Technical Report: Investigation of Carbon Cycle Processes within a Managed Landscape: An Ecosystem Manipulation and Isotope Tracer Approach

Atmospheric nuclear weapon testing in the 1950s and 1960s has been worrying, however, in many aspects it was extremely beneficial for environmental sciences. The artificial production of more than 6 x 1028 atoms or about 0.6 tons of 14C, leading to a doubling of the 14C/C ratio in tropospheric CO2 of the Northern Hemisphere has generated a prominent 14C spike in 1963. This &#8220;bomb-spike&#8221; has been used as transient tracer in all compartments of the carbon cycle, but also to study atmospheric dynamics, such as inter-hemispheric and stratosphere-troposphere air mass exchange. Moreover, our attempt to accurately determine total bomb produced 14C led to improved estimates of the atmosphere-ocean gas exchange rate and to a new constraint of the residence time of carbon in the terrestrial biosphere. Today, the transient bomb-radiocarbon signal has levelled off, and the anthropogenic input of radiocarbon-free fossil fuel CO2 into the atmosphere has become the dominant driver of the decreasing 14C/C ratio in atmospheric CO2; the observed trend may thus help scrutinising the total global release of fossil fuel CO2 into the atmosphere. Prominent examples where the bomb 14C disturbance has been successfully used to study dynamic processes in the carbon cycle are discussed as well as our current activities applying this unique isotope tracer for continental scale carbon cycle budgeting.

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Radiocarbon in modern carbon cycle research

10.5194/egusphere-egu21-4268 ◽

2021 ◽

Author(s):

Ingeborg Levin

Keyword(s):

Carbon Cycle ◽

Fossil Fuel ◽

Regional Scale ◽

Anthropogenic Input ◽

Isotope Tracer ◽

Continental Scale ◽

Nuclear Weapon Testing ◽

Bomb Radiocarbon ◽

Weapon Testing ◽

Transient Tracer

Atmospheric nuclear weapon testing in the 1950s and 1960s has been worrying, however, in many aspects it was extremely beneficial for environmental sciences. The artificial production of more than 6 x 1028 atoms or about 0.6 tons of radiocarbon (14C), leading to a doubling of the 14C/C ratio in tropospheric CO2 of the Northern Hemisphere, has generated a prominent spike in 1963. This &#8220;bomb-spike&#8221; has been used as transient tracer in all compartments of the carbon cycle, but also to study atmospheric dynamics, such as inter-hemispheric and stratosphere-troposphere air mass exchange. Moreover, our attempt to accurately determine total bomb produced 14C led to improved estimates of the atmosphere-ocean gas exchange rate and to a new constraint of the residence time of carbon in the terrestrial biosphere. Today, the transient bomb-radiocarbon signal has levelled off, and the anthropogenic input of radiocarbon-free fossil fuel CO2 into the atmosphere has become the dominant driver of the 14C/C ratio in global atmospheric CO2. The observed decreasing 14C/C trend in atmospheric CO2 may thus help scrutinising the total global release of fossil fuel CO2 into the atmosphere. On the local and regional scale, atmospheric 14C/C measurements are already routinely conducted to separate fossil fuel from biogenic CO2 signals and to estimate trends of regional fossil fuel CO2 emissions. Some prominent examples where the bomb 14CO2 disturbance has been successfully used to study dynamic processes in the carbon cycle are discussed as well as our current activities applying this unique isotope tracer for continental scale carbon cycle budgeting.

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