Hirotaka Oda

The HVEE Tandetron AMS system at Nagoya University

Abstract In 1996/97, we installed a second-generation AMS system (model 4130-AMS) manufactured by HVEE, B.V., The Netherlands. Although we encountered a lot of problems during the installation and tuning up of the machine, our new system has now reached good stability and reproducibility in performing 14 C / 12 C and 13 C / 12 C measurements. According to the reproducibility tests conducted in January 1999, where six graphite targets prepared from HOxII standard material were measured, the standard deviation for 14 C / 12 C reproducibility is around 1.6 ‰ (comparable with counting statistics) and that for 13 C / 12 C is 0.28 ‰ . The background level of the AMS system was measured using a pure graphite (commercial graphite rod). It lies between 50 and 55 ka BP. We are still on the way to reduce the background. However, we are now prepared to start routine measurements of unknown-age samples.

Fluctuation of the zooplankton community in Lake Biwa during the 20th century: a paleolimnological analysis

Detailed zooplankton records from a 26-cm sediment core with a time resolution of approximately 3–10 years were obtained from Lake Biwa, Japan, to examine the historical variations in the zooplankton community during the 20th century. In the sediments, selected zooplankton remains have fluctuated over the years. Daphnia – large zooplankton herbivores – did not occur from 1900 to 1920, and formed a very minor component of the zooplankton community in the following 30 years, while Bosmina – small zooplankton herbivores – were common during this period. In the mid-1960s, however, when eutrophication was noticeable in this lake, Daphnia numbers increased dramatically and became the dominant zooplankton thereafter. In contrast, Difflugia brevicolla and D. biwae, two amoeboid protozoans that live in connection with the lake bottom environment, occurred abundantly until the late 1950s, but gradually decreased after the mid-1960s. In particular, D. biwae, a species peculiar to this lake, was not found in sediment dated after 1980, suggesting its extinction. These results indicate that the zooplankton community structure changed greatly in the 1960s, and suggest that the eutrophication occurring at this time altered the relative strength of top-down and bottom-up forces on the zooplankton community in Lake Biwa.

Application of 14C Wiggle-Matching to Support Dendrochronological Analysis in Japan

14C wiggle-matching was applied to two wood samples closely related to geological and archaeological events with associated dendrochronological dates, to demonstrate the accuracy of 14C dating with accelerator mass spectrometry (AMS). Wiggle-matching on charred wood with bark, excavated from a pyroclastic mud-flow deposited by the huge 10th Century eruption of the Baitoushan Volcano, revealed the eruption age as cal A.D. 935 +8/−5 with 95% confidence. This date is consistent with the eruption age of A.D. 912 to A.D. 972 estimated by dendrochronology on two wooden boards that had clear stratigraphical connections to the B-Tm tephra deposit in Japan, an ash fall layer formed by the eruption of the Baitoushan Volcano. The date is also consistent with an A.D. 937–938 date estimated by the analysis of varved sediments from Lake Ogawarako in Aomori prefecture. The other wooden board collected from the Mawaki archaeological site in Ishikawa prefecture was wiggle-matched as 783 +13/−11 cal B.C. with 95% confidence, which is consistent with the dates of 830 cal B.C. to 759 cal B.C. obtained for seven wooden poles from the same wooden structures as the wooden board. These results are highly encouraging for obtaining accurate dates on wood when dendrochronology cannot be used.

Termite ecology in a dry evergreen forest in Thailand in terms of stable (δ13C and δ15N) and radio (14C, 137Cs and 210Pb) isotopes

Stable (δ13C and δ15N) and radio- (14C, 137Cs and 210Pb) isotopes were determined for termites that have been sampled from a dry evergreen forest in Thailand. A wood-feeding termite, Microcerotermes crassus, was separated from soil-feeders: Termes propinquus, Termes comis and Dicuspiditermes makhamensis by δ13C and δ15N values. The Termes group in Thailand had less diverse values in δ13C and δ15N than those in Australia, where the feeding habits of the ‘Termes’ group are more diverse. Other soil-feeding termites produced similar δ13C values, but a larger range in δ15N values. 14C-percent modern carbon (pMC) values suggest that the soil-feeding termites used younger carbon than the wood-feeding termites, and this was consistent with the termites from Cameroon, central Africa. Values of δ13C and 14C-pMC indicate that surface soil was used by a soil-feeding termite, D. makhamensis, in making the nest mounds, and deeper soil (10–30 cm) by a fungus-growing termite, Macrotermes carbonarius. 210Pb and 137Cs were scarcely incorporated into the termites, although 214Pb was recovered from the workers. The results suggest that stable- and radioisotopes are useful in the study of detritivorous animals, organic matter decomposition and ecosystem engineering.

Non-Destructive near Infrared Spectroscopic Measurement of Antique Washi Calligraphic Scrolls

Degradation of antique washi paper was examined by non-destructive near infrared spectroscopy. Difference second derivative spectra of the modern minus antique samples were analysed for the absorption peaks due to the main chemical components of washi paper, i.e. cellulose and hemicellulose. The absorption peaks were decreased for amorphous and semi-crystalline regions of cellulose and for hemicellulose, showing the results consistent with conventional, destructive sugar analysis. It is concluded that near infrared spectroscopy is a useful technique for the non-destructive monitoring of the degradation of the chemical properties of washi paper.

Neutron activation analysis of trace elements at sediment-water interface in the Biwa Lake, Japan

Concentrations of eighteen trace elements at the sediment-water interface in Biwa Lake were determined by neutron activation analysis. Release of iron, manganese and arsenic from the sediment to the pore water was observed under anoxic conditions. The concentrations of Sb in the pore water as well as Na were nearly constant between the surface and the depth of 40 cm. The behavior of Sb differed from that of As at the sediment-water interface, since the partition coefficient of Sb differed from that of As.

AMS 14C dating of iron artifacts: Development and application

We have developed a prototype carbon extraction system for accelerator mass spectrometry (AMS) radiocarbon dating of archaeological iron remains by combusting them with a RF induction furnace. We have also successfully tested and used a method of carbon extraction from iron using a CuCl2 solution. Modifications to our carbon extraction systems and methods provide us acceptable performances; carbon yield is normally around 80% and the 14C background level is as low as 4248 ka BP in 14C apparent age. We have also conducted an iron refining experiment to examine the sources for carbon 14C age derived from iron, using established AMS 14C dating and carbon extraction systems. Our refining experiment was conducted on iron slag, which are by-products formed during iron smelting methods in the 7th century AD, and using modern charcoal as fuel. The aim of the experiment was to determine whether original carbon characteristics in the original iron materials would be preserved, or if the carbon signature would be replaced to some degree by the modern charcoal. AMS 14C measurements on the refined iron yielded 14C ages equivalent to those of the modern charcoal fuel. The result indicates that the original carbon signatures in the iron slag from 7th century production was replaced completely by modern carbon used in our experiment. The experiment confirms the assumption that 14C ages on iron products are associated with the fuel source of the iron smelting or refining process. We also report on the dating of iron slag materials excavated from the Gennaitouge iron smelting site, where 14C dates were consistent with the age of the site estimated by archaeological evidence.

AMS radiocarbon dating of ancient Japanese sutras

Abstract Radiocarbon ages of ancient Japanese sutras whose historical ages were known paleographically were measured by means of accelerator mass spectrometry (AMS). Calibrated radiocarbon ages of five samples were consistent with the corresponding historical ages; the “old wood effect” is negligible for ancient Japanese sutras. Japanese paper has been made from fresh branches grown within a few years and the interval from trimming off the branches to writing sutra on the paper is within one year. The good agreement between the calibrated radiocarbon ages and the historical ages is supported by such characteristics of Japanese paper. It is indicated in this study that Japanese sutra is a suitable sample for radiocarbon dating in the historic period because of little gap by “old wood effect”.

The earliest-known humans in Fiji and their pottery: the first dates from the 2002 excavations at Naitabale (Naturuku), Moturiki Island

Until this study, the earliest-known people to have occupied the islands of Fiji were those who inhabited Matanamuani on Naigani Island as much as 1000 BC. Excavations at the Naitabale (Naturuku) site in southern Moturiki Island in June-July 2002 found an older settlement. From the nature of the pottery recovered from Naitabale, it appears to predate the Matanamuani site. Radiocarbon dates on charcoal from within the pits excavated at Naitabale confirm the site’s age. The dates show that the site could have been occupied as much as 1220 BC. A human burial (named “Mana”) found within the older layers of Pit T1 at Naitabale is that of a female, about 1.60 m tall, of slender build. The first radiocarbon date shows that she lived at least 650 BC, probably close to 950 BC. Further tests will determine her other characteristics.

AMS radiocarbon dating of ancient Japanese documents of known age

Radiocarbon ages of 17 ancient Japanese documents of known age and 3 unknown samples were measured by AMS. Radiocarbon dating on the known documents concluded that the Japanese paper is a suitable sample for radiocarbon dating because of small discrepancy between the calibrated radiocarbon age and the historical age due to the characteristics of Japanese paper. From the dating of the paper samples of unknown age, the wood-block prints, it was clarified that they had been produced between the 11th century and the first half of the 12th century as the historical information suggested.