| Summary: | This thesis presents an analytical framework for considering air-sea carbon partitioning on millennial timescales. after air-sea exchange of carbon dioxide has neared completion but before sediment and weathering interactions have had a significant impact. It is found that the final atmospheric partial pressure ofcarbon dioxide (PC02) on a millennial timescale is related to the initial partial pressure (Po) by: Where 81po, is the change in accumulated carbon emissions, 81,.. is the change in the terrestrial carbon inventory, 8Chin is the change in the average concentration of dissolved inorganic carbon (DIC) in the ocean due to the dissolution of soft biological tissue, 8CCaC03 is the change in the average ocean concentration ofDIC due to the dissolution of calcium carbonate hard tissue, 8Cdi. is the change in average ocean DIC concentration due to local air-sea disequilibrium, V is the volume ofthe ocean, 1A is the initial atmospheric inventory of carbon dioxide, 18 is the buffered carbon inventory ofthe air-sea system and lo(A-C) is the difference between the global ocean preformed inventories oftitration alkalinity and DIC. This equation (5.1) is found to predict the final PC02 ofa standard numerical box model ofthe air-sea systerp. to within 3% while 280<PC02<1080ppm and 8Crmm = 0, and to within 10% while 28O<PC02<1080ppm and - 0.02:::; 8Crmm :::; +0.03 moles m-3 • A method for using (5.1) to analyse model output it presented which allows the effect on PC02 ofeach carbon cycle change to be separated within a single model integration. This may allow future modelling studies to analyse the effect that different carbon cycle feedbacks have on atmospheric carbon dioxide in response to climate change, without running multiple integrations. A modelling study is conducted evaluating 1B over the last 400Ma of Earth history, and it is found that the present day has a small buffered carbon inventory. This small present day 1B (-3100GtC to 3500GtC) implies that emissions, terrestrial carbon reservoir changes, and soft tissue ocean carbon drawdown changes have a greater effect on PCO2 and climate in the present than for much ofthe last 400Ma.
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