Coral Calcifying-Fluid pH Gradient (2D Cross-Section)

This is a genuinely independent 2D counterpart to the 3D coral calcification model: instead of two lumped pH numbers, it numerically solves a reaction-diffusion partial differential equation across the actual calcifying-fluid layer, from the skeleton growth front to the calicoblastic membrane where the coral's Ca²⁺-ATPase pump actively extrudes protons. The steady-state spatial pH and aragonite-saturation profile that emerges is set by three competing processes running at once — diffusive exchange with seawater, active pumping at the membrane, and a localized precipitation reaction at the growth front — the same real biology the 3D sim describes, but computed a structurally different way that a single lumped equilibrium value cannot capture. Drive CO₂ and warming up, dial in pump strength and water flow, and toggle bleaching to watch the whole spatial gradient compress or collapse in real time.