Hitoshi Yonenobu

A complete terrestrial radiocarbon record for 11.2 to 52.8 kyr B.P

Dating Carbon Radiocarbon dating is the best way to determine the age of samples that contain carbon and that are younger than ∼50,000 years, the limit of precision for the method. There are several factors that complicate such age determinations, however, some of the most important of which include variability of the 14C production in the atmosphere (which affects organic samples whose radiocarbon inventories are derived from atmospheric CO2), surface ocean reservoir effects (which affect marine samples that acquire their radiocarbon signatures from seawater), and variable dead carbon fraction effects (which affect speleothems that derive their carbon from groundwaters). Bronk Ramsey et al. (p. 370; see the Perspective by Reimer) avoid the need to make such assumptions, reporting the 14C results of sediments from Lake Suigetsu, Japan. Analysis of terrestrial plant macrofossils in annually layered datable sediments yielded a direct record of atmospheric radiocarbon for the entire measurable interval up to 52.8 thousand years ago. Radiocarbon measurements of samples from Lake Suigetsu, Japan, extend the 14C time scale back to more than 50,000 years ago. Radiocarbon (14C) provides a way to date material that contains carbon with an age up to ~50,000 years and is also an important tracer of the global carbon cycle. However, the lack of a comprehensive record reflecting atmospheric 14C prior to 12.5 thousand years before the present (kyr B.P.) has limited the application of radiocarbon dating of samples from the Last Glacial period. Here, we report 14C results from Lake Suigetsu, Japan (35°35′N, 135°53′E), which provide a comprehensive record of terrestrial radiocarbon to the present limit of the 14C method. The time scale we present in this work allows direct comparison of Lake Suigetsu paleoclimatic data with other terrestrial climatic records and gives information on the connection between global atmospheric and regional marine radiocarbon levels.

Regulation of the monsoon climate by two different orbital rhythms and forcing mechanisms

The East Asian monsoon is responsible for transferring huge amounts of heat and moisture between the land and the adjacent ocean. Significant changes in its capacity to do this will have direct impacts on regional climatic gradients and global atmospheric circulation. Determining the mechanisms that force long-term variation in monsoon behavior is therefore important for understanding global climate change. Competing theories vary in the degree of importance attached to glacial forcing, other orbital rhythms, and internal feedback mechanisms as primary drivers of change. There is, however, no convincing explanation as to why different proxy records from closely neighboring regions are tuned to different orbital rhythms. Here we present quantitative climatic reconstructions for the past 450 k.y. based on a long pollen record from Lake Biwa in Japan. The data suggest that continental and oceanic air mass temperatures respond predominantly to the 100 k.y. orbital rhythm, whereas the land-ocean temperature gradient and monsoon vigor oscillate mainly at the 23 k.y. insolation cycle. We suggest that the mechanisms for this behavior lie in the differential response of land and ocean to solar forcing, and conclude that the 100 k.y. signal dominates monsoon intensity only when the amplitude of solar forcing falls below a threshold level.

Near-infrared spectroscopic observation of the ageing process in archaeological wood using a deuterium exchange method

The ageing degradation of the fine wood structure of dry-exposed archaeological wood was investigated by Fourier transform near-infrared spectroscopy with the aid of a deuterium exchange method. The archaeological wood sample was taken from an old wooden temple in Japan (late 7th century), which has been designated as a UNESCO world heritage site. Comparing the analytical results with those of a modern wood sample of the same species, the ageing process of archaeological wood was clarified as a change in the state of order on a macromolecular structural level. It can be concluded from NIR spectra that the amorphous region, and partially semi-crystalline region, in cellulose, hemicellulose, and lignin decreased by the ageing degradation, whereas the crystalline region in cellulose was not affected by the ageing. The accessibility of the diffusant to effect H/D-exchange was monitored by an OH-related absorption band obtained from FT-NIR transmission spectroscopy and characteristically varied with the ageing process of the wood samples, the absorption bands characteristic of a specific state of order and the diffusion agent. Finally, we proposed a morphological model to describe the variation of the fine structure of the microfibrils in the cell wall with ageing degradation. The state of microfibrils changed loosely by ageing, so that elementary fibrils were arranged loosely under 5 A, whereas several elementary fibrils in the modern wood were arranged in very close proximity under 3 A to each other.

Early Ceremonial Constructions at Ceibal, Guatemala, and the Origins of Lowland Maya Civilization

Early Mayan Architects Lowland Mayan civilizations began to construct dramatic pyramids beginning about 900 BCE. The cultural origins of these civilizations have been uncertain, particularly the connection to earlier Olmec cultures along the Gulf of Mexico. Inomata et al. (p. 467; see the cover; see the News story by Pringle) describe excavations and extensive radiocarbon dating at the early Mayan city of Ceibal in Guatamala. The site shows incipient plaza and pyramid construction beginning before those seen in the lowlands or Olmec areas, suggesting a broader cultural exchange through to the Pacific Coast as Mayan cultures evolved. Excavations at the Mayan city of Ceibal, Guatemala, reveal early examples of plazas and pyramids. The spread of plaza-pyramid complexes across southern Mesoamerica during the early Middle Preclassic period (1000 to 700 BCE) provides critical information regarding the origins of lowland Maya civilization and the role of the Gulf Coast Olmec. Recent excavations at the Maya site of Ceibal, Guatemala, documented the growth of a formal ceremonial space into a plaza-pyramid complex that predated comparable buildings at other lowland Maya sites and major occupations at the Olmec center of La Venta. The development of lowland Maya civilization did not result from one-directional influence from La Venta, but from interregional interactions, involving groups in the southwestern Maya lowlands, Chiapas, the Pacific Coast, and the southern Gulf Coast.

Development of sedentary communities in the Maya lowlands: coexisting mobile groups and public ceremonies at Ceibal, Guatemala.

Significance The results of our research at the lowland Maya site of Ceibal add to the growing archaeological understanding that the transition to sedentism did not necessarily occur simultaneously across different social groups within a region and that monumental constructions did not always postdate fully established sedentism. Whereas sedentary and mobile populations are, in many cases, interpreted to have maintained separate communities, our study suggests that groups with different levels of mobility gathered and collaborated for constructions and public ceremonies. These data indicate that the development of sedentism was a complex process involving interactions among diverse groups, and that collaborative construction projects and communal gatherings played a critical role in this social transformation by facilitating social integration among different groups. Our archaeological investigations at Ceibal, a lowland Maya site located in the Pasión region, documented that a formal ceremonial complex was built around 950 B.C. at the onset of the Middle Preclassic period, when ceramics began to be used in the Maya lowlands. Our refined chronology allowed us to trace the subsequent social changes in a resolution that had not been possible before. Many residents of Ceibal appear to have remained relatively mobile during the following centuries, living in ephemeral post-in-ground structures and frequently changing their residential localities. In other parts of the Pasión region, there may have existed more mobile populations who maintained the traditional lifestyle of the preceramic period. Although the emerging elite of Ceibal began to live in a substantial residential complex by 700 B.C., advanced sedentism with durable residences rebuilt in the same locations and burials placed under house floors was not adopted in most residential areas until 500 B.C., and did not become common until 300 B.C. or the Late Preclassic period. During the Middle Preclassic period, substantial formal ceremonial complexes appear to have been built only at a small number of important communities in the Maya lowlands, and groups with different levels of sedentism probably gathered for their constructions and for public rituals held in them. These collaborative activities likely played a central role in socially integrating diverse groups with different lifestyles and, eventually, in developing fully established sedentary communities.

Near-infrared spectroscopic monitoring of the water adsorption/desorption process in modern and archaeological wood.

We investigated the adsorption/desorption mechanism of water and the variation of water adsorption for modern and archaeological wood using near-infrared spectroscopy. A mixture model of water was used to decompose the near-infrared difference spectra into three components (free water molecules (S0), those with one OH group engaged in hydrogen bonding (S1), and those with two OH groups engaged in hydrogen bonding (S2)) based on a principal component analysis. The variations of each water component with relative humidity could be explained by proposing a model that describes water absorption in three stages. It was concluded that the aging phenomenon in wood is due to the decrease of adsorption sites on hemicellulose and amorphous cellulose.

Tracking aquatic change using chlorin‐specific carbon and nitrogen isotopes: The last glacial‐interglacial transition at Lake Suigetsu, Japan

Joint carbon and nitrogen isotope measurements were made from chlorins (chlorophyll a, phaeophytin a and pyrophaeophytin a) extracted from the last glacial-interglacial transition sediments of Lake Suigetsu, central Japan. These data highlight both the potential and difficulty of using chlorin-specific isotopes to track aquatic change from lake sediments. δ13C and δ15N of the three chlorins show coherent patterns with time, supporting the theory that phaeophytin a and pyrophaeophytin a are early diagenetic products of chlorophyll a and that despite this transition, their isotopic signatures remain intact. However, our data suggest that the isotopic composition of phaeophytin a and pyrophaeophytin a can be imprecise proxies for the isotope composition of chlorophyll a, possibly owing to the complex array of factors which affect the synthesis, transformation and sedimentation of these phaeopigments in nature. The total accumulation of organic matter in Lake Suigetsu appears to be controlled by the balance of allocthonous and authocthonous material as reflected by the C/N ratio. However, both bulk organic and chlorin-specific δ13C show similar changes, suggesting that the first order variability in bulk organic δ13C reflects aquatic change. By contrast, there is no similarity between chlorin and bulk δ15N, suggesting that interpretation of bulk δ15N in this setting is compromised by diagenetic alteration. The isotopic composition of chlorins are interpreted to reflect the response of aquatic primary productivity to post-glacial environmental change. However, further research into the synthesis and transformation of chlorins in the modern environment is required in order to facilitate a more rigorous approach to interpreting isotope ratios in chlorins extracted from sediments.

On the radial-growth variations of Japanese beech (Fagus crenata) on the northernmost part of Honshu Island, Japan

We developed ring-width chronologies for living trees of Japanese beech at two forest sites on the northern-most part of Honshu Island, Japan. A statistical threshold (running expressed population signal) yielded these site chronologies spanning 1853–1994 (142 years) and 1867–1994 (128 years). We examined two factors, climate and masting, that could affect the variations of radial growth. The response function analysis revealed that the ring width correlated positively with July and August temperatures of the previous growth year. The optimal radial growth of Japanese beech may largely depend on a warm previous summer with above-average temperatures. The years of good masting coincided mostly with those showing abrupt growth depression, although only the short-term records of masting were available.

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.

The Tunguska Event as recorded in a tree trunk.

A living spruce tree was collected near the explosion center of the Tunguska event that occurred in 1908. We measured annual ring width and studied anatomical features to reconstruct the possible vegetational changes caused by the biological aftereffects of the Tunguska explosion. Delta (super 14) C of annual rings from 1908 to 1910 was measured with a Tandetron accelerator mass spectrometer. The annual ring width decreased rapidly in 1908-1912, drastically increased in 1913, and decreased gradually thereafter. Traumatic resin ducts were observed in the transition zone between early- and latewood of the annual ring formed in 1908. We thus reconstruct these vegetational changes in the Tunguska forest: the Tunguska explosion damaged forest trees severely for ca. 3 yr, releasing rich nutrients from burned plants into the soil, and subsequently the vegetation was stimulated to recover by decreased socio-biological competition and better lighting conditions. Delta (super 14) C values range from -28.2 to -1.5 per mil for Tunguska spruce, and from -29.7 to 12.6 per mil for Hinoki cypress. These fluctuations are within the ranges presented in Stuiver and Becker (1993), suggesting no evidence of anomalies of cometary origin in carbon isotopic composition. We found no significant difference between Delta (super 14) C of Tunguska spruce and of Hinoki cypress.