8-1. Research Divisions

Division for Chronological Research
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Anthropogenic history and geochronology
Accelerator mass spectrometry
Electron probe microanalysis
Paleoclimate reconstruction and future Earth
Geosphere stability
Isotope geoenvironmental chemistry
CHIME dating
Development of new analytical methods

Short- and long-term forecasts of global environmental changes and their countermeasures are urgent issues.
Determining when an event occurred in the past, via “dating,” is important for understanding the present state of the Earthand predicting its future. We promote chronological studies on a broad range of subjects, from events in Earth’s history,
spanning 4.6 billion years, to archeological materials, cultural properties, and modern cultural assets.
The Division for Chronological Research conducts interdisciplinary research involving radiocarbon (14C) dating
using accelerator mass spectrometry to understand changes in the Earth’s environment and the cultural history ofhumankind from approximately 50,000 years ago to the present day, as well as research on and development of new 14C
analyses and dating methods. In addition, the laboratory studies near-future forecasts of Earth and space environments,focusing on spatio-temporal variations in cosmogenic nuclides, such as 14C and 10Be, and conducts research that integrates
art and science through collaborations between researchers in archeology, historical science, and other fields. Furthermore,using the chemical U-Th total Pb isochron method (CHIME), which was first developed at Nagoya University, andradiometric dating of long-half-life radioisotopes (Sr-Nd-Hf), we have shed light on events in Earth’s history from its
formation 4.6 billion years ago to approximately 1 million years ago. An electron probe microanalyzer (EPMA) has beenused to perform nondestructive microanalyses of rocks and other materials to reveal records of complex events recordedin zircon, monazite, and other samples.

Main Activities in FY2022
Validation of the stability of the West Antarctic ice sheet of the Amundsen Sea sediment core
A sector of the West Antarctic ice sheet draining into the Amundsen Sea is currently experiencing the largest ice loss
in Antarctica, and there is serious concern regarding a large-scale ice collapse in this area caused by global warming. TheInternational Ocean Discovery Program Expedition 379 drilled two sites in the Amundsen Sea area of the Southern Ocean
using the D/V JOIDES Resolution. The shipboard physicalproperties

andsedimentological

dataofsedimentcores

demonstrated strongly variable physical properties, high diatom
abundance, and ice-rafted debris occurrence from 4.2 to 3.2 million
years ago. This was interpreted to have been caused by the dynamicWest Antarctic ice sheet during an extended warm period (Gohl etal., 2021; Wellner et al., 2021; Gille-Petzoldt et al., 2022). Further
research is expected to elucidate the stability of the West Antarctic
ice sheet and the linkage between West Antarctic ice sheet changes
and climate change.
60 Institute for Space–Earth Environmental Research

An ice sheet in the Amundsen Sea, West Antarctica

8-1. Research Divisions

Radiocarbon dating of Ezo-Nishiki silk fabrics
In Japan, silk fabrics, known as Ezo Nishiki, are distributed throughout the Hokkaido and Tohoku areas of theHonshu Islands. On Ezo Nishiki, elegant designs of dragons, huge snakes, peonies, and other animals or plants are lacedwith gold, silver, and other color threads. Although silk fabrics were originally made in China as cloth for the uniformityof government officials, they were also given to the chieftains of the tribes and Amur Basin villages and imported intoSakhalin Island over the Mamiya Strait. Trade was performed by indigenous
peoples in the Amur Basin and Sakhalin Island, including the Nivkh, Nanai,
and the Ul’ch. Santan is a generic name for the indigenous people living in the
Amur Basin and Sakhalin Island. Silk fabrics were then spread southward
into Hokkaido Island by the Ainu people living on Sakhalin and Hokkaido
islands. Silk fabrics were brought to Honshu Island in Japan through the trade
between the Ainu and Matsumae clans, which ruled the southwest edge ofHokkaido. The route in which the Ezo Nishiki was introduced from China toJapan via the Amur Basin and Sakhalin Island is called “the Silk Road ofNortheast Asia” and the trade is called the Ezo-NishikiSantan trade. Although
the origin of the trade was obscure, Ezo-Nishiki radiocarbon dating indicatedthat it began at the end of the 14th century or the early 15th century, whenEmperor Yongle of the Ming Dynasty (1368–1644) expanded their territory.

The Ezo Nishi silk wrapping cloth was owned by theEsashi Town Board of Education (photographpresented by the Esashi Town Board of Education)

The analysis of fossil ostracod assemblage from the Sakari Shell Mound in Minamichita
Town, Chita District, Aichi Prefecture
The melting of glacier ice and ice sheets has been reported to increase the sea level associated with global warming
since the 20th century, and the rise in sea level after several hundred years has been estimated by several researchers.
Estimating sea-level changes in the future based on these data on the paleo-environment and sea level is important topredict the highly sensitive sea level. To reconstruct the paleo-environments and sea-level changes, we studied thereconstruction of the sea-level curve using fossil ostracods during the Holocene around Japan. In this study, a boreholecore was excavated from the Mazukari shell mound in Minamichita to reconstruct its paleoenvironment and paleowater
depth based on fossil ostracod assemblages. Six species
belonging to five ostracods genera were found in a sample
at approximately 9,600–8,600 cal BP. Meanwhile, thepaleo-water depth was estimated to be 12 m based on acomparison with the fossil ostracod assemblage in thisstudy and modern ostracod assemblages from Ise Bay. (Inthis sample, we used the part of the archival document“Mazukari shell mound unearthed information materials” ofthe Minamichita town board of education.)

GSEM photographs of the selected ostracod species

Radiocarbon dating to bronze implement
Radiocarbon dating is a useful method for samples containing carbon derived from CO2 in the atmosphere. Verdigris,CuCO3 and Cu (OH)2, is the rust produced on bronze implements. The reactants used were bronze, copper, and CO2 in
the atmosphere. When a verdigris is formed, it is a closed film that restrains the generation of new rust. Therefore, theverdigris should preserve atmospheric carbon when formed. We improved the carbon extraction method using CuCO3and Cu (OH)2. We then applied this method to archaeological samples of known age, measured radiocarbon ages, andaccumulated examples of verdigris radiocarbon dating to demonstrate that verdigris is suitable for radiocarbon dating.
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8-1. Research Divisions.
Radiocarbon age of Holocene carbonate concretions at Nagoya and Shimizu port
Carbonate concretions occur in diverse geological formations worldwide. We studied carbonate concretions from
Nagoya and Shimizu ports. Concretion samples often contain biological remains, and organic matter, such as organisms,
and is thought to be involved in the formation of concretion. To elucidate the formation process of concretions, it isimportant to conduct geochemical evaluations of concretions with known formation ages. In this study, to elucidate theformation rate of concretions, we measured 14C and δ13C ages of the shell and concrete parts of concretion samples
collected from the Nagoya and Shimizu ports The 14C ages of the shells are approximately 7850–7600 cal BP (Nagoyaport) and 7700–7500 cal BP (Shimizu port), and the 14C ages of the Shimizu port concretion are approximately 7840–7620 cal BP. Conversely, the 14C age of the Nagoya port concrete part was older than the 14C age of the encapsulatedshell; however, after age correction by estimating the contribution of soil organic carbon with old age from the δ13C value,
the age was close to that of the shell (8000–7800
cal BP). Oyama (2009) reported that the area
near the mouth of the Nagoya port changed frommarine transgression to regression at 7800–7300
cal BP, suggesting that the carbonate concretionsin the Nagoya and Shimizu ports formed rapidly
after the death of organisms in an environment
with the highest sea level and stagnant currents.
Further research is expected to estimate sea leveland paleoenvironmental changes during the sealevel rise of the Jomon period. (Minami, Kuma
et al., 2022, Journal of Geology, 128, 239-244.)

Left: Concretions and inclusions of crab fossils collected from the Nagoya port
Right: Mineral composition of crab shell and concrete (Qtz: Quartz, Cal: calcite, Dol:dolomite) From Minami et al. (2022)

Effect of benzalkonium chloride addition on 14C analysis of dissolved inorganic carbon
The 14C concentration of dissolved inorganic carbon (DIC) in water is an important indicator of the actual state of
biological activity and other conditions in seawater and terrestrial water. However, after sample collection and storage,
the 14C concentration may change owing to DIC formation or decomposition by microbial activity in the sample water.
Sterilization with HgCl2 is commonly used to prevent DIC changes due to microbial activity; however, the use of mercury,which has a high environmental impact, is highly restrictive. Therefore, we investigated benzalkonium chloride (BAC)
as a disinfectant that can be used to disinfect medical devices and that is easy to handle.
We investigated the changes in 14C concentrations in DIC due to microbial activity during water storage and foundthat 14C concentrations in natural waters (groundwater, seawater, river water, and lake water) without BAC increased
considerably in two weeks, whereas all BACadded

watersamples,demonstrated no change in

except14

seawater,

C concentrations.

Furthermore, the incorporation of carbon into
the water sample due to the BAC decomposition
or microbial degradation by BAC was negligible
in the 14C analysis. These results indicate that
BAC is very effective in

14

C analysis offreshwater samples as an inhibitor of DIC
changes, although to a lesser extent in seawatersamples.(Takahashi and Minami, 2022, Limnol.
Oceanogr.: Methods, 20, 605–617)
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14

C concentrations in natural water samples (seawater: SW03; groundwaters: GW04,GW05; lake waters: LW06, LW07; river water: RW08) for approximately 15-d and 30-dpreservation periods（□：initial water, ○：BAC-free water, ●：BAC-added water)

8-1. Research Divisions

Direct search for dark matter using minerals
Approximately a quarter of the universe is thought to be occupied by an unknown elementary particle called darkmatter. Dark matter is an unknown elementary particle with mass that hardly interacts with ordinary matter and cannot bedirectly observed optically. Diverse studies have been performed to detect dark matter.
In recent years, a direct search for unknown elementary particles, such as dark matter, using minerals has attractedattention. When dark matter interacts with atoms in minerals, it leaves tracks in the crystals. Using minerals on a geologicaltimescale, it is possible to realize a sensitivity exceeding that of large-scale experiments, even withsmall samples. For example, 100 mg of a 100-million-year-old mineral has a sensitivity equivalent
to that of a 10-year experiment with 1 t material (e.g., liquid xenon).
In FY2022, a feasibility study of the optical readout of tracks was performed by focusing onmuscovite. Additionally, we obtained muscovite specimens for which a sufficient number of samples
were available for future proof of principle. We carried out dating of the muscovite sample using the KAr method, and an age of approximately 650 million years was obtained. In the future, we will aim to
directly search for unknown elementary particles using diverse minerals, including the muscovite sample.

Muscovite sample

A growth curve estimate of Christ's thorn jujube in Northcentral Oman determined by a seriesof radiocarbon measurements
Ziziphus spina-christi, also known as Christ's Thorn Jujube, is a deciduous species. It is distributed in warmtemperate and subtropical regions, including North Africa, Southern Europe, the Mediterranean, Australia, tropical
America, Southeast Asia, and the Middle East. This tree was used as a medicinal plant in ancient Egypt. Due to its
extensive range of applications in human health, its commercial demand is increasing. Recently, habitat area expansion
was observed in the Mediterranean region. It is speculated that this expansion may have been facilitated by the rise intemperature caused by global warming, although the exact cause remains unknown. This study
was performed to comprehend the effects of temperature and precipitation on the growth ofmature Ziziphus spina-christi trees and to gain insights into their future geographicaldistribution. To construct the growth curve of Ziziphus spina-christi, which lacks clear annualrings, a 24 cm-long core sample was collected from Northcentral Oman and subjected toradiocarbon dating. Time-series datacomprising

approximately 100 radiocarbon

measurements were compared with a carbon-14 calibration dataset using the dynamic time
wrapping (DTW) method. By aligning the data, we were able to determine temporal changes
in the growth rate of Ziziphus spina-christi and shed light on how it is affected by climate change.

Estimating growth curve ofOmani Christ's Thorn Jujube
using DTW method

A special support project for regional contribution in FY2022, "How do we determine theages of rocks and archeological sites?”
On March 18 and 25, 2023, an experiential learning program targeting upper elementary school students wasimplemented. On the first day, a large bus was chartered to visit the Nakatsugawa City Mineral Museum, where students
learned about the formation of granite and quartz. They also used a portable radiation detector to measure the radiationlevels in rocks and minerals. Additionally, they had the opportunity to create micromounted
quartz specimens. On the second day, the program took place at Nagoya University, wherestudents learned about radioactive materials, radiation, natural radiation levels, andradiometric dating. Each student created a cloud chamber and observed the emission ofradiation by placing a pitchblende sample inside. This experiential learning provided avaluable experience that could not be obtained through regular school life and served as acatalyst for increasing interest of children in natural and earth science.

Children measuring radiationlevels in Naegi granite

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