Seawater Carbonate System Lab: Bjerrum Plot, Revelle Buffer and Aragonite Shell Health

What is the Seawater Carbonate System?

The seawater carbonate system is a complex equilibrium of chemical species that includes dissolved carbon dioxide (CO2), bicarbonate (HCO3-), and carbonate (CO3^2-) ions. This system plays a critical role in regulating ocean pH, which affects marine ecosystems and the health of calcifying organisms such as corals and shellfish.

The system is influenced by various factors including atmospheric CO2 levels, temperature, salinity, and biological activity. By manipulating these variables, we can observe how they affect the carbonate chemistry and its impact on marine life.

Bjerrum Plot: Visualizing Carbonate Equilibria

The Bjerrum plot is a graphical representation of the ionization constants for carbonic acid (H2CO3) in seawater. It shows how the concentrations of H2CO3, HCO3-, and CO3^2- change with pH. This plot helps us understand the equilibrium between these species and their interactions under different conditions.

By plotting the negative logarithm of the ionization constants (pKa values) against pH, we can visualize the distribution of carbonate species in seawater. The Bjerrum plot is a powerful tool for predicting how changes in CO2 levels will affect the carbonate chemistry.

Revelle Buffer and Ocean Acidification

The Revelle buffer refers to the resistance of seawater to pH change when CO2 is added. It is named after Frank Revelle, who first described this phenomenon in 1959. The Revelle factor quantifies how much a given increase in atmospheric CO2 will affect the pH of seawater.

As CO2 dissolves in seawater, it forms carbonic acid (H2CO3), which dissociates into bicarbonate and hydrogen ions (H+). This process lowers the pH of the water. The Revelle buffer means that as CO2 levels rise, the ocean's capacity to absorb additional CO2 decreases, leading to more significant changes in pH.

Aragonite Shell Health: Impacts of Ocean Acidification

Calcifying organisms like corals and shellfish rely on carbonate ions (CO3^2-) to form their calcium carbonate skeletons. However, as the ocean becomes more acidic due to increased CO2 levels, the availability of carbonate ions decreases, making it harder for these organisms to build and maintain their shells.

The aragonite saturation state is a measure of how much aragonite (a form of calcium carbonate) can dissolve in seawater. When this value drops below 1, the water becomes undersaturated with respect to aragonite, leading to shell dissolution. The simulation demonstrates how changes in CO2 levels affect the aragonite saturation state and the health of marine organisms.

Frequently asked questions

Try it live

Everything above runs in your browser — open Seawater Carbonate System Lab: Bjerrum Plot, Revelle Buffer and Aragonite Shell Health and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.