Abstract
ABSTRACTSince the 1950s, observations of radiocarbon (14C) in tropospheric carbon dioxide (CO2) have been conducted in both hemispheres, documenting the so-called nuclear “bomb spike” and its transfer into the oceans and the terrestrial biosphere, the two compartments permanently exchanging carbon with the atmosphere. Results from the Heidelberg global network of Δ14C-CO2 observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes. The recent development of global and hemispheric trends of Δ14C-CO2 are further discussed in regard to their suitability to continue providing constraints for 14C-free fossil CO2 emission changes on the global and regional scale.
Highlights
Atmospheric nuclear weapon testing in the 1950s and 1960s in the Northern Hemisphere was a period of great anxiety, it had significant side effects for environmental sciences in many aspects
The transient bomb-radiocarbon signal has levelled off, and the anthropogenic input of radiocarbon-free fossil CO2 into the atmosphere has become the dominant driver of the decrease of the 1.4 tons of radiocarbon (14C)/C ratio in global atmospheric CO2 (Levin et al 2010; Graven 2015)
This 14CO2-free anthropogenic CO2 flux from the burning of fossil fuels and cement production has increased globally by more than fourfold compared to the 1960s, and, together with ongoing land-use changes, has resulted in an increase of the atmospheric CO2 burden by more than 5 PgC (1 PgC = 1015 gC) or >0.5% per year in the last decade (Friedlingstein et al 2020)
Summary
Atmospheric nuclear weapon testing in the 1950s and 1960s in the Northern Hemisphere was a period of great anxiety, it had significant side effects for environmental sciences in many aspects. Results from the Heidelberg global network of Δ14C-CO2 observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes.
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