Biogeochemists have published a constellation of historically linked long-term element cycle box models over the last 50 years. Although these numerical tools have tracked changing subsets of elements, isotopes, and processes, many have sought to reconstruct the geological history of atmospheric oxygen, atmospheric carbon dioxide, and seawater major ion chemistry. This research is important because marine chemistry is intimately tied to atmospheric composition and long-term planetary habitability. However, the expansive collection of existing biogeochemical models and the interdependence of that modeling ecosystem make it difficult to evaluate new results in the context of prior work or to track the changing assumptions embedded in common frameworks. This presentation will provide a historical overview of long-term element cycle models such as those in Garrels and Lerman (1981), Sundquist (1986), Marshall et al. (1988), and Wallmann (2001), as well as BLAG, GEOCARB, COPSE, MAGic, LOSCAR, GEOCLIM, and SCION. By tracing how these models developed, diverged, and cannibalized one another, we will highlight the evolving treatment of the global carbon, oxygen, and sulfur cycles through time. A central conclusion is that, despite substantial progress, models do not yet robustly represent the temporal evolution of seawater major ion chemistry. Modeling the geological history of seawater chemistry, as well as the cascading timescales over which imbalances in ion fluxes can stabilize or disrupt the global carbon cycle, will require improving numerical representations of major ion sources, sinks, and feedbacks.

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