Diurnal variation of CO2 concentration, Δ14C and δ13C in an urban forest: estimate of the anthropogenic and biogenic CO2 contributions

Diurnal variation in the atmospheric CO₂ concentration and the carbon isotopic composition (Δ¹⁴C and δ¹³C) was measured in a forest in an urban area on 9 February 1999. The carbon isotope approach used in the present study differentiated between the quantitative contributions from anthropogenic and biogenic CO₂ sources in the urban atmosphere. The anthropogenic (fossil fuel) and biogenic (soil respiration) contributions was estimated, and they ranged from 1 to 16% and from 2 to 8% of the total atmospheric CO₂. The diurnal variation of the anthropogenic CO₂ was the major cause of the total atmospheric CO₂ variation, while the biogenic CO₂ remained relatively constant throughout the day. Estimating the contribution of soil respired CO₂ provided the mean residence time of soil respired CO₂ within the forest atmosphere.     

Determination of microbial versus root‐produced CO2 in an agricultural ecosystem by means of δ13CO2 measurements in soil air

The amounts of microbial and root‐respired CO₂ in a maize/winter wheat agricultural system in south western Germany were investigated by measurements of the CO₂ mixing ratio and the ¹³C/¹²C ratio in soil air. CO₂ fluxes at the soil surface for the period of investigation (1993–1995) were also determined. Root respired CO₂ shows a strong correlation with the plant mass above ground surface of the respective vegetation (R²≥0.88); the maximum CO₂ release from roots was in August for the maize (2.0±0.5 mmol m⁻² h⁻¹) and in June for winter wheat (1.5±0.5 mmol m⁻² h⁻¹). Maximum CO₂ production by roots correlate well with the maximum amount of plant root matter. Integrating the CO₂ production over the whole growing season and normalizing to the dry root matter yields, the CO₂ production per gram dry organic root matter (DORM) of maize was found to be 0.14±0.03 gC (g DORM)⁻¹. At the sites investigated, root‐produced CO₂ contributed (16±4)% for maize, and (24±4)% for winter wheat, respectively, to the total annual CO₂ production in the soil (450±50 gC m⁻² for maize, 210±30 gC m⁻² for winter wheat).     

天目山柳杉树轮δ13C对华东地区降水序列的重建

对采自天目山的柳杉树轮进行交叉定年后,得到树轮的δ¹³C年序列。将δ¹³C年序列去除大气CO₂的影响,保留其高频振荡部分。利用华东地区部分气象站的降水资料,通过主成份分析,分析了降水与树轮δ¹³C之间的关系。考虑滞后效应,利用回归方法重建了过去一百多年来的华东地区不同时段的降水序列,并分析其变化特征。     

In situ produced 14C by cosmic ray muons in ablating Antarctic ice

Samples of a core (52 m) of ablating Antarctic ice were analysed for ¹⁴CO and ¹⁴CO₂ by accelerator mass spectrometry. The data were compared with a ¹⁴C in situ production model that includes muon capture in addition to oxygen spallation by neutrons. The analysis reveals significant in situ ¹⁴C at depths below 10 m, which we attribute to ¹⁴C production by cosmic ray muons. The age of the ice was determined as 9.3±0.4 ¹⁴C ka BP.