21 Feedbacks and Coupling between Geosphere, Biosphere, Hydrosphere, and Atmosphere

Tuesday, 26 June 2001
10:00 AM - 3:00 PM

MODELING THE LONG-TERM EVOLUTION OF ATMOSPHERIC OXYGEN AND CARBON DIOXIDE

Paper number: 21-1
Program: GENERAL SESSIONS
Time: 1:50 PM – 2:10 PM

Authors

Abstract

Holland (1978) initially suggested that the atmospheric O2 level had been regulated by two major negative feedback mechanisms: (1) the negative response of the marine burial flux of organic carbon to pO2; and (2) the positive response of the O2 consumption flux by soil to pO2. This hypothesis has subsequently been discarded by Holland and other researchers for the lack of supportive evidence. Based on the following types of analysis, however, we have come to conclude that the atmospheric pO2 level has indeed been regulated by the above two negative feedback mechanisms: (a) a three-dimensional statistical analysis of the data reported in recent literature on the organic contents, DO and sedimentation rates of recent marine sediments; (b) a theoretical analysis of the kinetics of decomposition of organic matter by sulfur-reducing bacteria; and (c) an analysis of the available experimental data on the oxidation kinetics of organic carbon within the dynamics model of soil weathering.

We have also developed a series of rate equations linking the production and consumption fluxes of O2 to various parameters, such as atmospheric pO2 and pCO2, the global soil thickness, the total land area, and the volcanic fluxes of CO2, CH4 + CO, and H2. Using these equations, we have simulated the long-term (up to 4 Ga) changes in the pO2 and pCO2 of the atmosphere, the contents and carbon isotopic compositions of organic C and carbonate in new sediments, and the masses of organic C and carbonate reservoirs under a variety of scenarios. The results support the Dimroth-Ohmoto model for atmospheric evolution that suggests the development of a stable oxic atmosphere in < 50 Ma since the appearance of cyanobacteria > 3.5 Ga and a gradual decrease in pCO2 from ~1000 PAL to 1 PAL in ~4 Ga.