The atmospheric carbon dioxide variations associated with the glacial-interglacial cycles: Simulation with a global dynamical climate model of intermediate complexity

In order to understand the potential role of the atmospheric CO ₂ as a greenhouse gas in future climate system, we need to first investigate its role in paleoclimatic history. Reliable evidences, such as the ice core data from Vostok, Antarctica, show that the atmospheric CO₂ has experienced dramatic oscillations of various amplitudes and periodicities in the late Quaternary, but the causes of these oscillations and the role of the CO₂, possibly as an interactive dynamic variable in the global paleoclimate system, are still not clearly known. Many mechanisms, such as change of the deep ocean temperature, seawater salinity, strength of the biological pump, terrestrial carbon storage, rates of carbonate and silicate weathering, and so on, have been proposed to account for the atmospheric CO₂ variations over the glacial-interglacial time scale. Unfortunately, no hypothesis based on only one of these mechanisms can explain the CO ₂ variation to the right amplitude.; In this study, a more process-based model of intermediate complexity is designed. The ocean circulation pattern is described by a 10-box model; the marine biogeochemical processes that involve carbon of different species are deductively described using equations that govern the inorganic chemistry and biochemistry in ocean water and diagenesis in the sediment; and the varying global ice mass and the mean temperature of the deep ocean are described inductively using prognostic equations.; When driven with the Milankovitch cycles as the only external forcing, the model produces the major variabilities in the atmospheric CO₂, global ice mass, mean temperature of the deep ocean, sea-to-air fluxes of CO₂, calcite lysoclines, percentage of carbonate in the sediment for the past 500 ka during which glacial-interglacial oscillations of 100-ka periodicity dominated the variations. And the results are in good agreement with available paleodata. This model is the first of its kind to be capable of generating a multitude of climatic and geochemical indices over extended geologic time range and, in so doing, the model establishes plausible dynamic connections, or causal relationships, between more lines of geologic evidences, so that the global climatic scenario can possibly be extrapolated more reliably in the domain of time.