Ocean acidification traces what happens when rising atmospheric CO₂ dissolves into seawater. Carbonic acid forms, pH falls, and the carbonate ions that shelled organisms rely on become scarce. Slide the CO₂ control to watch the tank's chemistry — and its inhabitants' shells — respond live.
CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ lowers pH and depletes carbonate ions, dropping the aragonite saturation state Ω that shell-building organisms depend on.
Drag the CO₂ slider from the pre-industrial 280 ppm up to 1000 ppm. Watch the live pH and Ω readouts, the tank's colour, the dissolving bubbles and the shells of the tiny organisms.
Pteropods — tiny swimming sea snails nicknamed "sea butterflies" — are considered a bellwether species: their thin aragonite shells begin visibly pitting and dissolving even at CO₂ levels we may reach this century.
This canvas-based simulation models the chemistry behind ocean acidification: as atmospheric CO₂ rises, more of it dissolves into seawater and reacts to form carbonic acid (CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻). The released hydrogen ions lower the water's pH using the approximation pH ≈ 8.17 − 0.29 × ln(CO₂ / 280), and they consume carbonate ions that would otherwise be available for shell-building. The simulation derives a simplified aragonite saturation state, Ω, that falls from around 4 at pre-industrial CO₂ toward 1 as CO₂ rises. Undersaturation stress sets in well before Ω reaches 1 — pitting and thinning of thin aragonite shells is observed around Ω ≈ 1.5 in cold, high-latitude surface water — and below Ω = 1 seawater is corrosive, so shells dissolve faster than they form.
On screen, rising bubbles represent CO₂ dissolving into the water column, and small pteropod and coral-fragment organisms show the biological consequence directly: their shell outlines are solid when Ω is comfortably high (around 2.5 or more), then progressively pit, thin and grow ragged as Ω falls toward 1, and dissolve outright once it drops below 1. Move the CO₂ slider to explore the full range from the pre-industrial 280 ppm to a high-emissions scenario near 1000 ppm, and use the "simulate rising CO₂" toggle to watch the whole trajectory unfold automatically. All figures are simplified, real-world-informed approximations intended for teaching the underlying chemistry rather than precise oceanographic modelling.
What does this simulation show?
It models how rising atmospheric CO₂ dissolves into seawater, forms carbonic acid, lowers pH and reduces the carbonate ions available for shell-building organisms, tracked through a simplified aragonite saturation state, Ω.
How does CO₂ turn into an acid in seawater?
Dissolved carbon dioxide reacts with water molecules in a reversible chain: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. The carbonic acid (H₂CO₃) formed in the first step quickly releases hydrogen ions, which is what actually lowers the pH.
What is pH and why does it matter here?
pH measures hydrogen ion concentration on a logarithmic scale from acidic (low) to basic (high). Pre-industrial surface seawater averaged about pH 8.2; today it is roughly 8.05 and falling, a shift that is small in number but represents a large percentage increase in acidity because of the logarithmic scale.
Ω = [Ca²⁺][CO₃²⁻] / Ksp compares the actual concentration of calcium and carbonate ions in seawater to the concentration needed for aragonite (a form of calcium carbonate) to be stable. When Ω is well above 1, aragonite readily forms and organisms can build shells easily. When Ω drops below 1, seawater becomes corrosive to aragonite and existing shells can dissolve faster than new material is deposited.
As carbonate ions become scarcer, organisms like pteropods, corals, oysters and some plankton must spend more energy building and maintaining their calcium carbonate shells or skeletons. Below the Ω = 1 threshold, thin aragonite structures — such as pteropod shells — can visibly pit, thin and dissolve, with consequences that ripple up the marine food web.
The atmospheric CO₂ slider (280–1000 ppm) is the primary driver: it live-updates pH and Ω using simplified formulas and instantly changes the tank's colour tint, bubble activity and the condition of the organisms' shells. The "simulate rising CO₂" toggle lets CO₂ climb automatically over time, and Reset restores the present-day default of 420 ppm.
The direction and rough scale of every relationship are grounded in real ocean chemistry — CO₂ uptake lowers pH and carbonate availability, and low Ω genuinely corrodes aragonite shells. The exact formulas (pH ≈ 8.17 − 0.29×ln(CO₂/280) and an exponential approximation for Ω) are deliberately simplified for interactive teaching rather than a full carbonate-system equilibrium model, which requires solving several coupled equilibria and temperature/salinity corrections.
Since the start of the industrial era, average surface ocean pH has fallen from about 8.2 to roughly 8.1, corresponding to a roughly 30% increase in hydrogen ion concentration. Atmospheric CO₂ has risen from about 280 ppm pre-industrial to over 420 ppm today, and the ocean has absorbed roughly a quarter to a third of all human CO₂ emissions in that time.