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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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Presentation Transcript
slide1

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

slide2

30km

ATMOSPHERE

21km

15km

9km

0km

90°S

60°S

30°S

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

slide8

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
slide11

Observed zonal profiles of ocean surface D14C

data from Broecker et al., Key et al., Levin & Hesshaimer

slide13

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 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
slide16

Example: CFC simulations in a ¼ degree model

Integrated CFC content below 2000m

Year = 1980

PhD project: Alex Sen Gupta

slide17

Integrated CFC content below 2000m

Year = 2000

PhD project: Alex Sen Gupta

slide18

Integrated CFC content below 2000m

Year = 2020

PhD project: Alex Sen Gupta

slide19

Integrated CFC content below 2000m

Year = 2040

PhD project: Alex Sen Gupta