Abstract
AbstractEarth’s climate is considered to be stable on the order of > 106years, owing to a negative feedback mechanism in a carbon cycle system. However, any decrease in net input flux of CO2to the atmosphere-ocean system (i.e., volcanic-metamorphic CO2flux minus excess organic carbon burial flux) lowers the surface temperature and would eventually initiate global glaciation. TheFD-FOBdiagram (FD: the total CO2degassing flux,FOB: the organic carbon burial flux) is proposed as a measure of the susceptibility of the Earth to global glaciations. By using this diagram with the carbon fluxes estimated from a carbon cycle model during the Phanerozoic, the net input flux of CO2is found to have been very close to the critical condition for a global glaciation at the Late Paleozoic. During the Proterozoic, a carbon isotope mass balance model with this diagram shows that global glaciations occurred probably due to a decrease in the CO2degassing in addition to an increase in the organic carbon burial. Because the Sun becomes brighter as it evolves, the critical level of atmospheric CO2pressure to cause global glaciation will be lower than the critical CO2pressure for photosynthesis of C4 plants within 500 million years. At this point, the net input flux of CO2will be too large to cause global glaciations. Continuous volcanic-metamorphic activities (i.e., plate tectonics) may be one of the necessary conditions for the Earth and Earth-like planets in extrasolar planetary systems to keep liquid water and life over the timescales of planetary evolution.
Highlights
The climate of the Earth has been warm (>0◦C) during most of its geological history (Fig. 1), as suggested from evidence for the continued presence of liquid water and life (Walker, 1982; Kasting, 1989)
The FD–FBO diagram (FD: the total CO2 degassing flux, FBO : the organic carbon burial flux) is proposed as a measure of the susceptibility of the Earth to global glaciations. By using this diagram with the carbon fluxes estimated from a carbon cycle model during the Phanerozoic, the net input flux of CO2 is found to have been very close to the critical condition for a global glaciation at the Late Paleozoic
During the Proterozoic, a carbon isotope mass balance model with this diagram shows that global glaciations occurred probably due to a decrease in the CO2 degassing in addition to an increase in the organic carbon burial
Summary
The climate of the Earth has been warm (>0◦C) during most of its geological history (Fig. 1), as suggested from evidence for the continued presence of liquid water and life (Walker, 1982; Kasting, 1989) Such a long-term stability of the Earth’s climate is explained by a negative feedback mechanism within the carbon cycle system (Walker et al, 1981; Kasting, 1989; Kasting and Toon, 1989; Tajika and Matsui, 1990, 1992, 1993; Broecker and Sanyal, 1998). Donnadieu et al (2004b) argued that the decrease of pCO2 could have been caused by an increase in silicate weathering rate, owing to an increase in runoff and emplacement of flood basalt through the break-up of the supercontinent Rodinia It is, important to clarify the condition of the carbon cycle system to cause global glaciations. We propose the FD–FBO diagram (FD: the total CO2 degassing flux, FBO : the organic carbon burial flux)
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