Fig. 5. The GOE can be triggered by a decline in the influx of iron(II) and is sudden if b < c(a − 1).

Equilibrium E₂ (cyanobacteria dominate) gains stability and Equilibrium E₁ (APB dominate) loses stability when f₁ drops below $f_1^{\prime }$ and $f_1^{*}$, respectively. We set f₂ = 80, c = 10, a = 10, b = 80, and u₁ = u₂ = 10⁻³. a We simulate Eqs. (8) from Supplementary Note 1 with α₁ = α₂ = β₁ = β₂ = 1, and we set f₁ = 100 − 40(t/10⁵). t^* denotes the time at which Equilibrium E₁ loses stability. b Bifurcation plots reveal bistability for $f_1^{*}<f_1<f_1^{\prime }$.