The Use of Radiocarbon Measurements in Atmospheric Studies

Abstract

4C measured in trace gases in clean air helps to determine the sources of such gases, their long-range transport in the atmosphere, and their exchange with other carbon cycle reservoirs. In order to separate sources, transport and exchange, it is necessary to interpret measurements using models of these processes. We present atmospheric ' 4C02 measurements made in New Zealand since 1954 and at various Pacific Ocean sites for shorter periods. We analyze these for latitudinal and seasonal variation, the latter being consistent with a seasonally varying exchange rate between the stratosphere and troposphere. The observed seasonal cycle does not agree with that predicted by a zonally averaged global circulation model. We discuss recent accelerator mass spectrometry measurements of atmospheric 14CH4 and the problems involved in determining the fossil fuel methane source. Current data imply a fossil carbon contribution of ca 25%, and the major sources of uncertainty in this number are the uncertainty in the nuclear power source of 14CH4, and in the measured value for S'4C in atmospheric methane.

Relationship between solar activity and Δ14C peaks in AD 775, AD 994, and 660 BC

“…Furthermore, whereas the maximum SH tropospheric 14 C increase during the bomb spike was just 70% of mid-latitude NH values (Manning et al 1990), reflecting the fact that close to 100% of the input was generated within the NH, the M12 amplitude in the kauri is~90% of the mean of the NH stations ( Table 1), indicating that significant 14 C production occurred in both hemispheres. -17.3 ± 1.8 -6.2 ± 1.4 11.1 ± 2.3 California (sequoia) 36°N -17.6 ± 0.9 -2.1 ± 1.0 15.5 ± 1.4 New Zealand 36°S -23.8 ± 0.8 -9.7 ± 0.7 14.1 ± 1.0 *Average of data from two laboratories (Usoskin et al 2013) Large-scale stratospheric air transport is dominated by the so-called Brewer-Dobson circulation (Butchart 2014) characterized by injection of tropospheric air into the stratosphere in the tropics and subsequently by movement towards the winter pole and subsidence at high latitudes, driven primarily by seasonally varying large-scale eddy motions that act to reduce the mean zonal velocity of air parcels and thus induce a poleward drift (Holton et al 1995).…”

Seasonally resolved stable isotope chronologies from northern Thailand deciduous trees

“…This amount effect is commonly observed for regions heavily influenced by monsoon activity (typically south of the maximum northward extent of the Intertropical Convergence Zone (ITCZ) ( Figure 1 in [8]) whereas the reverse is true for northern regions where temperature effects dominate and yield heavy (light) δ 18 O rainfall values in summer (winter) [9][10][11]. In addition, δ 18 O of precipitation varies with altitude (depletion in heavy isotopes with increased elevation) and with the distance travelled over land relative to the source region (preferential condensation of heavy isotopes).…”

Compiled records of carbon isotopes in atmospheric CO<sub>2</sub> for historical simulations in CMIP6

“…Then the monthly values from the three laboratories were averaged, and used to calculate combined annual means. As a result of varying data availability, annual means for 1977-1990at SPO and 1980-1989 at MLO are based only on SIO data (with the offset applied), and the annual mean for 2015 is based only on CSIRO data.…”

“…Sustained, direct atmospheric measurements of 14 C in CO 2 began in 1955 in Wellington, New Zealand, capturing the dramatic changes over the weapons testing period (Rafter and Fergusson, 1957;Manning et al, 1990;Currie et al, 2009). Observations of 14 C at several more stations started in the late 1950s, with some ceasing operation by the 1970s (Nydal and Lövseth, 1983;Levin et al, 1985).…”