CO2SYS
CO2SYS Carbonate Chemistry Calculation · Also known as: CO2SYS, Carbonate System Solver
CO2SYS is a widely-used software package for calculating the speciation and equilibrium state of the marine carbonate system from measurements of two carbonate parameters. Developed by Ernie Lewis and Doug Wallace in 1998, CO2SYS enables oceanographers to compute all carbonate species (dissolved CO2, bicarbonate, carbonate), saturation states, and pH from pairs of measured parameters. The tool is essential for ocean acidification monitoring and research.
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When to use it
CO2SYS is essential for all ocean acidification research and carbonate-system studies. Use it whenever carbonate parameters are measured and full carbonate system characterization is needed. It is particularly important for studying pteropod and other pelagic mollusk habitats, assessing coral reef acidification stress, and documenting secular acidification trends. CO2SYS is less relevant for applications requiring only a single parameter (e.g., pH alone).
Strengths & limitations
- Provides rapid, standardized calculation of full carbonate system state from pairs of measurements
- Widely adopted; output is comparable across research groups and time periods
- Transparent thermodynamic framework enables critical evaluation of assumptions and propagation of measurement uncertainties
- Available in multiple platforms (Excel, MATLAB, Python) enabling integration with existing workflows
- Assumes seawater is in equilibrium with atmosphere; kinetically incomplete reactions or non-equilibrium conditions violate this assumption
- Equilibrium constants vary with temperature, pressure, and salinity; uncertainty in constants propagates to calculated parameters
- Measurement uncertainties (especially in alkalinity and DIC) directly affect calculated values; accurate measurement is critical
- Does not account for dissolved organic matter or organic acids that influence pH in some coastal waters
Frequently asked
Which pair of carbonate parameters should be measured for CO2SYS input?
pH and total alkalinity is the most common and accurate pair; both are easily measured in the field. Total inorganic carbon and pH is also common. pH and partial pressure of CO2 (pCO2) is used less often but avoids alkalinity measurement. The choice depends on available instrumentation and desired accuracy.
How sensitive is CO2SYS output to measurement uncertainty?
Sensitivity depends on which parameters are inputs. A 0.01 unit pH error propagates to approximately 10% error in calculated pCO2. Alkalinity measurement uncertainty (typically ±2 µmol/kg) translates to approximately 5% uncertainty in DIC. Propagation of uncertainty through CO2SYS is essential for quality assessment.
What is ocean acidification and how does CO2SYS demonstrate it?
Ocean acidification is the ongoing decrease in seawater pH caused by absorption of anthropogenic CO2. CO2SYS tracks this by computing pH from pairs of measured carbonate parameters over time. Time series show linear decreases in pH (approximately -0.02 units per decade) and decreases in saturation state, indicating progressive shift toward undersaturation and shell dissolution.
Sources
How to cite this page
ScholarGate. (2026, June 3). CO2SYS Carbonate Chemistry Calculation. ScholarGate. https://scholargate.app/en/oceanography/co2sys
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