Carbonate Saturation Horizon — Equilibrium Chemistry (2D)

This 2D companion to the 3D ocean-chemistry simulator replaces its hand-fitted exponential Ω(z) curve with a genuine solve of the seawater carbonate equilibrium system at every depth: total alkalinity and dissolved inorganic carbon are combined with temperature- and salinity-dependent dissociation constants (Lueker et al. 2000) to solve for pH via an analytic quadratic at the surface and depth-by-depth bisection below it, while the calcium-carbonate solubility product (Mucci 1983) is corrected for real hydrostatic pressure using the thermodynamic ΔV/Δκ formulation. The result is a saturation horizon that emerges from the same chemistry oceanographers actually compute, not an assumed decay curve — so the aragonite saturation horizon and calcite compensation depth separate for the right underlying reason, and the CO2 and temperature sliders shift the horizon through the correct physical channels (surface carbonate-ion depletion, and CaCO3's retrograde solubility) rather than an empirical multiplier. A left-hand strip plots the live Ω(z) profile alongside a right-hand field of sinking, dissolving shell particles driven by that same computed curve.