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The global bomb 14 C cycle. Stratosphere. nuclear bombs. nuclear bombs. stratosphere-troposphere exchange (STE). Troposphere. air-sea gas exchange. carbon exchange biosphere-atmosphere. Ocean. Biosphere. 30km. ATMOSPHERE. 21km. 15km. 9km. 0km. 90°S. 60°S. 30°S. 0°.
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The global bomb 14C cycle Stratosphere nuclear bombs nuclear bombs stratosphere-troposphere exchange (STE) Troposphere air-sea gas exchange carbon exchange biosphere-atmosphere Ocean Biosphere
30km ATMOSPHERE 21km 15km 9km 0km 90°S 60°S 30°S 0° 30°N 60°N 90°N BIOSPHERE OCEAN Leaves Twigs Wood Soil Setup of the 14C model bomb 14C 14C from nuclear industry natural 14C Land use change CO2 Fossil fuel & cement production CO2
Closing the global bomb 14C budget: difficulties to face (until ~2000) • bomb 14C production: large uncertainties • atmospheric models: not calibrated, • low resolution • observed bomb 14C inventories: • stratosphere (1955-1970) biased? • ocean (GEOSECS in 1970s) large spread • biosphere not available
Observed zonal profiles of ocean surface D14C data from Broecker et al., Key et al., Levin & Hesshaimer
Tritium 1 Tritium Unit (TU) = [T/H] = 10-18 Natural production of tritium is 5 TU/yr from interaction of cosmic rays in upper atmosphere with N: 14N + n → 15N → 12C + 3H, 3H → 3He + -β Human production: nuclear bomb testing 1952- 1970s Peak in 1963 with highest monthly of 10,000 TU Half life of 12.3 years so for 1963 Ottawa 2900 TU 1963 - 100; 1975 - 50%; 1988 - 25%; 2000 - 12.5%; 2012 - 6.3%
Tritium nowhere • Tritium is unstable, with half-life of 12.32 years • thus none naturally available • Can make it by bombarding 6Li with neutrons • extra n in D-T reaction can be used for this, if reaction core is surrounded by “lithium blanket” • Lithium on land in U.S. would limit D-T to a hundred years or so • maybe a few thousand if we get lithium from ocean • D-D reaction requires higher temperature, but could be sustained for many millennia
Example: CFC simulations in a ¼ degree model Integrated CFC content below 2000m Year = 1980 PhD project: Alex Sen Gupta
Integrated CFC content below 2000m Year = 2000 PhD project: Alex Sen Gupta
Integrated CFC content below 2000m Year = 2020 PhD project: Alex Sen Gupta
Integrated CFC content below 2000m Year = 2040 PhD project: Alex Sen Gupta