates regarding the amplitude, and duration and mechanisms of past climate transitions, and their possible influence on the development of early modern human cultures.

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.

The mountains of the Eastern Mediterranean have a long history of human occupation and exploitation of the natural environment (Grenon, Batisse 1989; McNeil 1992). Whilst the reconstruction of vegetation and human-induced landscape change is primarily based upon pollen analysis and other palaeoecological methods, the history of human occupation relies heavily upon archaeology, including field survey information and excavation reports. Both palaeoecology and archaeology are supplemented by historical accounts, especially for later periods, and when these data sources are combined they have the potential to provide a much fuller picture of settlement and landscape change than the reliance on a single source (Wagstaff 1985). There are, however, problems and limitations associated with each of the different data sources.

In situ cleaning of MOCVD-grown GaN/AlN/6H-SiC substrates using NH3-seeded supersonic molecular beams was investigated. Removal of surface carbon and oxygen contaminants was achieved by heating at 730°C under a hyperthermal NH 3 beam. Oxygen is removed primarily by thermal desorption; however, carbon removal requires an NH3 flux. Atomically smooth surfaces with regular steps are obtained after NH3 beam cleaning. Homoepitaxial growth of smooth, highly textured GaN films was accomplished at 700°C by employing a 0.61-eV NH3 beam and an effusive Ga source.

Homoepitaxial growth of GaN on MOCVD-grown GaN/AlN/6H-SiC substrates was investigated using NH3-seeded supersonic molecular beams and an effusive Ga source. Ga-limited growth is observed at 730 and 770°C for incident Ga fluxes ≤ 1.2×1015 cm−2 s−1 using a 0.25 eV NH3 beam. A Ga incorporation efficiency of 20–25% is observed under these conditions. Increasing NH3 kinetic energy in the 0.25 to 0.61 eV range results in a modest increase in the GaN growth rate which we ascribe to an enhancement in NH3 reactivity. A concomitant increase in surface roughness is observed with increasing GaN growth rate.

A new apparatus for III-V nitride growth by selected energy epitaxy (SEE) is described. The multi-chamber system comprises a doubly differentially pumped molecular beam source, UHV-compatible growth chamber, x-ray photoelectron spectroscopy (XPS) chamber, UHV transfer line, and loadlock. The growth chamber is equipped for in situ quadrupole mass spectrometry and reflection high-energy electron diffraction (RHEED). Preliminary results of GaN SEE using hyperthermal beams of trimethylgallium (TMG) and ammonia (NH3) are presented.

Gallium nitride films have been deposited on Si(100) and Al2O3(0001) substrates using triethylgallium and ammonia seeded into highly expanded helium gas streams. A two step deposition process that reproducibly results in continuous crystalline GaN films has been developed. The microstructure and composition of the resultant films were characterized by scanning electron microscopy, reflection high energy electron diffraction and Auger electron spectroscopy and film character was correlated to deposition conditions.

GaN films were deposited on sapphire (0001) from triethylgallium (TEG) and NH3 seeded in separate He free jets. as the dissociative chemisorption of NH3 is expected to be rate-limiting in GaN growth, the NH3/He nozzle temperature was varied to control the incident kinetic energy of the NH3 molecules. Using an NH3/TEG flow ratio of 205 and an NH3/He nozzle temperature of 400°C, stoichiometric films were deposited at substrate temperatures ≥530°C. Scanning electron microscopy revealed that films deposited at 580°C are polycrystalline α-GaN with randomly oriented 0.5-μm grains. Films with a closely similar morphology are deposited by using an NH3/He nozzle temperature of 90°C. IN contrast, films deposited at 580°C using an NH3/He nozzle temperature of 510°C consist of whiskers (aspect ratio = c A. 4) which exhibit a-GaN (0001)/sapphire (0001) heteroepitaxy, as evidenced by X-ray diffraction and reflection high-energy electron diffraction.

We describe two cases where it was necessary to remove teeth to biopsy the larynx for malignant disease. Immediate reimplantation of the teeth proved successful.