C02_P01

Carbon Isotope Changes Through the Recent Past: F¹⁴C and δ¹³C values in single barley grain from 1852 to 2020

Dunbar E¹,  Scott M², Tripney B¹, Addis H³

¹SUERC, University of Glasgow, Glasgow, UK, ²University of Glasgow, Glasgow, UK, ³Rothamsted Research, Hertfordshire, UK

Annual records are gaining increasing prominence, whether in the form of tree rings (with their growing importance in IntCal) and other reservoirs, or from the more recent past, such as grain with a single known year of growth.  Such annual F¹⁴C and δ¹³C data from the past 60 years has proven a useful tool in the study of both environmental processes and in forensic science, generating “bomb F¹⁴C curves”.

Presented here are F¹⁴C and ancillary δ¹³C values on barley grain (Hordeum vulgare L. spring barley) covering the period 1852 to 2021, collected from the sample archive of the Long-Term Experiments (LTEs) Hoosfield Spring Barley at Rothamsted Research (Hertfordshire, UK) – the oldest agricultural research station in the world, founded in 1843.

The barley grain data is presented alongside data from barley mash samples which have formed a part of several intercomparison studies undertaken in the past 30 years.  Together, these data add value to the post bomb F¹⁴C curves. Furthermore, it is now evident that recent F¹⁴C values for grain are approaching the nominal activity of an 1890 wood (F¹⁴C value of 1), raising the questions: When will the F¹⁴C value decrease below 1? Will this cause difficulties in establishing whether a sample derives from the pre- or post-nuclear era?

C02_P02

Radiocarbon Concentration Measurements in Tree Leaves near SOCOCIM (Rufisque, Senegal), A Cement Factory

NDEYE M¹

¹Laboratoire Carbone 14, Dakar, Senegal

Radiocarbon content in biogenic samples is widely used to study the variation of atmospheric CO₂ due to anthropogenic activities. A total of 20 samples of several types of tree leaves, were analyzed for this study. Sampling was carried out at the end of the rainy season in 2017 from the surrounding of the SOCOCIM cement factory in Rufisque town. Rufisque is located on the peninsula of Cape Verde, 25 km east of Dakar, where it is the «south gate» of the agglomeration. Reference samples of five different species were collected during the same period (2017) from a clean zone. The ¹⁴C method was used for the determination of Δ¹⁴C values. The data show that the ¹⁴C concentration in the studied sites was significantly lower than the clean area, due to the release of anthropogenic CO₂. To estimate the Suess effect, the fossil fuel fraction was determined based on equations of mass balance for CO₂ concentration, stable isotopic composition of carbon, and ¹⁴C concentration. The results show that selected locations are affected differently according to their distance from the factory and the wind direction.

Keywords :  Radiocarbon Concentration, Fossil Fuel Fraction, Tree Leaves, Cement  Factory

C02_P03

Influence of the human activity on the source of soil inorganic carbon in grassland from Tibet and Inner Mongolia

Ping D^1,2,  Yiwei C^1,2, Sanyuan Z^1,3, Chengde S^1,2, Ning W^1,2

¹State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, ²CAS Center for Excellence in Deep Earth Science, Guangzhou, China, ³State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China

Soil Inorganic carbon (SIC) in two Alpine Meadow soil profiles from Tibet (Nam Co, 30°46´12″ N, 90°57´13″ E, amsl. 4737 m & Dangxiong, 30°22´40″ N, 90°55´45″ E, amsl. 4294 m) and two grassland soil profiles from Inner Mongolia (DXC, 43°00'25″ N，117°29´43″ E, amsl. 1352 m & GYC, 43°34'32″ N, 116°40'16″ E, amsl. 1225 m) were investigated. ¹⁴C ages of soil organic carbon (SOC) and SIC in Tibet show a significant positive correlation (Nam Co, R2=0.95 & Dangxiong, R2=0.94) between each other, suggesting a stable contribution of SOC to the SIC since 4.0 – 5.0 ka. Shrink of Nam Co lake at 3.0 – 2.0 ka and weakening of summer monsoon precipitation likely played little influence on the source of SIC in Tibet since  mid-Holocene. For comparison, ¹⁴C ages of SOC and SIC in Inner Mongolia indicate an obviously positive correlation (DXC, R2=0.97 & GYC, R2=0.91) from 4.0 – 5.0 ka to 2.0 ka, and almost a stable ¹⁴C age of SIC after 2.0 ka, reflecting a different source of soil IC after 2.0 ka in Inner Mongolia grassland. Variation of monsoon precipitation from 4.2 to 2.1 ka seems did not change the correlation obviously during that time in Inner Mongolia. Intensive human activities, such as farming and grazing since 2.0 ka in Inner Mongolia, likely led to the deterioration of the grassland and then the deflation of deeper soil layers, which finally changed the source of SIC in the shallow layers.