Carbon Cycle Variations During the Past 50,000 Years: Atmospheric 14C/12C Ratio as an Isotopic Indicator

  1. E.T. Sundquist and
  2. W.S. Broecker
  1. Devendra Lal

Published Online: 18 MAR 2013

DOI: 10.1029/GM032p0221

The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present

The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present

How to Cite

Lal, D. (1985) Carbon Cycle Variations During the Past 50,000 Years: Atmospheric 14C/12C Ratio as an Isotopic Indicator, in The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present (eds E.T. Sundquist and W.S. Broecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM032p0221

Author Information

  1. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900605

Online ISBN: 9781118664322

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Keywords:

  • Carbon cycle (Biogeochemistry)—Congresses;
  • Atmospheric carbon dioxide—Congresses;
  • Geological time—Congresses;
  • Paleothermometry—Congresses;
  • Geology, Stratigraphic—Congresses

Summary

We explore the conditions under which the paleorecord of the atmospheric 14C/12C ratio can serve as an isotopic tracer for changes in the carbon cycle during the past 50,000 years. Climatic changes on time scales of 103–104 years are expected to cause appreciable changes in the carbon cycle, both in the sizes of the dynamic carbon reservoirs and in the rates of mixing between them. The atmospheric 14C paleorecord shows appreciable variations with amplitudes in the range of 2–10% at frequencies of 5×10−3–10−4 cycles per year. In order to study the information contained in atmospheric 14C specific activity, we have carried out sensitivity studies theoretically by varying the carbon cycle parameters over a range of frequencies. These studies show that whereas atmospheric 14C activity responds sensitively to certain changes, with the magnitude of change being in the range observed, the task of deducing changes in carbon cycle parameters from the 14C paleorecord is a complex one. It involves delineating changes in the global production rate of 14C due to terrestrial and extraterrestrial causes. An interesting conclusion of this work is that the observed slow decrease in the atmospheric 14C/12C ratio during the past 8000 years probably originated (in large part) from changes in the carbon cycle parameters. An interesting implication of this deduction to geomagnetic dipole field change during this period is discussed.