Coastal and estuarine regions are among the most dynamic of ocean environments. Concentrations of CO₂ in these settings can be highly variable on all time and space scales with ranges of pCO₂ varying from levels as low as open ocean, ~200-600 μatm, to as high as 5,000-10,000 μatm.

Variability over short time scales can result from:

• Water temperature changes
• Changes in river discharge from rain events
• Biology; diel cycles
• Wastewater discharge
• Storms, wind events

Variability over longer time scales can result from:

• Changes in biology; e.g. eutrification, or changes in dominant species
• Seasonal temperature and daylight changes
• Buildup of ice
• Industrialization and land use changes
• Seabed sediment reactions and organic breakdown, e.g., changes from aerobic to anaerobic conditions

There still exists a large uncertainty in estimates of carbon fluxes in coastal regions as a result of the great variability of CO₂ concentrations. This variability increases the importance of measuring pCO₂ in these areas, and  the choice of sensor depends on the monitoring constraints, with large-scale, short-term changes being easily measured with the Mini CO₂ sensor, and long-term changes requiring greater measurement stability and accuracy best suited to using the CO₂-Pro™ series of instruments.