HR: 17:30h
AN: PP54B-07    [Abstracts]
TI: Control of Atmospheric Carbon Dioxide over Glacial Cycles
AU: * Lassiter, R R
EM: rayrl@uga.edu
AF: University of Georgia, Marine Sciences Building University of Georgia, Athens, GA 30602 United States
AU: Cai, W J
EM: wcai@uga.edu
AF: University of Georgia, Marine Sciences Building University of Georgia, Athens, GA 30602 United States
AB: Over glacial cycles atmospheric pCO₂ is highly correlated to temperature, suggesting a strong linking mechanism. All mechanisms proposed to date have been met with counter arguments rejecting them as inadequate to explain the pattern and magnitude of CO₂ changes over glacial cycles. Our analysis of the carbon cycle supports a single, modulating, feedback-control mechanism that maintains atmospheric pCO₂ near a temperature-dependent control level. This mechanism is the dynamic variation of terrestrial vegetation and associated soil carbon. The control level is the level of atmospheric CO₂ at which global vegetation is stable, and is set by the biochemical properties of primarily C3 vegetation and its physiological and ecological loss fluxes as a function of temperature. The ocean's capacity for change by uptake and release of carbon vastly exceeds the capacity of vegetation plus soil carbon to oppose such changes, and indeed the mechanism does not oppose the direction of change set by the geochemistry of the ocean and atmosphere. Geochemistry of the ocean and atmosphere tends to increase ocean inorganic carbon and decrease atmospheric pCO₂ with decreasing temperature. Similarly the vegetation stability level of atmospheric pCO₂ decreases with decreasing temperature. However, if geochemical processes raise atmospheric pCO₂ above the vegetation stability level, vegetation will grow and remove that excess CO₂, or if geochemical processes lower atmospheric pCO₂ below the vegetation stability level, vegetation will moderate the lowering by die-off followed by release of CO₂ to the atmosphere. We have obtained this result using both simple steady-state models and a complex dynamic model incorporating ocean geochemistry and terrestrial vegetation and soil. The latter model computes the temperature dependent dynamics of carbon in atmospheric CO₂, vegetation, soil, as well as Alk, DIC, PIC, DOC, POC, and pH in shallow, mid-level, and deep oceanic waters. The general pattern of all ocean variables is to change with temperature such that dissolved inorganic carbon increases in the ocean as temperature decreases. Because of the compatible temperature functionality of vegetation, control of atmospheric pCO₂ by global terrestrial vegetation is achieved in concert with the tendencies inherent in the physics and geochemistry of the ocean. During the cold periods of the past glacial cycle, global vegetation and soil decreased by about 700 Pg due to climatically driven drawdown of CO₂ from the atmosphere. But due to the vegetation feedback, atmospheric pCO₂ remained very near the vegetation stability level of pCO₂. Indeed, the highly consistent pattern of pCO₂ over glacial cycles is the temperature-dependent vegetation stability pattern of pCO₂.
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 4806 Carbon cycling (0428)
DE: 4926 Glacial
DE: 4930 Greenhouse gases
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005